Electrochemical surface reordering of Pt(1 1 1): A quantification of the place-exchange process

Abstract

Electrochemical oxidation and reduction of well-defined Pt electrodes disorders their surfaces, causing the formation of various types of defects. The underlying place-exchange process has been studied for almost half a century at polycrystalline surfaces, with focus on hysteresis and irreversibility effects in the surface oxidation–reduction voltammetry. Only more recently were the structural aspects of the place-exchange process investigated using advanced in situ techniques. In the present study, a purely electrochemical method for assessing the state of the surface after oxidative treatment is employed. Based on the charges of voltammetric fingerprint signals corresponding to different types of site, the creation and inter-conversion of defects can be followed for various such treatments. Reordering of Pt(1 1 1) first produces disordered defects, presumably ad-atoms, small islands or pits, that are rearranged into more ordered steps if the potential is repeatedly cycled or pulsed. Steps of {1 0 0} orientation are eventually converted into more stable {1 1 0} (equivalently, {1 1 1}) steps. For potential-cycling experiments, this process behaves in accordance with a simple mechanistic model, the parameters of which were fitted to data. The dependence of these constants on the upper potential, together with the potential-dependences of various other place-exchange rate parameters, was investigated. It was also found that disordered terraces contain (1 1 1) domains large enough to adsorb both hydrogen and anions, as well as isolated sites or small ensembles that only adsorb hydrogen.