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David Rutherford,1 Jaroslav Jíra,1 Kateřina Kolářová,2 Iva Matolínová,3 Júlia Mičová,4 Zdenek Remeš,2 Bohuslav Rezek1 1Faculty of Electrical Engineering, Czech Technical University, Prague, Czech Republic; 2Author Affiliations Institute of Physics, Czech Academy of Sciences, Prague, Czech Republic; 3Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic; 4Institute of Chemistry, Slovak Academy of Sciences, Bratislava, Slovak RepublicCorrespondence: David RutherfordFaculty of Electrical Engineering, Czech Technical University, Technická 2, Prague, 6, Czech RepublicTel +420 224 352 334Email david.rutherford@fel.cvut.czPurpose: Nanomaterials for antimicrobial applications have gained interest in recent years due to the increasing bacteria resistance to conventional antibiotics. Wound sterilization, water treatment and surface decontamination all avail from multifunctional materials that also possess excellent antibacterial properties, eg zinc oxide (ZnO). Here, we assess and compare the effects of synthesized hedgehog-like ZnO structures and commercial ZnO particles with and without mixing on the inactivation of bacteria on surfaces and in liquid environments.Methods: Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria in microbial culture medium were added to reverse spin bioreactors that contained different concentrations of each ZnO type to enable dynamic mixing of the bacteria-ZnO suspensions. Optical density of the bacteria-ZnO suspensions was measured in real-time and the number of viable bacteria after 24 h exposure was determined using standard microbiological techniques. The concentration of zinc ion generated from ZnO dissolution in different liquid types was estimated from the dynamic interaction exposure. Static antibacterial tests without agitation in liquid media and on agar surface were performed for comparison.Results: A correlation between increasing ZnO particle concentration and reduction in viable bacteria was not monotonous. The lowest concentration tested (10 μg/mL) even stimulated bacteria growth. The hedgehog ZnO was significantly more antibacterial than commercial ZnO particles at higher concentrations (up to 1000 μg/mL tested), more against E. coli than S. aureus. Minimum inhibitory concentration in microwell plates was correlated with those results. No inhibition was detected for any ZnO type deposited on agar surface. Zinc ion release was greatly suppressed in cultivation media. Scanning electron microscopy images revealed that ZnO needles can pierce membrane of bacteria whereas the commercial ZnO nanoparticles rather agglomerate on the cell surface.Conclusion: The inhibition effects are thus mainly controlled by the interaction dynamics between bacteria and ZnO, where mixing greatly enhances antibacterial efficacy of all ZnO particles. The efficacy is modulated also by ZnO particle shapes, where hedgehog ZnO has superior effect, in particular at lower concentrations. However, at too low concentrations, ZnO can stimulate bacteria growth and must be thus used with caution.Keywords: antibacterial, biotechnology, nanomaterials, zinc oxide

The work is devoted to obtaining of transparent nanocomposite materials as low loss, highly thermally conductive materials for potential laser applications. We report Ho3+:Y2O3–MgO nanocomposite ceramics with excellent mechanical and optical properties by combining glycine-nitrate process and spark plasma sintering. Morphology, structural-phase state, infrared transmittance and luminescence depending on the holmium concentration (0–12 at.%) were studied for the first time. It was found that optical transmittance reaches 75%@6000 nm for 3 at.% Ho3+:Y2O3–MgO ceramics. The absorption cross-section at 1931 nm and the emission cross-section at 2118 nm were determined to be σabs = 0.51 × 10−20 cm2 and σem = 0.29 × 10−20 cm2, respectively. Based on the testing results of luminescent characteristics it was demonstrated that Ho3+:Y2O3–MgO nanocomposite is a promising material for high-power eye-safe lasers operating in the 2 μm wavelength range.

Currently, platinum is the most widely used catalyst for low temperature proton exchange membrane fuel cells (PEMFC). However, the kinetics at the cathode are slow, and the price of platinum is high. To improve oxygen reduction reaction (ORR) kinetics at the cathode, platinum can be alloyed with rare earth elements, such as yttrium. We report that Pt3Y has the potential to be over 2 times more active for the ORR compared with Pt inside a real fuel cell. We present detailed photoemission analysis into the nature of the sputtered catalyst surface, using synchrotron radiation photoelectron spectroscopy (SRPES) to examine if surface adsorbates or impurities are present and can be removed. Pretreatment removes most of the yttrium oxide in the surface leaving behind a Pt overlayer which is only a few monolayers thick. Evidence of a substochiometric oxide peak in the Y 3d core level is presented, this oxide extends into the surface even after Ar+ sputter cleaning in-situ. This information will aid the development of new highly active nanocatalysts for employment in real fuel cell electrodes.

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. As yttrium is easily oxidized, exposure of the Pt-Y catalyst layer to air causes the formation of an oxide layer that can be removed during acid treatment, leaving behind a highly active pure platinum overlayer. This paper presents an investigation of the overlayer composition and quality of Pt3Y films sputtered from an alloy target. The Pt3Y catalyst surface is investigated using synchrotron radiation X-ray photoelectron spectroscopy before and after acid treatment. A new substoichiometric oxide component is identified. The oxide layer extends into the alloy surface, and although it is not completely removed with acid treatment, the catalyst still achieves the expected high ORR activity. Other surface-sensitive techniques show that the sputtered films are smooth and bulk X-ray diffraction reveals many defects and high microstrain. Nevertheless, sputtered Pt3Y exhibits a very high activity regardless of the film's oxide content and imperfections, highlighting Pt3Y as a promising catalyst. The obtained results will help to support its integration into fuel cell systems.

