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

Subjecting platinum win electrodes to short periods (10 to 25 s) of intense heating (T>ca. 1200 degrees C) in an inert gas atmosphere leads to conside rable 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 particula r, enhanced premonolayer oxidation peaks in the positive sweep, were observ ed when such wires were subsequently immersed in aqueous media and investig ated using cyclic voltammetry. These unusual responses, which are similar t o those reported earlier following prolonged electrochemical activation of platinum (the thermal procedure is much shorter and the behaviour more cons istent), were further enhanced by subsequently polarizing the thermally tre ated samples at low potentials. For a number of reactions and, in particula r, methanol oxidation which is important from a fuel cell viewpoint, the el ectrocatalytic activity of platinum at low potentials was greatly enhanced. However, for other processes, e.g. hydrazine oxidation, thermal pretreatme nt 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 comparis on is made between the present results and those reported elsewhere for pla tinum single crystal electrodes where similar thermal pretreatment is frequ ently employed. (C) 1999 Elsevier Science Ltd. All rights reserved.