Segregated Chemistry and Structure on (001) and (100) Surfaces of (La1-xSrx)2CoO4 Override the Crystal Anisotropy in Oxygen Exchange Kinetics

Yan Chen, Helena Tellez Lozano, Mónica Burriel, Fan Yang, Nikolai Tsvetkov, Zhuhua Cai, David W. McComb, John A. Kilner, Bilge Yildiz

Research output: Contribution to journalArticle

54 Citations (Scopus)

Abstract

Attaining fast oxygen exchange kinetics on perovskite and related mixed ionic and electronic conducting oxides is critical for enabling their applications in electrochemical energy conversion systems. This study focuses on understanding the relationship between surface chemistry and the surface oxygen exchange kinetics on epitaxial films made of (La1-xSrx)2CoO4, a prototypical Ruddlesden-Popper structure that is considered as a promising cathode material for fuel cells. The effects of crystal orientation on the surface composition, morphology, oxygen diffusion, and surface exchange kinetics were assessed by combining complementary surface-sensitive analytical techniques, specifically low energy ion scattering, X-ray photoelectron spectroscopy, Auger electron spectroscopy, scanning transmission electron microscopy, atomic force microscopy, and secondary ion mass spectroscopy. The films were grown in two different crystallographic orientations, (001) and (100), and with two different Sr compositions, at x = 0.25 (LSC25) and 0.50 (LSC50), by using pulsed laser deposition. In the as-prepared state, a Sr enriched layer at the top surface and a Co enriched subsurface layer were found on films with both orientations. After annealing at elevated temperatures in oxygen, the Sr enrichment increased, followed by clustering into Sr-rich secondary phase particles. Both the LSC25 and LSC50 films showed anisotropic oxygen diffusion kinetics, with up to 20 times higher oxygen diffusion coefficient along the ab-plane compared that along the c-axis at 400-500 °C. However, no dependence of surface oxygen exchange coefficient was found on the crystal orientation. This result indicates that the strong Sr segregation at the surface overrides the effect of the structural anisotropy that was also expected for the surface exchange kinetics. The larger presence of Co cations exposed at the LSC25 surface compared to that at the LSC50 surface is likely the reason for the faster oxygen surface exchange kinetics on LSC25 compared to LSC50. This work demonstrated the critical role of surface chemistry on the oxygen exchange kinetics on perovskite related oxides, which are thus far underexplored at elevated temperatures, and provides a generalizable approach to probe the surface chemistry on other catalytic complex oxides. (Graph Presented).

Original languageEnglish
Pages (from-to)5436-5450
Number of pages15
JournalChemistry of Materials
Volume27
Issue number15
DOIs
Publication statusPublished - Aug 11 2015

Fingerprint

Anisotropy
Oxygen
Crystals
Kinetics
Surface chemistry
Oxides
Crystal orientation
Perovskite
Ions
Epitaxial films
Auger electron spectroscopy
Pulsed laser deposition
Energy conversion
Surface structure
Cations
Fuel cells
Atomic force microscopy
Ion exchange
Cathodes
X ray photoelectron spectroscopy

All Science Journal Classification (ASJC) codes

  • Chemistry(all)
  • Chemical Engineering(all)
  • Materials Chemistry

Cite this

Segregated Chemistry and Structure on (001) and (100) Surfaces of (La1-xSrx)2CoO4 Override the Crystal Anisotropy in Oxygen Exchange Kinetics. / Chen, Yan; Tellez Lozano, Helena; Burriel, Mónica; Yang, Fan; Tsvetkov, Nikolai; Cai, Zhuhua; McComb, David W.; Kilner, John A.; Yildiz, Bilge.

In: Chemistry of Materials, Vol. 27, No. 15, 11.08.2015, p. 5436-5450.

