Effect of Substitutional Elements on the Thermodynamic and Electrochemical Properties of Mechanically Alloyed La1.5Mg0.5Ni7−xMx alloys (M = Al, Mn)

The A2B7-type La-Mg-Ni-M-based (M = Al, Mn) intermetallic compounds were produced by mechanical alloying and annealing. The thermodynamic and electrochemical properties of these materials were studied. The nickel substitution by aluminum and manganese in the La-Mg-Ni system improves the kinetics of hydrogen absorption. The hydrogen desorption capacity of Mn substituted compounds is improved significantly, and it reaches the value of 1.79 wt.% at 303 K when the composition is La1.5Mg0.5Ni6.80Mn0.20. On the other hand, the La1.5Mg0.5Ni6.85Al0.15 shows a much higher reversible electrochemical capacity than the La1.5Mg0.5Ni7 materials at the 50th cycle. The electrochemical discharge capacity stability increases with the increasing value of Al and Mn up to x = 0.2 and 0.3, respectively. Additionally, a reduction in the discharge capacity was measured for the Al and Mn content above x = 0.25 and 0.5, respectively. From the practical aspect, only La1.5Mg0.5Ni6.80Mn0.20 has a potential in the application as a hydrogen storage material.