Hydrogel solar evaporator with a sodium sulfonate electrolyte backbone enabling continuous high-salinity desalination and energy generation

Abstract

Interfacial solar-powered desalination has emerged as a promising technology for freshwater production. However, the salt accumulation restricted the effectiveness of interfacial solar evaporators during long-term operation. Inspired by the Donnan effect, a series of sodium sulfonate-based polyanionic hydrogel evaporators are designed to enhance evaporation efficiency in highly concentrated brine. The confined Na⁺ ions within the polyanionic hydrogel matrix create a high chemical potential, establishing a Donnan equilibrium that significantly suppresses salt ion migration from the brine solution, which further prevents performance degradation resulting from salt accumulation. In 20 wt% brine, the polyanionic hydrogel evaporator exhibits a high evaporation rate of 2.23 kg m⁻² h⁻¹ under 1 sun irradiation. It is noteworthy that the polyanionic hydrogel evaporator demonstrates an acceptable evaporation performance, even in a challenging condition with low temperature (-4.8 ℃) and luminous flux (0.01 kW m⁻²). Furthermore, the polyanionic hydrogel evaporator is integrated with a thermoelectric module to exhibit a stable output power of 0.37 W m⁻² and an evaporation rate of 1.85 kg m⁻² h⁻¹. This work not only offers a novel technological approach for extracting fresh water from highly saline sources, but also presents a versatile application method for solar thermoelectric power generation.