In this work, we present a complex study of photoregeneration of a zinc phthalocyanine (ZnPc) sensor by illumination from light-emitting diodes (LEDs). It includes an investigation of photoregeneration effectivity for various wavelengths (412–723 nm) of incident light carried out at sensor operating temperatures of 55 °C. It is demonstrated that the efficiency of photoregeneration is increasing with a decrease in the light wavelength. In the region of longer wavelengths (723–630 nm), the regeneration degree (RD) was low and ranged from 12% to 15%. In the region of shorter wavelengths (518–412 nm), the RD rose from 35% for 518 nm to 94% for 412 nm. The efficiency of photoregeneration is also shown to be higher in comparison with the temperature regeneration efficiency. In order to understand the chemism of photoregeneration processes, the electrical measurements are supplemented with Raman and near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) studies. The spectroscopic results showed that nitrogen dioxide bonds to the Zn atom in ZnPc in the form of NO2− and NO−, i.e., partial decomposition of NO2 molecules occurs during the interaction with the surface. NAP-XPS spectra proved that light illumination of the ZnPc surface is essential for almost complete desorption of NOx species. At the same time, it is demonstrated that in case of long-time exposure or exposure of a ZnPc chemiresistor with a high concentration of NO2, the oxygen, released due to the NO2 decomposition, slowly but irreversibly oxidizes the layer. This oxidation process is most probably responsible for the sensor deactivation observed in sensor experiments with high NO2 concentrations. Based on these studies, the mechanism of nitrogen dioxide interaction with zinc phthalocyanine both under LED illumination and in dark conditions is proposed, and a special method for the sensor operation called “constant exposure dose” is established.

The aim of this study was to compare the antibacterial mode of action of silver ions (Ag+) and selected silver nanoformulations againstE. colistrains (E. coliJ53,Escherichia coliBW25113 and its derivatives: ΔompA, ΔompC, ΔompF, ΔompR, 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. Differences between the mode of action of silver ions and nanoformulations and the action of nanoformulations themselves were revealed. Based on the results of computational methods, we proposed an explanation of the differences in silver-outer protein interaction between silver ions and metallic silver; in general, the Ag0complexes exhibit weaker interaction than Ag+ones. Moreover, we identified two gutter-like areas of the inner layer of the ion channel: one more effective, with oxygen-rich side chains; and another one less effective, with nitrogen-rich side chains.

Dependence on noble metal catalysts is considered to be the main factor which hinders wider commercialization of proton exchange membrane fuel cells (PEM-FCs) and water electrolyzers (PEM-WEs). One way of lowering the loading of Pt and Ir is by using thin-film techniques for their deposition onto the high-surface conductive nanoparticles. Another approach, which is convenient in applications where the complete cycle of electricity - > H2 - > electricity takes place, is merging the PEM-WEs and PEM-FCs into one bi-functional system – the unitized regenerative fuel cell (PEM-URFC). In accordance with the above mentioned conception, this paper revolves around unconventionally prepared bi-functional magnetron sputtered lower-loading Pt-Ir catalysts for the anode side of PEM-URFC. Two geometries of catalyst coated membranes (CCM) were compared, differing in relative positioning of individual Pt and Ir thin films sputtered on TiC-based support sublayer; the sandwich-like Ir/TiC/Pt structure and the co-sputtered Pt-Ir/TiC structure. Wide arsenal of analytical methods, ranging from photoelectron spectroscopy to electrochemical atomic force microscopy determined that co-sputtering of Pt and Ir leads to alloy formation, thus preventing iridium to fully electro-oxidize to IrOx which in turn helps to explain why sandwich-like Ir/TiC/Pt structure, with no alloy, outperforms the co-sputtered Pt-Ir/TiC CCM in both operational regimes despite having the exactly same noble metal loading. The PEM-URFC single cell with sandwich-like bi-functional anode catalyst yielded 31.8% of round-trip efficiency at 1 A cm−2 in comparison to 34.2% achieved by combination of single-purpose cells with more than double the loading of noble metals.

Ceria represents a technologically indispensable reducible catalyst support. Besides the general impact on the surface chemistry, the oxygen content of the ceria surface directly influences the dispersion of ceria-supported metal nanoparticles, and the properties of ceria-supported metal catalysts. We investigate the role of oxygen atoms on a CeO2(111) surface in supporting Pt as smallest metallic Pt clusters or, concurrently, as monodispersed Pt2+ ions. We demonstrate that the necessary condition for the formation of Pt2+ ions is the availability of lattice O or excess O atoms at surface step edges. Although Pt2+ ions can exist on partially reduced surfaces, excess O atoms are required to maximize the capacity of the surface to accommodate Pt2+ and to trigger the redispersion of metallic Pt clusters. Our study provides atomic-level understanding and control of the highest dispersions of Pt on the ceria surface for advancing the state-of-the-art Pt/ceria catalysts that are presently identified at the verge of single-atom Pt dispersion.

Electrical characterisation of perovskite solar cells consisting of room-temperature atomic-layer-deposited aluminium oxide (RT-ALD-Al2 O3 ) film on top of a methyl ammonium lead triiodide (CH3 NH3 PbI3 ) 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 9.6 %, whereas that of solar cells containing 9 ALD cycles of depositing RT-ALD-Al2 O3 on top of CH3 NH3 PbI3 increased from 9.4 to 10.8 %. Spectromicroscopic investigations of the ALD/perovskite interface revealed that the maximum PCE with the ALD layer is obtained when the so-called perovskite cleaning process induced by ALD precursors is complete. The PCE enhancement over time is probably related to a self-healing process induced by the RT-ALD-Al2 O3 film. This work may provide a new direction for further improving the long-term stability and performance of perovskite solar cells.

