Reaction kinetics and X-ray absorption spectroscopy studies of yttrium-containing metal hydride electrodes

This is a study of electrode degradation mechanisms and reaction kinetics o f LaNi4.7Sn0.3, La(1-x)YxNi4.7Sn0.3 (x = 0.1, 0.2, and 0.3) and La0.7Y0.3Ni 4.6Sn0.3Co0.1 metal hydride electrodes. Alloy characterization included X-r ay diffraction, X-ray absorption (XAS), hydrogen absorption in a Sieverts a pparatus, and electrochemical cycling of alloy electrodes. The atomic volum e of H was determined for two of the alloys. Electrochemical kinetic measur ements were melds using steady-stare galvanostatic measurements, galvanodyn amic sweep, and electrochemical impedance techniques. XAS was used to exami ne the degree of corrosion of the alloys with cycling. Alloying with Y decr eased the corrosion rate. The results are consistent with corrosion inhibit ion by a Y-containing passive film. The increase in the exchange current de nsity of the hydrogen oxidation reaction with increasing depth of discharge was much greater on the Y-containing alloys. This may be due to the dehydr iding of the catalytic species on the surface of the metal hydride particle s. (C) 1999 The Electrochemical Society. S0013-4651(99)01-045-9. All rights reserved.