101. The mechanism of Li2S activation in lithium-sulfur batteries: Can we avoid the polysulfide formation?Alen Vižintin, Laurent Chabanne, Elena Tchernychova, Iztok Arčon, Lorenzo Stievano, Giuliana Aquilanti, Markus Antonietti, Tim-Patric Fellinger, Robert Dominko, 2017, izvirni znanstveni članek Opis: 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.
Ključne besede: Lithium-sulfur batteries
Li2S active material
XAS
UV/Vis spectroscopy
Li2S activation
Objavljeno v RUNG: 03.03.2017; Ogledov: 5119; Prenosov: 0
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102. Operando characterization of batteries using x-ray absorption spectroscopy: advances at the beamline XAFS at synchrotron ElettraGiuliana Aquilanti, marco Giorgetti, Robert Dominko, Lorenzo Stievano, Iztok Arčon, Nicola Novello, Luca Ivanc Olivieri, 2017, izvirni znanstveni članek Opis: 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.
Ključne besede: operando studies, x-ray absorption spectroscopy, Li-ion batteries, Li-S batteries
Objavljeno v RUNG: 03.03.2017; Ogledov: 6106; Prenosov: 0
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103. |
104. Correlations between photocatalytic activity and chemical structure of Cu-modified TiO2–SiO2 nanoparticle compositesT. Čižmar, Urška Lavrenčič Štangar, Iztok Arčon, 2016, izvirni znanstveni članek Opis: 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.
Ključne besede: Cu-modified TiO2–SiO2photocatalysts, Titanium dioxide, Metal doping, Cu K-edge XANES, EXAFS, Photocatalytic activitya
Objavljeno v RUNG: 17.01.2017; Ogledov: 5183; Prenosov: 0
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105. Donor doping of K0.5Na0.5NbO3 ceramics with strontium and its implications to grain size, phase composition and crystal structureJitka Hreščak, Goran Dražić, Marco Deluca, Iztok Arčon, Alojz Kodre, M. Dapiaggi, Tadej Rojac, Barbara Malič, Andreja Benčan, 2017, izvirni znanstveni članek Opis: 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.
Ključne besede: perovskite, potassium sodium niobate, donor doping, cation vacancies
Objavljeno v RUNG: 17.01.2017; Ogledov: 4857; Prenosov: 317
 Celotno besedilo (2,11 MB) |
106. Atomically resolved dealloying of structurally ordered Pt nanoalloy as an oxygen reduction reaction electrocatalystAndraž Pavlišič, Primož Jovanovič, Vid Simon Šelih, Martin Šala, Marjan Bele, Goran Dražić, Iztok Arčon, Samo B. Hočevar, Anton Kokalj, Nejc Hodnik, Miran Gaberšček, izvirni znanstveni članek Opis: 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.
Ključne besede: ORR activity, fuel cells, platinum alloy, nanoparticle stability, intermetallic ordering, kinetic Monte Carlo, dealloying, in situ ICP-MS
Objavljeno v RUNG: 27.09.2016; Ogledov: 5584; Prenosov: 0
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107. Arbuscular mycorrhizal fungi alter Hg root uptake and ligand environment as studied by X-ray absorption fine structureAlojz Kodre, Iztok Arčon, Marta Debeljak, Mateja Potisek, Matevž Likar, Katarina Vogel-Mikuš, 2017, izvirni znanstveni članek Opis: Mercury (Hg) – plant – fungal interactions are only poorly studied. Hg speciation and ligand environment
in maize roots inoculated with arbuscular mycorrhizal (AM) fungi were investigated in order to better
understand the role of AM in Hg soil to root transfer.
The maize plants were grown in Hg polluted substrate (50 mg g1 as dissolved HgCl2) and inoculated
with AM fungi originating from: a) highly Hg polluted environment of a former Hg smelting site in Idrija,
Slovenia, (Glomus sp. – sample AmI), and b) non-polluted environment (commercial AM inoculum
Symbivit1 – sample AmC). Hg speciation and ligand environment in maize roots was studied by Hg-L3
XANES and EXAFS with emphasis on XAS methodology – modelling and fitting the XAFS spectra to extract in a reliable way as much information on Hg coordination as possible. The AmI plants developed more arbuscules and less vesicles than the AmC plants, and also
accumulated more Hg in the roots. A clear difference in Hg coordination between the AM (AmC & AmI)
and the control (ConC & ConI) plants is recognized in Hg L3-edge EXAFS analysis: in the ConC & ConI
maize roots 73–80% of Hg is attached between two sulphur atoms at the distance of 2.34 Å. The remaining
ligand is nitrogen at 2.04 Å. In AmI & AmC roots another Hg-S attachment encompassing four thiol groups
at the S-distance of 2.50 Å are identified, accounting for 21–26%. AM fungi can modify Hg ligand environment in plant roots, thus playing an important role in biogeochemical cycling of Hg in terrestrial
ecosystems.
