The growth of a flat, covering, and single-crystalline IrO 2 (110) film with controlled film thickness on a single-crystalline TiO 2 (110) substrate is reported. The preparation starts with a deposition of metallic Ir at room temperature followed by a post-oxidation step performed in an oxygen atmosphere of 10 −4 mbar at 700 K. On this surface, additional Ir can be deposited at 700 K in an oxygen atmosphere of 10 −6 mbar to produce a IrO 2 (110) layer with variable thicknesses. To improve the crystallinity of the resulting IrO 2 (110) layer, the final film was post-oxidized in 10 −4 mbar of O 2 at 700 K for 5 min. The surface-sensitive techniques of scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and low-energy electron diffraction (LEED) are employed to characterize the morphology, crystallinity, and electronic structure of the prepared ultrathin IrO 2 (110) films and how these films decompose upon annealing under ultrahigh vacuum (UHV) conditions. STM provides evidence that the IrO 2 (110) films start already to reduce at 465 K under UHV conditions. Upon annealing to 605 K under UHV the reduction of IrO 2 intensifies (XPS), but the oxide film can readily be restored by re-oxidation in 10 −4 mbar of O 2 at 700 K. Thermal decomposition at 725 K leads, however, to severe reduction of the IrO 2 (110) layer (XPS, STM) that cannot be restored by a subsequent re-oxidation step. The utility of the IrO 2 (110)−TiO 2 (110) system as model electrodes is exemplified with the electrochemical oxygen evolution reaction in an acidic environment.

We combine operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) with on-line mass spectrometry (MS) to study the correlation between the oxidation state of titania-supported IrO2 catalysts (IrO2@TiO2) and their catalytic activity in the prototypical CO oxidation reaction. Here, the stretching vibration of adsorbed COad serves as the probe. DRIFTS provides information on both surface and gas phase species. Partially reduced IrO2 is shown to be significantly more active than its fully oxidized counterpart, with onset and full conversion temperatures being about 50 °C lower for reduced IrO2. By operando DRIFTS, this increase in activity is traced to a partially reduced state of the catalysts, as evidenced by a broad IR band of adsorbed CO reaching from 2080 to 1800 cm−1.

The solid solution of a reducible oxide with a (non or) less reducible oxide may open the way to incorporate substantial amounts of hydrogen by the simple exposure to H2...

Operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) is combined with online mass spectrometry (MS) to help to resolve a long-standing debate concerning the active phase of RuO2 supported on rutile TiO2 (RuO2@TiO2) during the CO oxidation reaction. DRIFTS has been demonstrated to serve as a versatile probe molecule to elucidate the active phase of RuO2@TiO2 under various reaction conditions. Fully oxidized and fully reduced catalysts serve to provide reference DRIFT spectra, based on which the operando CO spectra acquired during CO oxidation under various reaction conditions are interpreted. Partially reduced RuO2@TiO2 was identified as the most active catalyst in the CO oxidation reaction. This is independent of the reaction conditions being reducing or oxidizing and whether the starting catalyst is the fully oxidized RuO2@TiO2 or the partially reduced RuO2@TiO2.

The electrochemical growth of Au nanowires in a template of nanoporous anodic aluminum oxide was investigated in situ by means of grazing-incidence transmission small- and wide-angle x-ray scattering (GTSAXS and GTWAXS), x-ray fluorescence (XRF), and two-dimensional surface optical reflectance. The XRF and the overall intensity of the GTWAXS patterns as a function of time were used to monitor the progress of the electrodeposition. Furthermore, we extracted powder diffraction patterns in the direction of growth and in the direction of confinement to follow the evolution of the direction-dependent strain. Quite rapidly after the beginning of the electrodeposition, the strain became tensile in the vertical direction and compressive in the horizontal direction, which showed that the lattice deformation of the nanostructures can be artificially varied by an appropriate choice of the deposition time. By alternating sequences of electrodeposition with sequences of rest, we observed fluctuations of the lattice parameter in the direction of growth, attributed to stress caused by electromigration. Furthermore, the porous domain size calculated from the GTSAXS patterns was used to monitor how homogeneously the pores were filled.