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Exsolution of metal nanoparticles from perovskite-type oxides is a very promising approach to obtain catalysts with superior properties. One particularly interesting property of exsolution catalysts is the possibility of electrochemical switching between different activity states. In this work, synchrotron-based in-situ X-ray diffraction experiments on electrochemically polarized La0.6Sr0.4FeO3-δ thin film electrodes are performed, in order to simultaneously obtain insights into the phase composition and the catalytic activity of the electrode surface. This shows that reversible electrochemical switching between a high and low activity state is accompanied by a phase change of exsolved particles between metallic α-­Fe and Fe-oxides. Reintegration of iron into the perovskite lattice is thus not required for obtaining a switchable catalyst, making this process especially interesting for intermediate temperature applications. These measurements also reveal how metallic particles on La0.6Sr0.4FeO3-δ electrodes affect the H2 oxidation and H2O splitting mechanism and why the particle size plays a minor role.

This work introduces an additive direct-write nanofabrication technique for producing extremely conductive gold nanostructures from a commercial metalorganic precursor. Gold content of 91 atomic % (at. %) was achieved by using water as an oxidative enhancer during direct-write deposition. A model was developed based on the deposition rate and the chemical composition, and it explains the surface processes that lead to the increases in gold purity and deposition yield. Co-injection of an oxidative enhancer enabled Focused Electron Beam Induced Deposition (FEBID)—a maskless, resistless deposition method for three dimensional (3D) nanostructures—to directly yield pure gold in a single process step, without post-deposition purification. Gold nanowires displayed resistivity down to 8.8 μΩ cm. This is the highest conductivity achieved so far from FEBID and it opens the possibility of applications in nanoelectronics, such as direct-write contacts to nanomaterials. The increased gold deposition yield and the ultralow carbon level will facilitate future applications such as the fabrication of 3D nanostructures in nanoplasmonics and biomolecule immobilization.

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A focused ion beam (FIB) instrument has been used to mill surfaces in singlecrystal Si and single-crystal Cu for subsequent electron backscattering diffraction (EBSD) analysis. The FIB cuts were performed using a 30 keV and a 5 keV Ga ϩ ion beam at a stage tilt of 20°to provide a readily obtainable 70°surface for direct EBSD investigation in a scanning electron microscope (SEM). The quality of the patterns is related to the amount of FIB damage induced in the Cu and Si. These or similar methods should be directly transferable to a FIB/SEM dual beam instrument equipped with an EBSD detector.

Ab imetallic Cu/Cu 51 Zr 14 precatalyst,a ctivated in situ, for hydrogen generation from methanol and water providesv ery high CO 2 selectivity (> 99.9 %) and high H 2 yields. Referenced to the geometrics urface area of our model surface, highera ctivity of at least one order of magnitude was observed in comparison to supportedC u/ZrO 2 and Cu/ZnO/ZrO 2 catalysts. Evolution of structurala ctivation monitored by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and electron microscopy indicatest ransformation of the bimetallic Cu/Cu 51 Zr 14 precatalyst into an active, selective, and self-stabilizing state with coexistence of dispersed Cu and partially hydroxylated tetragonal ZrO 2 .The outstanding performance is assigned to the presence of ah igh interface-site concentration following in situ decompositiono ft he intermetallic compound. These actives ites result from the cooperation of Cu, responsible for methanol activation,a nd tetragonal ZrO 2 ,w hich activates the water by surface hydroxylation.Copper-based catalysts are widely used for technical applications in methanolc hemistry,w ell-known examples include methanol synthesis from syngasw ith an optimized CO/CO 2 ratio, hydrogenation/photoreduction of CO 2 to produce "renewable" methanol, and methanol steam reforming (MSR) as the reversal of the synthesis reactionf rom CO 2.[1] The ability to control product selectivity is ak ey criterion for technical usage. Therefore, to realize the efficient on-boardp roduction of clean hydrogen in, for example, automotive applications, the key targets for MSR are high CO 2 selectivity,l ow CO content,a nd maximum H 2 yield in the reformate.[2] With respect to the catalytic functiono fZ rO 2 in MSR, the simple addition of ZrO 2 to the conventionally used Cu/ZnO catalysts overcomes the inherent drawback of purely ZnO-based catalysts,t hat is, the poor sinterings tability.[2] Beneficial synergistic effectsf or methanol synthesis have also been described for Cu/Zn and the ternary Cu/Zn/Al system prepared by ac o-precipitation technique.[3]Synergistic Cu-ZrO 2 interactions have also been reported for Cu/ZrO 2 catalysts without ZnO, involving CuÀOÀZr bonds at the phase boundary. The Cu-ZrO 2 interactions are believed to play ac rucial role in steering the methanol reforming reaction to maximum CO 2 selectivity.[4] Specifically,ananocrystalline Cu/ tetragonal ZrO 2 catalyst synthesized by ap olymer templating technique [5] was reported to be more active, selective, and stable in MSR than the technical Cu/ZnO/Al 2 O 3 methanol synthesis catalyst.[6] Although the beneficial effects of the redox chemistry of Cu and the Cu 0 /Cu oxidized ratio at the interface has been suggesteda sa ni mportants electivity descriptor,a longside disorder and strain phenomena within the metallicC u phase, [2] ac ontradictingi nfluence hasa lso been reported. Both beneficial [4a, b] and adverse [4d] effectso ft he reducibility of Cu can be found in the literature. Nevertheless, any influence appears strongly connected to the quantity...

