Response Surface Methodology-optimized Single-batch Production of Herbal Residue-based N,P Co-doped Carbon Materials for Enhanced Electrochemical Efficiency

Abstract

N,P co-doped porous carbon (NPPC) was prepared as a high-performance electrode material for supercapacitors. NPPC materials were synthesized through a facile single-batch carbonization-activation strategy. Poria cocos residue was used as a renewable biomass precursor, potassium carbonate as the chemical activator, and melamine phosphate served as the dual N/P doping agent. A Box-Behnken design  in response surface methodology was utilized to optimize three critical process parameters: K₂CO₃ ratio, N,P co-doped ratio, and activation temperature, aiming at maximizing the specific capacitance. The morphological, structural, and electrochemical properties of the prepared carbon materials were systematically characterized by scanning electron microscopy, N₂ adsorption–desorption  isotherms, X-ray photoelectron spectroscopy, cyclic voltammetry, galvanostatic charge-discharge technique, and electrochemical impedance spectroscopy. The optimized NPPC exhibited hierarchical porous structure with a high specific surface area (reaching 2980 m²⋅g⁻¹), uniformly distributed N (12.3 at.%) and P (0.59 at.%) heteroatoms, and excellent supercapacitive performance. It achieved a maximum specific capacitance of 332 F⋅g⁻¹ at a current density of 1 A⋅g⁻¹ in a 6 M KOH electrolyte. This work realizes the high-value valorization of TCM solid waste and provides a green, cost-effective, and scalable route for the synthesis of high-performance supercapacitor electrode materials, aligning with the goals of waste recycling and carbon neutrality.