Sustainable, long-duration space exploration necessities the decoupling of operational consumable supplies from tenuous and expensive terrestrial supply chains. Herein, we examine the viability of utilizing the Martian water/brine cycle (enabled by perchlorate salts in the regolith depressing the freezing point of water) and the carbon dioxide rich atmosphere to produce ethanol through electrolysis. Ethanol is a valuable feedstock that exists as a liquid at typical Martian conditions. It can be used both as a fuel in combustion or electrochemical (fuel cell) systems and as a feedstock for further downstream processing into valuable chemicals such as polyethylene. The development of a high throughput CO2-to-ethanol electrolyzer also holds commercial promise for repurposing and valorizing terrestrial atmospheric CO2. Through the application of our electrolyzer polarization model (first detailed in AIChE Journal, 69(5):e18010 (2023)) to a hypothetical, zero-gap electrolyzer cell and a 10-cell stack, we examined the viable operational envelope of this electrolyzer across a range of operating temperatures, pressures (and backpressures) and inlet gas humidity. A range of catalyst candidates were considered and their effect on electrolyzer performance, product purity, side-reactions and overall throughput were determined to both identify promising CO2-to-ethanol catalyst candidates and to delineate desirable electrocatalytic parameters (overpotential, activity) to guide future catalyst development. We found that ethanol is thermodynamically favored compared to any other CO2 reduction produce except methane. The model indicates that CO2-to-ethanol electrolyzers are indeed viable under Martian conditions and can potentially produce ethanol with both high selectivity (>50%) and low energy consumption (~0.05 g ethanol per watt-hour). We also report the first (preliminary) experimental results demonstrating electrochemical CO2-to-ethanol reduction from CO2 saturated regolithic (perchlorate) brines. Acknowledgement: Partial support by University of Texas at San Antonio through a start-up grant and the GreenStar Endowed Fellowship and by NASA grant 80NSSC22K1766 and a NASA STTR sub-contract from Faraday Technology.
Shahid et al. (Sun,) studied this question.