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Atomically resolved dealloying of structurally ordered Pt nanoalloy as an oxygen reduction reaction electrocatalyst
Andraž Pavlišič, Primož Jovanovič, Vid Simon Šelih, Martin Šala, Marjan Bele, Goran Dražić, Iztok Arčon, Samo B. Hočevar, Anton Kokalj, Nejc Hodnik, Miran Gaberšček, original scientific article

Abstract: The positive effect of intermetallic ordering of platinum alloy nanoparticles on oxygen reduction reaction (ORR) activity has been well established. What is still missing is an understanding of selective leaching of the less noble metal from the ordered structure and its correlation to longterm ORR performance. Using a combination of kinetic Monte Carlo simulations and advanced characterization techniques, we provide unprecedented insight into dealloying of intermetallic PtCu3 nanoparticles a well-known binary alloy. Comparison of ordered and disordered samples with identical initial compositions and particle size distributions reveals an unexpected correlation: whereas the copper dealloying rates in the ordered and disordered counterparts are almost the same, in the ordered structure Pt atoms are surrounded by 15−30% more Cu atoms throughout all the stages of acid leaching. This more convenient Pt−Cu coordination explains the statistically significant increase of 23−37% in ORR activity of the ordered structure at all stages of alloy degradation.
Found in: osebi
Keywords: ORR activity, fuel cells, platinum alloy, nanoparticle stability, intermetallic ordering, kinetic Monte Carlo, dealloying, in situ ICP-MS
Published: 27.09.2016; Views: 2308; Downloads: 0
.pdf Fulltext (3,27 MB)

Donor doping of K0.5Na0.5NbO3 ceramics with strontium and its implications to grain size, phase composition and crystal structure
Jitka Hreščak, Goran Dražić, Marco Deluca, Iztok Arčon, Alojz Kodre, M. Dapiaggi, Tadej Rojac, Barbara Malič, Andreja Benčan, 2017, original scientific article

Abstract: In this study, the particular effects of A-site donor doping in a lead-free piezoceramic material K0.5Na0.5NbO3 (KNN) doped with Sr2+, i.e., the crystal-structure change, the secondary-phase formation and the grain-size decrease, were investigated. The already-reported causes of these effects upon doping KNN were critically discussed and a mechanism of the effects’ formation was suggested and experimentally supported with advanced analytical methods. Extended X-ray absorption fine structure (EXAFS) analyses proved that the Sr occupies the perovskite A-sublattice, and locally modifies the KNN monoclinic structure to cubic. With the help of Sr K-edge EXAFS and wavelength-dispersive X-ray spectroscopy, the Sr was found to be homogenously distributed in the KNN perovskite lattice with 0.5, 1 and 2% Sr and no Sr segregation on the nano level was found in any of the studied samples with transmission electron microscopy. Introducing Sr into the A-sublattice, as well as accounting for the charge-compensating A-site vacancies in the starting composition, causes increasing lattice disorder and microstrain, as determined from a Rietveld refinement of the synchrotron X-ray diffraction data. Above 2% Sr the system segregates the A-site vacancies in a secondary phase in order to release the chemical pressure, as revealed by Raman spectroscopy. All these effects result in an increasing number of low-angle grain boundaries that limit the grain growth and finally lead to a significant grain-size decrease.
Found in: osebi
Keywords: perovskite, potassium sodium niobate, donor doping, cation vacancies
Published: 17.01.2017; Views: 2104; Downloads: 195
.pdf Fulltext (2,11 MB)

Correlations between photocatalytic activity and chemical structure of Cu-modified TiO2–SiO2 nanoparticle composites
Iztok Arčon, Urška Lavrenčič Štangar, T. Čižmar, 2016, original scientific article

Abstract: Copper-modified TiO2–SiO2photocatalysts were prepared by sol–gel method based on organic copper,silicon and titanium precursors. Copper concentration varied from 0.1 to 3.0 mol%. A widely appliedmodel reaction of photocatalytic oxidation of terephtalic acid (TPA) in water solution was used in order toevaluate the catalytic activities of elaborated samples. The crystal structures of the titania components ofall tested titania–silica species were studied using XRD analysis. The influence of Cu2+cation incorporationon the crystal structure of titania, as well as the chemical states and the neighbouring structures of coppercations, have been examined by means of Cu K-edge EXAFS and XANES analysis. The experimental datashow that there is a ten times increase in photocatalytic activity when TiO2–SiO2matrix is modified with0.1 mol% of Cu. It can be supposed that an enhancement of photocatalytic activity of low-concentratedcopper-modified titania–silica nanocomposites is probably due to a close attachment of Cu2+cationsto the surfaces of photocatalytically active TiO2nanoparticles. In this case, Cu2+cations may possiblyact as free electron traps reducing the intensity of recombination between opposite free charge carriers(electrons, holes) available at the photocatalyst’s surface.
Found in: osebi
Keywords: Cu-modified TiO2–SiO2photocatalysts, Titanium dioxide, Metal doping, Cu K-edge XANES, EXAFS, Photocatalytic activitya
Published: 17.01.2017; Views: 2478; Downloads: 0
.pdf Fulltext (580,62 KB)

