Abstract
Segregation and phase separation of aliovalent dopants on perovskite oxide (ABO3) surfaces are detrimental to the performance of energy conversion systems such as solid oxide fuel/electrolysis cells and catalysts for thermochemical H2O and CO2 splitting. One key reason behind the instability of perovskite oxide surfaces is the electrostatic attraction of the negatively charged A-site dopants (for example, ) by the positively charged oxygen vacancies () enriched at the surface. Here we show that reducing the surface concentration improves the oxygen surface exchange kinetics and stability significantly, albeit contrary to the well-established understanding that surface oxygen vacancies facilitate reactions with O2 molecules. We take La0.8Sr0.2CoO3 (LSC) as a model perovskite oxide, and modify its surface with additive cations that are more and less reducible than Co on the B-site of LSC. By using ambient-pressure X-ray absorption and photoelectron spectroscopy, we proved that the dominant role of the less reducible cations is to suppress the enrichment and phase separation of Sr while reducing the concentration of and making the LSC more oxidized at its surface. Consequently, we found that these less reducible cations significantly improve stability, with up to 30 times faster oxygen exchange kinetics after 54 h in air at 530 °C achieved by Hf addition onto LSC. Finally, the results revealed a ‘volcano’ relation between the oxygen exchange kinetics and the oxygen vacancy formation enthalpy of the binary oxides of the additive cations. This volcano relation highlights the existence of an optimum surface oxygen vacancy concentration that balances the gain in oxygen exchange kinetics and the chemical stability loss.
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Neagu, D., Tsekouras, G., Miller, D. N., Ménard, H. & Irvine, J. T. S. In situ growth of nanoparticles through control of non-stoichiometry. Nature Chem. 5, 916–923 (2013).
Lee, K. T. & Wachsman, E. D. Role of nanostructures on SOFC performance at reduced temperatures. MRS Bull. 39, 783–791 (2014).
Bork, A. H., Kubicek, M., Struzik, M. & Rupp, J. L. M. Perovskite La0.6Sr0.4Cr1−xCoxO3−δ solid solutions for solar-thermochemical fuel production: strategies to lower the operation temperature. J. Mater. Chem. A 3, 15546–15557 (2015).
Hisatomi, T., Kubota, J. & Domen, K. Recent advances in semiconductors for photocatalytic and photoelectrochemical water splitting. Chem. Soc. Rev. 43, 7520–7535 (2014).
Hayd, J., Yokokawa, H. & Ivers-Tiffée, E. Hetero-interfaces at nanoscaled (La, Sr)CoO3−δ thin-film cathodes enhancing oxygen surface-exchange properties. J. Electrochem. Soc. 160, F351–F359 (2013).
Carter, S. et al. Oxygen transport in selected nonstoichiometric perovskite-structure oxides. Solid State Ion. 53, 597–605 (1992).
Shao, Z. & Haile, S. M. A high-performance cathode for the next generation of solid-oxide fuel cells. Nature 431, 170–173 (2004).
Cai, Z., Kubicek, M., Fleig, J. & Yildiz, B. Chemical heterogeneities on La0.6Sr0.4CoO3−δ thin films—correlations to cathode surface activity and stability. Chem. Mater. 24, 1116–1127 (2012).
Hjalmarsson, P., Søgaard, M. & Mogensen, M. Electrochemical performance and degradation of (La0.6Sr0.4)0.99CoO3−δ as porous SOFC-cathode. Solid State Ion. 179, 1422–1426 (2008).
Kubicek, M., Limbeck, A., Frömling, T., Hutter, H. & Fleig, J. Relationship between cation segregation and the electrochemical oxygen reduction kinetics of La0.6Sr0.4CoO3−δ thin film electrodes. J. Electrochem. Soc. 158, B727–B734 (2011).
Lee, W., Han, J. W., Chen, Y., Cai, Z. & Yildiz, B. Cation size mismatch and charge interactions drive dopant segregation at the surfaces of manganite perovskites. J. Am. Chem. Soc. 135, 7909–7925 (2013).
Yi, J. & Schroeder, M. High temperature degradation of Ba0.5Sr0.5Co0.8Fe0.2O3−δ membranes in atmospheres containing concentrated carbon dioxide. J. Membr. Sci. 378, 163–170 (2011).
Zhu, X. et al. Development of La0.6Sr0.4Co0.2Fe0.8O3−δ cathode with an improved stability via La0.8Sr0.2MnO3−δ film impregnation. Int. J. Hydrog. Energy 38, 5375–5382 (2013).
