MOF‐Derived FeNi/C Composites Constructed by Controlled Etching for High‐Performance Electromagnetic Wave Absorption

ABSTRACT The rapid growth of electronic devices has intensified electromagnetic wave pollution. Electromagnetic wave absorption (EWA) materials provide a green solution by converting electromagnetic energy into thermal energy. Achieving high‐performance EWA requires a fine balance between impedance matching and energy dissipation, demanding precise control of microstructure, interfaces, and electronic states of the materials. However, complex multiscale structures involve strongly coupled structural evolution, which reduces controllability and hinders clear structure–performance correlation. Here, a cobalt‐based metal–organic framework (Co‐MOF) is employed as the precursor. By regulating the contents of Ni 2 + and Fe 3 + , the structural evolution and the modulation of localized electronic states during the etching process are systematically elucidated. In addition, the in situ competitive coordination and etching‐competitive coordination systems reveal the mechanistic differences between atomic‐scale induced reconstruction and directional destructive reconstruction. Benefiting from synergistic regulation spanning atomic, nanoscale, and microscale levels, the obtained FeNi/C composite achieves an effective absorption bandwidth of 7.13 GHz at an ultrathin thickness of 1.97 mm. Combining DFT, COMSOL, and CST simulations, the role of etching engineering in enhancing EWA performance is elucidated from electronic, local‐field, and macroscopic perspectives, providing a theoretical basis for its controllable application and the rational design of high‐performance absorbers.