An electron delocalized organic polymer with enhanced redox active sites for conductive agent free high-rate aqueous proton storage

Abstract

Organic materials face constraints in serving as electrode materials for aqueous electrochemical energy storage due to factors such as inadequate active sites, low conductivity, and solubility stemming from their intrinsic structural properties. These limitations detrimentally impact their electrochemical rate capability and durability over multiple cycles. Consequently, there is a critical need for a systematic approach to engineer organic materials, ensuring they fulfill the criteria necessary for aqueous ion storage. In this study, a novel polymer (PNZI) was synthesized by using 2,3-Diaminophenazine (DPZ) and naphthalene-1,4,5,8-tetracarboxylic acid (NTCDA). The PNZI integrates the redox-active functional groups CO and CN from the original monomers. Moreover, the improved conjugation in PNZI not only ensures a stable molecular structure, but also guarantees excellent electronic conductivity characteristics due to the larger charge delocalization area. In the absence of added conductive agents, the semi-conductive PNZI material can be immediately utilized as an electrode for aqueous proton batteries (APBs). Throughout 5000 cycles, it maintains a discharge capacity of 159 mAh g−1 at 50 A g−1, exhibiting remarkable rate capability and cycling durability. By employing a comprehensive approach encompassing structural analysis alongside in situ or ex situ characterization methodologies, the pathway of proton migration within the PNZI structure has been rigorously developed. The PNZI-based all-polymer aqueous proton full cell and the high-performance aqueous proton full cell constructed with MnO2 (achieving a maximum energy density of 191.5 Wh kg−1) are presented. This endeavor will provide valuable insights for the design of organic electrodes and their application in aqueous electrochemical energy storage.