Anomalous Interface and Surface Strontium Segregation in (La1–ySry)2CoO4±δ/La1–xSrxCoO3−δ Heterostructured Thin Films

Feng, Zhenxing; Yacoby, Y.; Gadre, Milind; Lee, Yueh‐Lin; Hong, Wonbin; Zhou, Hua; Biegalski, Michael D.; Christen, H. M.; Adler, Stuart B.; Morgan, Dane; Shao‐Horn, Yang

doi:10.1021/jz500293d

Cited by 76 publications

(25 citation statements)

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“…In light of the cataytic importance of surface oxygen vacancies, this transition could have a significant effect on the catalytic activity of the MIEC. Similar conclusions were drawn by Feng et al [37], who observed segregation of strontium to the strongly catalytically active interface between LSC and the Ruddlesden-Popper precipitate (La,Sr) 2 CoO 4 . Fig.…”

Section: Resultssupporting

confidence: 88%

A variational approach to surface cation segregation in mixed conducting perovskites

Mebane

2015

Computational Materials Science

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Section: Resultssupporting

confidence: 88%

A variational approach to surface cation segregation in mixed conducting perovskites

Mebane

2015

Computational Materials Science

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“…To overcome this, threedimensional reconstruction of oxide surface and sub-surface structures have been consistently demonstrated using Coherent Bragg Rod Analysis (COBRA) 262, 263 -a phase-retrieval method that combines information from multiple crystal truncation rods to determine the crystal structure near the surface. Such studies have been applied to understanding electrocatalysis in solid oxide fuel cell applications 232,264 and oxide electronics, 233,[265][266][267] and could greatly benefit the study of oxide surfaces for the ORR/OER in alkaline solutions. However, the low atomic number of oxygen results in weak scattering, making X-ray scattering techniques better suited for studying the catalyst surface structure rather than the adsorbate structure.…”

Section: In Situ Spectroscopic Approachesmentioning

confidence: 99%

Toward the rational design of non-precious transition metal oxides for oxygen electrocatalysis

Hong

Risch

Stoerzinger

et al. 2015

Energy Environ. Sci.

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REVIEWThis journal is © The Royal Society of Chemistry 2013 J. Name., 2013, 00, 1-3 | 1 In this Review, we discuss the state-of-the-art understanding of non-precious transition metal oxides that catalyze the oxygen reduction and evolution reactions. Understanding and mastering the kinetics of oxygen electrocatalysis is instrumental to making use of photosynthesis, advancing solar fuels, fuel cells, electrolyzers, and metal-air batteries. We first present key insights, assumptions and limitations of well-known activity descriptors and reaction mechanisms in the past four decades. The turnover frequency of crystalline oxides as promising catalysts is also put into perspective with amorphous oxides and photosystem II. Particular attention is paid to electronic structure parameters that can potentially govern the adsorbate binding strength and thus provide simple rationales and design principles to predict new catalyst chemistries with enhanced activity. We share new perspective synthesizing mechanism and electronic descriptors developed from both molecular orbital and solid state band structure principles. We conclude with an outlook on the opportunities in future research within this rapidly developing field. Broader ContextThe formation of chemical bonds is an energy dense mode of storing energy. In both nature and technology, the electrochemical generation and consumption of fuels is one of the most efficient routes for energy usage. Solar and electrical energy can be stored in chemical bonds by splitting water or metal oxides to produce hydrogen and metal. These compounds can then be oxidized to produce energy when coupled to the reduction of oxygen. However, these device efficiencies are severely limited by the catalysis of oxygen electrochemical processes -namely the oxygen reduction reaction and oxygen evolution reaction, which have slow kinetics. Non-precious transition metal oxides show promise as cost-effective substitutes for noble metals in commercially viable renewable energy storage and conversion devices. Furthermore, this class of materials has ben efitted from a wealth of spectroscopic and first-principles studies in the past few decades, providing the frameworks and theories needed to understand the electronic structure and design optimal catalysts. The incredibly diverse range of chemistries and physical properties that can be explored in oxide families afford numerous degrees of freedom for conducting systematic investigations relating intrinsic mat erial properties to catalytic performance. Here, we present background on the fundamental concepts in catalysis for the rational design of transition metal perovskite oxide catalysts for oxygen electrocatalysis and critically examine the current understanding a nd its impact on future directions of perovskite catalysts.

