Hofmeister effect mediated hydrogel evaporator for simultaneous solar evaporation and thermoelectric power generation

Porous hydrogel with intrinsic hydrophilicity and reduced vaporization enthalpy has emerged as a rising star for solar-driven interfacial water distillation and desalination. However, the development of facile, general and scalable approaches capable of simultaneously engineering the molecular and microporous structure is urgently needed for hydrogel evaporators but a daunting challenge. Herein, a freeze-soak method based on Hofmeister effect is used to fabricate porous hydrogel evaporators with tunable molecular and microporous structure in large scale. The interconnected porous structure endows the hydrogel with adjustable water transport rate and exceptional desalination performance, while the changeable crystallinity allows the hydrogel with tunable water states. Benefiting from these properties, the hydrogel shows a high evaporation rate of 3.52 kg m-2h−1 with the conversion efficiency of 97.2 % under 1 Sun irradiation. Additionally, the integration of the hydrogel evaporator with a thermoelectric module enables the low-grade heat to electricity conversion. A power density of 0.65 W m−2 is achieved under 1 Sun irradiation. It is anticipated that the Hofmeister effect-mediated porous hydrogel without the assistance of freeze-drying will lay a solid foundation for the industrial fabrication of hydrogel for energy conversion and storage, environmental remediation, etc.