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

•The dehydrogenation process of MgH2 can be regarded as the dissociation of Mg-H and desorption of H2 from MgH2 surface.•The appearance of vacancy defects on the (110) surface significantly reduces the energy barrier required for H dissociation to 0.070 Ha.•Vacancy defects accelerate the transition of electrons from H− s orbit to Mg2+ 3s orbit, resulting in a decrement of the Mg−H bond strength.