Layered-structure N-doped expanded-graphite/boron nitride composites towards high performance of microwave absorption

High-efficiency microwave absorbers with broadband absorption are strongly desired for electromagnetic protection. Herein, we successfully synthesized a hybrid microwave absorbing material with two-dimensional layered structure, which consisted of expanded graphite (EG) and boron nitride (BN). The introduction of BN is to regulate the conductivity of EG and also to improve the thermal stability of the composite material. The ultrathin BN nano-sheets were uniformly wrapped on the EG sheets via chemical vapor deposition. Attributed to the dielectric loss and conductive loss, the as-prepared hybrid material exhibited high performance for microwave absorption. The effective absorbing bandwidth (reflection loss value < -10 dB) was achieved up to 9.37 GHz with the thickness of 2.4 mm in the frequency range of 5.75–6.98 GHz and 9.86–18 GHz. And the minimum reflection loss was -51.58 dB at the thickness of 3 mm. The excellent performance of microwave absorption was attributed to the dielectric loss, interfacial polarization loss and optimized impedance matching. Moreover, compared to pure EG, the thermal decomposition temperature of EG/BN composite materials had increased by about 100 °C which was up to 714 °C. Taking the advantages of high thermal stability of BN as well as the fine microwave absorbability of EG, the EG/BN composites would be applied in high-temperature microwave absorbing fields.