Structure-performance relationships of Ir-Ru electrodes for oxygen evolution during dynamic operation

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This project deals with the structure-performance relationships of Ir-Ru electrodes for oxygen evolution reaction during dynamic operation of proton exchange membrane water electrolysers. Whereas electrolyzers are key enablers for efficient storage of renewables within the "Energiewende", oxygen evolution is one of the most challenging and complex reactions hindering wide-spread application of this technology. The complexity grows even larger as the intermittent nature of renewable energy requires dynamic operation. For this purpose a fundamental understanding of the processes at the catalyst during dynamic oxygen evolution is required. Whereas state-of-the-art catalysts are based on pure Ir, Ir-Ru anodes show superior performance but lower stability, including changes in oxidation state, surface/bulk structure, morphology and even dissolution. The complex interaction of catalyst structure and electrochemical activity is not understood yet, but of utmost importance for enabling high performance, durable and low cost electrolyzers. The main objective of this proposal is to gain insight into the structure-performance relationships of Ir-Ru anodes for oxygen evolution during dynamic operation. Special focus is on changes of the catalyst composition and oxidation state and their effect on reaction kinetics, and as such on catalyst activity and durability. We will elucidate, how the structure and performance changes upon full load, partial load and dynamic operation and what limits the feasible operating range. To achieve these objectives, we will develop a methodology which interlinks in situ/operando spectroscopic and spectrometric methods, which characterize catalyst state and structure, with advanced electrochemical methods and kinetic modeling techniques, which analyze and predict performance for given catalyst states. This interdisciplinary approach includes new cells for operando X-ray spectroscopy to unravel the structure during dynamic operation and on-line inductively coupled plasma mass spectrometry and electrochemical spectroscopy setups for prescreening Ir:Ru compositions and in-depth mechanistic analysis. Results from operando spectroscopy and electrochemical characterization are combined with kinetic models that describe changes in reaction kinetics and catalyst structure and their interaction as a function of (dynamic) operating conditions. Experimentally validated kinetic models give insight into the processes at the catalyst and aid in interpreting measurements. In essence, this combination of experimental and theoretical efforts allows not only for a deeper understanding of structure-performance relationships of electrocatalysts, here exemplarily for oxygen evolution, but also for prediction of performance during dynamic operation and identification of favorable operating regimes. Moreover, the gained understanding of catalyst dynamics during oxygen evolution will pave the way for new catalysts.