Effect of Mg substitution on hydrogen absorption-desorption behavior and crystal structure of Gd2−xMgxNi7

A plateau region of Gd1.5Mg0.5Ni7 is observed between 0.06 H/M and 0.82 H/M. The reversible hydrogen content in the absorption-desorption cycle is approximately 1.0 H/M. The enthalpy of hydride formation is evaluated as −24 kJ/mol H2 from the Van't Hoff plot. The absorption-desorption behavior is excellent even at low temperatures below 243 K. The hydrogen storage property of Gd1.5Mg0.5Ni7 is markedly improved by Mg substitution.