Environmental Heat Harvesting in 3D Gel–Sponge Evaporators for Efficient High-Salinity Solar Desalination

Solar interfacial evaporation is promising for freshwater production, yet thermodynamic energy limits and mass transfer attenuation in high-salinity environments restrict practical applications. To address these challenges, a 3D high-efficiency evaporator is developed by cross-linking a hydrophilic composite gel onto a macroporous sponge scaffold. This spatially decoupled architecture enables fundamental water-state regulation and efficient environmental heat harvesting. Specifically, hydrophilic functional groups in the gel network reduce the equivalent enthalpy of vaporization of water to 1181.8 J g−1. Simultaneously, the 3D columnar structure induces a sidewall cold sink effect to extract additional ambient thermal energy. Through this synergy, the PCPH delivers a remarkable apparent evaporation rate of 8.59 kg m−2 h−1 under one standard sun. Furthermore, interconnected macropores within the sponge establish excellent convective pathways for rapid ion diffusion. Consequently, the device operated continuously for 8 h in a 10 wt% NaCl solution without significant blockage and decreased key metal ion concentrations in 3.5 wt% simulated seawater by 4 to 5 orders of magnitude. The purified water fully satisfies World Health Organization standards. This study offers an innovative strategy to surpass conventional photothermal bottlenecks and design highly durable water treatment materials.