MgH2/single-atom heterojunctions: effective hydrogen storage materials with facile dehydrogenation

Abstract

Magnesium hydride (MgH₂) is considered as a promising solid-state hydrogen storage material due to its high hydrogen storage mass density and environmental friendliness. However, its sluggish dehydrogenation kinetics are still the bottleneck that restricts practical applications. To address this challenge, very recent pioneering experiments found that MgH₂/single-atom catalyst (MgH₂/SAC) heterojunctions can be promising candidates for hydrogen storage. However, the reaction mechanism and design guideline were still not well understood. Herein, we design and analyze MgH₂/SAC heterojunction systems including nine 3d transition metals, using spin-polarized density functional theory calculations with van der Waals corrections. We found that the energy barriers of MgH₂ dehydrogenation are significantly reduced by 0.51–2.22 eV through the promotion effects of a heterojunction. Using ab initio molecular dynamics simulations, these promotion effects were analyzed in depth based on the observation of hydrogen diffusion behaviors. To provide further insights, the electron localization function, charge density difference, hydrogen adsorption energy, system electronegativity, d-band center, and crystal orbital Hamilton population were comprehensively analyzed to understand the origin of the high performance of MgH₂/SACs. In particular, we found that the system electronegativity of SACs can act as an effective descriptor that predicts the dehydrogenation energy barriers. Most importantly, this study provides important design guidelines of a brand-new type of MgH₂/SAC material and a promising solution to the sluggish kinetics of MgH₂ dehydrogenation in hydrogen storage.