ĐSTANBUL TECHNICAL UNIVERSITY INSTITUTE OF SCIENCE...
131
ĐSTANBUL TECHNICAL UNIVERSITY INSTITUTE OF SCIENCE AND TECHNOLOGY ELECTROPOLYMERIZATION OF 3,4-ETYHLENEDIOXYTHIOPHENE, CARBAZOLE DERIVATIVES MONOMER AND COMONOMERS ON CARBON FIBER MICROELECTRODE Ph.D. Thesis by Elif ALTÜRK PARLAK, M.Sc. Department : Polymer Science and Technology Programme: Polymer Science and Technology DECEMBER 2006
Transcript of ĐSTANBUL TECHNICAL UNIVERSITY INSTITUTE OF SCIENCE...
ĐSTANBUL TECHNICAL UNIVERSITY ���� INSTITUTE OF SCIENCE AND TECHNOLOGY
ELECTROPOLYMERIZATION OF 3,4-ETYHLENEDIOXYTHIOPHENE, CARBAZOLE DERIVATIVES MONOMER AND COMONOMERS ON
CARBON FIBER MICROELECTRODE
Ph.D. Thesis by Elif ALTÜRK PARLAK, M.Sc.
Department : Polymer Science and Technology
Programme: Polymer Science and Technology
DECEMBER 2006
ii
ACKNOWLEDGEMENT
I wish to thank at first place to my thsesis advisor Prof.Dr. A.Sezai Saraç for his expert guidance, motivation and support at all levels of this study. It was great pleasure for me to conduct this thesis under his supervision and to know him personally. I would like to express my thanks to Associate Prof. Dr. Esma Sezer and Associate Prof. Dr. Belkıs Ustamehmetoğlu their contributions, support and friendship. I would express my heartfelt thanks to all members of polymer science and technology proggramme and chemistry department, especially Porf. Dr. Candan Erbil, Associate Prof. Dr. Nurcan Tüzün, Associate Prof. Dr. Filiz Şenkal, Dr. Nermin Orakdöğen, Dr. Fevzi Çakmak Cebeci. I’m forever indepted to the love and caring of my families and to my husband. He has always been a source of constant support and love. Finally, I appreciate to my daughter who is my inspiration in all my life.
Elif Altürk Parlak
December 2006
iii
CONTENTS
ABBREVIATIONS vi
TABLE LIST vii
FIGURE LIST viii
SYMBOL LIST xıı
SUMMARY xııı
ÖZET xv
1. INTRODUCTION 1
1.1. Electrochemical Cells and Reactions 1
1.2. Conducting Polymers 3
1.3. Synthesis and structure 5
1.4. Kinetic Behaviour and Thermodynamical Considerations 8
1.5. Applications of Conducting Polymers 8
1.5.1. Electroluminescent and electrochromic devices. 11
1.5.2. Use as membrane and ion exchanger 11
1.5.3. Corrosion protection 12
1.5.4. Sensors 12
1.5.5. Artificial muscles 12
1.6. Poly(3,4ethylenedioxythiophenes) 13
1.7. Polycarbazoles 15
1.8. Carbon Fiber Microelectrode 16
1.9. Cyclic Voltammetry 17
1.10. Electrochemical Impedance Spectroscopy 18
1.10.1. Two different types of experiments for EIS 20
1.11. Supercapacitors and Ultracapacitors 23
iv
2. EXPERIMENTAL 24
2.1. Materials 24
2.2. Fiber Surface Morphology 24
2.3. ATR- FTIR Reflectance Spectrophotometry 25
2.4. UV-Visible Spectrophotometry 25
2.5. Scannig Electon Microscope 25
2.6. Monomer and Comonomer Synthesis 25
2.6.1. Synthesis of N-(Hydroxymethyl) carbazole 25
2.6.2. Synthesis of BEDOT 26
2.6.3. Bromination of BEDOT 26
2.6.4. Synthesis of 3-trimethyltin-9-ethylcarbazole 27
2.6.5. Synthesis of EtCz-BEDOT-EtCz 27
2.6.6. Synthesis of EDOT-EtCz-EDOT 29
3. RESULTS AND DISCUSSION 31
3.1. Electropolymerization and Characterization Cz and EDOT Derivatives 31
3.1.2. Elecrochemical Impedance Spectroscopy (EIS) 36
3.2. Microcomposite Electrochemical Capacitor: Electrocoating of Poly [N-
(Hydroxymethyl)carbazole] onto Carbon Fiber, Solvent Effect, Surface
Morphology, Spectroscopic Surface Characterization, Electrochemical
Impedance Spectroscopy 39
3.2.1. Electropolymerization of N-(Hydroxymethyl) carbazole 40
3.2.2. Effect of Scan rate and solvent on the electropolymerization of N-
(Hydroxymethyl) carbazole 43
3.2.3. Morphology of N-(Hydroxymethyl) carbazole 45
3.2.4. Reflectance FTIR Surface Spectra of Poly(MeOHCz) coated CFME 48
3.2.5. Electrochemical impedance spectroscopy 49
3.2.6. Comparative capacitance determination with cyclic voltammetry and
impedance spectroscopy 53
3.3 Electropolymerization of N-(hydroxyethyl) Carbazole on a CFME, and
Investigation of Capacitance Behavior with Electrochemical Impedance
Spectroscopy. 55
3.3.1. Electropolymerization of N-(hydroxyethyl) carbazole 55
3.3.2. FTIR-Reflectance spectrum of electro-grafted homopolymer on FME 56
v
3.3.3. Morphology of poly [N-(hydroxyethyl) carbazole] 57
3.3.4. Electrical properties poly [N-(hydroxyethyl) carbazole] 59
3.3.5. Spectroelectrochemistry of poly[N-(hydroxyethyl)carbazole] 63
3.4. Electrochemical Impedance Study of Poly(3,4 ethylenedioxythiophene)
on Carbon Ffiber Microelectrode 65
3.4.1. Electropolymerization of EDOT 65
3.4.2. Electrochemical Impedance Study of PEDOT 67
3.5. The Electropolymerization of Bis-3,4- Ethylenedioxythiophene and 3,6-
Bis[2-(3,4 ethylenedioxy)thienyl]-N-Ethyl Carbazole on Carbon Fiber
Microelectrode and Its Characterization. 75
3.5.1. Polymerization and Characterizationof poly[BEDOT-co-EEE] 76
3.5.2. Spectroscopic Charecterization of poly [BEDOT-co-EEE] 80
3.5.3. Polymer Morphology 83
3.6. Synthesis and Electrochemical Polymerization of N-Ethylcarbazole- Bis
3, 4 Etyhlenedioxythiophene-N-Ethylcarbazole Comonomer. 86
3.6.1. Polymer Synthesis and Characterization 86
3.6.2. Morphologyof PEBEE 91
3.7. Electrochemical Synthesis ofEDOT-ECZ-EDOT Copolymer on Carbon
Fiber Microelectrode 93
3.7.1. Polymerization and characterizationof PEEE. 93
3.7.2. Redox Behaviour and Stability of PEEE films 99
3.8. Comparative Study of Polymer Electrodes 100
4. CONCLUSION 104
REFERENCES 107
RESUME 114
vi
ABBREVIATIONS
Anı : Aniline Py : Pyrrole PANI : PolyAniline PPy : Polypyrrole ICP : Intrinsic Conducting Polymer
PEDOT : Poly(3,4-ethylendioxithiophene) PTh : Polythiophene PSS : Poly(styrene sulfonic acid) PCz : Polycarbazole CH2Cl2 : Dichloromethane CV : Cyclic voltammogram, EtCz : Ethyl carbazole Cz : Carbazole NVCz : N-Vinyl Carbazole MeOHCz : Hydroxymethyl Carbazole EtOHCz : Hydroxyethyl Carbazole TEAP : Tetraethylamoniumperchlorate PC : Propylene carbonate ACN : Acetonitrile SEM : Scanning Electron Microscope BEDOT : Bis 3,4-ethylendioxithiophene CFME : Carbon fiber microelectrode EEE : 3,4-ethylendioxithiophene-Ethyl carbazole-3,4- Ethylendioxithiophene EBEE : Ethyl carbazole-bis 3,4-ethylendioxithiophene- Ethyl carbazole PEEE : Poly(3,4-ethylendioxithiophene- Ethyl carbazole-3,4- Ethylendioxithiophene) PEBEE : Poly(ethyl carbazole-bis 3,4-ethylendioxythiophene-ethyl Carbazole) THF : Tetrahydrofurane
vii
TABLE LIST
Page No
Table 1.1 Qualitative properties of ICPs according to charging state ……... 9 Table 1.2 Some applications for conducting polymer ……………………… 10
Table 2.1 Proposed assignments for the main vibrations of ECz-BEDOT-ECz comonomer..............................................................................
29
Table 3.1 Redox parameters obtained from potentiodynamic growth of Cz derivatives........................................................................................
34
Table 3.2 Redox parameters of polymer films in TEAP/CH2Cl2 with scan rate of 100mV/s.…................................................................
35
Table 3.3 The Double Layer Capacitance of obtained polymer electrodes.… 38 Table 3.4 Effect of scan rate on the redox parameters of polymer
growth*[MeOHCz]:1mM……......................................................... 43
Table 3.5 Some data obtained from CV, and in-situ spectroelectrochemical study of homopolymers, copolymer and composites …….............
85
Table 3.6 Effect of swicthing potential on redox parameters of electrogrowth of EBEE on Pt electrode ………………….............
88
Table 3.7 Redox parameters of monomers and polymers …………............. 88
Table 3.8 Proposed assignment for the main vibration for PEEE film............ 98 Table 3.9 Redox parameters of polymeric films ……..................................... 99
viii
FIGURE LIST
Page No
Figure1.1 : Represantation of Reduction.............................................................. 1 Figure 1.2 : Representation of oxidation……………........................................ 2 Figure 1.3 : Effecting variables on electropolymerization................................... 3 Figure 1.4 : PEDOT molecular structure............................................................. 13 Figure 1.5 : PEDOT copolymers......................................................................... 15 Figure 1.6 : Theoretical impedance plane display for metal/polymer/electrolyte
case.................................................................................................. 21
Figure 1.7 : Theoretical impedance plane display for metal/polymer/metal case. ...............................................................................................
22
Figure 2.1 : N-Hydroxymethyl carbazole synthesis............................................ 26 Figure 2.2 : Bromination of BEDOT.................................................................. 27 Figure 2.3 : Synthesis of 3-trimethyltin-9-ethylcarbazole.................................... 27 Figure 2.4 : Synthesis of ECz-BEDOT-ECz........................................................ 28 Figure 2.5 : Synthesis of EDOT-ECz-EDOT....................................................... 30 Figure 3.1 : Some carbazole monomers. ............................................................. 31
Figure 3.2
: Potentiodynamic growth of Cz on CFME in 0.05M TEAP/CH2Cl2. 32
Figure 3.3 : Potentiodynamic growth of EtCz on CFME in TEAP/CH2Cl2....... 32 Figure 3.4 : Potentiodynamic growth of EtOHCz on CFME in 0.05M TEAP/
CH2Cl2. (scan rate:50mV/s)............................................................... 33
Figure 3.5 : Potentiodynamic growth of NVCz on CFME in 0.05M TEAP /CH2Cl2 .............................................................................................
33
Figure 3.6 : Potentiodynamic growth of BromoCz on CFME in 0.05M TEAP /CH2Cl2. (scan rate:50mV/s). .............................................................
34
Figure 3.7 : Polymer films electrografted on CFME in TEAP/CH2Cl2 with scan rate of 100mV/s. ........................................................................ 35
Figure 3.8 : Nyquist plot of bare CFME in 0.05M TEAP/CH2Cl2. Inset: Bode phase plot of bare CFME in 0.05M TEAP/CH2Cl2..........................
37
Figure 3.9 : The Nyquist plots of a)Cz, b) BrCz, c)NVCz, d) ETOHCz........... 37 Figure 3.10 : Bode plot of a) PBrCz, b)PCz, c)PNVCz, d)PECz, e)PEtOHCz..... 38 Figure 3.11 : The Bode phase angle graphs of a) PEtOHCz, b)PNVCz, c)PCz,
d)PECz, PBrCz.. .......................................................................... 39
Figure 3.12 : Potentiodynamic growth of MeOHCz on CFME in 0.05M TEAP/CH2Cl2. (scan rate:60mV/s) Inset: Potentiodynamic growth of Cz on CFME in 0.05M TEAP/CH2Cl2 (scan rate:60mV).......
40
ix
Figure 3.13 : Scan rate dependence of PMeOHCz on CFME in 0.05M TEAP containing CH2Cl2.(scan rate:100-400mV/s). Inset: Scan rate dependence of PCz on CFME in 0.05M TEAP containing CH2Cl2.........................................................................................
41
Figure 3.14 : Tentative mechanism of Electropolymerization of MeOHCz on CFME.................................................................................................
42
Figure 3.15 : Current density versus scan rate plot of polyMeOHCz in 0.05M TEAP a)ACN, b) PC, c) CH2Cl2.........................................................
44
Figure 3.16 : Current density vs charge-transfer resistance, Rct relationship........ 45 Figure 3.17 : SEM photographs of Poly [N-(Hydroxymethyl)carbazole]
a)3cycle,b)5cycle, c)10cycle, d) 15cycle........................................... 47
Figure 3.18 : Avarage increase in radius of polymer film (obtained from SEM photographs) vs cyclovoltametric scan number.................................. 48
Figure 3.19 : FTIR-ATR spectra of a)monomer, b) polymer obtained in TEAP/CH2Cl2 at 50mV/s, 5 cycle......................................................
49
Figure 3.20 : Nyquist plot of PMeOHCz in TEAP/CH2Cl2................................... 50 Figure 3.21 Nyquist plot of PMeOHCz in TEAP/ACN. Inset:Nyquist plot of
PMeOHCz in TEAP/ACN. (High frequency region was expanded).. 50
Figure 3.22 : Nyquist plot of PMeOHCz in TEAP/PC Inset: Nyquist plot of PMeOHCz in TEAP/PC. (High frequency region was expanded).....
51
Figure 3.23 : Bode plot of PMeOHCz a) PC, b) ACN, c)CH2Cl2.......................... 52 Figure 3.24 : CCV vs scan rate graph of PMeOHCz a)ACN, b) CH2Cl2, c) PC..... 54 Figure 3.25 : Cim vs frequency plot of PMeOHCz a)ACN, b) CH2Cl2, c) PC..... 54 Figure 3.26 : Potentiodynamic growth of EtOHCz on CFME in 0.05M
TEAP/CH2Cl2.(scan rate:50mV/s) .................................................... 55
Figure 3.27 : Scan rate dependence of PEtOHCz on CFME in 0.05M TEAP/ CH2Cl2.(scan rate:100-500mV/s).......................................................
56
Figure 3.28 : FTIR spectra of a.EtOHCz b. PEtOHCz obtained on CFME in TEAP/CH2Cl2.....................................................................................
57
Figure 3.29 : Scanning electron microphotographs of PEtOHCz at x3500 magnification......................................................................................
58
Figure 3.30 : Scanning electron microphotographs of PEtOHCz at x500 magnification ....................................................................................
58
Figure 3.31 : Nyquist of POHCz, 5 cycle, on CFME in TEAP containing CH2Cl2 ,Q: 11.27mC. Inset: .Nyquist of PCz, 5 cycle, on CFME in TEAP containing CH2Cl2 ,Q: 1.514mC. ...........................................
59
Figure 3.32 : Nyquist plots for CF/ PEtOHCz electrode a. doped at 1.2V for 2 min, b. undoped at -1.2V for 2min in TEAP/CH2Cl2.......................
60
Figure 3.33 : Nyquist plot of PEtOHCz at different potentials[-0.4V-0.1V]......... 61 Figure 3.34 : Nyquist plot of PETOHCz at different potentials[-0.6V-0.2V]....... 61 Figure 3.35 : Nyquist plot of PEtOHCz at different potentials[0.V-1.2V]........... 62 Figure 3.36 : Bode phase angle plot of PEtOHCz at different potentials............. 65 Figure 3.37 : Bode Magnitude graph of PEtOHCz at different potential............. 63 Figure 3.38 : In-situ UV visible study of PetOHCz on ITO electrode(-0.6V-2V) 63 Figure 3.39 : FTIR-ATR of PEtOHCz on CFME after applied 2.0V potential.... 64 Figure 3.40 : Potentiodynamic growth of EDOT(2.10-3M), on CFME in
LiClO4/PC with a scan rate of 100mV/s............................................. 65
Figure 3.41 : Scan rate dependence of PEDOT coated CFME in LiClO4/PC (100-500mV/s) ..................................................................................
66
Figure 3.42 : a)The current density vs scan rate, b) the current density vs
x
(scan rate)1/2 graph of PEDOT coated CFME. .................................. 67 Figure 3.43 : Nyquist plot of PEDOT at negative potentials[-0.1V-0.4V]........... 68 Figure 3.44 : Nyquist plot of PEDOT at positive potentials [0.1V-1.0V]............ 68 Figure 3.45 : Cyclic voltamogram of PEDOT at a scan rate of 100mV/s, in
LiClO4/PC after PEDOT was exposed to different potentials........ 69
Figure 3.46 : Charge vs potential graph of PEDOT............................................. 69 Figure 3.47 : Bode magnitude plot of PEDOT at different potential(-0.4V, 0.1V,
0.3V, 1V) ... 70
Figure 3.48 : Nyquist plot of PEDOT with charge of a) 0.88mC, b) 3.3mC........ 70 Figure 3.49 : Nyquist plot of PEDOT with charge of a) 3.3mC, b) 5.7mC, c)
6.6mC. Inset: Same graphic with same x-y scale............................ 71
Figure 3.50 : Bode phase angle of PEDOT a)0.88mC, b)1.7mC, c)3.3mC, d) 5.79mC, d)6.6mC............................................................................
71
Figure 3.51 : Magnitude of Z graph of PEDOT with different charges a)0.88mC, b) 1.79mC, c) 3.3mC, d) 6.6mC. ................................. 72
Figure 3.52 : Evaluation of imaginary capacitance vs frequency for 0.5 cm2 PEDOT coated CFME in 0.1 M LiClO4/PC.................................
73
Figure 3.53 : Evaluation of real capacitance vs frequency for 0.5 cm2 PEDOT electrode in 0.1 M LiClO4/PC.........................................................
74
Figure 3.54 Cdl and Csp vs polymerization charge plot of CFME/PEDOT (correlation coefficients : R =0.991 for CLF and R =0.997 for Cdl....
75
Figure 3.55a The polymer growth of BEDOT in 0.1M LiClO4 electrolyte /propylene carbonate(PC). .............................................................
77
Figure 3.55b : PolyBEDOT coated carbon fiber in 0.1M LiClO4 containing PC. Scan rate[ 20mV/sec-200mV/sec]..................................................
77
Figure 3.56a : The plot of polymer growth of EDOT-EtCz-EDOT in 0.1M LiClO4 electrolyte containing propylene carbonate(PC).Scan rate:20mV/sec, [EEE]=0.002M.......................................................
78
Figure 3.56b : PolyEEE coated carbon fiber in 0.1M LiClO4 /PC. Scan rate[ 20mV/sec-200mV/sec] ..................................................
78
Figure 3.57a : The plot of polymer growth of BEDOT-co-EEE in0.1M LiClO4 electrolyte in propylene carbonate(PC). Scan rate:20mV/sec........
79
Figure 3.57b : Poly(BEDOT-co-EEE) coated carbon fiber in 0.1M LiClO4 containing PC. Scan rate[ 100mV/sec-260mV/sec].......................
79
Figure 3.58a : In situ spectroelectrochemical study of P(BEDOT-co-EEE) on ITO containing 0.1MLiClO4 electrolyte solution in PC, in the range of [-1-0.6v]. .........................................................................
81
Figure 3.58b : Voltabsorbtemetric curve of P(BEDOT-co-EEE).......................... 81 Figure 3.59 : In situ spectroelectrochemical study of PEEE on ITO in
0.1MLiClO4 containing PC, in the range of [-1-0.6v]................... 82
Figure 3.60 : In situ spectroelectrochemical study of PBEDOT on ITO in 0.1MLiClO4 / in PC, in the range of [-1-0.6v]................................
82
Figure 3.61 : In situ spectroelectrochemistry of ITO/PBEDOT/PEEE composite 83 Figure 3.62 : SEM of random electrografted copolymers of P[BEDOT-co-
EEE] onto carbon fiber by potentiodynamically at 20mV/sec, on 3 single CF, surface area 0.0132 cm2, number of scan is 8................
84
Figure 3.63 : SEM of random electrografted copolymers of P[BEDOT-co-EEE] onto carbon fiber by potentiodynamically at 20mV/sec, 3 single CF, surface area 0.0033 cm2, number of scan is17..............
84
Figure 3.64 :SEM of composite of CF/PEEE/BEDOT obtained potentiodynami-
xi
cally, on 5 single CF, 20 mV /s, in the range of [-1.0V, + 0.7V ], surface area is 0.0165cm2, diameter of grafted fiber, 9.3 µ. ……..
85
Figure 3.65
: Potentiodynamic growth of ECz-BEDOT-ECz (4.10-3M), on Pt electrode in 0.1 M LiClO4 /propylene carbonate. (scan rate:100mV/s) .................................................................................
87
Figure 3.66 : Potentiodynamic growth of ECz-BEDOT-ECz (4.10-3M), on CFME electrode in 0.1 M LiClO4 /propylene carbonate. (scan rate:100mV/s) ................................................................................
89
Figure 3.67 : Scan rate dependence of P (ECz-BEDOT-ECz) on CFME in 0.1M LiClO4 / PC, (scan rate = 20mV-200mV .s-1).................................
90
Figure 3.68 : Potentiodynamic growth of ECz (2.10-3M), on CFME electrodes in 0.1M LiClO4 / propylene carbonate. (scan rate:100mV/s).........
90
Figure 3.69 : Scan rate dependence of PECz coated CFME in 0.1M LiClO4 / Propylene carbonate......................................................................
91
Figure 3.70 : SEM photograph of PEBEE obtained with 100mV/s 3 cycle in LiClO4 / PC on CFME. ..................................................................
92
Figure 3.71 : SEM photograph of PEBEE obtained with 100mV/s 40 cycle in LiClO4 / PC on CFME. ...............................................................
92
Figure 3.72 : SEM photograph of PEBEE deposited on CFME with 20mV/s and 50cycle............................................................................................
93
Figure 3.73 : Cyclic voltammograms for the oxidation of EEE on Pt(a) and CF(b) in 0.1 M LiClO4 /PC at 20 mv.s-1. .......................................
94
Figure 3.74 : Scan rate dependence of PEEE on CFME on Pt(a) and CF (b) in 0.1 M LiClO4 /PC . ...............................................................
