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1.
Lattice-matched ▫$Ta_3N_5/Nb_5N_6$▫ interface enables a bulk charge separation efficiency of close to 100%
Yitong Liu, Zeyu Fan, Ronghua Li, Andraž Mavrič, Iztok Arčon, Matjaž Valant, Gregor Kapun, Beibei Zhang, Chao Feng, Zemin Zhang, 2025, izvirni znanstveni članek

Opis: The interface between the semiconductor light absorber and the metal electrode is critical for facilitating the extraction of photogenerated charges in photoelectrodes. Achieving a lattice-matched semiconductor/electrode interface with low defect density is highly desirable but remains a challenge for Ta3N5 photoanodes. In this study, we synthesized niobium nitride thin film electrodes with controllable crystallographic phases to achieve a lattice-matched Ta3N5/Nb5N6 back contact. This results in an enhanced crystallinity of the Ta3N5 film and reduced interfacial defect density. Consequently, the photoanode with the lattice-matched back contact attains a record half-cell solar-to-hydrogen conversion efficiency of 4.1%, attributed to the bulk carrier separation efficiency of nearly 100%. This work highlights lattice-matching as an effective strategy to enhance the efficiency of thin film-based solar energy conversion devices.
Ključne besede: photoelectrochemistry, photoanode, interface, semiconductors
Objavljeno v RUNG: 28.03.2025; Ogledov: 348; Prenosov: 3
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2.
Beyond surface area : enhanced pseudocapacitive properties of cobalt layered double hydroxide through structural modifications
Anja Siher, Ksenija Maver, Uroš Luin, Albin Pintar, Iztok Arčon, Andraž Mavrič, 2025, izvirni znanstveni članek

Opis: Cobalt hydroxide and other first-row transition metal hydroxides have gained significant attention as pseudocapacitor materials due to their rapid and reversible redox processes. Their layered structures facilitate interactions between electrolyte anions and cobalt cation sites within the bulk of the material, enabling higher charge density and extending redox activity beyond the particle surface. By controlled precipitation under hydrothermal conditions, the structure and morphology of cobalt hydroxides can be optimized to enhance electrochemical performance. Challenging conventional assumptions, surface area alone is not the primary factor driving increased pseudocapacitive performance. The hexagonal hydrotalcite-like structure, characterized by lower skeletal density and larger basal plane spacing, outperforms the monoclinic cobalt carbonate hydroxide structure, achieving an order of magnitude higher capacitance. In situ X-ray absorption spectroscopy provides critical insights into the pseudocapacitive behavior, revealing enhanced accessibility of Co2+ sites for electrochemical oxidation. While monoclinic cobalt carbonate hydroxide exhibits minimal changes in the Co2+ oxidation state, indicative of surface-limited redox activity, the hydrotalcite-like cobalt hydroxides show substantial shifts in the Co K-edge position, highlighting oxidation of Co2+ sites throughout the bulk.
Ključne besede: pseudocapacitors, layered-double hydroxides, cobalt hydroxide, redox processes, in situ x-ray absorption spectroscopy
Objavljeno v RUNG: 14.03.2025; Ogledov: 481; Prenosov: 6
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3.
Iodine K- and L-edge X-ray absorption spectra of HI : the effect of molecular orbitals and core subshells
Robert Hauko, Jana Padežnik Gomilšek, Alojz Kodre, Iztok Arčon, Uroš Luin, 2024, izvirni znanstveni članek

Opis: Analysis of the recently measured absorption spectra of molecular HI at K and L edges of iodine, in parallel with previously measured spectra of noble gas Xe and the K edge spectrum of atomic I, is presented. A strong dependence of some valence multielectron photoexcitation features on the orbital momentum of the core vacancy is found, attributed to the change of the symmetry of the HI molecule: the shake-up coexcitation of a valence electron to a free molecular orbital is much stronger at L3 than L1 edge. The effect of angular momentum of the core hole on the shake processes of deeper multielectron photoexcitations is found negligible. Both HI and Xe exhibit a much weaker one-electron transition [1s]6p than monatomic I. At the K edge, the strength of coexcitations of 4d, 4p and 3d subshells in atomic I is close to the HI and Xe. The same is found for HI and Xe at the L edges, due to a weak contribution of the additional free molecular orbital in HI.
Ključne besede: X-ray absorption spectroscopy, K edge spectrum of atomic I, multielectron photoexcitations (MEPE), core vacancy angular momentum
Objavljeno v RUNG: 09.01.2025; Ogledov: 625; Prenosov: 6
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4.
Light-Assisted Catalysis and the Dynamic Nature of Surface Species in the Reverse Water Gas Shift Reaction over Cu/γ-Al2O3
Kristijan Lorber, Iztok Arčon, Matej Huš, Janez Zavašnik, Jordi Sancho-Parramon, Anže Prašnikar, Blaž Likozar, Nataša Novak Tušar, Petar Djinović, izvirni znanstveni članek

