Self-Encapsulated 2D Electrenes: A Promising Platform for Various Emergent Properties

Exploring unreported structural prototypes beyond conventional 2D electrides is crucial to overcome stability-functionality trade-offs and enable controlled interstitial anionic electron (IAEs) exposure. Given the correlation between 2D-distributed IAE configurations and structural topology, we identify MXene-like frameworks as ideal prototypes for electride design. By strategically substituting elements in the structural framework to construct electron-rich systems, we design a family of self-encapsulated electrides M(M'X)₂ featuring interlayer quasi-bonding, where both 0D- and 2D-distributed IAEs are confined within the structure. These materials, with the proposed synthesis through intercalation and high stability demonstrated after considering phase competition, enable controlled electron exposure owing to the low exfoliation energy and possess pseudoanionic electron sublattice dominant band characteristics near the Fermi level. Mg(AlN)₂ emerges as a topological 2D electrene. Ferromagnetic Li(AlN)₂ exhibits phase-dependent semiconducting/metallic characteristics. In addition, bilayer MgAlN obtained by either exfoliating the topmost AlN layer from Mg(AlN)₂ or depositing Mg onto the AlN monolayer demonstrates exceptional transition-metal-free ammonia synthesis activity, especially nitrogen activation activity due to the dual-origin nature of the IAEs, making it an intrinsic catalyst rather than a support. We report an electrene platform that allows for flexible encapsulation and exposure of IAEs. This platform serves as a highly active transition-metal-free catalyst in ammonia synthesis, suggesting promising opportunities for experimental exploration.