Polyimide-based graphene composite foams with hierarchical impedance gradient for efficient electromagnetic absorption

The development of high-performance microwave absorption materials with strong absorption capacity and broad bandwidth is highly desirable in the field of electromagnetic pollution protection. Herein, polyimide/graphene composite foam with a multi-hierarchical impedance gradient structure has been precisely designed and controllably constructed by two-step vacuum impregnation, which effectively facilitates further attenuation of electromagnetic waves entering the graphene skeleton due to the generation of interfacial polarization relaxation and internal multiple reflection/scattering, thereby endowing it with excellent broadband microwave absorption performance. Meanwhile, the microwave absorption performance can be controllably adjusted by optimizing the impedance gradient of the skeleton. As a result, the optimized PI–GP–rGO composite foam exhibits a minimum reflection loss of −32.87 dB with an effective bandwidth of 6.22 GHz (8.26–14.48 GHz) at 10.39 GHz when the thickness is 4.0 mm.