In Situ Electrochemical Polymerization of Nitro Compounds into Azo Cathodes: A Promising Strategy for Aqueous Zinc-Ion Batteries

The development of sustainable, high-performance cathode materials is crucial for advancing zinc-ion battery technology. In this study, we introduce a strategy for synthesizing azo polymer cathode materials via in situ electrochemical polymerization of nitro-substituted compounds. This process involves the reduction of nitro groups to form N═N linkages, which function as redox-active sites, enabling efficient energy storage. We focus on 2,7-dinitropyrenetetraone (DNPTO), a nitro-substituted conjugated carbonyl compound, to produce a cathode material with dual functional groups. Experimental results, supported by theoretical calculations, demonstrate that the initial discharge cycle irreversibly reduces the nitro groups to azo groups, leading to enhanced electrochemical performance. DNPTO exhibits a 2-fold higher capacity than PTO and significantly improved capacity retention compared to mononitropyrenetetraone (MNPTO), attributed to its in situ polymerization. This study highlights the potential of electrochemically synthesized azo polymers as promising cathode materials for aqueous ZIBs.