Umbrella evaporator for continuous solar vapor generation and salt harvesting from seawater

Abstract

Solar vapor generation, which uses photothermal materials to desalinate seawater by evaporation, is a promising technology to mitigate the water scarcity problem, but its performance is hindered by large heat leak and salt accumulation problems. Here we report an umbrella evaporator that achieves efficient vapor generation and salt harvesting concurrently via double-sided evaporation and reveal the salt nucleation, growth, and falling mechanism. The evaporator reaches an evaporation rate of 1.25 kg m −2 ·h −1 under ambient conditions, and its continuous operation for vapor and salt production from seawater is demonstrated. The salt mobility on the evaporation surface determines whether the salt could accumulate at the edge, which is influenced by water supply, solar intensity, salinity, and Mg 2+ and Ca 2+ contents.A simple salt creeping test on a glass slide is developed to determine whether and to what extent seawater needs to be pre-treated for continuous operation. • Umbrella evaporator achieves a high efficiency via double-sided evaporation • Central water supply results in salt accumulation at edges • Salt grows from the front by wicking water through its porous structures • Salt creeping behaviors indicate if Ca 2+ and Mg 2+ content is below the lower limit Solar evaporation could mitigate water stress problems, but challenges remain in structural improvement of devices, salt accumulation, and salt harvesting mechanisms. Ma et al. show an umbrella evaporator that achieves efficient vapor generation and salt harvesting concurrently via double-sided evaporation and reveal the salt nucleation, growth, and falling mechanism of salt harvesting.