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Electrochemical Techniques Electrochemical Techniques
1. Electrochemical parameters
- Charge transfer parameters; Rct, k0, i0 - Mass transfer parameters; DO, DR
2. Reaction mechanism - Mechanism
- n values 3. Analysis
- CO*, CR*
1. Hydrodynamic methods
- Rotating disk electrode (RDE) experiment
- Rotating ring-disk electrode (RRDE) experiment
2. Potential step methods
- Chronoampherometry, Chronocoulometry
3. Potential sweep methods
- Linear sweep voltammetry (LSV), Cyclic voltammetry (CV)
4. Bulk electrolysis
5. Ac impedance method
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Hydrodynamic methods: RDE experiment
Hydrodynamic methods: RDE experiment
1. Three-electrode configuration 2. Electrode area; small
- CO*, CR*; constant
3. Mass transfer; no migration (electrolytes) - Diffusion and convection
4. One-dimensional mass transfer
Assumptions
Assumptions
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Mass transfer by convection Mass transfer by convection
One-dimensional
mass transfer
Diffusion and convection Diffusion and convection
(Nernst diffusion layer)
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E (–)
Ei
0 t
E0'
a
b
c
d
e
Electrode potential; linear sweep
Electrode potential; linear sweep
Surface concentration as a function of Surface concentration as a function of
electrode potential
electrode potential
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Mass transfer in Nernst diffusion layer Mass transfer in Nernst diffusion layer
x x x
O* O* O*
O , t
ideal
real
O , t
Potential vs. Current
Potential vs. Current
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Conc. gradient vs. rotating speed
Conc. gradient vs. rotating speed
1. Three-electrode configuration 2. Electrode area; small
- CO*, CR*; constant
3. Mass transfer; no migration (electrolytes) - Diffusion
- No convection; no stirring
Potential sweep methods
Potential sweep methods
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Potential sweep methods Potential sweep methods
1. Linear sweep voltammetry 2. Cyclic voltammetry
Ei
0 t
E0'
a
b
c
d
e
E (-)
Linear sweep voltammetry Linear sweep voltammetry
Ei
0 t
E0'
a
b
c
d
e
E (-)
t D l = 2 0
E = E i-νt
↓ ↓
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Peak potential
Peak potential
Current vs. scan rate Current vs. scan rate
t D l = 2 0
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Cyclic voltammetry Cyclic voltammetry
EE0
Concentration gradient
Concentration gradient vs vs . time . time
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Cyclic voltammogram
Cyclic voltammogram
Q Q
ff>Q >Q
rr21
Electrochemically reversible
Electrochemically reversible
Oxidation of aniline
Oxidation of aniline
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Ni plating
Ni plating
Passivation of metal surfaces
Passivation of metal surfaces
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Cyclic voltammogram for adsorbed species
Cyclic voltammogram for adsorbed species
Pseudo
Pseudo - - capacitors capacitors
- EDLC; electric double-layer capacitors
Ideally polarized electrodes: Rct → ∞
* Charging current:
- Pseudo-capacitors: faradaic reactions