Flexible Amine-Linked 2D Covalent Organic Frameworks for Enhanced Charge Transport in Symmetric Supercapacitors

The development of high-performance aqueous supercapacitors necessitates electrode materials with large surface area, fast ion transport, and excellent structural stability. Covalent organic frameworks (COFs), characterized by ordered porosity, tunable chemistry, and extended π-conjugation, are promising candidates; however, simultaneous optimization of their structural and electrochemical properties remains challenging. Herein, a series of two-dimensional COFs (COF-AB, COF-AC, COF-AD, and COF-AE) were synthesized via solvothermal Schiff-base condensation using a flexible amine linker (TPT-NH 2 ) and four different aldehyde linkers. When evaluated as electrode materials, all COFs exhibited a wide electrochemical stability potential window of 2.1 V in a three-electrode configuration. Among them, COF-AB demonstrated the longest discharge time and the highest specific capacitance of 133.1 F g –1 at 0.5 A g –1 in 5 M aqueous (aq.) NaClO 4, along with excellent cycling stability. Symmetric supercapacitors based on COF-AB further delivered a superior specific capacitance of 85.2 F g –1 and an energy density of 52.2 W h kg –1 at 0.25 A g –1 . Remarkably, it retains 104.6% capacitance after 20,000 GCD cycles at 3 A g −1 . The enhanced performance of COF-AB is attributed to the synergistic effects of high surface area, well-defined porosity, extended π-conjugation, and nitrogen-rich imine linkages incorporating two triazine units, which collectively facilitate efficient ion diffusion, rapid charge transport, and stable charge storage. This work highlights the potential of rationally designed COF electrodes for high-performance aqueous supercapacitor applications.