Fundamentals of Electrodics

Fall semester, 2011

Shu-Yong Zhang

Electrode process

The totality of changes occurring at or near an electrode during the passage of current.

electrochemical step: involving gain or loss of electron

non-electrochemical step

Electrochemical thermodynamics

Electrochemical kinetics

1.1.1 Electrochemical apparatus:

galvanic cell

Electrolytic cell

Electrodes:

positive/negative electrode

anode / cathode

§1.1 Review of fundamental electrochemistry

1.1.2 Types of electrode:

1) metal / metal ion electrode

2) metal / insoluble salt electrode

3) redox electrode

4) membrane electrode

5) intercalation electrode

6) modification electrode

7) semiconductor electrode

8) insulator electrode

Conversion film formation

1.1.3 Kind of electrode reaction

DirectDirect

Reaction Reaction of of electrodeelectrode

1) Active Dissolution1) Active Dissolution

2) Surface finishing2) Surface finishing

3) Passivation3) Passivation

4) Surface conversion4) Surface conversion

5) Anodization5) Anodization

Reaction Reaction of species of species from from solutionsolution

1) Oxidation / Reduction1) Oxidation / Reduction

2) Polymerization2) Polymerization

3) deposition3) deposition

IndirectIndirect

via via electron electron mediamedia

Reaction Reaction of species of species in solutionin solution

1) Oxidation via Ce1) Oxidation via Ce4+4+

2) Reduction via V2) Reduction via V2+2+

3) Polymerization3) Polymerization

4) deposition4) deposition

Direct and indirect electrochemical reactions

working electrode (W. E.)

counter electrode (auxiliary electrode) (C. E.)

reference electrode (R. E.)

1) Three-electrode system/cell:

1.1.4 Measurement of electrode polarization

Luggin cappilary

Shape of working electrode

disk sphere wirering

band foil array Interdigitaled array

Commercial SCE

2) Typical reference electrode:

Commercial Ag/AgCl or Ag/Ag+ electrode

1 ） Faraday’s Law

m, mass of liberated matter; Q electric coulomb, z

electrochemical equivalence, F Faraday’s constant, M

molar weight of the matter.>

F = 1.6021917 10-19 6.022169 1023

= 96486.69 C mol-1 96500 C mol-1

§1.1.5 Important relationships

Qm M

zF

Valid only for reversible cell

ln ox

red

aRT

nF a y

2 ） Nernst equation:

ln ii

i

RTa

nF y

Dependent of electrode potential on species activities

lnc dC Da bA B

a aRTE E

nF a a y

3) Tafel equation:

The point of intersection of the extrapolation on the l

ine = 0 is log i0.

A is in fact the at j = 1 A cm-2.

= a + b log j

Valid only for irreversible cell

Pt electrode in aq. 0.01

M Fe3+, Sn4+, Ni2+ (1 M H

Cl)

Discharge series:

As potential moved to more negative values, the substance which will be reduced first is the oxidant with the least negative .

§1.2 Physical meanings of and I

1) Electrode potential

the highest occupied level

Electron gas

Metal atoms

unoccupied

Fermi Level

occupied

Energy bands

1( )

exp 1F

F EE E

kT

Fermi-Dirac distribution

FE E kT ( ) exp FE EF E

kT

FE E kT ( ) 1F E

FE E 1( )

2F E

cf. p. 16-18

2/32 3

2 8e

F

e

nhE

m

Electrode Solution

A + e- A-

Electrode Solution

Occupied MO

Vacant MO

Electrode Solution

Occupied MO

Vacant MO

Electrode Solution

A A+ + e-

HOMO approximately corresponds to of A/A-

LUMO approximately corresponds to of A+/A

physical meaning of ?

The tendency to accept or donate electrons is represented by the sign and absolute value of the standard electrode potentials.

The tendency to accept or donate electrons is represented by the sign and absolute value of the standard electrode potentials.

That means:

high positive potential values indicate a strong tendency for accepting electrons

A higher positive potential of a given half-cell with respect to another indicates that the former has stronger oxidizing ability than the latter.

That means:

high positive potential values indicate a strong tendency for accepting electrons

A higher positive potential of a given half-cell with respect to another indicates that the former has stronger oxidizing ability than the latter.

Current: the index of reaction rate

Consider 1 mole of A- is oxidized to A

A A + ne

Q = n N F

n: the number of e- transferred, N the number of mole of A

2) Electrochemical current

Q NI nF nFr

t t

I

rnFA

§1.3 Electrochemical methods

One cannot simultaneously control both E and I

Control E: potentiostatic methods

Control I: galvanostatic methods

Voltammetry

Voltammetric method

References: [1] 查全性等，《电极过程动力学导论（第三版）》，科

学出版社，北京， 2002.6.

[2] A. J. Bard, Electrochemical Methods–Fundamentals and

Applications (2nd, Ed.), John Wiley & Sons.

[3] Encyclopedia of Electrochemistry, (Ed. A.J. Bard), Wiley.

[4] Modern Electrochemistry, (Ed. J. O. Bockris ), Springer.

[5] Modern Aspects of Electrochemistry, Springer.

[6] A. H. Frumkin, Kinetics of Electrode Process, Science Pre

ss.

Allen J. Bard, Martin Stratmann, Encyclopedia of Electrochemistry, Wiley.

Vol. 1: Thermodynamics and Electrified Interfaces Vol. 2: Interfacial Kinetics and Mass Transport Vol. 3: Instrumentation and Electroanalytical Chemistry Vol. 4: Corrosion and Oxide Films Vol. 5: Electrochemical Engineering Vol. 6: Semiconductor Electrodes and Photoelectrochemistry Vol. 7: Inorganic Electrochemistry Vol. 8: Organic Electrochemistry Vol. 9: Bioelectrochemistry Vol. 10: Modified Electrodes Vol. 11: Index

Modern Aspects Of Electrochemistry, Vol. 42

Topics include:1) The electrochemistry and electrocatalysis of Ruthenium in regards to the d

evelopment of electrodes for Polymer Electrolyte Membrane fuel cells (PEM)

2) Breakthroughs in Solid Oxide Fuel Cell (SOFC) anodes and cathodes leading to improved electrocatalysis

3) Electrocatalysis of the electrochemical reduction of CO2 on numerous metals

4) The interfacial phenomena of electrodeposition and codeposition, and the need for new theoretical analyses of the electrode-electrolyte interface

5) Advantages of scanning tunneling microscopy (STM) in understanding the basics of catalysis, electrocatalysis and electrodeposition

6) The role of electrochemistry in emerging technologies including electrodeposition and electroforming at the micro and nano levels, semiconductor and information storage, including magnetic storage devices, and modern medicine

Bockris, John O'M., Reddy, Amulya K.N., Modern Electroc

hemistry, Springer.

Vol. 1 Ionics

Vol. 2A Fundamentals of Electrodics

Vol. 2B Electrodics in Chemistry, Engineering, Biology and

Environmental Science