1. Electrochemistry: Introduction Electrochemistry at your finger tips
Part 3: Cyclic voltammetry: adsorption, surface confined redox species, electrocatalysis. Polarography, rotating disk electrode, potential step methods

2. Adsorption of non-electrochemically active species on an electrode+ + -
clean electrode
capacitance current
double-charged layer
after adsorption
I / mA - +
background CVs + -
adsorbed species
E / V
 dielectric constant is changed

3. Adsorption of redox species on an electrode
Redox species adsorbing on the electrode
capacitance current
I / mA
background CV
E / V

4. Surface-confined redox species:
a special kind of electrochemistry E0
I / mA
Ep = 0 mV or very small
E / V

5. Comparison of the diffusional and surface-confined electrochemical processes – they have quite different shapes in voltammograms

6. ip= n2F2GAv/4RT Q=nFAG e- Ip / mA v / (mV s-1)
How can we recognize surface-confined electrochemical processes:
ip= n2F2GAv/4RT
Q=nFAG
I / mA e-
E / V
Time / sec
Ip / mA
1. No limiting current
2. Ip proportional to scan rate
3. Small peak-to-peak separation for the reversible processes
v / (mV s-1)

7. Electrochemical kinetics for the surface-confined processes
Laviron´s theory
To calculate the rate constant we need to know:
1. E as a function of the potential scan rate
2. Number of electrons per molecule
E / mV
Slope=-2.3RT/anF(cathodic peak)
log( v / mV s-1)
i=nFAks[G0exp{anF(E-E0’)RT-Grexp(1-a)nF(E-E0’)/RT}]

8. The peak area is used to calculate the surface concentration of the redox units.
I / mA
E / V
Practical tips have to be discussed!

9. Real problems in recognizing diffusional or surface confined electrochemical processes:
1. If the range of the used potential scan rates is not large, the difference between v and v1/2 is not significant.
2. If the process is quasi-reversible or irreversible, the peak-to-peak separation could be big for both mechanisms.
3. If the peak is close to the background discharge, the peak looks like a shoulder and the limiting current is not easy to see.

10. Catalytic waves in cyclic voltammograms
Surface-confined electrocatalyst

11. Diffusional electrocatalyst

12. Polarography is a linear sweep voltammetry performed on a mercury dropping electrode

15. Historical preface:
All modern electrochemistry starts from polarography technique developed by J. Heyrovsky
The dropping mercury electrode (DME) was introduced by J. Heyrovsky in 1920s.
J. Heyrovsky
M. Shikata
The first polarograph designed by J. Heyrovský and M. Shikata (1924)

16. Rotating disk electrode

17. Veniamin Grigorievich (Benjamin) Levich (1917-1987)
Levich plot & equation

18. Potential step methods: Chronoamperometry
Exponential decay
Diffusional redox process
Surface-confined redox process

19. Recommended textbooks
on electrochemistry:
Electrochemical Methods : Fundamentals and Applications, by A.J. Bard and Larry R. Faulkner
Analytical Electrochemistry,
by Joseph Wang
Broadening Electrochemical Horizons: Principles and Illustration of Voltammetric and Related Techniques,
Edited by Alan Bond