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

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) page42 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.

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 1-1-1- 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

(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

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

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

Differention between reversible, irreversible and quasireversible peaks Fig 8

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<0.5 ipf<ipr a>0.5 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.

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 = 0.5 ipr /ipf=1 a > 0.5 ipr /ipf<1 a < 0.5 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)

Two capped tetrahedron 1-3-2- The chemical meaning of electrochemically quasireversible process Fig 10 [CuIIL]2+ +e [CuIL] + Octahedral S4O2 Tetrahedral S4 Structural reorganization without fragmentation in the molecular framework Fig 11 [Os6(CO)18] +2e [Os6(CO)18]2- Two capped tetrahedron octahedron

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,…

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

Time scale of cyclic voltammetry : kf kr 1-4-1-1-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

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

properties of the potential Properties of the current 1-3-1- 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