Capillary-Flow-Optimized Heat Localization Induced by an Air-Enclosed Three-Dimensional Hierarchical Network for Elevated Solar Evaporation

Solar evaporation is a cost-effective way for obtaining clean water using renewable energy. However, many solar evaporation devices still show unsatisfactory performance and suffer from inefficient utilization of absorbed solar energy. Herein, numerical simulations of solar evaporation demonstrate that the heat management is a key factor governing the solar evaporation efficiency. This prediction is confirmed through using a bilayered solar steam generation architecture [hollow glass microsphere-carbon black (HS-CB)] both in laboratory- and pilot-scale studies. The HS-CB consists of a CB film as a solar-thermal conversion layer and three-dimensional hierarchical polyvinylidene fluoride skeleton cross-linking HSs as a heat localization and water-transporting layer. A balance between thermal insulation and capillary-driven water transport can be reached by tuning the porosity of the thermal-insulating layer, thus inducing optimized heat localization. The proposed structure evaporates water with an efficiency of 82.1% under 1 sun irradiance (1 kW m-2) in the laboratory and can even stably produce 4.63 L m-2 d-1 (average efficiency of 37%) of purified water from highly concentrated industrial waste water in the pilot study, demonstrating its promising potential for applications in seawater desalination and brackish water purification.