Freshwater Harvester with Ultra‐High Yield by Super‐Hygroscopic Composite Under Extremely Low Humidity Environment

Atmospheric water harvesting (AWH) is a promising strategy for freshwater production to alleviate water scarcity, but it remains challenging due to its limited daily water production volume at extremely low relative humidity (RH). Herein, a super-hygroscopic composite (CHG) is reported that is fabricated by using chitosan (CS), hyaluronic acid (HA), metal-organic frameworks (MOF-303), graphene oxide (GO), and calcium chloride (CaCl₂). In this strategy, the CS-HA serves as a cation/anion substrate to form stable hydrogel structure with CaCl₂ salt. MOF-303 and GO exhibit a significantly enhanced water harvesting capacity at low RH (≤30% RH). CaCl₂ additionally improves structural stability, firmly locking the MOF-303 and GO particles into the entangled chain structure of the micro-gel network. The hydrophilicity and porosity of CS-HA frameworks promote diffusion and storage of water molecules, realizing the effective atmospheric moisture capture of the CHG. The CHG realizes a high-water uptake of ≈0.78 g g^-1 at 20% RH, and after absorbing water to saturation at 45% RH, it achieves ≈0.93 g g^-1 in 120 min under 0.50-sun illumination. Especially, CHG on a large scale displays a high sorption-desorption efficiency, which achieves an excellent freshwater yield of ≈9.95 L kg^-1 day^-1 under ≈25% RH and temperature of ≈30 °C via the self-made device. This work offers new insights into the design of high-performance materials for AWH applications in water-lacking situations or arid regions.