Response surface methodology-optimized single-batch production of herbal residue-based N,P co-doped carbon materials for enhanced electrochemical efficiency

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.