Highly efficient ZrH2 nanocatalyst for the superior hydrogenation kinetics of magnesium hydride under moderate conditions: Investigation and mechanistic insights

Magnesium hydride (MgH 2 ) has attracted extensive attention over the past decades due to its highly reversible hydrogen storage density (7.6 wt%). But intrinsic high activation energy barriers for de/rehydrogenation of MgH 2 /Mg restrict its potential application as an on-board hydrogen carrier. Herein, ZrH 2 nanocatalyst homogeneously distributed on the surfaces of MgH 2 exhibits pronounced low temperature de/rehydrogenation kinetics, resulting from the vast lattice distortions between ZrH 2 and MgH 2 /Mg phases. The ZrH 2 doped MgH 2 composite (MgH 2 -ZrH 2 ) starts to release H 2 at 203 °C, 102 °C lower than that of undoped MgH 2 . Most importantly, MgH 2 -ZrH 2 quickly absorbs 5.90 wt% H 2 at the temperature as low as 65 °C. Further deep investigations found that H atoms preferentially accumulates around ZrH 2 , since the lower hydrogen dissociation energy on the surfaces of ZrH 2 (1.421 eV) than that of pure Mg (2.301 eV). Then, the large lattice disordered zone between ZrH 2 and Mg phases enables H atoms diffuse easily into the lattice of Mg nearby, thus triggering the formation of MgH 2 . These findings are critically important to understand the mechanism of other metal hydride catalysts, as well as offer an opportunity for the practical on-board fuel cell applications in the future.