Near-Ambient Pressure XPS of Higherature Surface Chemistry in Sr2Co2O5 Thin Films

Wesley T. Hong; Kelsey A. Stoerzinger; Ethan J. Crumlin; Eva Mutoro; Hyoungjeen Jeen; Ho Nyung Lee; Yang Shao-Horn

doi:10.1007/s11244-015-0532-4

Near-Ambient Pressure XPS of Higherature Surface Chemistry in Sr₂Co₂O₅ Thin Films

Wesley T. Hong, Kelsey A. Stoerzinger, Ethan J. Crumlin, Eva Mutoro, Hyoungjeen Jeen, Ho Nyung Lee, Yang Shao-Horn

Materials Science and Technology Div

Research output: Contribution to journal › Article › peer-review

33 Scopus citations

Abstract

Transition metal perovskite oxides are promising electrocatalysts for the oxygen reduction reaction (ORR) in fuel cells, but a lack of fundamental understanding of oxide surfaces impedes the rational design of novel catalysts with improved device efficiencies. In particular, understanding the surface chemistry of oxides is essential for controlling both catalytic activity and long-term stability. Thus, elucidating the physical nature of species on perovskite surfaces and their catalytic enhancement would generate new insights in developing oxide electrocatalysts. In this article, we perform near-ambient pressure XPS of model brownmillerite Sr₂Co₂O₅ (SCO) epitaxial thin films with different crystallographic orientations. Detailed analysis of the Co 2p spectra suggests that the films lose oxygen as a function of temperature. Moreover, deconvolution of the O 1s spectra shows distinct behavior for (114)-oriented SCO films compared to (001)-oriented SCO films, where an additional bulk oxygen species is observed. These findings indicate a change to a perovskite-like oxygen chemistry that occurs more easily in (114) SCO than (001) SCO, likely due to the orientation of oxygen vacancy channels out-of-plane with respect to the film surface. This difference in surface chemistry is responsible for the anisotropy of the oxygen surface exchange coefficient of SCO and may contribute to the enhanced ORR kinetics of La_0.8Sr_0.2CoO_3-δ thin films by SCO surface particles observed previously.

Original language	English
Pages (from-to)	574-582
Number of pages	9
Journal	Topics in Catalysis
Volume	59
Issue number	5-7
DOIs	https://doi.org/10.1007/s11244-015-0532-4
State	Published - Mar 1 2016

Funding

We give many thanks to Andrey Shavorskiy and Hendrik Bluhm for assistance with NAP-XPS measurements. This work was supported in part by the MRSEC Program of the National Science Foundation under award number DMR-0819762 and the Skoltech-MIT Center for Electrochemical Energy. The Advanced Light Source was supported by the Director, Office of Science, Office of Basic Energy Sciences of the U.S. Department of Energy under Contracts DE-AC02-06CH11357 and DE-AC02-05CH11231, respectively. The synthesis work at ORNL was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division. K.A.S. acknowledges support by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1122374.

Funders	Funder number
Skoltech-MIT Center for Electrochemical Energy
National Science Foundation	DMR-0819762
U.S. Department of Energy	DE-AC02-05CH11231, DE-AC02-06CH11357
Office of Science
Basic Energy Sciences
Division of Materials Sciences and Engineering	DGE-1122374

Keywords

Ambient pressure XPS
Electrocatalysis
Oxygen reduction
Solid oxide fuel cells
Strontium cobaltite

UN SDGs

This output contributes to the following UN Sustainable Development Goals (SDGs)

Access to Document

10.1007/s11244-015-0532-4

Cite this

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title = "Near-Ambient Pressure XPS of Higherature Surface Chemistry in Sr2Co2O5 Thin Films",

abstract = "Transition metal perovskite oxides are promising electrocatalysts for the oxygen reduction reaction (ORR) in fuel cells, but a lack of fundamental understanding of oxide surfaces impedes the rational design of novel catalysts with improved device efficiencies. In particular, understanding the surface chemistry of oxides is essential for controlling both catalytic activity and long-term stability. Thus, elucidating the physical nature of species on perovskite surfaces and their catalytic enhancement would generate new insights in developing oxide electrocatalysts. In this article, we perform near-ambient pressure XPS of model brownmillerite Sr2Co2O5 (SCO) epitaxial thin films with different crystallographic orientations. Detailed analysis of the Co 2p spectra suggests that the films lose oxygen as a function of temperature. Moreover, deconvolution of the O 1s spectra shows distinct behavior for (114)-oriented SCO films compared to (001)-oriented SCO films, where an additional bulk oxygen species is observed. These findings indicate a change to a perovskite-like oxygen chemistry that occurs more easily in (114) SCO than (001) SCO, likely due to the orientation of oxygen vacancy channels out-of-plane with respect to the film surface. This difference in surface chemistry is responsible for the anisotropy of the oxygen surface exchange coefficient of SCO and may contribute to the enhanced ORR kinetics of La0.8Sr0.2CoO3-δ thin films by SCO surface particles observed previously.",

keywords = "Ambient pressure XPS, Electrocatalysis, Oxygen reduction, Solid oxide fuel cells, Strontium cobaltite",

author = "Hong, {Wesley T.} and Stoerzinger, {Kelsey A.} and Crumlin, {Ethan J.} and Eva Mutoro and Hyoungjeen Jeen and Lee, {Ho Nyung} and Yang Shao-Horn",

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