Oxygen Vacancy-Rich 2D TiO2 Nanosheets: A Bridge Toward High Stability and Rapid Hydrogen Storage Kinetics of Nano-Confined MgH2

MgH₂ has attracted intensive interests as one of the most promising hydrogen storage materials. Nevertheless, the high desorption temperature, sluggish kinetics, and rapid capacity decay hamper its commercial application. Herein, 2D TiO₂ nanosheets with abundant oxygen vacancies are used to fabricate a flower-like MgH₂/TiO₂ heterostructure with enhanced hydrogen storage performances. Particularly, the onset hydrogen desorption temperature of the MgH₂/TiO₂ heterostructure is lowered down to 180 °C (295 °C for blank MgH₂). The initial desorption rate of MgH₂/TiO₂ reaches 2.116 wt% min^-1 at 300 °C, 35 times of the blank MgH₂ under the same conditions. Moreover, the capacity retention is as high as 98.5% after 100 cycles at 300 °C, remarkably higher than those of the previously reported MgH₂-TiO₂ composites. Both in situ HRTEM observations and ex situ XPS analyses confirm that the synergistic effects from multi-valance of Ti species, accelerated electron transportation caused by oxygen vacancies, formation of catalytic Mg-Ti oxides, and stabilized MgH₂ NPs confined by TiO₂ nanosheets contribute to the high stability and kinetically accelerated hydrogen storage performances of the composite. The strategy of using 2D substrates with abundant defects to support nano-sized energy storage materials to build heterostructure is therefore promising for the design of high-performance energy materials.