Revealing the effects of NbHx (x = 1, 2)/MgH2 interfaces on the dehydrogenation of MgH2 from first-principles

Abstract

The practical application of magnesium hydride (MgH₂) for solid-state hydrogen storage is hindered by high dehydrogenation temperatures and sluggish hydrogen absorption/desorption kinetics. Previous studies have demonstrated that pure niobium and its compounds can significantly enhance the hydrogen storage properties of MgH₂, likely due to the formation of niobium hydrides during the hydrogen absorption/desorption process. In this study, interface models were constructed to provide insight into the influence of niobium hydrides on hydrogen desorption from MgH₂. A first-principles approach was employed to investigate the structural, electronic, and energetic properties of the NbH_x(110)/MgH₂(110) (x = 1, 2) interfaces. The results indicate that the disordered NbH(110)/MgH₂(110) interface is more stable than the ordered NbH₂(110)/MgH₂(110) interface. For both interfaces, the dehydrogenation energy in the interface zone is significantly lower than that of bulk MgH₂, facilitating hydrogen desorption from thermodynamics. Regarding dehydrogenation kinetics, the diffusion behavior of H atoms in the MgH₂ phase in the interface region was studied using ab initio molecular dynamics simulations. By analyzing the mean square displacement and trajectories of H atoms, we found that niobium hydrides can directly promote hydrogen desorption from MgH₂, and hydrogen diffusion in both interface systems predominantly occurs within the interface plane. Furthermore, the NbH(110)/MgH₂(110) interface exhibits a notable enhancement in dehydrogenation compared to the NbH₂(110)/MgH₂(110) interface.