Atmospheric Pressure Dried Discontinuous Pore Gradient Structured CNF‐Based Aerogel for Ultra‐Low Reflection, Broadband, and Super‐High EMI Shielding

Abstract Large scale production of aerogels with ultra‐low reflection coefficients for electromagnetic interference (EMI) shielding remains a significant challenge. This work reports a gradient and large area composite nanocellulose fiber aerogel (CNA) with discontinuous pores structures using ice crystal dissolution/regeneration and atmospheric pressure drying strategies. The CNA consisting of three layers of ordered‐ordered‐disordered pore orientation achieved ultra‐high EMI shielding efficiency (>90 dB) across ultra‐broad electromagnetic wave (EMW) bands (L, S, C, X, Ku‐band) and exhibited ultra‐low reflection coefficient (R ≈ 0.20). Simulation results confirmed that the average pore sizes of layers 1 and 2 should be 120 and 40 µm for achieving excellent EMW transmission and absorption, respectively. The disordered pore structure of layer 3 with an average size of less than 345 µm showed significant characteristics in reflecting EMW and is unaffected by the material dielectric properties. Furthermore, the CNA demonstrated great potential in selective recovery of ethanol waste produced from the aerogel preparation process. It showed an evaporation rate of 3.3 Kg m −2 h at 1.0 sun and yielded a concentration of up to 96.1% in a natural environment. This study provides new insights and approaches for the pore structure design of aerogels in EMI shielding.