Reliable and Efficient Electrochemical Recovery of O2 from Metabolic CO2 at the International Space Station (ISS)

Maximum oxygen (O2) recovery from metabolic carbon dioxide (CO2) is desired for future long-duration missions beyond Low Earth Orbit. The O2 recovery for the Environmental Control and Life Support System (ECLSS) at the International Space Station (ISS), presently limited to 50% (Sabatier), must be highly reliable and efficient and recover a minimum of 75% O2 from metabolic CO2. An alternative technology development effort currently underway at NASA Marshall Space Flight Center via a Macro-fluidic Electrochemical Reactor (MFECR) approach has the potential to increase O2 recovery significantly and reduce the complexity of the ECLSS O2 recovery at the ISS as it would replace three pieces, the CO2 Reduction Assembly (CRA) (Sabatier reactor), the Oxygen Generation Assembly (OGA), and the Plasma Pyrolysis Assembly (PPA). The MFECR's electrochemical process generates ethylene (C2H4) and carbon monoxide (CO) instead of methane (CH4) (Sabatier) as a byproduct, eliminating the need for further dehydrogenation through the PPA. As in the OGA, the MFECR's electrochemical process generates O2 and hydrogen (H2) from the water electrolysis process. MSFC and the University of Texas in Arlington have jointly designed and fabricated/upgraded an MFECR's single cell that operates at ambient conditions and utilizes a catalyst highly selective on reducing CO2 to C2H4 and CO at the cathode. This approach is expected to substantially improve the ISS ECLSS sustainability and reduce power and weight requirements as the MFECR would replace three and potentially four units currently installed in the ISS. In this paper, the authors discuss the outcome of preliminary tests, the current development, the evaluation efforts on different alternatives for the cathode and the anode configurations, the use of MFECR's digital twin to upgrade its design at an engineering development unit (EDU) scale, and the evaluation efforts on different electrolyte alternatives and alkalinity effect.