A novel type of three-dimensional ultralight aerogel sphere, consisting of one-dimensional nanocellulose-derived carbon fibers and two-dimensional graphene layers, was prepared based on a developed drop-freeze-drying followed by carbonization approach. The nanofibrous carbon efficiently prevents the agglomeration of the graphene layers, which, in turn, reduces the shrinkage and maintains the structural stability of the hybrid carbon aerogel spheres. Consequently, the aerogel spheres showing an ultralow-density of 2.8 mg/cm³ and a porosity of 99.98% accomplish the tunable dielectric property and electromagnetic wave (EMW) absorption performance. The high-efficiency utilization of biomass-derived fibrous nanocarbon, graphene, and the porous structure of the hybrid aerogel spheres leads to the excellent EMW absorption performance. The aerogel spheres display an effective absorption bandwidth of 6.16 GHz and a minimum reflection loss of −70.44 dB even at a filler loading of merely 3 wt.%, significantly outperforming that of other biomass-derived carbon-based EMW absorbing materials. This work offers a feasible, facile, and scalable approach for fabricating high-performance and sustainable biomass-based aerogels, suggesting a tremendous application potential in EMW absorption and aerospace.

With the rapid development of the electronic industry and wireless communication technology, electromagnetic interference (EMI) or pollution has been increasingly serious. This not only severely endangers the normal operation of electronic equipment but also threatens human health. Therefore, it is urgent to develop high-performance EMI shielding materials. The advent of hydrogel-based materials has given EMI shields a novel option. Hydrogels combined with conductive functional materials have good mechanical flexibility, fatigue durability, and even high stretchability, which are beneficial for a wide range of applications, especially in EMI shielding and some flexible functional devices. Herein, the current progress of hydrogel-based EMI shields was reviewed, in the meanwhile, some novel studies about pore structure design that we believe will help advance the development of hydrogel-based EMI shielding materials were also included. In the outlook, we suggested some promising development directions for the hydrogel-based EMI shields, by which we hope to provide a reference for designing hydrogels with excellent EMI shielding performance and multifunctionalities.