Phosphorus-assisted Direct Air-Pyrolysis of Biomass Enabling Hybrid Porous Carbons for Efficient Microwave Absorption

Direct air-pyrolysis offers an efficient and attractive route for functional porous carbon materials. However, existing strategies severely suffer from specific precursors, limited yields, and additional agents, posing significant challenges for the scalable, direct conversion of biomass under open-air conditions. Herein, inspired by the intumescent flame-retardant design in polymer science, we present a simple phosphorus (P)-assisted, air-pyrolysis strategy that directly converts various biomass into P-doped porous carbon materials, exhibiting excellent electromagnetic wave absorption. By leveraging various commercial P-containing reagents as synergistic charring/doping agents and biomass with multi-hydroxyls as carbon sources, the mixtures were calcined directly in open-air without inert gas protection. Under the superior catalytic dehydration and charring effects of P, thermally stable P-doped intumescent chars were rapidly fabricated at elevated temperatures, resulting in high-quality porous carbons. Typically, P/PC-1 exhibits the specific surface area of 290.2 m2 g−1 and a high mass yield of up to 15.5%, achieving an effective absorption bandwidth of 7.68 GHz at 2.27 mm thickness and a minimum reflection loss of up to −77.70 dB (over 99.99999% absorption efficiency). Notably, our P-assisted air-pyrolysis strategy is applicable and scalable for various biomass species. This work demonstrates a facile, direct, and efficient air-pyrolysis carbonization strategy, offering scalable and economical routes for preparing biomass-derived functional porous carbon materials.