(Invited) Enhancement of Surface Oxygen Exchange Kinetics for Pr0.1Ce0.9O2-δ with Deposition of La or Sm Oxide

Fast oxygen exchange kinetics, a key figure of merit in solid oxide fuel cell (SOFC) electrodes, is often dramatically hindered by the presence of even small concentrations of impurities at the surface. Si, for example, is common in ceramics processing. As discussed in this presentation, it was found that rapid degradation of oxygen exchange kinetics occurred on dense thin films of Pr_0.1Ce_0.9O_2-d (PCO), a mixed ionic electronic conducting electrode for SOFCs. A new optical transmission relaxation (OTR) technique was developed to aid in measuring kinetics on the bare film surfaces. A key advantage of this technique is that it does not require current collectors typical of conventional measurements. Si was identified by TEM and XPS as a significant surface impurity, which forms a blocking layer on the electrode surface. Deposition of a La oxide film was found to result in full recovery of oxygen exchange kinetics on the measured sample. La and Si oxides were found to interact with each other as identified by a shift in the O1s XPS peak and a systematic OTR study of films that likely react with Si (e.g. La, Sm oxides) and those that do not (e.g. Nb, Ti, Zn oxides). These results indicate that La may "clean" the surface of the SOFC electrode, thereby dramatically improving oxygen transport kinetics. Preliminary measurements of OTR on a La-PCO solid solution indicates improved long-term electrode kinetics stability, demonstrating the commercial potential of this method to achieve Si impurity tolerance.