Nitric Acid Modification of Graphene Nanosheets Prepared by Arc- Discharge Method and Their Enhanced Electrochemical Properties

Large-scale synthesis of few-layer graphene nanosheets (GNSs) with high crystallinity and electrical conductivity (1680 S·m-1) is achieved by an arc-discharge method. The GNSs exhibited good morphologies as observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). However, electrochemical testing showed that the performance of the graphene (GNS) electrodes in supercapacitors was poor. To increase the surface active sites for electrochemical reactions and promote the wettability by aqueous electrolyte of the GNSs, a nitric acid treatment was used to chemically modify their surface. The acid treatment introduced more oxygen/nitrogen-containing functional groups onto the GNS surface, and clearly enhanced the hydrophilicity. The nitric-acid-modified GNSs (H-GNSs) showed vastly better electrode performance, with a maximum specific capacitance of 65.5 F·g-1 (about 30 times that of original GNSs) at a current density of 0.5 A·g-1 in 2 mol·L-1 KOH electrolyte. In addition, the H-GNS electrode showed good cycling stability and lifetime after running 2000 cycles. Therefore, H-GNSs may be an attractive candidate as electrode materials for supercapacitors.