A Facile Freeze-Drying Strategy To Prepare Hierarchically Porous Co/C Foams with Excellent Microwave Absorption Performance

The hierarchically porous Co/C foam with low density has been successfully prepared by a facile sequential process of foaming–lyophilization–carbonization. In the hierarchical structure, the macro- and mesoscopic pores are created by surfactant-assisted foaming and lyophilization processes, while the nanoscale pores spring from the etching reaction between gelatin-derived carbon and metal oxides during the high-temperature carbonization. By adjustment of the carbonization temperature and loading of the as-prepared absorbent, a maximum reflection loss (RL) achieves −56.5 dB at the thickness of 2.49 mm, and a broad effective absorption bandwidth (EAB) of 6.0 GHz is reached. The corresponding mechanism demonstrates that such an outstanding performance is rooted in the synergetic loss capacities from dielectric and magnetic components. Therefore, it is believed that this work provides a significant guidance for exploring high-performance and lightweight microwave absorbents.