Boosting Hydrogen Storage Performance of MgH 2 by Oxygen Vacancy-Rich H-V 2 O 5 Nanosheet as an Excited H-Pump.

MgH2 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 V2 O5 nanosheets (H-V2 O5 ) are specifically designed and used as catalysts to improve the hydrogen storage properties of MgH2 . The as-prepared MgH2 -H-V2 O5 composites exhibit low desorption temperatures (Tonset  = 185 °C) with a hydrogen capacity of 6.54 wt%, fast kinetics (Ea  = 84.55 ± 1.37 kJ mol-1 H2 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 VH2 /V catalysts, unique 2D structure of H-V2 O5 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 MgH2 , but also indirectly affect the activity of the catalytic phase VH2 /V, thereby further boosting the hydrogen storage performance of MgH2 . This work highlights an oxygen vacancy excited "hydrogen pump" effect of VH2 /V on the hydrogen sorption of Mg/MgH2 . The strategy developed here may pave a new way toward the development of oxygen vacancy-rich transition metal oxides catalyzed hydride systems.