Chen, Y. et al. Segregated chemistry and structure on (001) and (100) surfaces of (La1−xSrx)2CoO4 override the crystal anisotropy in oxygen exchange kinetics. Chem. Mater. 27, 5436–5450 (2015).
Druce, J. et al. Surface termination and subsurface restructuring of perovskite-based solid oxide electrode materials. Energy Environ. Sci. 7, 3593–3599 (2014).
Dulli, H., Dowben, P. A., Liou, S. H. & Plummer, E. W. Surface segregation and restructuring of colossal-magnetoresistant manganese perovskites La0.65Sr0.35MnO3 . Phys. Rev. B 62, R14629–R14632 (2000).
Tellez, H., Druce, J., Kilner, J. A. & Ishihara, T. Relating surface chemistry and oxygen surface exchange in LnBaCo2O5+δ air electrodes. Faraday Discuss. 182, 145–157 (2015).
Chen, Y. et al. Impact of Sr segregation on the electronic structure and oxygen reduction activity of SrTi1−xFexO3 surfaces. Energy Environ. Sci. 5, 7979–7988 (2012).
Gong, Y. et al. Stabilizing nanostructured solid oxide fuel cell cathode with atomic layer deposition. Nano Lett. 13, 4340–4345 (2013).
Lee, D. et al. Enhanced oxygen surface exchange kinetics and stability on epitaxial La0.8Sr0.2CoO3−δ thin films by La0.8Sr0.2MnO3−δ decoration. J. Phys. Chem. C 118, 14326–14334 (2014).
Kuklja, M. M., Kotomin, E. A., Merkle, R., Mastrikov, Y. A. & Maier, J. Combined theoretical and experimental analysis of processes determining cathode performance in solid oxide fuel cells. Phys. Chem. Chem. Phys. 15, 5443–5471 (2013).
Bikondoa, O. et al. Direct visualization of defect-mediated dissociation of water on TiO2(110). Nature Mater. 5, 189–192 (2006).
Diebold, U. The surface science of titanium dioxide. Surf. Sci. Rep. 48, 53–229 (2003).
Schaub, R. et al. Oxygen vacancies as active sites for water dissociation on rutile TiO2 . Phys. Rev. Lett. 87, 266104 (2001).
Ganduglia-Pirovano, M. V., Hofmann, A. & Sauer, J. Oxygen vacancies in transition metal and rare earth oxides: current state of understanding and remaining challenges. Surf. Sci. Rep. 62, 219–270 (2007).
Carrasco, J., Lopez, N. & Illas, F. First principles analysis of the stability and diffusion of oxygen vacancies in metal oxides. Phys. Rev. Lett. 93, 225502 (2004).
Janotti, A. et al. Hybrid functional studies of the oxygen vacancy in TiO2 . Phys. Rev. B 81, 085212 (2010).
Kofstad, P. & Anderson, P. B. Gravimetric studies of the defect structure of α-Nb2O5 . J. Phys. Chem. Solids 21, 280–286 (1961).
Zheng, J. X., Ceder, G., Maxisch, T., Chim, W. K. & Choi, W. K. First-principles study of native point defects in hafnia and zirconia. Phys. Rev. B 75, 104112 (2007).
Mizusaki, J., Mima, Y., Yamauchi, S., Fueki, K. & Tagawa, H. Nonstoichiometry of the perovskite-type oxides La1−xSrxCoO3−δ . J. Solid State Chem. 80, 102–111 (1989).
Sommeling, P. M. et al. Influence of a TiCl4 post-treatment on nanocrystalline TiO2 films in dye-sensitized solar cells. J. Phys. Chem. B 110, 19191–19197 (2006).
Tsvetkov, N. A., Larina, L. L., Shevaleevskiy, O., Al-Ammar, E. A. & Ahn, B. T. Design of conduction band structure of TiO2 electrode using Nb doping for highly efficient dye-sensitized solar cells. Prog. Photovolt. Res. Appl. 20, 904–911 (2012).
Salmeron, M. & Schlögl, R. Ambient pressure photoelectron spectroscopy: a new tool for surface science and nanotechnology. Surf. Sci. Rep. 63, 169–199 (2008).
Feng, Z. A., El Gabaly, F., Ye, X., Shen, Z.-X. & Chueh, W. C. Fast vacancy-mediated oxygen ion incorporation across the ceria–gas electrochemical interface. Nature Commun. 5, 4374 (2014).
Grass, M. E. et al. New ambient pressure photoemission endstation at Advanced Light Source Beamline 9.3.2. Rev. Sci. Instrum. 81, 053106 (2010).
