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Laporan Akhir Projek PenyelidikanJangka Pendek

Development of Zn-Mn02 Battery usingChitosan-ZnCI2. Gel Polymer Electrolytes

byDr. Ahmad AZ'min MohamadAssoc. Prof. Dr. Azizan A~ziz

ilIlHMIUNIVERSITI SAINS MALAYSIA

LAPO~NAKHIR PROJEK PENYELIDIKAN JANGKA PENDEKFINAL REPORT OF SHORT TERM RESEARCH PROJECTSila kemukakan laporan akhir ini melalui Jawatankuasa Penyelidikan di PusatPengajian dan DekanIPengarah/Ketua Jabatan kepada Pejabat Pelantar Penyelidika

1. Nama Ketua Penyelidik:Name ofResearch Leader

AHMAD AZMIN B.lN MOHAMAD

0 Profesor Madya ~ Dr. o EneikIPuan/CikAssoc. Prof Dr. Mr/Mrs/Ms.

2. Pusat Tanggungjawab (PTJ):School/Department/Unit

School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang.

3. Nama Penyelidik Bersama:Name ofCo-Researcher

Prof. Madya Dr. Azizan Aziz "

4. Tajuk Projek: .Title ofProject

Development of Zn-MnOz Battery Using Chitosan-ZnCIz Gel Polymer Electrolytes

5. Ringkasan Peniiaian/Summary ofAssessment: Tidak Boleh Sangat BaikMeneukupi Diterima Very GoodInadequate Acceptable

. 1 2 3 4 5

Ii) Peneapaian objektif projek: D D D D 0Achievement ofproject objectives

.~

ii) Kualiti output: D D D D 0Quality ofoutputs

iii) Kualiti impak: D D D D 0Quality ofimpacts

iv) Pemindahan teknologi/potensi pengkomersialan:\ D D 0' D D

Technology transfer/commercialization potential ,

v) Kualiti dan usahasama : D D D 0' DQuality and intensity ofcollaboration

vi) Penilaian kepentingan seeara keseluruhan: D D D D 0Overall assessment ofbenefits

Laporan Akhir Projek Penyelidikan Jangka PendekFinal Report OJShort Term Research Project

6. Abstrak Penyelidikan(Perlu disediakan di antara 100 - 200 perkataan di dalam Bahasa Malaysia dan juga Bahasa Inggeris.Abstrak ini akan dimuatkan dalam Laporan Tahunan Bahagian Penyelidikan & Inovasi sebagai satu carauntuk menyampaikan dapatan projek tuanlpuan kepada pihak Universiti & masyarakat luar).

Abstract ofResearch(An abstract ofbetween 100 and 200 words must be prepared in Bahasa Malaysia and in English).This abstract will be included in the Annual Report ofthe Research and Innovation Section at a later date as a meansofpresenting the projectfindings ofthe researcherls to the University and the community at large)

ABSTRACTThis project is divided into two main sections, that is to produce solid polymer electrolyte (SPE) as a proton conductor(H+) and to fabricate polymeric solid-state protonic battery with configuration of zinc (Zn)/SPE/manganese (IV) oxide(Mn02)' 1.0 g of chitosan was dissolved in 100 ml of 1 % acetic acid solution. The ammonium nitrate salt (NH4N03)

and plasticizer, ethylene carbonate (EC), were added accordingly. After casting the solution was left to dry at roomtemperature to form the films of pure chitosan acetate (CA), CA-NH4N03, and CA-NH4N03-EC. The temperaturedependence of chitosan-based SPE system was found to obey Arrhenius relationship. The highest conducting sample(3.48 x 10.3 Scm-I), 18 wt. % CA-12 wt. % NH4N03-70 wt. % EC (CA40N70E), possesses the lowest activationenergy (Ea) of 0.10988 eV. The electrochemical stability window for the cells was around 1.6 V - 1.8 V, that was thechitosan films breakdown voltage and become lower as temperatures increases. The cells were fabricated using SPE,which showed the highest value of conductivity, and characterized according to their electrochemical testing at 298,313, 333, and 353 K. The cells performance was excellent at 333 K, with achievement of discharge capacity of 42.7mAh, internal resistance (r) of 16.8 n, maximum power density (Pmax) of 14.6 mW cm-2 and a short-circuit currentdensity (J,c) of 31.0 mA cm-2. The highest open cifeuit voltage (OCV) was 1.479 V at 298 K. On the other hand, theelectrochemical properties of the cells at 353 K were decreased compared to the cells at 333 K. The decrease in theelectrochemical properties was correlated to the failure of the cells. Thus, the best electrochemical properties of thecells from this system were observed at temperature 333 K.

ABSTRAKProjek ini dibahagikan kepada dua bahagian utama iaitu penghasilan elektrolit polimer pepejal (SPE) sebagaikonduktor proton (H+) dan fabrikasi bateri proton keadaan pepejalpolimer dengan konfigurasi zink (Zn)/SPE/mangandioksida (Mn02)' 1.0 g kitosan dilarutkan dalam 100 mllarutan asid asetik 1 %. Garam ammonium nitrat (NH4N03)

dan bahan pemplastik etilena karbonat (EC) ditarnbahkan ke dalam larutan kitosan tersebut. Selepas penuanganlarutan, ia dibiarkan kering pada subu 'bilik untuk membentuk filem kitosan asetat (CA) tulen, CA-NH4N03 dan CA­NH4N03-EC. Kajian konduktiv,i-suhu bagi sistem SPE berasaskan kitosan didapati mematuhi persamaan 'Arrhenius'.Sampel dengan konduktiviti tertinggi (3.48 x to-3 S em-I), 18 wt. % CA-12 wt. % NH4N03-70 wt. % Ee (CA40N70E),mempunyai tenaga pengaktifan (E.J yang terendah, 0.to988 eV. Kestabilan elektrokimia untuk bateri proton adalahkira-kira 1.6 V - 1.8 V, sebagai voltan peeah tebat filem kitosan dan berkurangan apabila 'suhu meningkat. Seldifabrikasi dengan SPE yang mempunyai nilai konduktiviti tertinggi dan peeirian sel berdasarkan kajian elektrokimiapada subu 298, 313, 333 dan 353 K dijalankan. Prestasi sel yang terbaik adalah pada suhu 333 K, dengan kapastidiseas, rintangan dalaman (r), ketumpatan kuasa tertinggi (Pmax) dan ketumpatan arus litar pintas (J,c) masing-rnasingsebanyak 42.7 mAh, 16.8 n, 14.6 rnW ern-2dan 31.0 rnA em-2. Voltan litar terbuka (OCV) tertinggi adalah 1.479 Vpada suhu 298 K. Selain itu, perlakuan elektrokimia bagi sel pada suhu 353 K menurun berbanding dengan sel padasuhu 333 K. lni adalah berhubung kait dengan kegagalan sel tersebut. Justeru itu, perlakuan elektrokimia terbaik bagisel-sel daripada sistem ini adalah diperhatikan padltsuhu 333 K.

2

Laporan Akhir Projek Penyelidikan Jangka PendekFinal Report OfShort Term Research Project

7. Sila sediakan laporan teknikallengkap yang menerangkan keseluruhan projek ini.[Sila gunakan kertas berasingan)

Applicant are required to prepare a Comprehensive Technical Report explaning the project.(This report must be appended separately)

Senaraikan kata kunci yang mencerminkan penyelidikan anda:List the key words that reflects your research:

- Please see attachment

8.

Bahasa Malaysia

Kitosan, Ammonia Nitrat, Etilina Karbonat, elektrolitpolimer, bateri proton

Output dan Faedah ProjekOutput and Benefits ofProject

Ballasa Inggeris

Chitosan; ammonium nitrate; ethylen~ carbonate; polymerelectrolyte; protonic battery.

(a)

*Penerbitan JurnalPublication ofJournals

(Sila nyatakan jenis, tajuk, pengarang/editor, tahun terbitan dan di mana telah diterbitldiserahkan)(State type, title, author/editor, publication year and where it has been published/submitted)

i. L.S. Ng and A.A. Mohamad, Proton Battery b.ased on Plasticized Chitosan-NH4N03

Solid Polymer Electrolyte,Journal ofPower Sources 163 (2006) 382-385. (IF = 3.521).*

ii. L.s. Ng and A.A. Mohamad, Proton battery based on plasticized chitosan-NH4N03

solid polymer electrolyte atelevated temperatures, submitted to Journal ofPower Sources, 2007.

*Awarded Sanggar Sanjung Award (Publication Category) 2006 by USM.

(b) Faedah-faedah lain seperti perkembangan produk, pengkomersialan produklpendaftaran patenatau impak kepada dasar dan masyarakat.

State other benefits such as product development, product commercialisation/patent registration or impact on source an

i. Alternative to the expensive lithium-based battery.ii. Expand the uses ofour own J;:ountry chitosan sources.

iii. Contribution to knowledge.lt is envisage that the results spur from this research will be beneficial to othersresearching in this emerging field ofadvanced materials.

• Sila berikan salinan/Kindry provide copies

(c) Latihan Sumber ManusiaTraining in Human Resources

i) Pelajar Sarjana:Graduates Students(Perincikan nama, ijazah dan status)(Provide names, degrees and status)

I,

Mater o(Science, M. Sc,

I. Ng Li Sian, "Proton battery based on plasticized chitosan-NH-tN03 solid polymer electrolyte at highertemperatures", 2006/07 (Supervisors: Dr. Ahmad Azmin Mohamad)

3

Laporan Akhir Projek Penyelidikan Jangka PendekFinal Report OfShort Term Research Project

ii) Lain-lain:Others

Undergraduate Final Year Project. B. Eng. (Hons!

i. Fatiah Noor Tahiran, "Plasticizedpolyethylene oxide polymer electrolyte/or Zn-Mn02 Battery", 2005/06.ii. Lee Yee Wah, "Zinc-carbon based on hydroponics gel polymer electrolyte", 2005/06.iii. NgLi Sian, "Proton battery based onplasticizedchit()san-NH~OJsolidpolymer electrolyte", 2005/06.iv. Nurfaezah Khamis, "Zn-air battery based on hydroponics gelpolymer electrolyte", 2005/06.v. Sahlina Mat Nor, "Zinc-air battery based on polyacrylamide polymer electrolyte", 2005/06.vi. Yap Soo Chin, "Proton battery based on hydroponics gelpolymer electrolyte", 2005/06

9. Peralatan yang Telah Dibeli:Equipment that has been purchased

-None-

!eP- r -°1--Tarikh

Date

i,

4

Laporan Akhir Projek Penyelidikan Jangka PendekFinal Report a/Short Term Research Project

Komen Jawatankuasa Penyelidikan Pusat PengajianfPusatComments by the Research Committees ofSchools/Centres

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PUSAT PENGAJIANfPUSAT DateSignature ofChairman

[Research Committee ofSchool/Centre]

5

FINACIAL:

Please see Penyata Kumpulan Wang

Balance RM 887.72 already used to buy research materials. Please see the latest quotationIPO(RM885.00)

b •• ,

DEVELOPM.ENT OF Zn·Mn02 BATTERY USING CHITOSAN-ZnCI2 GEl. POLYMER 8.6...'lROlYTES..