Ključne besede: EXAFS
XANES
Arbuscular mycorrhiza
Phytoremediation
Toxicity
Hg coordination
Ligand environment
Objavljeno v RUNG: 27.09.2016; Ogledov: 6163; Prenosov: 0
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108. Identifikacija, porazdelitev in vezavne oblike železa v rižu (Oryza sativa L.) z rentgensko absorpcijsko in emisijsko mikro-spektroskopijoBojan Šuc, 2016, diplomsko delo Opis: V diplomskem delu smo raziskali vezavne oblike železa v različnih delih korenin riža s kombinacijo rentgenske absorpcijske spektroskopije in mikroskopije z metodo mikro-XANES. S tem smo želeli izboljšati razumevanje vnosa železovih spojin v rastline riža (Oryza sativa L.) na tkivnem nivoju. Rastline riža so bile vzgojene v hidroponskem sistemu z dodanim železom Fe2+ (kot FeSO4). Spektri mikro-XANES na absorpcijskem robu K železa so bili pomerjeni na prečnih rezinah korenin, zamrznjenih v tekočem dušiku, na žarkovni liniji ID21 sinhrotrona ESRF v Grenoblu v fluorescenčnem načinu. Pri analizi spektrov mikro-XANES smo preučili uporabnost metode linearnega kombiniranja referenčnih spektrov XANES železa izmerjenih na nizu referenčnih dvo- in trivalentnih železovih spojin. Rezultati so pokazali, da je možno s to metodo v rastlinskih vzorcih jasno ločiti med dvo- in trivalentnimi železovimi kompleksi in določiti njihov delež z natančnostjo ±1%. Prevladujoča valenca železa v vzorcih korenin je Fe3+. Prepoznavanje in razločevanje različnih železovih kompleksov je manj natančno. Natančnost pri določanju deleža različnih trivalentnih železovih kompleksov je med 10% in 30%. Nekaterih železovih kompleksov s to metodo ni mogoče razločiti med sabo, ker se njihovi spektri XANES premalo razlikujejo. Kot najpogostejše železove komplekse v koreninah riža smo prepoznali Fe2+-fitat med dvovalentnimi spojinami, med trivalentnimi pa: železov oksid/hidroxid Goethit α-FeOOH Fe3+-citrat in Fe3+-fitat. Na natančnost pri razločevanju železovih spojin znatno vplivajo statistični šum in sistematske napake v izmerjenih spektrih mikro-XANES. Rezultati razmerij med dvo- in trivalentnimi železovimi kompleksi v različnih delih korenin kažejo, da se rastline riža zaščitijo pred strupenim toksičnim dvovalentnim železom tako, da ga oksidirajo in tvorijo tako imenovani plak, oziroma oborino, s čimer omejijo vnos dvovalentnega železa.
Ključne besede: Rentgenska absorpcijska spektrometrija, riž, železo, mikro-XANES, metoda linearnega kombiniranja referenčnih spektrov
Objavljeno v RUNG: 06.09.2016; Ogledov: 7924; Prenosov: 241
Celotno besedilo (2,98 MB) |
109. Photocatalytic Activity of Zirconium- and Manganese- Codoped Titania in Aqueous Media: The Role of the Metal Dopant and its Incorporation SiteO. L. Pliekhov, Iztok Arčon, Nataša Novak Tušar, Urška Lavrenčič Štangar, 2016, izvirni znanstveni članek Opis: The development of efficient TiO2-based photocatalysts for
water treatment is mainly performed by doping with transition
metals or by establishing junctions between different phases,
metal–semiconductor or semiconductor–semiconductor. We
present, for the first time, the synthesis of Zr- and Mn-modified
TiO2 by a redesigned sol–gel technique that allows the formation
of heterometallic bridges on the TiO2 surface. Cations of
the doping metals are located in the pores of mesoporous
anatase and attached to the crystalline TiO2 walls. The presence
of the Zr enhances the photoactivity of the TiO2 catalyst.
However, the introduction of Mn decreases the photocatalytic
efficiency in a nonadditive manner. The inhibition effect was
assigned to the side reaction between hydroxyl radicals and
Mn ions. The fact that Mn effectively scavenges the hydroxyl
radicals and, consequently, inhibits the whole oxidation process
is direct proof that hydroxyl radicals are the main reactive
species in the photocatalytic oxidative processes on TiO2 surfaces
in aqueous media and the process of COH generation is the
rate-determining step, which was confirmed using a method
based on the decolorization of a commercial dye Bezaktiv Blau
in a reaction with Fenton’s reagent as a source of hydroxyl radicals.
Ključne besede: doping, manganese, oxidation, X-ray absorption spectroscopy, zirconium
Objavljeno v RUNG: 21.07.2016; Ogledov: 4158; Prenosov: 0
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110. |