95
Figure 3.75 : SEM pictures of PEEE films on CF obtained at different scan numbers; 3 (a), 10(b), 15 (c), 20 (d), and cross section (e) ............
97
Figure 3.76 : Variation of thickness of polymer film with scan number.............. 98 Figure 3.77 : Scan rate dependence of PEEE film in monomer free supporting
electrolyte(A) and variation of peak current with scan number (B). 99
Figure 3.78 : In-situ spectroelectrochemistry of PEEE film obtained at different applied potential in the range of -1.0 to 0.4 V...............................
100
Figure 3.79 : Polymeric film redox potentials at different conditions................ 101
Figure 3.80 : Csp values of Polymer electrodes obtained potentiodynamic method.............................................................................................
101
Figure 3.81 : Csp values of Polymer electrodes obtained potentiostatic method. 102
Figure 3.82a : Csp vs E1/2 graph of some polymer electrodes obtained potentiodynamic method.................................................................
102
Figure 3.82b : Csp vs E1/2 graph of some polymer electrodes................................. 103
xii
SYMBOL LIST Ea : Anodic peak potential Ec : Catodic peak potential ∆∆∆∆E : Anodic and catodic peak seperation E1/2 : Half wave peak potential ia : Anodic current ic : Cathodic current ia/ic : Anodic cathodic peak current ratio Cdl : Double Layer Capacitance Rct : Charge transfer resistance Rs : Electrolyte resistance f 0 : Frequency Csp : Specific Capacitance Zim : Imaginary impedance Zre : Real impedance Cim : Imaginary capacitance Cre : Real capacitance H2SO4 : Sülfiric Acid LiClO4 : Lithium perchlorate MO : Molecular orbital Γ : The time constant ϒϒϒϒo :Dielectric relaxation time constant Q : Charge Eonset : Onset potential φφφφ : Phase Angle Xc : Capacitive Reactance ωωωω :Angular frequency εεεεr :Dielectric constant of polymer phase κκκκ : Conductivity U : Potential δδδδ : Chemical shift
xiii
ELECTROPOLYMERIZATION OF 3,4-ETYHLENEDIOXYTHIOPHENE, CARBAZOLE DERIVATIVES MONOMER AND COMONOMERS ON
CARBON FIBER MICROELECTRODE
SUMMARY
In this study, electropolymerization of Cz and EDOT derivatives was performed. Electropolymerization depends strongly on the type of electrode material, scan rate, switching potential and the method used for electropolymerization. SEM and CV results helps to estimate the thickness of polymeric film and the homogenity of polymeric film. The micron-sized polymeric film was obtained. These results indicated that the thickness of the film can be contolled under the optimum conditions.
The oxidative electropolymerization of Carbazole(Cz), Bromocarbazole, N-vinyl carbazole, EtCz, EtOHCz were carried out in dichloromethane(CH2Cl2) with 0.05 Tetraethyl ammonium perchlorate (TEAP). The highest electroactivity and rate of electropolymerization were obtained for PNVCz. Polymer half wave potential is also the smallest in the case of PNVCz.. It is revealed that conjugation length is the longest for PNVCz. When they are compared to capacitance behavior, PEtOHCz has highest capacitance according to (Cdl), which shows the highest surface area for the polymer.
MeOH substituent on Cz also affects Cz electropolymerization such that the reversibility of MeOHCz is smaller than Cz. Moreover, the solvent effect was also investigated in this study. PMeOHCz has showed the highest electroactivity in ACN, however, the highest capacitance in PC.
EDOT was electropolymerized onto CFME, then the electrochemical capacitance behavior has been investigated with cyclic voltametry and Electrochemical Impedance Spectroscopy. PEDOT showed supercapacitor behavior that was supported with CV and impedance results.
In this study, Ecz-BEDOT-Ecz, EEE and BEDOT comonomers were synthesized and electropolymerizations were compared. Ecz side group comonomer (Ecz-BEDOT-Ecz) was only electropolymerized on CFME but not on the Platinium electrode. This reveals that the properties of electrode is very crucial in obtaining electroactive polymer film surface. However EEE comonomer was electropolymerized both CFME and Pt. It indicated that the side group of monomer affects electropolymerization, so the choice of side group of comonomer and the substrate is vitally important for successful polymerization. When EEE is electrocoated on ITO, its electrochromic behavior can be monitored clearly. UV of PEEE indicates that the polymer has two charge carriers, one is polaron , the other bipolaron.
xiv
Finally, random electropolymerization of EEE and BEDOT was studied. In situ UV study shows that the copolymer is different from PEEE, PBEDOT, and PEEE/BEDOT composite which is supported by UV results.
xv
KARBAZOL, 3,4 -ETĐLENDĐOKSĐTĐYOFEN MONOMER VE KOMONOMER TÜREVLERĐNĐN KARBON FĐBER ELEKTROT
ÜZERĐNDE ELEKTROPOLĐMERĐZASYONU
ÖZET
Bu çalışmada Cz ve EDOT monomerlerinin ve komonomerlerinin elektrokimyasal polimerizasonu çalışıldı. Kullanılan elektrot cinsinin, oksidasyon yapılan potansiyelin, tarama hızının, kullanılan methodun elektrokimyasal polimerleşmeyi oldukça etkilediği görüldü. Taramalı elektron mikroskobu ile yapılan çalışmalar ve Döngülü voltametrenin paralel kullanılması sayesinde elde edilen polimer filminin kalınlığı ve homojenliği hakkında sonuçlar elde edildi.
Farklı karbazol türevlerinin NVCz, Cz, ECz, EtOHCz ve BrCz elektrokimyasal polimerleşmesi aynı koşullarda karşılastırıldığında elektroaktivitenin ve reaksiyon hızının en yüksek PNVCz durumunda olduğu görüldü. Ayrıca en düşük yarı dalga potansiyeline yine PNVCz’ün sahip olduğu görüldü. Bu da Cz konjugasyonunun en uzun bu polimerde olduğunu gösterdi. Kapasitor davranışları karşılaştırıldığında ise PEtOHCz’ün kapasitansının en büyük olduğu görüldü. Bu sonuçlar elektrot yüzeyine kaplanan miktarın PEtOHCz da daha fazla olduğunu göstermektedir.
Cz üzerinde MeOH sübstitüyesi olması halinde bunun Cz elektrokimyasal polimerleşmesini nasıl etkilediğine bakıldı, ve karbazole göre tersinirliğinin bozulduğu gözlendi. Ayrıca bu çalışmada çözücü etkiside incelendi. ACN’in elektroaktivesinin en yüksek, kapasitif özelliğinde PC’de en yüksek olduğu görüldü.
PEDOT filmi KFME elektrot üzerinde oldukça kararlı ve süper kapasitor özelliği gösterdi. Bu davranış DV’daki dikdörtgen şeklinden ve Bode faz açısı grafiğinin 90o faz açısı çıkması ile ispatlandı.
ECz uçlu (ECz-BEDOT-ECz) komonomer sadece KFME üzerine kaplanırken Platin üzerine kaplanmadı. Polimerin elektrot yüzeyine tutunabilmesi için elektrodun yüzey özelliklerinin oldukça etkili olduğu görüldü. EDOT uçlu komonomerinin(EEE) elektropolimerizasyonu ise her iki elektrot üzerinde gerçekleşirken, bu da komonomerin uç grubunun filmin kaplanmasıyla doğrudan bir ilişkisi olduğunu gösterdi. EEE’nin ITO üzerindeki kaplamaları incelendiğinde ise uzun dalga boyunda çıkan iki pik katyon radikal ve dikatyon oluşmunu gösterdi. Bu ayrıca polimer filminin multikromik özelliği olduğunuda kanıtlamaktadır. Son olarak da EEE ve BEDOT konomerlerinin rastgele elektropolimerizasyonu çalışıldı. ITO üzerindeki in-situ UV çalışmaları elde edilen polimerin PEEE, PBEDOT ve PEEE/BEDOT kompositden farklı olduğunu bu sebebten elde edilen filmin homopolimer ya da kompozit olmadığı UV çalışmaları ile de ispatlandı.
1
1. INTRODUCTION
1.1 Electrochemical Cells and Reactions
Scientists have always interested in the processes and factors affacting transport of
the charge across interfaces between chemical phases. Almost always, one of the two
phases contributing to an interface of interest to us will be electrolyte which is
merely the phase through which charge is carried by movement of ions. Electrolytes
can be liquid solutions or fused salts or may be ionically conducting solids. The
second phase at the boundary might be another electrolyte or it might be an
electrode, that serves as a phase through which charge is carried by electronic
movement. Electrodes can be metals or semiconductor and they can be solid or
liquid.
Figure1.1 : Represantation of Reduction
2
In general, if the potential of electrode is changed to its equilibrium value toward
more negative potentials, the substance will be reduced. (Figure1.1) When the
potential of the electrode is moved from equilibrium value toward more positive
potential, the substance will be oxidized. (Figure 1.2) Furthermore, the substance
will be oxidized when the potential of the electrode is moved from the equilibrium
value towards more positive potential.
Figure1.2 : Representation of Oxidation
Two different process types take place at the electrodes. One of them is that charges
are transferred across metal-solution interface. This electron transfer causes
oxidation and reduction to occur. Since these reactions are governed by Faraday’s
Law (i.e. the amount of chemical reaction caused by flow of current is proportional
to the amount of electricity passed) they are called Faradaic Processes. Electrodes at
which faradaic processes occur are sometimes called charge-transfer electrodes.
Under some conditions a given electrode-solution interface will show range of
potentials where no charge transfer reactions occur because such reactions are
thermodynamically, kinetically unfavorable. However, processes such as adsorbtion
3
and desorbtion occur and the the structure of electrode-solution interface can change
with changing potential or solution composition. These processes are called
nonfaradaic processes.
An investigation of electrochemical behavior of a system consists of holding certain
variables of electrochemical cell constant and observing how other variables vary
with time changes in the controlled variables. (Figure 1.3) The electrochemical cell
is considered as a black box to which a certain excitation function (e.g. a potential
step) is applied, and a certain response function(e.g. the resulting variation of current
with time) is measured, with all other system variables held constant. The aim of the
experiment is to obtain information (thermodynamic, kinetic, analytical, etc.) about
the chemical system from observation of the excitation and response functions and a
knowledge of appropriate models of system.
Figure 1.3 : Effecting Variables on Electropolymerization.
1.2 Conducting Polymers
Traditionally polymers were thought as insulators and any electrical conduction in
polymers was generally regarded as an undesirable phenomenon. The residual
conductivity in common polymers can mostly be assigned to loosely bound protons.
Last decades, an opposite trend has started in as much as examinations directed to
the utilization of ionic conductivity of polymeric systems. The active research on
4
thermodynamic and kinetic properties of ion conducting polymers has led to the
wide use of polymer electrolytes and polyelectrolytes in electrochemical systems,
e.g. in power sources, sensors, and the development of all-solid-state electrochemical
devices [1-3]. Also in the 1970s somewhat surprisingly a new class of polymers
possessing high electronic conductivity (electronically conducting polymers) in
partially oxidized (or less frequently reduced) state has been discovered.
Electrochemistry has played a significant role in the preparation and characterization
of these novel materials. Electrochemical techniques are especially suitable for
controlled synthesis of these compounds and for tuning of a well-defined oxidation
state. The preparation, characterization and application of electrochemically active,
electronically conducting polymeric systems are still in the foreground of research
activity in electrochemistry. There are at least two major reasons for this intense
interest. First is the intellectual curiosity of scientists that focuses on understanding
the behaviour of these systems, in particular on the mechanism of charge transfer
and charge transport processes occurring in the course of redox reactions of
conducting polymeric materials. Second is the wide range of promising applications
in the field of energy storage, electrocatalysis, organic electrochemistry,
bioelectrochemistry, photoelectrochemistry, electroanalysis, sensors, electrochromic
displays, microsystem technologies, electronic devices, microwave screening and
corrosion protection etc. Several excellent monographies have been published,
mostly reviewing the knowledge accumulated regarding the development of polymer
film electrodes and their applications. These novel materials with interesting and
unanticipated properties have attracted the whole scientific community including
polymer and synthetic chemists [4], material scientists, organic chemists [5],
analytical chemists [6], as well as theoretical and experimental physicists . After 20
years the fundamental nature of charge propagation on the whole is understood, i.e.
the transport of electrons can be assumed to occur via an electron exchange reaction
(electron hopping) between neighbouring redox sites in redox polymers and by the
motion of delocalized electrons through conjugated systems in the case of so called
conducting polymers (polyaniline, polypyrrole). (In fact, several conduction
mechanisms, such as variable range electron hopping, fluctuation-induced tunneling,
have been considered). In almost every case, the charge is also carried by the motion
of electroinactive ions during electrolysis, i.e. these materials constitute mixed
conductors. Owing to the diversity and complexity of these systems, just to think of
5
the chemical changes (dimerization, cross-linking, ion-pair formation etc) and
polymeric properties (chain and segmental motions, changes in the morphology,
slow relaxation), much research is still needed to achieve a detailed understanding of
all processes related to the dynamic and static properties of several interacting
molecules, which are confined in a polymer network.
1.3 Synthesis and Structure
Polymers can be prepared by using chemical or electrochemical methods of
polymerization. The majority of the redox polymers have been synthesized by
chemical polymerization. Electrochemically active groups are either built in the
polymer structure inside the chain or as a pendant group (pre-functionalized
polymers), or incorporated into the polymer phase in the course of the
polymerization, or fixed at the polymer network in an additional step after the
coating procedure (postcoating functionalization) in the case of the polymer film
electrodes [1-6]. The latter approach is typical for ion-exchange polymers. Several
other alternative synthetic approaches exist, in fact virtually the whole arsenal of
synthetic polymer chemistry have been exploited. From the applied point of view the
electrochemical polymerization of cheap, simple aromatic benzoid or nonbenzoid
(mostly amines, e.g. aniline, o-phenylenediamine) and heterocyclic compounds (e.g.
pyrroles, thiophenes, indoles, azines) is of utmost interest. The reaction is usually
oxidative polymerization. Chemical oxidation [7-8] can also be applied (e.g. the
oxidation of pyrrole by Fe(ClO4)3 leads to conducting polypyrrole), but
electrochemical polymerization is preferable especially if the polymeric product is
intended to use as a polymer film electrode, thin layer sensor, in microtechnology
etc. because the potential control is a precondition of the production of good quality
material and the polymer film is formed at the desirable spot that serves as an anode
during the synthesis chemical route is recommended if large amount of polymer is
needed. The polymers are obtained in an oxidized, high conductivity state containing
incorporated counterions from the solution used in the preparation procedure. It is
easy to change the oxidation state of the polymer electrochemically e.g. by potential
cycling between oxidized, conducting and the neutral, insulating state, or by using
suitable redox compounds. In addition, the variation of the composition of the
contacting solution or that of the gas may also lead to the change of conductivity.
6
For instance, the increase of the pH of the solution [9] or the presence of an electron
donor molecule (e.g. NH3) in the gas phase result in a decrease of the conductivity of
polyaniline (PANI) or polypyrrole (PP) films [10-11]. By further chemical reactions
the structure and conductivity can be altered. The mechanism and the kinetics of the
electropolymerization, especially in the case of polyaniline [12-13] and polypyrrole
[14-15] have been investigated by many researchers. Two points have been
addressed, i.e. the chemical reaction mechanism and kinetics of the growth on a
conducting surface. Owing to the chemical diversity of the compounds studied a
general scheme cannot be given. However, it has been proved that the first step is the
formation of cation radicals. The further fate of this highly reactive species depends
on the experimental conditions (composition of the solution, temperature, potential
or the rate of the potential change, galvanostatic current density, material of the
electrode, state of the electrode surface etc). In favorable case the next step is a
dimerization reaction and then stepwise chain growth proceeds via association of
radical ions (RR-route) or that of a cation radical with a neutral monomer (RS-
route). Even there might be parallel dimerization reactions leading to different
products or to the polymer of a disordered structure. The inactive ions present in the
solution may play a pivotal role in the stabilization of the radical ions. Potential
cycling is usually more efficient than potentiostatic method, i.e. at least a partial
reduction of the oligomer helps the polymerization reaction. It might be the case if
RS-route is preferred, and the monomer carries a charge, e.g. a protonated aniline
molecule (PANI can be prepared only in acid media, at higher pH values other
compounds, such as p-aminophenol, azobenzene, 4-aminodiphenylamine, are
formed). A relatively high concentration of cation radicals should be maintained in
the vicinity of the electrode. The radical cation and the dimers can diffuse away from
the electrode, usually intensive stirring of the solution decreases the yield of the
polymer production. The radical cations can react with the electrode or take part in
side reactions with the nucleophilic reactants (e.g. solvent molecules) present in the
solution. Usually the oxidation of the monomer is an irreversible process and takes
place at higher positive potentials than that of the reversible redox reaction of the
polymer. However, in the case of azines (e.g. 1-hydroxy-phenazine [16] , methylene
blue [17], neutral red [18]) reversible redox reactions of the monomers occur at less
positive potentials and this redox activity can be retained in the polymer, i.e. the
polymerization reaction, that takes place at higher potentials does not alter
7
substantially the redox behavior of the monomer. For instance, the catalytic activity
of methylene blue towards oxidation of biological molecules (e.g. hemoglobin) is
preserved in the polymer [19] .
The knowledge of kinetics of the electrodeposition process is also of utmost
importance. It depends on the same factors enlisted above, although the role of the
material and the actual properties of the electrode surface is evidently more
pronounced. For example, the oxidation of aniline at Pt is an autocatalytic process.
The specific interactions, the wetting may determine the nucleation and the
dimensionality of the growth process. Two or more stages of the polymerization
process can be distinguished. In the case of PANI it has been found that first a
compact layer (L ∼200 nm) is formed on the electrode surface via a potential-
independent nucleation and a two-dimensional (2-D, lateral) growth of PANI
islands. In the advanced stage 1-D growth of polymer chain with continuous
branching leading to an open structure takes place [20] It is established that – in
accordance with the theory [21] – the density of the polymer layer decreases with the
film thickness, i.e. from the metal surface to the polymer:solution interface. The film
morphology (compactness, swelling) is strongly dependent on the composition of the
solution, notably on the type of counterions present in the solution, and the
plasticizing ability of the solventmolecules [22] .
It has been demonstrated that in the synthesis of polypyrrole (PPy) the current
density is a crucial parameter [23-24] . At low current densities the structure of PPy
is dominated by one-dimensional chains, while at high current densities two-
dimensional microscopic structures of the polymer are formed.
Although the region close to the electrode surface shows a more or less well-defined
structure, in general the polymer layer can be considered as an amorphous material
[25-26] However, there are rare reports on crystalline structure, too. For instance,
poly(p-phenylene) films obtained by electrooxidation of benzene in concentrated
H2SO4 emulsion show a highly crystalline structure [27].
8
1.4 Kinetic Behaviour and Thermodynamical Considerations
The electron conducting polymers can easily be switched between conducting and
insulating states just by changing the potential, i.e. by electrochemical (or chemical)
oxidation and reduction, respectively. When the oxidation state of the polymers is
varied not only their conductivity is altered but other properties (e.g. colour) also
change. It is the very feature that can be exploited in many practical applications.
The rate of this change is of utmost importance virtually in all cases, consequently
much effort has been made concerning the elucidationof the nature and mechanism
of the redox processes occurring in these systems [28].
1.5 Applications of Conducting Polymers
On a first view, the most interesting property of the intrinsically conducting
polymers (ICPs) is the high conductivity, almost metallic conductivity of a material
which has a good corrosion stability. This is important for the dry state. The second
point is given by the advantage that ICPs can be deposited from a liquid phase even
into complex topographies. Finally, ICPs belong to a small class of materials
changing their properties by a reversible redox process. Thus, in conctact with an
electrolyte, the redox properties of ICPs become dominant. Due to that redox
process, chemical, optical and ionic properties of ICP can be switched. These values
can be changed by a variation of anion size and preparation techniques, e.g.
inclusion of other chemical species (see earlier).When ICP is oxidized, the volume
of polymer increases or colour and some other properties changes. Qualitative data
are given in Table 1.1
9
Table1.1: Qualitative Properties of ICPs According to Charging State
Charging State Reduced Oxidized
Stoichometry Without anions
(or with cations)
With anions
(or without cations)
Content of solvent Small Higher
Volume Increase with oxidation
Colour Transparent or bright Dark
Electronic conductivity Semiconducting Metallic
Ionic conductivity Smaller Higher
Diffusion of molecules Dependent on structure
Surface Tension Hydrophobic Hydrophilic
In general, important functions are given by the application in thin film processes,
by the intrinsic pore structure and the redox process. This yields a first grouping of
applications described in Table 1.2. A specific function as wettability, optical or
membrane properties, leads to applications in special systems, e.g. displays, or
processes, e.g. metallisation of holes. These are arranged, however, under a
complementary grouping given by the technological fields, e.g. energy technology,
sensors and others. For extended descriptions see the reviews in [29]
10
Table 1.2: Some Applications for Conducting Polymer
General function Special function Application System
Reference
Thin film
technologies in
macro-or
microscopic
systems
e- Conducting film
e-Conducting film
holes
e-Conducting film
band structure, optical
transitions
Antistatic coating
Printed circuit
boards, through
hole plating
Capacitor
LED’s
PEDOT
PEDOT/epoxy
resin metal/
dielectric/
PEDOT
Metal/PPV/ITO
Material for
fillings, porous
membranes,
composites
Matrix/Membrane for
functional molecules
Membrane
Sensors
Mebrane,
seperation
PANI/glucose
oxidase
Py
Redox process Wettability
Optical properties
Intercalation
Change of volume and
length
Off-set printing
Smart windows
Active mass of
batteries
Actuators
(artificial muscles)
PTh
PEDOT
PTh/Li
PPy
Others Inibition, protection Corrosion protection PANI/Fe
11
In thin film technologies, ICPs can be used as conducting layer. A field with a wide
technical importance is the antistatic protection [30] and the electromagnetic
interference shielding by conducting polymers [31] . PANI, PPy and PTh
derivatives have been predominant. They are incorporated as fillers in common
polymeric materials like polyvinylchloride, polyvinylacetate or others to substitute
carbon black filled materials. Poly (3,4-ethylendioxithiophene) (PEDOT) is used as
a protective layer for photographic films.
The possibility of a reversible switching of conducting polymers between two redox
states rose speculations for rechargeable batteries. The first prototypes of
commercial batteries with conductive polymers used Li:polypyrrole (Varta-BASF)
or Li: polyaniline [32].
