Interface chemical coupling enables Janus elastomer-hydrogel composites for a roof-free evaporator with efficient hydrocooling condensation

Utilizing solar energy to produce fresh water is widely regarded as an effective approach to addressing global water scarcity. In recent years, solar-driven interfacial steam generation (SISG) has significantly enhanced water evaporation efficiency through the development of advanced photothermal conversion materials and innovative evaporator designs. However, traditional roof-mounted condensing structures, commonly used for fresh water harvesting, constrain both evaporation and collection efficiency. The resulting fresh water harvesting rate remains unsatisfactory to researchers. Herein, we have designed a roof-free solar-driven evaporator (SRFE) to improve the fresh water collection efficiency and optimize space utilization. In the SRFE, Janus-structured elastomer-hydrogel composites (JEHCs) were created, which can improve the utilization of solar energy and reduce the enthalpy change of evaporation. Simultaneously, when designed as the photothermal layer of the SRFE, JEHCs can effectively reduce steam loss due to the interaction forces between the hydrogel and elastomer. The system achieves a water harvesting rate of up to 1.536 kg m −2 h −1 under 1 sun irradiation (1000 W m −2 ), with a total photothermal evaporation–condensation efficiency of 82.02%. This Janus-interface engineering of SISG provides a novel strategy and solution for solar-driven fresh water harvesting of practical significance.