Radiative Cooling Sorbent towards High Performance All Weather Ambient Water Harvesting

Abstract

Emerging atmospheric water harvesting (AWH) technologies promise water supply to underdeveloped regions that have no access to liquid water resources. The prevailing AWH systems, including condensation- or sorption-based, mostly rely on a single mechanism and thus have a limited range of working conditions and inferior performance. In this study, we synergistically integrate multiple mechanisms, including thermosorption effect, radiative cooling, and multiscale cellulose-water interactions, and demonstrate a low-cost (~ 4 USD kg− 1) and high performance (up to 6.75 L kg− 1 day− 1 in field tests) AWH system requiring zero active energy input. The proposed system consists of a highly scalable and sustainable cellulose scaffold impregnated with hygroscopic deliquescent lithium chloride (LiCl) salt. Cellulose scaffold and coated LiCl synergistically interact with water at different scales from molecular, to nanometer, and micrometer scales, providing a fast harvesting rate and high yield over a wide operation range. Iterating radiative cooling and solar heating workflow achieves simultaneous enhancement of water capture and release through the so-called temperature-swing strategy. The captured water in return facilitates radiative cooling due to the intrinsically high infrared (IR) emissivity of the LiCl-cellulose composite. With our simple yet effective material design, the AWH working range extends to lower than ~ 10% relative humidity (RH), and the water uptake in the controlled lab test reaches 16 kg kg− 1 at 90% RH (sample at 19°C, i.e. 6°C below 25°C ambient temperature). In addition, we propose a theoretical model capable of elucidating the experimental water uptake curves and demonstrating the synergy among cellulose-LiCl-water-energy interaction. The promising performance emphasizes the potential of involving multiple AWH mechanisms and points to an alternative pathway to stimulate future improvement.

Pathways to Energy‐efficient Water Production from the Atmosphere

“…[49] Grasping energy from nature, some recent progress utilized radiative cooling (RC) to provide a cooling source to fabricate a passive CSAWH. [32,50] To this end, the extra cooling energy for adsorption is free from the sky and the cooling capacity could even achieve 145 W m −2 because the arid climate (low humidity) is beneficial to improving cooling capacity. Although the effect of radiative cooling can give a sub-ambient temperature with a limit temperature difference of ≈8 °C, [51] there is nearly no cooling capacity at this temperature difference.…”

All-in-one hybrid atmospheric water harvesting for all-day water production by natural sunlight and radiative cooling

“…Kim et al first reported the potential of nighttime radiative cooling to lower the temperature of sorbents, allowing the sorbents with mild water affinity to work under low RH conditions. 9 Recently, Wang et al 36 and Zhu et al 37 developed multifunctional sorbents with extraordinary water harvesting capacity, high stability, and radiative cooling functions. The nighttime radiative cooling enabled a low sorption temperature to facilitate the exothermic water harvesting process.…”