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Kyuho Lee1 2 Motoki Osada2 3 Harold Hwang2 4 Yasuyuki Hikita4

1, Stanford University, Stanford, California, United States
2, Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California, United States
3, Stanford University, Stanford, California, United States
4, Stanford Institute for Energy & Materials Sciences, SLAC National Accelerator Laboratory, Menlo Park, California, United States

Conversion of electrical energy into hydrogen gas via water electrolysis is a strong candidate as an efficient and environmentally-friendly energy storage mechanism for the compensation of the intermittent nature of leading renewable energy sources, such as solar and wind [1,2]. The key to improving the overall efficiency of water electrolysis lies in the development of high-performance catalysts for the oxygen evolution reaction (OER), the rate-limiting half-reaction of water electrolysis [2]. In particular, OER catalysts with high stability in acid are desired due to their compatibility with polymer electrolyte membrane (PEM) electrolyzers, which are more advantageous than the conventional electrolyzers in base due to operability at higher current density and lower gas crossover rate [3]. However, only a handful of materials, such as RuO2 and IrO2, are stable under acidic and strongly oxidizing potential conditions [2-4]. A recent breakthrough in OER catalysts is the development of SrIrO3 epitaxial films, currently the most active OER catalyst stable in acid [5]. Interestingly, this catalyst shows enhancement in catalytic activity over operating time via loss of Sr transforming into IrOx/SrIrO3, the mechanism behind which is yet to be understood. This strongly motivates the study of the relationship between catalytic activity and the structural variables of the initially synthesized films.
We synthesized SrIrO3 epitaxial films on SrTiO3 (001) substrates under various growth conditions using pulsed layer deposition [6]. We thoroughly characterized their structural properties and compared with their OER catalytic performance in acid. Surprisingly, we discovered that the catalytic activity is enhanced linearly with the film in-plane resistivity, surface cation stoichiometry, and film mosaicity. The detailed trend and the relationship between these variables will be discussed in the presentation. The identification of strong correlations between structural variables and catalytic activity not only provides guidelines to controllably synthesize catalysts and reveals deeper insight to the development of SrIrO3 catalyst, but also presents an effective approach to enhance catalytic activity of other electrocatalysts in general.

[1] Turner, J. A., Science 305, 972 (2004).
[2] Fabbri, E., et al., Catal. Sci. Technol. 4, 3800 (2014).
[3] Carmo, M., et al., Int. J. Hydrog. Energy 38, 4901 (2013).
[4] McCrory, C. C., et al. J. Am. Chem. Soc. 135, 16977 (2013).
[5] Seitz, L., et al., Science 353, 1011 (2016).
[6] Nishio, K., et al., APL Mater. 4, 036102 (2016).

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