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.