Includes bibliographical references. ; 2019 Summer. ; The objective of this thesis is to study the performance of proton-conducting ceramics as a Sabatier-Electrolyzer in the synthesis of methane. The National Aeronautics and Space Administration seeks innovative space technology that can make use of resources in space via In-Situ Resource Utilization (ISRU). ISRU will enable sustainable human exploration and living in space by minimizing the materials carried from Earth. Available resources on Mars include carbon dioxide, which makes up 95% of the Martian atmosphere, and water, which is available in the form of ice within craters or regolith. Proton-conducting ceramics have unique properties that can enable simultaneous processing of these two feedstocks to produce methane and oxygen. Carbon dioxide and steam are fed on opposite sides of a proton-conducting membrane in a ceramic Sabatier-Electrolyzer cell. Electrolysis separates the steam into protons and oxygen. Oxygen continues to flow out the exhaust, and protons are driven across the electrolyte to react with the carbon dioxide to form methane using a nickel catalyst. Methane and oxygen have many potential uses on Mars. For example, these products can fuel ascent vehicles to send samples and humans back to Earth, or beyond. Presented are catalytic performance results using a proton-conducting ceramic cell, in which the cathode and electrolyte are based on Ni-BaCe0.4Zr0.4Y0.1Yb0.1O3-d and the steam anode is a triple-conducting BaCo0.4Fe0.4Zr0.1Y0.1O3-d. High carbon dioxide conversion and methane selectivity with stability for more than 100 hours was demonstrated. Peak performance was obtained with 67% carbon dioxide conversion and 97 methane selectivity at 400 C and 4:1 hydrogen to carbon dioxide gas feed.