Design and synthesis of MOF-derived CuO/g-C3N4 composites with octahedral structures as advanced anode materials for asymmetric supercapacitors with high energy and power densities

In this study, two-component composites consisting of transition metal copper oxide (CuO) and graphite carbon nitride (g-C3N4) were successfully synthesized. Firstly, a typical metal–organic framework (MOF) material, namely CuBTC, was prepared by the hydrothermal method. Then, the hollow porous CuO/g-C3N4 composite with an octahedron structure was obtained by introducing a certain amount of g-C3N4 into the system using ultrasonic treatment and rapid thermal annealing. The synthesized CuO/g-C3N4 not only retains the unique octahedral morphology of the CuBTC template, but also is coated by a uniform carbon layer. This CuO/g-C3N4 displays a high reversible specific capacity (1530.4 F g−1, 2 A g−1) as an anode material. In addition, an asymmetric supercapacitor assembled with self-made NiCoMOF as the cathode and CuO/g-C3N4 as the anode achieves an excellent energy density of 50.8 W h kg−1 at a power density of 800 W kg−1 and stable cycling performance (70.1% capacity retention over 3000 cycles). These outstanding electrochemical properties are attributed to the synergistic effect between transition metal oxides and carbon-based materials as well as the unique structure of the composites, which also provides a facile design and synthesis idea to construct high-performance transition metal compounds with a unique hollow structure and C-coating for developing asymmetric supercapacitors with high energy and power densities.