Potential-Induced Pitting Corrosion of an IrO₂(110)-RuO₂(110)/Ru(0001) Model Electrode under Oxygen Evolution Reaction Conditions

Abstract

Sophisticated IrO2(110)-based model electrodes are prepared by deposition of a 10 nm thick single-crystalline IrO2(110) layer supported on a structure directing RuO2(110)/Ru(0001) template, exposing a regular array of mesoscopic roof-like structures. With this model electrode together with the dedicated in-situ synchrotron based techniques (SXRD, XRR) and ex-situ characterization techniques (SEM, ToF-SIMS, XPS) the corrosion process of IrO2(110) in acidic environment is studied on different length scales. Potential-induced pitting corrosion starts at 1.48 V vs. SHE and is initiated at so-called surface grain boundaries, where three rotational domains of IrO2(110) meet. The most surprising results is, however, that even when increasing the electrode potential to 1.94 V vs. SHE still 60-70 % of the IrO2 film stays intact down to the mesoscale and atomic scale and no uniform thinning of the IrO2(110) layer is encountered. Neither flat IrO2(110) terraces nor single steps or grain boundaries, where only two rotational domains meet, are attacked. Ultrathin single-crystalline IrO2(110) layers seem to be much more stable in the anodic corrosion than hitherto expected.

Visualizing Potential‐Induced Pitting Corrosion of Ultrathin Single‐Crystalline IrO2(110) Films on RuO2(110)/Ru(0001) under Electrochemical Water Splitting Conditions

“…Recently, the IrO 2 (110)‐RuO 2 (110)/Ru(0001) system was employed as a model electrode to gain insight into corrosion processes under OER conditions. The IrO 2 (110) film exhibits a roughness on the mesoscale (yet the terraces are atomically flat) in a regular array reminiscent of “roofs”: there is a sequence of ascending terraces up to the top of the roof that is followed by a symmetric descending series of terraces. For this reason we have introduced the term “rooflike structure” in our previous study .…”

“…The IrO 2 (110) film exhibits a roughness on the mesoscale (yet the terraces are atomically flat) in a regular array reminiscent of “roofs”: there is a sequence of ascending terraces up to the top of the roof that is followed by a symmetric descending series of terraces. For this reason we have introduced the term “rooflike structure” in our previous study . Due to this rooflike structure of the IrO 2 (110) film the corrosion of the model electrode could be studied on different length scales ranging from atomic (in situ SXRD/XRR) to mesoscale (ex situ SEM) .…”

“…Ex situ SEM experiments revealed that the corrosion is initiated by Ir dissolution at so‐called “surface grain boundaries” where rotational domains of the IrO 2 (110) film meet. Once the underlying RuO 2 (110)/Ru(0001) is reached, pitting corrosion is accelerated due to the instability of RuO 2 and Ru under these anodic conditions . A schematic representation of resulting pits is shown in Figure .…”

“…Figure S1 of the Supporting Information). Since the preparation conditions of the samples were identical to those of a previous contribution we assume the thickness of the IrO 2 (110) films to be ∼10 nm . The model electrodes were studied in two different ways which are explained in the following.…”

“…Recently, a dedicated model electrode consisting of a single‐crystalline IrO 2 (110) layer that fully covers a structure‐directing template RuO 2 (110)/Ru(0001) was developed to study the electrocorrosion under OER conditions . The alterations of the crystalline structure and morphology of the IrO 2 (110) film were followed upon anodic polarization, employing a combination of powerful in situ synchrotron radiation based techniques including X‐ray reflectivity (XRR) and surface X‐ray diffraction (SXRD) and most notably ex situ techniques such as scanning electron microscopy (SEM) and X‐ray photoelectron spectroscopy (XPS).…”