Assisting molybdenum trioxide catalysis by engineering oxygen vacancy for enhancing hydrogen storage performance of magnesium hydride

Magnesium hydride (MgH₂) as an ideal hydrogen storage carrier whose hydrogen storage performance can be effectively improved by transition metal-based catalysts. To construct highly active catalysts, much attention has been paid to the regulation of transition metal components while less attention has been paid to non-transition metal components especially oxygen, leading certain limitations. Herein, further improved hydrogen storage performance of MgH₂ can be obtained by adjusting oxygen vacancy content in molybdenum trioxide (MoO₃) catalyst. Specifically, compared with pure MgH₂ (1.1 wt%) and MgH₂-10 wt% MoO₃ (4.5 wt%), more hydrogen (5.9 wt%) can be released by MgH₂-10 wt% MoO_3-x (MoO₃ with abundant oxygen vacancies) at 300.0 °C within 499.0 s. Besides, superb capacity retention (6.1 wt%, 99.0 %) after 50 isothermal hydrogen ab/desorption cycles can be obtained for MgH₂-10 wt% MoO_3-x. Through rigorous comparative experiments and theoretical calculations, the excellent catalytic activity of MoO_3-x is demonstrated to come from the abundant oxygen vacancies and the active substances (polyvalent Mo and nano-sized MgO) it assists to form during ball milling process. This work verifies the feasibility for further improving the catalytic activity of transition metal-based catalysts by tuning non-transition metal elements and thus provides a new strategy in catalyzed MgH₂ system.