Uniformly Dispersed Freestanding Carbon Nanofiber/Graphene Electrodes Made by a Scalable Biological Method for High-Performance Flexible Supercapacitors

A novel facile and scalable strategy is developed to prepare freestanding carbon nanofiber/graphene nanosheet composites using a scalable membrane-liquid interface culture method followed by carbonization. The carbon nanofibers (CNFs) and graphene nanosheets (GNs) are uniformly dispersed in a three-dimensional (3D) conductive architecture. Robust mechanical properties are demonstrated with fine flexibility, good structure stability, and high specific surface area. As supercapacitor electrodes, the 3D nanocomposite delivers good electrochemical performance with a high capacitance of 215 F g(-1) at 1 A g(-1) and extraordinary cycling stability with no capacitance degradation after 5000 cycles, which are among the best carbon electrodes in supercapacitors. The energy density is as high as 20 Wh kg(-1) at a power density of 900 W kg(-1), superior to other CNF-based electrode materials. The superb electrochemical performance of the 3D nanocomposite electrode is ascribed to the unique structure: 3D conductive network, uniform dispersion of carbon nanofibers and graphene nanosheets, robust mechanical property, and large specific surface area. The combination of facile fabrication method, good performance, and robust mechanical property makes the 3D nanocomposites very promising as a new type of superior supercapacitor electrodes.