Oxygen Reduction on Polycrystalline Platinum in Alkaline Solution. III: Platinum Surface Modified by Hydrogen Evolution: Additional Data

Abstract

This paper presents and discusses data collected on the electroreduction of O2 (ORR) in 1 M NaOH on a polycrystalline Pt surface that initially was pretreated by H2 evolution at -250 mV in deaerated 0.5 M H2SO4 and then evolved with time in a spontaneous and rather slow way towards a full Nekrasov (N-Pt) type behavior, both in the cathodic- and in the anodic potential scan. This fact represents a clear demonstration that a polycrystalline metal surface is a dynamic system and allowed us to carry out the thorough study of the mechanism and kinetics of the ORR on a full N-Pt surface that was not possible in the previous work reported in the Part II of this series. Essentially, we concluded that the change does not alter the ORR mechanism, which is always a series mechanism coupled to disproportionation of the HO2- produced; what varies in a given potential range is the value of the rate constants of the different mechanistic steps. It was possible to get absolute values of these constants only for some potential ranges, although the analysis of the data collected provided relative information for the remaining ranges.