Understanding what controls the reaction rate of water oxidation on Iridium oxides

Caiwu Liang^a, Reshma Rao^a, Katrine Svane^c, Joseph Hadden^a, Benjamin Moss^b, Soren Scott^a, Jason Riley^a, Mary Ryan^a, Jan Rossmeisl^c, James Durrant^b, Ifan Stephens^a

^aImperial College London, Department of Materials, Royal School of Mines, London SW7 2AZ, UK

^bDepartment of Chemistry and Centre for Processable Electronics, Imperial College London, London, W12 0BZ, UK

^cDepartment of Chemistry, Center for High Entropy Alloy Catalysis, University of Copenhagen, Universitetsparken, 5, København, Denmark

Materials for Sustainable Development Conference (MATSUS)
Proceedings of MATSUS Fall 2023 Conference (MATSUSFall23)

#WATERCAT - Experiment and theory in the catalysis of water electrolysis and hydrogen fuel cells

Torremolinos, Spain, 2023 October 16th - 20th

Organizers: Serhiy Cherevko and Nejc Hodnik

Oral, Caiwu Liang, presentation 143
DOI: https://doi.org/10.29363/nanoge.matsus.2023.143
Publication date: 18th July 2023

Iridium oxide is the state-of-the-art electrocatalyst for water oxidation in polymer electrolyte membrane (PEM) electrolysers for green hydrogen production. Understanding what controls the reaction rate on such benchmark metal oxides is central to designing more active and stable electrocatalysts for water oxidation in PEM electrolysers.^[1]

In this talk, I will present our work on probing active sites and the intrinsic water oxidation rate on iridium-based catalysts using a combination of time-resolved operando optical spectroscopy, X-ray absorption spectroscopy (XAS), and electrochemical mass spectrometry (ECMS). This talk will focus on comparing two state-of-the-art iridium oxides structures- amorphous IrO_x versus crystalline rutile IrO₂. I will first discuss the intermediate states and catalytically active states on iridium oxides and show how we can use optical spectroscopy to identify and quantify these states . The nature of these states, including Ir oxidation state and surface absorbates on iridium sites, will be elucidated using a combination of XAS and Density Function Theory (DFT). The interaction between these states and its effect on controlling the free energy of elementary reaction steps in water oxidation will also be discussed. Finally, based on the resulting molecular level understanding, I will present a modified Sabatier volcano model to describe trends in OER activity that takes into account the effect of absorbate-absorbate interactions on binding energetics.

References:

[1] Caiwu, L, Reshma Rao, Karine Svane et al. Unravelling the effects of active site densities and energetics on the water oxidation activity of iridium oxides, 07 March 2023, PREPRINT (Version 1) available at Research Square [https://doi.org/10.21203/rs.3.rs-2605628/v1]

Acknowledgements:

The authors would like to acknowledge the funding support from Imperial College-Chinese Scholarship Council Studentship, which made this research possible.

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