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

Abstract 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 (CaCl 2 ). In this strategy, the CS‐HA serves as a cation/anion substrate to form stable hydrogel structure with CaCl 2 salt. MOF‐303 and GO exhibit a significantly enhanced water harvesting capacity at low RH (≤30% RH). CaCl 2 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.