The production of oxygen for life support and ascent vehicle propellant oxidant is essential for human expeditions to Mars. Solid oxide electrolysis (SOXE) stacks are capable of reducing carbon dioxide and water available on Mars to produce high purity oxygen. They can electrolyze CO₂ or water separately or co-electrolyze CO₂ and water together to produce oxygen and fuels such as methane for propulsion. OxEon’s team led the development of SOXE stacks in collaboration with the Jet Propulsion Laboratory (JPL) and Massachusetts Institute of Technology (MIT). The work resulted in delivering a set of flight qualified stacks to JPL. A packaged stack has been installed on the rover that is scheduled for launch next year for the Mars 2020 mission. The Mars Oxygen ISRU Experiment (MOXIE) will demonstrate the feasibility of producing high purity oxygen from Mars atmosphere carbon dioxide using a SOXE stack.

Since delivering the stacks, the OxEon team has designed and begun fabricating SOXE stacks of the cell area required for a manned Mars mission. Under the NASA NextSTEP-2 ISRU activity, this platform will be tested with conditions targeting the ISRU application. MOXIE testing was focused on the case of atmospheric ISRU for oxygen evolution at the anode and did not make use of the CO byproduct gas at the cathode.. In 2019, OxEon will demonstrate CO₂-steam co-electrolysis to produce carbon monoxide and hydrogen (synthesis gas) on the cathode and high purity oxygen at the anode. The synthesis gas will be converted to methane in an OxEon developed methanation reactor as an alternative to a water electrolysis coupled Sabatier system.

In addition, OxEon is investigating a combination of materials and engineering solutions to improve redox tolerance of nickel-based cathode. Traditionally, SOXE stacks use nickel – zirconia or nickel – ceria composite cathode. Nickel based electrodes are susceptible to oxidation by the feed gas (CO₂ or steam) at the inlet conditions unless reducing species (carbon monoxide or hydrogen) are also present. Button cell tests show that the new, modified cathode material exhibits good redox stability over multiple redox cycles with only a minor loss of performance after each cycle. Initial tests also show that under certain operating conditions the loss of performance can be recovered. Implementation of a redox tolerant cathode will eliminate the need for complex recycle loop that introduces a fraction of the product gases to the inlet in order to prevent nickel oxidation.

Acknowledgement: NextSTEP ISRU work is supported under NASA Contract 8-HQTR19C0006. The redox tolerant cathode work is done under a NASA Small Business Innovation Research Contract No. 80NSSC18P1940. The work related to MOXIE was based on support from NASA through JPL’s prime contract, under JPL subcontract number 1515459.