Donor-π-acceptor heterojunctions constructed from the rGO network and redox-active covalent organic frameworks for high-performance supercapacitors

To overcome the bottleneck of low energy density in graphene-based supercapacitors and endow them with advanced properties such as ultralong life cycles, a key rational strategy is to couple graphene sheets with multielectron, redox-reversible, and structurally stable organic compounds. This work demonstrates the synthesis and characterization of hybridizing redox-active covalent organic frameworks (COFs) with nickel bis(dithiolene) units and graphene via covalent linkages to form heterostructures for high-performance supercapacitors. Efficient electron transfer between COFs and rGO is observed which results from the orderly assembled Ni-bis(dithiolene) units with unique electronic structure, as well as the unique design of COF/rGO morphology. The obtained Ni-TAP/rGO and Ni-TAPP/rGO heterojunctions display a gravimetric capacitance of 346.0 F g-1 and 367.5 F g-1 at a current loading of 0.5 A g-1, volumetric/gravimetric specific energy densities up to 48.1 W h kg-1 and 51.04 W h kg-1, and power densities up to 1.81 kW kg-1 and 1.78 kW kg-1, as well as exceptional rate capability and cycling stability (capacitance retention of 97.01% after 10 000 cycles). The orderly assembled Ni-bis(dithiolene) units with unique electronic structure, heterostructure formed between COFs and rGO, and efficient electron transfer contribute to the outstanding supercapacitor performance.