We present our development of the Sabatier Electrolyzer to synthesize CH4 and O2 from CO2 and H2O feed streams. Our work seeks to integrate steam electrolysis and hydrogen production with carbon dioxide hydrogenation into a single Sabatier Electrolyzer reactor based on proton-conducting ceramic membranes and Sabatier catalysts. When powered by solar- and / or wind-energy, the Sabatier Electrolyzer has the potential to store intermittent renewable electricity in the form of commodity chemicals while simultaneously reducing carbon dioxide emissions, thereby addressing two principle societal concerns in a single device. The Sabatier Electrolyzer concept is illustrated in the figure. H2O and CO2 are fed to steam and fuel electrodes, respectively, of a protonic-ceramic electrolysis cell. An external power source drives H2O splitting at the steam electrode. The product O2 is exhausted 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 to facilitate thermal balance and high efficiency. Proton-conducting ceramic membranes transport reasonable rates of H+ ions at 400 - 500 ºC with low overpotentials for H2O splitting. This lower operating temperature is reasonably well matched with the CO2-methanation reaction that thermodynamically favors lower-temperatures. The Ni-based catalyst is active for both H2 evolution from the protonic-ceramic material and catalytic methanation of CO/CO2, further promoting the technological combination. Integration of the methanation reactor with the electrolyzer simplifies the system, improves reliability, and provides increased performance within a smaller package than more-prevalent two-stage systems. We have pioneered a larger-area (active area is 5 cm2) Sabatier Electrolyzer cell composed of 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 demonstrated CO2 conversion and CH4 selectivity at 55% and 63%, respectively, at 450 °C. This result represents the highest reported electrochemical conversion of CO2 and H2O into CH4 in a single device. In this presentation, we will review our efforts in Sabatier Electrolyzer development, targeting the thermodynamically predicted CO2 conversion and CH4 selectivity of 70% and 95%, respectively. Figure 1

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

Intense efforts are currently in progress to study various sources of basal plane dislocations (BPDs) in SiC epitaxial layers. BPDs can generate Shockley-type stacking faults (SSFs) in SiC epitaxial layers, which have been shown to be associated with the degradation of power devices. This study shows that the star-shaped defect can be a source of several BPDs in the epitaxial layer. We investigate the complex microstructure of the star defect, the generation of BPDs, and expansion of SSFs using various complementary microscopy and optical techniques. We show direct evidence that star-defects can be a nucleation point of single-SSFs that can expand at the core of the defect. Newly found secondary dislocation arrays extending over a few centimeters away are found to be emanating from the primary arms of the star defect. The presence of such dislocation walls and the expansion of single-SSFs will affect the yield of numerous die on a wafer. Further understanding of the formation mechanism of stacking faults generated from star-defects as provided in this study helps understand their effect on SiC-based devices, which is crucial to assess device reliability.