Operando Stability Studies of Ultrathin Single-Crystalline IrO₂(110) Films under Acidic Oxygen Evolution Reaction Conditions

The anodic corrosion behavior of 50 Å thick single-crystalline IrO₂(110) films supported on slightly bulk-reduced TiO₂(110) single crystals is studied during acidic water splitting by a unique combination of operando techniques, namely, synchrotron-based high-energy X-ray reflectivity (XRR) and surface X-ray diffraction (SXRD) together with highly sensitive inductively coupled plasma mass spectrometry (ICP-MS). Corrosion-induced structural and morphological changes of the IrO₂(110) model electrode can be followed on the atomic scale by operando XRR and SXRD that are supplemented with ex situ scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS), whereas with ICP-MS, the corrosion rate can be quantified down to 1 pg·cm^-2·s^-1with a time resolution on the second scale. The operando synchrotron-based X-ray scattering techniques are surprisingly sensitive to Ir corrosion of about 0.10 monolayer of IrO₂(110) in ∼26 h, i.e., 0.4 pg·cm^-2·s^-1. The present study demonstrates that single-crystalline IrO₂(110) films are much more stable than hitherto expected. Although the dissolution rate is very small, ICP-MS experiments reveal a significantly higher dissolution rate than the operando high-energy XRR/SXRD experiments. These differences in dissolution rate are suggested to be due to the different modi operandi encountered in ICP-MS (dynamic) and operando XRR/SXRD experiments (steady state), a fact that may need to be considered when hydrogen production is coupled to intermittent energy sources such as renewables.