In situ Synchrotron X-ray Studies of Dense Thin-Film Strontium-Doped Lanthanum Manganite Solid Oxide Fuel Cell Cathodes

Abstract

Using a model cathode-electrolyte system composed of epitaxial thin-films of La1-xSrxMnO3-δ (LSM) on single crystal yttria-stabilized zirconia (YSZ), we investigated changes in the cation concentration profile in the LSM during heating and under applied potential using grazing incidence x-rays. Pulsed laser deposition (PLD) was used to grow epitaxial LSM(011) on YSZ(111). At room temperature, we find that Sr segregates to form Sr enriched nanoparticles and upon heating the sample to 700°C, Sr is slowly reincorporated into the film. We also find different amounts of Sr segregation as the X-ray beam is moved across the sample. The variation in the amount of Sr segregation is greater on the sample that has been subject to 72 hours of applied potential, suggesting that the electrochemistry plays a role in the Sr segregation.

Reversible aging behavior of La0.8Sr0.2MnO3 electrodes at open circuit

“…Most literature reports demonstrate a change in the degree of strontium enrichment that depends on the thermal history of the sample. Of particular significance to the present work are results of Fister et al [16] and Chang et al [17], both of whom demonstrate a decrease in surface strontium enrichment as the temperature of dense LSM films increases from 300 C up to 900 C.…”

“…Strontium enrichment of the surface of LSM perovskites has been well-documented using a variety of techniques: Auger electron spectroscopy (AES) [15], total reflection x-ray fluorescence (TXRF) [16,17], x-ray photoelectron spectroscopy (XPS) [1,18,19], various methods of soft x-ray spectroscopy [20], and chemical analysis of an LSM surface etched by an acid solution. 3,13 Similar enrichment of the Sr:La ratio was reported with the perovskite La 0.6 Sr 0.4 CoO 3 (LSC) by Kubicek et al using time-of-flight secondary ion mass spectroscopy (ToF-SIMS) on an LSC thin film as well as chemical analysis of the LSC surface etched by an acid solution [21].…”

A-Site Diffusion in La1 −xSrxMnO3: Ab Initio and Kinetic Monte Carlo Calculations

“…13 Since cathode performance may depend quite sensitively on surface composition, finding the cause of Sr segregation is of significant interest. [14][15][16] Kinetic demixing is a general phenomenon 17 in compound oxides that can occur anytime there is a chemical potential gradient in O. [14][15][16] Kinetic demixing is a general phenomenon 17 in compound oxides that can occur anytime there is a chemical potential gradient in O.…”

Examination of the mechanism for the reversible aging behavior at open circuit when changing the operating temperature of (La0.8Sr0.2)0.95MnO3 electrodes

“…Cathode performance is sensitive to changes in the available surface area for oxygen reduction and to changes in the cathode's specific surface catalytic activity for oxygen reduction through changes in the surface composition. Previous studies have shown that cation segregation can occur within thin films and bulk samples of common SOFC cathode materials such as La 1 − x Sr x MnO 3 (LSM) [2][3][4][5][6][7][8][9][10][11] and La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 (LSCF) [11][12][13][14][15][16][17][18][19]. The degree to which certain cations build up at the electrode/ gas surface depends upon the temperature and the oxygen partial pressure.…”