OB.A/:IMAD AZMINMQtW~

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PerbeJanjaan Tanggungan Perbelanjaan Jum/ah JumJah Bal<i PeruntukanPerun/ukan sehingga semasa Semasa Perbefanjaan Perbelanja.3n Semasa31/12/2006 2007 2007 2007 Terkumpul 2007(a) (b) (e) (d) (e+d) (b+r:td) (a-(b+e+d)

2,140.05 0.00 0.00 0.00 0.00 0.00 2,140.052,000.00 15.'5.00 0.00 0.00 0.00 155.00 1,845.00300.00 2'-3.30 0.00 0.00 0.00 2'-3.30 270.709,073.95 0.00 0.00 0.00 0.00 0.00 9,073.952,140.00 1;!.452.72 1:40.22 1,300.54 1,940.76 15,393.48 (13,253.48)2,000.00 1,093.00 0.00 95.50 95.50 1,188.50 811.5017,6f04.oA 14,730.02 640.22 1,396.04 2,036.26 __1~ 887.7217,654.00 14,730.02 640.22 1,396.04 2,036.26 16,7E16.28 887.72

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ACCOMPANIED BY THIS· COPY

ELSEVIER

Available online at www.sciencedirect.com

ScienceDirect

Journal of Power Sources 163 (2006) 382-385

Short communication

JeUMAlOI

POWERIOURelS

www.elsevier.com/locate/jpowsour

Abstract

Protonic battery based on a plasticized chitosan-NH4N03solid polymer electrolyte

L.S. Ng, A.A. Mohamad *School oIMaterials and Mineml Resources Engineering. Universiti Sains Malaysia. 14300 Nibong Tebal. PelUlIlg. Malaysia

Received 9 June 2006; received in revised form 3 August 2006; accepted 14 September 2006Available online 7 November 2006

Plasticized chitosan-proton conductor polymer electrolyte films were prepared by dissolving chitosan powder. ammonium nitrate (NH 4 NOJ)salt and ethylene carbonate (EC) plasticizer in acetic acid solution. The highest conductivity of the chitosan-salt with 40 wI. % NH4NOJ in thefilm at room temperature was 8.38±4.11 x 10-' Scm-I and this increased to 9.93± 1.90 x IO-JScm-1 with 70wt.% EC. Baueries with aconfiguration of: Zn +ZnS04·7H20/18 wt.% CA-12 wt.% NH4 NOJ -70 wt.% EC/Mn02 provided an open-circuit voltage of 1.56 ± 0.06 V. Thedischarge characteristics using a I mA constant cunent demonstrated a capacity of 17.0 ± 2.6 mAh. The internal resistance was 29.8 ± 5.1 Q.

While the highest power density was 8.70 ± 1.91 mW cm-2.© 2006 Elsevier B.Y. All rights reserved,

Keywords: Chitosan; Ammonium nitrate; Ethylene carbonate; Polymer ele~trolyte; Proton battery

1. Introduction

Chitosan is a biopolymer and has various usages. It is aunique polysaccharide and attracts much attention in manyfields such as manufacturing and medicine [I]. Recently chi­tosan have been used as a polymer host to study solid polymerelectrolytes (SPE) for batteries [2-5] and t.he proton exchangemembranes (PEM) for fuel cells [6,7]. A proton conductor basedon chitosan-NH4N03 has been reported witB\ a conductivityaround 10-5 Scm-I at room temperature [8]. However, this con­ductivity value is too low for application in a solid-state protonicbattery.

To enhance the conductivity, several approaches were sug­gested in the literature, including the use of blend polymers, theaddition of a ceramic filler, plasticizer and even radiation. Com­pared to other methods, plasticization is the simplest, lowest cost\and most effective way to improve the conductivity of a SPE.Among a number of plasticizers, the most used plasticizers areethylene carbonate (EC), propylene carbonate (PC), dimethylcarbonate (DMC) and diethyl carbonate (DEC) [9].

• COITesponding author. Tel.: +6045996118; fax: +604594 1011.E-mail address:azmin@eng.usm.my (A.A. Mohamad).

0378-7753/$ - see front matter © 2006 Elsevier B, V. All rights reserved.

doi: 10.10 16fi.jpowsour,2006.09.042

To the best of our knowledge there are no systematic studieson proton batteries based on a chitosan SPE. In this paper, astudy is carried out on chitosan-NH4N03-EC systems, and thenapplied to Zn + ZnS04·7HzO/MnOz proton batteries.

2. Experimental

Chitosan films were prepared from highly viscous pow­der supplied by Chito-Chem, Malaysia. One gram of chitosanwas dissolved in 100 ml of I% acetic acid solutions. NH4N03(Merck) and EC (Aldrich) were added accordingly. The mix­ture was dispersed and stirred for 24 h. After complete disso­lution, the solutions were cast onto petri dishes and left to dryby evaporation at room temperature (25 "C) to form films ofpure chitosan acetic (CA), CA-NH4N03 and CA-NH4N03-EC.The films were then transferred into a desiccator for continuous

drying.When the films were formed, they were cut into a suitable

size and placed between blocking stainless steel electrodes in aconductivity cell which was connected to a computer. Electricalconductivity measurements were performed using an AutolabPGSTAT 30 Frequency Response Analyzer (Eco Chemie B.Y.)in a frequency range of between I Hz and I MHz. The measure­ments were carried out at room temperature.

LS. Nil. A.A. Mohamad I JOl/mal of Power Sources 163 (2006) 382-385

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80 u

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20 4.0 60 8.0 100 12.0 14.0 160 18.0t--~-~--'---~-'---'--~-~----t120

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16

14

~CIlell 10II)...."'5 08>

06

04

0.2

0.00.0

2 4 6 8 10 12 14 16 18 20 22 24 26

Time (h)

Fig. 3. Protonic battery open-circuit voltage during 24 h of storage.

384

201.91817161514

~131.2

CIl 1.1ell 1.0~ 090 0.8::- 07

06050.4030.20100

0

3.3. Battery characterizationFig. 5. The plot of I-V and I-P for proton batteries.

• Cell # 1

• Cell # 2

• Cell # 3

The OCY characteristic of the proton batteries at room tem­perature is shown in Fig. 3. There seems to be a voltage delay atthe time of assembly when the voltage was observed higher inthe lirst 2 h and later stabilized at ~ 1.56 V. The OCY remain~d

constant at 1.56 ± 0.06 Y until the 24th hour of storage.Fig. 4 shows the discharge characteristic of three batteries at .­

a constant current of I mAo It can be observed that the voltageof the batteries drop immediately before reaching a flat dis­charge plateau at 1.30 ± 0.04 v. This phenomenoll may be dueto the activation polarization. The activation polarization was.present when the rate of an electrochemical reaction at an elec­trode surface was controlled by sluggish electrode kinetics [12].It also shows that the discharge was sustained for 17.0 ± 2.6 huntil the cut-off voltage of 1.00 V. The discharge capacity was17.0 ± 2.6 mAh, which was greater compared to reports else­where [13].

Fig. 5 shows the J-V and J-P characteristics for the pro­tonic batteries at room temperature. The J- V curve had asimple linear form, which indicates that the <~olarization onthe electrode was primarily dominated by ohmic contribu­tions. The plot of the operating J-P suggests that the con­tact between electrolyte/electrod~s was good. The voltage

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Fig. 4. Discharge curves using a constant currenl at I rnA.

of the battery dropped to a short circuit current density of16.0 mA cm-2 and the maximum power density was determinedto be 8.70 ± 1.91 mW cm-2 . The internal resistance of the bat­tery was obtained from the gradient of the I-V graph, which was29.8 ± 5.1 n, which was lower than other chitosan-based SPEbatterie~ [4,5].

4. Conclusion

The conductivity ofCA-NH4N03 was successfully increasedfrom 10-5 to 10-3Scm-I employing a plasticization methodusing EC. This proton conductor was evaluated for protonic bat­teries at room temperature with the achievement of an OCYof 1.56 ± 0.06 Y, the discharge capacity of 17.0 ± 2.6 mAh anda maximum power density of 8.70 ± 1.91 mW cm-2 . Theseresults imply that CA-NH4N03-EC is a promising proton con­ductor for proton batteries.

Acknowledgements

L.S.N. is a Final Year Project student and would like to thanktechnicians of SMMRE for their experimental helps. A.A.M.also wishes to thank USM for the Short Term Grant 2005/2007given.

References

[I] S. Aiba. Advances in Chitin and Chitosan, Elsevier Applied Science, Bark­

ing. UK, 1992.[2] N.S. Mohamed. R.H. Y. Subban, A.K. Arof. J. Power Sources 56 (1995)

153.l3] N.M. Morni, A.K. Arof. J. Power Sources 77 {I 999) 42.[4] N.M. Morni, N.S. Mohamed. A.K. Arof. Mater. Sci. Eng. B 45 (1997)

140.[5] R.H.Y. Subban. A.K. Arof. S. Radhakrishna, Mater. Sci. Eng. B 38 (1996)

156.l6] P. Mukoma. B.R. Jooste, H.C.M. Vosloo, J. Power Sources 136 (2004) 16.[7] B. Smitha, S. Sridhar, A.A. Khan, Macromolecules 37 (2004) 2233.[8j S.R. Majid, A.K. Arof, Physica B 355 (2005) 78.

Protonic Battery based on a Plasticized Chitosan-NH4N03 Solid Polymer Electrolyte

at Elevated Temperatures

L.S. Ng and A.A. Mohamad*

School of Materials and Mineral Resources Engineering,

Universiti Sains Malaysia, 14300 Nibong Tebal, Penang, Malaysia.

