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Thermal decomposition of glycine molecules on cerium oxide films is defined by the type of cerium cations on the surface.

Understanding how reaction conditions affect metal-support interactions in catalytic materials is one of the most challenging tasks in heterogeneous catalysis research. Metal nanoparticles and their supports often undergo changes in structure and oxidation state when exposed to reactants, hindering a straightforward understanding of the structure-activity relations using only ex situ or ultrahigh vacuum techniques. Overcoming these limitations, we explored the metal-support interaction between gold nanoparticles and ceria supports in ultrahigh vacuum and after exposure to CO. A combination of in situ methods (on powder and model Au/CeO2 samples) and theoretical calculations was applied to investigate the gold/ceria interface and its reactivity toward CO exposure. X-ray photoelectron spectroscopy measurements rationalized by first-principles calculations reveal a distinctly inhomogeneous charge distribution, with Au+ atoms in contact with the ceria substrate and neutral Au0 atoms at the surface of the Au nanoparticles. Exposure to CO partially reduces the ceria substrate, leading to electron transfer to the supported Au nanoparticles. Transferred electrons can delocalize among the neutral Au atoms of the particle or contribute to forming inert Auδ− atoms near oxygen vacancies at the ceria surface. This charge redistribution is consistent with the evolution of the vibrational frequencies of CO adsorbed on Au particles obtained using diffuse reflectance infrared Fourier transform spectroscopy.

Ru evaporation from the surface of a Ru/CeO2 catalyst is demonstrated.

Stabilization of cathode catalysts in hydrogen-fueled proton-exchange membrane fuel cells (PEMFCs) is paramount to their widespread commercialization. Targeting that aim, Pt-Au alloy catalysts with various compositions (Pt

Platinum-based bimetallic alloys have been largely investigated during the last few years as a valid alternative to bare Pt cathode catalysts for proton-exchange membrane fuel cells (PEMFCs) to improve their cost-efficiency. Nonetheless, Pt bimetallic alloys are characterized by a reduced stability, which is poorly understood at a fundamental level. It is thus essential to describe the entire chain of interconnected degradation mechanisms to formulate a comprehensive model of catalyst degradation that will help interpret bimetallic alloy behavior in real complex fuel cell systems. By combining in situ inductively coupled plasma mass spectroscopy, in situ grazing-incidence small-angle X-ray scattering, and ex situ scanning electron microscopy, we have studied the morphological evolution of PtXNi100–X model catalysts with different Ni contents (ranging from 0 to 75%) undergoing potentiodynamic cycling to two different upper potentials mimicking the different operational conditions of a PEMFC: 1.0 and 1.3 VRHE. Data analysis allowed us to develop a methodology to distinguish the influence of Ni dissolution, particle coalescence, and Ostwald ripening on particle size distribution and interparticle distance and to realize time-dependent interplay maps to highlight the timeframe in which the aforementioned phenomena are prevailing or coexisting. Results show that Ni dissolution is the only phenomenon inducing morphological evolution when the lower upper potential is chosen. On the contrary, at 1.3 VRHE, Ni dissolution is rapidly overcome by particle coalescence at first and by Ostwald ripening in the later stages of the investigated time range. The onset of every phenomenon was found to occur earlier in time for larger values of Ni concentrations.

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

Single-atom catalysts represent an essential and ever-growing family of heterogeneous catalysts. Recent studies indicate that besides the valuable catalytic properties provided by single-atom active sites, the presence of single-atom sites on the catalyst substrates may significantly influence the population of supported metal nanoparticles coexisting with metal single atoms. Treatment of ceria-based single-atom catalysts in oxidizing or reducing atmospheres was proven to provide precise experimental control of the size of the supported Pt nanoparticles, and, correspondingly, control of catalyst activity and stability. Based on dedicated surface science experiments, ab-initio calculations and kinetic Monte-Carlo simulations we demonstrate that the morphology of Pt nanoparticle population on ceria surface is a result of a competition for Pt atoms between Pt single-atom sites and Pt nanoparticles. In oxidizing atmosphere, Pt single-atom sites provide strong bonding to single Pt atoms and Pt nanoparticles shrink. In reducing atmosphere, Pt single atom sites are depopulated and Pt nanoparticles grow. We formulate a generic model of Pt redispersion and coarsening on ceria substrates. Our model provides a unified atomic-level explanation for a variety of metal nanoparticle dynamic processes observed in single-atom catalysts under stationary or alternating oxidizing/reducing atmospheres, and allows to classify the conditions when nanoparticle ensembles on single-atom catalysts substrates can be stabilized against Ostwald ripening.

