Graphene sheets assembled into three-dimensional networks of carbon nanofibers: A nano-engineering approach for binder-free supercapacitor electrodes

Abstract

The design and synthesis of flexible and free-standing carbon nanofibers membrane with good electrochemical properties have recently attracted much attention in energy storage applications. Herein, we fabricated graphene sheets-incorporated three-dimensional carbon nanofibers membrane (3D-GCNFs) as effective electrode materials for supercapacitors. The electrospun two-dimensional (2D) graphene oxide sheets-incorporated polyacrylonitrile nanofibers (GO/PAN NFs) were transformed into 3D membrane by a gas-forming technique using sodium borohydride. Subsequent thermal treatment converted the 2D-assembled GO/PAN NFs membrane into the low-density 3D-GCNFs membrane. The morphology and electrochemical performances of the as-prepared 3D membrane were systematically investigated using state-of-the-art techniques. It was found that the electrochemical performance of the as-obtained 3D-GCNFs membrane was greatly improved compared to the 2D counterparts. As a binder-free electrode, the materials exhibited a high areal capacitance of 318 mF/cm2 at a current density of 1 mA/cm2 and good cyclic stability of up to 98.5% after 5000 cycles. In addition, a symmetrical supercapacitor was constructed using the 3D-GCNFs membrane as both negative and positive electrodes. The device exhibited areal capacitance of 240 mF/cm2 at a current density of 1 mA/cm2, an energy density of 33.33 mWh/cm2, a power density of 1000 mW/cm2, and capacitance retention of 103% after 5000 cycles. The improved performance of the 3D-GCNFs membrane was attributed to its high electrical conductivity due to the absence of binders, high porosity, and conductive networks that form efficient channels for electrolyte penetration and effectively shorten the transmission distance. We believe that this study not only provides a reference for the introduction of 3D CNFs-based composite membranes, but also demonstrates their great potential for energy storage applications.