*E-mail address:azmin@eng.usm.my

Abstract

A plasticized proton conductor solid polymer electrolyte (SPE) based on chitosan were

prepared by dissolving chitosan powder, ammonium nitrate (NH4N03) salt and ethylene

carbonate (EC) plasticizer in acetic acid, solution. The temperature dependence of

.chitosan-based SPE system was found to obey'Arrhenius relationship. The highest

conducting sample, 18 wt. % CA + 12 wt. % NH4N03 + 70 wt. % EC (CA40N70E)

possesses the lowest activation energy, 0.11 eV. The electrochemical stability windows

for the film are about 1.6-1.8 V, at temperatures 298-353 K. The highest open circuit

voltage is 1.479 V at 298 tK. The cell was fabricated using zinc powder (Zn) + zinc

sulfate heptahydrate (ZnS04.7.f-hO) + acetylene black (AB) + polytetrafluoroethylene

(PTFE) I CA40N70E I manganese (IV) oxide (MnOz) + AB + PTFE. The cell

performance is excellent at 333 K, with achievement of discharge capacity of 42.7 mAh,

internal resistance of 16.8 .0, maximum pO,wer density of 14.6 mW cm-z and a short­

circuit current density of 31.0 rnA cm-z.

Keywords: Chitosan; ammonium nitrate; ethylene carbonate; polymer electrolyte;

protonic battery.

- 1 -

2. Experimental

The polymer electrolyte films were prepared from chitosan (Chito-Chem,

Malaysia), NH4N03 (Merck) and EC (Merck). The details of this procedure were

reported in previous study [7]. The composition of the samples were coded as CA,

60 wt. % CA + 40 wt. % NH4N03 (CA40N), 48 wt. % CA + 32 wt. % NH4N03 +

20 wt. % EC (CA40N20E) and 18 wt. % CA + 12 wt. % NH4N03 + 70 wt. % EC

(CA40N70E).

Zn powder (Merck) and ZnS04.7H20 (Univar) were mixed with acetylene

black (AB, Gunbai) and polytetrafluoroethylene (PTFE, Fluka) using composition

of 72.6:24.2:2.4:0.8 (weight ratios) to form an anode pellet of the cell. A cathode

pellet was prepared with procedures similar to the anode. A mixture of Mn02, AB

and PTFE with the composition of 90.9:8.1: 1.0 (weight ratios) were used to form

the cathode pellet.

The ionic !conductivity was measured with an Autolab PGSTAT 30

Frequency ResponseCAnalyzer (Eco Chemie B.V.) using frequency range of 1 Hz

to 1 MHz and in the temperature range of 298-393 K. The measurement was

carried out by sandwiching the chitosan-based SPE between two stainless steel

(SS) electrodes. A linear sweep "voltammetry (LSV) was conducted with a

scanning rate of 1.0 mVIs. The sample was mounted inside the SS electrodes and

placed into an oven coupled with a temperature controller which was carried out

at different temperatures, 298-353 K.

- 3 -

Fig. 2 shows the relationship of variation of activation energy (Ea

) and (j at

room temperature. The highest conducting film (CA40N70E), gave the lowest Ea

at 0.11 eV. It indicates that when conductivity increases, the Ea

for transferring H+

ions will be reduced.

3.2 Linear sweep voltammetry analysis

Fig. 3 shows the LSV curves of the polymer electrolyte system of sample

CA40N70E. The current onsets of the sample are detected about 1.80, 1.75, 1.70,

and 1.60 V at temperatures of 298, 313, 333, and 353 K, respectively. The current

onset is assumed to be the films breakdown voltage. It can be observed that the

breakdown voltage reduces when temperature increases from 298 to 353 K. Thus,

this voltages are high enough' to allow safe use of chitosan-based SPE in

fabrication of protonic batteries, since the electrochemical window standard of

protonic battery is about ~ 1 V [8].

3.3 Open circuit voltaie analysis

The OCV char'Wteri~tic of protonic batteries at 298-353 K is shown in Fig.

4. It can be observed that as the temperatures increase, the OCV become lower

which is of the same trend as for the results obtained by LSV. The highest OCV is

1.479 V at room temperature (29~ K). This phenomenon suggests that the,

electrode materials possess considerable catalytic properties at low temperatures.

From the results obtained, it can be concluded that the fabricated cells at 298, 313,

and 333 K are reasonably stable in open cell condition. However, at the highest

temperature (353 K), continuously heating the cell for a longer duration causes

- 5 -

inferred that deterioration of the SPE has occurred at 353 K. When reaching an

optimum condition, which is after 333 K, the cell performance was obviously

degraded.

3.5 Current-voltage analysis

Fig. 6 (a) and 6 (b) show the plot of 1- V and J-P curves for protonic

batteries at elevated temperatures. From the 1- V curves obtained, each curve

shows a simple linear form, which indicates that the polarization on the electrode

is primarily dominated by ohmic contribution [11]. The resistance of the protonic

batteries can be calculated from the slope of 1- V curves. The curves show that as

temperature increases, the internal~esistance (r) of the cells decreases. The lowest

r is 16.8 Q at 333 K. At 353 K, the deterioration of the cell's materials occurs

which implies that the interfacial contact between the chitosan-based SPE and

electrodes may be deteriorating. The deterioration can be demonstrated by the

enhancement of r value of 23.0 Q. The r of the cells is considered high, whereas

the resistance of ,'the SPE is less than - 3.0 Q in the temperature range

investigated. The high r is attributable to the interfacial resistance between

SPE/electrodes. However, compared to the reports elsewhere [8, 12], the r from

present work is considered low.

•,

The plot of the operating J-P curves (Fig. 6 (b)) suggests that the contact

between electrolyte/electrodes was good. The maximum power density (Pmax)

increases with enhancement of temperatures. The highest Pmax is achieved by the

cell at 333 K, with Pmax of 14.6 mW cm-2 and a short-circuit current density (Jsc)

- 7 -

Q, 14.6 mW cm-2 and 31.0 rnA cm-2, respectively. The failures of the cells mainly

contributed to the degradation of the chitosan film SPE.

Acknowledgements

LSN (M.Sc. student) and AAM wish to thank USM for the Short Term Grant

(304.PBahan.60335149) 2005/07 given.

References

[1]. lH. Kim, J.Y. Kim, Y.M. Lee, K.Y. Kim, J Appl. Polym. Sci. 45 (1992) 1711.

[2]. N.M. Morni, A.K. Arof, J Power Sources 77 (1999) 42.

[3]. N.M. Morni, N.S. Mohamed, A.K. t-rof, Mater. Sci. Eng. B 45 (1997) 140..

[4]. M.Z.A Yahya, AX. Arof, Eur. Polym. J 39 (2003) 897.

[5]. AS.A Khiar, R. Puteh, A.K. Arof,Physica B 373 (2006) 23.

[6]. T. Winie, A.K. Arof, Ionics 12 (2006) 149.

[7]. L.S. Ng, A.A. Mohamad, J Power Sources 163 (2006) 382.

[8]. R. Pratap, B. Singh, S. Chandra, J Power Sources 161 (2006) 702.

[9]. 1 Broadhead, RC. Kuo, Electrochemical Principles and Reactions. 3rd ed.

Handbook of Batteries, D. Linden, T.B. Reddy (Eds). 2001, McGraw-Hill: New

York, Chapter 2.

[10]. R.RY. Subban, A.K. Arof, J Powe.,r Sources 134 (2004) 211.

[11]. S.C. Yap, A.A. Mohamad, Electrochem. Solid-State Lett. 10 (2007) A139.

[12]. N.S. Mohamed, R.RY. Subban, AK. Arof, J Power Sources 56 (1995) 153.

- 9 -

Figure Captions

Fig. 1: The temperature dependence of conductivity for chitosan-based SPE systems.

Fig. 2: Variation of Ea and cr at room temperature.

Fig. 3: LSV curves of sample CA40N70E at 298,313,333, and 353 K.

Fig. 4: OCV curves of protonic batteries at 298, 313, 333, and 353 K.

Fig. 5: Discharge curves at a constant current profile of 1.0 rnA at 298,313,333, and

353 K.

Fig. 6: The plot of (a) J-Vand (b) J-P curves of protonic batteries at 298,313,333,

and 353 K.

•,

- 11 -

Fig. 2:

5.0E-04

3.0E-03 :;EC.l

2.5E-03 eIi:

b2.0E-03 i­

's;:;:;

1.5E-03 ~"Cr:::

1.0E-03 <3

3.5E-03

\----O--==--"-----.:==:A-------1 6.0E-08

r-------------------, 4.0E-031.10

1.00

0.90

>.!. 0.80w..>. 0.70·e'CII 0.60r:::wr:::

0.500:;:;ell

.C: 0.40....C.l

<I:0.30

0.20

0.10

CA CA40NCA40N20E CA40N70E

Sample Name

i,

- 13 -

5 10 15 20 25 30 35 40 45 50 55 60 65

Time (hours)

Fig. 4:

1.8

1.6

~1.4

Ql 1.2Cl111....~ 1.0;t:::l 0.8l:!

<3c 0.6QlQ,

0 0.4

0.2

0.00

• 298 K

o 313 K

• 333 K

o 353 K

Cbooooooooo

i,

- 15 -

Fig. 6:

1.8(a)

1.6

14

1.2

~ 1.0CIIClco 0.8~

0.6

04

0.2

0.00.0 20.0 40.0 60.0

Current (rnA)

-298K

-0-313 K

-11-333 K

-0--353 K

800 100.0

16.0(b)

14.0;;-E 12.0CJ

3: 10.0E

~ 8.0UIr:::CII 6.00~

CII~ 4.00

Q.

2.0

0.00.0 5.0

-298K

-0-313 K

-11-333 K

-0-- 353 K

10.0 15.0 20.0 25.0 30.0 35.0 40.0

Current Density (rnA crn'Z)

,,

- 17 -

UNIVERSITI SAINS MALAYSIA

FINAL REPORT SHORT TERM GRANT USM 2005 -2006

Development of Zn-Mn02 Battery Using Chitosan­ZnCh Gel Polymer Electrolytes

No Akaun Geran: 304/PBAHAN/6035149

Prepared by:

Ng Li Sian

Dr. Ahmad Azmin B. Mohamad,

Pusat Pengajian Kejuruteraan Bahan & S. MineralKampus Kejuruteraan

Universiti Sains Malaysia

Tempoh Penyelidikan: 15 June 2005 -14 June 2007

NOTE:

Based on proposed title we want to use Chitosan-ZnCh, however due to complexation

problems between polymer (chitosan) and salt (ZnClz) we changed the salt (ZnClz) to

NH4N03• The Chitosan-NH4N03 systems have shown very promising results when

applied in Zn-Mn02 (proton) Battery.