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.

For several years, scientists have been trying to understand the mechanisms that reduce the long‐term stability of perovskite solar cells. In this work, we examined the effect of water and photon flux on the stability of CH3NH3PbI3 perovskite films and solar cells using in situ near‐ambient pressure X‐ray photoelectron spectroscopy (NAP‐XPS), field emission scanning electron microscopy (FESEM), and current density–voltage (J–V) characterization. The used amount of water vapor (up to 1 mbar) had a negligible impact on the perovskite film. The higher the photon flux, the more prominent were the changes in the NAP‐XPS and FESEM data; also, a faster decline in power conversion efficiency (PCE) and a more substantial hysteresis in the J‐V characteristics were observed. Based on our results, it can be concluded that the PCE decrease originates from the creation of Frenkel pair defects in the perovskite film under illumination. The stronger the illumination, the higher the number of Frenkel defects, leading to a faster PCE decline and more substantial hysteresis in the J‐V sweeps., Solar cell deactivation: For similar exposures, the soaking of light proves more detrimental to the perovskite film than water vapor. Absorbed photons create Frenkel defects in the perovskite crystal. The number of created Frenkel defects depends strongly on the used illumination. The higher the photon flux, the higher the creation of Frenkel defects, and thus the stronger the degradation of power conversion efficiency and the stronger the hysteresis in the J–V characteristics.

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.

Simultaneous plasma etching of a proton-exchange membrane (PEM) and deposition of a cerium oxide layer during reactive magnetron sputtering leads to the formation of a pronounced fiber-like structure on its surface. The level of structural porosity can be adjusted by varying the working pressure during the process. A PEM treated this way can be subsequently coated with a thin layer of iridium, forming an anode-side catalyst-coated membrane (CCM) for applications in water electrolysis. Due to the significantly enlarged surface of the membrane, there is no necessity for any additional, potentially corroding, support nanoparticles to achieve efficient in-cell operation. Moreover, utilizing a rotatory frame-shaped substrate holder and a multitarget deposition apparatus, the sputter-etching process can be used in the preparation of a full anode/cathode thin-film CCM in a single vacuum entry. This structure yields remarkable performance characteristics in an electrolyzer cell, considering its low combined noble metal loading of just 220 μg cm−2. Using this completely dry process for CCM manufacturing may facilitate efficient large-scale future production.

Comprehensive understanding of the catalyst corrosion dynamics is a prerequisite for the development of an efficient cathode catalyst in proton-exchange membrane fuel cells. To reach this aim, the behavior of fuel cell catalysts must be investigated directly under reaction conditions. Herein, we applied a strategic combination of in situ/online techniques: in situ electrochemical atomic force microscopy, in situ grazing incidence small angle X-ray scattering, and electrochemical scanning flow cell with online detection by inductively coupled plasma mass spectrometry. This combination of techniques allows in-depth investigation of the potential-dependent surface restructuring of a PtNi model thin film catalyst during potentiodynamic cycling in an aqueous acidic electrolyte. The study reveals a clear correlation between the upper potential limit and structural behavior of the PtNi catalyst, namely, its dealloying and coarsening. The results show that at 0.6 and 1.0 VRHE upper potentials, the PtNi catalyst essentially preserves its structure during the entire cycling procedure. The crucial changes in the morphology of PtNi layers are found to occur at 1.3 and 1.5 VRHE cycling potentials. Strong dealloying at the early stage of cycling is substituted with strong coarsening of catalyst particles at the later stage. The coarsening at the later stage of cycling is assigned to the electrochemical Ostwald ripening process.

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.

This article presents an investigation of the sensing properties of chemiresistors based on Cu2O/CuO core–shell nanowires containing p–p′ heterojunctions. The nanowires were synthesized by a conven...

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.

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.

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

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...

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 Pt

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.

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.

A Pt-Co nanoalloy thin film catalyst was prepared by using simultaneous magnetron sputtering of Pt and Co. The catalyst was characterized during accelerated degradation test using in-situ electrochemical atomic force microscopy complemented with ex-situ techniques such as energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy and synchrotron radiation photoelectron spectroscopy. The combined results gave the full step-by-step picture of the catalyst behavior during the aging test.

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.

