N/O Co-doped Porous Carbons Derived from Coal Tar Pitch for Ultra-high Specific Capacitance Supercapacitors

In this paper, a series of N/O co-doped porous carbons (PCs) were designed and used to prepare coal tar pitch-based supercapacitors (SCs). The introduction of N/O species under the intervention of urea effectively improves the pseudocapacitance of PCs. The results show that the specific surface area of synthesized N₃PC_4-700 is 1914 m² g^-1, while the N and O contents are 1.3 and 7.2%, respectively. The unique interconnected pore structure and proper organic N/O co-doping, especially the introduction of pyridine-N and pyrrole-N, are beneficial for improving the electrochemical performance of PCs. In the three-electrode system, the specific capacitance and rate capability of N₃PC_4-700 are 532.5 F g^-1 and 72.5% at the current densities of 0.5 and 20 A g^-1, respectively. In addition, the specific capacitance of N₃PC_4-700 in a coin-type symmetric device is 315.5 F g^-1 at 0.5 A g^-1. The N₃PC_4-700 electrode provides an energy density of 43.8 W h kg^-1 with a power density of 0.5 kW kg^-1 and still maintains a value of 29.7 at 10 kW kg^-1. After 10,000 charge/discharge cycles, the retention rate was as high as 96.7%. In order to obtain high-performance carbon-based SCs, the effective identification and regulation of organic N/O species is necessary.