Cation interdiffusion model for enhanced oxygen kinetics at oxide heterostructure interfaces

Gadre, Milind; Lee, Yueh‐Lin; Morgan, Dane

doi:10.1039/c2cp23033j

Cited by 62 publications

(68 citation statements)

References 33 publications

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“…were placed on only one side of the slab. To avoid the fictitious dipole moment, dipole corrections 33,34 were applied in computing all of the energies reported here. 43,44 O 2 adsorption calculations were performed for one molecule per surface unit cell, corresponding to a surface coverage of 25% with four equivalent adsorption sites.…”

Section: Ground-state Structures and Energiesmentioning

confidence: 99%

“…Very recently, Gadre et al, based on DFT calculations, proposed that the enhancement of interfacial ORR activity in this system could be caused by significant Sr interdiffusion from LSC 113 into LSC 214 . 34 The large extent of Sr enrichment in LSC 214 was expected to induce the formation of a large amount of oxygen vacancies and accelerate the oxygen incorporation kinetics. 34 While this is a reasonable hypothesis, in our ongoing experimental work 35 we do not find any evidence to a detectable amount of Sr segregation in LSC 214 near the LSC 113 /LSC 214 interface.…”

Section: Introductionmentioning

confidence: 99%

“…34 The large extent of Sr enrichment in LSC 214 was expected to induce the formation of a large amount of oxygen vacancies and accelerate the oxygen incorporation kinetics. 34 While this is a reasonable hypothesis, in our ongoing experimental work 35 we do not find any evidence to a detectable amount of Sr segregation in LSC 214 near the LSC 113 /LSC 214 interface. Furthermore, it is not clear how the increased amount of oxygen vacancies in LSC 214 is to enhance the ORR activity by several orders of magnitude since the interstitial path into LSC 214 and similar RP phase compounds is already very fast.…”

Section: Introductionmentioning

confidence: 99%

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Mechanism for enhanced oxygen reduction kinetics at the (La,Sr)CoO3−δ/(La,Sr)2CoO4+δ hetero-interface

Han

Yildiz

2012

Energy Environ. Sci.

114

118

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The recently reported fast oxygen reduction kinetics at the interface of (La,Sr)CoO 3-δ (LSC 113 ) and (La,Sr) 2 CoO 4+δ (LSC 214 ) phases opened up new questions for the potential role of dissimilar interfaces in advanced cathodes for solid oxide fuel cells (SOFCs). Using first-principles based calculations in the framework of density functional theory, we quantitatively probed the possible mechanisms that govern the oxygen reduction activity enhancement at this hetero-interface as a model system. Our findings show that both the strongly anisotropic oxygen incorporation kinetics on the LSC 214 and the lattice strain in the vicinity of the interface are important contributors to such enhancement. The LSC 214 (100) surface exposed to the ambient at the LSC 113 /LSC 214 interface facilitates oxygen incorporation because the oxygen molecules very favorably adsorb on it compared to the LSC 214 (001) and LSC 113 (001) surfaces, providing a large source term for oxygen incorporation. Lattice strain field present near the hetero-interface accelerates oxygen incorporation kinetics especially on LSC 113 (001). At 500 °C 4×10 2 times faster oxygen incorporation kinetics is predicted in the vicinity of the LSC 113 /LSC 214 heterointerface with 50% Sr-doped LSC 214 compared to that on the single phase LSC 113 (001) surface.Contributions from both the anisotropy and local strain effects are of comparable magnitude. The insights obtained in this work suggest that hetero-structures which have a large area of (100) surfaces and smaller thickness in [001] direction of the Ruddlesden-Popper phases, and larger tensile strain near the interface would be promising for high-performance cathodes.Keywords: solid oxide fuel cell, oxygen reduction reaction, cathode, anisotropy, strain, perovskite, Ruddlesden-Popper, (La,Sr)CoO 3 , (La,Sr) 2 CoO 4+δ , density functional theory * Corresponding author. Email: byildiz@mit.edu 2 Graphical AbstractAnisotropic oxygen incorporation on (La,Sr) 2 CoO 4+δ and the lattice strain near the (La,Sr)CoO 3-δ / (La,Sr) 2 CoO 4+δ interface serve as two possible sources to accelerate the oxygen reduction kinetics on the hetero-structure by 4×10 2 times at 500 °C. Broader contextHigh efficiency and fuel flexibility of Solid Oxide Fuel Cells (SOFCs) render them attractive as a sustainable energy conversion technology. There is growing interest in the design of dissimilar interfaces at the nano-scale to enable high-performance SOFC cathodes with fast oxygen reduction reaction (ORR) kinetics at lower temperatures than their traditional operation temperature of 800 °C. A motivating example for this purpose has been the hetero-structure made of the (La,Sr)CoO 3-δ and (La,Sr) 2 CoO 4+δ phases with highly active interfaces. Two previous experimental reports have observed 10 3 -10 4 times enhancement in ORR kinetics at 500-550 °C arising from the interface of these two phases. However, these empirical observationshave not yet reached a fundamental understanding of why these interfaces are so highly active...

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Section: Ground-state Structures and Energiesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Mechanism for enhanced oxygen reduction kinetics at the (La,Sr)CoO3−δ/(La,Sr)2CoO4+δ hetero-interface

Han

Yildiz

2012

Energy Environ. Sci.

114

118

View full text Add to dashboard Cite

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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 .…”

mentioning

confidence: 99%

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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Understanding and Controlling the Work Function of Perovskite Oxides Using Density Functional Theory

Jacobs

Booske

Morgan

2016

Adv Funct Materials

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141

116

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Perovskite oxides containing transition metals are promising materials in a wide range of electronic and electrochemical applications. However, neither their work function values nor an understanding of their work function physics have been established. Here, we predict the work function trends of a series of perovskite (ABO 3 formula) materials using Density Functional Theory, and show that the work functions of (001)-terminated AO-and BO 2 -oriented surfaces can be described using concepts of electronic band filling, bond hybridization, and surface dipoles. The calculated range of AO (BO 2 ) work functions are 1.60-3.57 eV (2.99-6.87 eV). We find an approximately linear correlation (R 2 between 0.77-0.86, depending on surface termination) between work function and position of the oxygen 2p band center, which correlation enables both understanding and rapid prediction of work function trends. Furthermore, we identify SrVO 3 as a stable, low work function, highly conductive material. Undoped (Ba-doped) SrVO 3 has an intrinsically low AO-terminated work function of 1.86 eV (1.07 eV). These properties make SrVO 3 a promising candidate material for a new electron emission cathode for application in high power microwave devices, and as a potential electron emissive material for thermionic energy conversion technologies.2

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Cation interdiffusion model for enhanced oxygen kinetics at oxide heterostructure interfaces

Cited by 62 publications

References 33 publications

Mechanism for enhanced oxygen reduction kinetics at the (La,Sr)CoO3−δ/(La,Sr)2CoO4+δ hetero-interface

Mechanism for enhanced oxygen reduction kinetics at the (La,Sr)CoO3−δ/(La,Sr)2CoO4+δ hetero-interface

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

Understanding and Controlling the Work Function of Perovskite Oxides Using Density Functional Theory

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