Nitrogen, oxygen and sulfur co-doped hierarchical porous carbons toward high-performance supercapacitors by direct pyrolysis of kraft lignin

The O-N-S co-doped hierarchical porous carbons are prepared by direct pyrolysis of kraft lignin which is the byproduct from papermaking black liquor . The proposed preparation method is extremely facile, green-environmental, and low-cost without any additional activating agents, additives or templates. The kraft lignin-derived carbon materials possess large specific surface areas (338−1307 m 2  g −1 ), hierarchical porous structures and abundant multi-heteroatoms co-doping (9.84–19.91 wt%). Benefiting from above synergistic advantages, the as-fabricated symmetric supercapacitor in aqueous electrolyte delivers a high specific capacitance of 244.5 F g −1  at 0.2 A g −1 , excellent rate-capability (81.8% retention of initial capacitance at 40.0 A g −1 ), and outstanding cycling stability (91.6% retention over 10000 cycles). Importantly, this device in aqueous electrolyte delivers an energy density of 8.5 W h kg −1  at a power density of 100 W kg −1 . Furthermore, a remarkable energy density of 66.8 W h kg −1  at a power density of 1.75 kW kg −1  has been achieved and 32.2 W h kg −1 is still maintained even at an ultrahigh power density of 40.0 kW kg −1 when ionic liquid serves as electrolyte. This study demonstrates the successful conversion of low-valued natural biomass derivative into sustainable high-performance supercapacitor electrode materials with a simple, low-cost, and green-environmental production process.