The impact of vacancy defective MgH2 (001)/(110) surface on the dehydrogenation of MgH2@Ni-CNTs: A mechanistic investigation

The vacancy defect exhibits a remarkable improvement in the dehydriding property of MgH2@Ni-CNTs. However, the corresponding mechanism is still not fully understood. Herein, the impact of vacancy defects on the dehydrogenation properties of MgH2@Ni-CNTs was studied by DFT simulation, and the corresponding models were constructed based on MS. The dehydrogenation process of MgH2 can be regarded as the dissociation of Mg−H and desorption of H2 from the MgH2 surface. In view of the whole dehydrogenation, the dissociation of H– is the rate-determining step, which is the main reason for restricting the dehydrogenation kinetics. Compared with vacancy vacancy-defective MgH2 (001) surface, the appearance of vacancy defects on the (110) surface substantially reduces the energy barrier required for H dissociation to 0.070 Ha. The reason is that vacancy defects accelerate the transition of electrons from the H– s orbit to the Mg2+ 3s orbit, resulting in a decrement of the Mg−H bond strength, which makes H atoms more easily dissociated from the MgH2 (110) surface. Therefore, the existence of vacancy defects improves the dehydriding kinetic of MgH2. Most importantly, this research offers crucial directions for developing hydrogen storage materials as well as a potential fix for the slow dehydrogenation kinetics of nano-confined MgH2.