•,

-ii-

LIST OF CONTENTS

NOTE

LIST OF CONTENTS

ABSTRACT

ABSTRAK

ii

111

v

vi

CHAPTER 1 INTRODUCTION

1.1 Polymer Electrolytes 1

1.2 Chitosan 2

1.2.1 Chitosan as a Polymer Electrolyte 3

1.3 Components of Cells and Batteries 4

1.4 Protonic Batteries 5

1.5 Problems Statement 7

1.6 The Objective 8

1.7 Approach of Study 8

CHAPTER 2 METHODOLOGY

2.1 Introduction

2.2 Sample Preparation: Chitosan-based Polymer Electrolyte Films

2.3 Sample Preparation: Electrode Anod~

2.4 Sample Preparation: Electrode Cathode

2.5 Configuration of Protonic Battery

2.6 Conductivity-Temperature Study

2.7 Linear Sweep Voltammetry

- iii -

10

10

11

12

13

14

17

2.8 Protonic Battery Characterization

2.8.1 Open Circuit Voltage

2.8.2 Discharge Characteristic

2.8.3 Current-Voltage Characteristic

CHAPTER 3 RESULTS AND DISCUSSIONS

18

18

19

20

3.1 Introduction 23

3.2 Conductivity-Temperature Study 23

3.2.1 Solid Polymer Electrolytes Characterization:CA-NH4N03

System 24

3.2.2 Solid Polymer Electrolytes Characterization:CA-NH4N03-EC

System25

3.2.3 Temperature Dependence27

3.3 Linear Sweep Voltammetry29

3.4 Open Circuit Voltage31

3.5 Discharge Characteristic32

3.6 Current-Voltage Characteristic36

CHAPTER 4 CONCLUSlON AND SUGGESTIONS

REFERENCES

•,

- IV-

40

41

ABSTRACT

This project is divided into two main sections that are to produce solid polymer

electrolyte (SPE) as a proton conductor (H+) and to fabricate polymeric solid-state

protonic battery with configuration of zinc (Zn)/SPE/manganese (IV) 0 xide (MnOz).

1.0 g of chitosan was dissolved in 100 ml of 1 % acetic acid solution. The ammonium

nitrate salt (NH4N03) and plasticizer, ethylene carbonate (EC), were added accordingly.

After casting the solution was left to dry at room temperature to form the films of pure

chitosan acetate (CA), C A-NH4N03, and C A-NH4N03-EC. T he highest conductivity

for chitosan + 40 % NH4N03 film at room temperature is (8.38 ± 4.11) x 10'5 S cm'l

and increases to (9.93 ± 1.90) x 10'3 S cm'l after added with 70 % EC. The temperature

dependence of chitosan-based SPE system was found to obey Arrhenius relationship.

The highest conducting sample (- 10'3 S cm'I), 18 wt. % CA-12 wt. % NH4N03-70 wt.

% EC (CA40N70E), possesses the lowest activation energy (Ea) of 0.10988 eV. The

electrochemical stability window for the cells was around 1.6 V - 1.8 V. The cells were

fabricated using SPE, which showed the highest value of conductivity, and

Icharacterized according to their electrochemical testing at 298, 313, 333 and 353 K.

The cells performance was excellent at 333 K, with achievement of discharge capacity

of 42.7 mAh, internal resistance (r) of 16.8 n, maximum power density (Pmax) of

14.6 mW cm'z and a short-circuit current density (Jsc) of 31.0 mA cm·z. The highest

open circuit voltage (OCV) was 1.4'19 V at 298 K. On the other hand, the

electrochemical properties of the cells at 353 K were decreased compared to the cells at

333 K. The decrease in the electrochemical properties was correlated to the failure of

the cells. Thus, the best electrochemical properties of the cells from this system were

observed at temperature 333 K.

-v-

BATER! PROTON BERASASKAN PEMPLASTIKKAN ELEKTROLITPOLIMER KEADAAN PEPEJAL KITOSAN-NH4N03 PADA SUHU TINGGI

ABSTRAK

Projek ini dibahagikan kepada dua bahagian utama iaitu penghasilan elektrolit polimer

pepejal (SPE) sebagai konduktor proton (H+) dan fabrikasi bateri proton keadaan

pepejal polimer dengan konfigurasi zink (Zn)/SPE/mangan dioksida (Mn02). 1.0 g

kitosan dilarutkan dalam 100 ml larutan asid asetik I %. Garam ammonium nitrat

(NH4N03) dan bahan pemplastik etilena karbonat (EC) ditambahkan ke dalam larutan

kitosan tersebut. Selepas penuangan larutan, ia dibiarkan kering pada suhu bilik untuk

membentuk filem kitosan asetat (CA) tulen, CA-NH4N03 dan CA-NH4N0

3-EC.

Konduktiviti yang tertinggi bagi filem kitosan + 40 % NH4N03 pada suhu bilik adalah

(8.38 ± 4.11) x 10-5

S em-I dan meningkat kepada (9.93 ± 1.90) x 10-3 S em-1 setelah

ditambahkan dengan 70 % EC. Kajian konduktiviti-suhu bagi sistem SPE berasaskan

kitosan didapati mematuhi persamaan 'Arrhenius'. Sampel dengan konduktiviti

tertinggi (- 10-3

S em-I), 18 wt. % CA-12 wt. % NH4N03-70 wt. % EC (CA40N70E),

mempunyai tenaga pengaktifan (Ea) yang terendah, 0.10988 eV. Kestabilan

elektrokimia untuk batc:rri proton adalah kira-kira 1.6 V - 1.8 V. Sel difabrikasi dengan

SPE yang mempunyai nil~i konduktiviti tertinggi dan pecirian sel berdasarkan. kajian

elektrokimia pada suhu 298, 313, 333 dan 353 K dijalankan. Prestasi sel yang terbaik

adalah pada suhu 333 K, dengan kapasti diseas, rintangan dalaman (r), ketumpatan

kuasa tertinggi (Pmax) dan ketumpatan arus litar pintas (Jsc) masing-masing sebanyak•,

42.7 mAh, 16.8 n, 14.6 mW em-2 dan 31.0 rnA em-2. Voltan litar terbuka (OCV)

tertinggi adalah 1.479 V pada suhu 298 K. Selain itu, perlakuan elektrokimia bagi sel

pada suhu 353 K menurun berbanding dengan sel pada suhu 333 K. Ini adalah

berhubung kait dengan kegagalan sel tersebut. Justeru itu, perlakuan elektrokimia

terbaik bagi sel-sel daripada sistem ini adalah diperhatikan pada suhu 333 K.

- vi-

CHAPTERl

INTRODUCTION

1.1 Polymer Electrolytes

Polymer-based electrolytes are receiving considerable attention as solid polymer

materials in advanced applications such as rechargeable lithium ion batteries because

their use allows the fabrication of safe batteries and pennits the development of thin

batteries and electrochemical devices with design flexibility (Yahya and Arof, 2003).

Polymer-based electrolyte materials have been reported as promising materials for use

in batteries due tot heir unique properties such as high ionic conductivity, ability to

provide good electrode/electrolyte 'contact, physical flexibility, show good mechanical

properties and film fonns ability (Winie and Arof, 2006). Besides, such electrolyte has

potentially promising applications in other electrochemical devices such as fuel cells,

supercapacitors, electrochromic windows and sensors (Song et al., 1999). The use of

solid polymer electrolytes (SPE) can avoid problems associated with liquid electrolytesI

such as leakage and gas fonnation that arises from solvent decomposition. This leads to~

improvement in battery design. Solid polymer batteries constructed with only thin-film

electrodes and electrolytes can be made to be very compact, 1ightweight and highly

reliable (Mohamed and Arof, 2004).

•,

Polymers that have been used in making of proton-conducting films are includes

polyethylene oxide (PEO) (Ali et al., 1998; Majid and Arof, 2005; Maurya et al., 1992),

polyacrylic acid (PAA) (Bozkurt et al., 2003) and polyvinyl alcohol (PVA) (Vargas et

al., 2000). These polymers have been complexed with various salts, which provide the

- 1 -

ions for conduction. Several ammonium salts such as NH4I (Maurya et aI., 1992),

(NRt)2S04 (Ali et al., 1998) and (NH4)SCN (Majid and Arof, 2005) were used as

doping salts. Various combinations of salts and polymers forming polymer-salt

complexes have been investigated with particular attention to chitosan-based

complexes (Majid and Arof, 2005; Khiar et al., 2006; Mohamed et al., 1995).

1.2 Chitosan

The chitin that has a high degree of N-deacetylation is known as chitosan. Chitosan is

more useful for biomedical/manufacturing applications and dehydrations of aqueous

solutions than chitin, since it has both hydroxyl and amino groups that can be easily

modified (Majid et aI., 2005).

Chitosan is a virtually non-toxic polymer with a wide safety margin. Moreover,

chitosan is a biodegradable, biocompatible, positively charged polymer, which shows

many interesting properties, such as biodegradable edible coating or film in food

packaging, a dietary fibre, a ~iomaterial in medicine.

Previous studies have prbven that chitosan can be used as a polymer matrix for ionic

conduction (Yahya and Arof, 2003). Each of the nitrogen and oxygen atoms in chitosan

has a lone pair electron where complexation can occur. Thus chitosan satisfies one of

the criteria to act as a polymer host for ~he solvation of salts. In addition, it is stable in

neutral conditions. Amine and hydroxyl groups on the glucosamine unit can form

strong inter- and intra- molecular hydrogen bond to crystallize. Figure 1.1 shows the

molecular structure of segments of chitosan (Majid and Arof, 2005).

- 2 -

o

OH :NH~

Figure 1.1: Chitosan (Majid and Arof, 2005).

1.2.1 Chitosan as a Polymer Electrolyte

Chitosan is a polymer which has been shown to be a promising solid electrolyte for

solid state cells (Momi and Arof, 1999). Chitosan is soluble in various acidic solvents

such as in acetic, citric, formic, glycolic, lactic and malic acids because chitosan is a

weak polybase (Yahya and Arof, 2003). It has been used as the base polymer for the

studies on proton-conducting films.. .In its actual state, a chitosan film has a very low

electrical conductivity. Although the structure of chitosan monomer has three

hydrogens, they are strongly bonded to the structure and cannot be mobilized under the

action of an electric field to make it a proton conductor (Mohamed et al., 1995).

Some OpInIOnS stated ,'that if chitosan is dissolved in acetic acid and the resulting

solution is cast into a thin film, then the H+ or H30+ and CH3COO· ions in the

'acetylated chitosan' film will be dispersed in the immobilized chitosan solvent and

these ions can be mobilized under the influence of an electric field. If H+ or H30+ ions

are more mobile than the CH3COO· ions\the film becomes a proton conductor. Further,

it should be possible to produce a more ionically conducting film by dissolving

chitosan in acetic acid solutions of increasing concentration since more H+ (or H30+)

will be contributed by the acetic acid (Mohamed et al., 1995).

- 3 -

1.3 Components of Cells and Batteries

A battery is a device that converts the chemical energy contained in its active materials

directly into electric energy by means of an electrochemical oxidation-reduction (redox)

reaction. In the case of a rechargeable system, the battery is recharged by a reversal of

the process. Oxidation-reduction reaction involves the transfer of electrons from one

material to another through an electric circuit (Linden, 2002).

