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

Burke Stevens, M., Stanford University
Lee, K., Stanford University
Wette, M., Stanford University
Boubnov, A., Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory
Hikita, Y., Stanford University
Mehta, A., SLAC National Accelerator Laboratory
Bare, S. R., Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory
Higgins, D., Stanford University
Jaramillo, T. F., Stanford University
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 IrOx and RuOx 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.

  1. C. C. L. McCrory, S. Jung, I. M. Ferrer, S. M. Chatman, J. C. Peters, and T. F. Jaramillo: Benchmarking Hydrogen Evolving Reaction and Oxygen Evolving Reaction Electrocatalysts for Solar Water Splitting Devices. J. Am. Chem. Soc. 137(13), 4347 (2015).
  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).