Poly(ionic liquid)-assisted reduction of graphene oxide to achieve high-performance composite electrodes

Abstract

Direct reduction of graphene oxide (GO) to graphene often results in an irreversible agglomeration and hence suppressing its effective surface available for energy storage. In this work, GO was solvothermally reduced in the presence of imidazolium-based poly(ionic liquid) (PIL) of poly(1-butyl-3-vinylimidazolium hexafluorophosphate) to produce a PIL-modified reduced GO (PIL-rGO) composite. The integration of PILs with rGO is capable of preventing the restacking of rGO sheets, and hence, providing a large electrolyte ion-accessible surface and an abundant interior space for charge storage by enlarging the interlayer spacing in PIL-rGO. The PIL-rGO composite was then used as the supercapacitor electrode associated with a compatible IL of 1-butyl-3-methylimidazolium hexafluorophosphate as the electrolyte. The PIL herein improves the interface wettability between the electrode and electrolyte, and the IL electrolyte enables a wide potential window as well. Specific capacitances correspond to 196 F/g at a current density of 1 A/g, 160 F/g at 2 A/g, and 144.8 F/g at a scan rate of 60 mV/s, which are much higher than those (104 F/g at 2 A/g, and 48.1 F/g at 60 mV/s) of pure rGO. The capacitance retention is as high as 80.7% after 1000 charge-discharge cycles at a discharge current density of 2 A/g. The interfacial charge-transfer resistance of the PIL-rGO electrode (4.6 Ω) is also much lower than that of the rGO electrode (18.7 Ω). Such graphene-base electrodes may promise a candidate for high performance supercapacitors.