(499e) Oxygen Reduction Kinetics and Surface Chemistry of Doped Lanthanum Ferrites

Solid oxide fuel cells (SOFCs) show great promise for generating clean power from a variety of fuels. The major roadblock against their implementation is a large cathodic resistance, which causes insufficient power densities and high fabrication costs. The large cathodic resistance is caused by slow oxygen activation kinetics and oxide ion transport of the current manganite-based cathode. Thus, the development of highly active and ionically conductive materials suitable for use as cathodes is needed to help SOFCs realize their wide-scale application.

Recent research has shown that cathode behavior becomes co-limited by oxygen reduction kinetics and ionic transport for transition metal perovskite materials. Ongoing research in our group focuses on oxygen mobility in doped-lanthanum ferrites. The present work studies the kinetics of the oxygen reduction reaction, oxygen-surface interactions, and the surface chemistry of doped-lanthanum ferrites. Results show trends with strontium dopant levels on the lanthanum site, transition metal dopant levels on the iron site, temperature, and oxygen partial pressure in the surrounding environment. Kinetic measurements are made through oxygen equilibration experiments during simultaneous thermogravimetric (TGA) and differential scanning calorimetric (DSC) analyses, cyclic voltammetry (CV), and isotopic oxygen exchange studies.

The kinetic results are supported by a thorough surface characterization by using methanol as a probe molecule and X-ray photoelectron spectroscopy (XPS). The nature and quantity of active surface sites and their surface chemistry are determined by pulsed methanol chemisorption and methanol temperature-programmed desorption, respectively. The majority of sites are basic in nature, but a small amount of redox sites exist. Further insight is provided through techniques such as X-ray diffraction, Raman spectroscopy, and temperature-programmed techniques.