La1−xCaxCoO3 perovskite-type oxides: Identification of the surface oxygen species by XPS

Merino, Nora Andrea; Barbero, Bibiana P.; Eloy, Pierre; Cadús, Luís E.

doi:10.1016/j.apsusc.2006.02.035

Cited by 482 publications

(256 citation statements)

References 21 publications

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“…The high BE is related to the oxygen-containing species which occurs relatively near the surface and/or surface OH group caused by hydroxyl environment. [35][36][37][38][39][40] For the sample that was heat-treated at 700…”

Section: Resultsmentioning

confidence: 99%

Co-Deposition and Poisoning of Chromium and Sulfur Contaminants on La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δCathodes of Solid Oxide Fuel Cells

Wang

O’Donnell

et al. 2015

J. Electrochem. Soc.

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The presence of both chromium and sulfur (Cr/S) contaminants on the microstructure and electrocatalytic activity properties of La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) electrodes of solid oxide fuel cells (SOFCs) is studied, using Confocal laser Raman spectroscopy, XRD, scanning electron microscopy, X-ray photoelectron spectroscopy (XPS) and electrical conductivity relaxation (ECR) methods. LSCF dense bar samples were heat treated in the presence of Cr 2 O 3 and 20 ppm SO 2 and in the temperature range of 600-900 • C. The deposition and reaction products between LSCF and Cr/S depend on the temperature: SrCrO 4 only forms on LSCF samples at 900 • C and 800 • C, while formation of SrSO 4 phase occurs at all temperatures studied. The results indicate that sulfur shows a higher activity with LSCF, as compared to gaseous Cr species. Segregated SrO is more likely to react with gaseous Cr species at higher temperatures, however, reaction with SO 2 is more pronounced at lower temperatures, forming SrSO 4 . ECR results indicate that co-deposition of Cr and sulfur significantly deteriorates the surface exchange and diffusion processes for the O 2 reduction reaction on LSCF electrodes. The durability of a solid oxide fuel cell (SOFC) is critically related to the degradation behavior of its cathodes such as La 0.8 Sr 0.2 MnO 3 (LSM) and La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) in the presence of impurity species such as chromium from the chromia-forming interconnect, silica, boron and volatile alkaline elements from the glass seals sealant and sulfur from air.1-8 Among them, gaseous chromium species vaporized from the chromium oxide scale of chromia-forming metallic interconnect are probably the most investigated contaminants affecting the performance of SOFCs' cathodes. The mechanism and process of the deposition and poisoning of chromium species at the cathodes of SOFCs have been extensively investigated, including LSM, 9-11 LSCF 12 and Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ (BSCF). 13 In the case of LSCF electrodes, deposition of Cr species preferentially take place on the surface of the LSCF electrode, resulted from the interaction between the segregated SrO and gaseous Cr species.14,15 Both the humidity in the air stream and operation temperature have a significant effect on the Cr deposition. 16 Cr deposition decreases significantly with the decrease of temperature, most likely due to the reduced Sr segregation as well as the decrease of the partial pressure of gaseous Cr species at reduced temperatures. 17The sulfur in the form of SO 2 or H 2 S in the air stream is another important contaminant affecting the performance stability of SOFC cathodes. SO 2 content in air can be in the range of 10-340 μg m −3 (3.5 × 10 −3 -0.12 ppm) in cities. 18 Despite the low concentration of SO 2 , sulfur in the air stream can accumulate at the cathodes of SOFC cells, degrading the performance.5 Wang et al. 19 studied the polarization performance behavior of LSCF in the presence of 0.1 ppm SO 2 and observed two-stages of performance degrad...

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Section: Resultsmentioning

confidence: 99%

Co-Deposition and Poisoning of Chromium and Sulfur Contaminants on La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δCathodes of Solid Oxide Fuel Cells

Wang

O’Donnell

et al. 2015

J. Electrochem. Soc.

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“…The O 1s spectra can be separated into two peaks at around 528.6-529.2 eV and 530.5 eV. The higher binding energy one with less intensity was ascribed to adsorbed oxygen or surface hydroxyl species [27,28], referred to as O α , whereas the lower binding energy one was due to lattice oxygen O 2´ [ 28,29], denoted as O β . The value of binding energy of O β decreased from 529.2 to 528.6 eV when the calcination temperature increased from 773 to 973 K. The binding energies of 529.2 and 528.6 eV were attributed to the lattice oxygen of anatase TiO 2 and rutile TiO 2 , respectively.…”

Section: Xps Characterizationmentioning

confidence: 99%

Characterization and Catalytic Activity of Mn-Co/TiO2 Catalysts for NO Oxidation to NO2 at Low Temperature

et al. 2016

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Abstract:A series of Mn-Co/TiO 2 catalysts were prepared by wet impregnation method and evaluated for the oxidation of NO to NO 2 . The effects of Co amounts and calcination temperature on NO oxidation were investigated in detail. The catalytic oxidation ability in the temperature range of 403-473 K was obviously improved by doping cobalt into Mn/TiO 2 . These samples were characterized by nitrogen adsorption-desorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM) and hydrogen temperature programmed reduction (H 2 -TPR). The results indicated that the formation of dispersed Co 3 O 4¨C oMnO 3 mixed oxides through synergistic interaction between Mn-O and Co-O was directly responsible for the enhanced activities towards NO oxidation at low temperatures. Doping of Co enhanced Mn 4+ formation and increased chemical adsorbed oxygen amounts, which also accelerated NO oxidation.