Opis: The reverse water gas shift (RWGS) reaction converts CO2 and H2 into CO and water. We investigated Cu/γ-Al2O3 catalysts in both thermally driven and light-assisted RWGS reactions using visible light. When driven by combined visible light and thermal energy, the CO2 conversion rates were lower than in the dark. Light-assisted reactions showed an increase in the apparent activation energy from 68 to 87 kJ/mol, indicating that light disrupts the energetically favorable pathway active in the dark. A linear correlation between irradiance and decreasing reaction rate suggests a photon-driven phenomenon. In situ diffuse reflectance infrared Fourier transform spectroscopy and TD-DFT analyses revealed that catalyst illumination causes significant, partly irreversible surface dehydroxylation, highlighting the importance of OH groups in the most favorable RWGS pathway. This study offers a novel approach to manipulate surface species and control activity in the RWGS reaction.
Ključne besede: light-assisted catalysis, reaction mechanism, in situ spectroscopy, hydroxyl, copper, RWGS
Objavljeno v RUNG: 07.01.2025; Ogledov: 627; Prenosov: 6
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5.
Nickel-decorated ZnO nanoparticles for effective solar reduction of hexavalent chromium and removal of selected pharmaceuticals
Miha Ravbar, Ksenija Maver, Tilen Knaflič, Iztok Arčon, Nataša Novak Tušar, Urška Lavrenčič Štangar, Andraž Šuligoj, 2025, izvirni znanstveni članek

Opis: The efficient visible light driven photocatalytic reduction of hexavalent chromium, Cr(VI) was demonstrated using ZnO nanoparticles (NPs) decorated with oxo-clusters of transition metals. The ZnO NPs were synthesized by a facile one-pot solvothermal synthesis followed by a fast microwave-assisted (MW) grafting of transition metals on the surface of NPs. Nickel was found to be the most active transition metal for photocatalytic activity as demonstrated by reduction of Cr(VI) to Cr(III). The optimally grafted samples contained 0.5 wt% Ni and increased photocatalytic activity by almost one-fold. The oxo-clusters did not enter the lattice of ZnO but rather resided on the surface and their efficient bonding to the ZnO surface was proved by Raman, TEM and X-Ray absorption techniques. Influence of MW power was studied and shown that excessive power load leads to formation of elongated structures of ZnO which decreases the photocatalytic activity. It was demonstrated by measuring fluorescent radical products that electrons, efficiently transferred via oxygen, were the main active species in combination with the unchanged oxidation power of holes and • OH in the grafted samples. The applicability of the materials was tested in immobilized plug flow photoreactor system degrading five pharmaceuticals simultaneously where their long-term use was shown.
Ključne besede: Zinc oxide, Pharmaceuticals, Grafting, Cr(VI), Zn XANES, Zn EXAFS
Objavljeno v RUNG: 24.10.2024; Ogledov: 886; Prenosov: 5
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6.
Structural and chemical analysis of hard carbon negative electrode for Na-ion battery with X-ray Raman scattering and solid-state NMR spectroscopy
Ava Rajh, Matej Gabrijelčič, Blaž Tratnik, Klemen Bučar, Iztok Arčon, Marko Petric, Robert Dominko, Alen Vižintin, Matjaž Kavčič, izvirni znanstveni članek

Opis: This study explores the structural changes of hard carbon (HC) negative electrodes in sodium-ion batteries induced by insertion of Na ions during sodiation. X-ray Raman spectroscopy (XRS) was used to record both C and Na K-edge absorption spectra from bulk HC anodes carbonized at different temperatures and at several points during sodiation and desodiation. Comparing the [pi]*/[sigma]* regions in the C K-edge spectra sp2/sp3 hybridization ratio of material was determined. Higher carbonization temperatures led to increased order in graphitic structure and shorter bond lengths. Sodiation caused a decrease in graphitic layer order due to inserted Na ions. Complementary operando solid state 23Na nuclear magnetic resonance (ssNMR) studies confirmed the structural changes, while showing pore filling mechanism, which is not observed in ex situ measurements, primarily at higher carbonization temperatures. XRS analysis of Na K-edge spectra revealed systematic variations in the solid electrolyte interface (SEI) composition during cycling. Changes in XRS spectra were attributed to both SEI composition alterations, accompanied by the insertion/adsorption of Na ions at defect sites within the carbon structure.
Ključne besede: hard carbon, RIXS, carbon XANES, EXAFS, NMR, Na battery
Objavljeno v RUNG: 10.09.2024; Ogledov: 1635; Prenosov: 3
.pdf Celotno besedilo (7,76 MB)
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7.
Gases
Alojz Kodre, Iztok Arčon, Jana Padežnik Gomilšek, 2024, znanstveni sestavek v slovarju, enciklopediji, leksikonu

