Hierarchical Engineering of Sorption‐Based Atmospheric Water Harvesters

Harvesting water from air in sorption‐based devices is a promising solution to decentralized water production, aiming for providing potable water anywhere, anytime. This technology involves a series of coupled processes occurring at distinct length scales, ranging from nanometer to meter and even larger, including water sorption/desorption at the nanoscale, condensation at the mesoscale, device development at the macroscale and water scarcity assessment at the global scale. Comprehensive understanding and bespoke designs at every scale are thus needed to improve the water‐harvesting performance. For this purpose, a brief introduction of the global water crisis and its key characteristics is provided to clarify the impact potential and design criteria of water harvesters. Next the latest molecular‐level optimizations of sorbents for efficient moisture capture and release are discussed. Then, novel microstructuring of surfaces to enhance dropwise condensation, which is favorable for atmospheric water generation, is shown. After that, system‐level optimizations of sorbent‐assisted water harvesters to achieve high‐yield, energy‐efficient, and low‐cost water harvesting are highlighted. Finally, future directions toward practical sorption‐based atmospheric water harvesting are outlined. The potential applications for atmospheric water harvesting are tantalizing. This review provides an up‐to‐date summary of the most recent developments and challenges for developing practical sorption‐based atmospheric‐water harvesters. The sorbent design at the nanoscale, condensation enhancement at the mesoscale, device development at the macroscale, and water scarcity assessments at the global scale are discussed in detail.