Abstract: Preparation of electromagnetic (EM) wave-absorbing composites by interface engineering has been the main strategy to obtain high-performance absorbers. However, the conventional strategy is tedious and time-consuming, which hinders the scalable synthesis of stable EM wave-absorbing composites. Herein, interface engineering by a redox reaction between transition metal elements in Co-based spinel ferrites was employed to create EM wave-absorbing composites to solve the above problem. Among serial MCo₂O₄ (M = Ni, Cu, and Zn) spinel ferrites, redox reactions during synthesis only occurred between Cu and Co elements, thus leading to the presence of multiple crystal phases on final samples. With the aid of increased polyethylene glycol (PEG) molecular weight (MW), more heterogenous interfaces between CuO and CuCo₂O₄ phases as well as induced crystal defects were generated. Under synergetic interface engineering by means of PEG-assisted redox reaction, interfacial polarization, and defect-induced polarization loss were markedly enhanced on a CuCo₂O₄-based sample that was prepared with PEG MW of 100 K. The effective absorption bandwidth of the corresponding sample could reach 6.48 GHz (11.52-18 GHz) with a thickness of 2.28 mm. In short, this work provides a novel strategy for designing EM wave absorbing composites by interface engineering through redox reaction instead of the conventional composition coupling process.

Key words: Electromagnetic wave absorption, Redox reaction, Interfacial engineering, Spinel ferrite