Dataset of "On the Growth and OER Stability of Hydrous Iridium Oxide"

Hydrous iridium oxide (HIROF) is a highly active catalyst for oxygen evolution reaction (OER) with applications in pH sensing and charge storage devices. However, the mechanisms driving its growth and iridium dissolution remain incompletely understood. To address this gap, online inductively coupled plasma mass spectrometry (ICP-MS) is employed to monitor iridium dissolution during electrochemical cycling on sputtered thin films of varying thicknesses. Complementary techniques, including atom probe tomography (APT), ellipsometry, and X-ray photoelectron spectroscopy (XPS), are used to study oxidation states and interface composition. Our findings reveal a tri-phase interface comprising metallic iridium, compact anhydrous oxide, and hydrous oxide. Dissolution predominantly occurs at the metal-compact oxide interface, driven by transient processes during cycling. HIROF growth strongly depends on iridium grain size, with smaller grains inhibiting growth due to the accumulation of an inner compact IrO₂ layer. This effect is linked to increased oxophilicity, which lowers the reducibility of the compact oxide. These insights advance understanding of HIROF growth mechanisms, offering strategies to optimize its performance and stability, particularly in proton exchange membrane water electrolyzers (PEMWEs), where iridium scarcity is critical. Broader implications extend to hydrous oxide formation on other noble and non-noble metals, potentially further advancing other electrochemical applications.