Pd-promoted La0.6Sr0.4Co0.2Fe0.8O3 cathodes

Porous La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) electrodes supported on Ce0.9Gd0.1O1.95 (CGO) electrolyte were impregnated with small amounts of Pd and the electrochemical impedances resolved by AC impedance spectroscopy. The optimum Pd loading resulted in 3-4 times lower cathodic impedance in the temperature range 400-750 degrees C. Single cell Solid Oxide Fuel Cells (SOFCs) were fabricated by tape casting CGO electrolyte onto an anode support. Under d.c operation, the addition of Pd to the LSCF cathode was found to decrease the overall cell resistance by 15% at 650 degrees C and 40% at 550 degrees C. This suggests that the SOFC becomes more limited by the performance of the cathode at lower temperatures and hence the greater benefit of Pd promotion. Finally, Pd particles were deposited on dense smooth LSCF substrates and Isotope Exchange Depth Profiling (IEDP) and Secondary Ion Mass Spectrometry (SIMS) were carried out to determine the tracer diffusion (D*) and surface exchange (k) coefficients. D* was not significantly effected but k decreased by well over an order of magnitude with Pd loadings similar to those applied to the electrode. (C) 1998 Published by Elsevier Science B.V. All rights reserved.