Molten Salt Construction of Nitrogen, Oxygen, Sulfur Co-Doped Hierarchical Porous Carbon for Zinc Ion Hybrid Capacitors

Abstract

Heteroatoms doped hierarchical porous carbon shows great potentiality as electrode materials for zinc ion hybrid capacitors. Herein, nitrogen, oxygen, and sulfur co-doped hierarchical porous carbon (NSPC) is synthesized by one-step pyrolysis of the mixture of KHCO₃, starch, and acesulfame potassium. The obtained NSPC-700 samples possess 3D interconnected hierarchical porous architecture, high specific surface area, and rich nitrogen, oxygen, and sulfur functional groups. Result from the synergistic effect, the obtained NSPC-700 electrode shows a high specific capacitance of 382 F g⁻¹ at 0.5 A g⁻¹ and outstanding electrochemical stabilization with the capacitance retention of 101.5%. Density functional theory (DFT) results show that co-doping with N, O, and S can improve the adsorption capacity of zinc ions and enhance the charge transfer rate. The assembled Zn//ZnSO₄(aq)//NSPC-700 hybrid capacitor achieves an energy density of 120.84 Wh kg⁻¹ at a power density of 100 W kg⁻¹ with excellent electrochemical stabilization (90.9% capacity retention after 10,000 cycles).