Highly Stable Sp² Conjugated Redox-Active Covalent Organic Framework for Pseudocapacitive Energy Storage

Covalent organic frameworks (COFs) with reversible redox-active units are promising materials for electrochemical energy storage devices. The highly extended π-conjugated redox-active PPDA-TFPT-COF is synthesized via Schiff-base condensation between p-phenylenediamine (PPDA) and 2,4,6-tris-(p-formylphenoxy)1,3,5-triazine (TFPT) monomers. The ample redox active sites of PPDA-TFPT-COF enabled exceptional energy storage, achieving a maximum specific capacitance of 250 F g^-1 and an energy density of 34.72 Wh kg^-1 at a power density of 500 W kg^-1 at 1 A g^-1 current density. The material demonstrated extraordinary cycling stability, retaining over 100% capacitance after 5000 cycles at 7 A g^-1 current density. This superior performance is attributed to π-π interactions, abundant redox-active centers, and an efficient charge transport pathway, making it an ideal supercapacitor electrode material. The presence of diamine moieties enhanced conductivity, while redox-active imine sites facilitated hydrogen ion storage. Electrochemical investigations under acidic conditions revealed significant perturbations in the electronic structure, elucidating the redox charge storage mechanism. Density functional theory (DFT) calculations further confirmed extended π-conjugation in HOMO and LUMO orbitals, providing key insights into charge mobility. This study presents a novel strategy for designing redox-active COFs for high-performance pseudocapacitive energy storage.