PtCu bimetallic alloys are known to provide better activity than pure platinum in proton exchange membrane fuel cells. However, such catalysts undergo complex degradation processes during fuel cell operation, resulting in deterioration of their activity. By using in situ electrochemical (EC) atomic force microscopy combined with in situ EC infrared reflection absorption spectroscopy, we provide a comprehensive investigation of morphological and structural transformations of PtCu model thin film catalysts during accelerated degradation tests (ADTs). The ADTs consist of potentiodynamic cycling to three different upper potentials relevant for different modes of fuel cell operation. The results show that, depending on the upper potential limit, PtCu alloy electrocatalysts are subject to drastic changes in the surface composition, morphology, and structure.

Reactions of reduced cerium oxide CeOx with water are fundamental processes omnipresent in ceria-based catalysis. Using thin epitaxial films of ordered CeOx, we investigate the influence of oxygen vacancy concentration and coordination on the oxidation of CeOx by water. Upon changing the CeOx stoichiometry from CeO2 to Ce2O3, we observe a transition from a slow surface reaction to a productive H2-evolving CeOx oxidation with reaction yields exceeding the surface capacity and indicating the participation of bulk OH species. Both the experiments and the ab initio calculations associate the effective oxidation of highly reduced CeOx by water to the next-nearest-neighbor oxygen vacancies present in the bixbyite c-Ce2O3 phase. Next-nearest-neighbor oxygen vacancies allow for the effective incorporation of water in the bulk via formation of OH- groups. Our study illustrates that the coordination of oxygen vacancies in CeOx represents an important parameter to be considered in understanding and improving the reactivity of ceria-based catalysts.

The adsorption of adenine, one of the structural units of DNA and RNA, on nanostructured cerium oxide was studied using synchrotron radiation based techniques: photoelectron and X-ray absorption spectroscopies. Using a systematic approach, we studied this biomolecule’s bonding to the inorganic surface and examined the effects of different stoichiometry, morphology and composition of cerium oxide films, as well as two methods of molecular deposition (evaporation in vacuum and deposition from aqueous solution). The adenine molecule chemisorbs on the stoichiometric (IV) cerium oxide intact via nitrogen atoms, independent of the oxide morphology and deposition technique. Annealing of the adenine adlayer at 250 °C causes CeO2 surface partial reduction, along with the partial deprotonation of the nitrogen. The reaction of adenine with ex situ prepared CeO2 films (nanostructured compact and porous) activates Ce4+ cation reduction not only on the surface but also in the subsurface layers accompanied by water deso...

Electron beam lithography was used to fabricate platinum μ-contacts over tungsten oxide nanorods formed on a mica substrate. This made possible the measurement of sensorial response of these self-assembled tungsten oxide nanorods to hydrogen gas for the first time. The nanorods were prepared by thermal evaporation from an oxide source. Consequently, two types of conductometric sensors were assembled: a) percolating network of nanorods and b) set of individually contacted WO3 nanorods. The preparation procedures are described in detail and the comparison of response of both types of assemblies is given. The first sensorial measurements revealed a good response of the b) type of sensor and the minimum repeatedly detected concentration of H2 was 50 ppm.

A new method based on transformation of magnetron sputtered platinum thin films into platinum nanostructures enclosed by high-index facets, using electrochemical potential cycling in a twin working electrode system is reported. The controllable formation of various Pt nanostructures, described in this paper, indicates that this method can be used to control a selective growth of high purity Pt nanostructures with specific shapes (facets or edges). The method opens up new possibilities for electrochemical preparation of nanostructured Pt catalysts at high yield.

Simultaneous mass production of high quality vertically oriented graphene nanostructures and doping them by using an inductively coupled plasma chemical vapor deposition (ICP CVD) is a technological problem because little is understood about their growth mechanism over enlarged surfaces. We introduce a new method that combines the ICP CVD with roll-to-roll technology to enable the in-situ preparation of vertically oriented graphene by using propane as a precursor gas and nitrogen or silicon as dopants. This new technology enables preparation of vertically oriented graphene with distinct morphology and composition on a moving copper foil substrate at a lower cost. The technological parameters such as deposition time (1&ndash, 30 min), gas partial pressure, composition of the gas mixture (propane, argon, nitrogen or silane), heating treatment (1&ndash, 60 min) and temperature (350&ndash, 500 &deg, C) were varied to reveal the nanostructure growth, the evolution of its morphology and heteroatom&rsquo, s intercalation by nitrogen or silicon. Unique nanostructures were examined by FE-SEM microscopy, Raman spectroscopy and energy dispersive X-Ray scattering techniques. The undoped and nitrogen- or silicon-doped nanostructures can be prepared with the full area coverage of the copper substrate on industrially manufactured surface defects. Longer deposition time (30 min, 450 &deg, C) causes carbon amorphization and an increased fraction of sp3-hybridized carbon, leading to enlargement of vertically oriented carbonaceous nanostructures and growth of pillars.

