Ultra-lightweight asymmetric hierarchical porous structure for high-efficiency absorption-dominated electromagnetic interference shielding

In this work, ultra-lightweight composite aerogels with a hierarchical pore structure consisting of hollow Fe₃O₄ microspheres (∼250 nm), hollow MXene microspheres (∼580 nm) and pores (10–40 μm) in polyimide (PI) aerogel are developed through directional freezing, followed by freeze drying and thermal annealing. The composite aerogels exhibit a distinct asymmetric structure, with a top Fe₃O₄/PI aerogel layer designed for impedance matching and a bottom MXene/PI aerogel layer aimed at enhancing attenuation. This deliberate structure design not only reduces the density of the composite aerogels but also greatly enhances their absorption of electromagnetic waves. The composite aerogel demonstrates an impressive X-band EMI SE of 69.7 dB, a remarkable absorption coefficient (A) of 0.73, and an excellent surface-specific SE (SE divided by material density and thickness) of 13352 dB cm² g⁻¹, achieved at a density of just 0.034 g/cm³. Moreover, the composite aerogel exhibits outstanding stability in compression and shielding performance. Following 100 cycles of compression, the compressive strength remains at 94.9 % of the initial compressive strength (98 kPa), and its EMI SE maintains 68.5 dB with a retention rate of 98.2 %. Additionally, the composite aerogel presents outstanding thermal insulation (0.046 W m⁻¹ K⁻¹) and thermal resistance (initial decomposition temperature > 500 °C). This work provides novel insights into the design and fabrication of ultra-lightweight and absorption-dominated EMI shielding materials.