Computational Investigation of MgH2/NbOx for Hydrogen Storage

Hydrogen storage is one of the key challenges for hydrogen economy. Among various storage candidates, magnesium hydride (MgH2) offers excellent storage capacity and cost performance, but its sluggish dehydrogenation hinders its practical applications. This computational work investigated MgH2/metal oxides composites (MgH2/MOx), focusing on the fundamental understanding on how metal oxide catalysts promote MgH2 dehydrogenation. Using NbOx as an example, our first-principles calculations demonstrated that (i) both Nb and O can interact with surface oxygen, generating a stable local state (LS) and resulting in a low-barrier desorption path; (ii) adsorbed Nb and O show a strong synergetic effect on hydrogen diffusion and desorption; and (iii) a similar promotion mechanism has been confirmed in other metal oxides, including VOx and TiOx. Critically, it is found that hydrogen shows negative and positive charges over metal and oxygen, respectively; consequently, H(delta(+)) and H(delta(-)) present static attraction and lower the barrier for H-2 formation. Given that metal oxides have been experimentally employed as dehydrogenation catalysts for years, the computational understanding can serve as a guideline for advanced rational design of MgH2/MOx composites to address the sluggish dehydrogenation issue for the MgH2 system.