KNO3-assisted potassium tartrate co-activation synthesis of lignin-based hierarchical porous carbon for supercapacitors

Porous carbon (PC), characterized by tunable pore structures and high specific surface area (S BET ), is regarded as an outstanding material for supercapacitors (SCs). Notably, exploiting a gentle strategy to build high-yield-high-performance N/S co-doped hierarchical porous carbons (NSHPCs) faces huge challenges. Herein, we introduced a novel strategy to prepare NSHPCs via KNO 3 -assisted C 4 H 4 O 6 K 2 co-activation craft. Thereinto, NH 4 -kraft lignin, gained by precipitating the black liquor with (NH 4 ) 2 SO 4 , was used as precursors, while C 4 H 4 O 6 K 2 served as the main activator and KNO 3 was the assisted-activator/foaming agent. Compared with T -NSHPC activated by single C 4 H 4 O 6 K 2 , N - T -NSHPC acquired by KNO 3 -C 4 H 4 O 6 K 2 co-activation achieved 31.2 % high yield and unique mesoporous-dominated hierarchical porous structures with a high S BET of 1987.9 m 2 /g, a large pore volume of 1.04 cm 3 /g, 2.40 % N and 2.82 % S, respectively. Electrochemical tests revealed that N - T -NSHPC achieved an outstanding specific capacitance of 338.2 F/g at 0.5 A/g. When assembled as symmetrical SCs, it manifested an impressive energy density of 33.38 Wh/kg at a power density of 500 W/kg. Meanwhile, it retained 98.3 % initial capacitance after 5,000 charge–discharge tests at a high current density of 20 A/g. This insight not only presents a feasible approach to achieve high-value utilization of lignin but also provides a gentle and efficient sight for designing high-yield-high-performance NSHPCs for SCs.