Hofmeister effect assists in improving solar vapor generation via tuning configuration of water and polymer chains

Solar vapor generation emerges as a sustainable method to generate fresh water in recent years. Reducing vaporization enthalpy of water has been considered as a promising route to improve solar evaporation performance. However, many previous works just attribute the reduced vaporization enthalpy to the intermediate water induced by hydratable polymers, which lack detailed mechanism and deep understanding. Herein, inspired by biological phenomena, we intentionally select chaotropic salt potassium iodide according to Hofmeister series, which influences the configuration of polymer chains as well as corresponding water structure, making the hydrogen bond network inside hydrogel highly weakened and the content of intermediate water improved from 48 % to 73.5 %. The result of Molecular dynamics simulations shows the average number of hydrogen bonds on individual water molecule decreased from 1.65 to 1.51, thus the developed (polyvinyl alcohol/ graphene oxide/ iodide) PGI evaporator achieved a high record rate of 2.32 kg·m−2·h−1 under 1 sun irradiation. In this work, we verified the improved solar evaporation performance attributed to the weakened hydrogen bond and further reduced the vaporization enthalpy for the first time, the presented strategy also provides a simple, low-cost and generalizable method to reduce the energy imposed on tuning the configuration of water-contained polymers.