(617ga) A Highly Active and Stable IrOx/SrIrO3 Catalyst for the Oxygen Evolution Reaction

Electrochemical water oxidation plays a key role in processes such as water splitting and CO₂ reduction which are highly studied for conversion of renewable energy sources into fuels and chemicals. However, water oxidation catalysts suffer from slow kinetics, and previously reported catalysts are limited to >330 mV overpotential to reach 10 mA/cm²_oxide of intrinsic activity when normalized to actual catalyst surface area.^{1, 2} Furthermore, there exists a significant need to develop water oxidation catalysts that operate in acidic electrolyte as there are only a few current candidates.

We present investigation of a novel water oxidation catalyst, IrO_x/SrIrO₃, which has demonstrated remarkable activity and stability in acidic electrolyte.³ Thin, crystalline films of SrIrO₃ are deposited using pulsed laser deposition and the active catalyst is formed via Sr leaching from surface layers. This leaching process leaves behind IrO_x layers which significantly outperform rutile IrO₂ and RuO₂, the only other OER catalysts to have reasonable stability and activity in acidic electrolyte. XPS and inductively coupled plasma results indicate leaching of Sr from the material surface during initial electrochemical testing in acidic electrolyte, which likely contribute to material restructuring at the surface and result in the activity increase observed over the first 2 hours of electrochemical testing. Additionally, the low surface roughness of these films allows activity normalization to the catalyst surface area (measured using atomic force microscopy) and reveals only 270 â?? 290 mV overpotential to reach 10 mA/cm²_{oxide_AFM} during extended testing. Lastly, density functional theory calculations reveal possible surface structures that could be formed during Sr leaching, and suggest the formation of highly active surface layers with IrO₃ or anatase IrO₂ motifs.

1. C. C. L. McCrory, S. Jung, I. M. Ferrer, S. M. Chatman, J. C. Peters and T. F. Jaramillo, JACS, 2015, 137, 4347-4357.

2. M. S. Burke, L. J. Enman, A. S. Batchellor, S. Zou and S. W. Boettcher, Chemistry of Materials, 2015, 27, 7549-7558.

3. 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, In review., 2016.