2024 AIChE Annual Meeting
(735n) Hydrogen from Air (SAWH2): A Decentralized Sorption Based Atmospheric Water-Hydrogen Production Device
Joseph P. Mooney1,2*, Chad T Wilson1, Omer Refet Caylan1, David Keisar1, Carlos Díaz Marin1, Bachir El Fil1*
1Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
2School of Engineering, University of Limerick, V94 T9PX, Ireland
jpmooney@mit.edu ; belfil@mit.edu
The escalating challenges posed by climate change and water scarcity necessitate innovative solutions in the energy sector. A key component of this innovation is the adoption of hydrogen as a clean, versatile alternative to traditional energy sources. Hydrogen, particularly when produced through the process of electrolysis using renewable energy sources like solar power, stands at the forefront of the transition towards a more sustainable and low-carbon future. This process, known as green hydrogen production, is gaining traction as a viable method for clean energy generation. However, the path to fully harnessing green hydrogen's potential is fraught with obstacles, including the significant demand for water and the limitations in production efficiency due to the reliance on natural sunlight alone. The production of green hydrogen, especially in arid or water-scarce regions, faces the critical challenge of water availability. This issue underscores the need for green hydrogen production methods that are not only efficient but also sustainable in their water use. Furthermore, green hydrogen systems often struggle to surpass energy conversion efficiencies of 10%, hindered by suboptimal energy capture, oxygen and hydrogen bubble transport, conversion processes, and losses during electrolysis. Overcoming these efficiency and sustainability barriers is crucial for the scalability and broader application of green hydrogen as a reliable energy carrier. Sorption-based atmospheric water harvesting (SAWH) emerges as an energy-efficient solution for obtaining ultra-pure water off-grid, crucial for applications such as green hydrogen production. This technology harnesses ambient thermal energy for water adsorption and desorption, minimizing the need for external power sources. Additionally, SAWH can be integrated into the thermal management of photovoltaic (PV) cells, enhancing their efficiency and longevity by mitigating heat stress. Furthermore, by expanding the usable wavelength range of the solar spectrum, SAWH contributes to a marked increase in the efficiency of hydrogen production, leveraging the full solar spectrum. In this work we propose a decentralized green hydrogen production (SAWH2) device that integrates water adsorption-desorption processes with solar energy conversion, offering a dual solution to the pressing needs for energy and clean water. This approach not only enhances the efficiency and sustainability of hydrogen production but also harnesses atmospheric humidity as a water source. By improving water resource utilization and energy conversion efficiency, the system paves the way for a scalable and sustainable method of solar-powered green hydrogen production.
The system comprises a sorbent-based atmospheric water harvesting material (desiccant) strategically deployed either as a coating on a photovoltaic (PV) cell or within a separate dedicated unit, a hydrogen production cell, and a hydrogen storage unit. During water adsorption, the desiccant absorbs water vapor from the surrounding air, either passively or actively. Solar energy is used to produce electricity from the PV cell while simultaneously desorbing water from the desiccant, which is then employed for water splitting via electrolysis of water. Using our high-performance low-cost polyacrylamide Lithium chloride (PAM-LiCl) hydrogel sorbent (1.79 and 3.86 gg−1at relative humidity (RH) of 30% and 70%, salt loading of 15-20 gram of salt per gram of polymer, and at a cost of <0.1 $/kg of material, respectively). Preliminary results show a device water production capacity of ~2L/m2/day and a hydrogen production capacity of 5 mL/min. We will also present a heat and mass transfer analysis to optimize the system level performance of this device, such as PV to Proton Exchange Membrane (PEM) scaling, sorbent to hydrogen production comparisons as well as novel insights into passively replenishing the PEMs surface while maintain adequate pressure between the anode and cathode. We increase hydrogen production enhance efficiency while lowering the overall cost. Due to findings that the device is PV-PEM limited, we also demonstrate that our device can supply both energy and potable fresh water. Our device presents an alternative solution to green hydrogen production when presenting a starting point to getting closer to the DOE’s target levelized cost of hydrogen (LCOH) of $1/kg to make it more competitive and economically viable in the broader energy landscape. Our SAWH2 device is also expected to have an efficiency enhanced by >40% as compared to state-of-the-art devices. The implications of this technology extend far beyond its immediate environmental benefits. By providing both energy and water, two fundamental components for human health and prosperity, the system has the potential to transform communities worldwide. Its decentralized and affordable nature makes it particularly suitable for remote and arid regions, where access to clean water and reliable energy sources is often limited. Applications range from supplying clean drinking water and powering agricultural projects to enabling local energy production and supporting healthcare facilities. Additionally, this technology could play a crucial role in disaster relief operations, where immediate access to clean water and energy is critical.