Maximizing Polarization Responses in Non‐Equilibrium Heterostructures via Fast Joule Heating for Highly Efficient Microwave Absorption

ABSTRACT Constructing multiphase heterojunctions endowed with high‐density defects and asymmetric charge distributions is a promising strategy for highly efficient microwave absorption. However, protracted thermodynamic synthesis inherently drives materials toward a low‐energy equilibrium state, triggering interfacial thermal relaxation and defect annihilation that severely deplete active polarization centers. To overcome these thermodynamic constraints, we develop a fast Joule heating strategy combined with in situ selenization to precisely regulate the continuous Co–Se phase evolution pathway. By delivering a non‐equilibrium thermal shock within seconds, this process dynamically arrests the intermediate state of phase evolution, thereby retaining electronically asymmetric, metastable Co 3 Se 4 /CoSe/NC heterojunctions. Bypassing interfacial thermal relaxation, this kinetically frozen structure preserves abundant unrelaxed defects and induces profound localized electron rearrangement, generating potent interfacial polarization centers. This kinetic trapping enhances localized dielectric loss while achieving a moderate degree of graphitization within the carbon matrix for ideal macroscopic impedance matching. Consequently, the optimized composite achieves an outstanding minimum reflection loss of −70.01 dB at a thickness of only 1.5 mm, alongside a broad effective absorption bandwidth of 5.79 GHz at 1.7 mm. This work goes beyond the constraints of traditional thermodynamic synthesis by establishing a non‐equilibrium phase‐engineering approach, thereby creating new possibilities for developing electromagnetic microwave absorption materials.