The Chemical Evolution of the La0.6Sr0.4CoO3−δ Surface Under SOFC Operating Conditions and Its Implications for Electrochemical Oxygen Exchange Activity

Abstract

Owing to its extraordinary high activity for catalysing the oxygen exchange reaction, strontium doped LaCoO 3 (LSC) is one of the most promising materials for solid oxide fuel cell (SOFC) cathodes. However, under SOFC operating conditions this material suffers from performance degradation. This loss of electrochemical activity has been extensively studied in the past and an accumulation of strontium at the LSC surface has been shown to be responsible for most of the degradation effects. The present study sheds further light onto LSC surface changes also occurring under SOFC operating conditions. In-situ near ambient pressure X-ray photoelectron spectroscopy measurements were conducted at temperatures between 400 and 790 °C. Simultaneously, electrochemical impedance measurements were performed to characterise the catalytic activity of the LSC electrode surface for O 2 reduction. This combination allowed a correlation of the loss in electro-catalytic activity with the appearance of an additional La-containing Sr-oxide species at the LSC surface. This additional Sr-oxide species preferentially covers electrochemically active Co sites at the surface, and thus very effectively decreases the oxygen exchange performance of LSC. Formation of precipitates, in contrast, was found to play a less important role for the electrochemical degradation of LSC. Electronic supplementary material The online version of this article (10.1007/s11244-018-1068-1) contains supplementary material, which is available to authorized users.

Surface Restructuring of Thin-Film Electrodes Based on Thermal History and Its Significance for the Catalytic Activity and Stability at the Gas/Solid and Solid/Solid Interfaces

“…Herein, we would like to draw attention to a recent study on a similar HT-grown LSC64 film. 56 The study observed the new growth of La containing SrO species at operation temperatures above 400 °C using an in situ near-ambient pressure XPS. Most interestingly, the new species preferentially grew on the electrochemically active Co sites.…”

Novel Sample-Stage for Combined Near Ambient Pressure X-ray Photoelectron Spectroscopy, Catalytic Characterization and Electrochemical Impedance Spectroscopy

“…In the case of SOFCs and SOECs, model cells with a thin film working electrode as seen in Figure 1 are an excellent configuration for mechanistic kinetic studies, which allow simultaneous determination of electrochemical performance by measuring the current-voltage characteristics as well as observation of surface chemistry and reaction intermediates by NAP-XPS. Several of such studies were already carried out at synchrotron facilities in two-electrode cells with ceria-based electrodes [12][13][14][15] and perovskite-type electrodes [12,[16][17][18][19][20]. Recently, also the XPS investigation of operating Ni-GDC anodes in two-chamber cells and a three-electrode geometry were reported [21,22].…”

Chemical Degradation of the La0.6Sr0.4Co0.2Fe0.8O3−δ/Ce0.8Sm0.2O2−δ Interface during Sintering and Cell Operation

“…By taking into account the previous deduction concerning La diffusion, the second doublet is assigned to lanthanum in the ceria environment. The classical figure of Sr 3d spectra in LSCF exhibits two contributions, the one at low binding energy corresponding to the bulk and the one at high binding energy corresponding to the surface [68][69][70]. Thus, for the tested interface, the doublet at 131.6 eV was attributed to the bulk component and the doublet at 134.2 eV to the surface component.…”