Mechanism of electron transfer during the course of oxidation of N-phenyl-p-phenylenediamine polythiophene and poly-3-methylthiophene coated electrodes: Redox catalysis versus outer-sphere heterogeneous electron transfer

Comparative studies of the mechanism of anodic oxidation of N-phenyl-p-phenylenediamine (NPPD) on a bare platinum electrode as well as on platinum coated with poly-3-methylthiophene (P3MT) or polythiophene (PT) films have been carried out. The shift of the voltammetric peak potential corresponding to the first one-electron oxidation step of NPPD on coated electrodes on varying the potential scan rate or the corresponding shift of half-wave potential towards more positive values in the series Pt < Pt/P3MT < Pt/PT have been observed. Two alternative models of kinetics of solute redox reactions such as the model of catalytic reactions mediated by conventional redox-polymers and the thermodynamic model of electrochemical doping of π-conjugated polymers with regard to the kinetics of outer-sphere electron-transfer reactions have been discussed in an attempt to account for the experimental results obtained. Evidence in favour of the applicability of the second model have been summarized.