In today´s developed world, there is a huge pressure on increasing the amount of electricity produced by renewable sources. With growing percentage of electricity from wind and solar power plants, new challenges arise. The biggest issue seems to be the instability of generated electricity during the days. Possible solution can be offered by Proton Exchange Membrane Water Electrolyzers (PEM-WE) and Proton Exchange Membrane Fuel Cell (PEM-FC) through electricity-hydrogen-electricity conversion cycle. Although PEM-WE technology is well suited for scale-up, one major drawback – its dependence on noble metal catalysts remains to be solved. Both, Ir on the anode and Pt on the cathode, which are traditionally used, are extremely rare and expensive, thus their partial replacement by other materials can lead to the noticeable decrease of PEM-WE price. More focus is usually laid on the anodic oxygen evolution reaction (OER) which is catalytically much more demanding. Ruthenium catalyst appears to be an interesting alternative due to its high activity towards OER. However, low electrochemical stability of Ru renders it inapplicable in its pure form. This problem can be solved by using mixed iridium-ruthenium catalyst which benefits from stability of iridium and from the lower price and high activity of ruthenium. In this work we present magnetron sputtered thin-film iridium-ruthenium mixed catalyst for the OER on the anode of PEM-WE. Magnetron sputtering is a mean of catalyst deposition which allows the preparation of a thin films of exact concentration and thickness. Moreover, it is also possible to use it on industrial scales. Usage of magnetron sputtering provides several important advantages. Firstly, we are able to cut down the amount of used catalyst significantly -- usually 10 times less than in the case of powder catalyst. Secondly, it is possible to prepare small systems for detailed electrochemical and surface analysis and also bigger systems for testing of our catalysts at real electrolyzer. This allows us to narrow the gap between the model and controlled studies and real industrial systems. In our work, we present four concentration of mixed iridium-ruthenium catalyst prepared by magnetron sputtering. Each catalyst was prepared either on Glassy Carbon electrode, or on Nafion® NR212. Measurement on Nafion® NR212 helps us to pick the industrially most suitable candidate. Measurements on the Glassy Carbon electrodes allows to investigate the activity and stability of given catalysts and correlate it with their structural and chemical properties. Numerous techniques were used, specifically Rotation Disk Electrode (RDE), Potential Electrochemically Impedance Spectroscopy (PEIS), Scanning Electron Microscopy, Energy Dispersive X-Ray spectroscopy (EDX), X-Ray Photoelectron Spectroscopy (XPS) and X-Ray Diffraction (XRD). Combination of these techniques revealed that 25:75 Ir:Ru sputtered thin-film catalyst outperforms the benchmark pure Ir counterpart while retaining comparable electrochemical stability. Figure 1

Proton-exchange membrane fuel cell (PEMFC) performance is strongly related to the complex transport of gas and charge carriers in the cathode catalyst layer. Thus, we investigated the transport properties of catalyst layers at different ionomer/carbon ratios, ranging from 0.1 to 1, focusing on oxygen, proton and electron transport. Oxygen transport was studied using the limiting current technique, separately analyzing the contributions of molecular, Knudsen, and ionomer transport resistances by changing the temperature and gas pressure. The proton and electron resistance of the catalyst layers were determined by impedance spectroscopy and current-voltage measurements, respectively. The results showed that the performance of fuel cells can be enhanced by selecting a suitable ionomer/carbon ratio and that increasing the ionomer content decreases the proton resistance and increases the electron resistance of catalyst layers. Accordingly, low oxygen transport and proton resistance at an ionomer/carbon ratio of 0.6 (26.5%wt.) led to the highest fuel cell power density (595 mW cm−2). These results fully support well-established in numerous works optimal ionomer content, revealing the underlying mechanisms of high fuel cell performance. Furthermore, the porosimetry results and electron microscopy measurements confirmed that transport properties strongly affect fuel cell performance.

This study used non-reactive magnetron sputtered polycrystalline cerium oxide thin films as model substrates to mimic the surface morphology of cerium oxide nanoparticles. We investigated the interaction between dextran and polycrystalline cerium oxide surfaces by atomic force microscopy, X-ray photoelectron spectroscopy, and reflection-absorption infrared spectroscopy. A simplified sample preparation method probing solid-liquid interface was set up by conducting aqueous adsorption procedures in an argon-filled glove bag connected to an ultra-high vacuum chamber. We found that the adsorption of dextran from aqueous solution onto the polycrystalline cerium oxide surface leads to a mutual charge transfer between dextran and cerium ions, creating a surface accumulation of Ce3+. In the aqueous environment, dextran hydroxyl groups adsorbs on the polycrystalline cerium oxide surface competitively with the dissociated hydroxyl groups from water. By investigating glucose adsorbed onto polycrystalline ceria prepared by physical vapor deposition, we further confirmed the role of hydroxyl groups from polysaccharide during interaction with ceria. Thermal annealing of the dextran adsorbed polycrystalline cerium oxide surface results in desorption of weakly bonded dextran below 100 °C and decomposition of dextran above 100 °C.

The progress in the design of a perspective alloy catalyst relies on correct interpretation of its photoelectron spectra. Particularly, X-ray photoelectron spectroscopic (XPS) analysis of platinum-copper alloys represents a serious challenge for both qualitative and quantitative analyses due to the complexity of the Pt 4f spectra arising from its overlapping with the Cu 3p region. Studies regarding XPS investigation of Pt-Cu alloys often ignore the Cu 3p contribution while fitting Pt 4f spectra, which leads to partially incorrect interpretation of measured XPS data. This is most noticeable for alloys containing more than 50 % of platinum where the low-intensity Cu 3p core levels can be hidden under a more intense contribution of Pt 4f. In this work, we present the correct way of processing photoemission spectra of such systems. First, we thoroughly examine the XPS Cu 3p spectra of pure copper surfaces of different oxidation states, namely Cu°, Cu+, and Cu2+. Then, the obtained results are applied for the fitting of Pt 4f spectra of both metallic and oxidized Pt-Cu systems. The precise curve-fitting and data analysis procedure showcased in this study can be utilized to eliminate uncertainties in the analysis of Pt-Cu photoemission spectra.

Candle soot deposited from the candle flame was used as a catalyst support for an anode catalyst in a proton exchange membrane fuel cell. The results showed that Pt/soot hybrids prepared by magnetron sputtering of 5 nm platinum films on candle soot exhibit very high mass activity in the fuel cell, which is more than one order of magnitude higher than that for commercial catalyst. The elementary preparation, high surface-to-volume ratio, good conductivity and hydrophobicity make candle soot a promising type of the support for PEMFCs catalyst.

