The redox behaviour of thermally pretreated, highly disrupted, states of platinum surfaces in aqueous media

Subjecting platinum wire electrodes to short periods (10 to 25 s) of intense heating ( T>ca. 1200°C) in an inert gas atmosphere leads to considerable changes in the surface microstructure of the metal; metastable active states become frozen-in as the temperature of the thermally excited sample drops rapidly to ambient values. Unusual redox responses and, in particular, enhanced premonolayer oxidation peaks in the positive sweep, were observed when such wires were subsequently immersed in aqueous media and investigated using cyclic voltammetry. These unusual responses, which are similar to those reported earlier following prolonged electrochemical activation of platinum (the thermal procedure is much shorter and the behaviour more consistent), were further enhanced by subsequently polarizing the thermally treated samples at low potentials. For a number of reactions and, in particular, methanol oxidation which is important from a fuel cell viewpoint, the electrocatalytic activity of platinum at low potentials was greatly enhanced. However, for other processes, e.g. hydrazine oxidation, thermal pretreatment resulted in a decrease in electrocatalytic activity; it appears that in some cases the active sites become overoxidised. A synopsis is given of the active site behaviour of platinum surfaces in aqueous media and a comparison is made between the present results and those reported elsewhere for platinum single crystal electrodes where similar thermal pretreatment is frequently employed.