Effect of temperature on electrolytic loading of hydrogen into palladium

The electrolytic insertion of hydrogen into palladium was investigated in the temperature range from 25 to 175°C in 85 and 100% H3PO4 electrolyte. At each temperature reduction of the H3PO4 molecule couples with the hydrogen evolution reaction (her): although this poses no problem to hydrogen insertion, it may lead to Pd cathode deactivation at 175°C. Electrolytically achieved H:Pd stoichiometric ratios were correlated with the corresponding equilibrium hydrogen pressure (pH2 ) using known isotherms of the H2-Pd system. Electrolytic insertion, equivalent to loading under high pH2 at 25°C, thus loses its efficiency as temperature increases: the kinetics of the her at Pd explain such behaviour. Nevertheless, up to around 100°C, the Pd hydride electrode still achieved thermodynamic potentials which were much higher than that of H2 at one atmosphere and the same temperature. © 1998 Elsevier Science S.A. All rights reserved.