Ladder‐Type Redox‐Active Polymer Achieves Ultra‐stable and Fast Proton Storage in Aqueous Proton Batteries

Affordable and safe aqueous proton batteries (APBs) with unique “Grotthuss mechanism,” are very significant for advancing carbon neutrality initiatives. While organic polymers offer a robust and adaptable framework that is well‐suited for APB electrodes, the limited proton‐storage redox capacity has constrained their broader application. Herein, a ladder‐type polymer (PNMZ) has been designed via a covalent cycloconjugation conformational strategy that exhibits optimized electronic structure and fast intra‐chain charge transport within the high‐aromaticity polymeric skeleton. As a result, the polymer exhibits exceptional proton‐storage redox kinetics, which are evidenced by in‐operando monitoring techniques and theoretical calculations. It achieves a remarkable proton‐storage capacity of 189 mAh g−1 at 2 A g−1 and excellent long‐term cycling stability, with approximately 97.8% capacity retention over 10,000 cycles. Finally, a high‐performance all‐polymer APB device has been successfully constructed with a desirable capacity retention of 99.7% after 6,000 cycles and high energy density of 56.3 Wh kg−1.