Highly transparent sponge-like hydrogel substrates regulated by NaCl for efficient solar water evaporation

Solar-driven interfacial evaporation (SDIE) is widely regarded as a promising and sustainable approach for water resource regeneration. However, most studies primarily focus on optimizing photothermal materials or device configurations to enhance evaporation performance, whereas the efficient utilization of incident solar energy remains underexplored. In this work, highly transparent sponge-like hydrogels (HTSH) were fabricated via NaCl-regulated photopolymerization of acrylamide under a semi-frozen, temperature-controlled condition. Owing to their macroporous architecture and high water content within the gel matrix, the resulting polyacrylamide sponge-like hydrogels effectively suppress interfacial optical scattering, enabling deeper light penetration and enhanced solar light utilization. Polydopamine was polymerized in situ onto the hydrogel substrate to construct an integrated SDIE device. As a result, the synergistic integration of enhanced light utilization, efficient water transport, and tailored surface morphology enabled a water evaporation rate of 1.92 kg·m −2 ·h −1 under one-sun irradiation, demonstrating the effectiveness of evaporative architectures derived from HTSH substrates.