HYDRIDE EFFECT ON THE KINETICS OF THE HYDROGEN EVOLUTION REACTION ON NICKEL CATHODES IN ALKALINE MEDIA

The time-dependent hydrogen evolution reaction (HER) on Ni electrodes shows a large increase in electrode overpotential with time. This is ascribed to hydride formation at active Ni cathode surfaces. Hydride formation was detected by x-ray diffraction, morphological changes at the electrode surfaces, and resulting changes in secondary electron emissivities. Nickel electrodes annealed for 2 h in an argon atmosphere at 1000-degrees-C after HER did not show x-ray lines assigned to hydride. On the other hand, hard nickel electrodes (180 HV5/30) show high overvoltages as well as hydride x-ray diffraction lines after HER. By taking the variation of the nickel electronic density of state following hydrogen sorption into account, we are able to satisfactorily explain the increase in nickel overpotential after a few hours of HER.