Boosting Hydrogen Storage Performance of MgH by Oxygen Vacancy-Rich H-VO Nanosheet as an Excited H-Pump.

MgH is a promising high-capacity solid-state hydrogen storage material, while its application is greatly hindered by the high desorption temperature and sluggish kinetics. Herein, intertwined 2D oxygen vacancy-rich VO nanosheets (H-VO) are specifically designed and used as catalysts to improve the hydrogen storage properties of MgH. The as-prepared MgH-H-VO composites exhibit low desorption temperatures (T = 185 °C) with a hydrogen capacity of 6.54 wt%, fast kinetics (E = 84.55 ± 1.37 kJ mol H for desorption), and long cycling stability. Impressively, hydrogen absorption can be achieved at a temperature as low as 30 °C with a capacity of 2.38 wt% within 60 min. Moreover, the composites maintain a capacity retention rate of ~ 99% after 100 cycles at 275 °C. Experimental studies and theoretical calculations demonstrate that the in-situ formed VH/V catalysts, unique 2D structure of H-VO nanosheets, and abundant oxygen vacancies positively contribute to the improved hydrogen sorption properties. Notably, the existence of oxygen vacancies plays a double role, which could not only directly accelerate the hydrogen ab/de-sorption rate of MgH, but also indirectly affect the activity of the catalytic phase VH/V, thereby further boosting the hydrogen storage performance of MgH. This work highlights an oxygen vacancy excited "hydrogen pump" effect of VH/V on the hydrogen sorption of Mg/MgH. The strategy developed here may pave a new way toward the development of oxygen vacancy-rich transition metal oxides catalyzed hydride systems.