Composition and structure control of ultralight graphene foam for high-performance microwave absorption

Macroscopic lossy foam has been expected to be the most promising candidate for lightweight high-performance microwave absorption (MA). However, inferior MA behaviors of conventional foams reported previously are disappointing. The emerging graphene foam (GF) has broken this paradoxical state of affairs. Here, series of GFs with various chemical compositions and physical structures have been prepared via a facile and controllable method and their MA performance is investigated in 2-18 GHz. The in-depth analyses of the GF's composition, structure and MA property demonstrate that the MA performance of the GF is strongly correlated with the C/O ratio, conjugated carbon domain size and graphene framework's microstructure. A maximum absorption value of -34.0 dB as well as 14.3 GHz qualified bandwidth with reflection loss below -10 dB is achieved for the GF with an ultralow bulk density of 1.6 mg/cm³, of which the average absorption intensity and the specific MA efficiency are much higher than those of the best available MA materials in previous literature. The composition & structure-performance relationship of MA foams is revealed. The balance between small interfacial impedance gap and high loss characteristic has wide implications in improving the MA performance of the GF and other porous materials.