Nitrogen-doped and carbon-coated activated carbon as a conductivity additive-free electrode for supercapacitors

Abstract

The development of supercapacitors with high volumetric capacitance and high-rate performance has been an important research topic. Activated carbon (AC), which is a widely used material for supercapacitor electrodes, has different surface structures, porosities, and electrochemical properties. However, the low conductivity of the electrode material is a major problem for the efficient use of AC in supercapacitors. To tackle this challenge, we prepared conductive, additive-free electrodes for supercapacitors by a simple one-pot treatment of AC with melamine (nitrogen source), pitch, and sucrose (both carbon source). Nitrogen-doped and carbon-coated AC was successfully generated after high-temperature heat treatment. The AC was doped with approximately 0.5 at.% nitrogen, and coated with carbon leading to a decreased oxygen content. Thin carbon layers (~10 nm) were coated onto the outer surface of the AC, as shown in TEM images. The modification of the AC surface with a sucrose source is favorable, as it increases the electrical conductivity of AC up to 3.0 S cm−1, which is 4.3 times higher than in unmodified AC. The electrochemical performance of the modified AC was evaluated by conducting agent-free electrode. Although the obtained samples had slightly reduced surface areas after the surface modification, they maintained a high specific surface area of 1700 m2 g−1 . The supercapacitor delivered a specific capacitance of 70.4 F cc−1 at 1 mA cm−1 and achieved 89.8% capacitance retention even at a high current density of 50 mA cm−2 . Furthermore, the supercapacitor delivered a high energy density of 24.5 Wh kg−1 at a power density of 4650 W kg−1 . This approach can be extended for a new strategy for conductivity additive-free electrodes in, e.g., supercapacitors, batteries, and fuel cells.