N-doped hollow porous carbon flowers with controllable cavity size prepared via confined nanospace pyrolysis enable efficient electromagnetic wave absorption

Carbon materials offer advantages such as low density and high conductivity but suffer from poor impedance matching. Although constructing hollow porous structures can address this issue, conventional templating and template-free strategies often lead to severe agglomeration and structural collapse during high-temperature processing. To overcome these limitations, this study successfully prepared N-doped hollow porous carbon flowers (N-HPCF) with a tunable cavity size using a confined-space pyrolysis strategy. By carbonizing PAD@PDVB precursors with different divinylbenzene (DVB) coating amounts, a series of N-HPCF with various cavity size were obtained. The optimized N-HPCF2 (PAD:DVB = 24:18) exhibits a specific surface area of 85.71 m²·g −1 , and a pore volume of 0.5676 cm³ ·g −1 . It achieves excellent EMWA performance with a minimum reflection loss (RL min ) of −56.79 dB, an effective absorption bandwidth (EAB) of 5.02 GHz at 2.0 mm, and a radar cross-section reduction of 28.8 dB·m 2 . The enhanced performance is attributed to the synergistic effect of the N-doped, flower-like morphology and hollow porous structure, which optimize impedance matching and provide multiple loss mechanisms. Furthermore, a metamaterial design (N-HPCF1–2-3) achieved an EAB of up to 12 GHz (6–18 GHz) in reflectivity simulations, demonstrating that rational structural design effectively enhances EMW absorption performance.