While the term "battery" is often used, the basic electrochemical unit being referred to

is the "cell". A cell provides a source of electric energy by direct conversion of

chemical energy. The cell consists of an assembly of electrodes, separator, electrolyte,

container and terminals. A battery consists of one or more of these cells, connected in

series or parallel, or both, depending orr the desired output voltage and capacity. Figure

1.2 shows an example of the cell components. The cell consists of three major

components (Linden, 2002):-

1. The anode or negative electrode - the reducing or fuel electrode, which gives up

electrons to the external circuit and is oxidized during the electrochemical

reaction.

n. The cathode or positive electrode - the oxidizing electrode, which accepts

electrons from the external circuit and is reduced during the electrochemical

reaction.

lll. The electrolyte or the ionic conductor - which provide the medium for transfer•,

of charge, as ions, inside the cell between the anode and cathode. The

electrolyte is typically a liquid (water or alcohols solvents), with dissolved salts,

acids or alkalis to impart ionic conductivity. Nowadays, some batteries use solid

electrolytes.

- 4-

anions<===:J

cationsc==:>

Electron flowc==:>

Electrolyte

Figure 1.2: The cell components (discharge operation) (Linden, 2002).

1.4 Protonic Batteries

.A significant characteristic of a protonic battery is that charging/discharging can be

done by shifting protons '(H+) (NEe TOKIN, 2004). The source of H+ is from

electrolyte. The electrolyte can be prepared either in liquid, gel or solid-state form. For

a successful protonic battery, an anode capable of supplying or injecting H+ ions into

the battery electrolyte, a proton conducting electrolyte and a reversible cathode withI

layered oxides are needed (Pratap et al., 2006). In protonic battery, zinc (Zn) and..manganese (IV) oxide (Mn02) have been used as anode and cathode material,

respectively. The optimum concentration of electrolyte will provide highest mobility of

H+ ions. Consequently the conductivity of electrolyte can be enhanced. The simplified

•,anodic reaction, cathodic reaction and overall cell reaction are show in Equation (1.1),

(1.2) and (1.3) (Scarr et al., 2002; Linden, 2002).

- 5 -

At the anode, Zn is oxidized with the release of two electrons, and zinc sulfate

heptahydrate (ZnS04.7H20) provides the sources ofH+ ions,

Zn -. Zn2++ 2e'0.7618 V

-0.8277 V ...(1. 1)

At the cathode, Mn02 is reduced with the acceptance of electrons,

1.2240 V

2H+ + Mn022- -. H2Mn02... (1.2)

The overall cell reaction is the combination of Zn, ZnS04.7H20 and Mn02. with

Zn(OHh, H20, ZnS04 and H2Mn02 as the reaction products.

Zn + ZnS04.7H20 + Mn02

-. Zn(OHh + 5H20 + ZnS04 + H2Mn02 1.2899 V ...(1.3)

The standard potential of a cell can be calculated from the standard electrode potentials

as follows (the oxidation potential is the negative value of the reduction potential)

(Linden, 2002):-

Anode (oxidation potenlial) + cathode (reduction potential) = standard cell

potential ... (1.4)

Thus, the standard protonic batteries potential is:-

-(0.7618-0.8277) + 1.2240 = 1.2899 V;,

- 6-

....(1.5)

1.5 Problems Statement

In most common batteries the electrolyte is a liquid. However, liquid electrolyte might

lead to problems such as leakage, corrosion and contamination of electrode and

electrolyte which will degrade the battery efficiency (Chandra, 1981). Batteries with

liquid electrolytes involve complicated and higher cost processes and equipment. The

availability of solids capable of being fabricated into electronically insulating elements

with fairly low overall ionic resistance has stimulated the development of solid

electrolytes batteries.

As in polymer-salt complexes, a major drawback of these complexes is the low ionic

conductivity at ambient temperature which cannot be applied as an electrolyte in a

battery (Winie and Arof, 2006). FUT!hermore, the difficulty is, to find a material with

suitable electrochemical properties that are available at elevated temperatures. At

higher temperature, the efficiency of polymer electrolyte/electrode might be

deteriorated.

To the best of our knbwledge, there were no systematic studies on protonic battery

~

based on chitosan acetate (CA)-ammonium nitrate (NH4N03)-ethylene carbonate (EC)

SPE at higher temperatures. A study to the behavior of electrolyte/electrode at different

temperatures is necessary because utilization of this knowledge will be an advantage

for designing of a protonic battery at dif~rent environments.

-7 -

1.6 The Objective

In this work, chitosan biopolymer has been used as the medium for the transport of H+

ions. A convenient solvent for chitosan is dilute acetic acid. The main purpose of this

work is:-

1. To apply chitosan as a polymer host and NH4N03as a doping salt.

11. To enhance conductivity behavior of CA-NH4N03system with plasticizer EC at

room temperature.

Ill. To study conductivity-temperature behavior of the CA-NH4N03-EC system.

IV. To fabricate and study the electrochemical properties of protonic batteries with

configuration of Zn + ZnS04.7H20 /18 wt. % CA-12 wt. % NH4N03-70 wt. %

EC / Mn02 at high temperatures.

1.7 Approach of Study

The chitosan films were prepared from chitosan, NH4N03, and EC by the solution cast

technique and left to dry at room temperature (25°C) to form films of CA, CA-

NH4N03 and CA-NH4N03-EC. The films were characterized by conductivity-

temperature study (2~8-393 K) and linear sweep voltammetry (LSY) (298-353 K).

When t he films were fodned, t hey were cut into a suitable size a nd placed between

blocking stainless steel electrodes in a cell which was connected to a computer. The

cell was then put into an oven coupled with a temperature controller. At room

temperature, optimum concentration of. polymer electrolytes of CA-NH4N03 and CA-,

NH4N03-EC system were determined.

- 8 -

For protonic battery, it was fabricated by the highest conducting film, 18 wt. % CA-12

wt. % NH4N03-70 wt. % EC (CA40N70E). The cells were assembled by sandwiched

the sample CA40N70E between a pellet anode and a pellet cathode. The cell

measurements include open circuit voltage (OCV), discharge, current-voltage (1- V), and

current density-power density (J-P) characteristics were carried out at various

temperatures, 298-353 K.

i,

- 9 -

CHAPTER 2

METHODOLOGY

2.1 Introduction

In this work, chitosan has been used as a host polymer electrolyte for fabrication of

protonic batteries. Conductivity-temperature studies and linear sweep voltammetry

(LSV) have been used to characterize the chitosan films. On the other hand, open

circuit voltage (OCV), discharge, current-voltage (1- V) and current density-power

density (J-P) characteristics were used to characterize protonic batteries at high

temperatures.

2.2 Sample Preparation: Chitosan-based Polymer Electrolyte Films

Chitosan films were prepared from chitosan powder by the solution cast technique.

1.0 g of chitosan (Chito-Chem, Malaysia) was dissolved in 100 ml of 1% acetic acid

(Merck) solutions. NH4N03 (Merck) and ethylene carbonate (EC, Merck) were added

accordingly. The mixture was dispersed and stirred continuously in a sealed conical

flask with am agnetic f tirrer for 24 hours until homogeneous solution was 0 btained.

After complete dissolutio~ the solutions were cast onto plastic petri dishes and left to

dry by evaporation at room temperature (25°C) to form films of pure chitosan acetate

(CA), CA-NH4N03 and CA-NH4N03-EC. The films were then transferred into a

desiccator (with silica gel desiccant) for continuous drying. A free standing and plastic-•,

like film was obtained for all systems.

- 10 -

Concentration of NH4N03 was varied from 10 wt. % to 60 wt. %. For sake of

simplicity, the films will be simply coded as CA, 60 wt. % CA-40 wt. % NH4N03

(CA40N), 48 wt. % CA-32 wt. % NH4N03-20 wt. % EC (CA40N20E) and 18 wt. %

CA-12 wt. % NH4N03-70 wt. % EC (CA40N70E), respectively for the conductivity-

temperature study. Figure 2.1 shows an example of film formed after drying process.

Chitosan film Plastic petri dish

Figure 2.1: Appearance of chitosan film after drying process.

2.3 Sample Preparation: Electrode Anode

To prepare an anode pellet (active area 2.5447 cm2, weight 2.3 g and thickness - 0.2

cm), Zn powder (Merck) and ZnS04.7H20 (Univar) were mixed with acetylene blackI

(AB, Gunbai) and polytetratluoroethylene (PTFE, Fluka). The anode contains a mixture<\

of Zn and ZnS04.7H20 in the ratio of 3: 1. The mixture was subsequently put in a die

and gently pressed. The anode pellet was formed by hydraulic press (Carver) to

sandwich the stainless steel mesh into the powder mixture. A few drops of ethanol as a

wetting agent was added into the mixtu}e in order to make the pressing process easier.

Stainless steel mesh was used as a current collector in the middle of the pellet. The

function of PTFE and AB were as binding agent and to introduce the electronic

conductivity, respectively (Pratap et al., 2006). Figure 2.2 shows an example of anode

pellet pressed by pressing machine.

- 11 -

Anode pellet ~Plastic petri dish

Figure 2.2: Appearance ofanode pellet pressed by hydraulic press.

2.4 Sample Preparation: Electrode Cathode

The cathode pellet (active area,2.5447 cm2, weight 2.1 g and thickness _ 0.2 cm) was

prepared with similar"procedures to the anode. A mixture of Mn02 (Battery grade,

Aldrich) with AB and PTFE were used to form the cathode pellet. This mixture was

poured in a die and lightly pressed. Figure 2.3 shows an example of cathode pellet

formed by pressing maohine.

I

•,

- 12 -

~Plastic petri dish

}

i

Figure 2.3: Appearance of cathode pellet formed by hydraulic press.

2.5 Configuration of Protonic Battery

In this work, the cells were fabricated by using chitosan films which showed the

highest value of conductivity, sample CA40N70E. Chitosan film was sandwiched

between a pellet anode and a pellet cathode as illustrated in Figure 2.4. The entire

assembly was finally compacted to get a button shape polymeric solid-state protonic

battery. The Teflon container is able to endure condition at higher temperatures with

melting point, tensiltt strength and dielectric strength up to 312 °c, 23.5 MPa and

39.4 x 106 VIm. It is water-resistant and highly chemical-resistant (Brady et aI., 2002) .

.,

- 13 -

Stainless steel electrode-------....

14---Teflon

Cathod~

CA40N70E ~

~--Teflon

Anode~-------"T--,

Stainless steel electrQd------..

<4

Figure 2.4: Schematic diagram of a protonic battery.

