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 of LaNi4.7Sn0.3, La(12x)YxNi4.7Sn0.3 (x 5 0.1, 0.2, and 0.3) and La0.7Y0.3Ni4.6Sn0.3Co0.1 metal hydride electrodes. Alloy characterization included X-ray diffraction, X-ray absorption (XAS), hydrogen absorption in a Sieverts apparatus, and electrochemical cycling of alloy electrodes. The atomic volume of H was determined for two of the alloys. Electrochemical kinetic measurements were made using steady-state galvanostatic measurements, galvanodynamic sweep, and electrochemical impedance techniques. XAS was used to examine the degree of corrosion of the alloys with cycling. Alloying with Y decreased the corrosion rate. The results are consistent with corrosion inhibition by a Y-containing passive film. The increase in the exchange current density of the hydrogen oxidation reaction with increasing depth of discharge was much greater on the Y-containing alloys. This may be due to the dehydriding of the catalytic species on the surface of the metal hydride particles. © 1999 The Electrochemical Society. S0013-4651(99)01-045-9. All rights reserved.