Study on the hydrogen storage and electrochemical properties of Mm0.75Mg0.25Ni3.5Co0.2Alx (x = 0.0-0.4) alloys

Mm0.75Mg0.25Ni3.5Co0.2Alx (x = 0.0-0.4) alloys were prepared by the magnetic induction melting method. The influence of Al content on the hydrogen storage and electrochemical properties of the alloy was investigated. The results show that the hydrogen storage capacity is gradually reduced as the Al content increases. The (La,Pr,Nd)Ni5 cell volume and the change of enthalpy also decrease as Al is added. Although the discharge capacity decreases with increasing Al content, the addition of Al can reduce the stability of Mm0.75Mg0.25Ni3.5Co0.2Alx (x = 0.0-0.4) hydride and improve the performance of hydrogen desorption thermodynamics. For the alloy electrode without Al, the maximum discharge capacity (Cmax) and retention discharge capacity after 100 charge-discharge cycles (C100) is 385 mA h g−1 and 202 mA h g−1, respectively. For the alloy electrode with x = 0.4, while Cmax is only 323 mA h g−1, C100 is 273 mA h g−1, which is much higher than that of the alloy without Al. The addition of Al can improve the charge-discharge cycle lifetime effectively and can increase the limiting current IL. The kinetic performance of the Mm0.75Mg0.25Ni3.5Co0.2Alx (x = 0.0-0.4) alloy electrode can also be improved by increasing the Al content.