A natural gain strategy of passive cycling water vapour escape toward efficient freshwater purification

Abstract

Solar interfacial evaporation offers an economical and efficient solution to the global shortage of freshwater resources, and the introduction of the side evaporation surface brings new insights into its efficiency. However, water vapour accumulation slows the evaporation speed at high evaporation rates, and further improvements in its performance have reached a bottleneck. Herein, we develop a zero-carbon tower-type integrated solar evaporator (TIE), which relies solely on solar photothermal power at the bottom to achieve an effective water vapour escape cycle by natural convection, eliminating the need for forced convection (e.g. fins, ducts, etc.). Meanwhile, the hierarchical evaporation surface of the TIE constructed by highly oriented fiber bundles achieves efficient interfacial sunlight absorption and continuous water evaporation in seawater environments. Interestingly, we show that the evaporation rate with this natural gain strategy reaches 5.7 kg m⁻² h⁻¹ under one sun intensity, which is about 32% higher than the average level of the reported three-dimensional solar evaporators. The solar chimney framework overcomes the application limitations of solar evaporators. Our strategy holds the potential to enable the implementation of efficient water evaporation systems to provide a water vapour escape cycle by natural convection without the assistance of other energy losses.