Another field of application is given by the excellent ionic conductivity allowing
high discharge rates. The use as electrode materials in supercapacitors is a good
example. Supercapitors require high capacitance and quick charge:discharge
electrode materials. Compared with classical used carbon materials conducting
polymers shows promising characteristics [33]. Further, ICPs are now used as
electrode material in capacitors [34-35]. They show an enlarged stability against
breakdown phenomena because of the loss of conductivity at higher field strength.
1.5.1 Electroluminescent and Electrochromic Devices.
Electrochromic devices could be realized with ICPs. In that case, the response time
of the conducting polymers must be fast enough [36](100 ms) and a reversibility of
the charging:discharging must be achieved (up to 105 cycles or more) [37]. Smart
windows based on a sandwich structure of ITO: PEDOT-PSS:ITO between glass
were developed [38].
1.5.2 Use as Membrane and Ion Exchanger.
Conducting polymers can be regarded as membranes due to their porosity. They
could be used for the separation of gas or liquids. Free standing (on supporting
substrates) chemically prepared PANI films are permeated selectively by gases. In
general, the larger the gas molecule the lower the permeability through the film.
12
1.5.3 Corrosion Protection
Conducting polymers can be deposited as corrosion protection layer. PANI, PPy and
PTh (and their derivatives) were used [39-40]. Favourite substrate of the
investigation is mild steel, but also dental materials are discussed [41]. The
application of the conducting materials takes place directly by electrodeposition on
the active material or by coating of formulated solutions of these polymers. The
efficiency and mechanism of corrosion protection are not yet classified. On iron an
anodic protection is discussed [42]. Due to the redox processes taking place, thicker
layers of iron oxide are formed and are stabilised against dissolution and reduction.
An inhibition is also reasonable due to a geometric blocking and a reduction of the
active surface.
1.5.4 Sensors
The use of conducting polymers in sensor technologies consists as an electrode
modification to improve selectivity, to impart selectivity, to suppress interference
and to support as a matrix for sensor molecules. All electrochemical transducer
principles can be realised with conducting polymer modified electrodes. The role of
the conducting polymer may be active (for instance as catalytic layer, as redox
mediator, as switch, or as chemical modulated resistor) or passive (for instance as
matrix) [43]. Sensors with conducting polymers exist for different substances, for
example for gases like SO2 and NO2 [44], glucose [45] , urea [46] , hemoglobin,
xanthin [47] or humidity [48].
1.5.5 Artificial muscles
Conducting polymers show a swelling with increasing oxidation (doping). The
ingress of counter-anions into the polymer leads to a structural change of the
polymer backbone and to an increase in volume up to 30% [49]. These
electromechanical properties are used in actuators like the polymer based artificial
muscle. Bi-layer structures on the base of PPy are described. Three layer muscles,
formed of two layers of conducting polymers divorced by a flexible insulating foil,
are developed to avoid the use of a separate, metallic counter electrode [50] .
13
1.6 Poly(3,4ethylenedioxythiophene)
During the second half of the 1980s, scientists at the Bayer AG research laboratories
in Germany developed a new polythiophene derivative, poly(3,4-
ethylenedioxythiophene), having the backbone structure shown below.(Figure1.4)
[51].
Figure1.4 : PEDOT Molecular Structure
This polymer, often abbreviated as PEDOT, was initially developed to give a soluble
conducting polymer that lacked the presence of undesired α-β, and β-β,couplings
within the polymer backbone. Prepared using standard oxidative chemical or
electrochemical polymerization methods, PEDOT was initially found to be an
insoluble polymer, yet exhibited some very interesting properties. In addition to a
very high conductivity (ca. 300 S/cm), PEDOT was found to be almost transparent in
thin, oxidized films and showed a very high stability in the oxidized state. [52] The
solubility problem was subsequently circumvented by using a water-soluble
polyelectrolyte, poly(styrene sulfonic acid) (PSS), as the charge balancing dopant
during polymerization to yield PEDOT/PSS. This combination resulted in a water-
soluble polyelectrolyte system with good filmforming properties, high conductivity
(ca. 10 S/cm), high visible light transmissivity, and excellent stability. [53] Films of
PEDOT/PSS can be heated in air at 100 oC for over 1000 h with only a minimal
change in conductivity. With this new system, now known under its commercial
name BAYTRON P (P stands for polymer), Bayer researchers have been able to
develop several applications. Although initially used as an antistatic coating in
photographic films from AGFA, several new applications have been implemented
over the past few years (e.g., electrode material in capaci-tors, material for through-
hole plating of printed circuit boards), and more are expected. [54]
14
Examining the range of polymers that have been accessed using the PEDOT building
block, one is struck by its synthetic flexibility and utility. Its highly electron-rich
nature plays a profound role in the optical, electrochemical, and electrical properties
of the resultant polymers. The conducting form of PEDOT stands out for its high
degree of visible light transmissivity and concurrent environmental stability, which
is important for industrial applications. EDOT polymerizes rapidly and efficiently,
leading to highly electroactive PEDOT films that adhere well to typical electrode
materials and have a low oxidation potential, which provides for facile, long-term
electrochemical switching. As illustrated by the many derivatives shown above,
PEDOT provides materials with a range of bandgaps, yielding films having colors
over the entire spectral range. The synthetic flexibility of EDOT, coupled with its
recent commercial availability as BAYTRON M, has made it an excellent
component for variable-bandgap conjugated polymers. In general, the electronic
bandgap of a conjugated chain is controlled by varying the degree of p-overlap along
the backbone via steric interactions, and by controlling the electronic character of the
p-system with electrondonating or accepting substituents. The latter is accomplished
by using substituents and co-repeat units that adjust the highest occupied molecular
orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of
the p-system. A broad family of EDOT-based polymers has been prepared with
higher energy gaps than the parent PEDOT. By using a series of oxidatively
polymerizable bis-EDOT-arylenes, polymers with bandgaps ranging from 1.4±2.5
eV have been prepared. As such, neutral polymer with colors ranging from blue
through purple, red, orange, green, and yellow have been made available. This is
illustrated in Figure 1.5, which shows the rainbow of colors possible in PEDOT
derivatives.
15
Figure1.5 : PEDOT Copolymers
Examining the range of polymers that have been accessed using the PEDOT building
block, one is struck by its synthetic flexibility and utility. Its highly electron-rich
nature plays a rofound role in the optical, electrochemical, and electrical properties
of the resultant polymers. The conducting form of PEDOT stands out for its high
degree of visible light transmissivity and concurrent environmental stability, which
is important for industrial applications. EDOT polymerizes rapidly and efficiently,
leading to highly electroactive PEDOT films that adhere well to typical electrode
materials and have a low oxidation potential, which provides for facile, long-term
electrochemical switching. As illustrated by the many derivatives shown above,
PEDOT provides materials with a range of bandgaps, yielding films having colors
over the entire spectral range.
1.7 Polycarbazoles
Polycarbazole, among conducting polymers, is attributed with good electroactivity,
and useful thermal, electrical andphotophysical properties [55]. However, π→π*
electron system along its backbone imparts rigidity to the polymer and, therefore,
makes it infusible and poorly processable. Due to this reason, it was not initially
employed as widely in devices as other conducting polymers. Recent advances in
synthesis methods have, however, revived interest in polycarbazole [56-57].
Investigations related to chemical modification or co-polymerization of carbazole
with other monomers have led to the use of polycarbazole and its derivatives as
redox catalysts, photoactive devices, sensors, electrochromic display,
electroluminescent devices and biosensors [58] .
16
It is well-known that carbazole compounds exhibit photoconductive properties and
have internal donor group in the 9-position. After the various acceptor groups are
introduced to 3- and 6-positions, carbazole compounds show both photoconductivity
and secondorder nonlinearity [59]. Carbazole monomers and polymers used as a
photoconductive component and an EO chromophore have already been developed
[60].
The π-electron system along the polymer backbone, which confers rigidity, and the
crosslinking points between polymer chains, make polycarbazole insoluble, infusible
and therefore poorly processable. Co-processing of polycarbazole may, therefore
offer improvements in mechanical properties and processing technology. Carbazole-
based polymer systems have received much attention [61-63] because of their
interesting thermal, electrical and photophysical properties. Researches have
continued for important properties of carbazole polymers by means of chemical
modification or copolymerisation of N-vinyl carbazole with the other monomers
[61, 64].
1.8 Carbon Fiber Microelectode
Carbon due to different allotropes (graphite, diamond, ly.fullerenes /nanotubes),
various microtextures (more or less ordered) owing to the degree of graphitization, a
rich variety of dimensionality from 0 to 3D and ability for existence under different
forms (from powders to fibres, foams, fabrics and composites) represents a very
attractive material for electrochemical applications, especially for storage of energy.
Carbon electrode is well polarizable, however, its electrical conductivity strongly
depends on the thermal treatment, microtexture, hybridization and and content of
heteroatoms. Additionally, the amphoteric character of carbon allows use of the rich
electrochemical properties of this element from donor to acceptor state. Apart from
it, carbon materials are environmentally friendly. During the last years a great
interest has been focused on the application of carbons as electrode materials
because of their accessibility, and easy proceessibility and relatively low cost. They
are chemically stable in different solutions(from strongly acidic to basic) and able
for performance in a wide rnge of temperatures. Already well-established chemical
and physical methods of activation allow to produce materials with a developed
surface area and a controlled distribution of pores that determine the
17
electrode/electrolyte interface for electrochemical applications. The possibility of of
using the activated carbon without binding substance, e.g., fibrous fabrics or felts,
gives an additional profit from construction point of view.
Taking into account all mentioned characteristics, carbon as a material for the
storage of the energy in electrochemical capacitors seems to be extremely attractive.
High performance carbon fibers can be combined with thermoset and thermoplastic
resin systems. Polyacrylonitrile (PAN) based carbon fibers are under continual
development and are used in composites in order to produce materials of lower
density and greater strength. They are used for weaving, braiding, filament winding
applications, unidirectional tapes and as prepreg tow for fiber placement having
excellent creep, fatigue resistance, high tensile strength and stiffness characteristics.
The application of a polymeric/copolymeric ‘interface’, acting as a coupling agent,
can improve the interfacial properties between reinforcing (carbon) fibers and the
polymeric matrix [65-66]. However, these interfacial reactive groups need to be
strongly bound to the carbon surface so that these copolymer materials can survive
other subsequent treatments, i.e., treatment with thermoset thermoplastic resin
systems or for the immobilization of enzymes (for biosensor microelectrode
fabrication). The surfaces of these systems can also be reacted with metal catalysts,
which bind strongly to the carbon fiber due to the presence of suitable functional
groups in the conductive copolymer coating. For these reasons, the detailed
characterization of strongly bound polymers or copolymers, having a homogeneous
thin film, is important. Electrografting of copolymers with conductive and
nonconductive contents onto carbon fibers were studied recently [57, 67 -69].
1.9 Cyclic Voltammetry
Cyclic voltametry is a popular member of a family of dynamic electrochemical
methods in which the potential applied to electrochemical cell is scanned. The
resulting current is output vs potential. A typical three-electrode cell suitable for
studies of materials includes reference electrode, a counter electrode, and a working
electrode. Instrumentation for modern cyclic voltametry is based on three electrode
potantiostat [70] which controls the potential of working electrode vs reference
electrode, while compansating for as much of the cell resistance possible. The
18
potansiostat and cell design allow events at working electrode to be monitored
during the experiment.
The potential waveform input to the electrochemical cell is triangular or cyclic. The
potential scan is programmed to begin at an initial potential where no electrolysis
occurs. The scan continues at the desired linear scan rate to the switching potential,
then reverse direction and returns to the initial potential.
The output of cyclic voltametry is a plot of the current flowing in the
electrochemical cell during the cyclic potential scan. Consider a solution containing
electroactive species O in the cellwith a metal working electrode. This solution also
contains a large concentrations (e.g. 0,01 to 1M) of inert electrolyte to lower the cell
resistance and minimize electrical migration. Suppose that O is reversibly and
rapidly reduced. Then, reaction (1.1) takes places, where n is the number of electrons
transferred from electrode to O.
O+ne-→R (1.1)
This reaction is called diffusion controlled because the cell current is governed by
the rate of diffusion O to the electrode surface. On the otherhand, kinetic control
may be active if the rate of electrode reaction is slow with respect to the rate of
potential scan.
1.10 Electrochemical Impedance Spectroscopy
Electrochemical impedance spectroscopy, is a small time technique for the
investigation of the capacitive behavior constant which is related to the electrical
charge transfer at the carbon materials.
Theoretical models have been developed to explain the impedance characteristics of
homogeneous film [71] and porous membrane [72]. For the uniform films a model
considering the diffusional transport of single type of charge carrier (electron or ion)
across the film with a charge transfer process at metal–film interface was proposed.
This model could explain the Randles circuit behavior, the Warburg contribution and
the capacitive responses at low frequencies. On the other hand, in the advanced
homogeneous models, diffusion– migration transport of electrons and/or ions and
nonequilibrium charge transfer across the interfaces at the boundaries of the films
19
were considered and explained through introduction of one or more capacitive
elements in parallel with charge transfer resistances in the equivalent circuits.
The generalized transmission line circuit model predicts the relevant impedance
features of such a system in terms of a Nyquist plot that was proposed in [73], based
on a mathematical approach. The two semi-circles at the highest frequencies,
induced by the processes at the metal/polymer and polymer/solution interfaces, are,
in practice, not always detectable. Sometimes, only one or even one-half semi-circle
is observed; for other cases, these two semi-circles are partially overlapped to each
other, the actual situation observed depending on the characteristics of the interfacial
processes in terms of energy (resistance) to overcome at the relevant interface.
Moreover, these semi-circles are very often depressed, most probably due to non-
homogeneous separation surfaces [74]. Furthermore, they can also overlap to the
mid-frequency Warburg impedance quasi-45°-slope segment that reflects the
diffusion–migration of ions at the boundary surface between solution and polymer,
inside the latter medium. Finally, the 90°-trend at the lowest frequencies, due to a
capacitive impedance, accounts for the charge transport process inside the bulk of
the film
It has already examined how a working electrode/solution interface responds to
various perturbations including potential steps and potential sweeps. These
perturbations are usually of a large amplitute, and they generally drive the working
electrode far from equilibrium. Another approach is to perturb the cell
alternating(usually sinusodial)signal of small amplitute(nominally a few milivolts
peak to peak) and observe the manner in which the system follows the perturbation
at steady state. A major advantage with this ac impedance spectroscopic technique is
that the responce theoretically treated via linearized current-potential characteristic.
This leads to important modeling simplifications matters related to diffusion and
charge/ion transport kinetics.
The parameter(electrical ) impedance Z is the ac analog of the resistance, R for dc
circuits and express the relationship between a sinusoidal signal and corresponding
responce
e=E.sinωt. (1.2)
20
i= I(Sinωt + φ) (1.3)
Z=e/i (1.4)
The phase angle φ is negative for capacitive circuits and is 90 o for a pure capacitor.
The impedance, then is obviously a vector quantity and as usual, we can employ
both rectangular and polar coordinates to denote a vector. In the former format, the
vector Z is given by R-jXc, where j=(-1)1/2 and Xc is termed capacitive
reactance(equal to 1/ωC, ω=2πf, where f is the ac frequency in hertz. Simply put Xc
is a frequency sensitive variable resistor that switches from infinity at low frequency
to zero at high frequency. The magnitude of Z(|Z|) is (R2 + Xc2)1/2 and phase angle is
given by
tanφ = Xc/R=1/ωRC (1.5)
In polar coordinates, Z can be written in Eular form as
Z=|Z|eiφ (1.6)
Seperation of impedance components into ′real′ and ′imaginary′ components is a
bookkeping measure and simply embodies the fact that there is phase lag between
the applied signal and measured responce. Thus, we can model the systems responce
in terms of complex plane impedance plots and expect the responce in ters of
complex plane impedance plots and expect the responce from a purely resistive
circuit to be distributed along abscissa. On the other hand, a ‘pure’ capacitor will
manifest a responce along the ordinate. Intermediate values of φ are expected for
other RC circuits [75]
At high frequencies, the semicircle is attributable to the process at the polymer-
electrolyte interface, which is expected to be the double-layer capacitance (Cdl ) in
parallel with the charge-transfer resistance (Rct) due to the charge exchange and
compensation at the polymer-solution interface [76].
21
1.10.1 Two different types of experiments for EIS
In order to understand the impedance responce of conducting polymer, it is
necessary to consider in detail [77] the impedance responces from two types of
experiment
1.10.2 Case1: Metal/Polymer/Electrolyte
In this case the conducting polymer(P) is on a metal substrate(M) and immersed in
an electrolyte solution(S). At sufficiently low frequencies across the M/P interface
the electrons will be at equlibrium whilts the anions will be at equilibrium across the
P/S interface. In order to predict the impedance responce we make the following
assumptions.
1) The polymer layer is a homogenous bulk phase sandwiched between metal
and electrolyte.
2) Electroneutrality holds within the polymer phase except for two space charge
regions-one at the P/M interface and one at P/S interface.
3) The penetration of these space charge regions into the polymer is small
compared to the thickness of polymer phase.
4) Only electrons can cross the M/P interface.
5) Only anions can cross the P/S interface. This is not likely to the case at low
oxidation levels in the polymer when there is incomplete exclusion of anions.
Figure 1.6: Theoretical Impedance Plane Display for Metal/Polymer/Electrolyte
Case
22
It is not necessary to assume that there is only one type positive charge in the
polymer, or that ion pairs do not exist. The form of impedance spectrum is given
Figure1.6. This can be broken down into seveeral clearly defined regions.
The impedance is measured from the tip of the reference electrode to the metal
surface, therefore the impedance of the electrolyte phase between the reference
electrode and polymer must be included. Thus the high frequency responce of the
system will consist of, in addition to the electrolyte component(which is resistance R
in parallel with a capacity Ce), a semicircle due to the resistance Rct of polymer
phase in parallel with its geometric capacity. From this, provided the film thickness
is known, dielectric constant of polymer phase,εr, and its conductivity,κ, can be
calculated.
Cg=εr. εoA/d (1.7)
and
Rb=d/Aκ (1.8)
A is the electrode area. The maximum of the bulk polymer semicircle occurs at a
radial frequency ω.
1.10.3 Case2: Metal/Polymer/Metal
In this case the polymer film(P) is sandwiched between two metal electrodes(M),
with little or no electrolyte solution present, though there may course be molecules
of solvent trapped within the film. Electrons will be in equilibrium across the tow
M/P interfaces as in the above case. The anions clearly can not leave the membrane.
The impedance responce of this system will be similar to that in case 1 in some
frequency ranges. However, there will be some important differences (Figure1.7)
23
Figure 1.7 : Theoretical Impedance Plane Display for Metal/Polymer/Metal Case.
(1) At high frequencies there will be no component due to the solution, hence the
first semicircle observed should be due to the bulk resistance of the polymer
and geometric capacitance of the polymer film alone.
(2) There is only one charge transfer semicircle possible in this case, that for
electrons crossing the M/P interfaces. If this is present then, as there are two
identical interfaces, Rct will actually be one-half of that represented by the
semicircle.
(3) After the Wardburg region a low frequency capacitive limit will not be
observed since, although the anions are blocked at both interfaces, the
electronic charge is free to move throughout the system at all times(i.e. is not
blocked) and current can flow. Hence the impedance responce will fall to the
real axis on the Nyquist plot at limiting low frequencies.
1.11 SuperCapacitors or Ultracapacitors
Performance of a supercapacitor (or ultracapacitor) combines simultaneously two
kinds of energy storage i.e. an electrostatic attraction as in electric double layer
capacitors(EDLC) and faradaic reactions similar to processes proceeding in
accumulators. Pseudocapacitance arises when, for thermodyamic reasons, the charge
q requiredfor the progression of an electrochemical process is a continously
changing function of potential U. Then the derivative C=dq/dU corresponds to a
faradaic kind of capacitance. In this case charge accumulated in the capacitor is
strongly dependent on the electrode material.
24
2. EXPERIMENTAL
2.1 Materials
All chemicals were used as received from Aldrich Chemical without further
purification, otherwise stated. A high strength (HS) carbon fibers C 320.000A (CA)
(Sigri Carbon, Meitingen, Germany) containing 320000 single filaments in a roving
were used as working electrodes. All of the electrodes were prepared by using CF
(diameter = 7 µm) attached to a copper wire with a Teflon tape. The electrode area
keeps up constant (~ 0.3-0.5 cm2) by adjusting the dipping length and covering the
rest of the fibers with the Teflon tape.
Polymerization reactions were performed electrochemically in using
dichloromethane (CH2Cl2) solution containing 0.05 M TEAP and monomer. Cyclic
voltammogram (CV), of the polymers was performed with Parstat 2263-1(software:
powersuit). In a three-electrode setup employing CFME as working. The reference
electrode was AgAgCl was stocked in 3M NaCl. Some experiments were done
with Ag wire. The pseudo-reference was calibrated externally using a 5 mM solution
of ferrocene (Fc / Fc+) in the electrolyte [E1/2(Fc / Fc+) = +0.13 V vs. silver wire in
0.1 M LiClO4/ PC].
Electrochemical Impedance measurements were conducted in monomer free
electrolyte solution with a perturbation amplitude 10mV over a frequency range
0.01Hz-100kHz with Parstat 2263-1 (software: powersuit). Ubbelohde viscosimeter
was used for measuring of viscosity of solvents at 40oC.
2.2 Fiber Surface Morphology
All modified carbon fibers were analyzed by scanning electron microscopy (SEM)
using a Hitachi S-2700 scanning electron microscope (Nissei Sangyo GmbH,
Rathingen, Germany), which was connected to an energy dispersive X-ray micro
analyzer (EDX) (Kevex type delta V, Foster City, CA, USA). The excitation energy
was 10 keV at a beam current of 0.5 nA.
25
2.3 FTIR –ATR Reflectance Measurements
Thin Polymeric film electrografted onto carbon fiber surface were analysed by
FTIR reflectance Spectrometer, using Perkin Elmer with an ATR attachment of
spectrum one B with an ATR attachment Universal ATR- with diamond and ZnSe.
2.4 UV-visible Spectroscopy
UV Visible and spectroelectrochemical measurements were performed with
Shimadzu 160 A recording spectrophotometer.
2.5 Scanning Electron Microscope
Samples were analyzed by scanning electron microscope (SEM) using a Hitachi S-
2700 scanning electron microscope( Nissei Sangyo GmbH, Rathingen, Germany),
which was connected to an energy dispersive X-Ray microanaylzer (EDX)(Kevex
type type delta V, Foster City, CA, USA). The excitation energy was 10keV at a
beam current of 0.5nA.
