Nickel- and Ruthenium-Doped Lanthanum Chromite Anodes: Effects of Nanoscale Metal Precipitation on Solid Oxide Fuel Cell Performance

Abstract

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 (La0.8Sr0.2Cr1−ynormalXynormalO3−δ,X=Ni,Ru) surfaces, respectively, after exposure to hydrogen at 750–800°C . Ni nanoclusters were typically ∼10nm in diameter immediately after reduction and coarsened to ∼50nm over ∼300h at 800°C . In contrast, Ru cluster size was stable at ≤5nm , and the cluster density was 10 times larger. SOFC tests were done with the doped lanthanum chromite anodes on La0.9Sr0.1Ga0.8Mg0.2normalO3−δ electrolyte-supported cells. Ni nanocluster nucleation improved cell performance and reduced anode polarization resistance compared to cells with undoped (La0.8Sr0.2CrO3−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.

Evolution of the electrochemical interface in high-temperature fuel cells and electrolysers

“…Such enhanced stability is also observed in SOFC 92 or other catalytic applications 36,84 . Another notable consequence of particle anchorage is reflected in their remarkable coking resistance whilst maintain activity for desirable reactions 36,84 .…”

“…This not only allows for such attractive structural interplay, but also for combining it with other desirable electrode functionality (see Figure 2a) 84,87,89,91,95 , chromite 86,90,94 or chromite-manganite 93,96 perovskite supports. These have been applied to solid oxide fuel cells 86,90,92,94,97 , electrolysis cells 95,98 and for other catalytic process 36,84,85 .…”

“…Evidence so far suggests that redox exsolution from perovskites is a phase decomposition process driven by reduction and controlled by bulk and surface defects and external conditions 36,87,92 . Initially the lattice is reduced, losing oxygen and gaining electrons until the point where metal nucleation becomes favourable.…”

“…Initially the lattice is reduced, losing oxygen and gaining electrons until the point where metal nucleation becomes favourable. Nucleation is likely to occur primarily on the surface of the host lattice where the nucleation barrier is lowered by crystal defects 36,92 . The surface nucleation process drains exsolvable ions from the nearby perovskite lattice which causes additional reducible ions to diffuse to the surface to balance the compositional gradient and fuel the growth of the metal clusters.…”

The Electrochemical Properties of Sr(Ti,Fe)O3-δfor Anodes in Solid Oxide Fuel Cells

“…34 This Fe0 formation was accompanied by strongly increased electrochemical water splitting kinetics. Improvement of the hydrogen electrode performance by exsolution of easily reducible transition metals was also demonstrated on various (La,Sr)TiO 3 based materials, 9,55,56 (La,Sr)FeO 3-δ , 33 (La,Sr)CrO 3-δ based materials, [57][58][59][60] and rare earth vanadates. 61 Decreased anode polarization resistance in cells with (La,Sr)(Cr,Ru)O 3-δ anodes was quantitatively modelled by enhanced hydrogen dissociative adsorption at exsolved Ru nanoparticles.…”