A Molten Alkali Approach to Tailor Hydroxyl Groups of Hexaazatrinaphthalene Toward High‐Capacity and Low‐Potential Anode of Aqueous Proton Batteries

Abstract Hexaazatrinaphthalene (HATN) has attracted a lot of attention in aqueous proton batteries (APBs). However, its redox potential as an anode is insufficiently negative. The introduction of electron‐donating substituent groups, such as hydroxyl groups, is considered as a good approach to reduce the redox potential of HATN. Nevertheless, manufacturing hydroxyl‐substituted HATN (HATN‐OH) requires either expensive precursors or multi‐step process, limiting their research. Herein, a straightforward strategy is proposed to synthesize HATN‐OH based on the nucleophilic substitution reaction of halogenated HATN in a molten alkali. The redox potential of 1,2,7,8,13,14‐hexahydroxy‐5,6,11,12,17,18‐hexaazatrinaphthalene (34‐HATN‐6OH) electrode may be lowered by 0.15 V in comparison to HATN, and exhibits a high specific capacity, low redox potential, remarkable rate capability, and outstanding long‐term cycling performance. The electrochemical redox kinetics is significantly enhanced owing to the formation of rapid proton transport channels created by intermolecular hydrogen bond network. The assembled MnO ₂ ||34‐HATN‐6OH full battery delivers a high discharge voltage (1.16 V) and cycling stability (74% capacity retention after 5000 cycles). This study provides a general cost‐effective molten alkali approach for the synthesis of hydroxyl‐substituted conjugated small molecules from their halogenated counterparts and further enriches the regulation means of electro‐chemical performances of organic electrodes for enabling high‐capacity and high‐voltage APBs.