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

A ladder-type rigid-coplanar polymer with highly ordered molecular arrangement has been designed via a covalent cycloconjugation conformational strategy. Benefitting from the extended π-electron delocalization in the highly aromatic ladder-type polymeric backbone, the prepared polymer exhibits fast intra-chain charge transport along the polymeric chain, realizing extraordinary proton-storage capability 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.