Mg²⁺ Aliovalent Substitution Coupled Proton-Tuned Desolvation for NH₄ ⁺ Storage Enhancement in α-MoO₃

Aqueous NH₄ ⁺ storage holds great promise but is hindered by its strongly hydrated shell, which elevates the desolvation barrier. Notably, α-MoO₃ stands out for its layered structure and multivalent redox activity, yet its wide bandgap significantly slows down interfacial reactivity. To tackle these challenges, we propose a strategy by integrating host material coupled with electrolyte design. Specifically, Mg²⁺ aliovalent substitution could optimize α-MoO₃ band structure, thereby enhancing its electronic conductivity. Meanwhile, the introduction of a proton-enriched electrolyte disrupts the NH₄ ⁺ solvation shell and reduces the desolvation barrier. Remarkably, the optimized electrode delivers a specific capacity of 239.2 mAh g^-1 at 2 A g^-1 with a capacity retention of 87.8% after 5000 cycles. Moreover, the assembled aqueous symmetric device delivers a high-energy density of 46.7 Wh kg^-1 at 800.6 W kg^-1. In situ/ex situ characterizations and DFT calculations reveal a synergistic NH₄ ⁺/H⁺ costorage mechanism in MMO-A, involving reversible Mo⁶⁺/Mo⁵⁺ transitions, MoO bond evolution and dynamic MoOH formation, as well as increased NH₄ ⁺ adsorption energy and interfacial charge transfer. This work offers insightful design principles and application prospects for advanced aqueous NH₄ ⁺ storage systems.