Graphene/Carbon Paper Combined with Redox Active Electrolyte for Supercapacitors with High Performance

Graphene/carbon paper is prepared by pyrolyzing graphene modified cellulose filter paper and directly used as a binder-free electrode to assemble a supercapacitor (SC) with a redox active electrolyte, containing a Fe³⁺/Fe²⁺ additive. By the graphene incorporation and the carbonization of the cellulose fibers, both the microstructure and the electrical conductivity of the carbon paper are promoted greatly. The filter paper derived carbon (FPC) electrode exhibits a specific capacitance (C_s) of 2832 F·g^-1 in a 1 M H₂SO₄ + 0.5 M Fe³⁺/Fe²⁺ electrolyte at 1 A·g^-1, which is about 81 times that in a normal H₂SO₄ electrolyte. With the modification of graphene, the capacitive performance of the SC is enhanced further and a remarkable C_s of 3396 F·g^-1 at 1 A·g^-1 is achieved for a graphene modified filter paper carbon (GFPC) electrode, which remains at ~632 F·g^-1 at 10 A·g^-1. The free standing GFPC electrode also exhibits good cycling stability (93.8% of capacitance retention after 2000 cycles) and an energy density of 118 Wh·kg^-1 at a power density of 500.35 W·kg^-1, all of which are much higher than those of FPC. These encouraging results suggest that the graphene modification of electrode materials combined with a Fe³⁺/Fe²⁺ redox active electrolyte is a prospective measure to fabricate SC with an ultrahigh performance.