2.6 Monomer Synthesis
2.6.1 Synthesis of N-(Hydroxymethyl) Carbazole
N-(Hydroxymethyl)carbazole (N-MeOHCz) (Figure 2.1) was prepared by Tawney
method. To a suspension of 10 g (0.06 mol) of carbazole in 25 ml of 37 %
formaldehyde, 2 ml of 5 % sodium hydroxide was added at 300C. Within 10 min. all
of the carbazole had dissolved and a mildly exothermic reaction had raised the
temperature to 33 0C. Separation of the product began promptly. After 2.5 hours at
room temperature the solution was filtered, dried in vacuum. Several
recrystallization was made from n-Hexane. The product have resulted a m.p: 133 0C,
and yield obtained as 65%. 1H-NMR, FTIR absorption frequencies data was as
following:
26
N
CH2
OH
NaOH
30o
H
O
C H
N
H
+
Figure 2.1: Monomer Synthesis
1H-NMR (DMSO-d6), (ppm): 5.7-5.9 (d,2H ),6.3-6.6 (t,1H), 7.2-8.2 (m,8H).
The structure of the product N-(Hydroxymethyl)carbazole was confirmed
spectroscopically .
1H-NMR spectrum recorded in DMSO-d6 evidenced resonance signals of -CH2, –OH
and aromatic protons of relative intensities corresponding to the number and type of
protons. The FTIR-ATR spectrum of N-(Hydroxymethyl)carbazole indicated that the
peak at 3414cm-1 attributed to alcohol band stretching, 2916cm-1 methyl(CH2)
groups of N-(Hydroxymethyl)carbazole , 1539cm-1 is due to aromatic ring of Cz, at
1223cm-1 (carbazole C-N strecthing), at 745cm-1 evidence for out of plane bending
of aromatic C-H deformation.
2.6.2 Synthesis of BEDOT
Bis-3, 4 etyhlenedioxythiophene (BEDOT) was prepared via Ullmann coupling
utilizing lithiated EDOT and Copper (II) Chloride as described before [78] .
1H-NMR (CDCl3) δ=4.3 ppm (4H, s), 6.2 ppm (2H, 2).
2.6.3 Bromination of BEDOT
To a stirred solution of BEDOT (0.6 g, 2.1mmol) in CHCl3 (40mL) was added N-
bromosuccinimide (NBS) (0.8g, 4.5mmol) in CHCl3 (50mL) via dropping funnel.
The reaction mixture was stirred for 3hours at 0oC under nitrogen atmosphere. It was
then poured into water. Then it was extracted with CHCl3. Organic extracts were
dried with Na2SO4 and the solvent was evaporated and dried under vacuum. It
should be handled carefully and used just after preparation. The overall yield was 70
% and H-NMR spectra in CDCl3 contains only the peak at δ=4.3 ppm that
27
corresponds to etyhlenedioxythiophene ring and H belong the thiophene ring at
δ=6.2 ppm was disappeared due to dibromination.
O O
S
O O
SBrBr
O O
S
O O
S
CHCl3
0oC ,
NBSS
Figure 2.2: Bromination of BEDOT
2.6.4 Synthesis of 3-Trimethyltin-9-Ethylcarbazole
To a 30mL THF ECz (1.0 g, 5.12mmol) was added under nitrogen purge.
The solution was cooled to -78oC by means of liquid N2 bath. To this solution n-
BuLi (3mL, 5.12mmol 2.5M in hexane) was added. The resulting solution was
stirred for 1 hour then, added to trimethyltin chloride (1.2 g, 5.12 mmol). The
reaction mixture was continued to stir 1 hour more at –40 oC then, it was stirred at
room temperature for a further 24 hours. After the reaction completed, solution was
poured into water and extracted with CH2Cl2. Organic extracts were dried with
Na2SO4. Golden brown oily product was in vacuum overnight.
1)BuLi, -78 oC, THF
)2)Sn(CH3 3Cl2
Sn(CH3)3
CH2CH3
CH2CH3
N N
Figure 2.3 : Synthesis of 3-Trimethyltin-9-Ethylcarbazole
1H-NMR (CDCl3) δ= 8.09 ppm (2H,d), 7.4-7.3 ppm (5H, m), 4.2 ppm (2H,t), 1.2
ppm (3H,d), 0.35 ppm (9H, s).
2.6.5 Synthesis of ECz-BEDOT-ECz
To a solution of di-bromoBEDOT (0.5 g, 1.14 mmol) and 3-trimethyltin-9-
ethylcarbazole (0.4 g, 1.11 mmol) in 100 ml THF (trans-dicholoro
bistriphenylphosphine palladium (II) chloride (0.02g, 0.5 mmol) were added,
28
refluxed under N2 atmosphere for 24hours. Then reaction mixture is poured into
water. It was extracted with CHCl3 and dried with Na2SO4 and the concentrated in
vacuum. The crude product were purified by flash chromatography on SiO2 column
eluting with petroleum ether-Diethyl ether (4/3, v/v). Melting point of ECz-BEDOT-
ECz is obtained as 65.5-66.0oC
Sn(CH3)3
CH2CH3
CH2CH3CH2
CH3
O O
S
O
SBr+
Stille coupling
/toluenePd(PPh3)2Cl
2
20hrs,reflux
N
O
Br
NN
O
O O
S
O
S
Figure 2.4 : Synthesis of ECz-BEDOT-ECz
1H-NMR (CDCl3) δ= 8.2 ppm (4H, d), 7.4-7.3 ppm (14H, m), 4.4 ppm (8H, t),
4.2(4H), 1.25 ppm (6H, d).
29
Table 2.1: Proposed as Signments for the Main Vibrations of ECz-BEDOT-ECz
Comonomer
Wavenumber, cm-1 Assignments
2980(v), 3050(s) δ(C-H) (aromatic C-H)
1616(s), 1500(s), 1466(s) ν(C-C)ring
1316(s) ν (C-CH3) of ECZ
1283(w),1250(s),1166(s) ν(C=C) ν(C-C) of thiophene ring and
ν(−COROC-)
931(s), 908(s), 847(s),
808(s), 750(s), 710(s)
ν(C-S) and δ(C-S) and δ(C-H)
s:strong, w:weak, v:variable
2.6.6 Synthesis of EDOT-ECz-EDOT
2-trimethyltin EDOT, 3,6 dibromoethylcarbazole and were synthesized as reported
before. EDOT-ECz-EDOT that is extensively conjugated, low oxidation potential
monomer was synthesized by Stille Coupling instead of Grignard coupling as
reported in literature.
30
CH3
S
O O
Sn(CH3)3
CH3
Pd(PPh3)2Cl
2
N
CH2
Br Br
+
-78o
N
CH2
S
O O
S
O O
Figure 2.5: Synthesis of EDOT-ECz-EDOT
1H-NMR (CDCl3) δ= 1.2 ppm (3H,t), 4.2 ppm (2H,q), 4.3 ppm (4H,s), 6.2 ppm
(2H,2), 7.2 ppm (2H,d), 7.4 ppm (2H,d), 8.2 ppm (2H,s).
31
3. RESULTS AND DISCUSSION
3.1 Electropolymerization of Substituted Cz Derivatives on CFME.
The oxidative electropolymerization of Carbazole(Cz), 1-Bromo-1 methyl-karbozoyl
methyl ester carbazole(BrCz), N-vinyl carbazole, EtCz, EtOHCz was carried out in
dichloromethane(CH2Cl2) with 0.05 TEAP.(Figure3.1)
CH2
N
H
CH2
CH2
CH3
CH2
CH3
N-ethylcarbazole
N
N-Vinyl CarbazoleCarbazole
N
HC=CH 2
OH
N
N-hydroxy ethyl carbazole
N
O
C=O
CH
Br
1-Bromo-1methyl-carbazoyl-methyl ester
Figure 3.1 : Some Carbazole Monomers.
Cyclic voltammograms corresponding to the potentiodynamic electrooxidation (and
electrochemical coating) of Cz derivatives on carbon fiber micro electrode(CFME)
with scan rate of 50mV/s and 5 cycle in TEAP/CH2Cl2 are presented in Figuree3.2-6.
32
-0,2 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6
-2
-1
0
1
2
3
4
N
H
current,µA
/cm
2
potentia l vs Ag/AgC l
Figure 3.2 : Potentiodynamic Growth of Cz on CFME in 0.05M TEAP Containing
CH2Cl2,(scan rate:50mV/s), [Cz]=10mM.
The cyclic voltamogam of carbazole in dichloromethane exhibits a weak oxidation
(Epa:0.99V vs Ag/AgCl), but correponding cathodic wave (Epc: 0.68V vs Ag/AgCl)
is higher current density. Gradual increase in the intensity of cathodic wave with
repeated sweeps indicates that the reaction product is gradually deposited on the
surface of the CFME.
-0,2 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6
-0,4
0,0
0,4
0,8
1,2
1,6
2,0
2,4
2,8
3,2
3,6
CH2CH 3
N
current,µA
/cm
2
potential vs Ag/AgCl
Figure 3.3 : Potentiodynamic Growth of EtCz on CFME in 0.05M TEAP
/CH2Cl2.(scan rate:50mV/s), [EtCz]=10mM.
33
-0,2 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6
-0,04
0,00
0,04
0,08
0,12
0,16
0,20
0,24
0,28
0,32
CH2CH
2OH
N
current,µA
/cm
2
potential vs Ag/AgCl
Figure 3.4: Potentiodynamic Growth of EtOHCz on CFME in 0.05M TEAP /
CH2Cl2.(scan rate:50mV/s), [EtOHCz]=10mM.
-0,2 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6
-1
0
1
2
3
4
N
HC=CH2
current,µA
/cm
2
potential vs Ag/AgCl
Figure 3.5 : Potentiodynamic Growth of NVCz on CFME in 0.05M TEAP /
CH2Cl2.(scan rate:50mV/s) ,[NVCz]=10mM.
34
-0,2 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6
-0,4
0,0
0,4
0,8
1,2
1,6
CH2
CH3
N
O
C=O
CH
Br
current,µA
/cm
2
potential vs Ag/AgCl
Figure 3.6 : Potentiodynamic Growth of BrCz on CFME in 0.05M TEAP / CH2Cl2.(scan rate:50mV/s) ,[BrCz]=10mM.
Table 3. 1: Redox Parameters Obtained from Potentiodynamic Growth of Cz
Derivatives from 5th Cycle.
Monomer Eonset,V Qpg,mC Ea, V Ec,V ∆∆∆∆E,V ia/ic
Cz 0.81 5.00 0.99 0.68 0.31 0.13
EtCz 1.13 2.50 1.00 0.91 0.15 0.63
EtOHCz 0.84 0.48 1.08 - - -
NVCz 0.79 7.07 0.96 0.87 0.09 0.71
BrCz 0.79 1.98 1.02 0.84 0.17 0.51
35
0,0 0,2 0,4 0,6 0,8 1,0 1,2
-0,2
-0,1
0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
PCz
PEtOHCz
PECz
PNVCz
PBrCz
current,µA
/cm
2
potential vs Ag/AgCl
Figure 3.7 : Polymer Films Electrografted on CFME in TEAP/CH2Cl2 with Scan Rate of 100mV/s.
The electroactivity of polymer films can be determined from CV of polymer films
in monomer free electrolyte. PNVCz>PEtOHCz≈PBrCz>PCz>PECz compared
according to current values at peak potentials.
Table 3.2: Redox parameters of polymer films in TEAP/CH2Cl2 with scan rate of
100mV/s.
Polymer Ea,V Ec,V ∆∆∆∆E,V E1/2,V Đa,µµµµA/cm2 ic,µµµµA/cm2 ia/ic
PNVCz 0.97 0.87 0.10 0.92 17.00 7.04 0.41
PBrCz 1.07 0.93 0.14 1.00 18.17 2.29 0.13
PEtOHCz 1.05 - - - 14.81 6.84 0.46
PCz 1.02 - - - 8.20 2.95 0.36
PECz 1.05 - - - 2.60 - -
Redox parameters of polymer electrodes was summarized in Table3.2. The lowest
E1/2 values is 0.92V for PNVCz, several groups have reported that a decrease in the
oxidation potential of the polymer provides with a better stability in the oxidized
state.
36
When the reversibility of electrodes compared with respect to current ratios,
PEtOHCz and PNVCz electrodes more reversible than the others. The separation
between anodic and cathodic peaks is associated with ion transport resistance
involved in these redox reactions. Thus, the difference between anodic and cathodic
peaks (∆E) can serve as an indication for resistance of ion migration in the electrode.
The value of ∆E generally increases with the polymer film coated on the electrode.
This is expected since an increase in polymer film thickness leads to an increase in
resistance for ion penetration. The value of ∆E of PNVCz and PBrCz is higher
(compared to )the rest of electrodes that may be the thickness were higher for
these electrodes. (which might be due to the thickness which is higher in these
cases )
3.1.2 Elecrochemical Impedance Spectroscopy(EIS)
The Nyquist plot of CFME is presented in Figure 3.8. It shows capasitor
behavior(low Csp), but the value of spesific capacitance can be rised up if the
electrode coated with conducting polymer. Then CFME was electrocoated with
substituted carbazoles. The Nyquist and Bode phase plots(Figure3.9-10) for the PCz,
PetCz, PEtOHCz, PNVCZ, PBrCz, were performed to estimate the values of
specific capacitance(Csp). (eqn 3.1)
Csp= 1/ 2πf .Zim (3.1)
37
0 1 2 3 4 5 6
0
1
2
3
4
5
6
0,01 0,1 1 10 100 1000 10000 100000
0
10
20
30
40
50
60
70
80
90
bode phase angle
frequency,Hz
-Zim,Mohm
Zre, Mohm
Figure 3.8 : Nyquist Plot of Bare CFME in 0.05M TEAP/CH2Cl2. Inset: Bode phase
plot of bare CFME in 0.05M TEAP/CH2Cl2.
0 1 2 3 4 5
-2
0
2
4
6
8
10
12
14
BrCzNVCz
EtOHCz ECz
CZ
-Zim,Mohm
Zre,Mohm
PCz
PECz
PEtOHCz
PNVCz
PBrCz
Figure 3.9 : The Nyquist Plots of a)Cz, b) N-BrCz, c)NVCz, d) N-EtCz, e) N-EtOHCz in 0.05M TEAP/CH2Cl2.(All Polymer Electrodes are Obtained in 0.05M
TEAP/CH2Cl2 ,Scan Rate of 50mV/s, [Monomer]=10mM)
38
1E-3 0,01 0,1 1 10 100 1000 10000 100000 1000000
0
5
10
15
PBrCz
PCz
PNVCz
PECz
PEtOHCz
Z,Mohm
frequency,Hz
Figure 3.10 : The Bode Plot of a) PBrCz, b)PCz, c)PNVCz, d)PECz, e)PEtOHCz in 0.05M TEAP/CH2Cl2. .(All Polymer Electrodes are Obtained in 0.05M
TEAP/CH2Cl2 , Scan Rate of 50mV/s, [Monomer]=10mM)
Table 3.3: The Double Layer Capacitance of Obtained Polymer Electrodes.
Polymer Cdl,mF/g Csp,mF/g
PCz 0.33 6.0
PEtOHCz 8.90 23.0
PECz 0.46 21.0
PNVCz 0.44 9.6
PBrCz 0.38 7.0
Bare CFME 0.30 5.0
When carbon fiber is electrocoated with different PCzs, The specific capacitance
increased up to 23mF/g (for PEtOHCz). The specific capacitance of the polymer
electrodes are increased that can be due to a rise in the area of the electrode. The
highest Csp is PEtOHCz, more polymer electrocoated that is also supported with
CV. ( The current is in CV higher)
39
1E-3 0,01 0,1 1 10 100 1000 10000 100000 1000000
0
20
40
60
80
100
bode phase angle,degree
frequency,Hz
PEtOHCz
PNVCz
PCz
PECz
PbrCz
Figure 3.11: The Bode Phase Angle Graphs of a) PEtOHCz, b)PNVCz, c)PCz, d)PECz, e)PBrCz in 0.05M TEAP/CH2Cl2. .(All Polymer Electrodes are Obtained
in 0.05M TEAP/CH2Cl2 ,scan rate of 50mV/s, [monomer]=10mM)
All polymer electrodes showed capacitive behavior close 80 degree, only PNVCz
electrode was 70 degree.(Figure 3.11) Since vinyl group spoil the conjugation of
polymer, the conductivity is lower for PNVCz that may cause decrease in the bode
phase angle.
3.2 Microcomposite Electrochemical Capacitor : Electrocoating of Poly[N-
(Hydroxymethyl)carbazole] onto Carbon Fiber, Solvent Effect, Surface
morphology, Spectroscopic Surface Characterization, Electrochemical
Impedance Spectroscopy
In this part, the electrochemical thin film coating of PMeOHCz onto carbon fiber
micro electrodes, and characterization of surface functionalities and surface
morphology by FTIR reflectance, Cyclic voltammetry, and Scanning electron
microscope (SEM) was maintained. Evaluation of capacitor performance by
different techniques, e.g. voltammetry, Electrochemical impedance spectroscopy
(EIS), charge/discharge characteristics are reported. Effect of solvent and scan rate
on the redox properties and structure of thin polymeric film which was
electrocoated onto CFME , was also investigated.
40
3.2.1 Electropolymerization of N-(Hydroxymethyl)carbazole
Electrochemical coatings of N-(Hydroxymethyl)carbazole (initial monomer
concentration of 1mM) on CFME working electrode was carried out in 0.05M
TEAP/CH2Cl2 by cyclovoltammetric method [Fig.3.2.1].Electrochemical behaviour
and redox properties of the PMeOHCz /CFME was followed by CV during the
electrogrowth process . For comparison, the electropolymerization of Carbazole (Cz)
monomer was also carried out under similar conditions.(Inset of Figure 3.2.1)
-0,2 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8
-400
0
400
800
1200
1600
-0,2 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6
-1000
-500
0
500
1000
1500
current, µA
/cm
2
potential vs Ag/AgCl
-1000
1000
1500
cu
rr
en
t,
µA
j, µµ µµA/cm2
potential vs Ag/AgCl
Figure 3.12: Potentiodynamic Growth of MeOHCz on CFME in 0.05M TEAP/CH2Cl2. (scan rate:60mV/s) Inset: Potentiodynamic Growth of Cz on CFME
in 0.05M TEAP/CH2Cl2(scan rate:60mV), [MeOH]=1mM
Cyclic voltammograms corresponding to the potentiodynamic electrochemical
coating (and electrooxidation of film electrocoated onto CFME) of N-
(Hydroxymethyl)carbazole (MeOHCz) monomer on carbon fiber micro
electrode(CFME) was given in Figure 3.12. Application of potential between 0 and
1.6 V vs Ag/AgCl reference electrode induces the development of a redox system
corresponding to the doping/undoping process of the growing film. A redox system
grows rapidly at about 0.87V vs Ag/AgCl with a slower electrodeposition rate than
PCz (Fig3.2.1 inset). A regular growth was observed for both polymers since a linear
41
increase in current with subsequent cycles,indicating the polymer electrodeposition
on CFME.(SEM pictures were also confirmed it.Figure 3.17)
The effect of scan rate on the electropolymerization was shown in Figure
3.13. Scanning in monomer free solution (only in 0.05M TEAP/CH2Cl2 electrolytic
solution) was performed to understand the diffusion properties and the effect of
electrolyte on electrodeposited polymer film (at 1mM MeOHCz monomer in 0.05M
TEAP/CH2Cl2). The peak currents in the cyclic voltamogram appeared to increase
linearly with the increase of scan rate suggesting that electroactive layer is deposited
on the electrode and the oxidation and reduction process are not limited by diffusion.
The half wave potential (E1/2) of the PMeOHCz is about 0.85V vs Ag/AgCl ,which is
higher than PCz (E1/2:0.45V) indicating the PMeOHCz electrode is more stable.
-0,2 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0
-500
-400
-300
-200
-100
0
100
200
300
400
500
600
700
400mV/s
300mV/s
200mV/s
100mV/s-0,2 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4
-200
-100
0
100
200
300
400
500
600
current,µA/cm
2
potential vs Ag/AgCl
j, µµ µµA/cm2
potential vs Ag/AgCl
Figure 3.13: Scan rate Dependence of PMeOHCz on CFME in 0.05M TEAP Containing CH2Cl2.(scan rate:100-400mV/s). Inset: Scan Rate Dependence of PCz
on CFME in 0.05M TEAP Containing CH2Cl2
Figure 3.14 represents the electrochemical oxidation and growth mechanism of
MeOHCz on CFME, initial formation of radical cation is followed by coupling and
deprotonation results a dimer(and oligomer,polymer ) formations . The electrocoated
polymer shows a relatively highest electroactivity in ACN. (Figure 3.15) The order
of the current densities in different solvents (Figure 3.16) indicates the ease of
42
coupling reaction of radical cation species in ACN than PC and CH2Cl2, where
charge transfer resistance in double layer is the lowest among these solvents (Figure
3.14)
Figure 3.14: Tentative Mechanism of Electropolymerization of MeOHCz on CFME
43
3.2.2 Effect of Scan rate and Solvent on the Electropolymerization of N-
(Hydroxymethyl)carbazole
The effect of scan rate was also investigated for the electropolymerization
process of N-(Hydroxymethyl)carbazole(Table3.4). The change of scan rate was
affected the redox parameters of electrogrowth. The peak separation between anodic
and cathodic peak potentials (∆E) during polymer growth was the smallest for
20mV/s of scan rate, indicating the better reversibility of polymer growth.
Table 3.4: Effect of scan rate on the redox parameters of polymer growth*[MeOHCz]:1mM
Scan rate,
mV.s-1 Ea, V Ec, V ∆∆∆∆E, V ia/ic
20 0.739 0.668 0.071 0.619
40 0.811 0.609 0.202 0.264
60 0.839 0.636 0.203 0.233
80 0.837 0.687 0.150 0.293
*Redox parameters is determined from 2nd cycle.
Electropolymerization of MeOHCz was also performed at constant potential (1.4V)
(in addition to the Cyclovoltammetric coatings) for 1 hour. After
electropolymerization poly( MeOHCz) coated CFME electrode was washed with
monomer free electrolyte and than the effect of solvent on the redox behavior of
these electrode was studied.(Figure3.15) Polymer electrode was stable up to
1000mV/s in all solvents, however the anodic currents determined at 0.69V for
1000mV/s scan rate was the highest in ACN. The order of the current densities in
different solvents are as following ACN (2099µA/cm2)> PC(502µA/cm2) > CH2Cl2
(175µA/cm2) . It can be seen from Figure3.15, that the polymer shows a relatively
highest electroactivity in ACN.
