Iridium-based materials are among the most active and stable electrocatalysts for the oxygen evolution reaction. Amorphous iridium oxide structures are found to be more active than their crystalline counterparts. Herein, we combine synchrotron-based X-ray photoemission and absorption spectroscopies with theoretical calculations to investigate the electronic structure of Ir metal, rutile-type IrO₂, and an amorphous IrO_x. Theory and experiment show that while the Ir 4f line shape of Ir metal is well described by a simple Doniach–Šunjić function, the peculiar line shape of rutile-type IrO₂ requires the addition of a shake-up satellite 1 eV above the main line. In the catalytically more active amorphous IrO_x, we find that additional intensity appears in the Ir 4f spectrum at higher binding energy when compared with rutile-type IrO₂ along with a pre-edge feature in the O K-edge. We identify these additional features as electronic defects in the anionic and cationic frameworks, namely, formally O^I− and Ir^III, which may explain the increased activity of amorphous IrO_x electrocatalysts. We corroborate our findings by in situ X-ray diffraction as well as in situ X-ray photoemission and absorption spectroscopies

Iridium oxide based electrodes are among the most promising candidates for electrocatalyzing the oxygen evolution reaction, making it imperative to understand their chemical/electronic structure. However, the complexity of iridium oxide's electronic structure makes it particularly difficult to experimentally determine the chemical state of the active surface species. To achieve an accurate understanding of the electronic structure of iridium oxide surfaces, we have combined synchrotron-based X-ray photoemission and absorption spectroscopies with ab initio calculations. Our investigation reveals a pre-edge feature in the O K-edge of highly catalytically active X-ray amorphous iridium oxides that we have identified as O 2p hole states forming in conjunction with Ir(III). These electronic defects in the near-surface region of the anionic and cationic framework are likely critical for the enhanced activity of amorphous iridium oxides relative to their crystalline counterparts.

Glassy carbon is widely used in electrochemistry due to its properties of high temperature resistance, hardness, low density and low electrical resistance. The present study focuses on the chemical resistance under electrochemical oxidative conditions, which occur under oxygen-involving reactions like oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The electrochemical performance of glassy carbon investigated in alkaline, neutral and acidic media reveal the same chemical processes during the OER but showing different degradation mechanism. The electrochemical signature of the corrosion in different media could be directly associated with the formation of oxygen functional groups determined by spectroscopic methods like Raman, infrared (IR) and x-ray photoelectron spectroscopy (XPS). The morphology change of the carbon surface caused by carbon oxidation was investigated by microscopy. A rough surface was obtained in the acidic case, whereas dents were seen in alkaline media. It is assumed that the glassy carbon electrode in acidic media degrades by forming surface oxides by acid catalyzed process leading to ring opening in the graphitic structure and therefore oxidation in the bulk. In alkaline media OH radicals preferentially react with alkyl site chains, leading to oxidation of the edges of carbon layers until they become hydrophilic and dissolve

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The design of solid catalysts for industrial processes remains a major challenge in synthetic materials chemistry. Based on the investigation of the industrial Cu/ZnO/Al₂O₃ catalyst, a modular concept is introduced that helps to develop novel methanol synthesis catalysts that operate in different feed gas mixtures. SA=surface area, SMSI=strong metal–support interaction