Anisotropic strain variations during the confined growth of Au nanowires

The electrochemical growth of Au nanowires in a template of nano-porous 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 2-dimensional surface optical reflectance (2D-SOR). 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 to 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.Comment: Short communication manuscript. Four figure

In situ\textit{In situ} hydride breathing during the template-assisted electrodeposition of Pd nanowires

We investigated the structural evolution of electrochemically fabricated Pd nanowires $\textit{in situ}$ 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 $\beta$-phase Pd hydride is formed. Suspending the electrodeposition then leads to a phase transition from $\beta$- to $\alpha$-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.Comment: 17 pages, 11 figures, 4 appendice

Structure and chemical properties of CeO2 on a curved Cu(111) crystal

Resumen del póster presentado al DPG Spring Meetings, celebrado de forma virtual del 1 al 4 de marzo de 2021.The system CeOx/Cu has attracted interest as an inverse catalyst for CO oxidation, water-gas shift and CO2 hydrogenation. While previous work focused on characterizing this system and the named reactions on Cu(111) or with powdered samples, we investigated this system on the vicinal surfaces of Cu(111), which are shown to be much closer to a nanostructured catalysts compared to the low index surfaces. We grew CeO2 on a curved Cu(111) single crystal with well defined vicinal surfaces and a continuous variation of step density depending on the vicinal angle. We characterized the CeOx/Cu system with LEED, STM and XPS. XPS analysis indicates only Ce(IV) oxide formed regardless of the position on the curved crystal. On the Cu(111) part of the curved sample, CeO2 nanostructures seems to grown on Cu-oxide areas, leaving the remaining Cu(111) surface uncovered. On both A- and Bstep vicinal surfaces of the curved crystal, facets build up after CeO2 deposition. The stable facets of the B-step vicinals are (111) and (110). At the A-step side three stable facets have been observed, namely the (111), (223) and an additional one at 22º with respect to (111). STM measurements reveal that the CeO2 structures mainly cover the Cu(111), leaving the (223) facet CeO2 free.Peer reviewe

Inserted Hydrogen Promotes Oxidation Catalysis of Mixed Ru0.3Ti0.7O2 as Exemplified with Propane Combustion and the HCl Oxidation Reaction

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

Hydrogen Incorporation in Ru_xTi_1−xO₂ Mixed Oxides Promotes Total Oxidation of Propane

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