N, P Co-doped porous biochar derived from cornstalk for high performance CO₂ adsorption and electrochemical energy storage

Modification of biomass-derived porous biochar by heteroatomic doping can significantly improve CO₂ adsorption and capacitance performance of supercapacitors. In this study, a novel N, P co-doped porous biochar was developed by facile two-step pyrolysis using widely available and low-cost cornstalks as the carbon source, melamine as the N source, phytic acid as the P source, and a mild K₂CO₃ as an activating agent. The pore structures and surface chemical characteristics of the as-prepared N, P co-doped cornstalk-derived porous biochar (abbreviated as NPCPB) were regulated by adjusting the pyrolysis temperature and K₂CO₃ ratio. The as-prepared NPCPB-600-3 (600 represents an activation temperature of 600 °C, and 3 represents the mass ratio of K₂CO₃ to the carbon composite precursor is 3) was characterized by various methods, and its CO₂ adsorption and electrochemical properties were studied. Results indicated that narrow micropores and N, P doping together determined the adsorption capacity, which was 3.11 mmol g⁻¹ for CO₂ at 1 bar and 25 °C, with almost no decay after 10 consecutive cycles. NPCPB-600-2 had a superior specific capacity of 203.5 F g⁻¹ at a current density of 1 A g⁻¹ and an outstanding cycling stability with a good capacity retention of 106% after 5000 cycles at a high current density of 10 A g⁻¹. This work reveals that heteroatomically doped porous biochar from biomass has a promising application in CO₂ capture and supercapacitors.