Co/O2 contact regulation by rGO of the Co/rGO composites towards superior microwave absorption

Abstract

The interface and phase effective adjustment of Co provide promising perspective for designing high performance microwave absorbers. Here, Co particles with face-centered cubic and hexagonal close-packed structures are obtained and loaded onto the rGO sheets. During different oxidation times (0–60 min), the rGO sheet can limit the diffusion of O₂ and thus tune the contact of Co with O₂ with tunable oxidation kinetics. Kirkendall effects effectively tune the particle size and the Co changes to CoO and/or Co₃O₄ and can completely transfers to Co₃O₄ under oxidation time of 60 min. The phase changes should show influences on the micro-heterogeneous interface and thus enhance interfacial polarization. The Co/rGO-10 composite exhibits superior microwave absorption (MWA) performance with a minimum reflection loss (RL_min) of −48.2 dB at 17.76 GHz (2.3 mm thickness) and an effective absorption bandwidth (EAB) of 6.32 GHz at 3.0 mm thickness. The enhanced performance is primarily attributed to interfacial polarization effects, and the synergistic interaction between dielectric loss and magnetic loss. The conductive, dipole polarization loss together with the interfacial polarization caused by built-in electric field in the heterogeneous interfaces contribute to the efficient MWA performance. Theoretical calculations further reveal the interfacial charge transfer and work function modulation mechanisms (built-in electric field) at the heterogeneous interfaces, providing atomic-level insights into the enhanced dielectric response. This work deepens the understanding of rGO sheet roles in oxidation of Co, and provides a promising strategy for interface tunable oxides MWA materials through oxidation.