Nickel- and ruthenium-doped lanthanum chromite anodes: Effects of nanoscale metal precipitation on solid oxide fuel cell performance

This paper compares the effects of Ni and Ru dopants in lanthanum chromite anodes by correlating structural characterization and electrochemical measurements in solid oxide fuel cells (SOFCs). Transmission electron microscope observations showed that nanoclusters of Ni or Ru metal precipitated onto lanthanum chromite (La_0.8 Sr_0.2 Cr_1-y X _y O_3-δ, X=Ni,Ru) surfaces, respectively, after exposure to hydrogen at 750-800°C. Ni nanoclusters were typically ∼10 nm in diameter immediately after reduction and coarsened to ∼50 nm over ∼300 h at 800°C. In contrast, Ru cluster size was stable at ≤ 5 nm, and the cluster density was > 10 times larger. SOFC tests were done with the doped lanthanum chromite anodes on La_0.9 Sr_0.1 Ga _0.8 Mg_0.2 O_3-δ electrolyte-supported cells. Ni nanocluster nucleation improved cell performance and reduced anode polarization resistance compared to cells with undoped (La_0.8 Sr _0.2 CrO_3-δ) anodes, but the improvement was much less than that for Ru. This comparison suggests that the smaller size of the Ru nanoclusters played an important role in enhancing anode electrochemical kinetics.