Double alkali metal salts synergistic activation coupled with S-doped cotton derived honeycomb porous carbon for enhanced zinc ion storage capability

Biomass-derived carbon materials are ideal electrode materials due to their inherent eco-friendliness, easily available and unique micro-morphology. Herein, zinc ion capacitors (ZICs) are designed utilizing S doped honeycomb porous carbon nanosheet cathode, which is obtained via synergistic activation from sodium thiosulfate and potassium carbonate. The honeycomb microstructure is result from the pore-forming effect of double alkali metal salts, which can promote the electrolyte ion fast migration in the cathode. Besides, the S doping in carbon array can regulate the electron distribution within the carbon framework and lower the energy barrier for the chemical absorption of Zn²⁺/H⁺, which is demonstrated by density functional theory calculation and expected to produce additional capacitance. Further, the ex-situ X-ray photoelectron spectroscopy reveals the consistent changes in C-O-H and C-O-Zn throughout the charging and discharging cycles, which demonstrate the S doping can promote the reversible chemical adsorption and desorption reaction of Zn²⁺/H⁺. As a result, the S doping honeycomb porous carbon nanosheet cathode can achieves a high discharge capacity of 147.2 mAh g^-1 and high energy density of 92.7 Wh kg^-1. Additionally, the obtained material exhibits good cycling stability at 20 A g^-1, retaining 99.9% of its initial capacity after 2000 cycles. This research presents a versatile approach to synthesizing heteroatom-doped carbon materials from biomass waste for ZICs.