From pollutant to high-performance supercapacitor: Semi-coking wastewater derived N–O–S self-doped porous carbon

Heteroatom-doped porous carbon has attracted enormous attention in fabricating high-performance supercapacitors . However, designing heteroatoms containing carbon materials through an eco-friendly and cost-effective route remains challenging. In this work, N-O-S self-doped porous carbon materials are prepared from semi-coking wastewater-based phenolic resin (SWPR) via a simple Na 2 CO 3 activation strategy. The abundant phenols , NH 4 + , and SO 4 2- in semi-coking wastewater endows the versatile N, O, and S doping in porous carbon material, remarkably enhancing its conductivity. The optimal SWPR-700–2.5 porous carbon material is obtained at an activation temperature of 700 °C and a mass ratio of 2.5:1 for SWPR: Na 2 CO 3 . The symmetrical supercapacitor is assembled with SWPR-700–2.5, exhibiting a high specific capacitance of 170.5 F g −1 at 0.5 A g −1 , with a high energy density of 5.92 Wh kg −1 at 124.9 W kg −1 . After 10,000 cycles, the Coulombic efficiency and capacity retention are 100% and 99.4%, respectively, at a current density of 20 A g −1 . The excellent performance of SWPR-700–2.5 based capacitor is attributed to the porous structure with a large specific surface area (718 m 2 g −1 ) and abundant N-O-S self-doping (2.739 at% N, 8.627 at% O and 1.378 at% S). This study provides a simple route to prepare N-O-S self-doped porous carbon for supercapacitors and pushes forward the advancement of semi-coking wastewater treatment.