Electrocatalyst degradation, often caused by oxidative processes, forms a large barrier for the wide-spread application of electrolysers and fuel cells, which are crucial for a sustainable energy society. A detailed understanding of the catalyst surface structure under oxygen evolution reaction (OER) conditions is, therefore, required to design more stable catalysts. Here, we study the oxidation of a Pt(111) model electrode under operando conditions combining High-Energy Surface X-ray Diffraction (HE-SXRD) with a Rotating Disk Electrode (RDE) in a unique experimental setup. This approach allows us to follow the atomic structure of the electrode-electrolyte interface under oxygen evolution reaction conditions under hitherto unexplored potential regimes. We find that the Pt(111) surface gets electro-oxidized in a layer-by-layer fashion. From ex situ X-ray Reflectivity (XRR) and X-ray Photoelectron Spectroscopy (XPS) measurements we find that a sub-nm thick, PtO2 oxide film is forming, which deactivates the surface and leads to surface roughening. Our results provide important insights into the electrochemical oxidation of platinum electrocatalysts and resolves crucial differences to thermal oxidation processes.

The exsolution process enables to produce and control the formation of stable and catalytically active nano particles via reductive extraction of uniformly incorporated precious metal ions from a solid oxide solution. Here we consider the simple and stable perovskite LaFeO3 (LFO) where 10% of Fe on B sites are substituted by ruthenium (LFRO). Hydrogen reduction of LFRO at 800 °C leads to the formation of socketed ruthenium particles whose low-temperature activity in the total propane oxidation reaction at 210 °C is substantially lower than that of the original LFRO. Upon increasing the reaction temperature once to 400 °C, the exsolved catalyst undergoes self-activation so that the activity at 210 °C turns out to be five times higher than that of the original LFRO. High-resolution transmission electron microscopy and nanometer-resolved element mapping, together with averaging characterization methods, including X-ray diffraction and X-ray photoelectron spectroscopy, Raman spectroscopy, and diffuse infrared spectroscopy, unveil that after reduction at 800 °C the exsolved Ru particles are slightly alloyed with Fe and encapsulated by an inert and protecting LaOx layer. Mild oxidative treatment at 400 °C leads to the removal of the conforming LaOx layer, while the uncovered RuFe alloy particle transforms to catalytically active oxidic Ru species, with no indication of a separate FeOx phase. We exemplify with our case study of LaFe0.9Ru0.1O3 that careful redox treatment enables to control the exsolution process and to avoid deactivation. This may be of importance for the whole class of exsolvable materials.

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 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 at elevated temperatures, as exemplified by the mixture of RuO2 and TiO2. We are able to incorporate 17.6 mol% hydrogen into the mixed oxide Ru0.3Ti0.7O2 by H2 exposure at 250 °C, while this is not possible for pure RuO2 and rutile TiO2 that is either reduced to metallic Ru or does not allow for hydrogen absorption, respectively. Hydrogenated Ru0.3Ti0.7O2 may be utilized in hydrogenation catalysis. In this study, however, we demonstrate that hydrogen-incorporated Ru0.3Ti0.7O2 improves substantially the catalytic performance in oxidation reactions such as the propane combustion and HCl oxidation reaction. Hydrogen induced lattice strain in Ru0.3Ti0.7O2 accompanied with altered electronic properties is likely to be the reason for the observed enhanced catalytic activity. Hydrogen treatment can be performed in the reactor, thus providing an additional parameter to fine-tune in situ the catalytic performance of a mixed oxide catalyst.

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.

A rational synthetic approach is introduced to enable hydrogen insertion into oxides by forming a solid solution of a reducible oxide with a less reducible oxide as exemplified with RuO2 and TiO2 (Ru_x, a mixture of x% RuO2 with (100−x)% TiO2). Hydrogen exposure at 250 °C to Ru_x (Ru_x_250R) results in substantial hydrogen incorporation accompanied by lattice strain that in turn induces pronounced activity variations. Here, we demonstrate that hydrogen incorporation in mixed oxides promotes the oxidation catalysis of propane combustion with Ru_60_250R being the catalytically most active catalyst.

We investigated the structural evolution of electrochemically fabricated Pd nanowiresin situby 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 (2D-SOR). This shows how electrodeposition and the hydrogen evolution reaction (HER) compete and interact during Pd electrodepositon. During the bottom-up growth of the nanowires, we show thatβ-phase Pd hydride is formed. Suspending the electrodeposition then leads to a phase transition fromβ-phase Pd hydride toα-phase Pd. Additionally, we find that grain coalescence later hinders the incorporation of hydrogen in the Pd unit cell. GTSAXS and 2D-SOR provide complementary information on the volume fraction of the pores occupied by Pd, while XRF was used to monitor the amount of Pd electrodeposited.