Opis: X-ray absorption spectroscopy of gases is seldom used for structural analysis, except in as much as the extended X-ray absorption fine-structure (EXAFS) signal is used to monitor some specific molecular process. Gas spectroscopy, however, has been the main tool in the systematic study of higher-order photoabsorption processes, multielectron photoexcitations (MEEs), which were introduced with an experiment at the K edge of argon. Along with noble gases, where MEEs are studied in the pure form, free of the structural signal, measurements have been extended to monatomic metal vapours, although at the cost of considerable experimental difficulties. Several types of absorption cells have been devised, among them the ceramic double cell and the heat-pipe cell for experiments in the low-energy region. In a high-temperature oven with considerable technical refinement, edge profiles of nonvolatile metals were measured up to 2500 K. Edge profiles and MEEs, which are strongly dependent on electron correlation, provide sensitive tests of the theory of atomic and molecular structure.
Ključne besede: X-ray absorption spectroscopy, absorption cells, gas and vapour samples, multielectron photoexcitation, effects of electron correlation
Objavljeno v RUNG: 05.09.2024; Ogledov: 1206; Prenosov: 4
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8.
Structural and chemical analysis of Na-ion batteries with X-ray Raman scattering spectroscopy
Ava Rajh, Matej Gabrijelčič, Alen Vižintin, Klemen Bučar, Iztok Arčon, Marko Petric, Robert Dominko, 2024, objavljeni povzetek znanstvenega prispevka na konferenci

Ključne besede: X-Ray Raman, Na-ion batteries
Objavljeno v RUNG: 05.07.2024; Ogledov: 1668; Prenosov: 4
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9.
XAS analysis of bifunctional Ni/ZSM-5 catalysts
Iztok Arčon, Hue-Tong Vu, Goran Dražić, Janez Volavšek, Gregor Mali, Nataša Zabukovec Logar, Nataša Novak Tušar, 2024, objavljeni povzetek znanstvenega prispevka na konferenci

Opis: In a bifunctional Ni/ZSM-5 zeolite type catalyst, catalytic properties are usually tuned via varying Al and Ni contents [1]. Here we present a systematic structural study of the Ni/ZSM-5 materials by Ni K-edge XANES and EXAFS analyses, to monitor the changes of local structure and chemical state of Ni species in the catalysts as a function of Al and Ni content. A series of Ni/ZSM-5 type zeolites with different Al to Si and Ni to Si molar ratios were synthesized by a “green”, template free technique [2]. With a combination of XAS, XRD and TEM we resolved the changes in the local environment of Ni species induced by the different Al contents in the Ni/ZSM-5 catalysts. Ni species in Ni/ZSM-5 exist as NiO nanocrystals and as charge compensating Ni2+ cations. The Ni K-edge XANES and EXAFS results enabled the quantification of Ni-containing species. At a low Al to Si ratio (nAl/nSi < 0.04), the NiO nanoparticles predominate in the samples and account for over 65% of Ni phases. However, NiO is outnumbered by Ni2+ cations attached to the zeolite framework in ZSM-5 with a high Al to Si ratio (nAl/nSi = 0.05) due to a higher number of framework negative charges imparted by Al. The obtained results show that the number of highly reducible and active NiO nanocrystals is strongly correlated with the framework Al sites present in Ni/ZSM-5 zeolites.
Ključne besede: Ni EXAFS, XANES Ni/ZSM-5 catalyst
Objavljeno v RUNG: 05.07.2024; Ogledov: 1489; Prenosov: 4
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10.
Non-oxidative calcination enhances the methane dry reforming performance of ▫$Ni/CeO_{2−x}$▫ catalysts under thermal and photo-thermal conditions
Kristijan Lorber, Vasyl Shvalya, Janez Zavašnik, Damjan Vengust, Iztok Arčon, Matej Huš, Andraž Pavlišič, Janvit Teržan, Uroš Cvelbar, Blaž Likozar, Petar Djinović, 2024, izvirni znanstveni članek

Opis: We analyzed the effect of the calcination atmosphere and visible-light contribution to an accelerated reaction rate and improved H2 selectivity over 2 wt% Ni/CeO2−x nanorod catalysts. Spectroscopic and structural characterization was performed by operando DRIFTS, in situ Raman, UV-vis and XAS techniques, which were complemented by DFT calculations. Calcination in an argon or H2 atmosphere yields 15% more active catalysts in the thermally driven reaction, which are also more susceptible to light-induced rate acceleration compared to the catalyst calcined in air. The most active 2Ni/CeO2 catalyst calcined in hydrogen converts methane with a rate of 7.5 mmol (gcat min)−1 and produces a H2/ CO ratio of 0.6 at 460 °C when stimulated by a combination of visible light and thermal energy. In the absence of visible light illumination and at an identical catalyst temperature, the achieved methane rate was 4.2 mmol (gcat min)−1 and the H2/CO ratio was 0.49. The non-oxidative calcination improves nickel dispersion and the formation of subnanometer sized Ni clusters, together with a higher abundance of surface and bulk oxygen vacancies in ceria nanorods. The Ni–Ov–Ce3+components constitute the catalytically active sites under visible light illumination, which enable the DRM reaction to proceed with an Ea value of 20 kJ mol−1. Visible light also induces the following changes in the 2Ni/CeO2−x catalyst during the DRM reaction: (1) decomposition and desorption of carbonates from the nickel–ceria interface sites, (2) reduced population of nickel surface with carbonyl species and (3) promoted adsorption and dissociation of methane.
Ključne besede: methane dry reforming performance, calcination
Objavljeno v RUNG: 05.07.2024; Ogledov: 1850; Prenosov: 21
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