Concurrent CO ₂ Control and O ₂ Generation for Space Suits and Other Advanced Life Support: A Feasibility Study

The partial electrochemical reduction of carbon dioxide (CO₂) using ceramic oxygen generators (COGs) is well known and widely studied. Conventional COGs use yttria-stabilized zirconia (YSZ) electrolytes and operate at temperatures greater than 700 °C. Operating at a lower temperature has the advantage of reducing the mass of the ancillary components such as insulation and heat exchangers (to reduce the COG oxygen output temperature for comfortable inhalation). Moreover, complete reduction of metabolically produced CO₂ (into carbon and oxygen) has the potential of reducing oxygen storage weight if the oxygen can be recovered.

Recently, the University of Florida developed novel ceramic oxygen generators employing a bilayer electrolyte of gadolinia-doped ceria and erbia-stabilized bismuth oxide (ESB) for NASA's future exploration of Mars. To reduce landed mass and operation expenditures during the mission, in-situ resource utilization was proposed using these COGs to obtain both life-supporting oxygen and oxidant/propellant fuel, by converting CO₂ from the Mars atmosphere. The results showed that oxygen could be reliably produced from CO₂ at temperatures as low as 400 °C. These results indicate that this technology could be adapted to CO₂ removal from a spacesuit and other applications in which CO₂ removal was an issue.

The strategy for CO₂ removal in advanced life support systems employs a catalytic layer combined with a COG so that it is reduced all the way to solid carbon and oxygen. Hence, a three-phased approach was used for the development of a viable low weight COG for CO₂ removal. First, to reduce the COG operating temperature a high oxide ion conductivity electrolyte was developed. Second, to promote full CO₂ reduction while avoiding the problem of carbon deposition on the COG cathode, a removable catalytic carbon deposition layer was designed. Third, to improve efficiency, a pre-stage for CO₂ absorption was proposed to concentrate CO₂ from the exhalate before sending it to the COG. These subsystems were then integrated into a single CO₂ removal system. This paper describes the progress to date on these tasks.