(465i) Exploring Possible Active Sites for IrOx/SrIrO3, a Highly Active Oxygen Evolution Catalyst

The Oxygen Evolution Reaction (OER) plays a key role in the renewable production of fuels and chemicals and is a source of inefficiency due to its sluggish kinetics. In addition to possessing high activity, OER catalysts must be stable for thousands of hours under operation. This is particularly challenging at the acidic conditions present in proton-exchange membrane electrolyzers. Currently, only Ir-based catalysts are practically stable for these applications,¹ and improving the intrinsic activity of these catalysts provides a pathway to decreasing Ir usage. We have discovered a novel catalyst that forms in-situ as Sr leaches from SrIrO₃ surface layers, leaving behind a remarkably active and acid-stable IrO_x film with multiple orders of magnitude improvement over rutile IrO₂ and RuO₂.²

Herein, we use Density Functional Theory calculations to propose an explanation of the exceptional observed OER activity. We find the nominally prepared SrIrO₃ perovskite to be thermodynamically unstable relative to aqueous Sr²⁺ and propose possible Sr-deficient overlayer structures that may form with electrochemical testing. Through a combination of lattice matching and ab initio molecular dynamics, we arrive at anatase IrO₂ and IrO_3 overlayers that possess active sites at the peak of the theoretical activity volcano.

¹C. C. L. McCrory, S. Jung, J. C. Peters, T. F. Jaramillo (2013). Benchmarking Heterogeneous Electrocatalysts for the Oxygen Evolution Reaction. Journal of the American Chemical Society, 135(45), 16977â??16987. http://doi.org/10.1021/ja407115p

²L. 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 (2016). A Highly Active and Stable SrIrO3/IrOx Catalyst for the Oxygen Evolution Reaction. In Review.