Microstructure evolution and electromagnetic wave absorption of CoNi@Pangdahai-derived carbon composites

Widespread deployment of wireless technologies has aggravated electromagnetic (EM) radiation pollution. Developing high-performance electromagnetic wave (EMW) absorbers with low density, thin-layer, excellent absorption, and broad bandwidth is of critical strategic significance. Traditional carbon-based absorbers, relying solely on dielectric loss, exhibit insufficient absorption and severe impedance mismatch. Herein, a biomass-directed interface modulation strategy is demonstrated. Using Pangdahai, a traditional Chinese medicinal plant, as a biocarbon precursor, three-dimensional (3D) porous sponge-like cobalt/nickel (Co/Ni) bimetallic carbon composites are synthesized via facile impregnation and high-temperature carbonization. The layered pore structure acts as a micro-resonant cavity, greatly enhancing the internal multiple reflections and scattering of EMW. Meanwhile, tuning the molar loading of Co and Ni salts optimizes the complex permittivity and permeability, enabling synergistic effects of interfacial polarization and conductive loss, complemented by the magnetic loss effect. The synthesized composite demonstrates superior EM absorption capabilities, evidenced by a minimum reflection loss (RL min ) of −75.46 dB. By modulating the loading of Co and Ni, an effective absorption bandwidth (RL < -10 dB) of 5.89 GHz is achieved. This work provides a green, low-cost, and scalable strategy for fabricating high-performance and lightweight EMW absorbers from sustainable biomass waste.