Chasing down the active state: Near-ambient-pressure X-ray photoelectron spectroscopy was used to study the surface of a Pt electrode during the oxygen evolution reaction (OER). A hydrated Pt metal phase with dissolved oxygen in the near-surface region is OER-active and considered to be the precursor of the analytically detected PtO2 , which is in fact the deactivation product of the electrode.

Iridium oxide is one of the most important catalysts for water oxidation. The atomic structure of this catalyst remains unknown. We have studied anodically grown iridium oxide catalyst films using Raman spectroscopy. In addition to deuteration and 18O substitution experiments, theoretical models were also constructed using density functional theory to interpret the experimental data. The material was characterized over a large potential range which included that for the oxygen evolution reaction (0.0–1.8 V). The material was found to be composed of [IrO6] n edge-sharing polyhedra (with n ≥ 3). Ir centers are connected to each other via μ-O type oxygen linkages that allow for the Ir centers to electronically couple to each other. The most intense peaks in Raman spectra were characterized by stretching movement of Ir−μ-O bonds in the basal plane of the octahedra coupled to OH bending movements of hydroxyl groups bound to the Ir centers. Oxidation of Ir3+ to Ir4+ at 0.7–1.2 V within a μ-O linked polymeric geometry results in a blue coloration of the material at high potentials. Theoretical calculations indicate that the optical transition responsible for the color is essentially an Ir to Ir charge transfer transition. The active compound that carries out oxygen evolution is resistant to further structure-directing influence of oxidation. In the course of oxidation, it was observed that IrO2 with a rutile structure could form at potentials greater than 1.2 V as a side product of the reaction.

There is great interest in electrochemical water splitting for the efficient utilization of sustainable energy. As an alternative to high-priced materials, carbon offers considerable potential. However, carbon is limited as an electrode material for the oxygen evolution reaction (OER), owing to its thermodynamic instability against electrochemical oxidation. In this study, we investigated the electrochemical degradation of multiwall carbon nanotubes (MWCNTs) under the acidic OER environment. Electrochemical oxidation of MWCNTs induces structural changes and the formation of oxygen-containing functional groups on the carbon surface. As a consequence, the electrochemical and physicochemical properties of the MWCNTs are changed during electrochemical oxidation. We carried out electrochemical, microstructural, and spectroscopic analysis to investigate the degradation of MWCNTs. By changing of the electrochemical properties of MWCNTs during the oxidation process, the carbon electrode is initially activated and can then be kinetically stabilized with prolonged oxidation under the OER conditions

The structure of anodic iridium oxide (IrO) under water oxidation was explored using in situ Raman spectroscopy and theoretical calculations. Isotopic substitution experiments and theoretical calculations confirmed formation of an Ir[double bond, length as m-dash]O species during oxygen evolution reaction.