Hybrid Nanofiber-Based Atmospheric Water Harvesters: Sunlight-Driven Operation in Low-Humidity and Low-Illumination Environments

Aerogels incorporating hygroscopic salts have been widely explored for atmospheric water harvesting (AWH). However, the scalability of these sorbents remains limited due to their reliance on energy-intensive and time-consuming drying methods such as lyophilization or supercritical drying. Here, we present a simple and scalable approach to drying hydrogels with desirable AWH properties using a freezing process followed by solvent exchange and thawing at room temperature. Our system consists of cellulose and silica nanofibers, forming hybrid xerogels with ultralow density (10.86 ± 0.32 mg cm^-3), high specific surface area (104.22 m² g^-1), excellent water stability, and mechanical strength. By incorporating carbon-based photothermal materials and lithium chloride as a hygroscopic salt, the xerogels achieve exceptional water uptake capacities ranging from 0.90 to 3.21 g g^-1 across a relative humidity (RH) range from 15 to 75%. Under natural sunlight, the AWH xerogel produces water at a rate of 1.17 g g^-1 day^-1. These results highlight a sustainable and scalable AWH strategy, leveraging ambient-dried xerogels as an energy-efficient solution to mitigate water scarcity.