The Sabatier Electrolyzer: Harnessing Proton-Conducting Ceramics to Upgrade Carbon Dioxide into Methane

Abstract

We present our development of the Sabatier Electrolyzer incorporating Sabatier catalysts into proton conducting ceramic membranes to synthesize CH4 and O2 from CO2 and H2O feed streams. Our work seeks to combine steam electrolysis and hydrogen production with carbon dioxide hydrogenation into a single Sabatier Electrolyzer reactor based on proton conducting ceramic membranes and Sabatier catalysts. Proton-conducting ceramic membranes transport reasonable rates of H+ ions at lower overall cell voltages at 400 - 500 ºC with low overpotentials for H2O splitting. The decreased electric power requirements for the Sabatier Electrolyzer are further enabled by autothermal operation; ohmic heating maintains the electrolysis cell at the necessary temperatures for high H+ conduction and effective Sabatier chemistry. Integration of the catalyst with the electrolyzer simplifies the system, improves reliability, and provides increased performance within a smaller package. Figure 1 illustrates the Sabatier Electrolyzer concept. H2O and CO2 are fed to opposing electrodes of a protonic-ceramic electrolysis cell. Steam is electrolyzed with the product O2 exhausting from the cell. The product protons are driven across the protonic-ceramic membrane to the fuel electrode, where they react with CO2 to form CH4 and H2O. The combination of processes can match the exothermicity of CO2 hydrogenation with the endothermicity of H2O electrolysis, promoting thermal balance and high efficiency. The Sabatier Electrolyzer cell features a BaCe0.4Zr0.4Y0.1Yb0.1O3-δ (BCZYYb4411) electrolyte, a Ni-BCZYYb4411 fuel electrode support, and a BaCo0.4Fe0.4Zr0.1Y0.1O3-δ (BCFZY) steam electrode. The Ni-cermet fuel electrode serves as the CO2-upgrading catalyst. To date, we have CO2 conversion and CH4 selectivity were demonstrated to be 28% and 43%, respectively, at 450 °C. This result is encouraging but still much lower than the thermodynamic predictions (~70% for CO2 conversion and ~95% for CH4 selectivity). In this presentation, we will review our efforts to achieve the thermodynamically predicted CO2 conversion and CH4 selectivity of 70% and 95%, respectively. Figure 1