La_0.8Sr_0.2Cr_{1 - x}Ru_xO_{3 - δ}-Gd_0.1Ce_0.9O_1.95 solid oxide fuel cell anodes: Ru precipitation and electrochemical performance

Composites containing La_0.8Sr_0.2Cr_{1 - x}Ru_xO_{3 - δ} (LSCrRu) with x = 0-0.25 and Gd_0.1Ce_0.9O_1.95 (GDC) were studied as anodes in solid oxide fuel cells (SOFCs) with La_0.9Sr_0.1Ga_0.8Mg_0.2O_{3 - δ} (LSGM) electrolytes. Electrode polarization resistance R_P decreased during initial SOFC operation before reaching a minimum. The decrease was more rapid, and the ultimate R_P value reached was generally lower, with increasing temperature and Ru content x. R_P 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 R_P 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 R_P values generally decreased with increasing Ru nano-particle surface area.