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Electrochemical Techniques Electrochemical Techniques

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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*

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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

(3)

3

Hydrodynamic methods: RDE experiment

Hydrodynamic methods: RDE experiment

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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

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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

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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

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Potential vs. Current

Potential vs. Current

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Conc. gradient vs. rotating speed

Conc. gradient vs. rotating speed

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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 (-)

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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

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Current vs. scan rate Current vs. scan rate

t D l = 2 0

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17

Cyclic voltammetry Cyclic voltammetry

EE0  

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Concentration gradient

Concentration gradient vs vs . time . time

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Cyclic voltammogram

Cyclic voltammogram

(20)

Q Q

ff

>Q >Q

rr

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Electrochemically reversible

Electrochemically reversible

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Oxidation of aniline

Oxidation of aniline

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Ni plating

Ni plating

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Passivation of metal surfaces

Passivation of metal surfaces

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Cyclic voltammogram for adsorbed species

Cyclic voltammogram for adsorbed species

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Pseudo

Pseudo - - capacitors capacitors

- EDLC; electric double-layer capacitors

Ideally polarized electrodes: Rct → ∞

* Charging current:

- Pseudo-capacitors: faradaic reactions

참조

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