A simple and green approach to develop porous carbons from biomass lignin for advanced asymmetric supercapacitors

We present the biomass lignin-derived porous carbons (LPCs) prepared by a simple and environmentally friend hydrothermal treatment in presence of H₂SO₄ catalysts and then KOH activation to boost specific surface area and the corresponding electrochemical performance. The resultant LPC products were further subjected to simultaneous heteroatom N-doping during activation process, resulting in the activated N-doped LPCs (N-LPCs) for supercapacitors. The morphologies, crystal structures and textural properties of the obtained N-LPCs were studied by scanning electron microscopy, X-ray diffraction and nitrogen sorption isotherms. The N-LPCs exhibited highly porous microstructure (BET surface area: 1990.49 m² g⁻¹) and excellent capacitance value of 301 F g⁻¹ at 1 A g⁻¹, good rate capacitance of 70.9% at various densities from 1 A g⁻¹ to 20 A g⁻¹, and outstanding cycling performance of 91.3% over 20,000 charge-discharge cycles. Further, full-cell supercapacitor device assembled using the N-LPCs (as anode) and nickel cobalt layered double hydroxide (NiCo-LDH, as cathode) demonstrated an excellent specific capacitance (250 F g⁻¹ at 1 A g⁻¹), high retention (60% at 15 A g⁻¹) and remarkable energy density of 78 Wh kg⁻¹.