Synthesis by reactive ball milling and cycling properties of MgH2–TiH2 nanocomposites: Kinetics and isotopic effects

MgH2, MgH2–TiH2 nanocomposites and their deuterated analogues have been obtained by reactive ball milling and their kinetic and cycling hydrogenation properties have been analysed by isotope measurements and high-pressure differential scanning calorimetry (HP-DSC). Kinetics of material synthesis depends on both Ti-content and the isotopic nature of the gas. For pure Mg, the synthesis is controlled by isotope diffusion in Mg and therefore MgH2 forms faster than MgD2. For the MgH2–TiH2 nanocomposites, the synthesis is controlled by the efficiency of milling. Kinetics of reversible hydrogen/deuterium sorption in nanocomposites have been studied at 548 K. The rate limiting step is isotope diffusion for absorption and Mg/MgH2 interface displacement for desorption. HP-DSC measurements demonstrate that the TiH2 phase acts as a gateway for hydrogen sorption even in presence of MgO and provides abundant nucleation sites for Mg and MgH2 phases. The 0.7MgH2–0.3TiH2 nanocomposite exhibits steady hydrogen storage capacity after 100 cycles of absorption–desorption.