Correlations between photocatalytic activity and chemical structure of Cu-modified TiO [sub] 2-SiO [sub] 2 nanoparticle composites
T. Čižmar, Iztok Arčon, Urška Lavrenčič Štangar, 2016, published scientific conference contribution abstract

Found in: osebi
Keywords: Cu-modified TiO2-SiO2, sol-gel, XANES, EXAFS
Published: 06.02.2017; Views: 1614; Downloads: 0
.pdf Fulltext (378,67 KB)

Operando characterization of batteries using x-ray absorption spectroscopy: advances at the beamline XAFS at synchrotron Elettra
Nicola Novello, Iztok Arčon, Lorenzo Stievano, Robert Dominko, marco Giorgetti, Giuliana Aquilanti, Luca Ivanc Olivieri, 2017, original scientific article

Abstract: X-ray absorption spectroscopy is a synchrotron radiation based technique that is able to provide information on both local structure and electronic properties in a chemically selective manner. It can be used to characterize the dynamic processes that govern the electrochemical energy storage in batteries, and to shed light on the redox chemistry and changes in structure during galvanostatic cycling to design cathode materials with improved properties. Operando XAS studies have been performed at beamline XAFS at Elettra on different systems. For Li-ion batteries, a multiedge approach revealed the role of the different cathode components during the charge and discharge of the battery. In addition, Li-S batteries for automotive applications were studied. Operando sulfur K-edge XANES and EXAFS analysis was used to characterize the redox chemistry of sulfur, and to relate the electrochemical mechanism to its local structure.
Found in: osebi
Keywords: operando studies, x-ray absorption spectroscopy, Li-ion batteries, Li-S batteries
Published: 03.03.2017; Views: 3295; Downloads: 0
.pdf Fulltext (1,59 MB)

The mechanism of Li2S activation in lithium-sulfur batteries: Can we avoid the polysulfide formation?
Robert Dominko, Tim-Patric Fellinger, Markus Antonietti, Giuliana Aquilanti, Lorenzo Stievano, Iztok Arčon, Elena Tchernychova, Laurent Chabanne, Alen Vižintin, 2017, original scientific article

Abstract: Electrochemical reactions in the LieS batteries are considered as a multistep reaction process with at least 2e3 equilibrium states. Here we report a possibility of having a conversion of Li2S into sulfur without detectible formation of polysulfides. That was confirmed by using a novel material system consisting of carbon coated Li2S particles prepared by carbothermal reduction of Li2SO4. Two independent in operando measurements showed direct oxidation of Li2S into sulfur for this system, with almost negligible formation of polysulfides at potentials above 2.5 V vs. Li/Liþ. Our results link the diversity of first charge profiles in the literature to the Li2S oxidation mechanism and show the importance of ionic wiring within the material. Furthermore, we demonstrate that the Li2S oxidation mechanism depends on the relative amount of soluble sulfur in the electrolyte. By controlling the type and the amount of electrolyte within the encapsulating carbon shell, it is thereby possible to control the reaction mechanism of Li2S activation.
Found in: osebi
Keywords: Lithium-sulfur batteries Li2S active material XAS UV/Vis spectroscopy Li2S activation
Published: 03.03.2017; Views: 2378; Downloads: 0
.pdf Fulltext (2,98 MB)

An extracellular polymeric substance quickly chelates mercury(II) with N-heterocyclic groups
Claudia Faleri, Dario Battistel, Salvatore Daniale, Michele Gallo, Franco Baldi, Alojz Kodre, Iztok Arčon, 2017, original scientific article

Abstract: A strain of Klebsiella oxytoca DSM 29614 is grown on sodium citrate in the presence of 50 mg l−1 of Hg as Hg(NO3)2. During growth, the strain produces an extracellular polymeric substance (EPS), constituted by a mixture of proteins and a specific exopolysaccharide. The protein components, derived from the outer membrane of cells, are co-extracted with the extracellular exopolysaccharide using ethanol. The extracted EPS contains 7.5% of Hg (total amount). This indicates that EPS is an excellent material for the biosorption of Hg2+, through chemical complexation with the EPS components. The binding capacity of these species towards Hg2+ is studied by cyclic voltammetry, and Hg L3-edge XANES and EXAFS spectroscopy. The results found indicate that Hg2+ is mainly bound to the nitrogen of the imidazole ring or other N-heterocycle compounds. The hydroxyl moities of sugars and/or the carboxyl groups of two glucuronic acids in the polysaccharide can also play an important role in sequestring Hg2+ ions. However, N-heterocyclic groups of proteins bind Hg2+ faster than hydroxyl and carboxyl groups of the polysaccharide.
Found in: osebi
Keywords: Klebsiella oxytoca, Biosorption, Proteins, Polysaccharide, Cyclic voltammetry, EXAFS analysis
Published: 03.03.2017; Views: 1977; Downloads: 0
.pdf Fulltext (1,66 MB)

