New Approaches for Continuous Atmospheric Water Harvesting with Hydrogels through Radiative Energy Exchange with Space and Waste Heat Utilization

Access to clean water is a global challenge since by 2025, almost 2 billion people will live in areas with absolute water scarcity. Atmospheric water harvesting (AWH) is a promising solution to obviate water scarcity. The atmosphere is estimated to hold 12,9 tera tons of water, six times the total volume of rivers worldwide. AWH refers to a different set of technologies to capture and collect water from the atmosphere anywhere, anytime, one of which is the sorbent-based AWH (SAWH). Sorbents are hygroscopic porous materials that capture (adsorption process) water from the atmosphere due to water concentration difference according to Fick’s law. The elevated temperature of hydrated sorbent material initiates the vapor release process (desorption process), generating fresh liquid water in an enclosed chamber. In 2017, the first proof-of-concept published in Science journal showed water harvesting from the air in arid outdoor conditions using porous metal-organic frameworks. To date, numerous simple lab-scale devices for SAWH have been introduced, primarily demonstrating a simple operational strategy with ambient moisture adsorption during the night and water release during the daytime using solar energy. This single-cycle (diurnal) strategy has limits concerning energy and mass efficiency owing to the underachieved utilization of sorbent materials in 24h. The solution to this challenge is the introduction of continuously operated SAWH devices, operating in either batch- or truly continuous manner. Thus far, current off-grid continuous solar-driven prototypes with multiple daily adsorption-desorption cycles show a major bottleneck, pertinent to material properties, and large variation of all-day ambient temperature, relative humidity, and available solar thermal energy. The next logical step is to obviate those recognized drawbacks with the synergistic materials-system co-design development. The primary objective of the proposed research project is to develop a continuously-operated sorbent-based AWH device that is both high-performance and energy-efficient. This project aims to make a breakthrough in this field through an advanced thermal engineering approach that harnesses renewable and sustainable energy sources, including solar thermal energy, radiative heat exchange with the cold universe, and waste heat utilization. This approach will be combined with the use of advanced hygroscopic hydrogel materials containing embedded salt and spectrally selective photothermal particles. The proposed project intends to build a strong framework for advanced architecture of continuously operated SAWH devices with five important scientific points: 1. Demonstration of the truly auto- and continuously-operated SAWH, 2. A device- and material-level synergistic co-design strategy to obviate the current drawbacks of sorbent materials, 3. Hybrid desorption mode, providing both renewable-based solar- and waste-heat-driven desorption for 24-hour non-interrupted water provision, 4. Enhanced heat and mass transfer by virtue of radiative heat exchange with the cold space for increased adsorption and condensation rates, 5. Scalability aspect: deploying a high-compact water harvester with viable scale-up suggestions. The research and development of such a device will be based on a coupled theoretical and experimental investigation in indoor and outdoor conditions. Inherent to the current research hotspot of the SAWH field, the novel research results will be disseminated primarily through scientific articles. To bring the SAWH field forward to the general public, including undergraduate and postgraduate students, the results will be adequately disseminated through a wide range of media, various stakeholders, policymakers, lectures, and summer schools for youth. On a global scale, this proposed research project intends to promote renewable and sustainable energy resources and freshwater generation, paving the road to green global transition.