Effects of temperature on hydrogen absorption into palladium hydride electrodes in the hydrogen evolution reaction

On the basis of the Volmer-Tafel route of the hydrogen evolution reaction, and thermokinetic considerations involving H-H interactions and stress fields of hydrogen in beta-PdHx, we discuss the analytical and numerical effects of temperature on the loading ratio, charging rate and self-stress for hydrogen absorption into electrodes of beta-phase PdHx under galvanostatic and potentiostatic charging conditions. It was found that changes in the loading ratio, overpotential and current density with temperature can be expressed in terms of four parameters, i.e. enthalpies of adsorption and absorption of hydrogen on (into) palladium, and apparent activation energies of exchange current density of the Volmer and Tafel reactions, in addition to the usual physical quantities such as temperature and overpotential etc., although more factors are involved in the actual process. With increasing temperature, the absorption process tends to be determined by the surface reaction and the self-stresses decrease under the galvanostatic charging condition; however, the absorption time decreases but the self-stresses change slightly for the potentiostatic charging. Finally, our theory is consistent with the available experimental results. (C) 2000 Elsevier Science S.A. All rights reserved.