Phosphorus-induced tuning of hierarchically porous N-doped lignin carbon material for boosting high-power supercapacitor performance

Lignin possesses the advantages of high carbon content and abundant functional groups, making it suitable as a supercapacitor electrode material. However, the microstructure of lignin-derived electrode materials obtained through traditional methods limits the effective utilization of energy storage capacity, resulting in a significant loss of electrochemical efficiency. Doping with heteroatoms in lignin-derived carbon can enhance its electrochemical performance and is a promising method for performance improvement. We employed a green and universal approach to design lignin-derived carbon materials by covalently grafting phosphorus source (DOPO) and nitrogen source (HDI) onto the lignin macromolecular framework through organic synthesis. Using modified lignin (NPAL) as a precursor, we achieved simultaneous carbonization and activation through a one-pot method. The nitrogen and phosphorus doping synergistically enhances pseudocapacitance activity (redox reactions), optimizes the hierarchical pore structure (increasing the specific surface area to 1756.79 m²/g), and improves charge transfer kinetics (reducing charge transfer resistance to 6.63 Ω). This results in a high specific capacitance (276.3 F/g @ 0.25 A/g, an increase of 275.56% compared to undoped materials), high energy density (12.5 Wh/kg), and cycling stability (capacity retention of 92.5% after 10,000 cycles), indicating a promising application prospect.