Fluorine-doped graphene composite hydrogels with high bulk density for supercapacitors application

The low bulk density and the lack of pseudocapacitive active sites greatly limit the practical application of graphene electrode materials. Herein, nanocellulose/fluorine-doped graphene composite hydrogels (NFGHs) were fabricated by a hydrothermal strategy. In this synthesis system, graphene oxide was used as carbon source and the regulator of the sample’s bulk density, and can also form the initial porous structure of NFGHs. Nanocellulose was used as upholder and electrolyte transport medium to improve the porous structure and hydrophilicity of the products. Besides, hydrofluoric acid acts as reducer and heteroatom source to fulfill the fluorine doping of NFGHs. The as-prepared NFGHs show high bulk density, copious pseudocapacitive active sites, fine porous structure, and good hydrophilicity. Therefore, the aqueous symmetric supercapacitors fabricated by NFGH5 exhibit large gravimetric (264.3 F g⁻¹) and volumetric (309.2 F cm⁻³) specific capacitance, good rate characteristics, and excellent cycle durability. Furthermore, the flexible solid-state supercapacitors (FSSC) built by NFGH5 also deliver high specific capacitance (142.6 F g⁻¹), benign rate capability (73.8% specific capacitance retention at 10 A g⁻¹), and long service life. The strategy of this paper opens up a new idea for improving the implementation value of graphene-based supercapacitors.