Nano-to-Macro Design of Ultra-scalable Hygroscopic Hydrogels for High-Performance Water Capture

Hygroscopic hydrogels have recently emerged as low-cost and scalable sorbent materials for a wide range of applications including passive cooling, thermal energy storage, building dehumidification, and atmospheric water harvesting. Despite extensive efforts in the synthesis of novel hydrogels, their performance, as quantified by their a) water uptake and b) sorption kinetics, remains limited. Moreover, the rational engineering of hygroscopic hydrogels has been largely unexplored, hindering their optimization for sorption applications. In this work, we leverage physical models we have developed to enable the hydrogel design across different length scales, ranging from the polymer network scale to the macroscopic material scale, for high-performance water sorption. Specifically, we demonstrate a) high water uptakes of 1.74 g/g at 30% RH, exceeding by 15% previous state-of-the-art hydrogels, achievable by maximizing the salt content during synthesis, and b) the impact of polymer nanostructure on sorption kinetics, providing a path to fast kinetics by adequately engineering the polymer network. By simultaneously improving uptake and kinetics, our results demonstrate superior hygroscopic hydrogels which can enable high-power density thermal energy storage, efficient passive cooling, and large-scale water harvesting.