High capacitance and long cycle-life of nitrogen doped reduced graphene oxide

Abstract

The quality of chemically synthesized few-layered graphene, which is known as reduced graphene oxide (RGO) depends on the oxidation of graphite, effective exfoliation of graphite oxide and complete reduction of graphene oxide. Herein, we report the preparation of nitrogen doped RGO by a modified Hummer's method using potassium manganate along with potassium permanganate to achieve improved oxidation of graphite and a small amount of bovine serum albumin as a dispersant to avoid restacking of graphene sheets. Besides reducing the agglomeration of graphene layers, bovine serum albumin also serves as a nitrogen dopant. The quality of as-prepared nitrogen doped RGO is examined by morphological and structural studies. While microscopic studies confirm the formation of thin, well dispersed RGO sheets, X-ray photoelectron spectroscopic studies confirm the doping of nitrogen in RGO. A specific surface area of 286 m(2) g(-1) is obtained for nitrogen doped RGO, which is mainly contributed by the basal planes and ordered mesoporosity of RGO. The capacitance properties of as-prepared nitrogen doped RGO without any conductive additive are evaluated by cyclic voltammetry and galvanostatic charge-discharge cycling. A specific capacitance of 142 F g(-1) obtained at a current density 1 A g(-1) is almost twice the specific capacitance obtained for commercial graphene platelet aggregates (75 F g(-1)). The rate performance of as-prepared nitrogen doped RGO is comparable to that of commercial graphene platelet aggregates. It is also found that nitrogen doped RGO electrode can be charged and discharged for at least 2000 cycles without fade in the capacitance.