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

Magnesium hydride (MgH2) 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 MgH2/Mg restrict its potential application as an on-board hydrogen carrier. Herein, ZrH2 nanocatalyst homogeneously distributed on the surfaces of MgH2 exhibits pronounced low temperature de/rehydrogenation kinetics, resulting from the vast lattice distortions between ZrH2 and MgH2/Mg phases. The ZrH2 doped MgH2 composite (MgH2-ZrH2) starts to release H-2 at 203 degrees C, 102 degrees C lower than that of undoped MgH2. Most importantly, MgH2-ZrH2 quickly absorbs 5.90 wt% H-2 at the temperature as low as 65 degrees C. Further deep investigations found that H atoms preferentially accumulates around ZrH2, since the lower hydrogen dissociation energy on the surfaces of ZrH2 (1.421 eV) than that of pure Mg (2.301 eV). Then, the large lattice disordered zone between ZrH2 and Mg phases enables H atoms diffuse easily into the lattice of Mg nearby, thus triggering the formation of MgH2. 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.

Automated summary

The study enhanced the low temperature de/rehydrogenation kinetics of MgH2 by uniformly distributing ZrH2 nanocatalyst on its surface, lowering the temperature for hydrogen release and accelerating hydrogen absorption. It was found that H atoms preferentially accumulate around ZrH2, and the lattice disordered region between ZrH2 and Mg phases facilitates H atom diffusion into the Mg lattice.