ABSTRACT: Humidity in the air is a vast water resource representing 6 times more freshwater than all rivers and lakes. This humidity can be converted to drinking water via moisture sorption-desorption, serving as a potentially decentralized, passive, and low-cost pathway to mitigate the pressing water scarcity challenge. However, the productivity and potential of this approach has been severely limited by the performance, scalability, and durability of conventional moisture sorbent materials. In this talk, I will discuss the material-level to application-level development of low-cost (<$0.1/kg of material) hydrogel-salt composites that capture record amounts of water from the air and produce liquid water even in extreme conditions like the Atacama Desert, Chile. Firstly, I will discuss the physics-based models I developed to elucidate the key thermodynamic interactions and transport mechanisms in hydrogel-salt composites. Through comprehensive synthesis and characterization, I demonstrated that these models accurately predict the sorption performance metrics (uptake, enthalpy, and kinetics) of hydrogel-salt composites from their composition. Secondly, I will present how these insights guided the synthesis of hydrogels with the highest capability ever demonstrated of any material to capture and store water from the air (~2 kg of water/kg of material), even in arid conditions (30% relative humidity) through an optimized swelling-based approach. Thirdly, I will discuss how my thermodynamic and transport models guided the design of a hydrogel-based atmospheric water harvesting device that was tested in the Atacama Desert, in Chile. Using these models, I tuned key design parameters to achieve ~1 L/m 2 /day water productivity even at ~30% relative humidity in the desert. Critically, through the demonstrated combination of low-cost, high productivity, and high material durability we provide a path towards <$0.01/L decentralized water production from the air. I will conclude the talk discussing opportunities at the intersection of soft matter, sorption, and transport phenomena for sustainability and energy. By combining improved fundamental understanding, material development, and system-level demonstration, these directions can critically advance technologies for waste heat-powered direct air capture of carbon dioxide, non-vapor compression moisture heat pumps with high coefficient of performance, and energy-efficient biomass preprocessing.

BIO: Carlos D. Díaz-Marín is a Fellow at the Advanced Research Projects Agency– Energy (ARPA-E). Carlos combines expertise in soft matter, sorption, and heat and mass transfer for energy and sustainability challenges. At ARPA-E, he develops funding/potential programs on macroalgae cultivation and bioconversion, nonfluorinated cation exchange materials, and datacenter waste heat use. Carlos obtained his PhD in Mechanical Engineering at MIT. His work, under Profs. Gang Chen and Evelyn N. Wang, combined polymer physics, transport phenomena, and scalable hydrogel synthesis for freshwater production from the air, culminating in state-of-the-art material-level and system-level moisture capture from air. He obtained his M.S. in Mechanical Engineering from MIT (2021) and double B.S. degrees in Mechanical Engineering (2017) and Physics (2018) from the University of Costa Rica. Carlos has been recognized as an MIT Martin Family Sustainability Fellow (2023), the Caltech Young Trailblazing Researcher in Mechanical and Civil Engineering (2023), a Rising Star in Mechanical Engineering (2023), and a Rising Star in Soft and Biological Matter (2024).