44
0 200 400 600 800 1000
0
200
400
600
800
1000
1200
c
b
a
0
10
20
30
40
50
60
70 PC
ACN
CH2Cl
2
dielectric constant
j,µµ µµ A/cm2
Scan rate, mV/s
ACN
PC
CH2Cl
2
Figure 3.15 : Current Density Versus Scan Rate Plot of PolyMeOHCz in 0.05M TEAP a) ACN, b) PC, c) CH2Cl2
The separation between anodic and cathodic peaks is associated with ion transport
resistance involved in these redox reactions [79-82]. Thus, the difference between
the anodic and cathodic peak potentials (∆E ) can serve as indication for the
resistance of ion migration in the electrode. The variation of ∆E with different
solvents for Poly(MeOHCz) /CFME indicated that in CH2Cl2 (∆E CH2Cl2=0.28) the
highest resistance of ion migration was obtained. This fact was also proved by Rct
values obtained in different solvents by EIS, i.e., highest Rct was obtained for
CH2Cl2 and smallest Rct was obtained for ACN.(Figure3.16). Poly(MeOHCz)
/CFME in ACN(∆E ACN=0.05) revealing to a lower resistance electrolyte
penetration. The electroactivity of Poly(MeOHCz) /CFME is also higher in ACN
than that of PC and CH2Cl2 (and the rate of charge transport is higher too). Solvent
viscosity has an effect on ion mobility too, for higher solvent viscosity ion mobility
decreases toward working electrode electrophoretically. Both results (CV and EIS)
seems to be due to the difference in the enviroment of diffusion of the
solvents/electrolyte , and due to combination of dielectric and viscosity effect of
solvents [83].
Additionaly, inverse relationship between Current density and charge-transfer
resistance, Rct was obtained ,and decrease in conjugation (decrease in current
45
density of peak in electrocoated polymer film )results an increase in charge-transfer
resistance. (Fig.3.2.4)
0 100 200 300 400 500 600 700 800
0
500
1000
1500
2000
2500
current density,ipa(mA/cm2)
charge-transfer resistance ,R ct(ohm)
Figure 3.16 : Current Density vs Charge-Transfer Resistance, Rct Relationship
3.2.3 Morphology of Poly[N-(Hydroxymethyl)carbazole]
The morphologies of the polymers obtained with different scan numbers were
investigated comparatively by scanning electron microscopy (SEM) (Figure3.17).
Poly [N-(Hydroxymethyl)carbazole] on CFME were grown potentiodynamically(by
cyclovoltammetry) with scan rate of 50mV/s from solution of 1mM MeOHCz in
0.05M TEAP/CH2Cl2.
46
a) PMeOHCz, 3 Cycle
b) PMeOHCz, 5 Cycle
47
c) PMeOHCz 10, Cycle
d) PMeOHCz, 15 Cycle
Figure 3.17: SEM Photographs of Poly [N-(Hydroxymethyl)carbazole] a) 3cycle, b) 5cycle, c) 10cycle, d) 15cycle.
48
Since the aromatic and heterocyclic structure of MeOHCz is same to Cz except the
N-(Hydroxymethyl) substituent on Carbazole nitrogen, Poly(MeOHCz) structure
resembles to PCz.(Cauliflower-like) [84]. Increasing scan number (corresponds to
increase in applied charge) during electrodeposition, results an increase in radius of
CFME. The thickness vs scan number graph was plotted according to average
thickness as measured from SEM of samples. The data obtained under these
conditions, can be used as calibration curve for different scan numbers, so, after
getting the graph, CV results can be used to determine the thickness of the film
(Figure3.18).
2 4 6 8 10 12 14 16
0,0
0,5
1,0
1,5
2,0
2,5
3,0
increase in radius,micrometer
scan number
Figure 3.18: Avarage Increase in Radius of Polymer Film (Obtained from SEM Photographs) vs Cyclovoltametric Scan Number.
3.2.4 Reflectance FTIR Surface Spectra of Poly(MeOHCz) Coated CFME
The FTIR-Reflectance (FTIR-ATR) spectra of electro-grafted Poly [N-
(Hydroxymethyl)carbazole] prepared at constant potential electrolysis condition was
taken (30 mins electrolysis at 1.4 V) . The monomer has characteristics peaks; at
3414, 1626, 1599, 1451, 1323, 1223, 987, 749, 722cm-1 (Figure3.19a). In the FTIR-
ATR spectrum of PMeOHCz coated CFME surface, some shifts and some new
peaks appearances are observed when it is compared with the monomer spectrum.
Figure3.19 (curve b) represents the Reflectance FTIR spectra of Poly(MeOHCz)
coated on CFME, the peak at 796cm-1 attributed to C-H deformation of out of plane
of tri-substituted 1,2,4 carbazole cycle and 748 cm-1 (C-H deformation out of plane-
49
adjacent 4H 1,2,3,4- at the end of chains of disubstituted carbazole cycle the band
located at 1313 cm-1 is confirmed by the valence vibration of C-N bond of carbazole
cycle.Moreover, the peaks at 1090, which is attributed to doping of ClO4- anion
coming from the electrolytes of TEAP / CH2Cl2 . The peak is also at 1596-1460 cm-1
evidence for aromatic stretching of double bond C=C.
Figure 3.19: FTIR-ATR Spectra of a) Monomer, b) Polymer Obtained in TEAP/CH2Cl2 at 50mV/s, 5 Cycle.
3.2.5 Electrochemical Impedance Spectroscopy
Electrochemical impedance spectroscopy (EIS) allows to study the charge transfer,
ion diffusion and capacitance of conducting polymer-modified electrodes. The
typical Nyquist plots of Poly[N-(Hydroxymethyl)carbazole] coated CFME in
different solvents is given in Figure3.20 to Figure3.22. The results indicated the
semicircle behavior at high frequency and capacitive behavior at low frequency.
That semicircle can be attributable to the process at high frequencies at the
50
polymer-electrolyte interface, which is expected to be the double-layer
capacitance (Cdl ) in parallel with the charge-transfer resistance (R ct) due to the
charge exchange and compensation at the polymer-solution interface.
500 1000 1500 2000 2500 3000 3500 4000 4500
0
200
400
600
800
1000
1200
1400
-Z//,ohms
Z/,ohms
Figure 3.20 : Nyquist Plot of PMeOHCz in TEAP/CH2Cl2.
0 200 400 600 800 1000
0
100
200
300
400
500
600
40 60 80 100
0
100
ACN
-Z'',ohms
Z/, ohms
ACN
-Z'',ohms
Z/, ohms
Figure 3.21 : Nyquist Plot of PMeOHCz in TEAP/ACN. Inset:Nyquist plot of PMeOHCz in TEAP/ACN. (High frequency region was expanded)
51
0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
0
5000
10000
15000
20000
0 2000
0
500
1000
1500
2000
2500
-Z//,ohms
Z/,ohms
PC
-Z//,ohms
Z/,ohms
Figure 3.22: Nyquist Plot of PMeOHCz in TEAP/PC Inset: Nyquist plot of PMeOHCz in TEAP/PC. (High frequency region was expanded)
Bode magnitude plot gives extrapolating this line to the log Z axis at w = 1 (log w
= 0) yields the value of Cdl from the relationship:
|Z|=1/Cdl (3.1)
The double layer capacitance (Cdl) is attributed to charge accumulation at polymer-
solution interface that was highest (5650µF/cm2) for ACN. The Rct values can be
associated with redox processes within the polymeric film. As can be seen in Table2,
Rct values are higher in CH2Cl2 and PC than ACN, however, the lowest Rct
values were obtained in ACN that this solvent has the medium dielectric constant
and lowest viscosity among the solvents used.
The results indicated the importance of the choice of solvent which is crucial to
increase the capacitance of the thin polymer film coated CFME.
From the frequency ( f 0 ) corresponding to the maximum of the imaginary
component (Z’’) of the semicircle, the time constant Γ of every electrode can be
calculated using Eq1:
52
Γ= 1/ 2πf 0 (1) (3.2)
The values of Γ obtained from the Nyquist plots. are 3.8 ms(CH2Cl2), 0.24ms(ACN)
and 0.13ms (PC) for PMeOHCZ /CFME in corresonding solvents. The lower Γ value
is preferred for electrochemical capacitor for fast charge/discharge processes [32]
PMeOHCz /CFME show faster charge/discharge process in PC.
In the Bode phase plot of PMeOHCz in TEAP/ PC, the bode phase angle approaches
a plateau (61o), in the frequency region 49mHz-89mHz film indicates capacitor
behaviour, In the frequencies, 0.16Hz-41 Hz phase , transition from capacitor to
resistor was observed. In the frequencies, 41Hz-698 Hz film showed resistor
behaviour, in the frequency region of 698Hz-100kHz indicated transition from
resistor to capacitor behaviour. (Figure3.23)
The Bode plot of PMeOHCz/CFME in TEAP/ACN was indicated that at higher
frequency>100Hz, because of the prevailing influence of the electrolyte resistance,
it behaves like ideal resistor and by having a very low bode phase angle. In the
frequencies 1-100Hz, the capacitor shows transiton from resistor to capacitor. At
frequencies <1Hz, the bode phase angle approaches a plateau, and this time scale,
the electric signal reaches maximum penetration in the pores of the PMeOHCz
electrode.(Figure3.23)
1E-3 0,01 0,1 1 10 100 1000 10000 1000001000000
0
10
20
30
40
50
60
70
a
b
c
-phase of z
frequency,Hz
Figure 3.23 : Bode Plot of PMeOHCz a) PC, b) ACN, c)CH2Cl2
53
In the Bode plot of PMeOHCz in CH2Cl2 , two plateau was observed between
45Hz and 10mHz , however, the bode phase angle was 18o meaning that the
PMeOHCz/CFME in CH2Cl2 indicates lower capacitive behaviour than PC and
ACN.
Figure3.23 also indicates the solvent effect on the polymer capacitor behaviour.
Capacitance behaviour increases with following order in respective solvents,
PC>ACN>CH2Cl2 .
3.2.6 Comparative capacitance determination with cyclic voltammetry and impedance spectroscopy.
Capacitance can be determined both by cyclic voltammetry and Impedance
Spectroscopy. However, results are different each other.(Fig 3.24-25) When cyclic
voltammetry is used, polymer films are exposed to charging and discharging. During
polymer oxidation process, bipolarons are formed, involving the formation of
quinoid-like flattened structures are formed. As a consequence of this process the
discharging should occur at more negative potentials, generating strong hysteresis in
voltamograms. Other suggestions include intermolecular π interactions, shielding,
and structural changes. Very recent studies reveals that upon oxidative charging,
intermolecular coupling processes between conjugated changes generate stabilized
network with σ interchain bonds that sigma bond formation produces a marked
stabilization of the charged polymer and, in addition, results in localized charges.
However, in impedance measurements, very small alternative current (10mV
amplitude) is applied with different time interval, that like steady-state condition. So
polymer structure or phase change are not dominant in this case.
54
0 200 400 600 800 1000
0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
CCV, mF/cm
2
Scan rate, mV.s-1
ACN
PC
CH2Cl
2
Figure 3.24: CCV vs Scan Rate Graph of PMeOHCz a)ACN, b) CH2Cl2, c) PC
1E-3 0,01 0,1 1 10 100 1000 10000 100000 1000000
0
4
8
12
16
20
24
28
0.8mF/cm2
4mF/cm2
24mF/cm2
Cim,m
F/cm
2
frequency,Hz
ACN
CH2Cl2
PC
Figure 3.25 : Cim vs Frequency Plot of PMeOHCz a) ACN, b) CH2Cl2, c) PC
55
3.3 Electropolymerization of N-(hydroxyethyl) carbazole on a CFME, and
Investigation of Capacitance Behavior with Electrochemical Impedance
Spectroscopy
N-(hydroxyethyl) carbazole was electropolymerized on a carbon fiber micro
electrode, and modified CFME was characterized with FTIR-ATR and its capacitor
behavior was investigated with electrochemical impedance spectrometry(EIS).
3.3.1 Electropolymerization of N-(hydroxyethyl) carbazole
Polymerization reaction were performed electrochemically at a constant potential or
potentiodynamically in 0.05M TEAP/CH2Cl2 and 1mM N-(hydroxyethyl) carbazole
(EtOHCz). Application of potential between 0 and 1.4 vs Ag/AgCl induces the
development of a redox system corresponding to the doping/undoping process of the
growing film. Figure 3.26 also showed that nucleation loop was seen that indicates
polymerization starts. During successive scans, one-well defined redox systems
quickly grow and correspond to the deposition of an electroactive film onto the
electrode surface. The peak current of redox system regularly increases during six
successive scans.
-0,2 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6
-400
0
400
800
1200
CH2CH
2OH
N
current,µA
/cm
2
potential vs Ag/AgCl
Figure 3.26: Potentiodynamic Growth of EtOHCz on CFME in 0.05M TEAP /
CH2Cl2.(scan rate:50mV/s)
56
The film then washed with monomer-free electrolyte solution and its redox behavior
was studied. Two oxidation peaks are observed at respectively, 0.99 and 1.28V by
increasing applied potential(Fig 3.27). These anodic processes are associated with
two cathodic waves occurring, respectively, at 0.83 and 1.12V by reversing scans.
-0,2 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6
-200
-160
-120
-80
-40
0
40
80
120
160
200
240
280
320
current,µA
/cm
2
potential vs Ag/AgCl
Figure 3.27: Scan Rate Dependence of PEtOHCz on CFME in 0.05M TEAP Containing CH2Cl2.(scan rate:100-500mV/s).
This behavior might correspond to the formation of the radical cations of carbazolic
units during the first oxidation step followed by their oxidation into dications
through the second step as already described for poly(N-alkyl carbazole) [86]
Between 20-200mV/s, the peak current of the redox system evolves linearly with
the square root of scan rate, which indicates diffusion limited redox process [87].
3.3.2 FTIR-Reflectance Spectrum of Electro-Grafted Homopolymer on CFME
The FTIR-Reflectance spectra of electro-grafted polyEtOHCz prepared at constant
potential one and half hour at 1.4V vs Ag/AgCl. The EtOHCz monomer has bands
at 3195, 1624, 1458, 1244, 996, 748-750cm-1(Figure3.28a). In the FTIR spectrum of
PEtOHCz, there are some shifts in the band place and some new peaks appeared
when it is compared with the monomer spectrum.
57
Figure 3.28: FTIR Spectra of a.EtOHCz b. PEtOHCz Obtained on CFME in TEAP/CH2Cl2.
Fig. 3.28 (curve b) represents the FTIR-ATR spectra of Poly EtOHCz obtained
electropolymerization on CFME, the peaks at 827-794 attributed to C-H deformation
of out of plane of tri-substituted 1,2,4 carbazole cycle and 749 cm-1 (C-H
deformation out of plane- adjacent 4H 1,2,3,4- at the end of chains of disubstituted
carbazole cycle [88] the band located at 1234 cm-1 is confirmed by the valence
vibration of C-N bond of carbazole cycle [89]. Moreover, the peaks at 1045, which is
attributed to doping ClO4- anion coming from the electrolytes in TEAP / CH2Cl2
[90]. Finally, this spectrum shows that the bands of this polymer at 1615-1499 cm-1
evidence for aromatic stretching of double bond C=C [91].
3.3.3 Morphology of Poly [N-(hydroxyethyl) carbazole]
In order to understand the surface appearance of the polmer electrode on CFME
scanning electron microscope was used (SEM). The SEM of electro-grafted poly [N-
(hydroxyethyl) carbazole] prepared at constant potential one and half hour at 1.4V vs
Ag/AgCl is shown in Figure3.29-30. Polycarbazole has been known as it shows a
cauliflower-like structure [92]. The SEM microphotograps (Figure3.3.4-5)of
electrochemically prepared POHCz resembles PCz morphology.
58
Figure 3.29: Scanning Electron Microphotographs of PEtOHCz at x3500 Magnification
Figure 3.30: Scanning Electron Microphotographs of PEtOHCz at x500 Magnification
59
3.3.4 Electrical properties poly [N-(hydroxyethyl) carbazole]
The Nyquist plots for the PEtOHCz and PCz were performed to estimate the values
of capacitance.(Figure3.31) At low frequency, the imaginary part of the impedance
sharply increases, and plot tend to a vertical line characteristic of capacitive
behavior. For PCz, the influence of electrode porosity and also thickness indicates a
shift the low frequency capacitive behavior along the real axis toward more resistive
values.
0 50 100 150 200 250 300 350 400
0
50
100
150
200
250
300
0 1 2 3 4 5
0 ,0
0 ,5
1 ,0
1 ,5
2 ,0
2 ,5
zim
, Mohm
z re a l, M o h m
P C z
zim,kohm
zreal, kohm
Figure 3.31: Nyquist of PEtOHCz, 5 Cycle, on CFME in TEAP Containing CH2Cl2
, Q: 11.27mC. Inset: .Nyquist of PCz, 5 Cycle, on CFME in TEAP Containing
CH2Cl2 , Q: 1.514mC.
PCz and PEtOHCz were potentiodynamically coated on CFME, and then EIS
measurements were achieved. Nyquist plot of PEtOHCz indicated that the modified
electrode showed better capacitance behavior especially at lower frequency.
Magnitude of Bode plot vs frequency plot gives Double layer capacitance. For
Polymer electrodes, Cdl is calculated for the polymer electrodes; 1.0.10-6F/cm2 for
PCz, 1.0.10-5 F/cm2 for PEtOHCz. It is indicated that the surface area of PEtOHCz
is greater than that of PCz.
60
0 10 20 30 40 50 60
0
10
20
30
40
50
b
a
z'',kohm
z', kohm
Figure 3.32: Nyquist plots for CFME/ PEtOHCz Electrode a. Doped at 1.2V for 2
min, b. Undoped at -1.2V for 2min in TEAP/CH2Cl2.
The generalized transmission line circuit model predicts the relevant impedance
features of such a system in terms of a Nyquist plot that was proposed in [93], based
on a mathematical approach. The two semi-circles at the highest frequencies,
induced by the processes at the metal/polymer and polymer/solution interfaces, are,
in practice, not always detectable. Sometimes, only one or even one-half semi-circle
is observed; for other cases, these two semi-circles are partially overlapped to each
other, the actual situation observed depending on the characteristics of the interfacial
processes in terms of energy (resistance) to overcome at the relevant interface.
Moreover, these semi-circles are very often depressed, most probably due to non-
homogeneous separation surfaces [94]. Furthermore, they can also overlap to the
mid-frequency Warburg impedance quasi-45°-slope segment that reflects the
diffusion–migration of ions at the boundary surface between solution and polymer,
inside the latter medium. Finally, the 90°-trend at the lowest frequencies, due to a
capacitive impedance, accounts for the charge transport process inside the bulk of
the film. Figure3.32. shows complex-plane plots obtained for doped and undoped
PEtOHCz. The spectra obtained for reduced state of PEtOHCz present two
semicircles from which value of ohmic resistance(Rs; 29kohm) and charge transfer
resistance (Rct; 205kohm) were obtained by extrapolation of higher-frequency and
61
lower frequency, respectively, to the real impedance axis,however, doped PEtOH
showed more capacitive behavior.
0 100 200 300 400
-100
0
100
200
300
400
500
600
700
800
-0.4V
0.7V -0.2V
0.5V
0.3V
0.1V
-zim,kohm
zre,kohm
Figure 3.33: Nyquist Plot of PEtOHCz at Different Potentials[-0.4V-0.1V]
0 100 200 300 400
-20
0
20
40
60
80
100
120
140
160
180
200
220
240
260
-zim,kohm
zre,kohm
-0.2V
-0.4V
-0.6V
Figure 3.34: Nyquist Plot of PEtOHCz at Different Potentials[-0.6V-0.2V]
62
-50 0 50 100 150 200 250 300 350 400
-100
0
100
200
300
400
500
600
700
800
zim,kohm
zre,kohm
0.1V
0.3V
0.5V
0.7V
1.2V
Figure 3.35: Nyquist plot of PEtOHCz at Different Potentials[0.V-1.2V]
Fig(3.33-35) presents a wide spectrum of potential effect on EIS, these results
indicate potential has a strong influence on the capacitance. From -0.6V to 0.1V
Nyquist plot indicates almost vertical to Zre axis, however, when potential increases
from 0.3V-1.2V decreases phase angle of capacitor(Figure3.36).
1E-3 0,01 0,1 1 10 100 1000 10000 100000 1000000
0
10
20
30
40
50
60
70
80
Phase angle,degree
frequency,Hz
-1V
-0.8V
-0.6V
-0.4V
-0.2V
0.1V
0.3V
0.5V
0.7V
0.9V
1.2V
Figure 3.36: Bode Phase Angle Plot of PEtOHCz at Different Potentials
63
1E-3 0,01 0,1 1 10 100 1000 10000 100000 1000000
1000
10000
100000
1000000
magnitude of Z
frequency,Hz
-1V
-0.8V
-0.6V
-0.4V
-0.2V
0.1V
0.3V
0.5V
0.7V
0.9V
Figure 3.37: Bode Magnitude Graph of PEtOHCz at Different Potentials
3.3.5 Spectroelectrochemistry of Poly[N-(hydroxyethyl)carbazole]
PEtOHCz film have been deposited on ITO glass substrates at constant potential at
1.4V from 0.01M OHCz monomer in TEAP/CH2Cl2 solution for 1 min. Then at all
potentials, polymer was kept for 30sec and UV-visible spectrum for each sample
were taken. (Fig3.38) The high absorbtion at lower energies in the oxidized state of
polymer makes it useful for some applications in the near-IR region.
Figure 3.38: In-situ UV –Visible Study of PEtOHCz on ITO Electrode.(-0.6V-2V)
64
Figure 3.39: FTIR-ATR of PEtOHCz on CFME after Applied 2.0V Potential.
Three absorbtion maxima present in the optical spectrum of PEtOHCz , the band at
385nm attributed to π→π* for the EtOHCz monomer ,and corresponding transition
is obtained at about 400 nm for carbazole. The band at around 400nm and 800nm
were characteristic respectively of cation radicals and dication radicals of
poly(EtOHCz). These bands are at around 630 and 875 nm for polycarbazole [95].
PEtOHCz was stable up to 2.0V since there is no any decrease absorbance of the
band at 400nm and 800nm. The FTIR-ATR of PEtOHCz (Figure 3.39) indicated that
structure of PolyN-(hydroxyethyl) carbazole change very little when it is compared
with Figure 3.28b. That is also supported with UV- Visible results.
65
3.4 Electrochemical Impedance Spectroscopic Study of Poly(3,4
Ethylenedioxythiophene) on Carbon Fiber Microelectrode .
Ethylenedioxythiophene(EDOT) was electropolymerized on carbon fiber micro
electrode in LiClO4/PC electrolyte, and then Electrochemical Impedance
Spectroscopic Study was performed. Supercapacitor behaviour was observed for
Polyethylenedioxythiophene thin film coating on the Carbon fiber microelectrode
by exhibiting 900 of phase of angle, behavior.
