Phosphomolybdic Acid Induced Water Clusters Formation in Freezing Seawater: Enabling Ultra‐Low Enthalpy and Efficient Solar Evaporation

Abstract Interfacial solar desalination in polar regions requires robust materials with efficient water activation at sub‐zero temperatures. Here, a fluoropolymer evaporator is designed via high internal phase emulsion templating method, embedding phosphomolybdic acid (PMA) in hierarchical microchannels of porous polymer matrix. Crucially, PMA disrupts hydrogen‐bond networks among water molecules, increases the intermediate water ratio by 133%, and promotes the formation of bimodal water clusters, as revealed by Raman spectroscopy, low‐field NMR, and molecular dynamics simulations. Evaporation in the form of water clusters is further validated by Li‐ion carrying experiments. Which results in the reduction of evaporation enthalpy by 28%. By coupling with carbon nanotube‐enhanced light absorption, the evaporator achieves a photothermal efficiency of 93.3% and the record evaporation rates of 2.38 kg m −2 h −1 at 25 °C and 1.84 kg m −2 h −1 at −3 °C, representing the first demonstration of sustained evaporation from sub‐zero seawater in freezing ambient environment. The C─F bonded matrix maintains 30‐day stability under UV and salt fog. By synergistically regulating water‐state transitions and interfacial energy transfer, this work provides a molecular‐engineered solution for extreme‐environment desalination.