Emerging Nitroso/Hydroxylamine Redox Chemistry for High-Performance Organic Cathodes in Aqueous Proton Batteries

Organic cathode materials are emerging candidates for aqueous proton batteries due to their structural tunability and sustainability. However, the simultaneous realization of high voltage, low solubility, and high capacity remains a major challenge. In this study, we introduce a biomimetic redox pair, nitroso/hydroxylamine (─N═O ⇌ ─NH─OH), for the first time in energy storage systems. We report 1-(hydroxyamino)anthracene-9,10-dione (NHOH-A), a rationally designed aromatic hydroxylamine compound capable of undergoing a highly reversible proton-coupled two-electron redox process. Benefiting from its strong hydrogen bonding, uniform charge distribution, and extended π-conjugation, NHOH-A delivers a high discharge voltage of 1.15 V, excellent capacity of 224 mAh g⁻¹, and remarkable cyclability (> 13,000 cycles) when coupled with a Zn anode. Furthermore, leveraging its intrinsic proton-donating capability, we construct a rocking-chair type all-organic proton battery by pairing NHOH-A with an alloxazine anode. The full cell maintains 164 mAh g⁻¹ at 100 C (1 C = 224 mA g⁻¹) and delivers an energy density of 125 Wh kg⁻¹, among the highest for all-organic proton batteries. This work establishes the N═O/NHOH chemistry as a promising redox platform, opening new avenues for developing advanced organic cathodes in energy storage systems.