3.4.1 Electropolymerization of EDOT
Electropolymerization of EDOT on carbon fiber microelectrode (CFME) was
achieved by applying potential cycling between 0-1.2V at a scan rate of 100mV/s
(Figure 3.40). The onset potential of EDOT was 1.06V. Figure 3.40 indicates that
polymer peak current is independent of potential in the potential range [0-1.06V].
The current increases with the cycle number, indicates insoluble polymer film was
coated on CFME.(Figure3.40)
0,0 0,2 0,4 0,6 0,8 1,0 1,2
-10
0
10
20
30
40
50
60
70
current,µΑ
/cm
2
potential,V
Figure 3.40: Potentiodynamic Growth of EDOT(2.10-3M), on CFME in LiClO4/PC with a Scan Rate of 100mV/s.
The polymer electrodeposited on CFME from 2.10-3M EDOT monomer and
electrolyte (0.1M LiClO4/PC), thin films were characterized by cyclic voltametry in
(0.1M LiClO4/PC) monomer free solution. The influence of scan rate was
66
investigated for PEDOT film as shown Figure3.41. The peak currents in the cyclic
voltamogram appeared to increase linearly with the increase of scan rate suggesting
that electroactive layer is deposited on the electrode and Fig 3.42a and 42b shows the
relationship between current density vs scan rate and square root of scan rate. Linear
scan rate dependence(correlation coeff.0.999) rather than square root of scan rate
dependence (corr.coeff.0.992) indicates that the process is mainly controlled by thin
film formation in addition to the diffusion of ions of electrolyte into the polymer thin
film. Cyclic voltamogram of PEDOT film like a rectangular box shape that indicates
PEDOT is a supercapacitor.(Figure3.41)
-0,6 -0,4 -0,2 0,0 0,2 0,4 0,6 0,8 1,0 1,2
-30
-20
-10
0
10
20
30
current,µA
/cm
2
potential,V
Figure 3.41: Scan rate Dependence of PEDOT Coated CFME in LiClO4/PC (100-500mV/s)
67
100 200 300 400 500
-16
-14
-12
-10
-8
-6
-4
-2
0
2
4
6
8
10
12
14
16
current density,µA/cm
2
scan rate
10 12 14 16 18 20 22 24
(scan rate]1/2
b
a
Figure 3.42: a)The Current Density vs Scan Rate, b) The Ccurrent Density vs (scan rate)1/2 Graph of PEDOT Coated CFME.
3.4.2 Electrochemical Impedance Study of PEDOT
Theoretical models have been developed to explain the impedance characteristics of
homogeneous film [96] and porous membrane [97] . For the uniform films a model
considering the diffusional transport of single type of charge carrier (electron or ion)
across the film with a charge transfer process at metal–film interface was proposed
[98]. This model could explain the Randles circuit behavior, the Warburg
contribution and capacitive responses at low frequencies. On the other hand, in the
advanced homogeneous models, diffusion– migration transport of electrons and/or
ions and nonequilibrium charge transfer across the interfaces at the boundaries of the
films were considered and explained through introduction of one or more capacitive
elements in parallel with charge transfer resistances in the equivalent circuits .
Electrochemical impedance spectroscopy (EIS) allows to study the charge transfer,
ion diffusion and capacitance of conducting polymer-modified electrodes. At
different bias PEDOT electrocoated CFME was kept for 2 min, and then impedance
measurements were taken. The typical Nyquist plots of PEDOT in LiClO4/PC is in
Figure3.43 to Figure3.44 The line indicating vertical to real axis that means it’s
supercapacitor. PEDOT shows supercapacitor behavior from -0.2V to 0.5V. At 1.0V
68
a small deviation was seen from ideal supercapacitor behavior, i.e, phase of angle
was shifted 87o to 800.
0 50 100 150 200 250 300 350 400 450 500 550 600 650 700
-100
0
100
200
300
400
500
600
700
-Zim,kohm
Zre,kohm
-0.4V
-0.2V
-0.1V
Figure 3.43: Nyquist Plot of PEDOT at Negative Potentials[-0.1V-0.4V]
0 50 100 150 200 250 300 350 400 450 500 550 600 650 700
0
100
200
300
400
500
600
700
-Zim, kohm
Zre,kohm
0.1V
0.3V
0.5v
1.0V
Figure 3.44: Nyquist Plot of PEDOT at Positive Potentials [0.1V-1.0V]
PEDOT electrodes were exposed to different potentials by Lineer Scan, then Cyclic
voltamogram of the electrodes were taken in LiClO4/PC at 100mV/s scan
rate.(Figure3.45)Small decreases of the electroactivity of the film with potential
69
increase was observed (Figure 3.45). PEDOT electrodes still have capacitive
behavior and stable.
0,0 0,2 0,4 0,6 0,8 1,0
-60
-40
-20
0
20
40
60
current density,µA/cm
2
potential,V
-0.4V
-0.2V
0.1V
1.0V
Figure 3.45: Cyclic Voltamogram of PEDOT at a Scan Rate of 100mV/s, in LiClO4/PC after PEDOT was Exposed to Different Potentials.
-0,2 0,0 0,2 0,4 0,6 0,8 1,0
320
330
340
350
360
370
380
Q, µC
potential,V
Figure 3.46: Charge vs Potential Graph of PEDOT
The charge consumed calculated from CV of PEDOT , and charge vs potential graph
were plotted. since electroacitvity decreases, charge declines with the
potential(Figure3.46)
70
1E-3 0,01 0,1 1 10 100 1000 10000 100000 1000000
100
1000
10000
100000
1000000
bode m
agnitude
frequency,Hz
Figure 3.47: Bode Magnitude Plot of PEDOT at Different Potential(-0.4V, 0.1V, 0.3V, 1V)
Bode magnitude plot indicates that PEDOT film conductivity are not affected with
potential since values of resistance stayed constant(Figure3.47) That may be due to
no polymer structure changes occurred with the applied potential.
0 50 100 150 200 250 300 350
-50
0
50
100
150
200
250
300
350
b.1.7mC
a.0.887mC
-Zim, kohm
zre,kohm
Figure 3.48: Nyquist Plot of PEDOT with Applied Polymerization Charge of a) 0.88mC, b) 3.3mC.
Typical impedance spectra of CFME/PEDOT electrode in 0.1 M LiClO4 are
presented in Fig3.48-49, The impedance plots are dominated by a 90° capacitive
71
line, which extends down to very low frequencies (0.01 Hz) for thick films of
PEDOT, as shown by Bobacka [99] . At high frequencies, there is only a slight
deviation from the capacitive line, indicating fast charge transfer at the metal
|polymer and polymer |solution interfaces, as well as fast charge transport in the
polymer bulk.
0 1 2 3 4 5 6 7
-20
0
20
40
60
80
100
120
140
160
0 20 40 60 80 100 120 140 160
-20
0
20
40
60
80
100
120
140
160
-zim,kohm
zre,kohm
c.6.6mC
b.5,7mC
a.3.3mC
-zim,kohm
zre,kohm
Figure 3.49: Nyquist Plot of PEDOT with Applied Polymerization Charge of a) 3.3mC, b) 5.7mC, c) 6.6mC. Inset: Same Graphic with Same x-y Scale.
1E-3 0,01 0,1 1 10 100 1000 10000 100000 1000000
0
20
40
60
80
100
-Bode phase angle,degree
frequency,Hz
3.3mC
0.88mC
1.79mC
6.6mC
5.79mC
Figure 3.50: Bode Phase Angle of PEDOT with Applied Polymerization Charge of a)0.88mC, b)1.7mC, c)3.3mC, d) 5.79mC, d)6.6mC
72
PEDOT with charge of 5.79 and 6.6mC gives phase angle of 88o that is ideal
capacitor behavior (close to 90o) PEDOT with lower charge also gives phase of anle
84o, it is also good however smaller than PEDOT with the charge of 5.79 and 6.6mC.
It may be due to higher charge meaning more PEDOT coated on electrode surface.
(Fig3.50)
1E-3 0,01 0,1 1 10 100 1000 10000 100000 1000000
100
1000
10000
100000
magnitute of Z
frequency,Hz
0.88mC
1.79mC
3.3mC
6.6mC
Figure 3.51: Magnitude of Z Graph of PEDOT with Applied Polymerization Charge of a) 0.88mC, b) 1.79mC, c) 3.3mC, d) 6.6mC.
The typical Bode plots for PEDOT with different charges are shown in Figure 3.51.
The logaritm of absolute impedance value |Z| is linearly proportinal to the logaritm
of frequency in low frequency region with slope of -1 for all PEDOT coated CFME.
This results indicates that PEDOT films behave as an ideal capacitors [100]. Charge
of PEDOT increseases film resistance decreases, that may may be due to longer
conjugation length of the polymer.
73
1E-3 0,01 0,1 1 10 100 1000 10000 100000 1000000
-5
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
Cim, µF
frequency, Hz
0.88mC
1.79mC
3.33mC
5.79mC
6.66mC
Figure 3.52: Evaluation of Imaginary Capacitance vs Frequency for 0.5 cm2 PEDOT Coated CFME in 0.1M LiClO4/PC.
2)(
)(
ωω
ω
Z
ZC
′′=′ (1)
2
///
)(
)(
ωω
ω
Z
ZC = (2)
Cre(ω) is the real part of the capacitance C(ω). The low frequency value of Cre(ω)
coresponds to capacitance of the cell. Cim is the imaginary part of the capacitance
C(ω). It corresponds to energy dissipation by an irreverisible process that can lead to
hysteresis.[101] Figure3.52 presents the evaluation of Cim vs frequency according to
an equation 2. The imaginary part of the capacitance goes through a maximum at a
frequency f0, defining a time constant as ϒ0 =1/ f0 . This time constant has been
described as a dielectric relaxation time characteristic of the whole system. It is time
needed to return to electrical neutrality after carrier injection or extraction. When
charge of PEDOT increases, dielectric relaxation time increases from 0.12 s to 0.59s.
74
1E-3 0,01 0,1 1 10 100 1000 10000 100000 1000000
0
50
100
150
200
Cre, µF
frequency,Hz
0.88mC
1.79mC
3.3mC
5.79mC
6.6mC
Figure 3.53: Evaluation of Real Capacitance vs Frequency for 0.5 cm2 PEDOT Electrode in 0.1 M LiClO4/PC.
Figure 3.53 presents the real part of capacitance change vs frequency according to
equation 1. The capacitance change is one commonly described in the literature
[102], that is, when frequency decreases, Cre sharply increases, then tends to be less
frequency dependent. This characteristic of the electrode structure and
electrode/electrode interface.The applied polymerization charge of PEDOT
increases, value of capacitance increases, since surface area of PEDOT increases
with charge.(Fig3.53).
75
0 2 4 6 8
0
20
40
60
80
100
120
140
160
180
200
CLF, µµµµF
Cdl ,µF
Polymerization charge , mC
Csp, µµ µµF
0
2
4
6
8
10
12
14
16
18
20
Cd l , µµ µµ
F
Figure 3.54: Cdl and Csp vs Polymerization Charge Plot of CFME/PEDOT (correlation coefficients : R =0.991 for CLF and R =0.997 for Cdl
The specific and double layer capacitance increase linearly with the polymerization
charge of PEDOT film, as shown in Fig 3.54. Since Capacitance of the electrode
increases with the surface area of the electrode this also related with polymerzation
charge.
3.5 The Electropolymerization of Bis-3,4-Ethylenedioxythiophene and 3,6-Bis[2-
[3,4(Ethylenedioxy)thieny]]-N-ethyl Carbazole on Carbon Fiber Microelectrode
and Its Characterization.
Redox active electrochromic polymers are synthesized from low oxidation
monomer and comonomer such as Bis, 3-4 ethylenedioxythiophene (BEDOT) and
3,6-bis[2-(3,4 ethylenedioxy)thienyl]-N-ethylcarbazole (EDOT-ECZ-EDOT or EEE)
on carbon fiber microelectrodes. The electrogrowth and of monomers and redox
behavior of polymer is followed spectroelectrochemically by using Indium Tin
oxide (ITO) electrode. The polymers were characterized by Cyclic voltametry(CV),
Ultra-Violet-visible Spectrophotometer, and Scanning Electron Microscope(SEM).
Spectroelectrochemical results of Poly(BEDOT-co-EDOT-ECZ-EDOT) copolymer
shows that the band gap of copolymer is between polyBEDOT and polyEDOT-
ECZ-EDOT) and it is stable. Reversible and stable redox behaviour of polymeric
76
film and flexibility and biocompatibility of the carbon fiber make poly(BEDOT-co-
EDOT-Ecz-EDOT) film favaroble to different application such biosensor or
electrochromic devices.
3.5.1 Polymerization and Characterizationof Poly[BEDOT-co-EEE]
BEDOT and EDOT-ECz-EDOT and mixture of two monomers polymerized
potentiostatically in O.1M LiClO4 containing PC with 20mV/sec(Fig 3.55a, 3.56a,
3.57a). BEDOT electrochemically polymerized in O.1M LiClO4 containing PC at
20mV/sec scan rate utilizing repeated potential scan . Figure 3.55a depicts the
polymerization of BEDOT and CV of PBEDOT coated CFME at different scan
rates. Oxidation of monomers becomes apparent at 0.9 V with a peak current at
0.3V. Figure 3.55b gives the redox behaviour of PBEDOT coated CFME at
different scan rates. Proportional scan rate dependence of current intensities on scan
rate suggest a electrode supported reactions. When EEE was polymerized in 0.1M
LiClO4 containing PC, oxidation of monomer was 0.60v. Also the redox behaviour
of PEEE coated CFME at different scan rates indicated that proportional scan rate
dependence of current intensities on scan rate suggest a electrode supported
reactions(Figure 3.56b).
Cyclic voltammogram of mixture of two monomers shows a behavior that resembles
both monomers and suggest that reaction happens between them(Figure3.57a).
Oxidation of BEDOT and EDOT-ECZ-EDOT and mixture of two monomers takes
place at 0.90, 0.60, 0.70V vs Ag wire respectively and on the subsequent cycling
new peaks occurred at 0.40, 0.3 and 0.5v due to polymer growth .
77
-0,2 0,0 0,2 0,4 0,6 0,8 1,0
-20
0
20
40
60
80
-0 ,2 0 ,0 0 ,2 0 ,4 0 ,6 0 ,8 1 ,0
-20
0
20
40
60
80
E / V
I/µA
E / V
I/µA
Figure 3.55a: The Polymer Growth of BEDOT in 0.1M LiClO4 Electrolyte / Propylene Carbonate(PC).
-0,6 -0,4 -0,2 0,0 0,2 0,4-80
-60
-40
-20
0
20
40
60
80
100
1201)0.1 V s−12)0.2 V s−13)0.3 V s−14)0.4 V s−1
4
3
2
1
E / V
I / µA
Figure 3.55b: PolyBEDOT Coated Carbon Fiber in 0.1M LiClO4 Fontaining PC. Scan Rate[ 20mV/sec-200mV/sec]
78
-0,6 -0,4 -0,2 0,0 0,2 0,4 0,6 0,8 1,0
-20
-10
0
10
20
30
40
I / µA
E / V
Figure 3.56a: The Plot of Polymer Growth of EDOT-EtCz-EDOT in 0.1M LiClO4 Electrolyte Containing Propylene Carbonate(PC).Scan Rate:20mV/sec,
[EEE]=0.002M.
-0,2 0,0 0,2 0,4 0,6 0,8 1,0
-100
-50
0
50
100
150
200
250
I / µA
E / V
Figure 3.56b: PolyEEE Coated Carbon Fiber in 0.1M LiClO4 /PC. Scan Rate[ 20mV/sec-200mV/sec]
79
-0,6 -0,4 -0,2 0,0 0,2 0,4 0,6 0,8 1,0-40
-20
0
20
40
60
80
100
I / µA
E / V
Figure 3.57a:The plot of Polymer Growth of BEDOT-co-EEE in0.1M LiClO4 Electrolyte in Propylene Carbonate(PC). Scan Rate:20mV/sec.
-0,6 -0,4 -0,2 0,0 0,2 0,4 0,6 0,8 1,0
-200
-100
0
100
200
300
I / µA
E / V
Figure 3.57b: Poly (BEDOT-co-EEE) Coated Carbon Fiber in 0.1M LiClO4
Containing PC. Scan Rate[ 100mV/sec-260mV/sec]
Scan rate dependence of homopolymer and copolymer films in monomer free
electrolyte were obtained ( Figure 3.55b and Figure 3.56b, Figure 3.57b) and found
to be linearly proportional anodic and peak cathodic currents with the square root of
80
the scan rate which suggest a diffusion controlled electrochemical redox process
[87]. PEEE film indicated peak potential (Ep) at 0.61v and a shoulder at 0.37v,
however Poly(BEDOT-co-EEE) film showed peak potentials at 0.26 and 0.38v. It is
showed that copolymer formation results in decreasing peak potentials (Figure 3.56b
and Figure 3.57b).
3.5.2 Spectroscopic Charecterization of poly [BEDOT-co-EEE]
In situ UV-VIS spectra were recorded during cycling of poly [BEDOT-co-EEE] film
on ITO in monomer free electrolyte solution in the range of -1.0 V to 0.6 V. (Figure
3.58a) The absorbance assigned to π→π* transition at 457 and 542 nm decreases, the
new absorbance increases at 826 nm (polaron) as doping proceeds from –1.0 v to 0.2
v. There is a drastic change in the spectra at 0.3V, two new absorbances appeared in
the spectrum at 600 nm and 1000 nm that is assumed to correspond to bipolaron
structure [103-104]. In a comparison test in situ UV-VIS spectra of PEEE were
recorded during cycling a polymer film in monomer free electrolyte between –1.0
and 0.6V (Figure 3.59). For PEEE, as potential increased π→π* transition at 423 nm
decreased and new peaks at 600nm and 1000nm occurred. At mild oxidized potential
it becomes green and further oxidation it turns to dark blue as suggested in literature.
PEEE film started to oxidize on ITO at 0.2v, however poly(BEDOT-co-EEE) is at -
0.8v. So oxidation of polymer film started very low potentials with copolymer
formation(Figure3.58a and Figure3.59).
The absorbance assigned to π→π* transition at 600 nm for PBEDOT film decreases
continuously as doping proceeds, new absorbances at 850 and 1000 nm occurred
(Figure3.60). Similar results have been reported [105] for in situ UV-VĐS absorption
spectra of PEDOT film on ITO during oxidation process in the range of [-1.0-0.6 V];
the absorbance assigned to π→π* transition at 580 nm decreases continuously as
doping proceeds while a new absorbances occurred above 700nm.
In accordance with these results copolymer film shows the characteristic behavior of
both monomers and favor more colors(three) which is important for electrochromic
applications.
PEEE electrodeposited on ITO electrode than PBEDOT coated on PEEE/ITO
electrode so composit formation was studied and compared with the copolymer
structure. In situ UV-VIS spectra of composite (Figure 3.61) were recorded during
81
cycling a polymer film in monomer free electrolyte solution between –1.0 and 0.6v.
Absorbance assigned to π→π* transition at 400nm decreases continuously while
doping proceeds when new absorbances at about 600nm and 900nm corresponds to
polaron and bipolarons appeared.
Figure 3.58a. In situ Spectroelectrochemical Study of P(BEDOT-co-EEE) on ITO Containing 0.1MLiClO4 Clectrolyte Solution in PC, in the Rrange of
[-1-0.6v].
-0 ,8 -0,4 0,0 0,4 0,8-100
-50
0
50
100
E / V
I / µA
0,05
0,10
0,15
0,20
0,25
0,30
0,35
0,40
457nm
800nm
600nm
1000nm
ABS
Figure 3.58b. Voltabsorbtemetric Curve of P(BEDOT-co-EEE)
82
Figure 3.59: In situ Spectroelectrochemical Study of PEEE on ITO in 0.1MLiClO4
Containing PC, in the Range of [-1-0.6v].
Figure 3.60: In Situ Spectroelectrochemical Study of PBEDOT on ITO in 0.1MLiClO4 / in PC, in the Range of [-1-0.6v].
83
Figure 3.61: In Situ Spectroelectrochemistry of ITO/PBEDOT/PEEE Composite.
3.5.3 Polymer Morphology
SEM’s of copolymers of EEE with BEDOT obtained electrochemically at different
scan number and composite are given in Figure3.62-64. The results indicate that
current density, and electrolysis time affects the morphology of grafted surface. The
coatings exhibit polymeric nuclei, when compared with the uncoated fiber.
Electrochemically oxidized C320000 fibers show nucleation growth on certain sites
but not across the whole fiber surface. When comparing the ’’original’’, uncoated
fibers, it can be seen that longitudinal striations on the coated samples have been
filled with small grain or microspherical structure. A more continuous and even
thicker copolymer coating can be observed after a few minutes. Coating thickness
for carbon fiber depends on the charge passed through the fibers; an increase of
charge increased thickness. Figure3.64 showed that composite of PEEE/ PBEDOT
has different structure than copolymers
84
Figure 3.62: SEM of Random Electrografted Copolymers of P[BEDOT-co-EEE] onto Carbon Fiber by Potentiodynamically at 20mV/sec, on 3 Single CF, Surface
Area 0.0132 cm2, Number of Scan is 8
Figure 3.63: SEM of Random Electrografted Copolymers of P[BEDOT-co-EEE]
onto Carbon Fiber by Potentiodynamically at 20mV/sec.
85
Figure3.64:SEM of Composite of CF/PEEE/BEDOT Obtained Potentiodynamicaly, on 5 Single CF, 20 mV /s ,in the Range of [ - 1.0 V , + 0.7 V ], Surface Area is
0.0165 cm2 , Diameter of Grafted Fiber , 9.3 µ.
Table3.5: Some Data Obtained from CV, and in-Situ Spectroelectrochemical Study of Homopolymers, Copolymer and Composites.
Polymer
Eonset, V E1/2, V ∆E, V Ea, V Ec, V Eg,
eV
PBEDOT -0.50 -0.09 0.06 0.12 0.06 1.65
PEEE 0.05 0.56 0.10 0.61 0.51 2.53
PEBEE 0.70 0.82 0.05 0.60 0.55 -
PECz 0.64 1.22 0.10 1.2 1.3 -
PEDOT 1.1 0.1 0.0 0.1 0.1 1.77
P(BEDOT-
co- EEE)
-0.40 0.38 0.00
0.38 0.38 1.91
CF/PEEE/
BEDOT
-0.20 0.21 0.23 0.10 0.33 2.53
CF/PBED
OT/EEE
-0.40 0.11 0.21 0.00 0.21 -
86
3.6 Synthesis and Electrochemical Polymerization of N-Ethylcarbazole- Bis-3, 4
Ptyhlenedioxythiophene- N-Ethylcarbazole Pomonomer
A new co-monomer ECz-BEDOT-ECz (ECz: N-Ethylcarbazole- BEDOT:2,2‘-bis-
(3,4 ethyhlenedioxy)thiophene) has been firstly synthesized, characterized and
electropolymerized on carbon fiber microelectrode (CFME) and Pt. Side group of
monomer play an important role on the physical properties of resulting copolymer
and it resembles the behavior of homopolymer of monomer at the end of co-
monomer,namely ethylcarbazole. Environmental stability of PBEDOT was increased
by incorporation of ECZ monomer into structure. For ECZ ending monomers CFME
seems better substrate than Pt to obtain an electroactive polymer film.