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“…For LaO-LFO, a third peak is present at ~2.3 eV higher binding energy, termed "surf". Such a surface feature has been often observed for epitaxial perovskite films of unknown termination, as well as perovskite particles, and has been attributed to a host of potential species such as carbonates, 29,30 adsorbed water, 31,32 hydroxyls, [31][32][33] peroxide species, 34 undercoordinated oxygen, 35,36 and the terminal layer(s) of a polar surface due to a shift in Madelung potential. 17 Considering the AP-XPS spectra collected at 300 °C in 100 mTorr oxygen (and similarly at ~24 mTorr oxygen, Figure S4), we rule out the presence of carbonates and adsorbed water, and the lack of such a feature on the FeO 2 -terminated surface suggests it does not arise from a change in Madelung potential at the surface.…”

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confidence: 99%

Influence of LaFeO₃ Surface Termination on Water Reactivity

Stoerzinger

Comès

Spurgeon

et al. 2017

J. Phys. Chem. Lett.

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The polarity of oxide surfaces can dramatically impact their surface reactivity, in particular with polar molecules such as water. The surface species that result from this interaction change the oxide electronic structure and chemical reactivity in applications such as 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 2 photoelectrochemistry, but are challenging to probe experimentally. Here we report a detailed study of the surface chemistry and electronic structure of the perovskite LaFeO 3 in humid conditions using ambient pressure X-ray photoelectron spectroscopy. Comparing the two possible terminations of the polar (001)-oriented surface, we find that the LaO-terminated surface is more reactive toward water, forming hydroxyl species and adsorbing molecular water at lower relative humidity than its FeO 2 -terminated counterpart. However, the FeO 2 -terminated surface forms more hydroxyl species during water adsorption at higher humidity, suggesting adsorbate-adsorbate interactions may impact reactivity. Our results demonstrate how the termination of a complex oxide can dramatically impact its reactivity, providing insight that can aid in the design of catalyst materials. TOC GRAPHICSPerovskite oxides such as LaFeO 3 show great promise as catalysts for energy conversion and storage. Applications such as electrocatalysis, 1-4 photoelectrochemistry, 5-7 and gas sensing 8-10 all take place in an aqueous or humid environment, where the interaction with water plays a key role in determining the functionality of these complex oxides. [11][12][13] The formation of surface hydroxyl groups and adsorption of water can impact the surface electronic structure 14 and ultimately the mechanisms and kinetics of surface chemical reactions. 15,16 Initial studies have considered the reactivity of perovskites with water using ambient pressure X-ray photoelectron spectroscopy 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 3 (AP-XPS), 12,17 enabling study of the surface species present in equilibrium with water vapor. The hydroxylation of these surfaces appeared greater than that of binary transition metal oxides. 18However, the chemical nature of the hydroxyl site in such systems remained elusive due to the unknown surface termination.The polar layers of (001) Figure 1, confirm the excellent quality and epitaxy of the film. We observe differences in the surface termination, although damage resulting from TEM sample preparation makes it difficult to unambiguously identify the surface layer. Instead, the termination of the as-prepared film was confirmed by angle resolved XPS (Table S1) and remained unchanged during AP-XPS experiments ( Figure S2). 5TiO 2 -te...

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La1−xCaxCoO3 perovskite-type oxides: Identification of the surface oxygen species by XPS

Cited by 482 publications

References 21 publications

Co-Deposition and Poisoning of Chromium and Sulfur Contaminants on La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δCathodes of Solid Oxide Fuel Cells

Co-Deposition and Poisoning of Chromium and Sulfur Contaminants on La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δCathodes of Solid Oxide Fuel Cells

Characterization and Catalytic Activity of Mn-Co/TiO2 Catalysts for NO Oxidation to NO2 at Low Temperature

Influence of LaFeO₃ Surface Termination on Water Reactivity

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La1−xCaxCoO3 perovskite-type oxides: Identification of the surface oxygen species by XPS

Cited by 482 publications

References 21 publications

Co-Deposition and Poisoning of Chromium and Sulfur Contaminants on La0.6Sr0.4Co0.2Fe0.8O3-δCathodes of Solid Oxide Fuel Cells

Co-Deposition and Poisoning of Chromium and Sulfur Contaminants on La0.6Sr0.4Co0.2Fe0.8O3-δCathodes of Solid Oxide Fuel Cells

Characterization and Catalytic Activity of Mn-Co/TiO2 Catalysts for NO Oxidation to NO2 at Low Temperature

Influence of LaFeO3 Surface Termination on Water Reactivity

Contact Info

Product

Resources

About

Co-Deposition and Poisoning of Chromium and Sulfur Contaminants on La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δCathodes of Solid Oxide Fuel Cells

Co-Deposition and Poisoning of Chromium and Sulfur Contaminants on La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δCathodes of Solid Oxide Fuel Cells

Influence of LaFeO₃ Surface Termination on Water Reactivity