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 degrees 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 degrees C. Electrolytically achieved H/Pd stoichiometric ratios were correlated with the corresponding equilibrium hydrogen pressure (pH(2)) using known isotherms of the H-2-Pd system. Electrolytic insertion, equivalent to loading under high pH(2) at 25 degrees C, thus loses its efficiency as temperature increases: the kinetics of the her at Pd explain such behaviour. Nevertheless, up to around 100 degrees C, the Pd hydride electrode still achieved thermodynamic potentials which were much higher than that of H-2 at one atmosphere and the same temperature. (C) 1998 Elsevier Science S.A. All rights reserved.