La0.8Sr0.2Cr1 − xRuxO3 − δ–Gd0.1Ce0.9O1.95 solid oxide fuel cell anodes: Ru precipitation and electrochemical performance

Composites containing La0.8Sr0.2Cr1 − xRuxO3 − δ (LSCrRu) with x = 0–0.25 and Gd0.1Ce0.9O1.95 (GDC) were studied as anodes in solid oxide fuel cells (SOFCs) with La0.9Sr0.1Ga0.8Mg0.2O3 − δ (LSGM) electrolytes. Electrode polarization resistance RP decreased during initial SOFC operation before reaching a minimum. The decrease was more rapid, and the ultimate RP value reached was generally lower, with increasing temperature and Ru content x. RP was stable at longer times except for x = 0.25 where it increased slightly. SOFCs with x = 0.18 anodes at 800 °C yielded power densities as high as 0.53 W/cm2 with an RP value, including the (La,Sr)(Co,Fe)O3–GDC cathode, of < 0.15 Ω cm2. Transmission electron microscopy revealed Ru nano-particles on LSCrRu surfaces; their size increased and their density decreased with increasing temperature. Increasing the Ru content increased the density of Ru surface particles at a given time and temperature. Measured early-stage Ru surface coverage values were consistent with a model where Ru supply to the LSCrRu surface was limited by Ru bulk out-diffusion, but the coverage saturated at longer times. There was surprisingly little Ru particle coarsening over times up to 1000 h at 800 °C, with Ru particles sizes remaining < 10 nm. The cell RP values generally decreased with increasing Ru nano-particle surface area.