Stacked dual-interface bi-hydrophilic structuration boosting solar vapor-to-water conversion

Generating solar vapor through thermal localization is a promising solution to address the global water shortage. However, incident light attenuation and latent heat accumulation of front-end condensing interface have led to a negative cascade effect between low condensing efficiency and heat loss, constraining the water evaporation rates (WER) and specific water productivity (SWP). This study presents an innovative approach of stacked front-end heat recovery architecture (SFE-HRA) developed based on a bi-hydrophilic transparent micro-nano-film (biH-TMNF). The biH-TMNF is designed and functionalized as a circulatable front-end vapor condensation cooling component that integrates a liquid film condensation module with two-phase functionalization and a porous hydrogel module. The biH-TMNF allows solar vapors from the bottom to adhere to the anti-fogging hydrophilic surface as a micro-liquid film while maintaining as high a light incidence as possible (> 90 %). At the same time, the latent heat of vapor is released to the second stage of the transparent hydrogel evaporator to drive the next stage of the latent heat of the vapor cycle. A 3-stage stacked SFE-HRA was constructed and demonstrated with the conventional solar evaporator [(SFE-HRA)-CSE]. The (SFE-HRA)-CSE system obtained a considerable increase in water evaporation rates (WER) by 150 % and a substantial improvement in condensate recovery by 200–300 %. A critical role of the dual bi-hydrophilic interface has been emphasized in promoting the efficiencies of latent heat cycle and water harvesting. The proof-of-concept testing confirmed an unprecedented SWP efficiency of 130 % from (SFE-HRA)-CSE, surpassing all SWPs from the high-performance front-end evaporators that have been reported.