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“…[17,20,30] In the case of the LSC 214 decorated LSCF 113 , it has been proposed that low enhancement is observed because there is a negligible change of the surface Sr concentration at the heterostructured interface due to the initially high Sr surface concentration (∼100%) of the stable LSCF 113 (001) surface. This high Sr concentration cannot be easily increased.…”

Section: Functional Oxides Research Lettermentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…[13,19] Coherent Bragg rod analysis (COBRA) and density functional theory (DFT) have suggested that the enhanced oxygen surface exchange kinetics may be attributed to the Sr segregation at the LSC 214 -LSC 113 interface and the LSC 214 surface, resulting from a large driving force for A-site cation interdiffusion across the heterostructured interface. [14,15,20] In addition, the enhanced activity of LSC 113 may also be attributed to the stabilized LSC 113 surface by LSC 214 phase, which suppresses the formation of Sr-enriched secondary particles on the LSC 113 surface after a long-time annealing.[17] However, the heterostructured oxide interfaces formed by decorating LSC 214 on LSCF 113 perovskites have shown negligible enhancement (up to two times) of the oxygen surface exchange kinetics of LSCF 113 , [17] which can be attributed to no further [15,21] such an approach is inhibited by difficulties in the synthesis of RP phase with high Sr substitution. [22,23] In this study, we have developed the heterostructured oxide decoration on LSCF 113 , which leads to the enhancement of the surface activity of the LSCF 113 .…”

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Enhancement of oxygen surface exchange on epitaxial La0.6Sr0.4Co0.2Fe0.8O3-δ thin films using advanced heterostructured oxide interface engineering

Lee

Wang

et al. 2016

MRS Communications

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Engineering of a novel heterostructured oxide interface was used to enhance the oxygen surface exchange kinetics of La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3−δ (LSCF 113 ) thin films. A single-layer decoration of mixed (LaSr) 2 CoO 4±δ (LSC 214 ) and La 1−x Sr x CoO 3−δ (LSC 113 ) and a double-layer decoration of stacked LSC 214 and LSC 113 grown on the LSCF 113 markedly enhanced the surface exchange coefficients of the LSCF 113 by up to ∼1.5 orders of magnitude relative to the undecorated LSCF 113 . It is hypothesized that two different types of surface decorations can enable Sr segregation at the interface and surfaces of LSC 113 and LSC 214 , leading to enhancement of the oxygen surface exchange kinetics of decorated LSCF 113 .The development of highly active cathode materials is essential to lower the operating temperature of solid oxide fuel cells (SOFCs), where the slow kinetics of the oxygen surface exchange on the cathode surface limits the efficiency of SOFCs at intermediate temperatures (500-750°C). [1,2] Current cathode materials such as La 1−x Sr x MnO 3−δ (LSM 113 ) [3][4][5] with high electronic conductivity but low ionic conductivity [6] are inadequate for the usage in the intermediate temperature range due to insufficient surface activity.La 1−x Sr x Fe 1−y Co y O 3−δ (LSCF 113 ), which has beneficial materials properties such as high ionic and electronic conductivity, [7] and fast oxygen surface exchange, [8] therefore, has been developed as one of the most promising commercial cathode materials for intermediate temperature SOFCs. In particular, a solution infiltration process, in which a phase transition occurs from a liquid into a solid has been widely used to further enhance the surface activity of LSCF 113 . [9][10][11][12] Utilizing infiltrated LSM 113 coatings, it has been shown the enhanced electrocatalytic activity of LSCF 113 cathodes. [11,12] Infiltrated La 0.4875 Ca 0.0125 Ce 0.5 O 2−δ (LCC) [9] and Sm 0.5 Sr 0.5 CoO 3−δ (SSC) [10] coatings have also been used for better stability and activity of LSCF 113 electrodes. Although many studies have shown the enhanced cathodic performance of LSCF 113 by surface modification through a solution-based infiltration process, the origin responsible for the enhanced stability and activity of decorated LSCF 113 cathode is poorly understood.Ruddlesden-Popper (RP) phases (A 2 BO 4 ) have been utilized as a material for the La 1−x Sr x CoO 3−δ (LSC 113 ) surface modification, which results in the enhanced surface activity of LSC 113 significantly due to the formation of heterostructured oxide interfaces. [13][14][15][16][17][18] Using well-defined epitaxial thin film systems, remarkably enhanced oxygen surface exchange kinetics (up to ∼2 orders of magnitude) of LSC 113 has been reported by decorating (La 0.5 Sr 0.5 ) 2 CoO 4±δ (LSC 214 ) phase on the LSC 113 surface. [13,19] Coherent Bragg rod analysis (COBRA) and density functional theory (DFT) have suggested that the enhanced oxygen surface exchange kinetics may be attributed to the Sr segregation ...

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Anomalous Interface and Surface Strontium Segregation in (La_1–ySr_y)₂CoO_4±δ/La_1–xSr_xCoO_3−δ Heterostructured Thin Films

Cited by 76 publications

References 57 publications

A variational approach to surface cation segregation in mixed conducting perovskites

A variational approach to surface cation segregation in mixed conducting perovskites

Toward the rational design of non-precious transition metal oxides for oxygen electrocatalysis

Enhancement of oxygen surface exchange on epitaxial La0.6Sr0.4Co0.2Fe0.8O3-δ thin films using advanced heterostructured oxide interface engineering

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