Hygroscopic porous polymer gels for sorption-based atmospheric water harvesting: A review from sorption mechanisms to materials design

Sorption-based atmospheric water harvesting (SAWH), which converts atmospheric moisture into freshwater, is regarded as a potential solution for alleviating global water scarcity. Among these, sorbents serve as key media for water vapour capture and release, playing a critical role in SAWH technologies. Hygroscopic porous polymer gels (HPPGs), which feature high water retention capacity and exceptional design flexibility, have emerged as promising candidates for next-generation sorbents in this field. The discussion starts by examining the fundamental processes that govern water vapour sorption in SAWH. We then elucidate the key properties of HPPGs and commonly used hygroscopic agents, with particular emphasis on their specific water uptake mechanisms. Based on this, the performance regulation mechanisms and structural design strategies of HPPGs are systematically analyzed and summarized with a focus on four core indicators, namely high water uptake capacity, fast kinetics, low regeneration energy consumption, and excellent cycling stability. The mechanistic analysis presented in this review connects sorbent-water interactions with material design, thereby providing theoretical guidance and design insights for the development of ideal HPPGs for SAWH.