Electrochemical application on boron-doped diamond...
Transcript of Electrochemical application on boron-doped diamond...
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Electrochemical application on boron-doped diamond electrodes
Yasuaki EinagaDepartment of Chemistry
Keio UniversityJapan
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Boron concentration carbon density in diamond = 1.76×1023
boron solubility into diamond ≥ 1.4×1022
Boron-doped Diamond (BDD)
~ 1018 1019 1020 1021 1022No doping (cm-3)
0.01 % 0.1 % 1 %0B/C
[B]
Insulator Semiconductor
Diamond Electrodes
Metal 10-2Ωcm
Many studies
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Electrochemical Properties of Boron-doped Diamond (BDD) Electrodes
Wide potential window(-1.2~2.0V)
Low background current(100 nAcm-2)
Physically and chemically stable
Oxygen evolutionHydrogen evolution
Generation of active species (・OH etc)
Au
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Development of diamond electrodes (2000~)
Diamond Electrodes
Heavy metals, Chlorine, etc
Glucose, Uric acid, Oxalic acid, Cancer marker, Neurotransmitter
Environmental sensors
Bio, Medical sensors
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1.3 V
0
0.2
0.4
0.6
0.8
1
0.5 1 1.5
Potential (V vs. Ag/AgCl)
Glassy Carbon
Pt
Au
Diamond electrodes
Cur
rent
Den
sity
(mA/
cm2 )
1.3 V
0
0.2
0.4
0.6
0.8
1
0.5 1 1.5
Potential (V vs. Ag/AgCl)
Glassy Carbon
Pt
Au
Diamond electrodes
Cur
rent
Den
sity
(mA/
cm2 )
Detection of free chlorine
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Cur
rent
Den
sity
(mA
/cm2 )
120100806040200
Concentration (mg/l)
Calibration curve1.2
1.0
0.8
0.6
0.4
0.2
0.0
Cur
rent
Den
sity
(mA
/cm2 )
120100806040200
Concentration (mg/l)
Calibration curve
6
8
10
12
14
Time (min)
Cur
rent
(nA)
0 5 10
6
8
10
12
14
Time (min)
Cur
rent
(nA)
0 5 10
100
80
60
40
20
0C
urre
nt D
ensi
ty (m
A/c
m2 )2.01.51.00.50.0
Concentration (mg/L)
Even in low concentration region (0-2ppm), the detection was possible.
Calibration curve
6ClO- + 3H2O 3ClO3- + Cl- + 6H+ + 3/2O2 + 6e-
Hypochlorite ion
J. Electroanal. Chem., 612, 29 (2008).
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Prototype of Residual Chlorine Monitor (2018)
Functional Water Foundation
Press release: Aug. 30th, 2018
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In China (2019)Institute for Electronics and Information Technology in Tianjin, Tsinghua University清华大学天津电子信息研究院 ・ HORIBA(堀場製作所)
Cd detection in rice
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- High current density- High sensitivity - Steady-state current response- Negligible effect of IR dropthree dimensional diffusion
< Remarkable properties of microelectrodes >
5µm
Electrochemical analysis by BDD microelectrodes
Next generation electrodes for sensor
In vivo detection
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Simultaneous detection of phermacokineticsRecent Topics
Bumetanideloop diuretic drug[Uses] edema, neonatal seizures[Side Effects] hearing loss
Amplifier
Potentiostat
Guinea pig
Cochlea
Glass Microelectrode
syringe
Diamond Microelectrode
Drug concentration(Diamond microelectrode)
Hearing ability(Glass microelectrode)
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Hearing loss
Bumetanideinjection30 mg/kg
BumetanideSampling frequency0.2 Hz
EPSampling frequency40 Hz
Level of hearingEndocochlear potential : EP
(mV)
Bum
etan
ide
(µM
)
Nature Biomed. Eng. 1, 654 (2017).Science 359, 1287 (2018).[Highlight]
Real time measurement
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Development of diamond electrodes
Diamond ElectrodesFundamental
Study
Heavy metals, Chlorine, etc
Glucose, Uric acid, Oxalic acid, Cancer marker, Neurotransmitter
Environmental sensors
Bio, Medical sensors
2012~
Waste water treatment
Ozone generation
Electrochemical organic synthesis
Improvement of environment
CO2 reduction2014~
(2011~)
Electrochemiluminescence(ECL)
2016~ New!!
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• Fuel
• Plastics
CO2 CxHyOz
Surface
e-, H+
CO2 reduction using BDD electrodes
Reduction
CO2 Reduction
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Electrochemical reduction of CO2by conventional electrodes (1980~)
1) CO2 + 2H+ + 2e- → CO + H2O2) CO2 + 2H+ + e- → HCOOH3) CO2 + 6H+ + 6e- → CH3OH + H2O4) CO2 + 8H+ + 8e- → CH4 + 2H2O5) 2H+ + 2e- → H2 in MeOH
41 atm25 oC
CO2
Electrolyte
e-
CO2
ProductsOxidation
Power source H2
Hydrocarbon
HCOOH
J. Electrochem. Soc., 141, 2097 (1994); J. Electroanal. Chem., 404, 299 (1996).
Cu electrodesin H2O1-60 atm25 oC
Low efficiencyHigh pressure Low stability
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Electrochemical Properties of Boron-doped Diamond (BDD) Electrodes
Wide potential window(-1.2~2.0V)
Low background current(100 nAcm-2)
Physically and chemically stable
Oxygen evolution
Generation of active species (・OH etc)
Au
Supresshydrogen evolution !
