Thermally prepared Ti/RhOx electrodes: II H2 evolution in acid solution

Abstract

Ti/RhOx electrodes were prepared at 400-600°C by thermal decomposition of Rh chloride. Oxide layers were studied by SEM, cyclic voltammetry and steady-state E-j curves In 0.5 mol dm-3 H2SO4 solution. Voltammetric charge exhibits a maximum at 430°C with fresh electrodes which shifts to 470°C after use for H2 evolution. H2 discharge first produces a decrease in voltammetric charge, then an activation with final settlement to a constant behaviour for "aged" electrodes. H2 evolution on stable RhOx surfaces takes place with 40 mV Tafel slope and a reaction order of 2.5. The fractional reaction order indicates that the surface response to pH is that typical of oxides even for "aged" electrodes. A reaction mechanism is proposed.