Synthesis of nitrogen-doped porous carbon with superior performance as efficient supercapacitor electrodes from hazardous oily sludge waste

Nitrogen-doped porous carbon (NPC) for high-performance supercapacitors has been synthesized from oily sludge waste by using KOH activation combined with in situ nitrogen doping method. The NPC possesses a hierarchical porous structure with high surface area of 2514.7[Formula: see text]m2[Formula: see text]g[Formula: see text], large pore volume of 2.383[Formula: see text]cm3 g[Formula: see text] and nitrogen content of 4.32%. The NPC-based electrode can deliver an outstanding capacitance of 414.2[Formula: see text]F[Formula: see text]g[Formula: see text] at 0.5[Formula: see text]A[Formula: see text]g[Formula: see text] and a good capacitance rate performance of 307.5[Formula: see text]F[Formula: see text]g[Formula: see text] (74.2% retention) at 50[Formula: see text]A[Formula: see text]g[Formula: see text]. Moreover, the NPC exhibits an excellent cycling stability with little loss of capacitance after 5000 cycles at 5[Formula: see text]A[Formula: see text]g[Formula: see text].