Sulfur and nitrogen co-doping of peanut shell-derived biochar for sustainable supercapacitor applications

To enhance the biochar produced from biomass and utilize it in the development of electrodes for applications in supercapacitors, doping the biochar with multiple or double heteroatom elements could be more beneficial than single-element doping. The search for the right heteroatom doping sources and synthesis techniques is difficult but necessary. This study exhibited the synthesis of peanut shell-derived biochar doped with sulfur (S) and nitrogen (N) through carbonization, activation, and ex-situ doping with affordable melamine and thiourea as S and S/N sources. Characterizations such as XPS, XRD, TEM, Raman, EDS mapping revealed that the S and N co-doped biochar has multilayered nanosheet-like morphology, uniform heteroatom doping, and hierarchical pore structure. Electrochemical characterization showed that the S and N co-doped electrode material has a specific capacitance of 224 F/g, higher than those of 200 F/g and 178.94 F/g of N-doped and pristine biochar at 1 A/g, respectively. The supercapacitor fabricated by the developed electrodes at 1 A/g has a specific capacitance of 80.25 F/g with a density of energy of 11.15 Wh/Kg. It is considered that S and N co-doping can enhance the active regions and pore arrangement of peanut shell-derived biochar to improve the passage of ions of the electrolyte and transfer of charge to the electrode surface in supercapacitor applications.