Mueller, D. N., Machala, M. L., Bluhm, H. & Chueh, W. C. Redox activity of surface oxygen anions in oxygen-deficient perovskite oxides during electrochemical reactions. Nature Commun. 6, 6097 (2015).
Crumlin, E. J. et al. Surface strontium enrichment on highly active perovskites for oxygen electrocatalysis in solid oxide fuel cells. Energy Environ. Sci. 5, 6081–6088 (2012).
Hu, Z. et al. Difference in spin state and covalence between La1−xSrxCoO3 and La2−xSrxLi0.5Co0.5O4 . J. Alloys Compd. 343, 5–13 (2002).
Mizokawa, T. et al. Photoemission and X-ray-absorption study of misfit-layered (Bi, Pb)-Sr-Co-O compounds: electronic structure of a hole-doped Co-O triangular lattice. Phys. Rev. B 64, 115104 (2001).
Moodenbaugh, A. et al. Hole-state density of La1−xSrxCoO3−δ (0 ∼ x ∼ 0.5) across the insulator/metal phase boundary. Phys. Rev. B 61, 5666–5671 (2000).
Thomas, A. G. et al. Comparison of the electronic structure of anatase and rutile TiO2 single-crystal surfaces using resonant photoemission and X-ray absorption spectroscopy. Phys. Rev. B 75, 035105 (2007).
van der Laan, G. Polaronic satellites in X-ray-absorption spectra. Phys. Rev. B 41, 12366–12368 (1990).
Abbate, M. et al. Electronic structure and spin-state transition of LaCoO3 . Phys. Rev. B 47, 16124–16130 (1993).
Copie, O. et al. Structural and magnetic properties of Co-doped (La, Sr)TiO3 epitaxial thin films probed using X-ray magnetic circular dichroism. J. Phys. Condens. Matter. 21, 406001 (2009).
Fabricius, G. et al. Electronic structure of cubic SrHfO3: ferroelectric stability and detailed comparison with SrTiO3 . Phys. Rev. B 55, 164–168 (1997).
Lee, J. et al. Imprint and oxygen deficiency in (Pb, La)(Zr, Ti)O3 thin film capacitors with La-Sr-Co-O electrodes. Appl. Phys. Lett. 66, 1337–1339 (1995).
Momma, K. & Izumi, F. VESTA 3 for three-dimensional visualization of crystal, volumetric and morphology data. J. Appl. Crystallogr. 44, 1272–1276 (2011).
Adler, S. B. Factors governing oxygen reduction in solid oxide fuel cell cathodes. Chem. Rev. 104, 4791–4844 (2004).
Jamnik, J. & Maier, J. Generalised equivalent circuits for mass and charge transport: chemical capacitance and its implications. Phys. Chem. Chem. Phys. 3, 1668–1678 (2001).
Baumann, F. S., Fleig, J., Habermeier, H.-U. & Maier, J. Impedance spectroscopic study on well-defined (La, Sr)(Co, Fe)O3−δ model electrodes. Solid State Ion. 177, 1071–1081 (2006).
Ravel, B. & Newville, M. ATHENA, ARTEMIS, HEPHAESTUS: data analysis for X-ray absorption spectroscopy using IFEFFIT. J. Synchrotron Radiat. 12, 537–541 (2005).
Acknowledgements
The authors are grateful for funding support from the NSF CAREER Award of the National Science Foundation, Division of Materials Research, Ceramics Program, Grant No. 1055583, and from the National Aeronautics and Space Administration (NASA) in support of the Mars Oxygen ISRU Experiment (MOXIE), an instrument on the Mars 2020 rover mission. We thank M. Youssef for useful discussions on the defects in LSC and Q. Liu for experiment assistance at Advanced Light Source Beamline 9.3.2. The authors also acknowledge the use of the Center for Materials Science and Engineering, an MRSEC Shared Experimental Facility of the NSF at MIT, supported by the NSF under award number DMR-1419807. The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under Contract No. DE-AC02-05CH11231.
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N.T. and Q.L. prepared the samples. N.T. performed electrochemical measurements. Q.L., N.T., B.Y. and E.J.C. performed XPS and XAS measurements. All authors analysed and discussed the results and wrote the paper. B.Y. designed and supervised the research.
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Tsvetkov, N., Lu, Q., Sun, L. et al. Improved chemical and electrochemical stability of perovskite oxides with less reducible cations at the surface. Nature Mater 15, 1010–1016 (2016). https://doi.org/10.1038/nmat4659
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DOI: https://doi.org/10.1038/nmat4659
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