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.

In situ stability studies of an IrO2(110)-TiO2(110) model electrode are carried out under acidic water electrolysis conditions, employing synchrotron-based techniques including surface X-ray diffraction (SXRD) and X-ray reflectometry (XRR) with a photon energy of 21.5 keV. These experiments are complemented by ex situ scanning electron microscopy (SEM), scanning tunneling microscopy (STM), and Xray photoelectron spectroscopy (XPS) experiments. Even at an anodic current density of 250 mA center dot cm-2 during electrochemical water splitting, the IrO2(110)-TiO2(110) model electrode turned out to be stable against Ir dissolution. However, radiation induced damages of the IrO2(110) film are observed: Part of the IrO2(110) film delaminates upon heavy exposure to the synchrotron beam, while subsequently the uncovered TiO2(110) is subject to further (photon-induced) corrosion. We propose that the X-ray photons induce oxygen vacancy formation by displacing O2- ions of TiO2 from regular to interstitial sites, while the potential drop across the TiO2(110) substrate leads to a migration of interstitial O2- ions from interface toward bulk TiO2. This reduction step at the interface between IrO2(110) and TiO2(110) weakens the adhesion of the epitaxially grown IrO2(110) film to the TiO2(110) substrate so that the strained IrO2(110) film is partially delaminated. Higher X-ray photon energies of 60-90 keV mitigate this degradation process.

Characterizing electrode surface structures under operando conditions is essential for fully understanding structure-activity relationships in electrocatalysis. Here, we combine in a single experiment high-energy surface x-ray diffraction as a characterizing technique with a rotating disk electrode to provide steady state kinetics under electrocatalytic conditions. Using Pt(111) and Pt(100) model electrodes, we show that full crystal truncation rod measurements are readily possible up to rotation rates of 1200 rpm. Furthermore, we discuss possibilities for both potentiostatic as well as potentiodynamic measurements, demonstrating the versatility of this technique. These different modes of operation, combined with the relatively simple experimental setup, make the combined rotating disk electrode-surface x-ray diffraction experiment a powerful technique for studying surface structures under operando electrocatalytic conditions.

Mixed oxide catalysts Ru x Ir 1‐x O 2 with varying composition x ( x =0, 0.25, 0.5, 0.75, 1.0) supported on CeO 2 , γ‐Al 2 O 3 or ZrO 2 are successfully prepared and tested in the catalytic propane combustion in terms of activity and stability. Pure IrO 2 reveals a significantly lower activity than Ru x Ir 1‐x O 2 with x≥0.25. For low conversion, pure RuO 2 on CeO 2 turns out to be the most active catalyst, while at higher conversion, Ru 0.75 Ir 0.25 O 2 on ZrO 2 is found to be more active than RuO 2 , pointing towards synergism of Ru and Ir sites. Long‐term stability and also the resistance against water poisoning are highest for ZrO 2 ‐supported catalysts. The higher the Ir concentration in the active component Ru x Ir 1‐x O 2 the more susceptible is the catalyst to water poisoning. Water poisoning is shown to be reversible, consistent with a blocking of catalytically active sites by water adsorption.

We investigated the structural evolution of electrochemically fabricated Pd nanowires in situ by means of grazing-incidence transmission small- and wide-angle x-ray scattering (GTSAXS and GTWAXS), x-ray fluorescence (XRF) and 2-dimensional surface optical reflectance (2D-SOR). This shows how electrodeposition and the hydrogen evolution reaction (HER) compete and interact during Pd electrodepositon. During the bottom-up growth of the nanowires, we show that β-phase Pd hydride is formed. Suspending the electrodeposition then leads to a phase transition from β- to α-phase Pd hydride. Additionally, we find that grain coalescence later hinders the incorporation of hydrogen in the Pd unit cell. GTSAXS and 2D-SOR provide complementary information on the volume fraction of the pores occupied by Pd, while XRF was used to monitor the amount of Pd electrodeposited.

