Unifying Water Oxidation Chemistry of Iridium Oxide from Aqueous Model Systems to Proton Exchange Membrane Electrolysers
10 affiliations
- 1Department of Materials, Imperial College London, Exhibition Road, London, United Kingdom, SW7 2AZ
- 2Department of Chemistry
- 3University of Oxford
- 4Blounts Court
- 5Electrochemical Innovation Lab, Department of Chemical Engineering
- 6University College London
- 7Department of Interface Science, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4–6, Berlin, Germany, 14195
- 8Chemical Energy Division, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Albert-Einstein-Straße 15, Berlin, Germany, 12489
- 9Harwell Science and Innovation Campus
- 10Department of Chemistry, University College London, Torrington Place, London, United Kingdom, WC1E 7JE
Abstract
Understanding how water-oxidation electrocatalysts operate under device-relevant conditions is essential for the design of advanced proton-exchange-membrane (PEM) water electrolysers. Although substantial progress has recently been made in elucidating the oxygen-evolution chemistry of iridium oxide in aqueous model systems, how these molecular insights translate to practical membrane–electrode assemblies (MEA) remains unclear. Here, we bridge this gap by combining operando hard and soft X-ray absorption spectroscopy with time-resolved optical spectroscopy to probe the intrinsic water oxidation chemistry of identical IrOx catalysts across three-electrode, catalyst–ionomer, and MEA configurations. We show that Nafion™ ionomers do not alter the intrinsic metal- and oxygen-centred redox transitions or the formation of electrophilic oxygen species that drives O–O bond formation. Instead, the ionomer content primarily affects mass transport through oxygen trapping and microbubble accumulation, which can obscure operando spectroscopic signatures. Operando Ir L3-edge XAS reveals higher average Ir oxidation states in MEA than in aqueous electrodes despite identical initial states, which is explained by higher catalyst utilisation in the MEA catalyst layers, even at substantially higher mass loading. Open-circuit decay measurements further reveal similar rapid and slow discharge regimes in both systems, demonstrating that IrOx remains in high oxidation states for hours in the absence of hydrogen crossover. These findings establish unified redox transitions and active species in aqueous and MEA environments, while identifying catalyst utilisation and transport effects as the dominant origins of MEA–aqueous discrepancies, thereby providing a general framework for translating molecular insights from model systems to device-relevant conditions.
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BibTeX
@misc{liang2026unifying,
title = {{Unifying Water Oxidation Chemistry of Iridium Oxide from Aqueous Model Systems to Proton Exchange Membrane Electrolysers}},
author = {Caiwu Liang and James Murawski and Cindy Tseng and Yue Wen and Yemin Tao and Chris Zalitis and Colleen Jackson and Guangmeimei Yang and Timon Wagner and Thomas Götsch and Veronica Celorrio and Sid Halder and Yifeng Wang and Jiaze Sun and Benjamin Moss and Arno Bergmann and Beatriz Roldan Cuenya and James R. Durrant and Ifan E.L. Stephens and Rhodri Jervis and Reshma R Rao},
howpublished = {ChemRxiv},
year = {2026},
month = sep,
doi = {10.26434/chemrxiv.15008370/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15008370/v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Unifying Water Oxidation Chemistry of Iridium Oxide from Aqueous Model Systems to Proton Exchange Membrane Electrolysers
AU - Caiwu Liang
AU - James Murawski
AU - Cindy Tseng
AU - Yue Wen
AU - Yemin Tao
AU - Chris Zalitis
AU - Colleen Jackson
AU - Guangmeimei Yang
AU - Timon Wagner
AU - Thomas Götsch
AU - Veronica Celorrio
AU - Sid Halder
AU - Yifeng Wang
AU - Jiaze Sun
AU - Benjamin Moss
AU - Arno Bergmann
AU - Beatriz Roldan Cuenya
AU - James R. Durrant
AU - Ifan E.L. Stephens
AU - Rhodri Jervis
AU - Reshma R Rao
PY - 2026
DA - 2026/09/06
PB - ChemRxiv
DO - 10.26434/chemrxiv.15008370/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15008370/v1
AB - Understanding how water-oxidation electrocatalysts operate under device-relevant conditions is essential for the design of advanced proton-exchange-membrane (PEM) water electrolysers. Although substantial progress has recently been made in elucidating the oxygen-evolution chemistry of iridium oxide in aqueous model systems, how these molecular insights translate to practical membrane–electrode assemblies (MEA) remains unclear. Here, we bridge this gap by combining operando hard and soft X-ray absorption spectroscopy with time-resolved optical spectroscopy to probe the intrinsic water oxidation chemistry of identical IrOx catalysts across three-electrode, catalyst–ionomer, and MEA configurations. We show that Nafion™ ionomers do not alter the intrinsic metal- and oxygen-centred redox transitions or the formation of electrophilic oxygen species that drives O–O bond formation. Instead, the ionomer content primarily affects mass transport through oxygen trapping and microbubble accumulation, which can obscure operando spectroscopic signatures. Operando Ir L3-edge XAS reveals higher average Ir oxidation states in MEA than in aqueous electrodes despite identical initial states, which is explained by higher catalyst utilisation in the MEA catalyst layers, even at substantially higher mass loading. Open-circuit decay measurements further reveal similar rapid and slow discharge regimes in both systems, demonstrating that IrOx remains in high oxidation states for hours in the absence of hydrogen crossover. These findings establish unified redox transitions and active species in aqueous and MEA environments, while identifying catalyst utilisation and transport effects as the dominant origins of MEA–aqueous discrepancies, thereby providing a general framework for translating molecular insights from model systems to device-relevant conditions.
ER -