Oxygen exchange kinetics on a highly oriented La0.5Sr0.5CoO3−δ thin film prepared by pulsed-laser deposition

Abstract

Oxygen exchange at a highly oriented La0.5Sr0.5CoO3−δ thin film prepared on (100) surfaces of an yttria-stabilized zirconia single crystal by pulsed-laser deposition was studied with ac impedance spectroscopy under various temperatures and oxygen partial pressures. Three distinctive features observed in the impedance spectra were assigned to contributions from the ionic conduction of the electrolyte, oxide ion transfer across the electrode/electrolyte interface, and the oxygen exchange on the film surface. An equivalent circuit model was proposed to analyze the impedance results, from which the surface chemical exchange coefficients, kchem, were derived as a function of temperature and oxygen partial pressure.

In-Operando Determination of SOFC Cathode Oxygen Surface Exchange Coefficients for Enhanced Oxygen Reduction Reaction Kinetics

“…8,[16][17][18][19][20] The use of powder samples, with small particle size, provides the ability to dismiss any effect of bulk diffusion limited processes, unlike other surface exchange measurement techniques such as isotope exchange depth profiling and electrical conductivity relaxation. [21][22][23][24] * Electrochemical Society Fellow. z E-mail: ewach@umd.edu…”

Achieving fast oxygen diffusion in perovskites by cation ordering

“…7,8 The performance of perovskite oxides has been already optimized as much as possible mostly by means of various ion substitutions in both A and B sublattices, 6,7,8,9 but they still fail to operate at low enough temperatures ∼ 500…”

“…Only a few types of oxides, and perovskites ABO 3 (A is a rare-earth or an alkali-earth element and B is typically a transition metal) among them, have been found to possess these features. 1,2,3,4,5,6,7,8 Doped perovskites, which possess a high electronic conductivity in addition to the ionic one, are considered for using as electrodes in SOFC and as oxygen-selective membranes; for example, strontium-doped lanthanum manganese oxide, La 1−y Sr y MnO 3−δ , is a standard cathode material for SOFC applications operating at temperatures around 1000• C. 6 Recently, serious efforts are made to reduce the operation temperature of SOFC, and for the operation at 700 -800• C, strontium-doped lanthanum cobalt oxide, La 1−y Sr y CoO 3−δ , is considered to be the most promising cathode material.7,8 The performance of perovskite oxides has been already optimized as much as possible mostly by means of various ion substitutions in both A and B sublattices, 6,7,8,9 but they still fail to operate at low enough temperatures ∼ 500• C required for successful commercialization of the fuel cell technology.In this Letter, we show that the oxygen-ion diffusion in a doped perovskite can be enhanced by orders of magnitude if a simple cubic crystal [schematically shown in Fig.1(a)] transforms into a layered compound with ordered lanthanide and alkali-earth ions [ Fig. 1(b)], which reduces the oxygen bonding strength and provides disorder-free channels for ion motion.…”

Advanced Measurement and Modeling Techniques for Improved SOFC Cathodes

“…. This large value of capacitance has been observed for dense LSC electrodes with high levels of Sr doping, and is generally associated with the change of oxygen content in the oxide electrode [9,13] . The impedance of the LSC-82 electrode is more complex.…”

“…In the case of the perovskite mixed conductors La 1-x Sr x Co y Fe 1-y O 3-δ , workers have successfully addressed the first of these problems by making dense thin film electrodes [13,[43][44][45][46][47] . These films are often sufficiently thin (300~1000 nm) that bulk transport remains equilibrated, and thus interfacial rates can be isolated.…”