Integration of Solid Oxide Co-Electrolysis of Steam and CO2 in Future Closed-Loop Life Support Systems

Closed-loop environmental control and life support systems (ECLSS) are a mission priority for long-duration human space exploration campaigns, with >75% recovery of oxygen from carbon dioxide and reduction in system mass/kg oxygen identified as target improvement metrics. Existing approaches such as Sabatier, Bosch, and microfluidic CO2 electrocatalysis provide a spectrum of benefits and drawbacks. Within this landscape, we describe the specific benefits afforded by ECLSS that include solid oxide co-electrolysis (SOCE) of steam and CO2 as the primary oxygen generation and recovery mechanism. Using OxEon’s flight-proven MOXIE technology for converting H2O + CO2 to H2 + CO and O2 as a baseline, we provide a comparative analysis against the Sabatier-based legacy as well as leading alternative approaches. We provide key system considerations for SOCE integration to ECLSS, including thermophysical operating parameters and materials compatibility based on current state-of-the-art knowledge on both contaminant space and SOCE materials science. We project a baseline ECLSS performance and present in-house test data on a 10-cell solid oxide stack to validate subscale performance. Finally, we discuss an overview of downstream chemistry available with the products of SOCE for increasing oxygen recovery to >75% (including the Fischer-Tropsch and Boudouard reactions), and outline the needed future research to mature such technologies to fruition. Based on our preliminary analysis, we argue that SOCE-driven oxygen recovery will be a significant boon to long-duration human space exploration.