No abstract

In this article, we propose a novel mechanism for the atomic-level processes that lead to oxide formation and eventually Pt dissolution at an oxidized Pt(111) surface. The mechanism involves a Pt extraction step followed by the substitution of chemisorbed oxygen to the subsurface. The energy diagrams of these processes have been generated using density functional theory and were analyzed to determine the critical coverages of chemisorbed oxygen for the Pt extraction and O ads substitution steps. The Pt extraction process depends on two essential conditions: (1) the local coordination of a Pt surface atom by three chemisorbed oxygen atoms at nearestneighboring fcc adsorption sites; (2) the interaction of the buckled Pt atom with surface water molecules. Results are discussed in terms of surface charging effects caused by oxygen coverage, surface strain effects, as well the contribution from electronic interaction effects. The utility of the proposed mechanism for the understanding of Pt stability at bimetallic surfaces will be demonstrated by evaluating the energy diagram of a Cu ML /Pt(111) near-surface alloy.

The influence of electrolyte ions on the catalytic activity of electrode/electrolyte interfaces is a controversial topic for many electrocatalytic reactions. Herein, we focus on an effect that is usually neglected, namely, how the local reaction conditions are shaped by nonspecifically adsorbed cations. We scrutinize the oxygen evolution reaction (OER) at nickel (oxy)hydroxide catalysts, using a physicochemical model that integrates density functional theory calculations, a microkinetic submodel, and a mean-field submodel of the electric double layer. The aptness of the model is verified by comparison with experiments. The robustness of model-based insights against uncertainties and variations in model parameters is examined, with a sensitivity analysis using Monto Carlo simulations. We interpret the decrease in OER activity with the increasing effective size of electrolyte cations as a consequence of cation overcrowding near the negatively charged electrode surface. The same reasoning could explain why the OER activity increases with solution pH on the RHE scale and why the OER activity decreases in the presence of bivalent cations. Overall, this work stresses the importance of correctly accounting for local reaction conditions in electrocatalytic reactions to obtain an accurate picture of factors that determine the electrode activity.

The (100) crystallographic plane is the most active facet of iridium dioxide (IrO 2 ) for the oxygen evolution reaction (OER). Pulsed laser deposition was used to grow (100) IrO 2 on a (100) SrTiO 3 substrate at deposition temperature ranging from room temperature to 600 °C. Detailed structural and morphological characterization was performed using AFM, XRD, and X-ray reciprocal space mapping (RSM) to unravel the geometrical arrangement of [IrO 6 ] octahedra in the (100) IrO 2 thin films. It is shown that the symmetry mismatch between the substrate and the epitaxial thin film imposed an orthorhombic distortion of the tetragonal structure of IrO 2 and, as a consequence, the [IrO 6 ] geometry is distorted. These data were correlated to the OER characteristics established from electrochemical measurements. DFT modeling was employed to relate differences in surface relaxation of IrO 2 films prepared at different temperatures with changes in OER activity. Vacancy formation leads to higher surface stability at temperatures around 500 °C, which corresponds to the deposition temperature at which the electrocatalytic activity of (100) epitaxial IrO 2 film is maximal.