In this study, zinc oxide (ZnO)/polypyrrole (PPy) composites with flower- and rod-like structures were successfully fabricated by in situ polymerization and the hydrothermal method and used as microwave absorption (MWA) materials. The surface morphologies, crystal structures, and electromagnetic features of the as-prepared samples were measured by field-emission scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and vector network analyzer (VNA). The results show that the conductive polymer PPy was successfully decorated on the surface of ZnO substrates. The MWA ability of flower- and rod-like ZnO/PPy composites is significantly enhanced after introduction of PPy. Rod-like ZnO/PPy composites exhibited superior MWA properties than those of flower-like ZnO/PPy. The former achieved a minimum reflection loss (RLmin) of −59.7 dB at 15.8 GHz with a thickness of 2.7 mm, and the effective absorption bandwidth (EAB, RL < −10 dB) covered 6.4 GHz. PPy addition and stacked structure of rod-like ZnO/PPy composites can effectively improve the dielectric properties, form multiple reflections of incident electromagnetic waves, and generate an interfacial polarization effect, resulting in improved MWA properties of composite materials.

The design of hollow porous microstructure and the selection of reasonable dielectric composition are effective ways to obtain microwave absorbing (MWA) materials with outstanding performance. In this paper, polypyrrole decorated ZnO hollow porous composites (ZnO@PPy HPC) with improved MWA performance were successfully prepared by an in-situ polymerization method. The results showed that PPy was uniformly loaded on the surface of ZnO hollow porous microspheres (ZnO HPM) to build a hierarchically core-shell hollow structure. The addition and proportion regulation of PPy can effectively improve the dielectric properties, generate interfacial polarization effect and achieve good impedance matching, leading to enhanced MWA characteristics of composite materials. ZnO@PPy HPC exhibited promising broadband microwave absorption properties. The minimum reflection loss (RLmin) reached −48.5 dB at 14.5 GHz with broad effective bandwidth (less than −10 dB) of 6.2 GHz when the matching thickness was 2.2 mm. This study provides guidance for the development on a new type of microwave absorbing materials composed of hollow porous structure and conductive polymer.