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.

The surface chemical properties and the electronic properties of vapor grown carbon nanofibers (VGCNFs) have been modified by treatment of the oxidized CNFs with NH(3). The effect of treatment temperature on the types of nitrogen functionalities introduced was evaluated by synchrotron based X-ray photoelectron spectroscopy (XPS), while the impact of the preparation methods on the surface acid-base properties was investigated by potentiometric titration, microcalorimetry, and zeta potential measurements. The impact of the N-functionalization on the electronic properties was measured by THz-Time Domain spectroscopy. The samples functionalized via amination are characterized by the coexistence of acidic and basic O and N sites. The population of O and N species is temperature dependent. In particular, at 873 K nitrogen is stabilized in substitutional positions within the graphitic structure, as heterocyclic-like moieties. The surface presents heterogeneously distributed and energetically different basic sites. A small amount of strong basic sites gives rise to a differential heat of CO(2) adsorption of 150 kJ mol(-1). However, when functionalization is carried out at 473 K, nitrogen moieties with basic character are introduced and the maximum heat of adsorption is significantly lower, at approximately 90 kJ mol(-1). In the latter sample, energetically different basic sites coexist with acidic oxygen groups introduced during the oxidative step. Under these conditions, a bifunctional acidic and basic surface is obtained with high hydrophilic character. N-functionalization carried out at higher temperature changes the electronic properties of the CNFs as evaluated by THz-TDS. The functionalization procedure presented in this work allows high versatility and flexibility in tailoring the surface chemistry of nanocarbon material to specific needs. This work shows the potential of the N-containing nanocarbon materials obtained via amination in catalysis as well as electronic device materials.