Decreasing the Polarization Resistance of (La,Sr)CrO3-δ Solid Oxide Fuel Cell Anodes by Combined Fe and Ru Substitution

The perovskite compounds La0.33Sr0.67Cr1-x-yFexRuyO3-delta (LSCrFeRu, x = 0.62, 0.57, and 0.47; y = 0.05, 0.14, and 0.2, respectively) were synthesized and assessed as a new type of solid oxide fuel cell (SOFC) anode in composite with Gd0.1Ce0.9O2-beta (GDC) in La0.9Sr0.1Ga0.8Mg0.2O3-epsilon/La0.4Ce0.6O2 bilayer electrolyte-supported cells. By comparing anode polarization resistance R-P,R-A values for the LSCrFeRu compounds to the either exclusively Fe- or Ru-substituted (La,Sr)CrO3-delta perovskites, the present results demonstrate that the two substituent cations work synergistically to provide further reduction in R-P,R-A from 0.290 Omega.cm(2) for La0.33Sr0.67Cr0.33Fe0.67O3-delta (LSCrFe) and 0.235 Omega.cm(2) for La0.8Sr0.2Cr0.8Ru0.2O3-delta (LSCrRu) to 0.195 Omega.cm(2) for LSCrFeRu (all measured in humidified hydrogen at 800 degrees C). These impedance results also strongly suggest that hydrogen dissociative adsorption was the rate-limiting step in the hydrogen oxidation reaction sequence for LSCrFe anodes at some of the pH(2) and temperatures measured. However, the formation of Ru nanoparticles on LSCrFeRu and LSCrRu surfaces, observed by scanning and transmission electron microscopy, appears to promote hydrogen dissociation. Substituting even small amounts of Ru into (La,Sr)(Cr,Fe)O3-delta perovskites is thus sufficient to make hydrogen electrochemical oxidation the rate-limiting step, resulting in anodes with significantly reduced R-P,R-A.