Synergistic Dynamic Hydrogen-Bond Engineering in COF Cathode and Hydrogel Electrolyte for Durable NH₄ ⁺ Storage

Aqueous ammonium-ion batteries (AAIBs) have garnered considerable attention for sustainable energy storage, leveraging the rapid diffusion kinetics of NH₄ ⁺ ions enabled by Grotthuss-type proton transport through reversible hydrogen-bonding interactions. Nevertheless, their practical deployment is often constrained by irreversible side reactions and structural degradation from conventional liquid electrolytes and inorganic cathodes. Herein, we report a dual-zone design strategy of integrating a tailored hydrogel electrolyte with a redox-active covalent organic framework (COF) cathode to promote durable NH₄ ⁺ storage in AAIBs. In the electrolyte, a pH-modulated polyacrylamide-based hydrogel electrolyte with a uniform 3D network suppresses anion-induced salting-out effects and facilitates dynamic hydrogen-bond-enabled NH₄ ⁺ migration. Complementarily, a hexaazatrinaphthalene (HATN)-based COF (HATN-COF) cathode with abundant C═O/C═N groups provides multiple reversible hydrogen-bonding sites for stable NH₄ ⁺ storage. As expected, the assembled cell achieves a high initial capacity of 420 mAh g^-1 at 0.05 A g^-1 and retains a high reversible capacity of 126 mAh g^-1 at 2 A g^-1 with 70.8% capacity retention after 1300 cycles. This work demonstrates that the dual-zone design strategy holds great potential for advancing high-performance AAIBs.