N/S co-doped interconnected porous carbon nanosheets as high-performance supercapacitor electrode materials

The synthesis of porous carbon nanosheets without acid treatment for high-performance supercapacitors (SCs) is difficult. We report the construction of N/S co-doped porous carbon nanosheets (NS-PCNs) from coal tar pitch (CTP), using Na₂S₂O₃·5H₂O as the sulfur source and K₂CO₃ as an activator, under flowing ammonia at high temperature. NS-IPCN₈₀₀ prepared at 800 °C is composed of two-dimensional (2D) nanosheets with abundant pores and an interconnected 3D carbon skeleton. The abundant microspores increase the number of active sites for electrolyte ion adsorption and small mesopores act as channels for fast ion transmission. The 3D carbon skeleton provides paths for electron conduction. Heteroatom doping provides an additional pseudocapacitance for the NS-IPCN electrodes. As a result the NS-IPCN₈₀₀ electrode has a high capacitance of 302 F g⁻¹ at 0.05 A g⁻¹ in a 6 mol L⁻¹ of KOH electrolyte, and has a high energy density of 9.71 Wh kg⁻¹ at a power density of 25.98 W kg⁻¹. It also has excellent cycling stability with a capacitance retention of over 94.2% after 10 000 charge-discharge cycles. This work suggests an environmentally friendly way to produce NS-IPCNs from CTP for use as high-performance SC electrode materials.