2.6 Conductivity-Temperature Study

In this work, when the films (CA, CA-NH4N03, and CA-NH4N03-EC) were formed,

they were cut into a suitable size and placed between blocking stainless steel electrodes

in a cell which was connected to a computer. Electrical conductivity measurements

were performed using an Autolab POSTAT 30 Frequency Response Analyzer (Eco

Chemie B.V.) with frequency range of I Hz to 1 MHz and an amplitude of 10 mV in

- 14 -

the temperature range of 298 K (25 DC)-393 K (120 DC). The effective area for

measurement was 2.5447 cm2

• Three samples were used in order to get an average and

standard deviation values at each temperature. The electrical conductivity (cr) is given

by (Callister, 2000):-

t0"= --

RbA ... (2.1)

where t is the thickness of the film, Rb the bulk impedance obtained from the

impedance plot, and A the area of the film.

To determine the cr, the technique of impedance spectroscopy was employed. In

impedance spectroscopy, a time varying voltage is applied to the cell under

investigation and the sinusoidal current passing through the cell is detennined. It

involves measuring the impedance as a function of frequency of the applied signal over

a wide frequency range.

Figure 2.5 illustrates complex impedance p lots for a combination of a capacitor andI

resistor. For the capacitor and resistor in series, the plot defines a vertical spike

displaced to distance R along the real axis as frequency is increased and the impedance

of the capacitor is reduced. Whereas if consider the parallel combination, this defines a

semicircle in the complex impedance plane with a diameter 'r' extending along the real

axis from the origin. At the maximum of the semicircle, O)max the product of the

magnitude of the resistor and capacitor is equal to II O)max, i.e. RC = II O)max or O)max RC

= I (Arof et al., 1999).

- 15 -

In the capacitive term, -jlroC, j = (_1)1/2, ro is the angular frequency and C is

capacitance. Thus,

Z= R - jlroC

=Z'-Z" , ...(2.2)

Z is a complex quantity. Z' represents the real component = Z cose and Z" represents

the imaginary component = Z sine. The plot of -Z" versus Z' is called the complex

impedance plot or Cole-Cole plot (Arof et al., 1999).

Z"

C

Z"

,IR Z'

romaxRC = 1

r

Z'

Figure 2.5: Complex impedance plots for a combination of a capacitor and resistor

(Aref et al., 1999).

Consider the following equation (Callister, 2000):-;,

...(2.3)

where ao is the preexponential factor, Ea the activation energy of conduction, k the

Boltzmann constant (8.62 x 10-5 eV/atom-K), and Ttemperature in Kelvin.

- 16 -

a Ea- = exp (--)ao kT

a Ea2.303 log - =--

ao kT

Ealog a = - + log ao

2.303 kT ... (2.4)

By plotting the graph oflog a (S em-I) versus IOOOIT (K"I) (Arrhenius plot), gradient of

the graph is - Ea , where Eacan be determined from the gradient of graph.2.303 k

2.7 Linear Sweep Voltammetry

In this work, LSV was performed using the Potentiostat/Galvanostat of Autolab

PGSTAT 30 GPES (Eco Chemie B.Y.). The highest conducting sample ofCA40N70E

was mounted inside a cell which was sandwiched between two stainless steel self-

designed blocking electrodes at a scanning rate of 1.0 mVis. The initial potential and

end of potential were -2.0 V and 2.0 V, respectively. The cell was then placed into an

oven coupled with a temperature controller which was carried out at different

Itemperatures, 298 K (25 0q, 313 K (40 0q, 333 K (60 0q and 353 K (80 0q.

Figure 2.6 shows an example ideal curve of LSV. From the curve obtained, the

breakdown voltage of the polymer electrolyte can be determined as shown in Figure

2.10. •,

- 17 -

Current Density (rnA cm-2)

Breakdownvoltage

Voltage (V)

Figure 2.6: Example of sweep voltammetry curve.

2.8 Protonic Battery Characterization

In this work, all the cell characteristics were measured by using the

Potentiostat/Oalvanostat of Autolab POSTAT 30 OPES (Eco Chemie B.V.). The

measurements were done at elevated temperatures, 298 K (25°C), 313 K (40°C),

333 K (60°C) and 353 K (80°C). The characterization techniques include OCV,

discharge characteristic, 1- V, and J-P test.

2.8.1 Open Circuit Voltage

The OCV was measured for the cells stored at an open circuit condition for 60 hours.

The duration of running an OCV test was refers to the results of discharge characteristic.I,

Thereby, longer duration was carried out for OCV. Figure 2.7 shows an example result

of ideal OCV curve. A good battery should be displays constant voltage during storage.

- 18 -

Voltage (V)

Time (hours)

Figure 2.7: Example of an ideal OCV curve.

2.8.2 Discharge Characteristic

The cells were discharged at a constant current (Id) of 1.0, 5.0 and 10.0 rnA at room

temperature (298 K). Temperature·:dependence studies were also conducted on the cell

and were recorded at temperatures of 313, 333 and 353 K. Based on discharge curve

obtained, various secondary results can be determined which includes discharge

capacity, nominal voltage and specific energy.

IFigure 2.8 shows an example of ideal discharge curve. It shows that the discharge was

4

sustained for td hours until the cut-off voltage. The initial voltage (Va) drop is higher

before reaching a flat discharge plateau at Vp •

;,

- 19 -

Voltage (V)

~I

Time (hours)

Figure 2.8: Example ofan ideal discharge curve.

The following were the important results that can be determined from discharge

characteristic (Linden, 2002):-

I. Discharge Capacity (mAh) = Discharge Current (Id) x Discharge Time

... (2.5)

ii. Discharge Capacity (C) =Discharge Current (Id) x Discharge Time (td) ~ 3600 s

...(2.6)

iii. Nominal Voltage (Vp ) =Generally accepted as typical of the operating voltageI

of the battery (voltage at half condition from discharge

time).

iv. Specific Energy (mJ) = Discharge Capacity (C) x Nominal Voltage (Vp

) ...(2.7)

i,where Vo, Vp, and td can be obtained from a discharge curve as shows in Figure 2.8.

2.8.3 Current-Voltage Characteristic

Current drains ranging from 2.0 ~ to 100.0 rnA were used to plot the I-V and J-P

curves as show in Figure 2.9 and Figure 2.110. Each cell's voltage was monitored for

- 20-

each current drain after lOs of operation. The secondary results of current density (J)

and power density (P) were calculated from measured values of V and / (Equation 2.8

and Equation 2.9) and a graph ofP against J was then obtained (Choong, 2004).

. Current (l)Current Density (J) = ---------.:....:...---­

Area of electrode pellet (A)

P D't (P) Current (1) x Voltage (V)

ower ensI y =Area of electrode pellet (A)

Area of electrode pellet = 2.5447 cm2

Weight of active materials (anode - Zn + ZnS04.7H20) = 2.3365 g

Weight of active materials (cathode - Mn02) =2.1323 g

Voltage (V)

EI

~y:L _

~x

Current (A)

Figure 2.9: Example of an ideal /- V curve.

... (2.8)

... (2.9)

From Figure 2.13, it can be observe&- that a line with negative gradient is obtained

(Choong, 2004).

V=E-/r

V= -(r)/ + E

- 21 -

...(2.10)

This equation is equivalent to y = -mx + c where y = V, x = I, m = r, and c = E, hence

the internal resistance of the battery is given by (Choong, 2004):-

r = gradient of the line = m = IlyIlx

Power Density (mW cmo2)

Maximum power density (Pmax)II

----------~--~-----

... (2.11)

Current Density (rnA cmo2)

Figure 2.11 0: E~ample of an ideal J-P curve.

.,

- 22-

CHAPTER 3

RESULTS AND DISCUSSIONS

3.1 Introduction

As mentioned in Chapter 2, the films of pure CA, CA-NH4N03' and CA-NH4N03-EC

were characterized by conductivity-temperature studies and linear sweep voltammetry

(LSV). A systematic study on films and protonic batteries based on the highest

conductivity of chitosan-based solid polymer electrolyte (SPE) was carried out at room

temperature and elevated temperatures. Various characterization techniques, such as

open circuit voltage (OCV), discharge characteristic, current-voltage (I-V) and current

density-power density (J-P) characteristics, were conducted on the cells. In this chapter,

the fluctuation results of chitosan filrps and protonic batteries due to the influence of

heat treatment will be exhibited.

3.2 Conductivity-Temperature Study

In order to understand the conductivity mechanism of the chitosan-based systems, the

conductivity of the sam~les were measured at different temperatures. In its natural form

'"chitosan can exist in a a-helical or spiral coil form. Thus the neighbouring NHz group

could be closer to one another than if the chitosan occurs in a linear chain. At room

temperature, the C-N functional group in the samples is expected to vibrate accordingly

(Yahya and Arof, 2003). The C-N vibration could occur in such a way that the proton

ion (H+) which is datively bonded to the nitrogen atom may come in closer proximity

with another NHz group and get transferred to it. Therefore, the ease of the H+ ion to be

transferred along the NHz sites may depends on the activation energy (Ea) of the ionic

- 23 -

II

I.1!I.~

species. Hence, it is necessary to understand the conductivity-temperature relationship

at various temperatures.

3.2.1 Solid Polymer Electrolytes Characterization:CA-NH4N03

System

The films with a composition of CA-40 wt% NH4N03 has the lowest bulk resistance

(Rb) was achieved at the average of 55.0 n and the calculated surface contact was

around 20.1 n. From the Rb the specific conductivity of the polymer electrolyte was

calculated to be (8.38 ± 4.11) x 10-5 S em-I at the room temperature. The value was

almost similar to the previous research by Majid and Arof (2005) which gave an

electrical conductivity 2.53 x 10-5 S cm-l with 45 wt. % NH4N0

3.

Other electrical conductivity values, with the different amount of NH4N0

3were given

in Figure 3.1. It can be observed that the electrical conductivity increases sharply with

an addition of 10 wt. % of NH4N03 and it increases by an order of magnitude when a

10 wt. % to 40 wt. % of NH4N03 was added to the CA. In the preparation of the films,

100 ml of acetic acid solution was used to dissolve 1.0 g of chitosan. Different amounts

of NH4N03 were added to each solution. Hence, the volume of the host matrix (the

volume of acetylated chif6san) was the same for all the films. As more and more

NH4N03 were added, the host matrix becomes m ore crowded with the dopant ions.

Such overcrowding reduces the number of charge carriers due to the limitation of ionic

mobility (Mohamed et at., 1995). Thl1s, the conductivity decreases after 40 wt%,

- 24-

1.0E+00 --.-----------------------------,

1.0E-01 -

1.0E-02 -

1.0E-03 -

'"eu 1.0E-04-!!b

i 1.0E-05-

~::l

"CoU

1.0E-08

1.0E-09

70605040'3020101.0E-10 -I-----r------r-----r----....-----r------,..---~

o

Figure 3.1: Electrical condu9tivity versus NH4N03 concentrations in CA at room

temperature.

