3. The separation between reverse peak and forward peak is so large
The reduction potential is more cathodic than formal electrode potential
The separation between reverse peak and forward peak is so large
The forward peak is located at more negative potentials than reversible process
1-2- Irreversible processes
Fig 7

4. na the number of electrons in the slowest step
Boundary conditions:
Initial similar to rev.
Semi-infinite similar to rev.
Electrode surface different from rev.
Under equivalent conditions the height of the irreversible peak = 78.6% of the reversible peak; then a =0.5
na the number of electrons in the slowest step
Then =kox or kred) page a = transfer cofficient(0<a<1) or symmetry factor ko=standard rate constant(if E=Eo’
The transfer coefficient is a measure of the symmetry
of the energy barrier for electron transfer and has a value between
0 and 1.

5. 1-1-1- Diagnostic criteria to identify a reversible process
Epf shifts with scan rate
Calculation of a and na
Dependence of Ep with v, calculation of ko
Diagnostic criteria to identify a reversible process
Properties of the potential
Properties of the current
ipf/v1/2 = constant
No ipr/ipf exists
Calculation of a and ko

6. (breakage of the original molecular frame)
1-2-2-The chemical meaning of electrochemically irreversible process
activation barrier
(breakage of the original molecular frame)
irreversibility

7. 1-3- Quasireversible process
Transition zone between
1 and 2
Quasireversible
In low scan rate
Reversible
In high scan rate
Irreversible

8. Boundary condition: Electrode surface
The forward peak height is not proportional to v1/2
The shape of the peaks and the peak to peak
separation dependence:
assumption:
α =0.5 , D = Dox=DRed
In this case the peak to peak separation is much greater than that of a reversible process

9. Differention between reversible, irreversible and quasireversible peaks
Fig 8

10. 1-3-1- Diagnostic criteria to identify a quasireversible process
Eo′
Calculation as the average value between the forward and reverse peak
0.3<a<0.7
0.75
0.5
0.25 Ko
Calculation from the working curve (fig 9)
The effect of a on the shape of the voltammogram (large a = asymmetric-cathodic peak sharper as expected)
a< ipf<ipr
a> ipf>ipr
Page 81 - The transfer coefficient is a measure of the symmetry
of the energy barrier for electron transfer and has a value between
0 and 1.

11. a = 0.5 ipr /ipf=1 a > 0.5 ipr /ipf<1 a < 0.5 ipr /ipf>1
Quasireversible
process
current
ipf increases with v1/2
a = ipr /ipf=1
a > ipr /ipf<1
a < ipr /ipf>1
potential
Epf shifts (towards more negative potential values for reduction) with scan rate
DEp (25 oC) is higher than 59/n (mV)

12. Two capped tetrahedron
The chemical meaning of electrochemically quasireversible process
Fig 10
[CuIIL] e [CuIL] +
Octahedral
S4O2
Tetrahedral S4
Structural reorganization without fragmentation in the molecular framework
Fig 11
[Os6(CO)18] e [Os6(CO)18]2-
Two capped tetrahedron
octahedron

13. 1-4- the effect of chemical reactions coupled to electron transfers
Preceding (the electron transfer)
Chemical reaction
Following (the electron transfer)
Chemical reaction
Symbols
Homogeneous chemical (reaction(C
Heterogeneous chemical (reaction(E
None electro active species from the coupled chemical complication Y, Z,W,…

14. 1-4-1- preceding chemical reactions
influencing the amount of Ox, perturbing the forward peak
Y Ox
Ox + ne Red
Reversible e.t. 1
Irreversible e.t. 2

15. Time scale of cyclic voltammetry :kf kr
first order chemical reaction preceding a reversible electron transfer
Y Ox
Ox + ne Red
CrEr
Time scale of cyclic voltammetry :
reversible process n.F.v/R.T
quasireversible or irreversible process a. na .F.v/R.T

16. 1-4-1-1-first order chemical reaction preceding a reversible electron transfer
slow
kf+kr<< n.F.v/R.T
Large K
Small K
fast
kf+kr>> n.F.v/R.T
Large K (Eo′*)
(K→∞)
Small K
Ox + ne Red
Y Ox
Fig 12
intermediate
kf+kr≈ n.F.v/R.T
Current (ik)
ipr/ipf >1
Fig 13
Page 86

17. properties of the potential Properties of the current
Diagnostic criteria to identify a chemical reaction preceding a reversible e.t.
properties of the potential
Properties of the current
For a reduction process the Epf shifts towards less negative potential values with scan rate
ipf/v1/2 decreases with the scan rate
ipr/ipf is greater than 1 and further increases with scan rate