Mg ²⁺ Aliovalent Substitution Coupled Proton‐Tuned Desolvation for NH ₄ ⁺ Storage Enhancement in α‐MoO ₃

Aqueous NH 4 + storage holds great promise but is hindered by its strongly hydrated shell, which elevates the desolvation barrier. Notably, α‐MoO 3 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, Mg 2+ aliovalent substitution could optimize α‐MoO 3 band structure, thereby enhancing its electronic conductivity. Meanwhile, the introduction of a proton‐enriched electrolyte disrupts the NH 4 + 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 NH 4 + /H + costorage mechanism in MMO‐A, involving reversible Mo 6+ /Mo 5+ transitions, MoO bond evolution and dynamic MoOH formation, as well as increased NH 4 + adsorption energy and interfacial charge transfer. This work offers insightful design principles and application prospects for advanced aqueous NH 4 + storage systems.