3.6.1 Polymer Synthesis and Characterization
ECz-BEDOT-ECz comonomer was electropolymerized on carbon fiber
microelectrode (CFME) and Pt. Results from the electropolymerization of ECZ on
CFME electrode were compared with the results of the comonomer.
The Cyclic voltammogram (CV) obtained for electropolymerization (ECz-BEDOT-
ECz) on Pt in order to see the differences of growing films at different switching
potential (Figure3.65). From these measurements redox parameters were determined
and summarized in Table3.6. The results showed no significant differences between
anodic and cathodic scans with increasing switching potential.
Electropolymerization of ECz-BEDOT-ECz comonomer on carbon fiber
microelectrode (CFME) was achieved by applying potential cycling between 0-1.3V
at a scan rate of 100mV/s (Figure 3.65). The first redox process (0.84V in the
positive scan and 0.77V in the negative scan) corresponds to electron transfer
from/to electrodeposited PolyEBEE film. In order to compensate the change of
PEBEE film, anion transport from/to electrolyte solution, i.e, anion doping and
dedoping should occur. The second redox process (large currents) due to
superposition of two distinct process; one is the electron transfer from EBEE co-
monomer to the electrode corresponding to oxidation of co-monomer to produce a
precursor for PEBEE film, the other is the electron transfer from PEBEE film
corresponding to oxidation of PEBEE film.
87
Although current intensities increase as the scan number increases, deposition
process or insoluble film formation could not be detected in any experiments and the
color of solution converted to green when Pt electrode was used as a working
electrode (Figure3.65). This might be due to so-called oligomer approach that
accepted recently [106]. In this approach it is suggested that after the formation of a
dimer a sequence of subsequent dimerization step leads to the formation of soluble
oligomers. All this reaction probably occurs in solution without or only small
precipitation on electrode. Subsequently, deposition and growth process set in
triggered by nucleation reaction. In addition to these recent studies shows that rate
constant of dimerization of chainlike conjugated oligomers and their coupling steps
with the original monomers decrease with increasing chain length [107]. In our case
after dimerization and/or tetramer formation further coupling reaction become very
slow due to decrease in the rate constant. Formation of only soluble oligomers was
also supported by solution color which turns from light yellow to green as reaction
proceeds.
-0,2 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4
-0,5
0,0
0,5
1,0
1,5
2,0
2,5
3,0
3,5
current density,m
A/cm
2
potential vs Ag/AgCl
Figure 3.65: Potentiodynamic Growth of ECz-BEDOT-ECz (4.10-3M), on Pt Electrode in 0.1 M LiClO4 /Propylene Carbonate. (scan rate:100mV/s)
88
Table 3.6: Effect of Swicthing Potential on Redox Parameters of Electrogrowth of EBEE on Pt Electrode.
Eλλλλ (V)* Eonset(V) Q(mC) Ea(V) Ec(V) ∆∆∆∆E(V) Ia/Ic
1.20 0.776 1.163 0.898 0.776 0.122 0.778
1.22 0.756 1.424 0.853 0.775 0.078 0.669
1.24 0.754 1.601 0.846 0.767 0.079 0.682
1.26 0.761 1.557 0.843 0.765 0.078 0.659
1.28 0.753 1.956 0.851 0.768 0.083 0.658
1.30 0.759 1.955 0.847 0.769 0.078 0.676 *switching potential
The increase in current obtained from each scan during polymer growth was
compared for Pt and CFME. It can be easily seen that they are higher in the case of
CFME (Figure 3.65 and Figure 3.66) and this results suggests a conducting film on
electrode surface.
Electrochemically deposited films were washed with PC and placed into monomer-
free electrolyte solutions to study the redox properties. Figure 3.67 shows cyclic
voltamogram of polyEBEE at different scan rates and representative for also PECz
film. As illustrated by Figure3.67, Increase in current with the scan rate indicated
that the polymer, and all electroactive sites, is electrode supported. The resulting
polymer displays two oxidation processes, at 0.88V and 1.22V (Figure 3.67).
Appearance of green color on the electrode surface, higher value of current
intensities in accordance with Pt electrode and increase in the current density with
increasing scan number suggests a polymer film on CFME.
As can be seen in Table3.7, the oxidation potentials of the monomers scale with
half wave potentials for redox processes of the polymers. Poly EBEE redox potential
is lower 0.45V (with a E1/2,p=0.82V)than that of PECz.
Table 3.7: Redox Parameters of Monomers and Polymers
Monomer Eonset,m Ep,m E1/2,pa
Ecz 0.66 1.21 1.27
EBEE 0.70 1.30 0.82
BEDOT -0.30 0.80 0.15 aE1/2 were calculated at 100mV/s scan rate in LiClO4 containing PC.
89
Obtaining an insoluble deposition by changing the electrode from Pt to CFME might
be due to well known behavior of N-alkyl and phenyl substituted carbazole
monomers. The achievement anodic oxidation product as coherent films bound to
the nature of electrode and medium [108]. In acetonitrile although only soluble
dimers obtained in solution on Pt electrodes, insoluble deposition obtained for Au
and glassy carbon electrode. In our case since co-monomer contains ECZ end group,
it behaves similar to ECZ alone.
In our and other previous studies on a co-monomer that has the structure of EDOT-
ECz-EDOT gave resulted polymer coatings on both Pt and CFME electrodes under
the same conditions [109-110]
In the light of all these results it can be concluded that solubility of oxidized product
of ECZ-BEDOT-ECZ on Pt electrode might be due to either characteristic behavior
of ECZ or stop of polymerization and/or became very slow at oligomerization level
as suggested by oligomer approach.
In order to gain better understanding to this behavior, ECZ was also polymerized at
same conditions on both Pt and CFME electrodes. In the case of Pt electrodes, only
soluble green colored dimer was obtained in solution as suggested before [111]
-0,2 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4
-200
-150
-100
-50
0
50
100
150
200
250
300
current,mA/cm
2
potential vs Ag/AgCl
Figure 3.66: Potentiodynamic Growth of ECz-BEDOT-ECz (4.10-3M), on CFME Electrode in 0.1 M LiClO4 /Propylene Carbonate. (scan rate:100mV/s)
90
-0,2 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4
-50,0
-37,5
-25,0
-12,5
0,0
12,5
25,0
37,5
50,0
62,5
75,0
87,5
100,0
112,5
125,0
137,5
current,mA/cm2
potential vs Ag/AgCl
Figure 3.67: Scan Rate Dependence of P (ECz-BEDOT-ECz) on CFME in 0.1M LiClO4 / PC, (scan rate = 20mV-200mV .s-1)
-0,2 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4
-250
-125
0
125
250
375
500
current,mA/cm2
potential vs Ag/AgCl
Figure 3.68: Potentiodynamic Growth of ECz (2.10-3M), on CFME Electrodes in 0.1M LiClO4 / Propylene Carbonate. (scan rate:100mV/s)
91
Figure 3.69: Scan Rate Dependence of PECz Coated CFME in 0.1M LiClO4 / Propylene Carbonate.
On the other hand, by oxidation of ECZ in the same condition, deposition was
obtained on CFME electrode. As can be seen from the CV obtained during
polymerization (Figure 3.68), current intensities increases as subsequent scan. This
behaviour was not observed in the case of Pt that gives only soluble oligomers.
Cyclic Voltamograms of PECz (Figure 3.69) unambiguously indicate that oxidative
doping of this polymer is a two step phenomena since two redox species are seen. In
the sense that two reversible redox processes have been assigned to formation of
radical cation and dication states with in the carbazole unit Similar result was also
observed for Poly(3-octyl thiophene) . CV of PECZ coated CFME electrodes in
monomer free electrolyte shows two step oxidation at 0.93V and 1.23 V V having
linear dependence to scan rate (Figure 3.69).
3.6.2 Morphologyof PEBEE
Electropolymerization of the comonomer was performed potantiodynamically. The
monomer concentration of 4.10-3M EBEE electrografted on CFME with different
scan rate. The polymer obtained at 100mV/s and different cycle numbers polymer
coating was heteregenous(Figure 3.70 and 3.71). Regular polymer growth is
observed only 20mV/s scan rate with 50cycle(Figure3.72). A globular structure
resulting from a three dimensional nucleation growth mechanism as observed only in
that case. The SEM structure of PEBEE (Figure3.72) shows small clusters of
globules. The morphology of polymers obtained with 100mV/s scan rate were quite
different from that of obtained with 20mV/s.
92
Figure 3.70: SEM Photograph of PEBEE Obtained with 100mV/s 3 Cycle in LiClO4 / PC on CFME.
Figure 3.71: SEM Photograph of PEBEE Obtained with 100mV/s 40 Cycle in LiClO4 / PC on CFME.
93
Figure 3.72: SEM Photograph of PEBEE Deposited on CFME with 20mV/s and 50 Cycle.
3.7 Electrochemical Synthesis of EDOT-ECZ-EDOT Copolymer on Flexible
Carbon Fiber Micro-Electrodes
3,6 bis (3,4-ethylenedioxythiophenyl)-9-Ethylcarbazole (EDOT-ECZ-EDOT or
EEE) films are synthesized electrochemically on carbon fiber micro-electrodes.
Deposition conditions on the electroactivity of the resulting polymers are studied.
Structural studies of the polymers have been conducted using different techniques
such as cyclic voltammetry, ATR-FTIR, scanning electron microscopy, four-point
probe conductivity.
3.7.1 Polymerization and Characterizationof PEEE.
Cyclic voltammogram obtained during polymer film growth on both Pt and carbon
fiber micro electrodes were given in Figure 3.73 a and b respectively. Oxidation of
monomer starts around 0.35 V and gives a peak at 0.56 V on Pt and 0.6 V on CF
electrodes. Upon repeated scans new redox process appear at lower potentials,
indicating the formation of electroactive polymer film. Reversibility of film seems
better in the case of CFME. Polymers films were obtained at different scan rate
(Figure 3.74) that indicates the current increase is electrode supported in both
electrodes and also reversible. Their SEM photographs were taken (Figure 3.75). As
shown from SEM pictures increase in scan numbers, the thickness of film increases
94
as expected (Figure 3.75). From SEM’s of the cross section of electrodes (Figure
3.75e) the thickness was calculated since the thickness of naked CFME is known.
From the data obtained these measurements a graph between scan number and
thickness were plotted (Figure 3.76)
0,0 0,2 0,4 0,6 0,8 1,0 1,2
-2
-1
0
1
2
3
4
a
current,µA
potential,V
0,0 0,2 0,4 0,6 0,8 1,0 1,2
-40
-20
0
20
40
60
80
b
Current,µA
Potansiyel V
Figure 3.73: Cyclic Voltammograms for the Oxidation of EEE on Pt (a) and CF(b) in 0.1 M LiClO4 /PC at 20 mv.s-1.
95
0,0 0,2 0,4 0,6 0,8 1,0 1,2
-4,0
-3,5
-3,0
-2,5
-2,0
-1,5
-1,0
-0,5
0,0
0,5
1,0
1,5
2,0
2,5
3,0
3,5
4,0
4,5
5,0
a
current,µA
potential,V
0,0 0,2 0,4 0,6 0,8 1,0 1,2
-100
-80
-60
-40
-20
0
20
40
60
80
100
b
Current,µA
Potential V
Figure 3.74: Scan Rate Dependence of PEEE on CFME on Pt(a) and CF(b) in 0.1 M LiClO4 /PC .
96
a
b
97
c
d
e
Figure 3.75: SEM Pictures of PEEE Films on CF Obtained at Different Scan Numbers; 3 (a), 10(b), 15 (c), 20 (d), and Cross Section (e)
98
0 5 10 15 20
0,0
0,5
1,0
1,5
2,0
2,5
Thickness, µm
Scan number
Figure 3.76: Variation of Thickness of Polymer Film with Scan Number.
This graph can be used as calibration graph and one can easily estimate the thickness
of film from the scan number. This type of measurements can be introduced an
alternating methods to expensive thickness measurements techniques.
FTIR-ATR measurements of free standing PEEE film were taken and results
summarized in Table 3.8 and it shows characteristics of both EDOT and ECZ as
suggested in literature.
Table .8: Proposed Assignment for the Main Vibration for PEEE Film
Wavenumber, cm-1 Assignments
2601 ν(C-C)
1619,1579,1472,1441 ν(C-C)ring
1336 ν(C-CH3) of ECZ
1299,1258,1226,1157 ν(C=C)ν(C-C) of thiophene ring and ν(COROC-)
1046,622 Doping induced band
931,908, 847, 808, 750, 710 ν(C-S), δ(C-S) and δ(C-H)
99
3.7.2 Redox Behaviour and Stability of PEEE Films
Redox behaviour of polymer obtained at different scan number was tested in
monomer free supporting electrolyte by cyclic voltammetry (Figure 3.77). The scan
rate dependence of the peak currents found to scale linearly, indicative of an
electrode supported electroactive film (Figure 3.77 B). Similar slope for anodic and
cathodic peak currents also support reversible redox behaviour of film and it is better
than previously reported results on Pt electrodes. Depending on the scan number
during synthesis, peak potentials and formal potentials of polymer film shift towards
to anodic values as the thickness increases (Table 3.9). This might be due to increase
of thickness results difficulty of electron transfer.
0,0 0,2 0,4 0,6 0,8 1,0 1,2
-100
-80
-60
-40
-20
0
20
40
60
80
100
Current,µA
Potential V
A B
Figure 3.77: Scan Rate Dependence of PEEE Film in Monomer Free Supporting Electrolyte(A) and Variation of Peak Current with Scan Rate (B)
Table 3.9: Redox parameters of polymeric films
Scan number E1/2, V
3 480
5 485
10 490
In-situ spectroelectrochemical spectrum of PEEE indicates the evolution of mid-IR
absorptions as the polymer becomes conducting and it shows fast switching times
(second) for the large optical changes being attained (Figure 3.78). Optical band gap
of film obtained as 2.48 eV which is very close to N-methyl derivatives reported
before [110]. In the fully reduced form (at -1.0 V) polymer is yellow which
gradually changes to green upon mildly oxidizing potential (at 0.1 V) and at higher
100
potential it turns to deep blue. This type of multicolor behaviour is not common and
important for preparation of electrochromic materials.
Figure 3.78: In-Situ Spectroelectrochemistry of PEEE Film Obtained at Different Applied Potential in the Range of -1.0 to 0.4 V
3.8 Comparative Study of Polymer Electrodes
The corresponding copolymers are between these two values. E1/2 of PCzs decreased
from ~1.0V to 0.55V with EDOT inclusion into the structure of copolymer but the
results also showed that the application of optimum solvent and
electropolymerization method, the oxidation potentials of PCzs can be decreased by
the substitution of i.e., N-hydroxy methyl group by potentiostatic polymerization
method in CH2Cl2 solvent (E1/2=0.55V) (Figure 3.79). The capacitance of polymer
electrodes are given comparatively for the chosen electropolymerization methods
(Figure 3.80-3.81) Potentiostaticallyobtained PMeOHCz showed the highest specific
capacitance.(Figure 3.81). That may be due to more polymer electrodeposition by
this method that provides an increase the values of capacitance. In this study,
Electropolymerization of Cz and EDOT derivatives and their copolymers are
investigated in different conditions. Figure 3.82 indicated that the lowest E1/2
(highest Csp) belongs to PEDOT, since 3- and 4- positions of alkylenedioxy
substituted thiophenes facilitates the formation of linear polymer chains which
should lead to increase in conjugation length, where substitution lowers the
oxidation potential of polymer films. On the other hand, PCz has the highest E1/2
but lowest Csp due to its degeneracy(Figure 3.82a-b).
101
1 2 3 4 5 6 7 8 9 10
0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1,0
1,1
E1/2,V
Polymer electrodes
PEDOT
PEEE
PMeOHCz/CH2Cl
2
PMeOHCz/PC
PMeOHCz/ACN
PEBEE
PNVCz
PCz
PBrCz
PEtOHCz
Figure 3.79: Polymeric Film Redox Otentials at Different Conditions.
1 2 3 4 5 6 7 8
0
5
10
15
20
25
30
35
40
45
Csp, mF/g
polymer electrodes
CFME
PCz
PBrCz
PNVCz
PEBEE
PECz
PEtOHCz
PEDOT
Figure 3.80: Csp Values of Polymer Electrodes Obtained Potentiodynamic Method.
102
10 11 12
0
10000
20000
30000
40000
50000
Csp,m
F/g
Polymer electrodes
PMeOHCz/PC
PMeOHCz/CH2Cl
2
PMeOHCz/ACN
Figure 3.81: Csp Values of Polymer Electrodes Obtained Potentiostatic Method.
0.0 0.2 0.4 0.6 0.8 1.0
5
10
15
20
25
30
35
40
45
S
O OCH2
CH3CH2
CH3
O
O O
S
O
S
NN
N
HC=CH 2
N
H
Csp,m
F/g
E1/2,V
Figure 3.82a: Csp vs E1/2 graph of Some Polymer Electrodes Obtained
Potentiodynamic Method.
103
0,0 0,2 0,4 0,6 0,8 1,0 1,2
5
10
15
20
25
30
35
40
45
PEDOT
PEBEE
PNVCz
PBrCz
PCz
PEtOHCz
Csp, mF/g
E1/2,V
Figure 3.82b: Csp vs E1/2 graph of Some Polymer Electrodes
104
4. CONCLUSION
In our study, we investigated solvent effect on PMeOHCz, that is indicated that the
solvent must have high dielectric constant(to ensure the ionic conductivity of
electrolytic medium and a good electrochemical resistance against decomposition at
high potentials to oxidize monomer and should have low viscosity (electrophoteric
effect). Since PC has high viscosity which leads to a decrease of heterogeneous
electron-transfer rate, and the polymer in PC exhibits lower Cdl and higher Rct than
ACN, so ACN has low viscosity which should be an advantage for electrical
properties of polymer. Surface characterization of electrodeposited thin film of
Poly(MeOHCz) (170-2730nm) indicates that the electrodeposition conditions (e.g.
scan rate, solvent) had an effect on the resulting microcomposite electrode, and
PMeOHCz/CFME exhibited very high electrochemical stability up to scan rate of
1000mV/s. The thin conductive polymeric film showed better charge/discharge
process in PC and different redox properties and capacitive behaviours in different
solvents, indicating the crucial effect of solvents on polymeric thin film properties
(on carbon fiber surface). These results reveal that electrochemically modified
Carbon Fiber Microelectrodes (by conductive thin polymer film coating) can be used
for the storage of energy in electro chemical capacitors. (super micro- and nano-
capacitors). In this thesis, it is proven that, even nano and micron size coatings of
conductive polymers on micron sized carbon fibers allow nanoscale energy storage
applications with success.
N-ethylol- Carbazole was electropolymerized on carbon fiber micro electrode,
SEM indicated that PolyEtOHCz shows a cauliflower-like structure. The polymer
electrode showed good stability up to 2.0 V along with capacitive behavior.
PEDOT shows supercapacitor behavior from -0.2V to 0.5V. At 1.0V a small
deviation was seen from ideal supercapacitor behavior, i.e, phase of angle was
shifted from 87o to 800. PEDOT electrodes have capacitive behavior and stable with
a charge of 5.79 and 6.6mC by giving a phase angle of 88o ( ideal capacitor behavior
105
is 90o) In the thesis, in all studied monomers PEDOT gave the best capacitor
behavior in terms of bode phase angle and also rectangular box shaped CV of the
film. PEDOT is very stable in its doped state, and reaches conductivity as high as
200S/cm. PEDOT has a low band gap(1.6-1.7eV) due to the presence of the two
electron donating oxygen atoms coupled to the thiophene ring.
It has been well-known that multiple ring monomers with extended conjugation
undergo facile electropolymerization to form stable, electroactive, electrically
conducting polymers. These monomers polymerize at low enough potentials to avoid
detrimental side reactions such as β coupling and overoxidation of the monomer.
Another advantage for preparing multi-ring monomers is the ability to create
conducting copolymer which may exhibit properties of the different hetereocycles
incorporated within. So, PEEE films were firstly prepared on flexible carbon fiber
electrodes and deposition conditions on electroactivity of resulting polymers were
studied. Results suggest that polymeric films give rise to an array of different colors
which is dependent on deposition conditions and thickness of film. Simple
alternative methods were suggested for the determination of thickness of polymeric
film on CFME. Polymeric films were found very stable even at high potentials.
The anode material is a critical consideration since physicochemical properties of its
surface determine the nature and the strentgh of the bond between the polymer and
the electrode, which can affect both polymerization process and properties of the
resulting polymer. ECz-BEDOT-ECz comonomer was synthesized first time and
electropolymerized on Pt and CFME. ECz was also electropolymerized on CFME in
order to compare with Poly (ECz-BEDOT-ECz) and to gain further information.
Cyclic voltammogram of electrogrowth of Poly (ECz-BEDOT-ECz) obtained on
CFME, exhibits two oxidative processes at 0.88V and 1.22 V. There was no coating
obtained on Pt under same conditions, so the electrode material is an important
factor for electrocoating and electrochemical characterizations and due its character
and micron size CFME has the advantage of giving deposition and sensitive
detection of electroactive film. ECz-BEDOT-ECZ polymerization mechanism
depends on the switching potentials and chemical reaction becomes important at
higher switching potential. The scan rate used has an effect on the homogenity of the
resultant film. In literature, it is known that ECz is not electropolymerized except
under acidic conditions; however, we observed that ECz can be electropolymerized
106
on CFME under mentioned experimental conditions. CV of PECz coated CFME
electrodes in monomer free electrolyte shows two step oxidation at 0.93V and 1.23
V which has promising properties and needs to further investigation. Comparison of
results with previous study reveals the fact that chemical make up play an important
role on the properties of resulting polymers.
Copolymer formation results in a decrease in the potentials and band gap of PEEE
by improving the multicolored structure at different charging levels. Although these
values are higher from the PBEDOT film, this gives the advantage of better air
stability to the copolymer film. PBEDOT film shows the lowest onset potential, peak
potentials, and band gap values. Incorporation of PEEE into the copolymer structure
shifts these values towards to PEEE.
