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% H3PO 4 electrolyte. At each temperature reduction of the H3PO4 molecule cou ples with the hydrogen evolution reaction (her): although this poses n o problem to hydrogen insertion, it may lead to Pd cathode deactivatio n at 175 degrees C. Electrolytically achieved H/Pd stoichiometric rati os were correlated with the corresponding equilibrium hydrogen pressur e (pH(2)) using known isotherms of the H-2-Pd system. Electrolytic ins ertion, equivalent to loading under high pH(2) at 25 degrees C, thus l oses 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 whi ch were much higher than that of H-2 at one atmosphere and the same te mperature. (C) 1998 Elsevier Science S.A. All rights reserved.