Improving the hydrogen storage properties of MgH2 by reversibly forming Mg–Al solid solution alloys

•Supersaturated Mg–Al solid solution alloys are prepared by ball milling.•Lattice constants of Mg are reduced by dissolving of Al.•Reversible de/hydriding mechanisms of Mg–Al solid solution and Mg17Al12 are revealed.•Thermodynamics and kinetics of MgH2 are improved by forming Mg–Al solid solution alloys.

Supersaturated Mg(Al) solid solutions with reduced lattice constants were successfully prepared by ball milling Mg and Al powder mixtures. The microstructure and phase transition were investigated by XRD. The results indicated that disproportionation of supersaturated Mg(Al) solid solution to MgH2 and Al was caused by hydrogenation, then equilibrium Mg(Al) solid solution formed after dehydrogenation, while the intermetallic compound Mg17Al12 reversibly decomposed to MgH2 and intermediate phase Al3Mg2 which could further decompose to MgH2 and Al by hydriding. These reversible phase transitions make Mg–Al alloys show an observably lowered de/hydriding enthalpy and activation energy in comparison with pure Mg.