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Reduction of CO2Room TemperatureAmbient pressure
Angew. Chem. Int. Ed., 53, 871 (2014).Faradaic efficiency / %
Elec
trode
mat
eria
ls
Formaldehyde (HCHO) HCOOH
HCOOHHCHO
HCOOCH3
HCOOCH3 CO
CO CH4
H2
H2
H2
H2
HCOOCH3
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Recent trial for CO2 reduction
2. Produce more valuable compounds
1. 100% Faradaic efficiency
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Catholyte: 0.5 M KCl aq.Anolyte: 1.0 M KOH aq.
Formic acid production
Flow cell
CO2 + 2H+ + 2e− ➝ HCOOH(Current density: 2, 5, 10, 20 mA cm−2)
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Flow rate(mL min−1)
FE ofHCOOH (%)
FE of H2(%)
Total FE (%)
20 35 41 76
50 85 8.6 95
100 91 3.6 95
200 95 4.1 100
500 88 8.1 99
Dependence of electrolyte flow rate
Faradaic efficiency @ 2 mA cm−2
100
80
60
40
20
0
Fara
daic
Effi
cien
cy (%
)
5004003002001000Flow Rate (mL min-1)
HCOOH H2
Faradaic efficiency of HCOOH increased up to 95% with increasing flow rate.
⇒ Progress of CO2 mass-transport
Angew. Chem. Int. Ed., 57, 2639 (2018).
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Recent trial for CO2 reduction
2. Produce more valuable compounds(To control of the production)
1. 100% Faradaic efficiency
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Cu nanoparticleBDD electrode
CO2 ?aqueoussolution
C2/C3 compounds were produced!
C2H5OH (Ethanol)CH3CHO (Acetaldehyde)(CH3)2CO (Acetone)
Anolyte: KOH 0.5 MCatholyte: KCl 0.5 M
Electrochim. Acta., 266, 414 (2018).
(1) Cu-modified BDD electrodes
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Examples :1. MEA (Monoethanolamine) 2. EAE (N‐Ethylamino ethanol)3. DEA (Diethanolamine),
4. Ammonia solution [high loading capacity : 1.76 kg CO2/kg NH3
MEA = 0.55‐0.58 kg CO2/kg MEA ]
Mani, F. et al. Green. Chem. 2006, 8, 995‐1000
NH3(aq) + CO2 ?Reduction on BDD
Purpose :
(2) In Amine Solution
Amine solutions are used for CO2 absorber….
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NH3 + CO2 + H2O ⇄ NH4+ + HCO3
-
HCO3- + 5H2O + 6e- ⇄ CH3OH + 7OH-
Methanol is the main product
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pH 7.5 - 9.0 : HCO3- is dominant
Zhong, H. et al. J. Phys. Chem. C., 2015, 119, 55-61.
CO2 (aq) + H2O (l) H+(aq) + HCO3
-(aq) pK1 = 6.35
H+(aq) + HCO3
-(aq) 2H+
(aq) + CO32-
(aq) pK2 = 10.33
CO2 HCO3- CO3
2-
pH is also an important factor for the production!!
RSC Adv., 6, 102214 (2016).
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(3) Electrolyte
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Cation dependence
Li, Na << K, Rb, CsFaradaic efficiency for HCOOH production
100
80
60
40
20
0
Fara
daic
effi
cien
cy (%
)
LiCl NaCl KCl RbCl CsCl
HCOOH H2
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Buffer effects of alkali cation
26
Singh, M. R. et al. J. Am. Chem. Soc. 2016, 138, 13006-13012.CO2 reduction by Ag electrodes
pH near cathode
Large cation ⇒ High buffering effect
K+, Rb+, Cs+ : pH (near cathode) is stable
pH increase (near cathode)CO2 + 2H+ + 2e– → CO + H2O2H+ + 2e− → H2
[M+(H2O)n] ⇄ [MOH(H2O)n–1] + H+Buffering effect by Hydrated cations
CO2 concentration near cathode
High efficiency for HCOOH production K, Rb, Cs
K+, Rb+, Cs+: pH is stable
CO2 concentration is high (CO2 + H2O ← H+ + HCO3
−)
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Anion dependence
NO3‒ + H2O + 2e‒
→ NO2‒ + 2OH‒
HCOOHproduction
COproduction
ChemistrySelect, 3, 10209 (2018).
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(–2.1 V vs. Ag/AgCl)
80
60
40
20
0
Fara
daic
effi
cien
cy (%
)
KClO4 KCl
CO HCOOH H2
KClO4 KCl
J. Am. Chem. Soc., 141, 7414 (2019).
CO production in KClO4
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CO2+e- ꞏCO2
-(ad)
ꞏCO2-(ad) CO + CO3
2-+CO2, +e- ꞏCO2
-(ad) HCOO-
(ad)+H+, +e-
Electrode
CO2•‒
Electrode
CO2•‒
?
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in-situ ATR-IR
BDDSi
IR beam IR detector
CxHyOzCO2
Abso
rban
ce
1750 1700 1650 1600 1550Wavenumber (cm-1)
KClO4
KCl
0.003
KClAb
sorb
ance
1800 1700 1600 1500 1400 1300Wavenumber (cm-1)
0.004
30 min
5 min
Abso
rban
ce
1800 1700 1600 1500 1400 1300Wavenumber (cm-1)
0.004
30 min
5 min
KClO4
Intermediate
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Measurement by 13C BDD
Interaction between intermedeates (CO2•‒) and BDD electrodes are different.
CC
CO2•‒
⇒ COKClO4
CC
CO2•‒
⇒ HCOOHKCl
J. Am. Chem. Soc., 141, 7414 (2019).
CO2•‒