Opportunities for Electrochemical and Catalytic Processes That Support Human Activity on Mars

Abstract

Supporting human activity on Mars requires working with available resources, which include low-pressure CO2 (P CO2 » 5.8 mbar) even lower pressure N2 (P N2 » 0.12 mbar), sub-surface ice, and solar insolation (up to 300 W/m2 at the surface). Supporting life on Mars requires sustained production of O2, liquid H2O, food, heat, and fuel for rockets and mobility. This presentation explores electrochemical and chemical processes based on catalytic membrane reactors that can enable production of value-added products and/or their precursors from the in-situ resources. Many practical chemical technologies require H2 as a feedstock, which can be produced by steam electrolysis that also produces O2. An attractive approach to electrolysis uses proton-conducting ceramic membrane such as (BCZYYb) at intermediate temperatures (between 450 and 650 °C) [1-3]. Proton-conducting ceramics electrochemical cells (PCEC) provide advantages compared to liquid-based polymer electrolyte membrane electrolysis in that they can operate without the need for high-purity liquid H2O and they can incorporate carbonaceous feedstocks for combining electrolysis with other chemistries. In addition to producing H2, the electrolysis cell can be operated as an integrated H2 electrochemical compressor. Several viable catalytic hydrogenation processes can react H2 from the electrolysis cell with CO2 to produce fuels and chemicals. The Sabatier reaction for producing CH4 from CO2 and electrolysis derived H2 has been well studied with an optimal operating temperature around 400 °C [4]. More selective catalysts and novel membrane reactors can be developed to produce valuable fuels and chemicals that include methanol, ethylene, dimethyl ether, formic acid, etc. The desired product streams depend on selective catalysts and on operating pressures and temperature. In some cases, process performance may depend on the development of novel bi-functional catalysts and/or selective membranes. In addition to carbon-based products, applications such as fertilizers need ammonia. Available N2 in the atmosphere could react with H2 to synthesize NH3 via Haber-Bosch process. Many of these relevant catalytic processes require high pressure (at least tens of bar) and modest elevated temperature (300-500 ˚C). Depending on the product yield, downstream separations and purifications may be needed. Assuming limited space and need to high efficiency, process intensification [5] will likely play important roles in the development of in-situ resource utilization. This paper explores the opportunities and challenges for developing critical electrochemical processes for production of a variety of chemicals to support future human Martian activity. Fig.1. Cartoon illustration of a H2 membrane coupled catalytic reactor for CO2 hydrogenation to chemicals References C. Duan, J. Tong, M. Shang, S. Nikodemski, M. Sanders, S. Ricote, A. Almansoori, and R. O’Hayre. Science, 349:1321–1326, 2015.H. Zhu, S. Ricote, C. Duan, R.P. O’Hayre, and R.J. Kee. J. Electrochem. Soc., 165:F845–F853, 2018.C. Duan, R.J. Kee, H. Zhu, N. Sullivan, L. Zhu, L. Bian, D. Jennings, and R.P. OHayre. Nature Energy, 4:230240, 2019.K.P. Brooks, J. Hu, H. Zhu, R.J. Kee, “Methanation of carbon dioxide by hydrogen reduction using the Sabatier process in microchannel reactors”, Chem. Eng. Sci., 62(4):1161-1170, 2007.R.J. Kee, C. Karakaya, H. Zhu, “Process intensification in the catalytic conversion of natural gas to fuels and chemicals,” Proc. Combust. Inst., 36:51–76, 2017 Figure 1