Solar-powered nanostructured biopolymer hygroscopic aerogels for atmospheric water harvesting

Solar energy powered sorption-based atmospheric water harvesting (AWH) is a novel strategy for obtaining fresh water in water-scarce regions. The major challenge is to design a cost-effective all-in-one solid bulk sorbent that can capture water from air, even when outdoor conditions are cool, dry, and with low-intensity nature sunlight. Here, we report a strategy comprising solution exchange and lyophilization for integrating a lithium chloride hygroscopic agent, a nanofibrillated cellulose hydrophilic skeleton and a graphene solar absorber, to exploit a solar-powered nanostructured biopolymer hygroscopic aerogel (NBHA) for AWH. The intrinsic porous bilayer structure with interconnected micron- and nano-scale channels of NBHA enables it readily absorb moisture (even at a low relative humidity of ~18%), has a high-water storage capacity, and requires little energy from natural sunlight for solar-driven light-to-vapor conversion. Liquid water was successfully harvested outdoors in natural sunlight of 0.10–0.56 kW m−2 using a facile device based on the NBHA. This work provides a convenient, effective, and practical solution for AWH, even in severe environmental conditions.