Lee, Shiwoo
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Publication SOFC Anodes Based on Infiltration of La0.3Sr0.7TiO3(2008-09-22) Lee, Shiwoo; Vohs, John M; Gorte, Raymond J; Kim, GuntaeComposites formed by infiltration of 45 wt % La0.3Sr0.7TiO3 (LST) into 65% porous yttria-stabilized zirconia (YSZ) were examined for application as solid oxide fuel cell (SOFC) anodes. Although LST does not react with YSZ, the structure of the LST deposits was strongly affected by the calcination temperature. At 1373 K, the LST formed loosely packed, 0.1 µm particles that filled the YSZ pores. The conductivity of this composite depended strongly on the pretreatment conditions but was greater than 0.4 S/cm after heating to 1173 K in humidified (3% H,2O) H2. Following calcination at 1573 K, the LST had sintered significantly, decreasing the conductivity of the composite by a factor of approximately 5. The addition of a catalyst was critical for achieving reasonable electrochemical performance, with the addition of 0.5 wt % Pd and 5 wt % ceria increasing the power density of otherwise identical cells from less than 20 to 780 mW/cm2 for operation in humidified (3% H2O) H2 at 1073 K. Electrodes prepared from LST deposits calcined at 1373 K were found to exhibit a much better performance than those prepared from LST deposits calcined at 1573 K, demonstrating that the structure of the composite is critical for achieving high performance.Publication Investigation of the Structural and Catalytic Requirements for High-Performance SOFC Anodes Formed by Infiltration of LSCM(2009-01-12) Lee, Shiwoo; Kim, Guntae; Shin, J Y; Vohs, J M; Corre, G; Gorte, Raymond J; Irvine, J T SComposites formed by infiltration of 45 wt % La0.8Sr0.2Cr0.5Mn0.5O3 (LSCM) into a 65% porous yttria-stabilized zirconia (YSZ) scaffold were investigated in order to understand the reasons this material is able to provide excellent anode performance in solid oxide fuel cells (SOFCs). Scanning electron microscopy showed that the LSCM forms a film over the YSZ after calcination at 1473 K but that this film undergoes cracking to expose a long three-phase boundary after reduction at 1073 K. Coulometric titration demonstrated that the reduction of LSCM and La0.8Sr0.2MnO3 occurred over a similar range of P(O-2) and that reduction is the likely cause for film cracking. To achieve low anode impedances in humidified H-2 at 973 K, it was necessary to add a catalyst. The addition of 0.5-1 wt % Pd, Rh, or Ni was sufficient to increase the maximum power density of SOFCs with 60 mu m thick YSZ electrolytes to >500 mW/cm(2) in humidified H-2 at 973 K. The addition of either 1 wt % Fe or 5 wt % ceria also improved power densities but to a lesser extent. Finally, the use of Pt paste as the current collector increased performance to a similar extent as intentionally adding catalyst, showing the importance of using inert materials in electrode testing.