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Corrosion is the main factor limiting the lifetime of metallic materials, and a fundamental understanding of the governing mechanism and surface processes is difficult to achieve since the thin oxide films at the metal–liquid interface governing passivity are notoriously challenging to study. In this work, a combination of synchrotron-based techniques and electrochemical methods is used to investigate the passive film breakdown of a Ni–Cr–Mo alloy, which is used in many industrial applications. This alloy is found to be active toward oxygen evolution reaction (OER), and the OER onset coincides with the loss of passivity and severe metal dissolution. The OER mechanism involves the oxidation of Mo4+ sites in the oxide film to Mo6+ that can be dissolved, which results in passivity breakdown. This is fundamentally different from typical transpassive breakdown of Cr-containing alloys where Cr6+ is postulated to be dissolved at high anodic potentials, which is not observed here. At high current densities, OER also leads to acidification of the solution near the surface, further triggering metal dissolution. The OER plays an important role in the mechanism of passivity breakdown of Ni–Cr–Mo alloys due to their catalytic activity, and this effect needs to be considered when studying the corrosion of catalytically active alloys., QC 20231114

The solid-liquid interface, where corrosion reactions occur, is notoriously difficult to study in operando conditions. Few experimental techniques can provide surface sensitivity and spatial and temporal resolution and are compatible with liquid environments. 2-Dimensional surface optical reflectance (2D-SOR) is an emerging optical technique providing microscopic information with high temporal resolution. It complements methods such as ambient pressure X-ray photoelectron spectroscopy or inductively coupled plasma-mass spectrometry, which provides valuable chemical information from the surface and the dissolving species but lacks spatial resolution. Here, we show how 2D-SOR can be used to measure the formation and growth of corrosion products in operando through oscillations in the reflected signal caused by constructive and destructive interference of the light in the film of growing corrosion products. The total thickness of the corrosion product film obtained with 2D-SOR agrees well with that measured using scanning electron microscopy ex situ. 2D-SOR has proved to be an excellent and valuable tool for monitoring the corrosion process with spatial resolution in operating conditions., QC 20240626

A high-throughput method for the fabrication of ordered arrays of Au nanoparticles is presented. It is based on pulsed electrodeposition into porous anodic alumina templates. In contrast to many synthesis routes, it is cyanide-free, prior separation of the alumina template from the aluminium substrate is not required, and the use of contaminating surfactants/capping agents often found in colloidal synthesis is avoided. The aspect ratio of the nanoparticles can also be tuned by selecting an appropriate electrodeposition time. We show how to fabricate arrays of nanoparticles, both with branched bases and with hemispherical bases. Furthermore, we compare the different morphologies produced with electron microscopies and grazing-incidence synchrotron X-ray diffraction. We find the nanoparticles are polycrystalline in nature and are compressively strained perpendicular to the direction of growth, and expansively strained along the direction of growth. We discuss how this can produce dislocations and twinning defects that could be beneficial for catalysis.

We have combined high-energy surface X-ray diffraction (HESXRD) with 2D surface optical reflectance (2D-SOR) to perform in situ electrochemical measurements of a Au(111) electrode in 0.1 M HClO4 electrolyte. We show that electrochemically induced changes to Au(111) surface during cyclic voltammetry can be simultaneously observed with 2D-SOR and HESXRD. We discuss how small one atom high 1x1 islands, accommodating excess atoms after the lifting of the surface reconstruction, can lead to discrepancies between the two techniques. The use of HESXRD allows us to simultaneously detect parts of the truncation rods from the (1 x 1) surface termination and the p x root 3 electrochemically induced surface reconstruction, during cyclic voltammetry. The presence of reconstruction phenomena is shown to not depend on having an ideally prepared surface and can in fact be observed after going to very oxidizing potentials. 2D-SOR can also detect the oxidation of the Au surface, however no oxide peaks are detected in the HESXRD signal, which is evidence that any Au oxide is X-ray amorphous.

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.