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 LaNi{sub 4.7}Sn{sub 0.3}, La{sub (1{minus}x)}Y{sub x}Ni{sub 4.7}Sn{sub 0.3}(x = 0.1, 0.2, and 0.3) and La{sub 0.7}Y{sub 0.3}Ni{sub 4.6}Sn{sub 0.3}Co{sub 0.1} metal hydride electrodes. Alloy characterization included X-ray diffraction. X-ray adsorption (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. Allowing 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.