Evaporation above a bulk water surface using an oil lamp inspired highly efficient solar-steam generation strategy

Inspired by the traditional oil lamp, a solar-steam generation system with the evaporation surface located above the bulk water surface is realized using a cotton strand coated with a photothermal layer of polydopamine as a wick. The strong wicking effect of the cotton strand is able to rapidly transfer a significant amount of water to the evaporation surface located at >9 cm above the bulk water surface. The capability to separate the evaporation surface from the bulk water is highly advantageous as it decreases the dissipation of heat into the bulk water. This leads to highly localized light-to-heat energy conversion, which results in outstanding solar-steam generation performance. The energy conversion efficiency for the water evaporation system reaches 88.8% under 1.0 sun irradiation. This system was applied to decrease the salinity of seawater, demonstrating that clean water could be produced from salty water via evaporation with a residual Na concentration of only ∼0.31 ppm under 1.0 sun. The proposed strategy is simple, and the optimized design does not require photothermal materials to float on the water surface, but rather allows the photothermal material to be fixed at a considerable distance above the water surface. The overall system is both natural and cost effective and thus shows great potential for real-world applications particularly in developing countries where natural resources are already stretched, and access to clean drinking water is not guaranteed.