Rational design and sustainable preparation of high-performance carbonaceous electrode materials are important to the practical application of supercapacitors. In this work, a cost-effective synthesis strategy for nitrogen and oxygen co-doped porous carbon (NOC) from petroleum sludge waste was developed. The hierarchical porous structure and ultra-high surface area (2514.7 m2 g-1) of NOC electrode materials could provide an efficient transport path and capacitance active site for electrolyte ions. The uniform co-doping of N and O heteroatoms brought enhanced wettability, electrical conductivity and probably additional pseudo-capacitance. The as-obtained NOC electrodes exhibited a high specific capacitance (441.2 F g-1 at 0.5 A g-1), outstanding rate capability, and cycling performance with inconspicuous capacitance loss after 10,000 cycles. Further, the assembled all-solid-state MnO2/NOC asymmetrical supercapacitor device (ASC) could deliver an excellent capacitance of 119.3 F g-1 at 0.2 A g-1 under a wide potential operation window of 0-1.8 V with flexible mechanical stability. This ASC device yielded a superior energy density of 53.7 W h kg-1 at a power density of 180 W kg-1 and a reasonable cycling life. Overall, this sustainable, low-cost and waste-derived porous carbon electrode material might be widely used in the field of energy storage, now and into the foreseeable future.
Keywords: nitrogen/oxygen co-doping; petroleum sludge; porous carbon; supercapacitors.