Influence of Mo0.46Fe0.54 content in La0.7Ce0.3Ni4.2Mn0.9Cu0.3 Alloy for Hydrogen Ion Storage in Nickel–metal Hydride Battery

Abstract

The electrochemical hydrogen storage properties of a La0.7Ce0.3Ni4.2Mn0.9Cu0.3 hydrogen storage alloy were studied by displacing Mn with a commercial Mo0.46Fe0.54 alloy rather than a single molybdenum or single iron element. The microstructures and electrochemical properties of La0.7Ce0.3Ni4.2Mn0.9-xCu0.3(Mo0.46Fe0.54)x (x = 0–0.20) alloys were studied by X-ray diffraction and backscattered electron and electrochemical measurements, respectively. The results showed that a single LaNi5 phase with a hexagonal CaCu5-type structure existed in the pristine alloy. The La0.7Ce0.3Ni4.2Mn0.9-x Cu0.3(Mo0.46Fe0.54)x (x = 0–0.20) alloys had a multiphase structure: Besides the main LaNi5 phase, a small number of new molybdenum segregated phases were observed as well. With the decrease of the x value, the lattice parameters a, c, c/a and cell volume V of the LaNi5 matrix phase increased. While the x value increased from 0 to 0.20, the maximum discharge capacities (Cmax) of the La0.7Ce0.3Ni4.2Mn0.9-xCu0.3(Mo0.46Fe0.54)x (x = 0–0.20) alloy electrode material gradually decreased from 332.5 mAh.g-1 (x =0) to 310.2 mAh.g-1 (x=0.20). When the discharge current density was 1200 mA g-1, the high-rate dischargeability (HRD) of the La0.7Ce0.3Ni4.2Mn0.9-xCu0.3(Mo0.46Fe0.54)x (x = 0–0.20) alloy electrode material first increased from 51.6% (x = 0) to 63.6% (x = 0.10) and then decreased to 55.4% (x = 0.20). This was in line with the changing trend of the hydrogen diffusion coefficient, which illustrated that the kinetic characteristics are dominated by the hydrogen atom diffusion process in most alloys. The cycling capacity retaining rates (Sn) at the 100th charge/discharge cycle decreased gradually from 79.3% (x = 0) to 62.6% (x = 0.20), which was likely due to the deterioration of the corrosion resistance of the La0.7Ce0.3Ni4.2Mn0.9-xCu0.3(Mo0.46Fe0.54)x (x = 0–0.20) alloy electrode material in the process of charging/discharging.