Metal Ions Confined in Periodic Pores of MOFs to Embed Single-Metal Atoms within Hierarchically Porous Carbon Nanoflowers for High-Performance Electromagnetic Wave Absorption

Nanocarbons with single-metal atoms (M-SAs) have displayed considerable potential in various fields of application due to high free energy of M-SAs and strong metal-support interaction. However, the uniform dispersion of M-SAs within the whole carbon matrix still remains a great challenge. Herein, Ni-SAs are uniformly dispersed within hierarchically porous carbon nanoflowers (Ni-SA/HPCF) via a spatial confinement of Ni ions within the periodic pores in metal-organic frameworks (MOFs) with a subsequent carbonization process. The Ni-SA/HPCF with abundant mesopores and an ultrahigh surface area (1137.2 m(2) g(-1)) exhibits unexpected electromagnetic wave (EMW) absorption property with a minimal reflection loss of -53.2 dB and an effective absorption bandwidth of 5.0 GHz, while the filler ratio in the matrix is merely 10 wt.%. Density functional theory calculations and experimental results reveal that the uniformly dispersed Ni-SAs break local symmetry of the electronic structure and increase electrical conductivity of host carbon matrix, thereby enhancing the EMW absorption properties. In addition, the unique 3D hierarchical porous morphology boosts the impedance matching property, which synergistically improves the EMW absorption performance of the Ni-SA/HPCF. This study provides an efficient approach to uniformly disperse M-SAs within hierarchically porous nanocarbons for EMW absorption and other potential applications.