Abstract: MgH₂ is widely considered a great potential solid hydrogen storage material along with hydrogen energy and is recognized as a kind of renewable energy. However, its poor hydrogen absorption and desorption kinetics and high thermodynamic stability limit its application. In this work, CeO₂@NC (Nano-Carbon supported CeO₂ particles) nanosphere catalysts were synthesized by a one-step hydrothermal method, and the particle size of CeO₂ was about 7 nm and MgH₂ + x wt.% CeO₂@NC (x = 0, 2, 4, 6, 8) composites were prepared by ball milling. It was found that the generation of oxygen vacancy defects and the multivalent environment of carbon-supported Ce can play the role of hydrogen pump and synergistically catalyze MgH₂. Adding a carbon layer prevents nano-effect generation to a certain extent, which makes H atoms diffuse rapidly. The results show that MgH₂ + 6 wt.% CeO₂@NC can release 5.89 wt.% H₂ in 50 min at 593 K, and MgH₂ without catalyst can only release 0.31 wt.% H₂. As the amount of catalyst added increases, the dehydrogenation activation energy of the composite material decreases by 31.11 kJ/mol H₂. Through density functional theory calculation, it was found that the adsorption energy of the material increased by 1.21 eV after the addition of the catalyst, and the Fermi level of the density of states of the composite increased, which accelerated the electron transfer rate. This study can help workers catalytically modify the hydrogen storage performance of MgH₂. Introducing oxygen vacancy defects in carbon-based supported multivalent transition metal oxide catalysts gives them a unique electronic structure and excellent catalytic activity.

Key words: MgH₂, CeO₂@NC catalyst, Oxygen vacancy, Hydrogen storage kinetics, DFT