Coupled Ionic Conduction Loss and Dipole Polarization Loss in Atmospheric Water Harvesting Foams for Electromagnetic Wave Absorption

Water, an abundant resource with approximately 1.3 × 10 16 liters present in the atmosphere and essential for sustaining life, has long held untapped potential for electromagnetic wave absorption (EWA) due to persistent technical challenges, including difficulties in encapsulation, impedance mismatch, and restriction on a single loss mechanism. To address these limitations, this study develops a multi‐phase system via atmospheric water harvesting (AWH), wherein surface tension and capillary action confine inorganic solution to foam surfaces, forming ultrathin liquid films that enable synergistic interaction among the air/water/polymer phases and enhance impedance matching. Experimental results reveal that, within the temperature range of 283–323 K, CaCl 2 ‐PI@H 2 O attains a minimum reflection loss ( R L ) of −44.6 dB at 4 mm (30% RH ‐ 40% RH), effective absorption bandwidth (EAB) perfectly covers the X band (7.4–12.6 GHz). Whereas LiCl‐PI@H 2 O achieves an R L of −40.4 dB at 4 mm (60% RH ‐70% RH), EAB remarkably broadens to 8.4–18.0 GHz. The key innovation lies in the incorporation of water into a confined salt‐solution film, handling the inherent impedance mismatch and single‐loss mechanism limitation of water as an absorbing medium, thereby offering a novel and promising strategy for fabricating high‐performance liquid‐based EWA materials.