In this study, we report transmission electron microscopy and electron energy loss spectroscopy study of cerium oxide thin layer grown on graphite foil substrate by direct liquid injection chemical vapour deposition. Transmission electron microscopy experiments have revealed the porous morphology of the deposited layer. Energy electron loss spectroscopy measurements were also performed in scanning mode to study the evolution of the cerium valence. In addition to Ce 4+ inside the layer, the presence of reduced cerium oxide with Ce 3+ valence is pointed out at the layer surface and at the surface of the porosity developed by the layer. Besides, studies of high resolution images coupled to electron energy loss spectroscopy have indicated the presence of crystallized ceria nanoparticles, and the absence of cerium carbide.

In this work changes in surface chemistry and morphology of PtNi alloy induced by redox environments were investigated by photoelectron spectroscopy, atomic force microscopy and substantiated by theoretical calculations. PtNi was exposed to alternating oxidation (O2) and reduction (H2) gaseous atmospheres at different temperatures (298, 373, 523 K) to simulate its behavior as a cathode catalyst in proton exchange membrane fuel cells. Results showed that the PtNi alloy undergoes surface nickel enrichment under switched reactive environments. The most significant effects occurred at 523 K, when the Ni/Pt surface atomic ratio increased from 0.8 to 6.7 after five redox cycles, while the bulk Ni/Pt value reached 2.3. Along with compositional changes catalyst coarsening was observed. The revealed behavior of the PtNi alloy allows a better understanding of the structural dynamics of a bimetallic catalyst during its interaction with reactive environments that is a prerequisite for development of efficient fuel cell catalyst.

Fuel cells (FCs) are on the path to become a viable technology of clean and efficient power in the upcoming future. Especially, hydrogen-fueled Proton Exchange Membrane Fuel Cells (PEMFCs) are on the rise of practical applications. Yet, several factors limit the extensive commercialization of these FCs. The main obstacle is the high cost of platinum that is by far the most effective element used for FC catalysts. In addition, the short lifetime of FCs due to the degradation of the catalyst support and the catalyst itself is also a severe constraint. It is essential to overcome these limitations, and thus, the catalyst-support interface is of our primary concern for good FC efficiency. Herein, we deal with the study of cerium oxide (CeOx)-based catalyst enriched by platinum deposited on nitrogenated carbon (CNx) support via magnetron sputtering in an oxygen/argon atmosphere. The chosen method of preparation, magnetron sputtering, constitutes a fast and inexpensive way of preparing the high-surface-area nanostructured catalytic film [1]. The model studies of planar samples focused on variations of morphology and structure of Pt-CeOx layer due to the presence of the carbonaceous interlayers with different compositions are demonstrated in Fig. 1 by using Transmission Electron Microscopy (TEM). While for amorphous carbon (a-C), the slightly porous columnar structure is observed (Fig. 1a), in the case of CNx interlayer (Fig. 1b), the surface morphology is modified into the form of individual needles. Spectroscopy techniques, namely X-ray Photoelectron Spectroscopy and Electron Energy Loss Spectroscopy, reveal an important role of nitrogen incorporated in the CNx interlayer that enables formation of very porous surface structures. The model system with the largest achievable surface is chosen as a pattern for further improvement of the commercially available gas diffusion layer (GDL). By applying the CNx thin interlayer on top of the GDL support (Fig. 1d), the surface area of the Pt-CeOx catalyst is enlarged (Fig. 1e and f), as it is visible by Scanning Electron Microscopy (SEM) and TEM. In addition, it is demonstrated that tuning of catalyst film morphology provides a viable strategy towards higher performance in the PEMFC tests (Fig. 1g), complemented by better corrosion resistance of CNx interlayers under the start-up conditions of fuel cells [2]. Fig. 1 TEM cross-sectional micrographs of Pt-CeOx layers on the carbonaceous interlayers supported by a silicon substrate: CeOx /a-C (a), CeOx/CNx (b) and CeOx/CNx/a-C (c). SEM images of the GDL substrate coated by the CNx interlayer (d) and after the Pt-CeOx deposition (e), TEM side-view image of the Pt-CeOx/CNx/GDL system (f). Fuel cell performance as a function of the Pt concentration for the Pt-CeOx catalysts supported by the GDL substrate and the GDL substrate coated by the CNx interlayer (g). The authors acknowledge the financial support from the Czech Science Foundation (grant No. 18-06989Y). [1] I. Khalakhan, et al. Ceram. Int. 39 (2013) 3765–3769. [2] J. Novakova, et al. Appl. Surf. Sci., submitted. Figure 1

Nanodiamonds (NDs) and graphene oxide (GO) are modern carbon-based nanomaterials with promising features for the inhibition of microorganism growth ability. Here we compare the effects of nanodiamond and graphene oxide in both annealed (oxidized) and reduced (hydrogenated) forms in two types of cultivation media—Luria-Bertani (LB) and Mueller-Hinton (MH) broths. The comparison shows that the number of colony forming unit (CFU) of Escherichia coli is significantly lowered (45%) by all the nanomaterials in LB medium for at least 24 h against control. On the contrary, a significant long-term inhibition of E. coli growth (by 45%) in the MH medium is provided only by hydrogenated NDs terminated with C-HX groups. The use of salty agars did not enhance the inhibition effects of nanomaterials used, i.e. disruption of bacterial membrane or differences in ionic concentrations do not play any role in bactericidal effects of nanomaterials used. The specific role of the ND and GO on the enhancement of the oxidative stress of bacteria or possible wrapping bacteria by GO nanosheets, therefore isolating them from both the environment and nutrition was suggested. Analyses by infrared spectroscopy, photoelectron spectroscopy, scanning electron microscopy and dynamic light scattering corroborate these conclusions.

