Activation Mechanism and Nanostructuring of Solid Oxide Fuel Cell Cathodes

Thursday, November 11, 2010: 12:46 PM
Grand Ballroom H (Marriott Downtown)
M. Ali Haider and Steven McIntosh, Department of Chemical Engineering, University of Virginia, Charlottesville, VA

 

Perovskite structured oxides of series La1-xSrxMnO3-d (LSM) are widely used as cathode for oxygen reduction reaction in a solid oxide fuel cell (SOFC). To study the electrode mechanism, a geometrically well-defined model system was developed using dense thin-film cathode. Polycrystalline nanostructured dense La0.8Sr0.2MnO3-d (LSM) thin-film cathodes with an average thickness of 600 nm were fabricated on yttria stabilized zirconia (YSZ) or gadolinia doped ceria (CGO) substrate electrolyte using spray pyrolysis. The polarization resistance of the cathode was observed to be reduced on initial application of voltage or current bias. In order to understand this initial activation, the reaction mechanism was probed. This include altering the electrode surface by doping with La0.6Sr0.4FeO3-d nanoparticles, characterizing changes in bulk microstructure before and after application of current and changing the nature of electrode-electrolyte interface by introducing La2Zr2O7 impurities. Two different activation mechanisms were observed in the cathode. While applying current for a short duration (5 min) the activation was linked to changes in the surface activity, long term (16 hours) current application produced changes in bulk microstructure.

For surface doping of electrode, a reverse micelle (RM) based method was developed to synthesize highly active electrocatalytic nanoparticles of composition LaxSr1-xCoyFe1-yO3-d. The RM synthesis provides tight control over nanoparticle size and average particles size was changed from 14 nm to 50 nm by changing the water:surfactant ratio in the precursor RM solution. A noticeable difference in the sintering behavior of these nanoparticles was observed. While the bulk samples of the same perovskite materials sinter at high sintering temperatures, nanoparticles sinter into a pure perovskite phase at temperature as low as 823 K. The unit cell parameter (a=3.93 ) for cubic perovskite nanoparticles was found to be greater than the bulk material (a=3.89 ) of similar composition and structure.


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See more of this Session: Fuel Cell Technology
See more of this Group/Topical: Fuels and Petrochemicals Division