Electrochemical properties of LaY2Ni9 hydrogen storage alloy, used as an anode in nickel-metal hydride batteries

The electrochemical properties of LaY2Ni9 alloy used as an anode in nickel-metal hydride batteries were investigated at ambient and at different temperatures. Several techniques, such as the galvanostatic charging and discharging, the constant potential discharge, and the potentiodynamic polarization, were applied to characterize these electrochemical properties. The discharge capacity of the LaY2Ni9 alloy increases to reach 258 mAh g−1 after 5 cycles and decreases to 140 mAh g−1 after 100 cycles then stabilizes around this same value indicating good cycling held. The hydrogen diffusion coefficient DH in the bulky alloy is estimated to be (1.02 ± 0.11) × 10−11 cm2 s−1 correlated with the good stability of electrochemical capacity after 100 cycles. The evolution of the ratio DHa2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \frac{D_{\mathrm{H}}}{a^2} $$\end{document} and the corrosion current density and potential are correlated with the evolution of the electrochemical capacity during the activation and for a long cycling. The enthalpy, the entropy, and the apparent activation energy of the LaY2Ni9 hydride formation are evaluated. The calculated results show that the enthalpy change, the entropy change, and the activation energy are (−42.64 ± 1.08), (56.85 ± 2.11), and (14.84 ± 0.35) kJ mol−1, respectively.