The cross-boundary catalytic effect of anions and cations enhances the hydrogen storage performance of magnesium-based hydrogen storage materials

Abstract

Magnesium-based hydrogen storage materials (MgH2) offer several advantages, including a high hydrogen storage density of up to 7.6 wt% and low production costs, making them highly attractive for solid-state hydrogen storage applications. However, Mg/MgH2 possesses limited dissociation/recombination capability of H2/H-, along with slow hydrogen atom diffusion, leading to sluggish hydrogen storage kinetics and high dehydrogenation enthalpy that limit practical applications. Research has demonstrated that transition metals and their cations exhibit high catalytic selectivity for H2/H-, whereas anions such as F- preferentially adsorb H2 molecules. However, the synergistic effects between cations and anions have remained largely unexplored. To address this gap, the current study proposes a cross-interface catalytic approach aimed at improving the hydriding-dehydriding behavior of MgH2 materials. The partial etching process enables F- to become anchored onto Al3+ within the interlayer of MXene, followed by subsequent pairing with the supported TMx+. The proposed engineered surface provided bidirectional catalysis that actively facilitates both hydriding and dehydriding reactions in Mg/MgH2. Incorporation of Fe3+-V2AlCFx enables Mg to absorb 7.30 wt% of H2 within 8 hours, accompanied by a substantial decrease in the hydrogenation activation energy to 20.5 KJ/mol. During dehydrogenation, interactions between TM and Al-V-F lead to valence state modulation that remained actively involved in promoting H- release and improving H-atom affinity on TM surfaces, and ultimately accelerating their recombination into H2. The described phenomenon subsequently lowers the energy barrier for the MgH2 dissociation reaction to 38.99 KJ/mol. The current study further elucidated the influence of synergistic effects at cation-anion interfaces on the modulation of both dehydrogenation kinetics and thermodynamics in MgH2. Thus, this study provides new prospects for confined-phase transition catalytic systems in metal hydride applications.