Solid Oxide Electrolysis Cathode for Increased Robustness for ISRU Application

The production of oxygen for life support and ascent vehicle propellant oxidant is essential for human expedition to Mars. OxEon's team led the development of SOXE stacks for the Mars 2020 mission in collaboration with the Jet Propulsion Laboratory (JPL) and Massachusetts Institute of Technology (MIT). A stack that was installed in the Perseverance Rover has been operated five times so far to demonstrate the production of high purity oxygen by electrolyzing Mars atmosphere CO2.

Traditionally, SOXE stacks use nickel-zirconia or nickel-ceria composite cathode to reduce the oxidized species. Nickel based electrodes are susceptible to oxidation by the feed gas (CO2 or steam) at the inlet conditions and are often irreversibly damaged unless reduced species (carbon monoxide or hydrogen) are also present. This necessitates a complex, recycle loop that introduces a fraction of the product gases to the inlet, as was used for the Mars rover mission. Under the SBIR program OxEon investigated a combination of materials and engineering solutions to improve redox tolerance of the nickel-based cathode so that 100% dry CO2 could be fed directly into a stack without harming the electrode. OxEon has now successfully demonstrated this redox tolerance through the use of a modified nickel-based cathode composition, and a unique backbone and infiltrated cathode structure. Button cells and a stack have been shown to completely tolerate partial and full (i.e., complete oxidation of Ni to NiO before re-reduction) redox cycling, with performance recovery occurring in a matter of minutes using CO generated by the electrolysis reaction. The redox tolerant stack was also demonstrated to show improved coking tolerance over the traditional cathode material. This feature allows higher conversion of CO2 enabling increased O2 production.