Role of the redox state of cerium oxide on glycine adsorption: an experimental and theoretical study.

The role of the oxidation state of cerium cations in a thin oxide film in the adsorption, geometry, and thermal stability of glycine molecules was studied. The experimental study was performed for a submonolayer molecular coverage deposited in vacuum on CeO(111)/Cu(111) and CeO(111)/Cu(111) films by photoelectron and soft X-ray absorption spectroscopies and supported by calculations for prediction of the adsorbate geometries, C 1s and N 1s core binding energies of glycine, and some possible products of the thermal decomposition. The molecules adsorbed on the oxide surfaces at 25 °C in the anionic form the carboxylate oxygen atoms bound to cerium cations.

Comparison of Antibacterial Mode of Action of Silver Ions and Silver Nanoformulations With Different Physico-Chemical Properties: Experimental and Computational Studies.

The aim of this study was to compare the antibacterial mode of action of silver ions (Ag) and selected silver nanoformulations against strains ( J53, BW25113 and its derivatives: Δ A, Δ C, Δ F, Δ R, ompRG596AcusSG1130A, cusSG1130A). In this research we used various experimental methods and techniques such as determination of the minimal inhibitory concentration, flow cytometry, scanning electron microscopy, circular dichroism as well as computational methods of theoretical chemistry. Thanks to the processing of bacteria and silver samples (ions and nanoformulations), we were able to determine the bacterial sensitivity to silver samples, detect reactive oxygen species (ROS) in the bacterial cells, visualize the interaction of silver samples with the bacterial cells, and identify their interactions with proteins.

All-Oxide p-n Junction Thermoelectric Generator Based on SnO and ZnO Thin Films.

Achieving thermoelectric devices with high performance based on low-cost and nontoxic materials is extremely challenging. Moreover, as we move toward an Internet-of-Things society, a miniaturized local power source such as a thermoelectric generator (TEG) is desired to power increasing numbers of wireless sensors. Therefore, in this work, an all-oxide p-n junction TEG composed of low-cost, abundant, and nontoxic materials, such as n-type ZnO and p-type SnO thin films, deposited on borosilicate glass substrate is proposed.

Colloidal stability and catalytic activity of cerium oxide nanoparticles in cell culture media.

One of the biggest challenges for the biomedical applications of cerium oxide nanoparticles (CeNPs) is to maintain their colloidal stability and catalytic activity as enzyme mimetics after nanoparticles enter the human cellular environment. This work examines the influences of CeNP surface properties on their colloidal stability and catalytic activity in cell culture media (CCM). Near-spherical CeNPs stabilized different hydrophilic polymers were prepared through a wet-chemical precipitation method.

Cobalt Oxide-Supported Pt Electrocatalysts: Intimate Correlation between Particle Size, Electronic Metal-Support Interaction and Stability.

Oxide supports can modify and stabilize platinum nanoparticles (NPs) in electrocatalytic materials. We studied related phenomena on model systems consisting of Pt NPs on atomically defined CoO(111) thin films. Chemical states and dissolution behavior of model catalysts were investigated as a function of the particle size and the electrochemical potential by ex situ emersion synchrotron radiation photoelectron spectroscopy and by online inductively coupled plasma mass spectrometry.

Unraveling the Surface Chemistry and Structure in Highly Active Sputtered PtY Catalyst Films for the Oxygen Reduction Reaction.

Platinum is the most widely used and best performing sole element for catalyzing the oxygen reduction reaction (ORR) in low-temperature fuel cells. Although recyclable, there is a need to reduce the amount used in current fuel cells for their extensive uptake in society. Alloying platinum with rare-earth elements such as yttrium can provide an increase in activity of more than seven times, reducing the amount of platinum and the total amount of catalyst material required for the ORR.

Charge transfer and spillover phenomena in ceria-supported iridium catalysts: A model study.

Iridium-based materials are among the most active bifunctional catalysts in heterogeneous catalysis and electrocatalysis. We have investigated the properties of atomically defined Ir/CeO(111) model systems supported on Cu(111) and Ru(0001) by means of synchrotron radiation photoelectron spectroscopy, resonant photoemission spectroscopy, near ambient pressure X-ray photoelectron spectroscopy (NAP XPS), scanning tunneling microscopy, and temperature programmed desorption. Electronic metal-support interactions in the Ir/CeO(111) system are accompanied by charge transfer and partial reduction of CeO(111).

Spectroscopic Understanding of SnO and WO Metal Oxide Surfaces with Advanced Synchrotron Based; XPS-UPS and Near Ambient Pressure (NAP) XPS Surface Sensitive Techniques for Gas Sensor Applications under Operational Conditions.

The most promising and utilized chemical sensing materials, WO and SnO were characterized by means advanced synchrotron based XPS, UPS, NAP-XPS techniques. The complementary electrical resistance and sensor testing experiments were also completed. A comparison and evaluation of some of the prominent and newly employed spectroscopic characterization techniques for chemical sensors were provided.

Quantitative Analysis of the Oxidation State of Cobalt Oxides by Resonant Photoemission Spectroscopy.