Recently we have tested a magnetron sputtered Pt-Co catalyst in a hydrogen-fed proton exchange membrane fuel cell and showed its high catalytic activity for the oxygen reduction reaction. Here we present further investigation of the magnetron sputtered Pt-Co thin film catalyst by both experimental and theoretical methods. Scanning electron microscopy and transmission electron microscopy experiments confirmed the nanostructured character of the catalyst. The surface composition of as-deposited and annealed at 773 K Pt-Co films was investigated by surface analysis techniques, such as synchrotron radiation photoelectron spectroscopy and X-ray photoelectron spectroscopy. Modeling based on density functional theory showed that the surface of 6 nm large 1:1 Pt-Co nanoparticles is almost exclusively composed of Pt atoms (>90%) at typical operation conditions and the Co content does not exceed 20% at 773 K, in agreement with the experimental characterization of such films annealed in vacuum. According to experiment, the density of valence states of surface atoms in Pt-Co nanostructures is shifted by 0.3 eV to higher energies, which can be associated with their higher activity in the oxygen reduction reaction. The changes in electronic structure caused by alloying are also reflected in the measured Pt 4f, Co 3p and Co 2p photoelectron peak binding energies.

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.

Due to promising catalytic properties of cerium oxide, such based materials have been recognized as a suitable candidate for catalysts at the anode side of fuel cells. In order to achieve the largest active surface area, a commercially available gas diffusion layer used as Pt-CeOx catalyst support has been enhanced by the application of a CNx interlayer. Herein, the surface morphology modification, into the form of individual needles, observed by Scanning Electron Microscopy and Transmission Electron Microscopy, is presented. Furthermore, spectroscopy techniques, namely X-ray Photoelectron Spectroscopy, Electron Energy Loss Spectroscopy, and Energy Dispersive X-ray Spectroscopy reveal important role of nitrogen incorporated in the CNx interlayer that enables formation of very porous surface structures. In addition, it is demonstrated that tuning of catalyst film morphology provides a viable strategy towards higher performance in the PEMFC tests, complemented by better corrosion resistance of CNx interlayers under the start-up conditions of fuel cells.

In this study, PtxNi100-x (0 ≤ x ≤ 100) alloy catalysts were prepared using magnetron co-sputtering in order to reveal the correlation between their composition and catalytic properties as a cathode in proton exchange membrane fuel cells (PEMFCs). Fine power adjustment on magnetrons allowed to deposit alloys with precise composition and at the same time with identical thickness of 10 nm and similar morphologies. The powerful surface characterization techniques such as atomic force microscopy (AFM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), X-ray reflectivity (XRR) and X-ray photoelectron spectroscopy (XPS) were applied to thoroughly investigate the catalytic layers. The desired composition of the films was confirmed by EDX and XRD results. All deposited layers showed similar morphologies with vertical and horizontal roughness of ~0.35 nm and ~6 nm, respectively. XRD confirmed the alloy nature of the films with one crystalline phase of the fcc PtNi. The PtxNi100-x alloys showed significant enhancement of specific power (SP) comparing to the pure Pt in PEMFC. Particularly, the Pt25Ni75 sample exhibited the highest SP of 24 kW/g(Pt). This catalyst showed a 2- and almost 10-fold improvement in SP with respect to the Pt film and commercial nanopowder Pt catalyst, respectively.

The better understanding on the structural dynamics of a bimetallic catalyst during its interaction with reactive environments is a prerequisite for the development of an efficient catalyst for proton exchange membrane fuel cells (PEMFCs). The main focus should be given to the outermost layers of catalytically active material which are directly involved in catalysis. Herein, we applied the synchrotron radiation photoelectron spectroscopy (SRPES) and X-ray photoelectron spectroscopy (XPS) techniques to investigate surface chemistry aspects in a PtNi alloy catalyst under alternating oxidation (O2) and reduction (H2) atmospheres at different temperatures that simulate its behavior as a cathode catalyst in PEMFCs. The experimental results are substantiated by theoretical calculations on model PtNi nanoalloys. We showed that PtNi alloy does not maintain its chemical integrity and undergoes surface reconstruction during the switching between oxidizing and reducing conditions in terms of relative surface nickel enrichment. Along with compositional changes catalyst coarsening was observed by atomic force microscopy (AFM). The revealed behavior of the PtNi alloy provides valuable fundamental insights that help to gain advanced understanding of PtNi alloy catalytic activity in real conditions. Figure 1