A Diode-like Scalable Asymmetric Solar Evaporator with Ultra-high Salt Resistance

Passive solar-driven interfacial evaporation is an environmental-friendly approach for seawater desalination. However, non-volatile salts usually precipitate on the evaporator surface during evaporation, significantly reducing the evaporation rate and blocking the evaporator. Although several strategies have been proposed for this issue, they are usually only effective under low salinity conditions and natural solar irradiation. In this study, a scalable solar evaporator is proposed, which is expediently fabricated by carbonizing the commercially available coconut fiber cloth, through designing and optimizing an asymmetric bi-layer structure with a trapezoidal evaporation surface and a wide leg-strengthened water supply pathway. Both experimental and simulation results indicate that the evaporator presents ultra-high salt tolerance, which keeps running steadily for consecutive 14 days under the high salinity of 14 wt% NaCl and high irradiation of 4 suns. This excellent salt resistance arises from a diode-like ion migration introduced by its asymmetric structure. Meanwhile, a remarkable evaporation rate of 7.28 kg m⁻² h⁻¹ is also achieved under the harsh condition, resulting from the high solar absorbance and the reduced evaporation enthalpy of the evaporator. Such an evaporator is confirmed as a simple, low-cost, scalable, efficient, and long-term stable device for producing freshwater under harsh desalination conditions.