Microstructure and electrochemical hydrogen storage characteristics of La0.67Mg0.33−xCaxNi2.75Co0.25 (x = 0–0.15) electrode alloys

The microstructure and electrochemical hydrogen storage characteristics of La0.67Mg0.33−xCaxNi2.75Co0.25 (x = 0, 0.05, 0.10 and 0.15) alloys are investigated. The results show that all alloys mainly consist of (La, Mg)Ni3 and LaNi5 phases, besides a small amount of (La, Mg)2Ni7 phase. The cycle stability (S80) after 80 charge/discharge cycles of all alloy electrodes first increases from 60.1% (x = 0) to 64.2% (x = 0.05), then decreases to 45.9% (x = 0.15). The high rate dischargeability of all alloy electrodes first increases from 52.6% (x = 0) to 61.4% (x = 0.10), then decreases to 57.2% (x = 0.15). Moreover, the charge-transfer resistance (Rct) first decreases from 168.2 mΩ (x = 0) to 125.7 mΩ (x = 0.10), then increases to 136.6 mΩ (x = 0.15). All the results indicate that the substitution of Mg with a certain amount of Ca can improve the overall electrochemical characteristics.

Research highlights
► The microstructure of La0.67Mg0.33Ni2.75Co0.25 alloy is almost unchanged by substituting Mg with Ca.
► The cycle life of La0.67Mg0.33Ni2.75Co0.25 alloy is improved by substituting Mg with Ca (x = 0.05).
► The electrochemical kinetics of La0.67Mg0.33Ni2.75Co0.25 alloy is improved by substituting Mg with Ca (x = 0.10).