Passive interfacial photothermal evaporation and sky radiative cooling assisted all-day freshwater harvesting: System design, experiment study, and performance evaluation

The shortage of freshwater has become a great challenge for the sustainable development of human society. Desalination is considered to be the most practical way to provide a sustainable source of freshwater from seawater, but traditional solar desalination devices usually suffer from the shortcomings of low efficiency and nocturnal failure of freshwater harvesting. In this work, based on the judicious integration of solar-driven interfacial photothermal evaporation (IPTE) and sky radiative cooling (SRC), we design a novel all-day passive freshwater harvesting (FWH) system and carry out a systematic study on its FWH performance, including field experimental tests, performance modeling, and capacity predictions. During the daytime, the seawater is transported to the IPTE layer through the bionic plant water-drawing structure. The IPTE layer absorbs solar energy for seawater evaporation to increase the evaporation efficiency. Meanwhile, by utilizing the salt concentration difference for power generation, we achieve a 64.23% reduction in salt accumulation and a 7.69% enhancement in the seawater evaporation rate. At nighttime, the SRC coating cools the sloping surface and helps to harvest freshwater by condensing the moisture in the air. Outdoor experiment results and numerical prediction results confirm that the proposed system can passively produce freshwater during a 24-h day cycle in an uninterrupted manner, paving a bright future for freshwater resources at no active energy consumption.