CO oxidation on platinum oxide deposited by magnetron sputtering on flat (Si) and highly porous (multi-walled carbon nanotubes, MWCNT) substrates were examined using X-ray photoelectron spectroscopy, scanning tunneling microscopy, temperature-programmed desorption and temperature-programmed reaction in both UHV and ambient pressure conditions. Platinum in the freshly deposited thin film is present entirely in the 4+ oxidation state. The intrinsic CO oxidation capability of such catalyst proved to be significantly higher under approx. 480 K than that of pure platinum, presumably due to the interplay between metallic and cationic platinum entities, and the reaction yield can be further enhanced by increasing effective surface area when MWCNT is used as a support. The thermo-chemical stability of the platinum oxide, however, has its limitations as the thin film can be gradually thermally reduced to metallic platinum (with small residuum of stable Pt2+ species) and this process is further facilitated in the presence of reducing CO atmosphere.

Ceria containing highly dispersed ions of rhodium is a promising material for catalytic applications. The Rh–CeOx thin films with different concentrations of rhodium were deposited by RF magnetron sputtering and were studied by soft and hard X-ray photoelectron spectroscopies, Temperature programmed reaction and X-ray powder diffraction techniques. The sputtered films consist of rhodium–cerium mixed oxide where cerium exhibits a mixed valency of Ce4+ and Ce3+ and rhodium occurs in two oxidation states, Rh3+ and Rhn+. We show that the concentration of rhodium has a great influence on the chemical composition, structure and reducibility of the Rh–CeOx thin films. The films with low concentrations of rhodium are polycrystalline, while the films with higher amount of Rh dopants are amorphous. The morphology of the films strongly influences the mobility of oxygen in the material. Therefore, varying the concentration of rhodium in Rh–CeOx thin films leads to preparing materials with different properties.

Platinum is the mostly used element in catalysts for fuel cell technology, but its high price limits large-scale applications. Platinum doped cerium oxide represents an alternative solution due to very low loading, typically few micrograms per 1 cm2, at the proton exchange membrane fuel cell (PEMFC) anode. High efficiency is achieved by using magnetron sputtering deposition of cerium oxide and Pt of 30 nm thick nanoporous films on large surface carbon nanoparticle substrates. Thin film techniques permits to grow the catalyst film characterized by highly dispersed platinum, mostly in ionic Pt2+ state. Such dispersed Pt species show high activity and stability. These new materials may help to substantially reduce the demand for expensive noble-metals in catalytic applications. We measured Pt–CeOx thin film anode catalyst activity in a hydrogen PEMFC and compared it with performance of a standard reference cell. Photoelectron spectroscopy was used to investigate chemical composition of Pt–CeOx induced by the catalyst interaction with hydrogen. Nanostructured character of the catalyst was confirmed by electron microscopy.

In this study, we report transmission electron microscopy and electron energy loss spectroscopy study of cerium oxide thin layers deposited on silicon substrate. Transmission electron microscopy experiments have revealed the flat morphology of the deposited layers. In addition, studies of high resolution images have indicated the presence of mainly ceria crystallized nanoparticles. Energy electron loss spectroscopy measurements were also performed in scanning mode to study the evolution of the cerium valence. In addition to Ce4+ inside the layer, the presence of amorphous cerium silicate with valence +3 is pointed out at the vicinity of the substrate.

The high catalytic activity of Pt-Co nanoalloys in oxygen reduction and other reactions is usually attributed to their Pt-rich surfaces. However, identification of the precise near-surface structure is by no means easily achievable experimentally. In this work we systematically analyzed the chemical ordering and surface composition of PtXCo(79-X) and PtXCo(140-X) bimetallic nanoparticles by means of a recently developed method based on topological energy expressions and electronic structure calculations. Pt is found to segregate on the surface, especially on corner and edge sites, forming a one atomic layer thick skin independent of the size and composition of the nanoparticle. In turn, the subsurface shell of the particle is composed mostly of Co, whereas the core area has a mixed composition, which depends on the overall stoichiometry. The formation of an outer Pt shell is corroborated by thoroughly analyzed data of X-ray photoelectron spectroscopy experiments performed with various photon energies on annealed Pt-Co particles prepared in vacuum by magnetron sputtering. The core-shell structure of Pt-Co particles is calculated to be more stable than the respective L10 structure. The obtained topological energy expressions are shown to depend only very moderately on the nanoparticle size, which allowed us to apply them to determine the ordering in ∼4 nm big PtXCo(1463-X) species. The presented results deepen our understanding of the intrinsic structure of Pt-Co nanoparticles depending on their size and composition.

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.

The concept of single atom catalysis offers maximum noble metal efficiency for the development of low-cost catalytic materials. Among possible applications are catalytic materials for proton exchange membrane fuel cells. In the present review, recent efforts towards the fabrication of single atom catalysts on nanostructured ceria and their reactivity are discussed in the prospect of their employment as anode catalysts. The remarkable performance and the durability of the ceria-based anode catalysts with ultra-low Pt loading result from the interplay between two states associated with supported atomically dispersed Pt and sub-nanometer Pt particles. The occurrence of these two states is a consequence of strong interactions between Pt and nanostructured ceria that yield atomically dispersed species under oxidizing conditions and sub-nanometer Pt particles under reducing conditions. The square-planar arrangement of four O atoms on {100} nanoterraces has been identified as the key structural element on the surface of the nanostructured ceria where Pt is anchored in the form of Pt2+ species. The conversion of Pt2+ species to sub-nanometer Pt particles is triggered by a redox process involving Ce3+ centers. The latter emerge due to either oxygen vacancies or adsorption of reducing agents. The unique properties of the sub-nanometer Pt particles arise from metal-support interactions involving charge transfer, structural flexibility, and spillover phenomena. The abundance of specific adsorption sites similar to those on {100} nanoterraces determines the ideal (maximum) Pt loading in Pt-CeOx films that still allows reversible switching between the atomically dispersed Pt and sub-nanometer particles yielding high activity and durability during fuel cell operation.

