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

Heterostructured oxides have shown unusual electrochemical properties including enhanced catalytic activity, ion transport, and stability. In particular, it has been shown recently that the activity of oxygen electrocatalysis on the Ruddlesden-Popper/perovskite (La1-ySry)2CoO4±δ/La1-xSrxCoO3-δ heterostructure is remarkably enhanced relative to the Ruddlesden-Popper and perovskite constituents. Here we report the first atomic-scale structure and composition of (La1-ySry)2CoO4±δ/La1-xSrxCoO3-δ grown on SrTiO3. We observe anomalous strontium segregation from the perovskite to the interface and the Ruddlesden-Popper phase using direct X-ray methods as well as with ab initio calculations. Such Sr segregation occurred during the film growth, and no significant changes were found upon subsequent annealing in O2. Our findings provide insights into the design of highly active catalysts for oxygen electrocatalysis.

[1]  Y. Shao-horn,et al.  Revealing the atomic structure and strontium distribution in nanometer-thick La0.8Sr0.2CoO3−δ grown on (001)-oriented SrTiO3 , 2014 .

[2]  Yang Shao-Horn,et al.  Double perovskites as a family of highly active catalysts for oxygen evolution in alkaline solution , 2013, Nature Communications.

[3]  Yan Chen,et al.  Electronic Activation of Cathode Superlattices at Elevated Temperatures – Source of Markedly Accelerated Oxygen Reduction Kinetics , 2013 .

[4]  Y. Shao-horn,et al.  In Situ Studies of the Temperature-Dependent Surface Structure and Chemistry of Single-Crystalline (001)-Oriented La0.8Sr0.2CoO3-δ Perovskite Thin Films. , 2013, The journal of physical chemistry letters.

[5]  R. Clarke,et al.  Morphology and growth of capped Ge/Si quantum dots , 2013, Journal of Nanoparticle Research.

[6]  Hua Zhou,et al.  Atomic-layer synthesis and imaging uncover broken inversion symmetry in La 2 − x Sr x CuO 4 films , 2013 .

[7]  Meilin Liu,et al.  Suppression of Sr surface segregation in La(1-x)Sr(x)Co(1-y)Fe(y)O(3-δ): a first principles study. , 2013, Physical chemistry chemical physics : PCCP.

[8]  Yan Chen,et al.  Impact of Sr segregation on the electronic structure and oxygen reduction activity of SrTi1−xFexO3 surfaces , 2012 .

[9]  Roy Clarke,et al.  The limits of ultrahigh-resolution x-ray mapping: estimating uncertainties in thin-film and interface structures determined by phase retrieval methods , 2012 .

[10]  M. Islam,et al.  Vacancy and interstitial oxide ion migration in heavily doped La2−xSrxCoO4±δ , 2012 .

[11]  B. Yildiz,et al.  Chemical Heterogeneities on La0.6Sr0.4CoO3−δ Thin Films—Correlations to Cathode Surface Activity and Stability , 2012 .

[12]  D. Morgan,et al.  Surface strontium enrichment on highly active perovskites for oxygen electrocatalysis in solid oxide fuel cells , 2012 .

[13]  D. Morgan,et al.  Cation interdiffusion model for enhanced oxygen kinetics at oxide heterostructure interfaces. , 2012, Physical chemistry chemical physics : PCCP.

[14]  D. Morgan,et al.  Ab initio and empirical defect modeling of LaMnO(3±δ) for solid oxide fuel cell cathodes. , 2012, Physical chemistry chemical physics : PCCP.

[15]  B. Yildiz,et al.  Chemical Heterogeneities on La 0 . 6 Sr 0 . 4 CoO 3-δ Thin Films-Correlations to Cathode Surface Activity and Stability , 2012 .

[16]  J. Goodenough,et al.  A Perovskite Oxide Optimized for Oxygen Evolution Catalysis from Molecular Orbital Principles , 2011, Science.

[17]  D. Morgan,et al.  Prediction of solid oxide fuel cell cathode activity with first-principles descriptors , 2011 .

[18]  Y. Shao-horn,et al.  Enhanced oxygen reduction activity on surface-decorated perovskite thin films for solid oxide fuel cells , 2011 .

[19]  Y. Orikasa,et al.  X-ray Absorption Spectroscopic Study on La0.6Sr0.4CoO3−δ Cathode Materials Related with Oxygen Vacancy Formation , 2011 .

[20]  J. Goodenough,et al.  Erratum: Design principles for oxygen-reduction activity on perovskite oxide catalysts for fuel cells and metal-air batteries (Nature Chemistry (2011) DOI:10.1038/nchem.1069) , 2011 .

