Single-Atom Ni Supported on TiO 2 for Catalyzing Hydrogen Storage in MgH 2 .

As an efficient and clean energy carrier, hydrogen is expected to play a key role in future energy systems. However, hydrogen-storage technology must be safe with a high hydrogen-storage density, which is difficult to achieve. MgH 2 is a promising solid-state hydrogen-storage material owing to its large hydrogen-storage capacity (7.6 wt %) and excellent reversibility, but its large-scale utilization is restricted by slow hydrogen-desorption kinetics. Although catalysts can improve the hydrogen-storage kinetics of MgH 2 , they reduce the hydrogen-storage capacity. Single-atom catalysts maximize the atom utilization ratio and the number of interfacial sites to boost the catalytic activity, while easy aggregation at high temperatures limits further application. Herein, we designed a single-atom Ni-loaded TiO 2 catalyst with superior thermal stability and catalytic activity. The optimized 15wt%-Ni 0.034 @TiO 2 catalyst reduced the onset dehydrogenation temperature of MgH 2 to 200 °C. At 300 °C, the H 2 released and absorbed 4.6 wt % within 5 min and 6.53 wt % within 10 s, respectively. The apparent activation energies of MgH 2 dehydrogenation and hydrogenation were reduced to 64.35 and 35.17 kJ/mol of H 2 , respectively. Even after 100 cycles of hydrogenation and dehydrogenation, there was still a capacity retention rate of 97.26%. The superior catalytic effect is attributed to the highly synergistic catalytic activity of single-atom Ni, numerous oxygen vacancies, and multivalent Ti x+ in the TiO 2 support, in which the single-atom Ni plays the dominant role, accelerating electron transfer between Mg 2+ and H - and weakening the Mg-H bonds. This work paves the way for superior hydrogen-storage materials for practical unitization and also extends the application of single-atom catalysis in high-temperature solid-state reactions.