ABSTRACT Polarization relaxation has been regarded as an effective approach to convert electromagnetic energy into thermal energy by enhancing the dielectric loss of electromagnetic wave (EMW) absorbers. However, it is still challengeable to effectively construct multiple polarization centers to achieve broadband absorption. Herein, we design a novel self‐stacked structure that is constructed via stacking of nCo@NC (∼15 nm Co nanoparticles on the nonporous carbon) and pCo@NC (∼150 nm Co nanopart