Multiaxial electrospun generation of hollow graphene aerogel spheres for broadband high-performance microwave absorption

Although graphene aerogels (GA) have been attracted great attention, the easy-operation and large-scale production of GA are still challenges. Further, most GA have a monolith-like appearance, limiting their application-specific needs. Herein, we highlight graphene aerogel spheres with controllable hollow structures (HGAS) that are delicately designed and manufactured via coaxial electrospinning coupled with freeze-drying and calcination. The HGAS exhibit a spherical configuration at the macroscale, while the construction elements of graphene on the microscale showing an interconnected radial microchannel structure. Further, ball-in-ball graphene aerogel spheres (BGAS) are obtained by reference to the triaxial electrospinning technology. The as-prepared spheres possess the controllable integrated conductive networks, leading to the effective dielectric loss and impedance matching, thus bringing on high-performance microwave absorption. The as-obtained HGAS shows a minimum reflection loss of -52.7 dB, and a broad effective absorption bandwidth (f_E) of 7.0 GHz with thickness of 2.3 mm. Further, the f_E reaches 9.3 GHz for BGAS with thickness of 3.4 mm. Aforementioned superior microwave absorption of HGAS and BGAS confirms combination of multiaxial electrospinning and freeze-drying on the multiscale is an effective strategy for scalable fabrication of advanced microwave absorbing functional graphene aerogel spheres.