Moisture Harvesting by the Structure Regulation of Hygroscopic Hydrogel for Energy and Water Sustainability

Water and energy are the cornerstones of human development, with more than half of the world's population facing water scarcity issues. Atmospheric moisture is widely distributed around the globe, and the rational utilization of moisture can create tremendous value. Here, the sources of hygroscopic materials, methods of manufacturing hydrogels, properties of these hydrogels, and potential energy applications are concluded. To make the hydrogels with high hydrophilicity, ultrasonic oscillation, freeze drying, and spin coating can be used as the synthesis strategies. The main focus is on the characteristic parameters of hydrogels with water uptake, dehydration temperature, conductivity, mechanical stability, swelling behaviors, and heat transfer coefficient. These unique features will affect the performances of assembles, devices, and instruments. Subsequently, the potential applications of hydrogels are summarized, such as moisture harvesting and splitting with fuel production, dehumidification, thermal management in electronic devices, solar water evaporation, and electricity production. Finally, future directions and issues of interest are proposed to promote the diverse development of hydrogels and relational systems.