A Core–Shell Structured Hydrogel Sponge for Efficient and Long-Term Solar Evaporation

Hydrogel solar evaporators are emerging as a promising platform for solar-powered water purification. However, developing durable and highly efficient light-absorbing hydrogels remains challenging due to inevitable salt accumulation during desalination, difficulties in controlling surface topography, and poor mechanical properties of the hydrogel evaporator. This study employed a simple foam polymerization strategy to fabricate a sponge-like hydrogel with a three-dimensional interconnected porous structure. Additionally, we polymerized a layer of poly(3,4-ethylenedioxythiophene) (PEDOT) on its surface as a photothermal layer. Consequently, we generated a composite hydrogel featuring a distinct “core–shell” architecture comprising a PEDOT shell and a sponge-like hydrogel core layer. The resulting composite sponge-like hydrogel evaporator exhibits a tailored surface topography, exceptional elasticity and toughness, superior hydrophilicity, and excellent photothermal conversion performance. Under simulated sunlight (1.0 kW/m2), the evaporation rate can reach up to 2.83 kg/m2 h while maintaining long-term stability. Furthermore, the composite sponge-like hydrogel demonstrates an excellent self-cleaning ability and effectively inhibits the formation of salt crystals on the evaporation surface even under high concentrations of salt water (10 wt %). In summary, photothermal composite sponge-like hydrogels demonstrate remarkable evaporation and desalination properties that hold promising prospects for sustainable utilization in seawater desalination.