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

Hydrogen electrosorption into Pd-rich (>75 at.% Pd in the bulk) Pd-Pt alloys obtained by electrodeposition was studied in acidic solutions (0.5 M H2SO4) using cyclic voltammetry and chronoamperometry. The influence of temperature (in the range between 283 and 328 K) 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.