Thiocyanogen-modulated N, S Co-doped lignin hierarchical porous carbons for high-performance aqueous supercapacitors.

Synopsis: This study presents a thiocyanogen-modulated alkali activation strategy for preparing N, S co-doped lignin hierarchical porous carbon (NSLHPC). Thiocyanate acts as a surface modulation mediator to introduce nitrogen and sulfur heteroatoms via oxygen replacement reaction. NSLHPC exhibits excellent electrochemical performance and long cycling lifespan in both symmetric supercapacitors and zinc-ion hybrid capacitors. [Display omitted] • Thiocyanogen-modulated alkali activation strategy for the preparation of NSLHPC. • Oxygen replacement reaction between KSCN and lignin carbon for N, S co-doping. • NSLHPC exhibits an impressive SSA of 2705.3 m2/g and a pore volume of 3.27 cm3/g. • NSLHPC presents remarkable electrochemical performance in aqueous supercapacitors. • DFT calculations reveal that N, S co-doping reduces the adsorption energy barrier of Zn2+. Constructing heteroatom-doped porous carbons with distinct charge storage properties is significant for high-energy–density supercapacitors, yet it remains a formidable challenge. Herein, we employed a thiocyanogen-modulated alkali activation strategy to synthesize N and S co-doped lignin hierarchical porous carbon (NSLHPC). In this process, thiocyanogen serves as a surface modulation mediator to substitute oxygen with nitrogen and sulfur species, while the combination of KOH activation and MgO template generates numerous nanopores within the carbon structure. The three-dimensional interconnected nanosheet architecture facilitates rapid ion transfer and enhances accessibility to active sites. Density functional theory (DFT) calculations demonstrate that introducing N and S heteroatoms through oxygen substitution reduces the adsorption energy barrier of Zn2+. Consequently, the optimized NSLHPC exhibits a remarkable specific capacitance of 438F/g at 0.5 A/g in 6 M KOH, delivering an energy density of 10.4 Wh/kg in the symmetric supercapacitor and an impressive energy density of 104.9 Wh/kg in the zinc-ion hybrid capacitor. The NSLHPC cathode also shows an excellent lifespan with capacitance retention of 99.0 % and Columbic efficiency of 100 % over 10,000 cycles. This study presents innovative strategies for engineering high-performance porous carbon electrode materials by emphasizing pore structure modulation and N, S co-doping as crucial approaches. [ABSTRACT FROM AUTHOR]