Sandwich-structured rGO/Co x Ni y O z /N-doped carbon nanosphere aerogels for thermal insulation and broadband electromagnetic shielding.

The growing complexity of electromagnetic-wave detection environments calls for microwave absorbers that combine strong attenuation, broad bandwidth, light weight, and thermal management. Herein, we report a sandwich-structured hierarchical reduced graphene oxide (rGO) aerogel decorated with magnetic Co-Ni oxide nanoparticles on N-doped honeycomb-like mesoporous carbon nanospheres (MCN), fabricated via hydrothermal self-assembly. This sandwich-structured aerogel features rGO as both the cross-linker and lossy component, with MCN/Co x Ni y O z as the functional interlayer. This architecture synergistically integrates multiple loss mechanisms: N-doped carbon provides polar groups for dipolar polarization; metallic Co and Ni contribute to strong magnetic resonance loss, while the accompanying oxide phases (such as CoO and CoNiO2) provide abundant cation/oxygen vacancies and heterointerfaces that boost dielectric polarization; and the micro-meso-macro porous structure enables multi-scale scattering while preventing rGO restacking. The resulting aerogel achieves an outstanding minimum reflection loss (RLmin) of -45.51 dB and an effective absorption bandwidth (EAB, ≤-10 dB) of 6.32 GHz at 10 wt% loading. Additionally, over the thickness range of 2.6-3.8 mm, all samples exhibit an RLmin below -20 dB. It also exhibits excellent thermal insulation (16.5 °C surface temperature on a 90 °C hot plate), demonstrating dual functionality for microwave absorption and infrared stealth. This work suggests that sandwich-structured hierarchical engineering combined with compositional and interfacial design is a viable strategy for generating lightweight multifunctional microwave absorbers.