Microstructures and electrochemical characteristics of LaNi_3.70Co_0.2−xMn_0.30Al_0.15Cu_0.65(Mo_0.46Fe_0.54)_x hydrogen storage alloys

Highlights: • Commercial Mo_0.46Fe_0.54 is much cheaper and has lower melting point. • Alloys containing Mo_0.46Fe_0.54 consist of LaNi₅ phase and Mo phase. • Activation property is improved by increasing Mo_0.46Fe_0.54 content. • The alloy with x = 0.15 exhibits the best HRD. • C_max and cycling stability decrease with increasing x value. - Abstract: Electrochemical hydrogen storage properties of LaNi_3.70Co_0.2Mn_0.30Al_0.15Cu_0.65 alloy are improved by substituting Co with Mo_0.46Fe_0.54, rather than pure Mo and Fe. Microstructures and electrochemical properties of LaNi_3.70Co_0.2−xMn_0.30Al_0.15Cu_0.65(Mo_0.46Fe_0.54)_x (x = 0–0.20) hydrogen storage alloys are investigated. X-ray diffraction and backscattered electron results indicate that the pristine alloy is LaNi₅ phase with a hexagonal CaCu₅-type structure, while the alloys containing Mo_0.46Fe_0.54 consist of LaNi₅ matrix phase and Mo secondary phase. The relative abundance of Mo phase increases with the increase in x value. The lattice parameters a, c, c/a and cell volume V of LaNi₅ phase increase with increasing x value. As x increases from 0 to 0.20, maximum discharge capacity of the alloy electrodes monotonically decreases from 335.4 (x = 0) to 324.2 mA h/g (x = 0.20). The high-rate dischargeability of the alloy electrodes at the discharge current density of 1200 mA/g first increases from 59.8% (x = 0) to 69.6% (x = 0.15), and then decreases to 64.0% (x = 0.20). The cycling capacity retention rate at the 100th cycle decreases from 80.4% (x = 0) to 61.9% (x = 0.20), which should be ascribed to the deterioration of the corrosion resistance of alloy electrode with increasing x value