Study On Hydrogen Storage And Electrochemical Performance Of Re-Mg-Ni Based Compounds

The Re-Mg-Ni based electrode alloys with high discharge capacity, however, the charging-discharging stability unstable than AB5-type electrode alloys. So that, in orde to improve the charging-discharging stability of Re-Mg-Ni based alloys the element substitution method and annealing technique were applied and the hydrogen storage and electrochemical characteristics of Re-Mg-Ni based alloys were studied systemically in this paper.The experiments results showed that (La0.8Nd0.2)2Mg (Ni0.8-xCo0.1 Mn0.1Alx)9 (x=0～0.15) alloys were mainly composed of LaNi5, LaNi3 and LaMg3 phases. With the increasing Al contents hydrogen storage capacity of alloys first increased and then decreased. The maximum discharge capacity reached to 399.2mAh/g(x=0.00) after 1173K annealing, which higher than the as-cast alloys. After 30 charge/discharge cycles, the cyclic capacity retention rate of Annealed alloy electrodes were reached to 95.7%(x=0.15).The XRD analysis showed that (La0.8Nd0.2)2Mg(Ni0.85-xCo0.1MnxAl0.05)9 (x=0～0.15) alloys were mainly composed of La(Ni,Mn,Al)5, La(Nd)2Ni7 and LaMg3 phases. The hydrogen absorption capacity were decreased gradually with Mn content increasing, and the maximum hydrogen adsorption capacity was 1.44wt.%(x=0.00) at 303 K. With the increasing Mn content, the discharge capacity and the cycling stability of alloys electrodes were increased first and then decreased. The maximum discharge capacity of alloy electrodes were reached to 375.96 mAh/g when x=0.05. The cyclic capacity retention rate was increased from 73.5%(x=0) to 92.2%(x=1.0) after 50 charge/discharge cycles.For (La0.8Nd0.2)2Mg(Ni0.85-xCoxMn0.1Al0.05)9 (x=0～0.15) alloys, the XRD analysis showed that the alloys were composed La(Ni,Al)5,LaNi3and LaMg3 phases. The electrochemical investigation results showed that the maximum discharge capacity of alloy electrodes were increased first and then decreased with the increasing of Co content. The hydrogen absorption capacity and charging-discharging cycling stability of alloys electrodes were increased with Co content increasing. The maximum hydrogen absorption capacity was 1.21 wt.% when x=0.15. The cyclic capacity retention rate was increased from 68.3% (x=0) to 93.9% (x=0.15) after 50 charge/discharge cycles, which means that the cycling stability of alloy electrodes were significantly improved by partial substitution of Co for Ni in alloys.