Engineering Hydrogen Transport Networks in Mg-Based Solid-State Hydrogen Storage: From Activated Interfaces to Hierarchical Architectures.

Magnesium-based materials remain among the most intensively studied solid-state hydrogen storage systems because they combine high theoretical hydrogen capacity, elemental abundance, and comparatively low cost. Yet their practical performance is still constrained by sluggish sorption kinetics, difficult hydrogen release, surface passivation, and transport instability under repeated cycling. This perspective argues that these long-standing limitations are most coherently understood not as isolated thermodynamic or kinetic problems, but as a multiscale hydrogen transport-network problem. In this view, hydrogen storage performance depends on whether hydrogen can be admitted, transferred, redistributed, and released through a sufficiently continuous and durable sequence of interfaces, phases, defects, and microstructural pathways. The discussion therefore moves from activated interfaces, which govern hydrogen entry, to phase-network engineering, in which alloying reorganizes internal transport connectivity, and then to hierarchical architectures, where porous hosts, scaffolded secondary phases, and multicomponent microstructures amplify transport efficiency across scales. The perspective further emphasizes that these material-internal transport advantages become meaningful only when they remain compatible with heat and mass transfer at the level of a working storage body and device. Possible descriptors, including active-interface density, connected phase fraction, effective diffusion length, pathway tortuosity, apparent network efficiency, and rate retention during cycling, are further discussed to make this framework more operational. On this basis, the article proposes that future progress in Mg-based hydrogen storage will depend less on isolated optimization of additives or descriptors and more on the deliberate design of connected hydrogen transport networks from the atomic and interfacial scales to the system scale.