In Situ Synchrotron-Based Studies of IrO2(110)–TiO2(110) under Harsh Acidic Water Splitting Conditions: Anodic Stability and Radiation Damages

Abstract

In situ stability studies of an IrO2(110)–TiO2(110) model electrode are carried out under acidic water electrolysis conditions, employing synchrotron-based techniques including surface X-ray diffraction (SXRD) and X-ray reflectometry (XRR) with a photon energy of 21.5 keV. These experiments are complemented by ex situ scanning electron microscopy (SEM), scanning tunneling microscopy (STM), and X-ray photoelectron spectroscopy (XPS) experiments. Even at an anodic current density of 250 mA·cm–2 during electrochemical water splitting, the IrO2(110)–TiO2(110) model electrode turned out to be stable against Ir dissolution. However, radiation-induced damages of the IrO2(110) film are observed: Part of the IrO2(110) film delaminates upon heavy exposure to the synchrotron beam, while subsequently the uncovered TiO2(110) is subject to further (photon-induced) corrosion. We propose that the X-ray photons induce oxygen vacancy formation by displacing O2– ions of TiO2 from regular to interstitial sites, while the potential drop across the TiO2(110) substrate leads to a migration of interstitial O2– ions from interface toward bulk TiO2. This reduction step at the interface between IrO2(110) and TiO2(110) weakens the adhesion of the epitaxially grown IrO2(110) film to the TiO2(110) substrate so that the strained IrO2(110) film is partially delaminated. Higher X-ray photon energies of 60–90 keV mitigate this degradation process.