The anodic corrosion behavior of 50 angstrom thick single-crystalline IrO2 (110) films supported on slightly bulk-reduced TiO2 (110) single crystals is studied during acidic water splitting by a unique combination of operando techniques, namely, synchrotron-based high-energy X-ray reflectivity (XRR) and surface X-ray diffraction (SXRD) together with highly sensitive inductively coupled plasma mass spectrometry (ICP-MS). Corrosion-induced structural and morphological changes of the IrO2 (110) model electrode can be followed on the atomic scale by operando XRR and SXRD that are supplemented with ex situ scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS), whereas with ICP-MS, the corrosion rate can be quantified down to 1 pg.cm(-2).s(-1) with a time resolution on the second scale. The operando synchrotron-based X-ray scattering techniques are surprisingly sensitive to Ir corrosion of about 0.10 monolayer of IrO2 (110) in similar to 26 h, i.e., 0.4 pg.cm(-2).s(-1). The present study demonstrates that single-crystalline IrO2 (110) films are much more stable than hitherto expected. Although the dissolution rate is very small, ICP-MS experiments reveal a significantly higher dissolution rate than the operando high-energy XRR/SXRD experiments. These differences in dissolution rate are suggested to be due to the different modi operandi encountered in ICP-MS (dynamic) and operando XRR/ SXRD experiments (steady state), a fact that may need to be considered when hydrogen production is coupled to intermittent energy sources such as renewables.

While activity and kinetics of catalytic CO and propane combustion over RuO2depends sensitively on the carrier material, methane combustion on RuO2is hardly affected by the carrier.

Deactivation of CeO2‐based catalysts in the HCl oxidation reaction proceeds via selective bulk chlorination of the active CeO2 component to form CeCl3×nH2O. We study the reactivation of two bulk‐chlorinated CeO2‐based Deacon catalysts by oxygen treatment at 430 °C, namely pure CeO2 and 20 mol % of CeO2 supported on preformed ZrO2 particles (20CeO2@ZrO2), with a dedicated experiment. In the flow reactor setup we determine in‐situ the degree of chlorination of the catalyst by quantifying down‐stream with in‐situ UV‐Vis spectroscopy the total amount of chlorine in the catalyst that is exchanged by reoxidation at 430 °C. The activity of deactivated 20CeO2@ZrO2 can be fully restored by oxygen exposure at 430 °C, while that of pure CeO2 declines steadily. Since the UV‐Vis analytics is fast and sensitive, we can follow the kinetics of reoxidation. To rationalize the observed kinetics, we develop a modified Johnson‐Mehl‐Avrami‐Kolmogorov (JMAK) model based on a nucleation‐and‐growth approach for the reoxidation of the catalyst starting from the chlorinated phase. The fast reoxidation kinetics of chlorinated 20CeO2@ZrO2 is traced to a fast nucleation rate.

The interaction of ultrathin single-crystalline IrO2(110) films with the gas phase proceeds via the coordinatively unsaturated sites (cus), in particular Ir-cus the undercoordinated oxygen species on-top O (O-ot) that are coordinated to Ir-cus, and bridging O (O-br). With the combination of different experimental techniques, such as thermal desorption spectroscopy, scanning tunneling microscopy (STM), high-resolution core-level spectroscopy (HRCLS), infrared spectroscopy, and first-principles studies employing density functional theory calculations, we are able to elucidate surface properties of single-crystalline IrO2(110). We provide spectroscopic fingerprints of the active surface sites of IrO2(110). The freshly prepared IrO2(110) surface is virtually inactive toward gas-phase molecules. The IrO2(110) surface needs to be activated by annealing to 500-600 K under ultrahigh vacuum (UHV) conditions. In the activation step, Ir cus sites are liberated from on-top oxygen (O-ot) and monoatomic Ir metal islands are formed on the surface, leading to the formation of a bifunctional model catalyst. Vacant Ir-cus sites of IrO2(110) allow for strong interaction and accommodation of molecules from the gas phase. For instance, CO can adsorb atop on Ir-cus and water forms a strongly bound water layer on the activated IrO2(110) surface. Single-crystalline IrO2(110) is thermally not very stable although chemically stable. Chemical reduction of IrO2(110) by extensive CO exposure at 473 K is not observed, which is in contrast to the prototypical RuO2(110) system.

