(766f) Surface Characterization of IrOx/SrIrO3 Water-Splitting Catalysts

Electrochemical water-splitting is an important process that uses electrical energy to split water into hydrogen and oxygen, providing a storable form of chemical fuel. Catalysts are required to facilitate this electrochemical reaction efficiently. In contrast to basic electrolytes, which have many effective catalytic materials, in acidic environment, only IrO_x and RuO_x have reasonable catalytic properties¹. Recent work has shown that SrIrO₃ thin film catalysts show even higher activity and stability in acidic electrolytes and undergo strontium leaching, leading to a more active, iridium-rich phase². Further studies indicate that the activity can be tuned by changing the bulk structure of the as-prepared thin film³. This activity difference is due in part to surface area changes as well as intrinsic activity differences in the surface phase. Density functional theory calculations have predicted that the SrIrO₃ bulk can stabilize active iridium oxide overlayer structures, but it is difficult to observe these phases via standard materials characterization techniques². Specifically, the exact composition, thickness, distribution, and structure of this hypothesized active layer are yet unknown.

In this work, we use advanced materials and surface characterization to measure changes in material surface of these previously reported SrIrO₃ thin films during catalytic operation, probing properties including crystallographic structure, chemical state, and atomic composition. We utilize techniques such as time of flight-secondary ion mass spectrometry (TOF-SIMS), helium ion microscope-secondary ion mass spectrometry (HIM-SIMS), grazing incidence X-ray diffraction (GI-XRD), and grazing incidence X-ray absorption spectroscopy (GI-XAS) on pre-test and post-test catalyst films to quantify changes that occur during catalytic operation. Ultimately we aim to learn more about the nature of the electrochemically active site and translate this structural information to be able to design better OER catalysts.

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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, and T. F. Jaramillo: A highly active and stable IrOx/SrIrO3 catalyst for the oxygen evolution reaction. Science 353(6303), 1011 (2016).
3. K. Lee, M. Osada, H. Y. Hwang, and Y. Hikita: Oxygen Evolution Reaction Activity in IrOx /SrIrO3 Catalysts: Correlations between Structural Parameters and the Catalytic Activity. J. Phys. Chem. Lett. 10, 1516 (2019).