Theoretical and experimental research of hydrogen storage properties of Mg and Mg-Al hydrides

Abstract

In this work, we studied the effect of aluminum atoms addition on the properties of hydrogen accumulation and desorption in magnesium hydride. Using ab initio calculations and experimental methods, the role of alloying magnesium with aluminum was determined. The hydrogen content in the Mg and Mg–10 at%Al coatings was 1.8 wt% and 4.5 wt%, respectively. For the Mg–10 at%Al coating, the peak temperature of hydrogen desorption was about 425 °C, 17 °C lower than that for the Mg coating. The desorption rate for the Mg coating and Mg–10 at%Al coating was 3 × 10−14 mol(H2)/cm2 s and 31 × 10−14 mol(H2)/cm2 s, respectively. Compared with the Mg coating, the higher hydrogen content in the Mg–10 at%Al coating with the faster hydrogen desorption is related to the energetically more favorable Al-doped Mg system than the pure Mg system with H at the distance from Al at low hydrogen concentrations. The lower hydrogen desorption temperature of the Mg–10 at%Al coating is confirmed to be the consequence of the weakened MgH bond by the doped Al atom due to the higher electronegativity of the Al atom than that of the Mg atom. In addition, the aluminum binding energy decreases more significantly with the hydrogen concentration increase for hydrogen near Al atom than for hydrogen at a distance.