Switchable multicyclic adsorption-based atmospheric water harvesting with solar and radiative sky cooling thermal concentration and heat pumps

Water scarcity affects approximately four billion people worldwide and severely impacts 30 % of Europe's territory, particularly in arid, landlocked regions with limited surface water. The energy–air–water nexus underscores the complex interplay between atmospheric moisture and the energy required for freshwater production. While recent progress since 2017 has advanced single-cycle diurnal atmospheric water harvesting (AWH) using sorbent materials, few studies have addressed material-to-system co-design for scalable, cost-effective operation across diverse conditions. To fill this gap, we experimentally evaluated activated carbon fiber felt loaded with hygroscopic LiCl in controlled temperature and humidity chamber. Furthermore, we utilized a mathematical model coupling sorption rates dynamics with simulations of passive thermal concentration using radiative sky cooling, solar heating, and heat pump technologies. The key novelty of this work lies in a comprehensive design and calculation framework for switchable, multicyclic AWH systems, integrating material properties with system-level performance. This interdisciplinary approach enables more efficient control of adsorption and desorption processes critical for continuous atmospheric moisture extraction. Our research demonstrates the significance of leveraging sky-based cooling concentration (heat emitter reaching 10 °C) and solar thermal concentration (heat absorber reaching 115 °C) to achieve breakthroughs in entirely passive water harvesters for arid conditions, potentially almost tripling (2.7x and 2.9x) daily water release compared to the baseline scenario with adsorption/desorption at 25 °C/75 °C and RH 15–30 %/11 %, respectively. Additionally, we highlight that optimal refrigerant selection, considering operating temperatures and sorbent characteristics, can achieve a 138 % improvement when the coefficient of performance is coupled with material water release at RH15 %.