Computational Investigation of MgH₂/NbOx for Hydrogen Storage

Abstract

Hydrogen storage is one of the key challenges for hydrogen economy. Among various storage candidates, magnesium hydride (MgH 2 ) offers excellent storage capacity and cost performance, but its sluggish dehydrogenation hinders its practical applications. This computational work investigated MgH 2 /metal oxides composites (MgH 2 /MOx), focusing on the fundamental understanding on how metal oxide catalysts promote MgH 2 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(δ + ) and H(δ − ) 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 MgH 2 /MOx composites to address the sluggish dehydrogenation issue for the MgH 2 system.

The “burst effect” of hydrogen desorption in MgH2 dehydrogenation

“…AIMD simulations suggested that atomic H in the bulk diffuses only after the complete desorption of surface H. In addition, we found that the Mg–H bond strength continuously reduces with the progress of dehydrogenation, which accelerates H migration and desorption from subsequent layers. This phenomenon, which we assigned as the “burst effect”, provides a solution to the slow dehydrogenation kinetics of MgH 2 and offers essential guidance for designing novel MgH 2 -based composites for efficient hydrogen storage: promoting the initial dehydrogenation of MgH 2 by surface engineering ( e.g ., doping) 52,63,64 could be the key to facilitating hydrogen desorption.…”

Influence of Nanosized CoTiO3 Synthesized via a Solid-State Method on the Hydrogen Storage Behavior of MgH2

“…Among the various solid-state materials explored for hydrogen storage, MgH 2 has been regarded as a viable option to store hydrogen for onboard applications on the strength of its high hydrogen capacity (7.6 wt.%), high energy density (9 MJ/kg) over all the reversible hydrides, and outstanding reversibility [ 15 ]. However, the obstacles of MgH 2 for practical application include high temperature (>400 °C) to release hydrogen, sluggish sorption kinetics, and very stable thermodynamic properties (ΔH = 76 kJ/mol H 2 ) [ 16 , 17 ]. To tackle these drawbacks, several efforts, such as nanostructuring, nanoconfinement, alloying, and the addition of catalyst [ 18 , 19 , 20 , 21 ] have been proposed and developed to modify the Mg-based system performances.…”

Boosting Hydrogen Storage Performance of MgH2 by Oxygen Vacancy-Rich H-V2O5 Nanosheet as an Excited H-Pump

“…Moreover, the possible reaction between MgH 2 and V 2 O 5 would result in the consumption of Mg and continuous degradation of reversible hydrogen storage capacity, which may be ameliorated via the introduction of oxygen vacancies. The computational investigation further demonstrated that partially oxidized transition metal is helpful not only in facilitating hydrogen diffusion but also in reducing the H–H coupling barrier [ 30 – 33 ]. In the case of oxygen vacancy-rich 2D V 2 O 5 nanosheets, the presence of oxygen vacancies could lead to a shift in the position of the Fermi energy level towards the valence band, resulting in an increase in the number of available states for electron transfer.…”