Influence of temperature on hydrogen electrosorption into palladium-noble metal alloys. Part 2—Palladium–platinum alloys

Abstract

Hydrogen electrosorption into Pd-rich (>75at.% Pd in the bulk) Pd–Pt alloys obtained by electrodeposition was studied in acidic solutions (0.5M H2SO4) using cyclic voltammetry and chronoamperometry. The influence of temperature (in the range between 283 and 328K) on the amount of absorbed hydrogen, the potential of the α–β phase transition, the extent of absorption–desorption hysteresis and the potential of absorbed hydrogen oxidation was examined. It has been found that for the temperature range studied the potentials of the α→β and β→α phase transitions are shifted negatively with both increasing temperature and decreasing Pd content in the alloy bulk. Thermodynamic parameters (Gibbs free energy, enthalpy and entropy) of the β-phase formation and decomposition were determined. With decreasing Pd bulk content the process of the β-phase formation becomes less exothermic and the thermodynamic stability of the β-phase decreases. The maximum hydrogen absorption capacity of Pd–Pt alloys decreases with increasing temperature and decreasing Pd bulk content. The potential of absorbed hydrogen oxidation is shifted negatively with increasing temperature and decreasing Pd bulk content.