Assembly of 2D graphene sheets and 3D carbon nanospheres into flexible composite electrodes for high-performance supercapacitors

Flexible paper electrodes with high conductivity and hierarchical porosity have been intensely required to develop next-generation supercapacitors with high energy density and power density. Herein, glucose-derived hydrothermal carbon nanospheres (CNSs) are chemically activated into highly porous carbon nanospheres (HPCNSs), which are uniformly dispersed by graphene oxide (GO) in water. Upon filtration, the resultant GO/HPCNS composites are assembled into a flexible composite paper of HPCNSs embedded in a parallelly arranged GO framework. Upon chemical reduction from GO to reduced graphene oxide (rGO), the rGO/HPCNS composite paper as a binder-free electrode facilitates the assembly of flexible supercapacitors. The rGO/HPCNS composite paper with optimized rGO/HPCNS ratio delivers high specific capacitance (235.3 F g(-1) at 0.2 A g(-1)) and high cyclic stability (capacitance retention of 91% at 5 A g(-1) after 5000 charge/discharge cycles), attributing to their excellent structural stability, 3D conducive network and hierarchical porosity.