This paper reports the results of combined experimental and modeling studies of reversible solid-oxide cells. The tubular cells are fabricated using a Ni-YSZ ͑yttria-stabilized zirconia͒ fuel-electrode support, a dense YSZ electrolyte membrane, and a strontiumdoped lanthanum manganate-YSZ composite air electrode. Experiments are designed to systematically vary gas-phase species partial pressures and operating temperatures. The fuels are mixtures of H 2 , CO, H 2 O, CO 2 , and Ar. Performance is measured under anodic ͑fuel cell͒ and cathodic ͑electrolysis͒ polarization. The models consider reactive porous-media transport within the composite electrodes, thermal chemistry on Ni and YSZ surfaces, and charge-transfer chemistry. All chemistry is modeled with elementary reversible reactions. Close coupling between experimental measurements and model-based interpretation provides a basis for establishing reaction pathways and rates. In addition to advancing fundamental understanding, the resulting detailed reaction mechanisms are valuable for incorporation into predictive models that can be used for design and optimization of fuel-cell and electrolysis systems.

This LDRD involved a collaboration between Sandia and the Colorado School of Mines (CSM) ins solid-oxide electrochemical reactors targeted at solid oxide electrolyzer cells (SOEC), which are the reverse of solid-oxide fuel cells (SOFC). SOECs complement Sandia's efforts in thermochemical production of alternative fuels. An SOEC technology would co-electrolyze carbon dioxide (CO 2 ) with steam at temperatures around 800 ºC to form synthesis gas (H 2 and CO), which forms the building blocks for a petrochemical substitutes that can be used to power vehicles or in distributed energy platforms. The effort described here concentrates on research concerning catalytic chemistry, charge-transfer chemistry, and optimal cell-architecture. technical scope included computational modeling, materials development, and experimental evaluation. The project engaged the Colorado Fuel Cell Center at CSM through the support of a graduate student (Connor Moyer) at CSM and his advisors (Profs. Robert Kee and Neal Sullivan) in collaboration with Sandia. 4 ACKNOWLEDGMENTSThis report is based largely upon the thesis written by Connor Moyer for his degree of Master of Science (Engineering) at Colorado School of Mines, which this LDRD helped fund. This project also leveraged modeling results from Dr. Huayang Zhu at Colorado School of Mines, who was primarily funded by the Office of Naval Research via an RTC grant (N00014-05-1-03339).5