Electrochemical Carbon Dioxide Reduction with Room Temperature Ionic Liquids for Space Exploration Missions

Improved oxygen (O2) recovery from carbon dioxide (CO2) is a recognized capability needed to enable long-term human space exploration. It has applications for environmental control and life support systems (ECLSS) as well as for in-situ resource utilization (ISRU). Past trade studies of technologies for physio-chemical CO2 reduction processes have included the Sabatier process, the Bosch process, solid oxide co-electrolysis, and carbon formation reactors, but have not made mention of low temperature CO2 electrolysis. Aqueous, low temperature, electrochemical CO2 reduction and co-electrolysis processes offer potential advantages for ECLSS and ISRU systems, but they are not yet at sufficient technology readiness levels (TRL) to be considered for use onboard spacecraft. Various research avenues are currently advancing the maturity and performance of these processes, with one attractive prospect being the use of room temperature ionic liquids (RTIL). RTILs are non-volatile solvents with high CO2 solubility that are generally safer than other liquids used as CO2 solvents. In an electrochemical cell, RTILs can act as electrolytes with high electrochemical and thermal stability. Recently, RTILs have been seen to act as catalyst promoters that favor selective product formation with lower energy costs compared to conventional low temperature electrochemical CO2 reduction technologies. Because a variety of human space exploration mission scenarios could benefit from an RTIL-assisted electrochemical reduction system (ECRS), high-level conceptual designs are presented with a qualitative discussion of their potential advantages and challenges. Further, the performance metrics for an ECRS are translated to system-level design parameters (mass, volume, and power). This will allow for a first-order assessment of how an ECRS would fit within ECLSS or ISRU system budgets, and ultimately aid in assessing the feasibility and advancing the TRL of ECRS technologies.