Effect of Mo content on the microstructures and electrochemical performances of La0.75Mg0.25Ni3.2−xCo0.2Al0.1Mox (x = 0, 0.10, 0.15, 0.20) hydrogen storage alloys

Abstract

La0.75Mg0.25Ni3.2−xCo0.2Al0.1Mox (x = 0, 0.10, 0.15, 0.20) hydrogen storage alloys were synthesized via vacuum induction melting combined with a heat-treatment at 1173 K for 8 h. All alloys have multiphase constitutions including (La, Mg)2Ni7, (La, Mg)5Ni19, LaNi5 phase and there is residual Mo phase in the Mo-added alloys. Increasing Mo content, the abundance of (La, Mg)2Ni7 and (La, Mg)5Ni19 phase with super-lattice stacking structure initially increases and then decreases while that of LaNi5 phase shares a reverse trend. In all Mo-added alloys, Ni is partially substituted by Mo leading to an overall expansion in unit cell volumes. The electrochemical analyses show that the cyclic stability of the alloy electrodes are significantly improved after Mo is added especially when x = 0.15 the cyclic retention is 80.9%, which is 16.4% higher than that of the original one. The maximum discharge capacity are almost unchanged between the alloy electrodes for x = 0 and x = 0.15 while the high-rate discharge ability at the discharge current density of 1500 mA/g is enhanced from 55.2% to 60.1%. The comprehensive electrochemical properties reach a compromise for La0.75Mg0.25Ni3.05Co0.20Al0.10Mo0.15 alloy electrode which possesses remarkably improved cyclic stability, enhanced kinetic property and maintains almost unimpaired discharge capacity in the meanwhile.