Nanocurvature‐Activated Dipolar Polarization in M–N ₄ Single‐Atom Sites for High‐Performance Electromagnetic Wave Absorption

The dielectric response of carbon-based single-atom (SA) absorbers is intrinsically constrained by the highly symmetric charge distribution of planar M-N₄ coordination motifs, which suppresses dipole polarization and limits electromagnetic wave (EMW) attenuation. Here, a nanocurvature-driven symmetry-breaking strategy is proposed to activate latent dielectric polarization at SA sites through geometric regulation. By combining click chemistry with template-assisted synthesis, metal SAs are anchored onto hollow nitrogen-doped carbon spheres with precisely tunable diameters, enabling systematic modulation of local nanocurvature. Theoretical calculations and experimental analyses reveal that curvature-induced surface charge accumulation disrupts the electronic symmetry at Ni-N₄ centers, markedly enhancing local charge density, dipole moments, and polarizability. Consequently, the optimized Ni/HNC-200 absorber achieves an ultralow minimum reflection loss of -74.1 dB, representing a staggering 390% enhancement over HNC-200 (-15.1 dB), and exhibits a reduced radar cross section of -70.49 dB m². A flexible electronic patch further demonstrates over fivefold suppression of electric-field radiation from mobile phone chips. The universality of this mechanism is validated in Co- and Cu-based systems, establishing nanocurvature as a geometry-enabled design paradigm for high-performance SAs EMW absorbers.