Unifying Water Oxidation Chemistry of Iridium Oxide from Aqueous Model Systems to Proton Exchange Membrane Electrolysers
Year: 2026
Type: preprint
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.
Source: ChemRxiv
Authors: Caiwu Liang, James Murawski, Cindy Tseng, Yue Wen, Yemin Tao, Chris Zalitis, Colleen Jackson, Guangmeimei Yang, Timon Wagner, Thomas Götsch, Veronica Celorrio, Sid Halder, Yifeng Wang, Jiaze Sun, Benjamin Moss, Arno Bergmann, Beatriz Roldan Cuenya, James R. Durrant, Ifan E.L. Stephens, Rhodri Jervis, Reshma R Rao
Language: English
Field: Energy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7211872649