Unveiling the sp2─sp3 C─C Polar Bond Induced Electromagnetic Responding Behaviors by a 2D N‐doped Carbon Nanosheet Absorber

The infertile electromagnetic (EM) attenuating behavior of carbon material makes the improvement of its performance remain a significant challenge. Herein, a facile and low‐cost strategy radically distinct from the prevalent approaches by constructing polar covalent bonds between sp2‐hybridized and sp3‐hybridized carbon atoms to introduce strong dipolar polarization is proposed. Through customizing and selectively engineering the N moieties conjugated with carbon rings, the microstructure of the as‐synthesized 2D nanosheet is gradually converted with the partial transition from sp3 carbons to sp2 carbons, where the electric dipoles between them are also tuned. Supported by the DFT calculations, a progressively enhanced sp2─sp3 C─C dipolar polarization is caused by this controllable structure evolution, which is demonstrated to contribute dominantly to the total dielectric loss. By virtue of this unduplicated loss behavior, a remarkable effective absorption bandwidth (EAB) beyond ‐10 dB of 8.28 GHz (2.33 mm) and an ultrawide EAB beyond ‐5 dB of 13.72 GHz (4.93 mm) are delivered, which upgrade the EM performance of carbon material to a higher level. This study not only demonstrates the huge perspective of sp2─sp3‐hybridized carbon in EM elimination but also gives pioneering insights into the carbon–carbon polarization mechanism for guiding the development of advanced EM absorption materials. The sp2─sp3‐hybridized 2D carbon nanosheets are synthesized via a facile and low‐cost salt‐assisted thermal‐polymerization and pyrolysis strategy. The materials composed of only C and N atoms present ultrawide electromagnetic absorption bandwidth. This study excitingly reveals that sp2─sp3 C─C polar covalent bonds enable strong dipolar polarization loss.