Biotransformation of copper oxide nanoparticles by the pathogenic fungus Botrytis cinerea
Katarina Vogel-Mikuš, Darko Makovec, Tamás Papp, Iztok Arčon, Johannes Teun van Elteren, Marjana Regvar, Eva Kovačec, 2017, original scientific article

Abstract: Two plant pathogenic fungi, Botrytis cinerea and Alternaria alternata, isolated from crop plants, were exposed to Cu in ionic (Cu2þ), microparticulate (MP, CuO) or nanoparticulate (NP, Cu or CuO) form, in solid and liquid culturing media in order to test fungal response and toxic effects of the mentioned compounds for the potential use as fungicides. B. cinerea has shown pronounced growth and lower levels of lipid peroxidation compared to A. alternata. Its higher resistance/tolerance is attributed mainly to biotransformation of CuO and Cu NPs and CuO MPs into a blue compound at the fungal/culturing media interface, recognized by Cu K-edge EXAFS analysis as Cu-oxalate complex. The pronounced activity of catechol-type siderophores and organic acid secretion in B. cinerea induce leaching and mobilization of Cu ions from the particles and their further complexation with extracellularly secreted oxalic acid. The ability of pathogenic fungus to biotransform CuO MPs and NPs hampers their use as fungicides. However the results show that B. cinerea has a potential to be used in degradation of Cu(O) nanoparticles in environment, copper extraction and purification techniques.
Found in: osebi
Keywords: copper, metal oxide nanoparticles, detoxification mechanisms, metal pollution, Cu-oxalate
Published: 23.08.2017; Views: 1552; Downloads: 0
.pdf Fulltext (1,52 MB)

Electrochemical dissolution of iridium and iridium oxide particles in acidic media
Miran Gaberšček, Samo B. Hočevar, Vid Simon Šelih, Martin Šala, Marjan Bele, Milena Zorko, Barbara Jozinović, Iztok Arčon, Francisco Ruiz-Zepeda, Nejc Hodnik, Primož Jovanovič, 2017, original scientific article

Abstract: Iridium based particles as the most promising proton exchange membrane electrolyser electrocatalysts were investigated by transmission electron microscopy (TEM), and by coupling of electrochemical flow cell (EFC) with online inductively coupled plasma mass spectrometer (ICP-MS). Additionally, a thin-film rotating disc electrode (RDE), an identical location transmission and scanning electron microscopy (IL-TEM and IL-SEM) as well as an X-ray absorption spectroscopy (XAS) studies have been performed. Extremely sensitive online time-and potential-resolved electrochemical dissolution profiles revealed that iridium particles dissolved already well below oxygen evolution reaction (OER) potentials, presumably induced by iridium surface oxidation and reduction processes, also referred to as transient dissolution. Overall, thermally prepared rutile type IrO2 particles (T-IrO2) are substantially more stable and less active in comparison to as prepared metallic (A-Ir) and electrochemically pretreated (E-Ir) analogues. Interestingly, under OER relevant conditions E-Ir particles exhibit superior stability and activity owing to the altered corrosion mechanism where the formation of unstable Ir(>IV) species is hindered. Due to the enhanced and lasting OER performance, electrochemically pre-oxidized E-Ir particles may be considered as the electrocatalyst of choice for an improved low temperature electrochemical hydrogen production device, namely a proton exchange membrane electrolyser.
Found in: osebi
Keywords: Iridium Oxide Par-ticles, Electrochemical Dissolution of Iridium, Ir L3-edge XANES
Published: 23.08.2017; Views: 1288; Downloads: 0
.pdf Fulltext (1,43 MB)

Correlations between photocatalytic activity and Cu structure in Cu-modified TiO2-SiO2
T. Čižmar, published scientific conference contribution abstract

Found in: osebi
Keywords: Titanium dioxide, Cu-modified, TiO2-SiO2, photocatalysts, photocatalytic activity, Cu K-edge XANES, EXAFS
Published: 26.06.2017; Views: 1666; Downloads: 0
.pdf Fulltext (641,42 KB)

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