11. Study of Li-S batteries by S K-edge RIXS spectroscopyRobert Dominko, Iztok Arčon, Marko Petrič, Klemen Bučar, Matjaž Žitnik, Matjaž Kavčič, Alen Vižintin, 2016, published scientific conference contribution abstract Abstract: Li-S batteries are considered as one of the most promising candidates for future batteries in applications where high energy density is required [1]. Despite that the general principle of operation is known for a long time [2], the lack of detailed understanding of relevant operation mechanisms has so far prevented their extensive use. A Li-S battery is composed of a lithium metal anode and a sulfur based cathode, separated by a porous separator wetted with electrolyte. During the battery cycle the reduction and oxidation of S to Li2S and back proceeds through a complicated equilibrium mixture of compounds that are typically dissolved in the electrolyte in the form of long and short chain polysulfides. In order to improve our understanding of polysulfide formation and its interactions within electrode, which are essential to achieve the long term cycling stability, development and application of new analytical tools is required.
In this work sulfur K-edge resonant X-ray emission (RXES) measurements were performed on the Li-S battery in operando mode. The experiment was performed at the ID26 beamline at ESRF using the Johansson type tender x-ray emission spectrometer [3]. Full K-L RIXS maps were recorded on a set of chemically prepared Li2Sx sample standards characterized by different Li:S stoichiometric ratio, followed by the operando measurements on Li-S battery. Using the spectra recorded on Li2Sx standards two excitation energies were chosen and RXES spectra from the back of the battery cathode were sequentially acquired during one discharge cycle (C20). The relative amounts of each sulfur compound in the cathode during the discharge cycle were determined from the linear combination fit using measured reference standard spectra. Because of resonant excitation conditions the sensitivity for the polysulfide detection was significantly enhanced. Our work sets up S K-edge RIXS spectroscopy as an important analytical tool to study the mechanism of Li-polysulfide formation in the cathode and their interaction with the host matrix and electrolyte.
Found in: ključnih besedah
Summary of found: ...RIXS, RXES, Li-S battery, operando, Sulphur K-edge XANES, Lithium polysulphides, Li2S...
Keywords: RIXS, RXES, Li-S battery, operando, Sulphur K-edge XANES, Lithium polysulphides, Li2S
Published: 28.06.2016; Views: 4735; Downloads: 0
 Fulltext (60,50 KB) |
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13. Electrochemical dissolution of iridium and iridium oxide particles in acidic mediaMiran 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: ključnih besedah
Keywords: Iridium Oxide Par-ticles, Electrochemical Dissolution of Iridium, Ir L3-edge XANES
Published: 23.08.2017; Views: 3053; Downloads: 0
Fulltext (1,43 MB) |
14. Identifikacija, porazdelitev in vezavne oblike železa v rižu (Oryza sativa L.) z rentgensko absorpcijsko in emisijsko mikro-spektroskopijoBojan Šuc, 2016, undergraduate thesis Abstract: 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.
Found in: ključnih besedah
Summary of found: ...rentgenske absorpcijske spektroskopije in mikroskopije z metodo mikro- XANES. S tem smo želeli izboljšati razumevanje vnosa...
Keywords: Rentgenska absorpcijska spektrometrija, riž, železo, mikro-XANES, metoda linearnega kombiniranja referenčnih spektrov
Published: 06.09.2016; Views: 6703; Downloads: 230
Fulltext (2,98 MB) |
15. 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, original scientific article Abstract: 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.
Found in: ključnih besedah
Summary of found: ...environment in maize roots was studied by Hg-L3
XANES and EXAFS with emphasis on XAS methodology...
Keywords: EXAFS
XANES
Arbuscular mycorrhiza
Phytoremediation
Toxicity
Hg coordination
Ligand environment
Published: 27.09.2016; Views: 5106; Downloads: 0
Fulltext (1,82 MB) |
16. Correlations between photocatalytic activity and chemical structure of Cu-modified TiO2–SiO2 nanoparticle compositesIztok 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: ključnih besedah
Summary of found: ...have been examined by means of Cu K-edge EXAFS and XANES analysis. The experimental datashow...
Keywords: Cu-modified TiO2–SiO2photocatalysts, Titanium dioxide, Metal doping, Cu K-edge XANES, EXAFS, Photocatalytic activitya
Published: 17.01.2017; Views: 4352; Downloads: 0
Fulltext (580,62 KB) |
17. Correlations between photocatalytic activity and chemical structure of Cu-modified TiO [sub] 2-SiO [sub] 2 nanoparticle compositesT. Čižmar, Iztok Arčon, Urška Lavrenčič Štangar, 2016, published scientific conference contribution abstract Found in: ključnih besedah
Summary of found: ...Cu-modified TiO2-SiO2, sol-gel, XANES, EXAFS...
Keywords: Cu-modified TiO2-SiO2, sol-gel, XANES, EXAFS
Published: 06.02.2017; Views: 3315; Downloads: 0
Fulltext (378,67 KB) |
18. Correlations between photocatalytic activity and Cu structure in Cu-modified TiO2-SiO2T. Čižmar, published scientific conference contribution abstract Found in: ključnih besedah
Summary of found: ...dioxide, Cu-modified, TiO2-SiO2, photocatalysts, photocatalytic activity, Cu K-edge XANES, EXAFS...
Keywords: Titanium dioxide, Cu-modified, TiO2-SiO2, photocatalysts, photocatalytic activity, Cu K-edge XANES, EXAFS
Published: 26.06.2017; Views: 3586; Downloads: 0
Fulltext (641,42 KB) |
19. Chemical structure in Cu-modified TiO2-SiO2 nanocomposites calcined at 500 °C for 1 h in airT. Čižmar, Iztok Arčon, Urška Lavrenčič Štangar, 2017, published scientific conference contribution abstract Found in: ključnih besedah
Summary of found: ...TiO2-SiO2 photocatalysts, titanium dioxide, metal doping, Cu K-edge XANES, EXAFS, photocatalytic activity...
Keywords: Cu-modified TiO2-SiO2 photocatalysts, titanium dioxide, metal doping, Cu K-edge XANES, EXAFS, photocatalytic activity
Published: 22.08.2017; Views: 13441; Downloads: 0
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20. Role of Surface Cu-O-Zr Sites in the Photocatalytic Activity of TiO2 Nanoscale ParticlesNataša Novak Tušar, Iztok Arčon, Urška Lavrenčič Štangar, Olena Pliekhova, 2016, published scientific conference contribution abstract Found in: ključnih besedah
Keywords: Photocatalysis, Titanium dioxide, Copper, Zirconia, co-doping, EXAFS, XANES
Published: 23.08.2017; Views: 3775; Downloads: 0
Fulltext (426,28 KB) |