In the present work, we have studied the interaction of palladium adsorbed on SnO2 (110) surfaces, considering the possible formation of clusters on the surface using density functional theory (DFT) calculations. We report structure, adsorption, and bonding properties of Pdn (n = 1–5) on stoichiometric and reduced SnO2 (110) surfaces. Although palladium can be adsorbed as metal clusters on both types of surfaces, these clusters can be more easily decomposed into Pd atoms on the reduced SnO2 surface. Pd interacts mainly with bridging O atoms on stoichiometric surfaces while it bonds strongly with Sn on the reduced surface. Fil: Robina, A.. Universidad Nacional de la Patagonia "San Juan Bosco". Facultad de Ingeniería - Sede Comodoro; Argentina. Universidad Nacional del Sur; Argentina Fil: German, Estefania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina Fil: Pronsato, Maria Estela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina Fil: Juan, Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina Fil: Matolinová, I.. Charles University in Prague; República Checa Fil: Matolín, V.. Charles University in Prague; República Checa

Investigation of cerium oxide thin film deposition on silicon and silicon oxide is important due to many possible applications of cerium oxide based micro-systems in electronics and catalysis. rf-Magnetron sputtering is technologically the most suitable method of preparation of such systems. Mechanism of film growth is strongly influenced by interaction of Ce atoms with the substrate and their oxidation by oxygen containing rf plasma. We show using hard X-ray photoelectron spectroscopy with high information depth that cerium is reducing silicon oxide by forming complex silicate phase at the interface with Ce in the 3+ state. For this reason composition of very thin films of cerium oxide is strongly influenced by thin film–substrate interaction. A coating of the silicon oxide substrate by an intermediate thin carbon film provides conductive substrate for electrocatalytic applications and decreases the silicon oxide substrates–cerium oxide interaction essentially.

Treatment of polymer-electrolyte membrane with magnetron sputtering of CeO2 in Ar + O2 atmosphere creates a highly developed surface with an array of nanopillars and vertical pores. These superstructures can be used as a support for the catalyst layer homogeneously covering the surface by nanoclusters. Treated membranes with nanostructured catalyst layer exhibit high level of platinum utilization in hydrogen powered fuel cells reaching the power density of 15 kW g−1Pt. Moreover, due to the resistance to corrosion such systems have superior durability compared to the traditional carbon-supported catalysts.

Changes of stoichiometry in reducible oxides are inevitably accompanied by changes of the oxide structure. We study the relationship between the stoichiometry and the structure in thin epitaxial fi...

Radio Frequency Magnetron Sputtering is used to elaborate CeO x layers doped with platinum and/or tin on a SiO 2 /Si substrate. Morphology, chemical composition and crystallographic structures were investigated by Transmission Electron Microscopy. The presence of nanoparticles of mainly ceria and metallic platinum is exhibited.

Thin films of reduced ceria supported on metals are often applied as substrates in model studies of the chemical reactivity of ceria based catalysts. Of special interest are the properties of oxygen vacancies in ceria. However, thin films of ceria prepared by established methods become increasingly disordered as the concentration of vacancies increases. Here, we propose an alternative method for preparing ordered reduced ceria films based on the physical vapor deposition and interfacial reaction of Ce with CeO2 films. The method yields bulk-truncated layers of cubic c-Ce2O3. Compared to CeO2 these layers contain 25% of perfectly ordered vacancies in the surface and subsurface allowing well-defined measurements of the properties of ceria in the limit of extreme reduction. Experimentally, c-Ce2O3(111) layers are easily identified by a characteristic 4 x 4 surface reconstruction with respect to CeO2(111). In addition, c-Ce2O3 layers represent an experimental realization of a normally unstable polymorph of Ce2O3. During interfacial reaction, c-Ce2O3 nucleates on the interface between CeO2 buffer and Ce overlayer and is further stabilized most likely by the tetragonal distortion of the ceria layers on Cu. The characteristic kinetics of the metal-oxide interfacial reactions may represent a vehicle for making other metastable oxide structures experimentally available.

The elevated price of Pt limits the large-scale implementation of commercial proton exchange membrane fuel cells, which effectively convert chemical energy into electricity. In order to increase the cost-efficiency in proton-exchange membrane fuel cells, we have designed a family of novel anode catalysts consisting of thin films of ceria with low Pt loadings sputtered on a nanostructured carbon support. Remarkably, only such small amounts of Pt are necessary for achieving power density values comparable to the reference commercial catalysts, which results in excellent specific activities of our samples. By combining photoelectron spectroscopy and catalytic performance analysis, we have shown that the surface Pt 2+ species in cerium oxide exhibit high electrocatalytic activity. Density functional theory calculations show that the great stability of Pt 2+ species on ceria makes these resistant to reduction by hydrogenation and suggests that the formation of such stable surface complexes prevents degradation of the nanostructured composite.

Nanocomposite metal/plasma polymer films have been prepared by simultaneous plasma polymerization using a mixture of Ar/n-hexane and metal cluster beams. A simple compact cluster gas aggregation source is described and characterized with emphasis on the determination of the amount of charged clusters and their size distribution. It is shown that the fraction of neutral, positively and negatively charged nanoclusters leaving the gas aggregation source is largely influenced by used operational conditions. In addition, it is demonstrated that a large portion of Ag clusters is positively charged, especially when higher currents are used for their production. Deposition of nanocomposite Ag/C:H plasma polymer films is described in detail by means of cluster gas aggregation source. Basic characterization of the films is performed using transmission electron microscopy, ultraviolet–visible and Fourier-transform infrared spectroscopies. It is shown that the morphology, structure and optical properties of such prepared nanocomposites differ significantly from the ones fabricated by means of magnetron sputtering of Ag target in Ar/n-hexane mixture.

