Tuning capacitance of graphene films via a robust routine of adjusting their hierarchical structures

In this work, the nitrogen doped graphene films with hierarchical network structures have been successfully fabricated via a robust routine of adjusting the content of large- and small-sized reduced graphene oxide (RGO) sheets in the graphene films, where the large-sized RGO sheets act as the backbone to form the well-connected network structures and small-sized RGO sheets act as the interlayer and interpore linkers to connect the large-sized RGO sheets and large pores. A maximum capacitance of 429.7 F g ⁻¹ is obtained for the optimized RGO electrode with small-sized RGO content of 40 wt%, which is 61.9% improvement compared to the RGO electrodes with pure large-sized RGO sheets. While, the specific surface area and electrical conductivity of the optimized RGO electrode are 36.1% and 26.2% improvement compared to the pure large-sized electrode. Therefore, we attribute the improved capacitance primarily comes from the increasing of specific surface area due to the formation of fine hierarchical structures and the better connection of the network structures (the increasing of electrical conductivity) for the optimized RGO electrode. Besides, the optimized RGO electrode exhibits good cycle, rate performance, power and energy density compared to the previous carbon based supercapacitor. Herein, we can precisely control the specific surface area and electrical conductivity of RGO electrode by simply adjusting the content of large- and small-sized RGO, which may shed useful insight for the design of high performance supercapacitors and Li-ion batteries.