Electrocatalysis of the hydrogen oxidation and of the oxygen reduction reactions of Pt and some alloys in alkaline medium

The objectives of the present study were to find substitutes for platinum as electrocatalysts for alkaline fuel cells. For this purpose, electrode kinetic studies were carried out for the hydrogen oxidation reaction on the metals Pt and Ni and on the alloys PtNi, PtTi and NiTi and for the oxygen reduction on Pt and the alloys PtCr, PtTa and PtCrTa. For economic reasons, the electrodes were in the form of sputtered films on glass discs which could be mounted on the shaft of a rotating disc electrode apparatus. The rotating disc electrode experiments were conducted in 1 N KOH over the temperature range 25–70°C. The cyclic voltammetric technique was used to characterize the electrodes in the potential range of interest for fuel cell reactions. Analyses of the surface and bulk compositions of the alloys were made using Auger electron spectroscopy, electron spectroscopy by chemical analysis or energy dispersive X-ray techniques. Although for the hydrogen oxidation reaction platinum was found to be the best electrocatalyst, Ni and PtTi could be considered as potential substitutes. The results for Pt substitution were more encouraging for the oxygen reduction reaction. The alloy PtCrTa showed a considerably better performance than platinum. This alloy displayed a single Tafel slope (45 mV decade−1) at 55 and 70°C, while two Tafel slopes were observed for all other electrodes. The PtTa alloy also exhibited a better electrode kinetic behavior and like PtCrTa is a potential substitute for Pt for this reaction.