Hydrogen storage and electrochemical properties of Pr, Nd and Co-free La13.9Sm24.7Mg1.5Ni58Al1.7Zr0.14Ag0.07 alloy as a nickel-metal hydride battery electrode

A Pr, Nd and Co-free A2B7-type alloy, La13.9Sm24.7Mg1.5Ni58Al1.7Zr0.14Ag0.07, was prepared for use as a nickel-metal hydride battery electrode. The structural characteristics and hydrogen-storage and electrochemical properties of La13.9Sm24.7Mg1.5Ni58Al1.7Zr0.14Ag0.07 were investigated in detail. The La13.9Sm24.7Mg1.5Ni58Al1.7Zr0.14Ag0.07 alloy consisted of two phases (La2Ni7 and LaNi5) and showed excellent hydrogen-storage and electrochemical performance. The ΔH and ΔS values of this alloy were 24.4 kJ/mol H2 and 66.2 J/(mol·K), respectively. The high rate dischargeabilities were 97%, 86% and 78%, respectively, at discharge current densities of 330, 970 and 1600 mAh/g. The hydrogen desorption pressure of the La13.9Sm24.7Mg1.5Ni58Al1.7Zr0.14Ag0.07 alloy was 0.005 MPa at 233 K, which is favour for the low temperature discharging. The retention rate maintained a high value of 86.2% after 200 cycles at 1 C.