Exploration of Twin‐Modified Grain Boundary Engineering in Metallic Copper Predominated Electromagnetic Wave Absorber

High density and skin effect restrict the research progress of metal predominated electromagnetic wave absorbing (EMA) materials. Although some works try to solve it, they do not focus on the metal itself and do not involve the optimization of the active site of the inherent defects of the metal. In this work, the modulation of morphology, composition, interface, defects, and conductivity is achieved by adjusting the ratio of copper salt to reducing agent chitosan. Uniquely, the appearance of twin boundaries (TBs) accelerates the ability of the homogeneous interfaces to transfer charges, resists the oxidation of metal Cu-0, keeps the high electric conductivity of Cu-0 nanoparticles, and enhances the conduction loss, which provides a boost for electromagnetic wave dissipation. As a result, the metal Cu-0 predominated absorber (Cu-NC (N-doped carbon)-10,) exhibits an ultra-width effective absorption band of 8.28 GHz (9.72-18.00 GHz) at a thickness of 2.47 mm and the minimum reflection loss (RL) value of -63.8 dB with a thickness of 2.01 mm. In short, this work explores the EM regulation mechanism of TBs compared with grain boundaries (GBs), which provides a new insight for the rational design of metal predominated EMA materials.