Sophisticated IrO2(110)-RuO2(110)/Ru(0001) model electrodes are employed in the oxygen evolution reaction (OER) under acidic conditions. The potential-induced pitting corrosion of such electrodes is confirmed by a variety of experimental techniques, including scanning electron microscopy (SEM), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and operando scanning flow cell-inductively coupled plasma mass spectrometry (SFC-ICP-MS). The structure of the pits is reminiscent of a cylinder (evidenced by focused ion beam scanning electron microscopy: FIB-SEM), where the inner surface of the pits is covered by hydrous RuO2 (cyclic voltammetry, ToF-SIMS) that is formed by electrochemical oxidation of the metallic Ru(0001) substrate. The time evolution of the corrosion process at a fixed electrode potential (1.48 V vs. SHE) is followed via cyclic voltammetry and SEM. The passivating IrO2(110) layer results in an "induction period" for the pit growth that is followed by rapid corrosion of the RuO2(110)/Ru(0001) substrate. The observed narrow and time-independent size distribution relative to the mean size of the pits is attributed to a sluggish removal of the corrosion products by diffusion across the cracks of the pits covering IrO2 layer, leading to steady state corrosion during a total polarization time of 20 to 60 minutes.

We investigate with in situ surface X-ray diffraction (SXRD) and X-ray reflectivity (XRR) experiments the cathodic stability of an ultrathin single-crystalline IrO2(110) film with a regular array of mesoscopic rooflike structures that is supported on a RuO2(110)/Ru(0001) template. It turns out that the planarity of the single-crystalline IrO2(110) film is lost in that IrO2(110) oxide domains delaminate at a cathodic potential of -0.18 V. Obviously, the electrolyte solution is able to reach the RuO2(110) layer presumably through the surface grain boundaries of the IrO2(110) layer. Subsequently, the single-crystalline RuO2(110) structure-directing template is reduced to amorphous hydrous RuO2, with the consequence that the IrO2(110) film loses partly its adhesion to the template. From in situ XRR experiments we find that the IrO2(110) film does not swell upon cathodic polarization down to -0.18 V, while from in situ SXRD experiments, the lattice constants of IrO2(110) are shown to be not affected. The rooflike mesostructure of the IrO2(110) flakes remains intact after cathodic polarization to -0.18 V, evidencing that the crystallinity of IrO2(110) is retained.

Background The coat colour of fallow deer is highly variable and even white animals can regularly be observed in game farming and in the wild. Affected animals do not show complete albinism but rather some residual pigmentation resembling a very pale beige dilution of coat colour. The eyes and claws of the animals are pigmented. To facilitate the conservation and management of such animals, it would be helpful to know the responsible gene and causative variant. We collected 102 samples from 22 white animals and from 80 animals with wildtype coat colour. The samples came from 12 different wild flocks or game conservations located in different regions of Germany, at the border to Luxembourg and in Poland. The genomes of one white hind and her brown calf were sequenced. Results Based on a list of colour genes of the International Federation of Pigment Cell Societies ( http://www.ifpcs.org/albinism/ ), a variant in the MC1R gene (NM_174108.2:c.143 T > C) resulting in an amino acid exchange from leucine to proline at position 48 of the MC1R receptor protein (NP_776533.1:p.L48P) was identified as a likely cause of coat colour dilution. A gene test revealed that all animals of the white phenotype were of genotype CC whereas all pigmented animals were of genotype TT or TC. The study showed that 14% of the pigmented (brown or dark pigmented) animals carried the white allele. Conclusions A genome-wide scan study led to a molecular test to determine the coat colour of fallow deer. Identification of the MC1R gene provides a deeper insight into the mechanism of dilution. The gene marker is now available for the conservation of white fallow deer in wild and farmed animals.

The Pechini method allows for compositional and structural control of mixed ruthenium-iridium powder samples. Extensive characterization reveals that the calcination step leads to agglomerates with a metallic core that is encapsulated by the mixed RuxIr1-xO2 oxides. In the composition range of 21 up to 74 mol % ruthenium, the metal core reveals a miscibility gap with an Ir-rich fcc structure and a Ru-enriched hcp structure. Quite in contrast, the mixed oxide particles form a well-defined RuxIr1-xO2 solid solution throughout the entire composition range. Catalytic activity tests of the mixed RuxIr1-xO2 oxide catalysts are conducted with the prototypical CO oxidation reaction under oxidizing and under both stoichiometric reaction conditions; note that the metallic core is buried and does therefore not contribute to the activity. The least active catalyst is pure IrO2. At moderate reaction temperatures above 100 degrees C, the most active oxidation catalyst is identified with the Ir0.125Ru0.875O2 mixed oxide. All mixed RuxIr1-xO2 oxide catalysts are bulk-stable under the reaction conditions considered. However, upon CO oxidation reaction, the Ir4+ concentration at the mixed oxide surface is significantly enhanced with respect to its bulk composition. This information may be important for other catalytic oxidation reactions as well, such as the anodic oxygen evolution reaction in the electrocatalytic water splitting.