107
REFERENCES [1] Linford, R.G. (Ed.), 1987. Electrochemical Science and Technology of
Polymers, Elsevier, 1, England.
[2] Linford, R.G. (Ed.).,1990. Electrochemical Science and Technology of Polymers, Elsevier, 2., England.
[3] Bruce, P.G.,. 1995. Solid State Electrochemistry, Cambridge University Press,Cambridge.
[4] Skotheim, T.A. (Ed.), 1986. Handbook of Conducting Polymers, M. Dekker, Vols. 1–2, New York.
[5] Fujihira, M., in: Fry, A.J., Britton, W.E. (Eds.), 1986. Topics in Organic Electrochemistry, Plenum Press, p. 225., New York.
[6] Forster, R.J. and Vos, J.G., 1992. Comprehensive Analytical Chemistry, Elsevier vol. 27, Amsterdam. [7] Martin, C.R., Parthasarathy, R. and Menon, V.,1993. Electronically conductivepolymers as chemically-selective layers for membrane- based separations, Synth. Met., 55:57,1165-70. [8] MacDiarmid, A.G., 1989. Epstein, Polyanilines-A novel class of conducting polymer, Faraday Discuss.Chem. Soc. 88 317. [9] Paul, E.W., Ricco, A.J., and Wrighton, M.S., 1985. Resistance of polyaniline
Films as a function of electrochemical potential and the fabrication of polyaniline-based microelectronic devices , J. Phys. Chem., 89, 1441-1447.
[10] Miasik, J.J., Hooper, A. and Tofield, B., 1986. Conducting Polymer Gas Sensors, J. Chem. Soc. FaradayTrans. 82, 1117.
[11] Pei, Q.B. and Inganas, O., 1993. Electroelastomers-conjugated poly(3- octylthiophene) gels with controlled crosslinking - Synth. Met. 55:57, 3724-3729.
[12] Dunsch, L., 1975. Kinetics and mechanism of anodic aniline oxidation , J. of Electro.Anal.Chem, 61 (1), 61-80.
[13] Diaz, A.F. and Logan, J.A., 1980. Electroactive polyaniline films J. Electroanal. Chem. 111, 111-114.
108
[14] Diaz, A. F., Castillo, J.I., Logan, J.A. and Lee, W.-E.,1981. Electrochemistry of conducting Polypyrrole films, J. Electroanal.Chem., 129, 115-132. [15] Baker, C.K. and Reynolds, J.R.,1988. A quartz microbalance study of the
electrosynthesis of polypyrrole, J. Electroanal. Chem. 251,307-322.
[16] Miras, M.C., Barbero, C., Ko¨ tz, R., Haas, O. and Schmidt, V.M., 1992. A quartz microbalance study and probe beam deflection studies of poly(1-hydroxyphenazine modified electrodes, J.Electroanal. Chem., 338, 279-297.
[17] Schlereth, D.D. and Karyakin, A.A., 1995. Electropolymerization of Phenoxazine and phenazine derivatives-characterization of the polymers by UV-visible difference spectroelectrochemistry and fourier-transform IR spectroscopy, J. Electroanal. Chem., 395, 221-232.
[18] Karyakin, A.A., Bobrova, O.A. and Karyakina, E.E., 1995. Electroreduction of NAD(+) to enzymatically active NADH at poly(neutral red) fied electrodes J. Electroanal.Chem., 399, 179-184. [19] Brett, C.M.A., Inzelt, G. and Kerte´sz, V., 1999. Poly(methylene blue) modified electrode sensor for haemoglobin, Anal. Chim. Acta., 385, 119-123. [20] Cruz, C.M.G.S. and Ticianelli, E.A., 1997. Electrochemical and ellipsometric
studies of polyaniline films grown under cycling conditions, J. Electroanal. Chem., 428, 185-192.
[21] De Gennes, P.G., 1981. Polymer solutions near an interface. Adsorption and depletion layers, Macromolecules, 14, 1637-1644.
[22] Pruneanu, S., Csaho´k E., Kerte´sz V. and Inzelt G., 1998. Electrochemical quartz crystal microbalance study of the influence of the solution composition on the behaviour of poly(aniline) electrodes Electrochim.Acta, 43, 2305-2323.
[23] Ba´cskai, J., Inzelt G., Bartl A., Dunsch L. and Paasch G.,1994. In situ electrohemical ESR investigations of the growth of one-dimensional and 2-dimensional Polypyrrole films, Synth. Met., 67, 227-230.
[24] West, K., Jacobsen T., Zachau Christiansen B., Careem M.A. and Skaarup S., 1993. Electrochemical synthesis of Polypyrrole-influence of
current density on structure., Synth. Met., 55:57, 1412-1417.
[25] Cruz, C.M.G.S. and Ticianelli E.A., 1997. Electrochemical and ellipsometric studies of polyaniline films grown under cycling conditions, J. Electroanal. Chem., 428, 185-192.
[26] Bade, K., Tsakova V. and Schultze J.W., 1992. Nucleation growth
109
and branching of polyaniline from electrode experiments Electrochim. Acta., 37, 2255-2261.
[27] Levi, M.D. Pisarevskaya Yu. and E.Molodkina E.B., 1993. , Electrochemical behavior and structural charactterization of highly crystalline poly(p- phenylene) films obtained by oxidation of benzene in a concentrated sulfuric acid emulsion, Synth. Met., 54, 195-201. [28] Murray, R.W. (Ed.), 1992. Molecular Design of Electrode Surfaces Techniques of Chemistry, vol. 22, Wiley, NewYork . [29] Roncalli, J., 1992. Conjugated poly(thiophenes): synthesis, functionalization,
and applications, Chem. Rev., 92, 711-738.
[30] Heywang, G. And Jonas F., 1991.Poly(alkylenedioxythiophene)s - new, very Stable conducting polymers, Adv. Mater. 4 ,116-118. [31] Taka, T., 1991. EMI shielding measurements on poly(3-octyl thiophene) blends
Synth. Met. 41, 1177-1180.
[32] Naegele, D., and Bithin R.,1988. Electrically conductive polymers as rechargeable battery electrodes, Sol. State Ion., 28:30, 983-989. [33] Arbizzani, C., Mastragostino M., Meneghello L.,1997. Polymer-based redox
supercapacitors: A comparative study, Electrochim.Acta., 41, 21-26.
[34] Schopf, G. and Kossmehl G., 1997. Polythiophenes - Electrically conductive polymers - Introduction ,Adv. Polymer Sci. (Rewiev) 129, 3-145.
[35] Jonas, F. and Heywang G., 1994. Technical applications for conductive polymers Electrochim. Acta., 39, 1345-1347. [36] Winkels, S. and Lohrengel M.M.,1997. Time-resolved investigations of the anion intercalation in conducting polymers by microelectrodes,
Electrochim. Acta., 42 , 3117-3122.
[37] Otero, T.F., Rodriquez J., Angulo E., and Santamaria C., 1993. Artificial Muscles from bilayer structures, Synth. Met. 57(1), 3713-3717.
[38] Gustaffson-Carlberg, J.C., Inganaes O., Anderson M.R., Booth C., Azens A., and Granqvist G., 1995. Tuning the bandgap for polymeric Smart windows and displays, Electrochim. Acta., 40, 2233-2235.
[39] Wessling, B., 1994. Passivation of metals by coating with Polyaniline-corrosion potential shift and morphological changes, Adv. Mater. 6, 226-228.
[40] DeBerry, D.W., 1985. Modification of the electrochemical and corrosion behavior of stainless-steels with an electroactive coating, J. Electrochem. Soc., 132, 1022-1026.
110
[41] Roth, S., 1995. One Dimentional Metals, VCH Press Weinheim. [42] Ahmad, N. and MacDiarmid A.G., 1996. Inhibition of corrosion of steels with
the exploitation of conducting polymers, Synth. Met. 78, 103-105.
[43] Guiseppi-Elie, A., Wallace G.G., Matsue T. and Dekker M., 1998., Handbook of Conducting Polymers T.A.Skotheim (Ed.), 963, New York. [44] Hanawa, T. and Yoneyama H., 1989. Gas sensitives of Polypyrrole films to
electron acceptor gases, Bulletin of the chemical Society of Japan, 62 (6), 1710-1714.
[45] Janda, P. and Weber J., 1991. Quinone-mediated glucose-oxidase electrode with the enzyme immobilized in Polypyrrole, J. Electroanal. Chem.,
300, 119-127.
[46] Contractor, A.Q., Sureshkumar T.N., Narayanan R., Sukeerthi S., Lal R., and Srinivasa R.S., 1994. Conducting Polymer-based biosensors, Electrochim. Acta., 39, 1321-1324.
[47] Xue, H. and Mu S.,1995. Bioelectrochemical response of the polypyrrole xanthine oxidase electrode , J. Electroanal. Chem., 397, 241-247.
[48] Hwang, L.S., Ko J.M., Rhee H.W. and Kim C.Y., 1993. A polymer humudity sensor, Synt.Met. , 57 (1), 3671-3676.
[49] Abd El-Rahman, H.A. and Schultze J.W., 1996. New quaternized aminoquinoline polymer films: Electropolymerization and characterization, J. Electroanal.Chem., 416, 67-74.
[50] Kaneto, K., Kaneko M., Min Y. and MacDiarmid A.G.,1995. Artificial muscle- electromechanical actuators using Polyaniline films, Synth. Met., 71, 2211-2212.
[51] Jonas, F., Schrader L. , 1991.Conductive modifications of polymers with polypyrroles and polythiophenes, Synt.Met., 41 (3), 831-836.
[52] Dietrich, M., Heinze J., Heywang G. andJonas F.,1994. Electrochemical and spectroscopic characterization of polyalkylenedioxytthiophenes, J. Electroanal. Chem.369, 87-92.
[53] Jonas, F. and Heywang G.,1994 Technical applications for conductive polymers., Electrochim. Acta, 39, 1345-1347. [54] Groenendaal, L. B., Jonas F., Freitag D., Pielartzik H., and Reynolds J. R,
2000. Poly(3,4-ethylenedioxythiophene) and its derivatives: Past, present, and future, Adv.Mat., 12 (7), 481-494.
[55] Nishino, H., Yu G., Heeger A.J. and Chen T.A., 1995. R.D.Rieke,
111
Electroluminascence from blends films of poly(3-hexylthiophene) and poly(N-vinylcarbazole), Synth. Met. 68(3), 243-247.
[56] Taudi H., Bernede J.C., Del Valle M.A., Bonnet A. and Morsli M., 2001. Influence of the electrochemical conditions on the properties of polymerized carbazole, J. Mater. Sci. 36, 631-634.
[57] Bismarck, A., Menner A., Barner J., Lee A.F., Wilson K., Springer J., Rabe J.P., and Sarac A.S., 2001. Electrografting of 3-methyl thiophene
and carbazole random copolymer onto carbon fiber: characterization by FTIR-ATR, SEM, EDX, Surf. Coat. Technol. 145, 164-175.
[58] Kawde, R.B. and Santhanam K.S.V., 1995. An in-vitro electrochemical sensing of dopamine in the presence of ascorbic acid, Bioelectron. Bioenerg. 38 405-409.
[59] Zhang, Y. D., Wada, T.; Wang, L., Aoyama, T. and Sasabe, H., 1996. Photorefractive polymers containing a single multifunctional chromophore, Chem. Commun., 2325-2326.
[60]Kippelen, B., Tamura, K., Peyghambarian, N., Padias, A. B.,Hall, Jr. And H. K., 1993. Photorefractivity in functional side-chain polymer, Phys. Rev. B, 48, 10710-10718.
[61] Morisihima, Y, Kabayashi T, Nazakura S. and Webber SE., 1987. Preferential Excimer Emission from Amphiphilic Alternating Copolymers of 2-Vinylnaphthalene and Maleic Acid in Aqueous Solution, Macromolecules, 20, 807-813.
[62] Sarac, A.S, Tofail S.A.M. , Serantoni M, Henry J., Cunnane VJ. and McMonagle J.B. ,2004. Surface characterisation of electrografted
random poly[carbazole-co-3-methylthiophene] copolymers on carbon fiber: XPS, AFM and Raman spectroscopy, Applied Surface Science 222 148–165.
[63] Sarac, AS, Bismarck A, Kumru EM. and Springer J., 2001. Electrografting of poly ( Carbazole –co-acrylamide) onto several carbon fibers Electrokinetic and surface properties, Synt. Met, 123, 411-423.
[64] Sezer, E., Yavuz O., Sarac A.S.,2000. N-Vinylcarbazole-Acrylamide Copolymer Electrodes, Electrochemical Response to Dopamine, Journal of The Electrochemical Society, 147 (10), 3771-3774.
[65] Iroh, J.O. and Jordan K.M.S., 2000. Surf. Eng. 16 (2000) 303. [66] Park, J.M., Kim Y.M. and Yoon D.J., 2000. J. Colloid Interface Sci.231 (2000) 114. [67] Sezer, E. and Sarac A.S., 2007 Int. J. Polym. Mater.., in press.
112
[68] Bismarck, A., Menner A., Kumru E., Sarac A.S., Bistriz M. and Shulz E., 2002. J. Mater. Sci. 37 (3), 461–471. [69] Sarac, A.S., Sönmez G. and Cebeci F.C., 2003. J. Appl. Electrochem. 33(3–4)
295–301.
[70] Bard, A.J. and Faulkner L.R., 1980. Electrochemical methods. Wiley.Newyork. [71] Lang, G. and Inzelt G., 1991. Some problems connected with impedance
Analysis of polymer film electrodes-effect of the film thickness and thickness distribution, Electrochim. Acta., 36, 847-854.
[72] Nguyen, P.H. and Paasch G., 1999. Transfer matrix method for the electrochemical impedance of inhomogeneous porous electrodes and membranes J.Electroanal. Chem. 460 63-79.
[73] Johnson, B.W., Read D.C., Christensen P., Mamnet A. and Armstrong R.D.,1994. Impedance characteristics of conducting polythiophene films, J. Electroanal. Chem. 364, 103-109.
[74] Macdonald, J.R., 1990. Impedance spectroscopy-old problems and new developments, Electrochim. Acta 35, 1483-1492.
[75] Skotheim, TA, Elsenbaumer RL. and Reynolds JR., 1998. Handbook of Conducting Polymers, Secon Edition and Expanded, Newyork.
[76] Burke, A. F., 2000. Ultracapacitors: why, how, and where is the technology, J. Power Sources, 91, 37-50.
[77] Johnson, B.W., Read D.C., Christensen P., Mamnet A., and Armstrong R.D.,1994. Impedance characteristics of conducting polythiophene films, J. Electroanal. Chem. 364, 103-109.
[78] Sotzing, G.A., Reynolds J. And Steel P.J., 1997. Poly(3,4-ethylenedioxythiophene) (PEDOT) prepared via electrochemical polymerization of EDOT, 2,2'-bis(3,4-ethylenedioxythiophene) (BiEDOT), and their TMS derivatives, Adv. Mater., 9(10), 795-798.
[79] Kakiuchi, T., 1998. A theory of voltammetry of ion transfer across a liquid membrane in the absence of supporting electrolytes using the Nernst-Planck equation and electroneutrality assumption,. Electrochim Acta, 44, 171–179.
[80] Abd El-Rahman, HA., 1997. Stability and Behavior of poly-1-naphthol films towards charge transfer reactions, Thin Solid Films, 310, 208–216.
[81] Csahok, E., Vieil E., Inzelt G., 2000. In situ dc conductivity study of the
113
redox transformations and relaxation of Polyaniline films, J
Electroanal Chem, 482, 168–177.
[82] Robberg, K. and Paasch G, 1998. Dunsh L, Ludwig S. , The influence of porosity and nature of the charge storage capacitance on the impedance behavior of electropolymerized polyaniline films, J
Electroanal Chem, 443, 49–62.
[83] Conway, B.E., 1999. Electrochemical supercapacitors:Scientific, Fundemantals and Technological Applications, 366, Plenum, Newyork.
[84] Inzelt, G, 1983. Role of Polymeric properties in the electrochemical behavior of redox polymer modified Electrodes, Electrochim. Acta, 34, 83-91.
[85] Burke, A., 2000. Ultracapacitors; Why, How and Where is the technology, J. Power Sources, 91, 37-50.
[86] Siove, A., Ades D., N’gbilo E., and Chevrot C.,1990. Chain-length effect on the elctroactivity of Poly(N-alkyl-3,6-carbazolediyl), Thin Films, 38,
331-340.
[87] Tran-Van, F., Henri T. and Chevrot C., 2002.Synthesis and electrochemical properties of mixed ionic and electronic modified polycarbazole, Electrochimica Acta, 47, 2927-2936.
[88] Racchini, J.R., Wellinghoff S.T., Jenekhe S.A., Schwar S.T. and Herrera C.D., 1988. Synthesis and studies of poly(3,9-carbazolyl), a new conducting polymer displaying high optical transmittance in the visible, Synt.Met. , 22, 273-290.
[89] Kham, K., Sadki S. and Chevrot C., 2004. Oxidative electropolymerizations of carbazole derivatives in the presence of bithiophene, Synt. Metals, 145, 135-140.
[90] Papez, V., Ingonas O., Cimrova V. and Nespurek S., 1990. Electrochemical preparation and study of thin poly( N-vinylcarbazole) layers J.Electroanal.Chem., 282, 123-139.
[91] Sezer, E., Ustamehmetoglu B. and Sarac A.S.,1997. Chemical and electrochemical polymerization of of pyrrole in the presence of N-substituted carbazoles, Synt.Met., 107, 7-17.
[92] Taoudi, H., Bernede J.C, Bonnet A., Morsli M and Godoy A., 1997. Comparison of the properties of iodine-doped poly(N- vinylcarbazole) (PVK) thin films obtained by evaporation of pure powder followed by iodine post-deposition doping and iodine pre- doped powder, Thin Sol Films, 304 , 16-23.
[93] Johnson, B.W., Read D.C., Christensen P., Mamnet A. And Armstrong
114
R.D., 1994. Impedance Characteristics of conducting Polythiophene Films., J. Electroanal. Chem., 364, 103-109.
[94] Macdonald, J.R., 1990. Impedance Spectroscopy-old problems and new developments, Electrochim. Acta., 35, 1483-1492.
[95] Chevrot, C., Ngbilo E., Kham K. and Sadki S.,1996. Optical and electronic properties of undoped and doped poly(N-alkylcarbazole) thin layers, Synt.Met., 81, 201-204.
[96] Lang, G. and Inzelt G., 1991. Some problems connected with Impedance analysis of Polymer Electrodes, Electrochim. Acta, 36, 847-854.
[97] Nguyen, P. H. and Paasch G., 1999. Transfer matrix method for the Electrochemical impedance of inhomogeneous porous electrodes and membranes, J. Electroanal. Chem., 460, 63-79.
[98] Armstrong, R.D, 1986. Impedance plane display for an electrode with Diffusion restricted to a thin layer, J. Electroanal. Chem., 198, 177- 180.
[99] Bobacka, J., 1999. Potential stability of all-solid-state ion-selective electrodes using conducting polymers as ion-to-electron transducers, Anal. Chem., 71, 4932-4937.
[100] Budianto, Y., Aoki A. and Miyashita T.,2003. Ultrathin Polymer Film Capacitor Composed of Poly(N-alkylacrylamide) Langmuir-Blodgett Films, Macromolecules, 36, 8761-8765.
[101] Taberna, P.L, Simon P. and Fauvarque F., 2003. Activated Carbon/Conducting Polymer Hybrid Supercapacitors, J. Electro.Soc., 150(3), A645-A655.
[102] Guo, M., Diao P., and Tong R., 2000. Studies of adsorption kinetics and defects of self-assembled thiol monolayers on gold by capacitance plane plot, J.Chin. Chem.Soc., (Taipei), 47, 1197-1203.
[103] Chung, TC., Kaufman JH., Heeger A.J, and Wudl F., 1984. Charge Storage in doped Polythiophene-optical and electrochemical studes, Phys.Rew.B, 1984, 30, 702-710. [104] Kaneto, K., Kohno Y. and Yoshino K., 1984. Absorbtion-Spectra induced
photoexcitation and electrochemical doping in polythiophene, Solid State Commun, 51, 267-269.
[105] Kvarnström, C., Neugebauer H., Blomquist S., Ahonen H.J., Kankare J., and Ivaska A., 1999. Electrochim. Acta, 44, 2739-2750.
[106] Mullen, K. and Wegner G., 1998. Electronic Materials: in “The oligomer Approach”, Eds.), Weinheim: Wiley VCH.
115
[107]Heinze, J., 1993. Ultracapacitors in electrochemistry, Angew. Chem., 32 (9),
1268-1288.
[108] Desbene-Monvernay, AN, Lacaze PL and Dubois JE, 1981. Polaromicrotribometric (PMT) and IR, ESCA, EPR spectroscopic study of colored radical films formed by the electrochemical oxidation of carbazoles: Part I. Carbazole and N-ethyl, N-phenyl and N-carbazyl derivatives, J.Electroanal. Chem 129,229-241.
[109] Sezer, E, Sarac AS and Parlak AE, 2003. Electrochemical synthesis of EDOT-ECZ-EDOT copolymer on carbon fiber micro-electrodes, J. App. Electrochemistry, 33, 1233-1237.
[110]Sotzing, G.A., Reynolds J. and Steel P.J., 1997. Poly(3,4- ethylenedioxythiophene) (PEDOT) prepared via electrochemical
polymerization of EDOT, 2,2'-bis(3,4-ethylenedioxythiophene) (BiEDOT), and their TMS derivatives, Adv. Mater., 9(10), 795-798.
[111] Yavuz, Ö., Sezer E., and Sarac A.S., 2001. Oxidative polymerization of N- vinylcarbazole in polymer matrix, Polym. Int., 50, 271-276.
116
CURRICULUM VITAE Elif Altürk Parlak was born on 1974 in Giresun and stayed there till her graduation from high school. She has moved to Ankara on 1992 and spent one year at the English Preparation School of the Middle East Technical University (METU) and started her study of Chemisty at the Department of Education of the same university and graduated on 1997. Then get her master degree from Chemistry Department of Science and Art of METU on 1999. On the same year she has relocated to Istanbul and received Ph.D degree from Polymer Science and Technology Programme of Istanbul Technical University on 2006. During her study she has worked as Research Assitant. Her fields of interest are; conductive polymers, elechtrochemistry, thin films, supercapacitors, electrochromic devices and characterization of conductive polymers. She has produced 10 publications at SCI and 5 of them were related about her Ph.D thesis. Also, she has written a chapter in Encyclopedia of Nanoscience and Nanotechnology.
