Covalent Organic Frameworks as Negative Electrodes for High-Performance Asymmetric Supercapacitors

Abstract

New covalent organic frameworks (COFs), encompassing redox-functionalized moieties and an aza-fused π-conjugated system, are designed, synthesized, and deployed as negative electrodes in asymmetric supercapacitors (ASC), for the first time. The Hex-Aza-COFs are synthesized based on the solvothermal condensation reaction of cyclohexanehexone and redox-functionalized aromatic tetramines with benzoquinone (Hex-Aza-COF-2) or phenazine (Hex-Aza-COF-3). The redox-functionalized Hex-Aza-COFs show a specific capacitance of 585 F g−1 for Hex-Aza-COF-2 and 663 F g−1 for Hex-Aza-COF-3 in a three-electrode configuration. These values are the highest among reported COF materials and are comparable with state-of-the-art pseudocapacitive electrodes. The Hex-Aza-COFs exhibit a wide voltage window (0 to −1.0 V), which allow the construction of a two-electrode ASC device by combining them with RuO2. The complementary potential windows of Hex-Aza-COF-3 and RuO2 enable an asymmetric device with a high voltage window of 1.7 V. The RuO2//Hex-Aza-COF-3 ASC device achieves an energy density value of 23.3 W h kg−1 at a power density of 661.2 W kg−1. The newly developed negative COF materials open new prospects for the development of high-performance ASCs.