Robust Mix-Charged Polyzwitterionic Hydrogels for Ultra-Efficient Atmospheric Water Harvesting and Evaporative Cooling

Abstract

Atmospheric water harvesting (AWH) presents great potential in addressing the increasing global challenges in freshwater and energy supply, especially in arid and semi-arid regions. The recent AWH materials focus primarily on maximizing water uptake, while conventional approaches prioritize hygroscopicity at the expense of mechanical integrity, which severely limits their applicability in real-world scenarios. In this study, a novel tunable hygroscopic mix-charged polyzwitterionic hydrogel (THMPH) is reported that achieves dual excellence in outstanding moisture absorbency and mechanical robustness. Owing to the broad ionic crosslink's degree enabling the rigid skeletal framework and energy-dissipative sacrificial networks, THMPH exhibits more than 200 times higher mechanical ductility (225 kPa tensile strength retention at 200% mass swelling ratio) in comparison with the commonly-used AWH zwitterionic polybetaine. The optimized topological structure coupled with improved lithium chloride binding affinity results in excellent water uptake (2.9 g g⁻¹ at 25 °C, 70% RH). When THMPH is used for daytime photovoltaic panel cooling, it can provide a 15 °C temperature reduction of a PV panel under 1 kW m⁻² solar irradiation, resulting in a 7.33% increase in solar energy conversion efficiency. This hydrogel design paradigm, synergizing superior hygroscopicity with exceptional mechanical robustness, demonstrates significant potential for advancing practical applications.