High-Performance Supercapacitors Based on Nitrogen-Doped Porous Carbon from Surplus Sludge

N-doped porous carbon was synthesized by simple pyrolysis of surplus sludge, an abundant toxic by-product in microbiological treatment of wastewater, as manifested in scanning and transmission electron microscopic, X-ray diffraction, and Raman spectroscopic measurements. The resulting porous carbon exhibited a large surface area of 940 m²/g and pore volume of 3.14 m³/g, as estimated by nitrogen adsorption/desorption isotherm studies. X-ray photoelectron spectroscopic measurements showed that nitrogen was embedded within the graphitic matrix forming pyridine- and pyrrole-like structures. With low-resistance electron-transfer pathways and short ion diffusion channels, the sheet-like porous N-doped carbon exhibited great potentials as a unique electrode material for energy storage. In fact, electrochemical studies showed that the N-doped porous carbon possessed a high specific capacitance of 247 F/g at 1 A/g in 1 M H₂SO₄, and excellent cycle durability without an apparent decrease of the capacitance even after 10,000 cycles of charging and discharging. The strategy presented herein may be exploited for low-cost and large-scale production of N-doped porous carbon materials as electrodes for high-power supercapacitor application.