Research output: Contribution to journalArticle

Chen, Y, Tellez Lozano, H, Burriel, M, Yang, F, Tsvetkov, N, Cai, Z, McComb, DW, Kilner, JA & Yildiz, B 2015, 'Segregated Chemistry and Structure on (001) and (100) Surfaces of (La1-xSrx)2CoO4 Override the Crystal Anisotropy in Oxygen Exchange Kinetics', Chemistry of Materials, vol. 27, no. 15, pp. 5436-5450. https://doi.org/10.1021/acs.chemmater.5b02292
Chen, Yan ; Tellez Lozano, Helena ; Burriel, Mónica ; Yang, Fan ; Tsvetkov, Nikolai ; Cai, Zhuhua ; McComb, David W. ; Kilner, John A. ; Yildiz, Bilge. / Segregated Chemistry and Structure on (001) and (100) Surfaces of (La1-xSrx)2CoO4 Override the Crystal Anisotropy in Oxygen Exchange Kinetics. In: Chemistry of Materials. 2015 ; Vol. 27, No. 15. pp. 5436-5450.
@article{6e78a712ad5444e59f65a623b5a94fb7,
title = "Segregated Chemistry and Structure on (001) and (100) Surfaces of (La1-xSrx)2CoO4 Override the Crystal Anisotropy in Oxygen Exchange Kinetics",
abstract = "Attaining fast oxygen exchange kinetics on perovskite and related mixed ionic and electronic conducting oxides is critical for enabling their applications in electrochemical energy conversion systems. This study focuses on understanding the relationship between surface chemistry and the surface oxygen exchange kinetics on epitaxial films made of (La1-xSrx)2CoO4, a prototypical Ruddlesden-Popper structure that is considered as a promising cathode material for fuel cells. The effects of crystal orientation on the surface composition, morphology, oxygen diffusion, and surface exchange kinetics were assessed by combining complementary surface-sensitive analytical techniques, specifically low energy ion scattering, X-ray photoelectron spectroscopy, Auger electron spectroscopy, scanning transmission electron microscopy, atomic force microscopy, and secondary ion mass spectroscopy. The films were grown in two different crystallographic orientations, (001) and (100), and with two different Sr compositions, at x = 0.25 (LSC25) and 0.50 (LSC50), by using pulsed laser deposition. In the as-prepared state, a Sr enriched layer at the top surface and a Co enriched subsurface layer were found on films with both orientations. After annealing at elevated temperatures in oxygen, the Sr enrichment increased, followed by clustering into Sr-rich secondary phase particles. Both the LSC25 and LSC50 films showed anisotropic oxygen diffusion kinetics, with up to 20 times higher oxygen diffusion coefficient along the ab-plane compared that along the c-axis at 400-500 °C. However, no dependence of surface oxygen exchange coefficient was found on the crystal orientation. This result indicates that the strong Sr segregation at the surface overrides the effect of the structural anisotropy that was also expected for the surface exchange kinetics. The larger presence of Co cations exposed at the LSC25 surface compared to that at the LSC50 surface is likely the reason for the faster oxygen surface exchange kinetics on LSC25 compared to LSC50. This work demonstrated the critical role of surface chemistry on the oxygen exchange kinetics on perovskite related oxides, which are thus far underexplored at elevated temperatures, and provides a generalizable approach to probe the surface chemistry on other catalytic complex oxides. (Graph Presented).",
author = "Yan Chen and {Tellez Lozano}, Helena and M{\'o}nica Burriel and Fan Yang and Nikolai Tsvetkov and Zhuhua Cai and McComb, {David W.} and Kilner, {John A.} and Bilge Yildiz",
year = "2015",
month = "8",
day = "11",
doi = "10.1021/acs.chemmater.5b02292",
language = "English",
volume = "27",
pages = "5436--5450",
journal = "Chemistry of Materials",
issn = "0897-4756",
publisher = "American Chemical Society",
number = "15",

}

TY - JOUR

T1 - Segregated Chemistry and Structure on (001) and (100) Surfaces of (La1-xSrx)2CoO4 Override the Crystal Anisotropy in Oxygen Exchange Kinetics

AU - Chen, Yan

AU - Tellez Lozano, Helena

AU - Burriel, Mónica

AU - Yang, Fan

AU - Tsvetkov, Nikolai

AU - Cai, Zhuhua

AU - McComb, David W.

AU - Kilner, John A.

