Electrochemical and X-ray absorption spectroscopy studies of cobalt coatings on a hydrogen storage alloy

This work reports the results of a study on the effect of electroless surface deposition of Co on physical and electrochemical properties of a metal hydride alloy. Discharge curves obtained for the Co-covered alloy indicate an additional contribution of the Co redox process on the overall discharge capacity of the electrode. There is an increase on the cycle life of the metal hydride alloy on electrodes cycled until a cutoff potential of -800 mV (vs. Hg/HgO KOH 6 mol L-1), although for electrodes cycled until 2700 mV, there is an increase on the degree of the degradation processes. In situ X-ray absorption near-edge structure and extended X-ray absorption fine structure studies conducted at the K-edges of Co and Ni of the coated alloy have shown that there is some metal oxidation after the electrode cycling. There was no significant change in the cobalt environment with the alloy charging, except by an increase on the coordination number. This indicates the presence of a more ordered Co phase in the charged alloy. (C) 2003 The Electrochemical Society.