Modification of LSF-YSZ Composite Cathodes by Atomic Layer Deposition

composite, Solid-Oxide-Fuel-Cell (SOFC) electrodes of La0.8Sr0.2FeO3 (LSF) and yttria-stabilized zirconia (YSZ) were prepared by infiltration methods and then modified by Atomic Layer Deposition (ALD) of ZrO2, La2O3, Fe2O3, or La2O3-Fe2O3 codeposited films of different thicknesses to determine the effect of surface composition on cathode performance. Film growth rates for ALD performed using vacuum procedures at 573 K for Fe2O3 and 523 K for ZrO2 and La2O3 were determined to be 0.024 nm ZrO2/cycle, 0.019 nm La2O3/cycle, and 0.018 nm Fe2O3/cycle. For ZrO2 and Fe2O3, impedance spectra on symmetric cells at 873 K indicated that polarization resistances increased with coverage in a manner suggesting simple blocking of O2 adsorption sites. With La2O3, the polarization resistance decreased with small numbers of ALD cycles before again increasing at higher coverages. When La2O3 and Fe2O3 were co-deposited, the polarization resistances remained low at high film coverages, implying that O2 adsorption sites were formed on the co-deposited films. The implications fo these results for future SOFC electrode development are discussed

Modification of Pd/CeO2 catalyst by Atomic Layer Deposition of ZrO2

Modification of a 1 wt% Pd/CeO2 catalyst by Atomic Layer Deposition of thin ZrO2 films was studied. Calcination of the unmodified Pd/CeO2, prepared by precipitation of aqueous Ce(NO3)3 solutions, with Pd added by impregnation, caused a large decrease in surface area and an increase in crystallite size between 673 K and 1073 K; however, catalysts modified by 0.4 nm ZrO2 films showed no change in either surface area or CeO2 crystallite size upon calcination to 1073 K. Methane-oxidation rates in 0.5% CH4 and 5% O2 were slightly lower on the ZrO2-covered catalyst when both materials were calcined at 673 K but the activity of the ZrO2-modified catalyst did not decrease with catalyst calcination temperature. Both catalysts showed good activity for the water-gas-shift reaction but the ZrO2 film improved sulfur tolerance by preventing formation of cerium sulfates.This paper was also made possible by an NPRP Grant # 6-290-1-059 from the Qatar National Research Fund (a member of Qatar Foundation). The statements made herein are solely the responsibility of the authors. The authors would also like to thank M. Aulick�, T. Ducho? and K. Veltrusk� from Charles University in Prague for the XPS analysis.Scopu