The effects of crystalline defects on hydrogen absorption kinetics of catalyzed MgH2 at ambient conditions

The high operation temperature has limited the practical applications of magnesium hydride. Although several techniques can significantly improve Mg hydride`s high-temperature de/hydrogenation properties, the hydrogenation performance at relatively low temperatures degrades rapidly during cycling. Herein, we study the hydrogenation kinetics under ambient temperature after specific cycle numbers, and the microstructural evolution of the catalyzed Mg hydride during hydrogen sorption cycling. The results show that the average crystallite size increases with the increase of cycle numbers, and the dislocation density and microstrain decrease. However, the hydrogenation kinetic rate can be restored by subjecting the performance-degraded sample to an ultra-high-energy high-pressure planetary ball mill again. This suggests that the nanocrystalline structure with a high concentration of defects in the ball-milled Mg-based material is critical for achieving a good kinetic rate of hydrogen adsorption at room temperature. Furthermore, defect concentration effects on hydrogen absorption are more significant than crystallite size. This result provides a direction for improving Mg-based hydrogen storage materials for practical application.