STATE OF SURFACE OXIDE-FILMS AT PT ANODES AND VOLCANO BEHAVIOR IN ELECTROCATALYSIS FOR ANODIC CL-2 EVOLUTION

The kinetic behaviour of the electrolytic Cl//2 evolution reaction at Pt anodes is investigated in relation to the state of surface oxidation of the Pt electrode. Electrode surfaces in various states of preoxidation were examined with respect to the values of the recombination rate constant, k//2, for the Cl recombination rate-controlling step that characterizes the kinetics of the reaction at Pt in acid media. Interesting electrocatalytic effects are observed, depending on the state of oxidation of the Pt surface on which the Cl//2 evolution reaction proceeds. In particular, a clear 'volcano plot' is demonstrated in the relation between the recombination rate constant and the extent of surface oxidation of the Pt as measured by the reduction charge Q in separate negative-going potentiodynamic sweep experiments.