Phase transition and hydrogen storage properties of Mg-Ga alloy

Mg-based alloys are viewed as one of the most promising candidates for hydrogen storage; however, high desorption temperature and the sluggish kinetics of MgH2 hinder their practical application. Alloying and changing the reaction pathway are effective methods to solve these issues. As the solid solubility of Ga in Mg is 5 wt% at 573 K, the preparation of a Mg(Ga) solid solution at relatively high temperatures was designed in this paper. The phase transition and hydrogen storage properties of the MgH2 and Mg5Ga2 composite (hereafter referred to as Mg-Ga alloy) were investigated by X-ray diffraction (XRD), pressure-composition-isotherm (PCI) measurements, and differential scanning calorimetry (DSC). The reversible hydrogen storage capacity of Mg-Ga alloy is 5.7 wt% H2. During the dehydrogenation process of Mg-Ga alloy, Mg2Ga reacts with MgH2, initially releasing H2 and forming Mg5Ga2; subsequently, MgH2 decomposes into Mg with further release of H2. The phase transition mechanism of the Mg5Ga2 compound during the dehydrogenation process was also investigated by using in situ XRD analysis. In addition, the dehydrogenation enthalpy and entropy changes, and the apparent activation energy were also calculated.