Optimizing dielectric polarization for electromagnetic wave attenuation via an enhanced Maxwell-Wagner-Sillars effect in hollow carbon microspheres

The rational integration of dielectric components is a promising approach to optimize the Maxwell-Wagner-Sillars effect (MWSE) for developing lightweight and highly efficient electromagnetic wave (EMW) absorbers. However, the controllable modulation of the dielectric polarization relaxation response remains a great challenge, and impedes the further improvement of the absorption properties. Herein, an inside-out Ostwald ripening and phase-evolution strategy is proposed for the preparation of uniform-sized hollow N-doped carbon microspheres with embedded Ni/Ni2P heterojunctions (Ni/Ni2P/CNs). The resulting Ni/Ni2P/CNs microspheres well-integrated the Ni/Ni2P heterojunctions with a hollow carbon skeleton to optimize the impedance matching and the MWSE, thus reinforcing the dielectric polarization relaxation response. Consequently, the fabricated Ni/Ni2P/CNs exhibited superior EMW-absorption performances with a minimum reflection loss of -72.2 dB at a thin matched thickness of 1.7 mm and the absorption bandwidth reached 5.8 GHz. Such remarkable performances exceed most of the previously reported absorbers with a hollow structure. The experimental results and simulation analysis demonstrated that the Ni/Ni2P/CNs microspheres possessed large interior voids, well-defined heterojunctions, and enlarged electron-redistribution regions, which are crucial contributions to optimize the MWSE and strengthen dielectric polarization. This study presents a novel avenue for the controllable design of MWSE-strengthened absorbers and provides a feasible method to reinforce dielectric polarization with balanced conduction loss and polarization loss.