AU - Yildiz, Bilge

PY - 2015/8/11

Y1 - 2015/8/11

N2 - Attaining fast oxygen exchange kinetics on perovskite and related mixed ionic and electronic conducting oxides is critical for enabling their applications in electrochemical energy conversion systems. This study focuses on understanding the relationship between surface chemistry and the surface oxygen exchange kinetics on epitaxial films made of (La1-xSrx)2CoO4, a prototypical Ruddlesden-Popper structure that is considered as a promising cathode material for fuel cells. The effects of crystal orientation on the surface composition, morphology, oxygen diffusion, and surface exchange kinetics were assessed by combining complementary surface-sensitive analytical techniques, specifically low energy ion scattering, X-ray photoelectron spectroscopy, Auger electron spectroscopy, scanning transmission electron microscopy, atomic force microscopy, and secondary ion mass spectroscopy. The films were grown in two different crystallographic orientations, (001) and (100), and with two different Sr compositions, at x = 0.25 (LSC25) and 0.50 (LSC50), by using pulsed laser deposition. In the as-prepared state, a Sr enriched layer at the top surface and a Co enriched subsurface layer were found on films with both orientations. After annealing at elevated temperatures in oxygen, the Sr enrichment increased, followed by clustering into Sr-rich secondary phase particles. Both the LSC25 and LSC50 films showed anisotropic oxygen diffusion kinetics, with up to 20 times higher oxygen diffusion coefficient along the ab-plane compared that along the c-axis at 400-500 °C. However, no dependence of surface oxygen exchange coefficient was found on the crystal orientation. This result indicates that the strong Sr segregation at the surface overrides the effect of the structural anisotropy that was also expected for the surface exchange kinetics. The larger presence of Co cations exposed at the LSC25 surface compared to that at the LSC50 surface is likely the reason for the faster oxygen surface exchange kinetics on LSC25 compared to LSC50. This work demonstrated the critical role of surface chemistry on the oxygen exchange kinetics on perovskite related oxides, which are thus far underexplored at elevated temperatures, and provides a generalizable approach to probe the surface chemistry on other catalytic complex oxides. (Graph Presented).

AB - Attaining fast oxygen exchange kinetics on perovskite and related mixed ionic and electronic conducting oxides is critical for enabling their applications in electrochemical energy conversion systems. This study focuses on understanding the relationship between surface chemistry and the surface oxygen exchange kinetics on epitaxial films made of (La1-xSrx)2CoO4, a prototypical Ruddlesden-Popper structure that is considered as a promising cathode material for fuel cells. The effects of crystal orientation on the surface composition, morphology, oxygen diffusion, and surface exchange kinetics were assessed by combining complementary surface-sensitive analytical techniques, specifically low energy ion scattering, X-ray photoelectron spectroscopy, Auger electron spectroscopy, scanning transmission electron microscopy, atomic force microscopy, and secondary ion mass spectroscopy. The films were grown in two different crystallographic orientations, (001) and (100), and with two different Sr compositions, at x = 0.25 (LSC25) and 0.50 (LSC50), by using pulsed laser deposition. In the as-prepared state, a Sr enriched layer at the top surface and a Co enriched subsurface layer were found on films with both orientations. After annealing at elevated temperatures in oxygen, the Sr enrichment increased, followed by clustering into Sr-rich secondary phase particles. Both the LSC25 and LSC50 films showed anisotropic oxygen diffusion kinetics, with up to 20 times higher oxygen diffusion coefficient along the ab-plane compared that along the c-axis at 400-500 °C. However, no dependence of surface oxygen exchange coefficient was found on the crystal orientation. This result indicates that the strong Sr segregation at the surface overrides the effect of the structural anisotropy that was also expected for the surface exchange kinetics. The larger presence of Co cations exposed at the LSC25 surface compared to that at the LSC50 surface is likely the reason for the faster oxygen surface exchange kinetics on LSC25 compared to LSC50. This work demonstrated the critical role of surface chemistry on the oxygen exchange kinetics on perovskite related oxides, which are thus far underexplored at elevated temperatures, and provides a generalizable approach to probe the surface chemistry on other catalytic complex oxides. (Graph Presented).

UR - http://www.scopus.com/inward/record.url?scp=84938939843&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84938939843&partnerID=8YFLogxK

U2 - 10.1021/acs.chemmater.5b02292

DO - 10.1021/acs.chemmater.5b02292

M3 - Article

AN - SCOPUS:84938939843

VL - 27

SP - 5436

EP - 5450

JO - Chemistry of Materials

JF - Chemistry of Materials

SN - 0897-4756

IS - 15

ER -