Oxide growth dynamics at Pt(111) in absence of specific adsorption: A mechanistic study

A significant number of electrocatalytic reactions take place in a potential region in which the surface of platinum is partly covered by oxygenated species. Hence, the mechanism of the electrochemical formation and reduction of surface oxides is fundamental to understand how surface composition can determine the reactivity of the catalyst. In this paper, combined potential step chronoamperometry and cyclic voltammetry were performed to involve oxide formation and its evolution on Pt(1 1 1), in the absence of anion specific adsorption and keeping surface stability (0.95 < E < 1.1 V). As a first approximation, a simple mean field model scheme is outlined to describe the dynamics of the initial states of the electrochemical oxide growth on Pt(1 1 1). Qualitatively, the whole oxidation process can be properly described by the sequential electrochemical oxidation of water, in such a way that the main features of the cyclic voltammogram and potential step profiles can be explained. The results corroborate the existence of at least two different oxidation states of the surface. The first state is formed through a nucleation and growth mechanism controlled by the rate at which the nuclei are formed, i.e. it follows a progressive nucleation mechanism. The second state is a further ageing process that depends on the potential at which the oxide layer is fully developed. The final oxide film slows down subsequent water dissociation. (C) 2012 Elsevier Ltd. All rights reserved.