Highly redox-active polymer with extensive electron delocalization and optimized molecular orbitals for extraordinary proton storage

•A redox-active and π-electron delocalized polymer material is constructed with extended imine-conjugation.•Optimized molecular orbital endows an extremely small LUMO value of −3.26 eV in the polymer material.•Such polymer electrode shows large proton-storage capacity and long-term stability over 10,000 cycles.•Proton-storage redox behaviors are elucidated by multiple in-operando techniques and theoretical calculations.•A soft-package aqueous proton battery (APB) is constructed with reliable performances.