Abstract: Although MgH₂ has been widely regarded as a promising material for solid-state hydrogen storage, its high operating temperature and slow kinetics pose a major bottleneck to its practical application. Here, a nanocomposite catalyst with interfacial coupling and oxygen defects, Ni/CeO₂, is fabricated to promote H₂ desorption and absorption properties of MgH₂. The interface of Ni/CeO₂ contributes to both strong mechanical coupling towards stabilizing partial Ni and electronic coupling towards inducing a high concentration of oxygen vacancies in CeO₂. Theoretical calculations evidence that CeO₂ with oxygen vacancy assist Ni in weakening the energy of Mg-H bond as well as enhancing the adsorption energy of Ni upon hydrogen atoms, and the extent of this assistance surprisingly increases with increasing oxygen vacancies concentration. As a result, an impressive performance is achieved by MgH₂-5 wt.% Ni/CeO₂ with onset desorption temperature of only 165 °C, and it absorbs approximately 80% hydrogen in just 800 s at 125 °C. The generation mechanism of intermediate active species concerning Ni/CeO₂ in different states has been analyzed for the first time, and the relationship between interfacial coupling and phase evolution has been elucidated. Therefore, a mechanism of the catalysis-assisting effect regarding oxygen defects is proposed. It is believed that this work provides a unique perspective on the mechanism of interfacial coupling and the generation of defects in composite catalysts.

Key words: Hydrogen storage, Interfacial coupling, Oxygen defects, Catalysis-assisting