High performance aqueous supercapacitor based on nitrogen-doped coal-based activated carbon electrode materials

The performance of a supercapacitor (SCs) fabricated from coal-based activated carbon was studied in terms of its specific capacitance (C), life cycle and rate performance. In this work, a low cost modified nitrogen-doped coal-based activated carbon (MAC_N) was prepared by KOH/H₂O co-activation from lignite. Experimental results and density functional theory (DFT) calculations showed that introducing nitrogen atoms into the coal-based activated carbon leads to a rearrangement of the carbon skeleton structure and changes the surface chemical environment. Leading to the MAC_N internal disorder increases (I_D/I_G is up to 0.99), structural stability improves (TGA curves shift right), and various nitrogen functional groups (N-5, N-6, N-Q) are formed on the carbon surface. In addition, the MAC_N possesses high specific surface area (S_BET: 2129 m²/g), abundant micropores (V_mic: 0.62 cm³/g), appropriate mesopores (V_mes: 0.39 cm³/g, V_mes ratio: 38.6%), low impurity content, and highly N-doping (9.59 wt%). These characteristics of the MAC_N provide for a high C of 323 F/g at a current density of 0.5 A/g. The enhanced MAC_N is 64.8% higher than the undoped MAC. Furthermore, a high energy density of 10 Wh/kg can be achieved with a MAC_N-assembled symmetrical cell when the power density of 250 W/kg in 6 M KOH.