A redox-active covalent organic framework with azo units for supercapacitor applications

Abstract

Covalent organic frameworks (COF) exhibiting high specific surface area and pseudocapacitive activity are considered ideal candidates for energy storage electrode materials. Herein, two covalent organic frameworks (TFPAZO-COF and TFPDT-COF) with and without azo units in the backbone was synthesized and their potential application as a supercapacitor electrode material was explored. The specific surface area of the synthesized TFPAZO-COF was enhanced by using pyrrolidine in place of acetic acid as a catalyst, resulting in a value of 1010.9 m² g^-1. Moreover, TFPAZO-COF is enriched with abundant azo groups to achieve proton Grotthuss transfer and enhance the redox reaction of the electrode. The synergy between the double layer capacitance resulting from the adsorption of a large number of ions on the large specific surface area and the Faraday capacitance generated by the azo unit endows TFPAZO-COF excellent electrochemical properties. When evaluated in a three-electrode configuration with 1 M H₂SO₄ as the electrolyte, the specific capacity of TFPAZO-COF reaches 178 F/g at 0.5 A/g, significantly surpassing the performance of TFPDT-COF. Additionally, the asymmetric supercapacitor (ASC) device consisting of TFPAZO-COF and activated carbon (AC) achieved a maximum energy density and power density of 11.5 W h/kg and 450 W/kg, respectively. Furthermore, the TFPAZO-COF//AC ASC exhibits exceptional cycling stability, maintaining 86.1% of its initial capacitance after 8,000 cycles at 1 A/g.