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

Porous La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) electrodes supported on Ce0.9Gd0.1O1.9 5 (CGO) electrolyte were impregnated with small amounts of Pd and the elect rochemical 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 fa bricated by tape casting CGO electrolyte onto an anode support. Under d.c o peration, 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. T his suggests that the SOFC becomes more limited by the performance of the c athode at lower temperatures and hence the greater benefit of Pd promotion. Finally, Pd particles were deposited on dense smooth LSCF substrates and I sotope 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 decrease d by well over an order of magnitude with Pd loadings similar to those appl ied to the electrode. (C) 1998 Published by Elsevier Science B.V. All right s reserved.