Mixed bimetallic oxides offer great opportunities for a systematic tuning of electrocatalytic activity and stability. Here, we demonstrate the power of this strategy using well-defined thermally prepared Ir-Ni mixed oxide thin film catalysts for the electrochemical oxygen evolution reaction (OER) under highly corrosive conditions such as in acidic proton exchange membrane (PEM) electrolyzers and photoelectrochemical cells (PEC). Variation of the Ir to Ni ratio resulted in a volcano type OER activity curve with an unprecedented 20-fold improvement in Ir mass-based activity over pure Ir oxide. In situ spectroscopic probing of metal dissolution indicated that, against common views, activity and stability are not directly anticorrelated. To uncover activity and stability controlling parameters, the Ir-Ni mixed thin oxide film catalysts were characterized by a wide array of spectroscopic, microscopic, scattering, and electrochemical techniques in conjunction with DFT theoretical computations. By means of an intuitive model for the formation of the catalytically active state of the bimetallic Ir-Ni oxide surface, we identify the coverage of reactive surface hydroxyl groups as a suitable descriptor for the OER activity and relate it to controllable synthetic parameters. Overall, our study highlights a novel, highly active oxygen evolution catalyst; moreover, it provides novel important insights into the structure and performance of bimetallic oxide OER electrocatalysts in corrosive acidic environments.

The morphology, crystallinity, and chemical state of well-defined Ir oxide nanoscale thin-film catalysts prepared on Ti substrates at various calcination temperatures were investigated. Special emphasis was placed on the calcination temperature-dependent interaction between Ir oxide film and Ti substrate and its impact on the electrocatalytic oxygen evolution reaction (OER) activity. The Ir oxide films were characterized by scanning electron microscopy, transmission electron microscopy, scanning transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and cyclic voltammetry. Furthermore, temperature programmed reduction (TPR) was applied to study the Ir oxide species formed as function of calcination temperature and its interaction with the Ti substrate.A previously unachieved correlation between the electrocatalytic OER activity and the nature and structural properties of the Ir oxide film was established. We find that the crystalline high temperature Ir oxide species is detrimental, whereas low temperature amorphous Ir oxy-hydroxides are highly active and efficient catalysts for OER. Moreover, at the highest applied calcination temperature (550°C), Ti oxides, originating from the substrate, strongly affect chemical state and electrocatalytic OER activity of the Ir oxide film.

Because of the rising application of nanoparticles in food and food-related products, we investigated the influence of the digestion process on the toxicity and cellular uptake of silver nanoparticles for intestinal cells. The main food components--carbohydrates, proteins and fatty acids--were implemented in an in vitro digestion process to simulate realistic conditions. Digested and undigested silver nanoparticle suspensions were used for uptake studies in the well-established Caco-2 model. Small-angle X-ray scattering was used to estimate particle core size, size distribution and stability in cell culture medium. Particles proved to be stable and showed radii from 3.6 to 16.0 nm. Undigested particles and particles digested in the presence of food components were comparably taken up by Caco-2 cells, whereas the uptake of particles digested without food components was decreased by 60%. Overall, these findings suggest that in vivo ingested poly (acrylic acid)-coated silver nanoparticles may reach the intestine in a nanoscaled form even if enclosed in a food matrix. While appropriate for studies on the uptake into intestinal cells, the Caco-2 model might be less suited for translocation studies. Moreover, we show that nanoparticle digestion protocols lacking food components may lead to misinterpretation of uptake studies and inconclusive results.

A 5% Ni/MnO catalyst has been tested for the dry reforming of methane at different temperatures and reactant partial pressures. Changing the reactant ratio with time on stream results in a decrease in the deactivation rate of the catalyst. Graphitic carbon growth and metal particle sintering have been observed by applying in situ transmission XRD using synchrotron radiation under actual reaction conditions. Both methane and carbon monoxide separately result in graphitic surface carbon, which can then be oxidized by carbon dioxide. The morphology of the surface carbon has been analyzed by TEM, and the reactions of both methane and carbon monoxide result in the same graphitic multiwalled carbon nanotubes. The present combination of catalytic experiments and in situ techniques suggests that surface carbon acts as an intermediate in the formation of CO and that catalyst deactivation happens via metallic particle sintering. These results enable a more rational choice of reaction conditions to ensure high catalyst activity and long-term stability. Future catalyst advances must aim to prevent metal particle sintering.

Design and synthesis of ordered, metal-free layered materials is intrinsically difficult due to the limitations of vapor deposition processes that are used in their making. Mixed-dimensional (2D/3D) metal-free van der Waals (vdW) heterostructures based on triazine (C N ) linkers grow as large area, transparent yellow-orange membranes on copper surfaces from solution. The membranes have an indirect band gap (E = 1.91 eV, E = 1.84 eV) and are moderately porous (124 m g ). The material consists of a crystalline 2D phase that is fully sp hybridized and provides structural stability, and an amorphous, porous phase with mixed sp -sp hybridization. Interestingly, this 2D/3D vdW heterostructure grows in a twinned mechanism from a one-pot reaction mixture: unprecedented for metal-free frameworks and a direct consequence of on-catalyst synthesis. Thanks to the efficient type I heterojunction, electron transfer processes are fundamentally improved and hence, the material is capable of metal-free, light-induced hydrogen evolution from water without the need for a noble metal cocatalyst (34 µmol h g without Pt). The results highlight that twinned growth mechanisms are observed in the realm of "wet" chemistry, and that they can be used to fabricate otherwise challenging 2D/3D vdW heterostructures with composite properties.