The influence of A-and/or B-site doping of Ruddlesden−Popper perovskite materials on the crystal structure, stability, and dry reforming of methane (DRM) reactivity of specific A 2 BO 4 phases (A = La, Ba; B = Cu, Ni) has been evaluated by a combination of catalytic experiments, in situ X-ray diffraction, X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), and aberration-corrected electron microscopy. At room temperature, B-site doping of La 2 NiO 4 with Cu stabilizes the orthorhombic structure (Fmmm) of the perovskite, while A-site doping with Ba yields a tetragonal space group (I4/mmm). We observed the orthorhombic-to-tetragonal transformation above 170 °C for La 2 Ni 0.9 Cu 0.1 O 4 and La 2 Ni 0.8 Cu 0.2 O 4 , slightly higher than for undoped La 2 NiO 4 . Loss of oxygen in interstitial sites of the tetragonal structure causes further structure transformations for all samples before decomposition in the temperature range of 400 °C−600 °C. Controlled in situ decomposition of the parent or A/B-site doped perovskite structures in a DRM mixture (CH 4 :CO 2 = 1:1) in all cases yields an active phase consisting of exsolved nanocrystalline metallic Ni particles in contact with hexagonal La 2 O 3 and a mixture of (oxy)carbonate phases (hexagonal and monoclinic La 2 O 2 CO 3 , BaCO 3 ). Differences in the catalytic activity evolve because of (i) the in situ formation of Ni−Cu alloy phases (in a composition of >7:1 = Ni:Cu) for

The microstructure of the CO 2 -selective self-activating and self-stabilizing Cu-Zr bimetallic compound Cu 51 Zr 14 has been studied by a combination of high-resolution electron microscopy and energy-dispersive X-ray spectroscopy both before and after entering the CO 2 selective state in methanol steam reforming. Prior to catalysis, the phase composition of the catalyst is characterized by a microstructural mixture of Cu 51 Zr 14 and metallic Cu. The structure appears in a distinct needle-like morphology with a characteristic microstucture of small Cu particles embedded in the intermetallic matrix. In contrast, entering the CO 2 -selective state goes along with oxidative decompositioninvestigated by differential thermal analysis (DTA), thermogravimetry (TG) and mass spectrometry (MS) -and therefore massive structural and compositional changes of the Cu 51 Zr 14 compound both in the near-surface and bulk regions.The final state is then composed of a structurally very heterogeneous sample with Zr-rich and Cu-rich regions within the material bulk with a characteristic lamellar structure. Most importantly, the catalytically relevant surface regions are drastically corroded and depleted in Zr and are characterized by a majority of Cu in intimate contact with oxidized ZrO 2 exhibiting a well-ordered, predominantly tetragonal structure. This newly created Cu-ZrO 2 interface is believed to be the most significant descriptor steering the CO 2 selectivity. In due course, the new way of self-adjustment of the microstructure starting from well-defined intermetallic compounds in the catalytic reaction mixture might pave the way for a more systematic approach of controlled oxidative decomposition of intermetallic compounds acting as promising catalyst precursors.