Quantitative assessment of the charge transfer phenomena in cobalt oxides and cobalt complexes is essential for the design of advanced catalytic materials. We propose a method for the evaluation of the oxidation state of cobalt oxides with mixed valence states using resonant photoemission spectroscopy. The method is based on the calculation of the resonant enhancement ratio (RER) from the heights of the resonant features associated with the Co and Co states.

Sonochemical Formation of Copper/Iron-Modified Graphene Oxide Nanocomposites for Ketorolac Delivery.

A feasible sonochemical approach is described for the preparation of copper/iron-modified graphene oxide nanocomposites through ultrasonication (20 kHz, 18 W cm ) of an aqueous solution containing copper and iron ion precursors. Unique copper-, copper/iron- and iron-modified graphene oxide nanocomposites have a submicron size that is smaller than that of pristine GO and a higher surface area enriched with Cu O, CuO, and Fe O of multiform phases (α-, β-, ϵ-, or γ), FeO(OH), and sulfur- or carbon-containing compounds. These nanocomposites are sonochemically intercalated with the nonsteroidal anti-inflammatory drug ketorolac, which results in the formation of nanoscale carriers.

Enhanced absorption of TiO nanotubes by N-doping and CdS quantum dots sensitization: insight into the structure.

Anodization of titanium film sputtered on fluorine doped tin oxide (FTO) glass was performed to obtain highly ordered ∼2 μm long and ∼60 nm wide TiO nanotubes. The titania films were annealed in ammonia atmosphere to enable the doping with N. The annealing did not affect the nanotubular morphology and the porosity remained open which is a very important requirement for further deposition of CdS quantum dots.

Room-Temperature Atomic-Layer-Deposited Al O Improves the Efficiency of Perovskite Solar Cells over Time.

Electrical characterisation of perovskite solar cells consisting of room-temperature atomic-layer-deposited aluminium oxide (RT-ALD-Al O ) film on top of a methyl ammonium lead triiodide (CH NH PbI ) absorber showed excellent stability of the power conversion efficiency (PCE) over a long time. Under the same environmental conditions (for 355 d), the average PCE of solar cells without the ALD layer decreased from 13.6 to 9.

Electrifying model catalysts for understanding electrocatalytic reactions in liquid electrolytes.

Electrocatalysis is at the heart of our future transition to a renewable energy system. Most energy storage and conversion technologies for renewables rely on electrocatalytic processes and, with increasing availability of cheap electrical energy from renewables, chemical production will witness electrification in the near future. However, our fundamental understanding of electrocatalysis lags behind the field of classical heterogeneous catalysis that has been the dominating chemical technology for a long time.

Direct Conversion of Methane to Methanol on Ni-Ceria Surfaces: Metal-Support Interactions and Water-Enabled Catalytic Conversion by Site Blocking.

The transformation of methane into methanol or higher alcohols at moderate temperature and pressure conditions is of great environmental interest and remains a challenge despite many efforts. Extended surfaces of metallic nickel are inactive for a direct CH → CHOH conversion. This experimental and computational study provides clear evidence that low Ni loadings on a CeO(111) support can perform a direct catalytic cycle for the generation of methanol at low temperature using oxygen and water as reactants, with a higher selectivity than ever reported for ceria-based catalysts.

Structure-Dependent Dissociation of Water on Cobalt Oxide.

Understanding the correlation between structure and reactivity of oxide surfaces is vital for the rational design of catalytic materials. In this work, we demonstrate the exceptional degree of structure sensitivity of the water dissociation reaction for one of the most important materials in catalysis and electrocatalysis. We studied HO on two atomically defined cobalt oxide surfaces, CoO(100) and CoO(111).

In situ electrochemical AFM monitoring of the potential-dependent deterioration of platinum catalyst during potentiodynamic cycling.

A platinum catalyst undergoes complex deterioration process during its operation as a cathode in a proton exchange membrane fuel cell. By using in situ electrochemical atomic force microscopy (EC-AFM) with super-sharp probes, we quantitatively describe the roughening of platinum thin films during electrochemical cycling to different upper potentials, which simulate critical operation regimes of the proton exchange membrane fuel cell. The comprehensive quantitative analysis of morphology changes obtained using common roughness descriptors such as the root mean square roughness, the correlation length and the roughness exponent is correlated with cyclic voltammetry performed simultaneously.

An experimental and theoretical study of adenine adsorption on Au(111).

A model study of adenine adsorption on the Au(111) surface is reported for molecular adlayers prepared by evaporation in vacuum and deposition from saturated aqueous solution. The electronic structure and adsorption geometry of the molecular films were studied experimentally by X-ray photoelectron spectroscopy and near edge X-ray absorption fine structure spectroscopy. Adsorption models are proposed for the adlayers arising from the different preparation methods.

In Situ Investigation of Methane Dry Reforming on Metal/Ceria(111) Surfaces: Metal-Support Interactions and C-H Bond Activation at Low Temperature.

