Article pubs.acs.org/cm
Decreasing the Polarization Resistance of (La,Sr)CrO3−δ Solid Oxide Fuel Cell Anodes by Combined Fe and Ru Substitution Daniel E. Fowler,† Andreas C. Messner,‡ Elizabeth C. Miller,‡ Benjamin W. Slone,‡ Scott A. Barnett,‡ and Kenneth R. Poeppelmeier*,† †
Department of Chemistry, and ‡Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, United States ABSTRACT: The perovskite compounds La0.33Sr0.67Cr1−x−yFexRuyO3−δ (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 Gd 0.1 Ce 0.9 O 2‑β (GDC) in La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 3‑ε / La0.4Ce0.6O2 bilayer electrolyte-supported cells. By comparing anode polarization resistance RP,A values for the LSCrFeRu compounds to the either exclusively Fe- or Ru-substituted (La,Sr)CrO3−δ perovskites, the present results demonstrate that the two substituent cations work synergistically to provide further reduction in RP,A from 0.290 Ω·cm2 for La0.33Sr0.67Cr0.33Fe0.67O3−δ (LSCrFe) and 0.235 Ω·cm2 for La0.8Sr0.2Cr0.8Ru0.2O3−δ (LSCrRu) to 0.195 Ω·cm2 for LSCrFeRu (all measured in humidified hydrogen at 800 °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 pH2 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−δ perovskites is thus sufficient to make hydrogen electrochemical oxidation the rate-limiting step, resulting in anodes with significantly reduced RP,A.
1. INTRODUCTION Conductive oxides have been widely reported as potential candidates for solid oxide fuel cell (SOFC) anodes owing to the fact that they are mixed ionic and electronic conductors in typical anode conditions.1−8 Some of these oxide materials, including the perovskites La 0.75 Sr 0.25 Cr 0.5 Mn 0.5 O 3 and SrTi0.3Fe0.7O3−δ, have exhibited decidedly low anode polarization resistance RP,A values (≤0.2 Ω·cm2)1,7,9 that are reasonably close to those of typical SOFC anode material NiYSZ (
