Structure and hydrogen storage properties of AB3-type Re2Mg(Ni0.7 − xCo0.2Mn0.1Alx)9 (x = 0‒0.04) alloys

Re 2 Mg(Ni 0.7 −  x Co 0.2 Mn 0.1 Al x ) 9 ( x  = 0‒0.04) alloys are prepared by induction melting, and the influence of the partial substitution of Ni by Al on the structure, hydrogen storage, and electrochemical properties of the alloys are investigated systematically. These alloys mainly consist of two main phases with LaNi 5 phase and (La,Mg) 2 Ni 7 phase, and minor LaNi 2 phase. The pressure-composition isotherms shows that, with Al content increasing in the alloys, the maximum hydrogen storage capacity decreased from 1.16 wt% ( x  = 0) to 0.99 wt% ( x  = 0.04). The changes of enthalpy and entropy reveal that the thermodynamic stability and the disordered degree of the hydride alloys increase with the Al addition. Results of electrochemical studies indicate that the substitution of Al for Ni can noticeably improve the cycle stability of the alloy electrode. The capacity retention after 80 cycles is enhanced from 63.6% ( x  = 0) to 76.5% ( x  = 0.04). However, the maximum discharge capacity of the alloys decreases. The Re 2 Mg(Ni 0.7 −  x Co 0.2 Mn 0.1 Al x ) 9 ( x  = 0‒0.04) alloys exhibit excellent dischargeability.