Novel synthesis of sulfur-doped graphitic carbon nitride and NiCo2S4 composites as efficient active materials for supercapacitors

Abstract

Graphitic carbon nitride (g-C3N4) with high nitrogen contents and excellent thermal/chemical stability is widely applied as active material of supercapacitors (SC). Small surface area and electrical conductivity of g-C3N4 lead to poor electrochemical performance, which can be improved by heteroatom doping and metal compound incorporation. In this work, it is the first time to fabricate NiCo2S4/S-doped g-C3N4 (NCS-C) composite using thermal polymerization and hydrothermal reaction as active material of SC. The S-g-C3N4 electrode shows a higher specific capacitance (Csp) of 72.4 mF/g at 20 mV/s than that of 49.5 mF/g of g-C3N4 electrode. Using sulfur as doping source and anion in metal compound favors for improving compatibility of composites. NCS-C composite shows favorable S-g-C3N4 nanosheets-covered NCS flower-like structures. The NCS-C electrode presents a higher Csp value of 351.0 F/g at 1 A/g (886.2 F/g at 20 mV/s) than that of 348.9 F/g at 1 A/g (794.2 F/g at 20 mV/s) of NCS electrode, due to sulfur and nitrogen-rich carbon of S-g-C3N4 and abundant redox reactions of NCS. The symmetric SC with NCS/C electrodes delivers potential window of 1.0 V, maximum energy density of 9.7 Wh/kg at 0.65 kW/kg, and Csp retention of 97.6% and Coulombic efficiency of 90% after 10,000 charge/discharge cycles.