Spatially synthesized fluorine-modified graphene improves double times higher capacitance than theoretical capacitance of graphene in alkaline medium

Abstract

The practically low energy density limits the large-scale application of graphene in supercapacitors. Here, we propose a space-confined method for the preparation of fluorine-modified graphene (FG) by using fluorine-containing groups (PF₆^– or BF₄^–) as co-intercalated ions and reactants. The semi-ionic C–F bonds in FG contribute a brilliant capacitive performance in both acidic and alkaline electrolytes. Particularly, in alkaline medium, the FG electrode exhibited an ultrahigh specific capacitance (1210 F g⁻¹), surpassing 2 orders of the theoretical capacitance value of graphene. Meanwhile, the FG-assembled symmetrical supercapacitor device (FG-SSD) possesses ultrahigh energy density (418.7 Wh kg⁻¹) and power density (2 kW kg⁻¹) in acidic medium, highlighting the practical application of supercapacitors. Theoretical calculations revealed an increased electrochemical double layer capacitance and amplified the electrochemical window of FG-SSD. This work demonstrates a spatially confined method for the preparation of functional graphene and its spectacular potential for supercapacitor-related electronics.