Transition metal-mediated mechanochemical synthesis of size-tunable Mg nanograins with optimized thermodynamics and kinetics for hydrogen storage

Magnesium-based hydrides offer high hydrogen capacity but are often limited by sluggish sorption kinetics and high thermodynamic stability. Herein, transition metal-mediated reactive ball milling (RBM) was adopted to prepare Mg nanograins, with the synergistic size and strain effects for improving kinetics and thermodynamics. Mn, Ti, and Zr were evaluated as milling additives under identical RBM conditions. Mn induces the most pronounced grain refinement where the obtained Mg nanograins exhibit an estimated average characteristic size of ∼45 nm uniformly dispersed within a Mn matrix. The optimized Mg 0.25 Mn 0.75 composites show a better dehydrogenation with onset temperature of 170 °C, accompanied by an apparent activation energy of 110.25 kJ mol −1 and a desorption enthalpy of 73.40 kJ mol −1 H 2 . It reaches a Mg-normalized H 2 absorption capacity of 5.97 wt% at 25 °C and 4.0 MPa in just 11 min, with maintaining capacity of 93% after 50 cycles.