Highly homogeneous dispersed Ni/Co nanoparticles in carbon controlled by ion coordination to trigger polarization for enhanced microwave absorption

The local chemical structure of carbon can be effectively tuned by highly homogeneous dispersed Ni/Co nanoparticles with diameters of dozen nanometers by their catalysis for carbon graphitization during carbonization process of polymer which thereby induces multiple polarization relaxation, ultimately enabling excellent microwave absorption performance. However, realizing uniform distribution and precise size control remained challenging due to magnetic aggregation and Ostwald ripening during thermal treatment. Herein, a metal-ion coordination strategy achieves homogeneous nanoparticle dispersion by leveraging the strong chelation between tannic acid and metal ions. The differential stability of these coordination bonds dictates nanoparticle growth kinetics, enabling precise size control. This tailored nanoparticle size subsequently governs the chemical structure of the carbon to modulate polarization loss. Benefiting from these finely tuned graphitization percentage and distribution, the carbon with highly homogenous dispersed Ni nanoparticles of 12–14 nm in diameters (TAC Ni) concurrently established an efficient conductive network, abundant heterogeneous interfaces and ample defects for polarization centers, leading to optimized dielectric loss. Consequently, TAC-Ni achieved an impressive effective absorption bandwidth (EAB) of 6.0 GHz at a thickness of 2.19 mm. This work not only provided a novel and controllable synthetic route for highly-dispersed carbon with highly homogenous dispersed magnetic nanoparticles but also offered a new perspective for designing high-performance microwave absorbing materials (MAMs).