Hierarchically Designed Salt‐Resistant Solar Evaporator Based on Donnan Effect for Stable and High‐Performance Brine Treatment

Interfacial solar evaporation is considered to be a promising technology to treat brine with high energy transfer efficiency and a minimized carbon footprint. However, salt accumulation on solar evaporators during the brine treatment process has limited their widespread application. Herein, a hierarchically designed salt‐resistant solar evaporator is demonstrated, featuring confined Na+ with salt‐resistant ability based on the Donnan effect. The high chemical potential of confined Na+ leads to the Donnan distribution equilibrium, which minimizes the amount of the salt ions diffusing into the water supply layer and therefore fundamentally avoids salt accumulation. With this hierarchical design, the solar evaporator enables stable evaporation from high‐salinity brine (15 wt% NaCl) with a solar‐to‐vapor efficiency of 80% under 1 sun irradiation over a long period of time. Therefore, it provides an alternative and promising pathway for solar water treatment of high salinity brine. The unique feature of this hierarchically designed solar evaporator is the confined counter‐ion Na+ in mesoporous structure of the polyelectrolyte hydrogel, which reduces the amount of salt ions diffusing into the water supply layer based on Donnan equilibrium, minimizes the local salt concentration, and enables stable and efficient solar evaporation over the long term.