Hydrogen Release From Silicon─Hydrogen Systems: From Surface Chemistry to Higher-Coordinate Molecular Mechanisms

Hydrogen release from silicon-hydrogen systems spans a field ranging from extended silicon materials to discrete molecular compounds. Across these regimes, Si─H activation and H₂ evolution arise from the interplay of structure, coordination environment, and access to reactive geometries. In extended silicon systems, hydrogen release is governed by structure-dependent recombinative desorption processes. Zintl phases bridge solid-state and molecular silicon chemistry by enabling transfer of polyanionic silicon units into solution, thereby providing access to discrete Si─H reactivity. In molecular systems, metal-mediated and metal-free pathways contribute to hydrogen release, including oxidative addition, σ-bond metathesis, electrophilic activation, cooperative heterolysis, and donor-assisted Si─H activation. These mechanistic manifolds form a continuum in which variations in coordination environment and electronic structure determine whether dehydrocoupling, hydrogen transfer, or bond-forming processes dominate. A recurring mechanistic feature is the involvement of higher-coordinate silicon species. However, productive H₂ evolution depends on their formation, but also on the ability of the silicon framework to access reactive geometries through fluxional behavior and dynamic permutational isomerism. Overall, silicon-based hydrogen-release chemistry illustrates how structure, coordination, and molecular dynamics collectively govern bond activation and hydrogen evolution, providing a conceptual basis for the design of silicon-based hydrogen storage and release systems.