Pd-promoted La 0.6Sr 0.4Co 0.2Fe 0.8O 3 cathodes

Abstract

Porous La 0.6Sr 0.4Co 0.2Fe 0.8O 3 (LSCF) electrodes supported on Ce 0.9Gd 0.1O 1.95 (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°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°C and 40% at 550°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.