Structure and electrochemical properties of La2−xMgxNi7.0 (x = 0.3–0.6) hydrogen storage alloys

The structure and electrochemical properties of La2−xMgxNi7.0 (x = 0.3–0.6) alloys were investigated systematically. All alloys consist of a main phase with Ce2Ni7-type structure and a few impurities (mainly LaNi5 and PuNi3-type phase). As Mg content increases, the lattice parameters of unit cell of main phase represent a linear decrease. Equilibrium pressure of alloys during hydrogen absorption/desorption process rises and plateau becomes flatter and broader with the increase of Mg content. Measurements of electrochemical properties reveal that alloy electrode of La1.5Mg0.5Ni7.0 exhibits the best overall electrochemical properties. Linear polarization and electrochemical impedance spectra indicate that the reaction rate of hydrogen for alloy electrode of x = 0.4, 0.5 is better and that charge-transfer resistance is smaller. The experiments of potential-step and anodic polarizations show that hydrogen diffusion in alloy bulk is more important to influence the kinetic character of alloy electrodes.