Sorption-based atmospheric water harvesting: from atoms to applications

Abstract

Thirteen thousand trillion liters of water in the atmosphere is a natural resource found anywhere on the earth, and available to anyone. Sorption-based atmospheric water harvesting (SAWH) is the extraction of water vapor using sorbent materials across a broad spectrum of relative humidity, which opens new avenues to address water scarcity faced by two-thirds of the world’s population. SAWH technologies gained significant attention in 2017 with the development of a solar-powered system utilizing metal-organic framework (MOF) sorbents to extract water from the air. While groundbreaking, this proof-of-concept device produced only a few milliliters of water, far from sufficient to meet even a single person’s daily water needs. A large gap thus remains between laboratory discoveries and real-world applications. This thesis aims to advance the understanding of SAWH technologies from atoms to applications. It begins with a multiscale perspective on SAWH technologies towards real-world applications, addressing knowledge gaps across various length scales. Through this multiscale approach, we developed a framework that can bridge material innovations with device realization. At the molecular scale, the thesis seeks to address a fundamental challenge: the inability to directly observe water sorption processes. To overcome this long-standing challenge, we introduced the use of cryogenic transmission electron microscopy (cryo-TEM) to probe water sorption in nanoporous materials at the single-pore level. This approach allows us to image water sorption and material structures with atomic resolution. Owning to the high resolution and in situ capabilities of cryo-TEM, we resolved a partially water-filled state of MOF crystals and observed that water molecules tend to occupy the centers of pores and fill neighboring pores once adjacent ones are filled. This technique offers new insights into sorption mechanisms and holds significant potential for the development of new sorbent materials. Building on the material-device-bridging framework, we proposed a dual-stage device architecture inspired by multistage distillation in desalination, where condensation heat from one stage drives desorption in the next, increasing productivity and thermal efficiency. To guide materials selection based on operating conditions, a universal thermodynamic model is developed to predict the efficiency of sorbent materials given their sorption isotherms. Additionally, this analysis reveals practical strategies to improve devicelevel sorption kinetics and heat transfer performance, pushing the technology toward thermodynamic limits. At the global scale, the framework enables the optimization of material deployment tailored to diverse climatic conditions. The real-world impact is further demonstrated through a technoeconomic assessment, which illustrates SAWH technology’s competitiveness with bottled and tap water and pathways to further improve its cost-effectiveness. The thesis concludes with an outlook on future opportunities for SAWH technologies and a discussion of their societal and environmental impacts at scale, including their potential role in mitigating climate change.