The influence of chemisorbed sulphur on the kinetic parameters of the reduction of Fe3+ ions on a platinum electrode on the basis of the marcus theory of electron transfer

Abstract

The influence of chemisorbed sulphur on the kinetic parameters of the reduction of Fe3+ ions on a platinum electrode, studied in a previous work, was interpreted in this work on the basis of the Marcus theory of electron transfer. By analysis (according to Randles) of the voltammetric curves obtained on a turbulent type of rotating electrode, it was found that their shape corresponds to a dependence of the transfer coefficient on potential, with a value of the transfer coefficient at the formal potential equal to 0.5, in agreement with theory. In the presence of chemisorbed sulphur on the platinum surface, the fraction of poorly reducible oxide in the overall amount of oxide formed by anodic polarization is higher than in the absence of sulphur. If the poorly reducible oxide is present on the electrode surface, the rate constant for the reduction of Fe3+ ions is higher than in the absence of sulphur and, on the other hand, if only chemisorbed sulphur is present on the surface, it is lower. Based on the correlation between the values of the rate constant and the values of the reorganization energies, calculated from the dependence of the charge transfer coefficient on potential, we came to the conclusion, that changes in the rate constant are, in our case, caused mainly by changes in the reorganization energy. We attempted to support this explanation by calculation of the value of the reorganization energy according to the theory of electron transfer.