Cormorant-inspired macro-porous hydrogel thin film evaporators for boosting cost-effective solar water purification

Getting distilled water through solar energy is a green and sustainable way to purify water. The reduction of the evaporation enthalpy by hydrogels greatly improves the efficiency of water purification. However, the lack of heat localization functionality leads to low energy utilization efficiency, which seriously affects the performance of hydrogel-based evaporators. Herein, inspired by the hierarchical porous channel and thin structure of cormorant wings, a hydrogel thin film with interconnected micrometer macro-pores channels is proposed for simultaneous sufficient heat localization at the evaporation interface and adequate water supply. Benefiting from the macro-porous thin film structure, a device prepared from the hydrogel film can reduce the heat loss by 88% by reducing the heat transfer cross-sectional area and achieve a sustained water evaporation rate of 4.14 kg m-2 h-1 with 98% energy efficiency under 1 sun after shape optimization. Remarkably, the low raw material usage of thin film makes the cost as low as $0.87 m-2. Furthermore, the synthesis method of this macro-porous thin film structure can be generalized to a range of hydrogels, thus serving as a universal technology for improving heat localization. This work demonstrates the application of macro-porous hydrogel thin film evaporators in green and sustainable water purification. We develop a macro-porous hydrogel film strategy for solar water purification inspired by the structure of cormorant wings. The evaporation rate can reach 4.14 kg m-2 h-1 and the energy efficiency can reach 98% under one sun.