Liquid Polyether-Based Water Harvester for Near Ambient Temperature Operation via Hydrophilicity-Difference-Induced Water Transfer

Liquid moisture adsorbents recover water from the atmosphere and are used in applications such as atmospheric water harvesting (AWH) and desiccant air conditioning (DAC). Liquid adsorbents allow for flexible device design as well as lower regeneration temperatures. Although both the adsorption and desorption performance of liquid adsorbents is essential for energy efficiency, the latter has been less studied. Previously, we combined oligomeric poly(ethylene glycol) (PEG) and oligomeric poly(propylene glycol) (PPG), resulting in a lowered water desorption temperature and enhanced water desorption efficiency, which was facilitated by a “hydrophilicity-difference-induced water transfer (HWT)” mechanism. However, the inclusion of hydrophobic molecules limits the water adsorption capacity of the mixture. In this study, PEG-PPG copolymer combinations with PEG were investigated for enhancing HWT. The results of water adsorption and desorption experiments and thermogravimetric differential thermal analyses revealed that the PEG-PPG copolymer combinations effectively improved the water harvesting rate. The PEG-PPG random copolymer exhibited the highest water harvesting rate, above that of PEG. The improved water recovery originated from the synergistic effect of HWT and the collapse of water clusters. The proposed concept is expected to be applied to various hygroscopic liquids to develop energy-efficient liquid adsorbents for AWH and DAC.