Electride Hydrides with a Distinct Stabilization Mechanism: Anionic Electron Trapping and the Formation of H^δ-@ISQ...

Electrides, characterized by highly localized anionic electrons at interstitial sites (i.e., interstitial quasi-atoms [ISQs]), offer a unique platform with pre-existing electron reservoirs for host-guest chemistry. In this study, the incorporation of hydrogen (H) into the ISQ sites of the electrides Be₂Cu and Be₃Cu was theoretically investigated using first-principles calculations. Unlike conventional hydrides, in which H forms strong chemical bonds with metal atoms, these electride hydrides exhibited a distinct stabilization mechanism: H atoms underwent quantum-mechanical coupling with the ISQ electron cloud, forming H^δ-@ISQ composite states. This interstitial-electron-mediated trapping mechanism explained the anomalous coexistence of a negative hydride formation energy and positive H adsorption energy. Multilevel stability analyses predicted that Be₂CuH₁ and Be₂CuH₂ were thermodynamically and kinetically stable under ambient conditions. A preliminary extension of this study to the experimentally accessible Ca₂N electride further corroborated the broader applicability of the proposed mechanism. Although the Be-Cu system exhibited limited practical H-storage capacity, the mechanism discovered in this study provides a new design principle for developing H storage materials within the electride family, creating opportunities for further computational screening and experimental validation.