NiCo2O4/Hollow Mesoporous Carbon Nanosphere Hybrids Enabling Super‐Hydrophobicity, Thermal Insulation, and Highly Efficient Microwave Absorption

Abstract The combination of 2D magnetic nanosheets and mesoporous carbon with unique interfaces shows considerable prospects for microwave absorption (MA). However, traditional assembly procedures make it impossible to accurately manage the assembly of magnetic nanosheets in carbon matrices. Herein, a reverse strategy for preparing complex magnetic nanosheet cores inside carbon‐based yolk–shell structures is developed. This innovative approach focuses on controlling the initial crystallite formation sites in a hydrothermal reaction as well as the inflow and in situ growth behavior of 2D NiCo‐layered double hydroxide precursors based on the capillary force induced by hollow mesoporous carbon nanospheres. Accordingly, the as‐prepared YS‐CNC‐2 absorber exhibits remarkable MA performances, with an optimal reflection loss as low as −60.30 dB at 2.5 mm and an effective absorption bandwidth of 5.20 GHz at 2.0 mm. The loss of electromagnetic waves (EMW) depends on natural resonance loss, dipole polarization relaxation, and multiple scattering behavior. On top of that, the functionalized super‐hydrophobic MA coating is produced in spraying and curing processes utilizing YS‐CNC‐2 nanoparticles and fumed silica additives in the polydimethylsiloxane matrix. The excellent thermal insulation, self‐cleaning capability, and durability in diverse solutions of the coating promise potential applications for military equipment in moist situations.