Relationship between intrinsic capacitance and thickness of graphene nanosheets

A method to detect the intrinsic capacitance and thickness of graphene nanosheets (GNS) was developed. The ultrasonic-dispersed GNSs were separated by a kind of small-powder graphite (SG, 0.5-2 mu m) with almost no capacitance to prevent the ultra-thin graphene layer from restacking face to face. In order to separate the GNSs as much as possible, we increased the mass ratio of SG in the GNS-SG composite gradually from 1 : 10 to 1 : 250. The electrochemical properties of different GNS-SG composites as electrode materials for an electric double-layer capacitor (EDLC) have been systematically investigated. It was found that, as the content of GNSs decreased from pure GNS to 1/100 of the GNS-SG composite, specific capacitance increased progressively from 171.8 F g(-1) to 417.1 F g(-1). As the ratio of GNSs in the GNS-SG electrodes was decreased further (1 : 200, 1 : 250 and 1 : 300), the specific capacitance held a stable value of similar to 856.6 F g(-1), revealing the intrinsic capacitance of these GNSs. Based on the theoretical specific surface area of graphene and capacitance of a common graphite electrode, the layer number of GNSs here was calculated to be 2-11. This strategy can not only calculate the average layer number but also preliminarily judge the aggregation of GNSs from the capacitance data.