Study for Optimizing Mars Propellant Production System

Since developing the Solid OXide Electrolysis (SOXE) stacks for the MOXIE program, the OxEon team has made significant advancements in the scale and capabilities of the technology. Newer variants of the SOXE stack have been scaled by a factor of 33x the size of the device in MOXIE and been used in demonstrations for Lunar and Martian applications. A NASA NextSTEP-2 ISRU program resulted in development of an integrated mission-scale SOXE stack coupled with a methanation reactor system capable of producing O2 and CH4 from H2O and CO2. The SOXE stack operating voltage is limited when CO2 is present to avoid the formation of solid carbon by electrolysis of produced CO when compared to SOXE operation with steam alone. The SOXE operation penalty for operating with CO2 is nearly 50% compared to steam electrolysis alone. A NASA SBIR program funded the development of an improved cathode material that has demonstrated some resistance to coke formation. This advanced electrode has the potential to enable operation at higher cell voltage without the risk of carbon deposition. An alternative to co-electrolysis within the SOXE stack would be the thermal and process integration of a Reverse Water Gas Shift (RWGS) reactor with a SOXE stack run in steam electrolysis mode. Steam would be fed to the stack, then mixed with CO2 and passed over a RWGS catalyst to produce synthesis gas. OxEon is working with members of the Digital Engineering Design Center (DEDC) and JSC to conduct a study for optimizing 1) the overall CO2 and H2O feed, 2) comparing theoretical performance of SOXE co-electrolysis versus SOXE steam electrolysis paired with RWGS, and 3) evaluating thermal management in the methanation reactor for scaling considerations. The study will conclude in January 2024 and outcomes for a path to mission-scale Mars ISRU applications will be shared.