Extreme Water Uptake of Hygroscopic Hydrogels through Maximized Swelling-Induced Salt Loading

Area of Science:

• Materials Science
• Chemical Engineering
• Environmental Science

Background:

• Hygroscopic hydrogels are promising for atmospheric water harvesting, dehumidification, passive cooling, and thermal energy storage.
• Current hydrogel-based devices have limited performance due to insufficient water vapor uptake.
• Addressing water scarcity and energy crises requires enhanced water harvesting technologies.

Purpose of the Study:

• To characterize the swelling dynamics of hydrogels in lithium chloride solutions.
• To investigate the impact of salt loading on hydrogel-salt composites' water vapor uptake.
• To design hydrogels with extremely high salt loadings for improved water harvesting.

Main Methods:

• Characterization of hydrogel swelling in aqueous lithium chloride solutions.
• Synthesis of hydrogel-salt composites by tuning salt concentration and gel cross-linking.
• Measurement of water vapor uptake at various relative humidity levels.
• Modeling of salt-vapor equilibria to determine maximum leakage-free relative humidity.

Main Results:

• Synthesized hydrogels achieved extremely high salt loadings.
• Achieved unprecedented water uptakes of 1.79 g/g at 30% RH and 3.86 g/g at 70% RH.
• Water uptake at 30% RH exceeded metal-organic frameworks by over 100% and hydrogels by 15%.
• Uptake reached 93% of the theoretical limit for hygroscopic salts without leakage.

Conclusions:

• Hydrogel-salt composites with optimized properties enable significantly enhanced water vapor uptake.
• Insights into salt-vapor equilibria and swelling dynamics guide the design of high-performance hygroscopic materials.
• These advanced hydrogels can significantly advance sorption-based devices for water scarcity and energy solutions.