| AVS 55th International Symposium & Exhibition | |
| In Situ Microscopy and Spectroscopy: Interfacial and Nanoscale Science Topical Conference | Wednesday Sessions |
| Session IS+SY+SS-WeM |
| Session: | In Situ Spectroscopy – Interfacial Science and Catalysis |
| Presenter: | H. Bluhm, Lawrence Berkeley National Laboratory |
| Authors: | H. Bluhm, Lawrence Berkeley National Laboratory J.T. Newberg, Lawrence Berkeley National Laboratory Z. Liu, Lawrence Berkeley National Laboratory Z. Hussain, Lawrence Berkeley National Laboratory S.C. DeCaluwe, University of Maryland, College Park C. Zhang, University of Maryland, College Park G.S. Jackson, University of Maryland, College Park F. El Gabaly, Sandia National Laboratories R.L. Farrow, Sandia National Laboratories K.F. McCarty, Sandia National Laboratories M.A. Linne, Sandia National Laboratories A.H. McDaniel, Sandia National Laboratories |
| Correspondent: | Click to Email |
Solid-oxide fuel cells (SOFCs) are an important technology for converting chemical energy to electrical energy. A compelling advantage of SOFCs is the ability to utilize fuels such as hydrogen, synthesis gas, and hydrocarbons. In a conventional SOFC, selective catalytic and charge transfer processes produce O2- ions at the cathode/electrolyte interface, which then diffuse through a dense electrolyte to an anode/electrolyte interface where adsorbed fuel species are oxidized. Ceria (CeO2), a mixed conductor capable of transporting both O2- ions and electrons, is being considered as a coke-resistant anode catalyst to improve SOFC performance. A key unknown about ceria-catalyzed anodes is the cerium (Ce) oxidation state during fuel cell operation. Cell performance is critically affected by the Ce oxidation state because Ce3+ and Ce4+ states coexist in CeO2, and both electronic and ionic conductivities are determined by the abundance of Ce3+. To exploit the potential of ambient-pressure XPS to characterize functioning electrochemical devices, we have fielded an SOFC experiment on beamline 11.0.2 at the Advanced Light Source. A single chamber cell was created by patterning working and counter electrodes from ceria and platinum atop single crystal yttria-stabilized zirconia (YSZ) electrolyte. The cell was characterized in atmospheres of H2/H2O and H2/O2/H2O under forward and reverse polarization at approximately 973 K and 0.5 Torr. Standard chronoamperometric and impedance measurements were conducted simultaneously with ambient-pressure XPS. A focused x-ray beam (diameter < 0.1 mm) was used to spatially resolve changes in the Ce oxidation state as a function of position between counter and working electrodes under positive and negative bias. Electrochemically induced changes in the Ce oxidation state were directly observed and were dependent upon electrode polarization and proximity to electrochemically active regions. In addition, the oxidation state and surface potential of the YSZ electrolyte were also characterized. Implications of our findings on understanding the electrochemical mechanisms of SOFC operation with ceria anodes will be discussed.
This research was supported by the U. S. Department of Energy under Contract No.DE-AC04-94AL85000 (Sandia) and DE-AC02-05CH11231 (LBNL). UMD participants were supported by the Office of Naval Research under Contract No: N000140510711.