Significance

A layered, convection-limited atmospheric water capture approach is demonstrated, providing water in liquid form at extremely high rates even in low humidities. Inspired by tree frog skins and air plant cuticles, a thin, strong hydrogel acting as a membrane facilitates the transport of water from ambient air into a liquid desiccant for storage. Water in this liquid form is an important precursor for further distillation into drinking water or electrolytic processing for green hydrogen production—enabling new capabilities in arid regions. In addition, pure water can be released from the liquid desiccant using solar energy. Both water capture and release can occur simultaneously, maximizing the potential to harvest water.

Abstract

Transforming atmospheric water vapor into liquid form can be a way to supply water to arid regions for uses such as drinking water, thermal management, and hydrogen generation. Many current methods rely on solid sorbents that cycle between capture and release at slow rates. We envision a radically different approach where water is transformed and directly captured into a liquid salt solution that is suitable for subsequent distillation or other processing using existing methods. In contrast to other methods utilizing hydrogels as sorbents, we do not store water within hydrogels—we use them as a transport medium. Inspired by nature, we capture atmospheric water through a hydrogel membrane “skin” at an extraordinarily high rate of 5.50 kgm ^-2 d ^-1 at a low humidity of 35%. and up to 16.9 kgm ^-2 d ^-1 at higher humidities. For a drinking-water application, calculated performance of a hypothetical one-square-meter device shows that water could be supplied to two to three people in arid environments. This work is a significant step toward providing new resources and possibilities to water-scarce regions.

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https://www.pnas.org/doi/10.1073/pnas.2321429121