Biomimetic hydrogel evaporator with excellent salt-rejection performance via edge-preferential crystallization and ion-transport effects

Solar steam generation has been considered a compellent desalination technology due to its environmental friendliness and sustainability, while interfacial salt crystallization and low freshwater yield are two serious issues that constrain its widespread application. In this work, inspired by lotus seedpod, a biomimetic evaporator containing conductive hydrogel was fabricated through 3D printing. The printed evaporator has excellent solar absorption, good mechanical properties, high water capture ability, and reduced vaporization enthalpy, which are exactly desired by good evaporators. Furthermore, the vertical micro-channels and networks inside hydrogel promote the transport of ions from the interface to bulk seawater, and the constructed edge petals drive salt ions to crystallize at the edges, both of these strategies suppress the salt crystallization and ensure long-term continuous operation of the evaporator in concentrated (25 wt%) seawater. Due to these positive effects, the evaporator can achieve 2.413 and 1.889 kg·m−2·h−1 steam yield under one sun in pure water and concentrated (25 wt%) seawater, which is much higher than the 2D evaporator and competitive among the reported evaporators. This work paves the road for the practical utilization of hydrogel in solar desalination.