3.2.2 Solid Polymer Electrolytes Characterization:CA-NH4N03-EC SystemI

Figure 3.2 shows the variation of conductivity as a function of plasticizer content in a

CA-40 wt% NH4N03 system at room temperature. It can be observed that the highest

conductivity at room temperature was (9.93 ± 1.90) x 10-3 Scm-I, and achieved for the

film with 70 wt. % EC (CA40N70E). The value of Rb decreases at about 54.5 n and the

surface resistance was at 19.7 n when compared to the highest unplasticized film. An

addition of concentration of EC beyond 70 wt. % causes the poor mechanical strength.

Therefore, the amount of EC was maintained below 70 wt. % to ensure the acceptable

mechanical properties.

- 25 -

On addition of salt, the conductivity continues to increase by increasing the ion content

up to a certain amount. It can be inferred that the salt was responsible for the

conductance of the chitosan-based films. However the EC did not increased the ion

number, but the role of EC was to dissociate the salt thereby increasing the numbers of

mobile ions, which lead to conductivity enhancement (Osman et al., 200 I; Yahya and

Arof, 2003).

1.0E+00 ,------ _

1.0E-01

-'eI,) 1.0E-02-!!lb

~>..I,):::I~ 1.0E-03oo

8070605040

%EC

3010 20

1.0E-05 +----.....-..:.::"'---,-__-..,.. .--__....,.--__--.. .,--__-1

o

Figure 3.2: Electrical conductivity versus EC concentrations in CA-40 wt. % NH4N03

at room temperature.I,

- 26-

3.2.3 Temperature Dependence

The temperature dependence of conductivity for the chitosan-based SPE systems is

shown in Figure 3.3. T he plot shows that as temperature increases, the conductivity

increases. The conductivity-temperature relationship of chitosan-based SPE was

characterized as Arrhenius behavior, suggesting that the conductivity was thermally

assisted. The results also implies that the diffusion of H+ ions especially in the CA film

was liquid like and remains unchanged in the temperature range of298-393 K. The

conductivity of CA film was attributed to the conduction of H+ ions from acetic acid.

The H+ ions were able to detach themselves from the matrix and thus can hop from

complexation site to another during thermal agitation (Morni and Arof, 1999).

3.43.33.23.1

t···.'"

f

2.9 3.0

10001T (K·1)

•,

2.82.7

o CA40N

2.6

& CA40N20E

o CA40N70E

• CA

i::;;~ ;,;: :~:::: :~:::::~:::: ~!::.::: 1::::: i:::::: i::::::1::~...........~.. n T

·.. ··~····· .. f ..~1 .. I:.... !

···· ..1······.i

······1'.

-1

-2

J-3

-4

-...E -5ueb

-601.g

-7

-8

-9

-10

2.5

Figure 3.3: The temperature dependence of conductivity for chitosan-based polymer

electrolytes.

- 27-

Figure 3.4 shows the relationship of variation of Ea and cr at room temperature. The

highest conducting film (CA40N70E), gave the lowest Ea at 0.11 eV. It indicates that

when conductivity increases, the Ea for transferring H+ ions will be reduced. Table 3.1

shows the summarized results ofEa and cr for different samples at room temperature.

1.10 -,------------------------,.4.0&03

3.5&03

5.0&04

1.0&03

-...2.5&03 5

~Ii:

b2.0&03 ;5­

'S;

~::I

1.5&03 'goo

·3.0&03 .

Sanple Name:1- CA2- CA40N3 - CA40N20E4· CA40N70E

0.20·

0.30·

1.00

0.90·

0.10 ·1-----()ooO:::::::::::::=-----r---_...--_-=====*- l 6.0&08

o 2 3 4 5

:> 0.80·

.!.w· 0.70~e'~ 0.60·wco~ 0.50.~1:$c( 0.40

Sample Name

I

Figure 3.4: Variation ofEaand cr at room temperature.

.,

- 28 -

Table 3.1: Variation ofEa and cr for sample CA, CA40N, CA40N20E and CA40N70E

at room temperature.

Activation Energy, Ea Conductivity,O'RT

Sample Sample Name (eV) (S em-I)

CA 0.98459 6.15E-08

2 CA40N 0.31801 2.00E-04

3 CA40N20E 0.14841 8.30E-04

4 CA40N70E 0.10988 3.48E-03

3.3 Linear Sweep Voltammetry

Figure 3.5 shows the LSV curves of the polymer electrolyte system of sample

CA40N70E. The current onsets of the sample were detected about 1.80, 1.75, 1.70, and

1.60 V at temperatures of 298, 313, 333, and 353 K, respectively. The current onset

was assumed to be the films breakdown voltage (Table 3.2). It can be observed that the

breakdown voltage red1uces when temperature increases from 298 to 353 K. Thus, this

voltages were high enoug1:l to allow safe use of chitosan-based SPE in fabrication of

protonic batteries, since the electrochemical window standard of protonic battery is

about - 1 V (Pratap et al., 2006).

.,

- 29-

1.2...-------- -,

1.0

-+-298K

-0-313 K

-.-333K--0-353 K

2.502.001.00 1.50

Voltage (V)

0.50

0.0 .. ......

0.00

0.2

_ 0.8·"IEI.l

1~ 0.6·cGICC~=u 0.4

Figure 3.5: LSV curves of sample CA40N70E at 298,313,333 and 353 K.

Table 3.2: Breakdown voltage of sample CA40N70E at various temperatures.

Temperafture (K)

298

313

Breakdown Voltage (V)

1.80

1.75

333 1.70

353 1.60

- 30-

Table 3.3: OCV of protonic batteries at high temperatures.

1.479

1.434

1.402

1.378

OCV (V)

- 31 -

298·

313

333

353

Temperature (K).

3.4 Open Circuit Voltage

The OCV characteristic of protonic batteries at 298-353 K is shown in Figure 3.6. It

can be observed that as the temperatures increase, the OCV become lower which was

of the same trend as for the results obtained by LSV. The highest OCV was 1.479 V at

room temperature (298 K). This phenomenon suggests that the electrode materials

possess considerable catalytic properties at low temperatures. The OCV of other

temperatures are shown in Table 3.3. From the results obtained, it can be concluded

that t he fabricated cells at 2 98, 313, and 3 33 K were reasonably stable in open cell

condition. However, at the highest temperature (353 K), continuously heating the cell

for a longer duration causes the deterioration of the cell especially SPE. The SPE was

obviously burned and destroyed after the OCV characterization. The significant voltage

drop can be seen after 33 hours, which was due to SPE unable to endure condition at

353 K.

1.8 -,----------------------------,

1.4

~ 1.2

1.6 ¢¢¢¢

1iII••iiQQQ•• ~~~a~~~22000000000000000oooooo0o00oooooooo

•............~illillli~~~···············.·.···· ..•• <><><><><><><><><><><><><><><><><><><><><><><>•• <>

••••••••••••••

GIDl

~ 1.0~~::3l:! 0.8Uc8.o 0.6

0.4 0 298 K

• 313 K

0.2 ¢ 333 K

• 353 K

0.00 5 10 15 20 25 30 35 40 45 50 55 60 65

'Time (hours)

Figure 3.6: OCV curves of protonic batteries at 298,313,333 and 353 K.

3.5 Discharge Characteristic

From Figure 3.7, the discharge time increases as the discharge current decreases.

Meanwhile the voltag~ drop during the initial discharge was higher when the discharge

current was increased. If depicted that the discharge capacity was lower at higher

discharge rates which was 21.0, 6.0 and 2.5 mAh at discharge current of 1.0~ 5.0 and

10.0 rnA, respectively. The summarized results are shown in Table 3.4. The reason for

the low discharge time at high current qischarge rate could be attributed to the ability of,

the cell to delivery its electrical energy. It showed that the cell in this work was more

suitable when a constant discharge current of 1.0 rnA was used. Due to low diffusion

rate ofH+ ions inside the SPE, the cells discharged at 5.0 and 10.0 rnA lasted only for a

few minutes.

- 32-

1.8.----------------------------,

14001200

_1.0 rnA

-0-5.0 rnA

-.-10.0 rnA

10008006004002000.0t=-----,----..----":'""""'"----.------..-----,-------l

o

0.6

0.4 -

0.2

1.6 -

~ 1.0QlCl

~~ 0.8

Time (minutes)

Figure 3.7: Discharge curves of protonic batteries using constant currents of 1.0,5.0

and 10.0 rnA at room temperature.

Table 3.4: Discharge properties ofprotonic batteries at different discharge current

! profiles at room temperature (298 K).

... .............._.............~ ...

Discharge Discharge' Discharge Discharge Nominal Specific

Current Time Capacity Capacity Voltage Energy

(rnA) (hours) (mAh) (C) (V) (mJ)

1 21.00 21.0 .,

5 1.20 6.0

10 0.25 2.5

- 33 -

Temperature dependence studies at 298,313,333, alld 353 K of the cells are presented

in Figure 3.8. At 298 K, it can be observed that the voltage of the cell drop immediately

before reaching a flat discharge plateau at 1.181 V. This phenomenon may be due to

the activation polarization. The activation polarization occurred because the rate of an

electrochemical reaction at an electrode surface was controlled by sluggish electrode

kinetics (Broadhead and Kuo, 2002). Whereas at temperatures 313 and 333 K, the drop

in voltage was smaller as temperature increased. At 333 K, the discharge time was

much longer which implies that the discharge capacity (42.7 mAh) was optimum. It can

be observed that the discharge capacity of the cell increases with temperature increase

until 333 K. This demonstrated that the cell performance was improved when the

temperature was increased. This was consistent with the results obtained from the

conductivity-temperature characteristics -of sample CA40N70E. Since the ionic

conductivity of the polymer electrolyte increases with temperature, more energetic ions

were available for conduction between two electrodes. Thus, the cell gives a higher

discharge capacity at elevated temperatures. Ani ncrease in the d iffusivity of t he H +

ions through the cell when temperature was increased would also contribute to this

improvement (Subban apd Arof, 2004). At 353 K, although the drop in voltage was

smaller at a flat discharge plateau at 1.368 V, the discharge was sustained only for 20.0

hours. It inferred that deterioration of the SPE has occurred at 353 K. When reaching an

optimum condition, which was after 333 K, the cell performance was obviously

degraded. Table 3.5 shows the calculated values of discharge capacity, nominal voltagei,

and specific energy.