Interaction of water with fully oxidized and partially reduced CeO2(1 1 1) thin film model catalyst grown on a Cu(1 1 1) surface was investigated by photoelectron spectroscopy (PES), scanning tunneling microscopy (STM) and temperature programmed desorption (TPD). On the stoichiometric surface water adsorbs molecularly at low temperatures (

The interaction of Pt with CeO2 layers was investigated by using high resolution hard X-ray photoelectron spectroscopy. Pt doped CeO2 layers were deposited simultaneously by rf-magnetron sputtering on a SiO2/Si substrate and carbon nanotubes (CNTs) grown on a carbon diffusion layer of a polymer membrane fuel cell. In the case of the CNT support photoelectron spectra showed the formation of ionic platinum rich cerium oxide with Pt2+,4+ species, and with the Pt2+/Pt4+ ratio strongly dependent on the amount of platinum. Ce reveals 4+/3+ mixed valent character with Ce3+ concentration increasing with Pt content. In the case of the SiO2/Si substrate the film revealed Ce4+ and Pt4+ species only.

Aluminum oxide structures were grown on Cu–9 at.%Al(111) single crystals. Usually alumina grows in the form of an epitaxial thin film. The process is based on Al atom segregation and subsequent oxidation of the Al topmost surface. Strong temperature dependence of the alumina growth mode was observed during the oxidation of a Cu–9 at.%Al single crystal. In this work we have reported for the first time the formation of alumina wire-like nanostructures on the substrate surface during high-temperature oxidation at low pressure. The nanowire growth was observed during substrate annealing at 1070 K while annealing at 910 K led to the formation of a flat and continuous thin alumina layer. Morphology, chemical composition, and structure characterization of the prepared nanostructures was done by means of scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The experimental results point to the formation of Θ alumina phase nanowires due to surface segregation of Al atoms. Mechanism of alumina nanostructure formation is discussed. The experiment clearly showed that nanowire oxide structure growth can be obtained by a bottom-up process with a mass transfer from the substrate to the assembled nanostructure.

The growing of carbon nanotubes on a gas diffusion layer (GDL) was investigated using electron microscopy and photoelectron spectroscopy. The 30 nm thick Pt doped CeO2 layers were deposited by (rf) magnetron sputtering using a CeO2-Pt target on a carbon diffusion layer overgrown by carbon nanotubes. The anode prepared in such a way was tested in the proton exchange membrane fuel cell. Hydrogen/air fuel cell activity measurements normalized to the amount of used Pt revealed high specific power (W mg(-1) Pt). The high activity of this anode with CNT-grown is explained by high specific area of the catalyst, high conductivity of CNT-GDL junction and high activity of platinum present in cationic state Pt2,4+. Very high specific power and low cost together with physical vapor deposition of catalyst makes this anode preparation promising for micro fabrication of fuel cells to power mobile systems.

Pt on ceria (CeOx) particles supported on carbon black (CB) were synthesized using the combined process of hot precipitation and impregnation methods. During 30 cycles of cyclic voltammetry pre-treatment in the potential ranging from −0.2 to 1.3 V (V vs. Ag/AgCl), it was observed that a small amount of CeOx, which consisted of the interface region between Pt and CeOx, remained on Pt particles. Other free CeOx particles were dissolved into H2SO4 aqueous solution. To develop the Pt-CeOx/CB catalyst, the surface chemical states, the net chemical composition, morphology and electrochemical behavior in H2SO4 aqueous solution were characterized. Our microanalysis and electrochemical analysis indicate that the active CeO2 with high specific surface area provides the continuous amorphous cerium oxide (Ce3+ ,C e 4+) layer with pores on the surface of Pt particles. It is concluded that the amorphous cerium oxide layer on Pt inhibits the oxidation of Pt surface and contributes to enhancement of the activity on Pt cathode. The single cell performance was also improved using the Pt-CeOx/CB cathode. Based on all data, it is expected that the design based on characterization of the interface between Pt and small amount of amorphous cerium oxide layer could help in preparation of more active Pt catalyst.

Adjustable morphology and degree of reduction represent desirable properties of model oxide substrates for heterogeneous catalysis. We investigate these properties in CeO2 (ceria) thin films on Cu(111) using scanning tunneling microscopy and photoelectron spectroscopy. We identify growth mechanisms of ceria on Cu(111): formation of incomplete oxide interfacial layer and formation of three-dimensional ceria pyramids by stacking of monolayer-high islands. Using these mechanisms, we control the coverage, the number of open monolayers, and the step density of ceria thin films on Cu(111). Annealing in vacuum allows us to control besides the morphology also the degree of ceria surface reduction. We find a correlation between surface reduction and morphological stability in annealed ceria layers. Oriented and stoichiometric thin films of ceria on Cu(111) can be prepared at temperatures as low as 150 and 250 °C. Both the morphology and the surface reduction of these films readily change with increasing temperatur...

studied the effect ofpressure of argon as working gas at a constant distance of5cm between PTFE target and a substrate. It was shownthat both the chemistry, and the roughness of the surfacechanged with the Ar pressure during sputtering. Theauthorsconsideredthesurfaceroughnesstobeimportantfor the targeted super-hydrophobic effect. However, theroughness did not increase gradually with the pressure,but increased by a sudden jump for the highest pressure70Pa used. This result was interpreted as indicatingthat the plasma polymer clusters (nano and microparticles)formedintheplasmavolumewereburiedinto the plasma polymer film growing on the substrate.This happened under particular deposition conditions(flow of argon, RF power, target-substrate distance) atAr pressure of about 70Pa and higher. Based onscanningelectron microscopy (SEM) micrographs, this seemed toconfirmthehypothesisthatfluorocarbonplasmapolymerparticlesoriginatingintheplasmavolume(dustyplasma)were eventually embedded into the film growing onthe substrate.On the other hand, several research groups claimed thatclusters (actually PTFE crystals) grown from CF