The characterization of Pt/Sn catalyst for the electrochemical oxidation of methanol

Pt/Sn electrodeposited catalysts have been prepared, characterized and tested for the electro-oxidation of methanol. Catalyst activities were measured in 3 M H2SO4 electrolyte between ambient temperature and 95°C. Enhancement in specific activity by a factor of about 50 was found over electrodeposited platinum black. This behaviour is in contrast to that of alloys of platinum and tin which were found to have very low activities compared with platinum catalysts and to be readily corroded in H2SO4 electrolyte. ESCA (electron spectroscopy for chemical analysis) studies and Mossbauer spectroscopy showed the majority of the tin in the deposit to be present in an oxidized form. A small amount (∼17%) was present as a dilute alloy of tin in platinum. Surface area measurements and X-ray powder diffraction indicated that the increase in activity over platinum black was not attributable to smaller platinum particle size. It seems that the combination of platinum and tin results in a decrease in the poisoning effect by strongly adsorbed organic residues. Whether this arises from the operation of a cyclic Sn(II)/Sn(IV) redox system or from modification of the platinum surface remains unresolved.