Abstract: To address the severe electromagnetic (EM) pollution and thermal exhaustion issues in modern electronics, C@Mn_xO_y foams were first reported as an advanced multifunctional filler with superior microwave absorption, Radar wave stealth, and thermal dissipation. They were synthesized using a simple one-step annealing route, in which PVP and in-situ generated gas bubbles play a crucial role in the foam formation. Our results show that the C@Mn_xO_y foams possess excellent electrical insulation and a large thermal conductivity of 3.58 W (m K)^-1 at a low load of 5 wt.%. Also, they exhibit prominent microwave absorption capabilities (MWACs) with a strong absorption (-46.03 dB) and a wide bandwidth (11.04 GHz) in a low load (30 wt.%). When they are then used as a patch, the wideband Radar cross-section can be effectively reduced by up to 41.34 dB m². This performance outperforms most other heterostructures. Furthermore, the mechanism of dielectric loss and thermal transfer at the atomic level is revealed by the First-principle calculations of the density of states (DOS) and the phonon density of states (PDOS). The combination of C, MnO, and Mn₃O₄ disrupts local microstructure symmetry and induces extra electrical dipoles at the heterointerfaces, benefiting the enhanced MWACs of C@Mn_xO_y foams along with defect polarization and multiple scattering. Their enhanced TC could be credited to the co-transmission of low phonon-boundary/phonon-defect scattering and multiple-frequency phonons from C, MnO, and Mn₃O₄. Overall, the C@Mn_xO_y foams are highly promising for application in EM protection, absorption, and thermal management. What is more, this study provides a theoretical guide for designing heterostructures as effective microwave absorbing and thermally conductive materials used in modern electronics.

Key words: C@MnxOy foams, PVP-assisted annealing strategy, Thermal conductivity, Microwave absorption, Radar wave stealth, Theoretical calculation