3. towards more negative values towards more positive values
Second-order irreversible chemical reaction following a reversible electron transfer: dimerization
Slow dimerization reaction (small k2), or high scan rate only the reversible electron transfer is active
for a ten-fold increase in the scan rate /n (mV)
for a ten-fold increase in the concentration of Ox 20/n (mV)
Ox + ne Red
2 Red Z k2
Epf
towards more negative values
towards more positive values

4. How to calculate the kinetic parameter k2
measurement of the variation of Epf with the scan rate (fig 17)
measurement of the ipr/ipf at a given scan rate (fig 18)

5. Evaluation of ipr/ipf
Fig 18
recording a cyclic voltammogram at high scan rate (ipr/ipf =1 ) to be able to calculate Eo'
a cyclic voltammogram is then recorded at slow scan rate (0.5 ≤ ipr/ipf ≤ 0.9) setting Ef = Eo'- 100 mV
ipr/ ipf
graphical evaluation(fig 19):

6. Properties of the Potential Properties of the Current
Diagnostic criteria to identify an irreversible dimerization reaction following a reversible electron transfer
Properties of the Potential
1) Epf shifts towards more cathodic values by 20/n (mV) for every tenfold increase in the scan rate
2) Epf shifts towards more anodic values by 20/n (mV) for every tenfold increase in the concentration of Ox
Properties of the Current
1) ipr/ipf increases with the scan rate and decreases the concentration of Ox
2) ipf /v1/2, decreases slightly (at most by 20%) with the scan rate
dependence on the concentration of the redox active species

7. 1.4.2.4. Second-order irreversible chemical reaction following
a reversible electron transfer : disproportionation
variation of the peak current with the scan rate
Ox + ne Red
2 Red Z + Ox k2
decreasing the scan rate
allowing chemical reaction to regenerate Ox
a significant increase in the ipf

8. k2
ipr /ipf at a given scan rate, then use of the working curve,Fig 20
curve for a value of Ef more cathodic by 100 mV with respect to the Eo' of the couple Ox/Red
first a cyclic voltammogram at high scan rate (ipr/ipf = 1) to be able to calculate Eo'
cyclic voltammogram at slow scan rate
(0.7 ≤ ipr /ipf ≤ 0.9) setting Ef = Eo'- 100 mV
ipr /ipf be evaluated through the usual equation:
ipr /ipf

9. dependence on the concentration of the species ox
Diagnostic criteria to identify an irreversible disproportionation reaction following a reversible e. t.
dependence on the concentration of the species ox
Potential
Current
1) Epf shifts towards more
cathodic values by 20/n (mV) for every ten-fold increase in the scan
rate
2) Epf shifts to more anodic values by 20/n (mV) for every ten-fold increase in the concentration of Ox
1) ipr/ipf increases with the scan rate and decreases with the increase of the concentration of Ox
2) ipf /v1/2 decreases by more than a factor of two with scan rate

10. irreversibility of the complication 2
Catalytic regeneration of the reagent following a reversible electron transfer
Ox + ne Red
Red + Z O x + Y kf
pseudo-first-order reaction Z at concentrations much higher than that of Ox 1
irreversibility of the complication
powerful oxidant Z 2
no electrochemical intervention
electro inactive Z (at least in the potential region of interest) 3

11. Large kf (slow potential scan rates)
Small kf (high potential scan rates) kf
Amount of kf
Not having following chemical reaction (simple reversible electron Transfer)
Large kf (slow potential scan rates)
Higher ipf than that of a simple reversible electron transfer (regeneration of the reagent )
The increase in ipf on decreasing v continues up to a limiting value
Until no effect on the current(the rate with which the species Ox disappears, due to reduction at the electrode, equals the speed with which Ox is regenerated by the oxidant Z)
S-like shape response (Fig 21)

12. Fig 21
Scan rate
(a < b < c)
E1/2 = Eo’

13. If the value of kf allows the limiting conditions to be achieved
Evaluation of kf :
If the value of kf allows the limiting conditions to be achieved 1
If Dox , kf are known, the limiting current: 2a
Compare the value of the limiting current obtained at a given scan rate, ik with id 2b
Use of working curve in fig 22a

14. Properties of the Potential
Diagnostic criteria to identify a catalytic regeneration of the reagent following a reversible electron transfer
In addition to the eventual obtainment of a sigmoidal curve for either the forward and the reverse profile:
Properties of the Potential
In the case of an S-like wave, the E1/2 is independent from the scan rate
Otherwise Epf shifts towards less negative values for a maximum of 60/n (mV) for every ten-fold increase in the scan rate
Properties of the Current
Apart from the case of the s-like wave, ipr/ipf = 1
ipf /v1/2 significantly increases with the decrease of the scan rate up to a maximum value which is independent of v (formation of an S-like curve)

15. Simple irreversible electron transfer
Catalytic regeneration of the reagent following an irreversible electron transfer
Ox + ne Red
Red + Z Ox + Y ko kf
Small kf
Simple irreversible electron transfer
Large kf
The greater the potential scan rate the higher the peak
Current, continues up to a maximum value (S-like shape)
similar to the preceding case, with the difference that, given the irreversibility of the electron transfer, the return peak is missing

16. Diagnostic criteria to identify a catalytic regeneration of the reagent following an irreversible electron transfer
The same as the catalytic regeneration of the reagent following a reversible electron transfer, but ipr/ipf cannot be measured due to the absence of the return peak.