By introducing a heteroatom into carbon material, an effective improvement in capacitance can be realized owing to surface oxidation and reduction reactions of pseudocapacitors. Herein, a simple one-pot carbonization activation method was proposed to convert potassium citrate into three-dimensional interconnected porous carbon (PC). Then, an effective double heteroatom doping method by thiourea was used to prepare nitrogen–sulfur-doped PC (N,S-PC). This porous structure facilitates the storage of a large number of ions and reduces their diffusion path. The synthesized N,S-PC nanomaterial has a capacitance of 674 F/g at 1 A/g in a 1 M H2SO4 electrolyte, can retain 94.41% of the initial capacitance after 10 000 cycles at 5 A/g, and has a long cycle life. More importantly, a symmetric supercapacitor assembled with this material can exhibit an energy density of up to 32.6 (W·h)/kg at a high-power density of 750 W/kg. This is due to the high performance of N,S-PC in supercapacitor electrode materials.

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In this study, a strategy for the rapid and simple preparation of porous carbon (PC) using the microwave method was proposed. Oxygen-rich PC was synthesized by microwave irradiation in air, where potassium citrate and ZnCl 2 served as the carbon source and microwave absorber, respectively. ZnCl 2 achieves microwave absorption through dipole rotation, which uses ion conduction to convert heat energy in the reaction system. In addition, potassium salt etching improved the porosity of PCs. The PC prepared under optimal conditions had a large specific surface area (902 m 2 •g −1 ) and exhibited a significant specific capacitance (380 F•g −1 ) in the threeelectrode system at 1 A•g −1 . The energy and power densities of the assembled symmetrical supercapacitor device based on PC-375W-0.4 were 32.7 W•h•kg −1 and 0.65 kW•kg −1 , respectively, at a current density of 1 A•g −1 . Even after 5000 cycles at 5 A•g −1 current density, the excellent cycle life retained 94% of its initial capacitance.

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