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Gang Wan2 1 Dillon Fong2 John Freeland3 Zhenxing Feng4 Jin Suntivich5 Hua Zhou3

2, Argonne National Laboratory, Lemont, Illinois, United States
1, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai, Shanghai, China
3, Argonne National Laboratory, Lemont, Illinois, United States
4, Oregon State University, Corvallis, Oregon, United States
5, Cornell University, Ithaca, New York, United States

The design of efficient and stable oxide catalysts for the oxygen evolution reaction (OER) is crucial for the development of a number of electrochemical energy conversion devices, such as electrolyzers and metal−air batteries1-3. SrIrO3 has recently been reported to be highly active for the OER in acid2, where the active site was proposed to be IrOx, a structural oxide created from the dissolution of Sr2+ in SrIrO3. In an effort to better understand the nature of these active sites, we examine the structural evolution of model SrIrO3 films grown on DyScO3 (110) substrates using a combination of electrochemical measurements, synchrotron X-ray scattering, and X-ray spectroscopic studies, with an objective to identify how the Sr2+ dissolution activates the OER catalysts in acid. We find that SrIrO3 evolves into a new structure at the solid-liquid interface with a thickness of ~6 pseudo-cubic unit cells. A combination of X-ray spectroscopy and theoretical calculations show that these interfacial structure were formed from a coupled diffusional exchange of Sr2+ and lattice oxygen (O2-), resulting in a reconstructed Sr-Ir-O framework that protects the bulk oxide underneath from further dissolution. Our results illustrate the critical role of a coupled cation-anion exchange on the structural evolution of oxides, offering a new paradigm for achieving high activity and stability and providing a pathway toward future catalyst design for electrochemical energy devices.

References:
1. W. T. Hong, M. Risch, K. A. Stoerzinger, A. Grimaud, J. Suntivich, Y. Shao-Horn, Toward the rational design of non-precious transition metal oxides for oxygen electrocatalysis. En. Environ. Sci. 8 (2015) 1404-1427. DOI: 10.1039/c4ee03869j.
2. L. C. Seitz, C. F. Dickens, K. Nishio, Y. Hikita, J. Montoya, A. Doyle, C. Kirk, A. Vojvodic, H. Y. Hwang, J. K. Norskov, T. F. Jaramillo, A highly active and stable IrOx/SrIrO3 catalyst for the oxygen evolution reaction. Science 353 (2016), 1011-1014. DOI: 10.1126/science.aaf5050.
3. T. Binninger, R. Mohamed, K. Waltar, E. Fabbri, P. Levecque, R. Kotz, T. J. Schmidt, Thermodynamic explanation of the universal correlation between oxygen evolution activity and corrosion of oxide catalysts. Sci. Rep. 5, (2015) 12167-12174; DOI: 10.1038/srep12167.

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