[21]  A. Sum,et al.  Catalysis in solid oxide fuel cells. , 2011, Annual review of chemical and biomolecular engineering.

[22]  Juergen Fleig,et al.  Relationship between Cation Segregation and the Electrochemical Oxygen Reduction Kinetics of La0.6Sr0.4CoO3−δ Thin Film Electrodes , 2011 .

[23]  Juergen Fleig,et al.  Surface Cation Segregation and its Effect on the Oxygen Reduction Reaction on Mixed Conducting Electrodes Investigated by ToF-SIMS and ICP-OES , 2011 .

[24]  J. Maier,et al.  Surface Kinetics and Mechanism of Oxygen Incorporation Into Ba1 − x Sr x Co y Fe1 − y O3 − δ SOFC Microelectrodes , 2010 .

[25]  D. Leonard,et al.  Oxygen Reduction Kinetics Enhancement on a Heterostructured Oxide Surface for Solid Oxide Fuel Cells , 2010 .

[26]  Y. Orikasa,et al.  Catalytic activity enhancement for oxygen reduction on epitaxial perovskite thin films for solid-oxide fuel cells. , 2010, Angewandte Chemie.

[27]  C. H. Kim,et al.  Strontium-Doped Perovskites Rival Platinum Catalysts for Treating NOx in Simulated Diesel Exhaust. , 2010 .

[28]  Hua Zhou,et al.  Anomalous expansion of the copper-apical-oxygen distance in superconducting cuprate bilayers , 2009, Proceedings of the National Academy of Sciences.

[29]  Dane Morgan,et al.  Ab initio energetics of LaBO3(001) (B=Mn, Fe, Co, and Ni) for solid oxide fuel cell cathodes , 2009 .

[30]  Takashi Nakamura,et al.  Composite Cathode of Perovskite-Related Oxides, ( La , Sr ) CoO3 − δ ∕ ( La , Sr ) 2CoO4 − δ , for Solid Oxide Fuel Cells , 2009 .

[31]  N. Sakai,et al.  Enhancement of Oxygen Surface Exchange at the Hetero-interface of ( La , Sr ) CoO3 / ( La , Sr ) 2CoO4 with PLD-Layered Films , 2008 .

[32]  D. Schlom,et al.  Structural changes induced by metal electrode layers on ultrathin BaTiO 3 films , 2008 .

[33]  Harumi Yokokawa,et al.  Enhancement of oxygen exchange at the hetero interface of (La,Sr)CoO3/(La,Sr)2CoO4 in composite ceramics , 2008 .

[34]  S. Adler.  Factors governing oxygen reduction in solid oxide fuel cell cathodes. , 2004, Chemical reviews.

[35]  John B. Goodenough,et al.  Electronic and ionic transport properties and other physical aspects of perovskites , 2004 .

[36]  Roy Clarke,et al.  Direct determination of epitaxial interface structure in Gd2O3 passivation of GaAs , 2002, Nature materials.

[37]  Edward A. Stern,et al.  Direct atomic structure determination of epitaxially grown films:Gd2O3on GaAs(100) , 2002 .

[38]  J. Kilner,et al.  Oxygen transport in La1−xSrxMn1−yCoyO3±δ perovskites: Part II. Oxygen surface exchange , 1999 .

[39]  John A. Kilner,et al.  Optimisation of composite cathodes for intermediate temperature SOFC applications , 1999 .

[40]  C. Humphreys,et al.  Electron-energy-loss spectra and the structural stability of nickel oxide: An LSDA+U study , 1998 .

[41]  A. Lichtenstein,et al.  First-principles calculations of electronic structure and spectra of strongly correlated systems: the LDA+U method , 1997 .

[42]  Kresse,et al.  Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. , 1996, Physical review. B, Condensed matter.

[43]  H. Loye,et al.  Recent developments in perovskite-based oxide ion conductors , 1995 .

[44]  Blöchl,et al.  Projector augmented-wave method. , 1994, Physical review. B, Condensed matter.

[45]  A. Navrotsky,et al.  Energetics of La2-xSrxCoO4-y (0.5 < x < 1.5) , 1994 .

[46]  Hafner,et al.  Ab initio molecular dynamics for liquid metals. , 1995, Physical review. B, Condensed matter.

[47]  B. Steele,et al.  Oxygen transport in selected nonstoichiometric perovskite-structure oxides , 1992 .

[48]  Wang,et al.  Accurate and simple analytic representation of the electron-gas correlation energy. , 1992, Physical review. B, Condensed matter.

[49]  H. Tagawa,et al.  Nonstoichiometry of the perovskite-type oxides La1−xSrxCoO3−δ , 1989 .