Synergistically tuned hydrogen storage thermodynamics and kinetics of Mg-Al alloys by Cu formed in situ mechanochemically

Abstract

The high thermodynamic stability and unfavourable sorption kinetics during the formation of Mg hydride restrict its utilization, though Mg is environmentally friendly and abundantly available. In this paper, Cu formed in situ from mechanochemistry was introduced into Mg-Al alloys to tailor their hydrogen storage properties. The results showed that the onset desorption temperature was decreased from 295 °C for as-milled pure MgH2 to 175 °C for as-milled Mg90Al10-Cu. The destabilization of MgH2 was attributed to the formation of Mg-Cu and Mg-Al alloys during dehydriding. The phase structures and thermal analysis showed that the dehydrogenation of MgH2 in the Mg90Al10-Cu was composed of the following three steps: the reaction between MgH2 and Cu to form Mg2Cu as the first step, the reaction between MgH2 and Al to form Al12Mg17 as the second step, and the self-decomposition of the residual MgH2 as the third step. The apparent activation energy for dehydriding was reduced from 148.8 ± 4.91 kJ mol−1 for the as-milled pure MgH2 to 112.1 ± 1.36 kJ mol−1 for the Mg90Al10-Cu. The hydrogen absorption and desorption reaction enthalpies of Mg90Al10-Cu were decreased to 57.5 and 74.0 kJ mol−1 H2, respectively. The results indicated that the Cu formed in situ mechanochemically substantially improved the hydrogen storage thermodynamics and kinetics of Mg90Al10-Cu because the in situ-formed Cu and graphene nanoplates caused particle refinement.