- 34-

Figure 3.8: Discharge curves at a constant current profile of 1.0 rnA at 298,313,333

4540

o 298 K

• 313 Ko 333 K

.. 353 K

•••

••

35302520

"0o

Time (hours)

..o

o

15105

1.8

1.6

1.4

1.2

~ 1.0GlCl.fl"0 0.8>

0.6

0.4

0.2

0.00

and 353 K.

Table 3.5: Discharge properties ofprotonic batteries at different temperatures.

Disch~rge Discharge Discharge Nominal Specific

Temperature Time .,. Capacity Capacity Voltage Energy

(K) (hours) (mAh) (C) (V) (mJ)

298 21.0 75.6 1.181 89284

313 39.1 • 140.8 1.289 181491,

333 42.7 153.7 1.293 198734

353 20.0 72.0 1.368 98496

- 35 -

3.6 Current-Voltage Characteristic

Figure 3.9 and 3.10 show the plot of I-V an~ J-P curves for protonic batteries at

elevated temperatures. From the 1-V curves obtained, each curve shows a simple linear

form, which indicates that the polarization on the electrode was primarily dominated by

ohmic contribution (Li et a!., 2006). The resistance of the protonic batteries can be

calculated from the slope of1-V curves. The curves show that as temperature increases,

the internal resistance (r) of the cells decreases. The lowest r was 16.8 n at 333 K. At

353 K, the deterioration of the cell's materials occurs which implies that the interfacial

contact between the chitosan-based SPE and electrodes may be deteriorating. The

deterioration can be demonstrated by the enhancement of r value of 23.0 n. The r of

the cells was considered high, whereas the resistance of the SPE was less than - 3.0 n

in the temperature range investiga!ed.'The high r was attributable to the interfacial

resistance between SPE/electrodes. However, compared to the reports elsewhere

(Mohamed et al., 1995; Pratap et a!., 2006), the r from present work was considered

low. The summarized results are shown in Table 3.6.

The plot of the operat.lng J-P curves (Figure 3.10) suggests that the contact between

electrolyte/electrodes wat good. The maximum power density (Pmax) increases with

enhancement of temperatures. The summarized results are shown in Table 3.7. The

highest Pmax was achieved by the cell at 333 K, with Pmax of 14.6 mW cm-2 and a short-

circuit current density (Jsc) of 31.0 rnA pm-2• This demonstrates that heat treatment has

,

an adequate effect on cell performance which was in agreement with the results

obtained by conductivity-temperature and discharge characteristic. The effect c an be

explained by considering the interface resistance, or the adhesiveness of the polymer

electrolyte/electrode. At room temperature, the interfacial adhesion could be low thus

- 36-

Ii

giving rise to a high interfacial resistance and lower cell performance. The

adhesiveness of the electrolyte was improved by heat treatment as proved by the

conductivity-temperature studies. This leads to a decrease in interfacial resistance, an

enhancement in values of conductivity and consequently, raises the cell performances.

However, further increase in temperature, i.e. 353 K during long measurement

destroyed the natural properties chitosan-based SPE.

1.8 ....--- --.

1.6

1.4

1.2 .

~ 1.0IIICl

~~ 0.8·

0.6

0.4

0.2

-o-298K_313K

-+-333 K

-tr-353 K

90.080.070.060.040.0 50.0

Current (rnA)

30.0~20.010.00.0 +----.-........--.-----.-----..-----.---..----....----.----l

0.0

Figure 3.9: 1- V curves ofprotonic batteries at 298, 313, 333 and 353 K..

•,

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•

Table 3.6: Values r of protonic batteries at elevated temperatures.

Temperature (K) Internal Resistance, r (!l)

298 30.3

313 26.4.............. - - _ - - .- - .

333 16.8

353 23.0

16.0 .r-------- --,

35.0

-o-298K

_313K

-+-333K---lr-353 K

30.025.020.015.010.05.00.0 ...---..-------.-----.-----.-----.----....-----l

0.0

2.0

4.0

~

'Eu 10.0

~~ 8.0l!!GlC

~ 6.0·11.

12.0 .

14.0·

Current Density (rnA cm·2)

i,

Figure 3.10: J-P curves of protonic batteries at 298,313,333 and 353 K.

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:

Jb

_

Table 3.7: A short-circuit current density, and the maximum power density ofprotonic

batteries at various temperatures.

Temperature (K) A Short-Circuit Current Maximum Power Density, Pmax

,i

~

298 K

313 K

333 K

353 K

Density, Jsc (rnA cm-z)

16.0

16.0

31.0

24.0

i,

- 39-

6.4

8.6

14.6

10.4

·1

j

CHAPTER 4 CONCLUSION AND SUGGESTIONS

The conductivity ofCA-NH4N03 was successfully increased from 10-5 Scm-I to 10-3 S

cm-Iemploying plasticization method using EC. In conductivity-temperature study, the

films of pure CA, CA-NH4N03 and CA-NH4N03-EC systems shows Arrhenius

behavior. The highest conducting sample (CA40N70E) possesses the lowest Ea

, 0.11

eV and the electrochemical stability window about 1.6 - 1.8 V. The OCV values

measured were in good agreement with those voltages obtained by the LSV technique.

The electrochemical characteristics of the cell have been studied at different

temperatures. During the heat treatment up to 333 K, the cells show good properties

such as enhancement of discharge capacities, Jse> and Pmax' At the same time the r of the

cells also decrease with the increase~n the heat treatment temperatures. At 333 K, the

discharge capacity, r, Pmax andJsc ~ere 42.7 mAh, 16.8 n, 14.6 mW cm-2 and 31.0 rnA

cm-2

, respectively. The failures of the cells mainly contributed to the degradation of the

chitosan film SPE.

;,

-40 -

REFERENCES

Ali, A.M.M., Mohamed, N.S., and Arof, A.K. (1998). Polyethylene oxide' (PEO)­ammonium sulfate ((NH4)2S04) complexes and electrochemical cellperformance, Journal of Power Sources 74, pp 135-141.

Arof, A.K., Basirun, W.J., Kamarulzaman, N., and Osman, Z. (1999). ExperimentalTechniques in the Synthesis and Characterization of Materials for BatteryApplications, Publication of University Malaya, Kuala Lumpur.

Bozkurt, A., Meyer, W.H., and Wegner, G. (2003). PAA/imidazol-based protonconducting polymer electrolytes, Journal of Power Sources 123, pp 126-131.

Brady, G.S., Clauser, H.R., and Vaccari, J.A. (2002). Materials Handbook, 15 Edition,McGraw-Hill Companies, Inc., New York.

Broadhead, J., and Kuo, H.C. (2<:)02). Electrochemical Principles and Reactions, In:Handbook of Batteries, 3rd edition, Chapter 2, D. Linden and T.B. Reddy[editors], McGraw-Hill, New York.

Callister, W.D. (2000). Materials Science and Engineering: An Introduction, 5th edition,John Wiley & Sons, Inc, United States.

Chandra, S. (1981). ~uperionic Solids - Principles and Applications, North-HollandPublishing Company, Amsterdam, New York, Oxford.

Khiar, A .s.S., P uteh, R., a nd A rof, A.K. (2006). Conductivity studies 0 f a c hitosan­based polymer electrolyte, Physica B 373, pp 23-27.

Li, S., Sun, J., Sun, X., and Zhu, B. (2006). A High Functional Cathode Materials ­LaNio.4Feo.603 for Low-Temperature Solid Oxide Fuel Cells, Electrochemicaland Solid State Letters 9, pp A 86-A 87.

Linden, D. (2002). Basic Concepts, In: Handbook ofBatteries, 3rd edition, Chapter 1, D.Linden and T.B. Reddy [editors], McGraw-Hill, New York.

- 41 -

Majid, S.R, and Arof, AK. (2005). Proton-conducting polymer electrolyte films basedon chitosan-acetate complexed with NH4N03 salt, Physica B355, pp 78-82.

Majid, S.R., Idris, N.H., Hassan, M.F., Winie, T., Khiar, AS.A, and Arof, AX. (2005).Transport Studies on Filler-doped Chitosan Based Polymer Electrolytes, Ionic11, pp 451-455.

Maurya, K.K., Srivastava, N., Hashmi, S.A., and Chandra, S. (1992). Protonconducting polymer electrolyte: II polyethylene oxide + NH4I system.

Mohamed, N.S., and Arof, AK. (2004). Investigation of electrical and electrochemicalproperties of PVDF-based polymer electrolytes, Journal of Power Sources 132,pp 229-234.

Mohamed, N.S., Subban, R.H.Y., and Arof, AK. (1995). Polymer batteries fabricatedfrom lithium complexed acetylated chitosan, Journal of Power Sources 56, pp153-156.

Morni, N.M., and Arof, A.K. (1999).' Chitoson-lithium triflate electrolyte in secondarylithium cells, Journal ofPower Sources 77, pp 42-48.

NEC TOKIN Corporation. (2004). Proton polymer battery: The advantages of both abattery and a capacitor, http://www.nec-tokin.com/englishlproduct/protonpolymer/feature.html, 29 May 2007.

Osman, Z., Ibrahim, Z.~., and Arof, A.K. (2001). Conductivity enhancement due to iondissociation in plalticized chitosan based polymer electrolytes, CarbohydratePolymers 44, pp167-173.

Pratap, R, Singh, B., and Chandra, S. (2006). Polymeric rechargeable solid-state protonbattery, Journal of Power Sources 161, pp 702-706.

i,Scarr, RF., Hunter, lC., and Slezak, PJ. (2002). Alkaline-Manganese Dioxide

Batteries, In: Handbook ofBatteries, 3rd edition, Chapter 10, D. Linden and T.B.Reddy [editors], McGraw-Hill, New York.

Song, lY., Wang, Y.Y., and Wan, C.C. (1999). Review of gel-type polymerelectrolytes for lithium-ion batteries, Journal of Power Sources 77, pp 183-197.

- 42-

Subban, R.H.Y., and Arof, A.K. (2004). Charge-discharge characteristics ofLiCo02/mesocarbon microbeads battery with poly(vinyl chloride)-basedcomposite polymer electrolyte, Journal of Power Sources 134, pp 211-221.

Vargas, M.A., Vargas, R.A., and Mellander, B.E. (2000). More studies on thePVA1+H3P02+H20 proton conductor gels, Electrochimica Acta 45, pp 1399-1403.

Winie, T., and Arof, A.K. (2006). Transport properties of hexanoyl chitosan-based gelelectrolyte, Ionies 12, pp 149-152.

Yahya, M.Z.A., and Arof, A.K. (2003). Effect of oleic acid plasticizer on chitosan­lithium acetate solid polymer electrolytes, European Polymer Journal· 39, pp897-902.

i,

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