Hollow Ni/C microsphere@graphene foam with dual-spatial and porous structure on the microwave absorbing performance

In this study, a unique dual-spatial three-dimensional (3D) porous structure comprising Ni/C hollow microspheres was prepared from a Ni-based metal organic framework (Ni-MOF) embedded in graphene foam (GF) by the solvothermal method followed by calcination. The graphene foam-based composite, Ni/C@GF (NCGF), exhibited a stable spatial conductive network structure and diverse porous architecture, promoting the microwave absorption (MA) properties of composites. The NCGF with a Ni/C and GF ratio of 1:2.5 displayed a reflection loss (RL) value of ─63 dB with 15 wt% loading, while the thickness is only 1.76 mm. Further, its effective absorption bandwidth (EAB) reached to 5.4 GHz at 2 mm thickness. In addition, when the RL value is less than ─20 dB, the NCGF still manifests a wider bandwidth (2.2 GHz) and a relatively low thickness (1.76 mm). In addition to the extraordinary attenuation ability, the excellent MA performance is mainly ascribed to optimized impedance matching characteristics. Moreover, multiple reflections promoted by the dual-space structure also play a significant role during the microwave absorption process. • Ni/C microspheres are successfully embedded into graphene foam to improve the impedance matching. • Unique dual-spatial structure promotes the multiple reflections and scattering. • RL min is ─63 dB at 15.8 GHz with a thickness 2.1 mm and a low filler loading 15 wt%. • Effective absorption bandwidth (RL<─10 dB) reach to 5.4 GHz and the bandwidth with RL less than ─20 dB reach to 2.2 GHz.