Abstract

Heteroatom doping of nanoporous carbons is a promising strategy to enhance electrochemical energy storage by simultaneously improving electric double-layer capacitance and introducing pseudocapacitive contributions. However, conventional doping strategies typically rely on corrosive activating agents or procedures that are difficult to scale. This study reports a sustainable route to N,P co-doped nanoporous carbon from tannin via mechanochemical blending with non-corrosive ammonium phosphate salts, carbonization under N2, and CO2 physical activation. X-ray photoelectron spectroscopy (XPS) reveals that this green route establishes stable surface speciation dominated by pyridinic and graphitic nitrogen (N similar to 2 at %) and phosphate-type P groups (P similar to 4 at %). The best-performing material achieves a specific surface area and pore volume of up to 1615 m2 g-1 and 1.4 cm3 g-1, respectively, with a micro-mesoporous texture confirmed by N2/H2 adsorption isotherms. In symmetric two-electrode cells using 1 M H2SO4, the best-performing material delivers an electrode capacitance of ca. 254 F g-1 at 0.5 A g-1, retains 95.5% of its initial capacitance after 30,000 charge-discharge cycles, and provides 8.8 W h kg-1 at 164 W kg-1. These results demonstrate that renewable polyphenolic precursors processed by solvent-free mechanochemistry yield competitive carbon electrodes, offering a scalable and environmentally responsible pathway for electrochemical capacitors.