Interfacial Topology Engineering of Self‐Derived TiO ₂ Shells for Nucleation‐Controlled Fast Kinetics in MgH ₂

ABSTRACT Magnesium hydride (MgH ₂ ) is hampered by sluggish kinetics despite its high capacity. Here, we report a solvent‐free, single‐step mechanochemical strategy that drives the in situ reconstruction of titanium oxide acetylacetonate into a self‐derived, high‐coverage TiO ₂ nanolayer on MgH ₂ surfaces. Unlike conventional discrete particle catalysts, this surface‐anchored TiO ₂ phase maximizes the interfacial contact area. Kinetic analysis establishes a direct link between this high‐coverage interfacial topology and nucleation‐governed kinetics: the ubiquitous distribution of interfacial active sites shifts the dehydrogenation mechanism to be primarily controlled by 2D nucleation and growth, while rehydrogenation is initially driven by rapid surface‐chemisorption. Consequently, the composite unlocks exceptional kinetic activity at low temperatures, releasing 4 wt.% H ₂ at 186°C and absorbing 5.8 wt.% H ₂ at 26°C within 10 h, retaining 99% capacity over 100 cycles. Density functional theory elucidates the atomistic origin of this enhancement: the unique TiO ₂ /MgH ₂ band alignment channels electrons from hydrogen vacancies into Ti 3 d states. This interfacial electronic polarization significantly stabilizes hydrogen vacancies and lowers the desorption activation barrier to 81 kJ mol ⁻¹ , validating the interface‐dominated kinetic model. This work demonstrates that interfacial topological engineering via in situ reconstruction is a critical pathway to overcoming the kinetic bottlenecks of solid‐state hydrogen storage.