LAUSR

Hygroscopic hydrogels are emerging as scalable and low-cost sorbents for atmospheric water harvesting, dehumidification, passive cooling, and thermal energy storage. However, devices using these materials still exhibit insufficient performance, partly due to limited water vapor uptake of the hydrogels. Here we characterize the swelling dynamics of hydrogels in aqueous lithium-chloride solutions, its implications on hydrogel salt loading, as well as the resulting vapor uptake of the synthesized hydrogel-salt composites. By tuning the salt concentration of the swelling solutions and the crosslinking properties of the gels, we synthesize hygroscopic hydrogels with extremely high salt loadings which enables unprecedented water uptakes of 1.79 g/g and 3.86 g/g at a relative humidity (RH) of 30% and 70%, respectively. At 30% RH, this exceeds previously reported water uptakes of metal-organic frameworks by over 100% and of hydrogels by 15%, bringing the uptake within 93% of the fundamental limit of hygroscopic salts, while avoiding leakage problems common in salt solutions. By modeling the salt-vapor equilibria, we elucidate the maximum leakage-free RH as a function of hydrogel uptake and swelling ratio. These insights guide the design of hydrogels with exceptional hygroscopicity which enable sorption-based devices to tackle water scarcity and the global energy crisis. This article is protected by copyright. All rights reserved.