CoFe@C composites decorated with residual carbon as an ultrathin microwave absorber in the X and Ku bands

Achieving a wide effective absorption bandwidth in 8.0–18.0 GHz under ultrathin thickness (d < 2.0 mm) with a low filler ratio is difficult. Herein, Co/Fe metal–organic framework (MOF)-derived CoFe@C composite-decorated residual carbon (CoFe@C/RC) hybrids collected from coal gasification fine slag (CGFS) by removing the inorganic oxide components were synthesized via a technology by modulating the molar ratio of Co/Fe. The physicochemical properties of the synthesized CoFe@C/RC with different molar ratios of Co/Fe were studied via various analytical techniques, and then the electromagnetic parameters associated with the above research results were analyzed. The defects, microstructure and electromagnetic wave absorption (EMWA) performance of CoFe@C/RC changed with the change in the Co/Fe molar ratio. Impressively, the Co1Fe3@C/RC hybrids exhibited excellent EMWA capacity. Under a filler content of 20 %, the ternary hybrid with a molar ratio of Co/Fe of 1:3 showed a minimum reflection loss (RLmin) of −20.0 dB and a broad absorption bandwidth (fe, RL ≤ −10 dB) of 3.95 GHz at a thickness of 1.7 mm. Importantly, the ultrabroad fe reached 10.0 GHz (8.0–18.0 GHz); it covered the whole Ku and X bands by simply adjusting the thicknesses of the CoFe@C/RC absorber in 1.5–3.0 mm. The CoFe@C/RC hybrids possessed outstanding EMWA because of the excellent effective synergy of magnetic and dielectric losses. This work realizes the high-value application of coal gasification solid waste and offers an efficacious strategy for creating novel CGFS residual carbon-based ultrathin EMW absorbing materials at 8–18 GHz.