Studies with a series of metal/ceria(111) (metal=Co, Ni, Cu; ceria=CeO ) surfaces indicate that metal-oxide interactions can play a very important role for the activation of methane and its reforming with CO at relatively low temperatures (600-700 K). Among the systems examined, Co/CeO (111) exhibits the best performance and Cu/CeO (111) has negligible activity. Experiments using ambient pressure X-ray photoelectron spectroscopy indicate that methane dissociates on Co/CeO (111) at temperatures as low as 300 K-generating CH and CO species on the catalyst surface.

Exploiting micro-scale structural and chemical observations in real time for understanding chemical conversion: LEEM/PEEM studies over CeO-Cu(111).

Proper consideration of length-scales is critical for elucidating active sites/phases in heterogeneous catalysis, revealing chemical function of surfaces and identifying fundamental steps of chemical reactions. Using the example of ceria thin films deposited on the Cu(111) surface, we demonstrate the benefits of multi length-scale experimental framework for understanding chemical conversion. Specifically, exploiting the tunable sampling and spatial resolution of photoemission electron microscopy, we reveal crystal defect mediated structures of inhomogeneous copper-ceria mixed phase that grow during preparation of ceria/Cu(111) model systems.

Mass Spectrometry of Polymer Electrolyte Membrane Fuel Cells.

The chemical analysis of processes inside fuel cells under operating conditions in either direct or inverted (electrolysis) mode and their correlation with potentiostatic measurements is a crucial part of understanding fuel cell electrochemistry. We present a relatively simple yet powerful experimental setup for online monitoring of the fuel cell exhaust (of either cathode or anode side) downstream by mass spectrometry. The influence of a variety of parameters (composition of the catalyst, fuel type or its concentration, cell temperature, level of humidification, mass flow rate, power load, cell potential, etc.

Experimental and Theoretical Investigation of the Restructuring Process Induced by CO at Near Ambient Pressure: Pt Nanoclusters on Graphene/Ir(111).

The adsorption of CO on Pt nanoclusters grown in a regular array on a template provided by the graphene/Ir(111) Moiré was investigated by means of infrared-visible sum frequency generation vibronic spectroscopy, scanning tunneling microscopy, X-ray photoelectron spectroscopy from ultrahigh vacuum to near-ambient pressure, and ab initio simulations. Both terminally and bridge bonded CO species populate nonequivalent sites of the clusters, spanning from first to second-layer terraces to borders and edges, depending on the particle size and morphology and on the adsorption conditions. By combining experimental information and the results of the simulations, we observe a significant restructuring of the clusters.

Adsorption of ethylene on Sn and In terminated Si(001) surface studied by photoelectron spectroscopy and scanning tunneling microscopy.

Interaction of ethylene (C2H4) with Si(001)-Sn-2 × 2 and Si(001)-In-2 × 2 at room temperature has been studied using core level (C 1s) X-ray photoelectron spectroscopy with synchrotron radiation and scanning tunneling microscopy. Sn and In form similar dimer chains on Si(001)2 × 1, but exhibit different interaction with ethylene. While ethylene adsorbs on top of Sn dimers of the Si(001)-Sn-2 × 2 surface, the Si(001)-In-2 × 2 surface turned out to be inert.

Efficient Ceria-Platinum Inverse Catalyst for Partial Oxidation of Methanol.

Ceria-platinum-based bilayered thin films deposited by magnetron sputtering were developed and tested in regard to their catalytic activity for methanol oxidation by employing a temperature-programmed reaction (TPR) technique. The composition and structure of the samples were characterized by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Both conventional (oxide-supported metal nanoparticles [NPs]) and inverse configurations (metal with oxide overlayer) were analyzed to uncover the structural dependence of activity and selectivity of these catalysts with respect to different pathways of methanol oxidation.

Ambient pressure XPS and IRRAS investigation of ethanol steam reforming on Ni-CeO2(111) catalysts: an in situ study of C-C and O-H bond scission.

Ambient-Pressure X-ray Photoelectron Spectroscopy (AP-XPS) and Infrared Reflection Absorption Spectroscopy (AP-IRRAS) have been used to elucidate the active sites and mechanistic steps associated with the ethanol steam reforming reaction (ESR) over Ni-CeO2(111) model catalysts. Our results reveal that surface layers of the ceria substrate are both highly reduced and hydroxylated under reaction conditions while the small supported Ni nanoparticles are present as Ni(0)/NixC. A multifunctional, synergistic role is highlighted in which Ni, CeOx and the interface provide an ensemble effect in the active chemistry that leads to H2.

Creating single-atom Pt-ceria catalysts by surface step decoration.

Single-atom catalysts maximize the utilization of supported precious metals by exposing every single metal atom to reactants. To avoid sintering and deactivation at realistic reaction conditions, single metal atoms are stabilized by specific adsorption sites on catalyst substrates. Here we show by combining photoelectron spectroscopy, scanning tunnelling microscopy and density functional theory calculations that Pt single atoms on ceria are stabilized by the most ubiquitous defects on solid surfaces--monoatomic step edges.