Water bridge solar evaporator with salt-resistance and heat localization for efficient desalination

Abstract

Inadequate freshwater supply in remote and developing areas has motivated the growing demand for cost-effective and efficient desalination technologies. Solar-driven interfacial evaporation has emerged as an environment-friendly method for water desalination. However, salt precipitation on the evaporating surface compromises the efficiency and continuity of desalination considerably. In general, salt-resistance is achieved at the expense of massive heat loss, resulting in the inherent trade-off between salt resistance and heat localization. Herein, we report a water bridge solar evaporator (WBSE), whose thin water layer is elevated by capillary force, forming a bridge-shaped water layer. Notably, the water bridge reduces sunlight diffuse reflection, inhibits heat loss to bulk water, and simultaneously endows the evaporator with salt-resistance. Therefore, the solar-driven water evaporation rate of 1.64 kg m⁻² h⁻¹, with an energy efficiency of ∼102% under one-sun illumination in 3.5 wt% brine, is achieved. Moreover, no salt precipitation is observed during the evaporation process in high salinity brine, while a high evaporation rate (∼1.56 kg m⁻² h⁻¹) in 15–20 wt% brine under one-sun illumination is achieved. This WBSE offers new insights into the design of solar evaporators with high efficiency and long-term stability.