| 1. |
- Evertsson, Jonas, et al.
(författare)
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The thickness of native oxides on aluminum alloys and single crystals
- 2015
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Ingår i: Applied Surface Science. - : Elsevier BV. - 1873-5584 .- 0169-4332. ; 349, s. 826-832
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Tidskriftsartikel (refereegranskat)abstract
- We present results from measurements of the native oxide film thickness on four different industrial aluminum alloys and three different aluminum single crystals. The thicknesses were determined using X-ray reflectivity, X-ray photoelectron spectroscopy, and electrochemical impedance spectroscopy. In addition, atomic force microscopy was used for micro-structural studies of the oxide surfaces. The reflectivity measurements were performed in ultra-high vacuum, vacuum, ambient, nitrogen and liquid water conditions. The results obtained using X-ray reflectivity and X-ray photoelectron spectroscopy demonstrate good agreement. However, the oxide thicknesses determined from the electrochemical impedance spectroscopy show a larger discrepancy from the above two methods. In the present contribution the reasons for this discrepancy are discussed. We also address the effect of the substrate type and the presence of water on the resultant oxide thickness.
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| 2. |
- Ghadami Yazdi, Milad, et al.
(författare)
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Structure dependent effect of silicon on the oxidation of Al(111) and Al(100)
- 2019
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Ingår i: Surface Science. - : Elsevier. - 0039-6028 .- 1879-2758. ; 684, s. 1-11
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Tidskriftsartikel (refereegranskat)abstract
- The effect of sub-monolayer silicon on the oxidation of Al(111) and Al(100) surfaces was investigated using X-ray Photoelectron Spectroscopy (XPS) and density functional theory (DFT) calculations. On both surfaces the adatom site is preferred over substituting Si into the Al-lattice; on Al(100) the four fold hollow site is vastly favored whereas on Al(111) bridge and hollow sites are almost equal in energy. Upon O 2 exposure, Si is not oxidized but buried at the metal/oxide interface under the growing aluminum oxide. On Al(111), Si has a catalytic effect on both the initial oxidation by aiding in creating a higher local oxygen coverage in the early stages of oxidation and, in particular, at higher oxide coverages by facilitating lifting Al from the metal into the oxide. The final oxide, as measured from the Al2p intensity, is 25–30% thicker with Si than without. This observation is valid for both 0.1 monolayer (ML) and 0.3 ML Si coverage. On Al(100), on the other hand, at 0.16 ML Si coverage, the initial oxidation is faster than for the bare surface due to Si island edges being active in the oxide growth. At 0.5 ML Si coverage the oxidation is slower, as the islands coalesce and he amount of edges reduces. Upon oxide formation the effect of Si vanishes as it is overgrown by Al 2 O 3 , and the oxide thickness is only 6% higher than on bare Al(100), for both Si coverages studied. Our findings indicate that, in addition to a vanishing oxygen adsorption energy and Mott potential, a detailed picture of atom exchange and transport at the metal/oxide interface has to be taken into account to explain the limiting oxide thickness.
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| 3. |
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| 4. |
- Adams, Emma Catherine, et al.
(författare)
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The structure-function relationship for alumina supported platinum during the formation of ammonia from nitrogen oxide and hydrogen in the presence of oxygen
- 2016
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 18:16, s. 10850-10855
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Tidskriftsartikel (refereegranskat)abstract
- We study the structure-function relationship of alumina supported platinum during the formation of ammonia from nitrogen oxide and dihydrogen by employing in situ X-ray absorption and Fourier transform infrared spectroscopy. Particular focus has been directed towards the effect of oxygen on the reaction as a model system for emerging technologies for passive selective catalytic reduction of nitrogen oxides. The suppressed formation of ammonia observed as the feed becomes net-oxidizing is accompanied by a considerable increase in the oxidation state of platinum as well as the formation of surface nitrates and the loss of NH-containing surface species. In the presence of (excess) oxygen, the ammonia formation is proposed to be limited by weak interaction between nitrogen oxide and the oxidized platinum surface. This leads to a slow dissociation rate of nitrogen oxide and thus low abundance of the atomic nitrogen surface species that can react with the adsorbed hydrogen species. In this case the consumption of hydrogen through the competing water formation reaction and decomposition/oxidation of ammonia are of less importance for the net ammonia formation.
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| 5. |
- Adams, Emma, 1989, et al.
(författare)
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Structure-function relationship for alumina supported platinum during formation of ammonia from nitrogen oxide and hydrogen in presence of oxygen
- 2016
-
Ingår i: Physical Chemistry Chemical Physics. - 1463-9084 .- 1463-9076. ; 18:16, s. 10850-10855
-
Tidskriftsartikel (refereegranskat)abstract
- We study the structure-function relationship of alumina supported platinum during forma- tion of ammonia from nitrogen oxide and dihydrogen by employing in situ X-ray absorption and Fourier transformed infrared spectroscopy. Particular focus is directed towards the effect of increased levels of oxygen on the reaction as a model system for emerging technologies for passive selective catalytic reduction of nitrogen oxides. The suppressed formation of ammo- nia observed as the feed becomes net-oxidizing is accompanied by a considerable increase in the oxidation state of platinum as well as enhanced formation of surface nitrates and loss of NH-containing surface species. In the presence of (excess) oxygen, the ammonia formation is proposed to be limited by the weak interaction between nitrogen oxide and the oxidized platinum surface. This leads to slow dissociation rate of nitrogen oxide and thus low abun- dance of atomic nitrogen surface species that can react with adsorbed hydrogen atoms. In this case the consumption of hydrogen through the competing water formation reaction and decomposition/oxidation of ammonia are of less importance for the net ammonia formation.
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| 6. |
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| 7. |
- Bertram, Florian, et al.
(författare)
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In situ anodization of aluminum surfaces studied by x-ray reflectivity and electrochemical impedance spectroscopy
- 2014
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 116:3
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Tidskriftsartikel (refereegranskat)abstract
- We present results from the anodization of an aluminum single crystal [Al(111)] and an aluminum alloy [Al 6060] studied by in situ x-ray reflectivity, in situ electrochemical impedance spectroscopy and ex situ scanning electron microscopy. For both samples, a linear increase of oxide film thickness with increasing anodization voltage was found. However, the slope is much higher in the single crystal case, and the break-up of the oxide film grown on the alloy occurs at a lower anodization potential than on the single crystal. The reasons for these observations are discussed as are the measured differences observed for x-ray reflectivity and electrochemical impedance spectroscopy.
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| 8. |
- Evertsson, Anna J., et al.
(författare)
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Förord
- 2014
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Ingår i: Framtidens gudstjänst? Kyrkohandboksförslaget granskat. - Skellefteå : Artos & Norma bokförlag. - 9789175807201 ; , s. 7-16
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Bokkapitel (refereegranskat)
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| 9. |
- Evertsson, Jonas, et al.
(författare)
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Anodization of Al(100), Al(111) and Al Alloy 6063 studied in situ with X-ray reflectivity and electrochemical impedance spectroscopy
- 2017
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Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657. ; 799, s. 556-562
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Tidskriftsartikel (refereegranskat)abstract
- We present results from the anodization of single crystal Al(100) and Al(111) surfaces and the aluminum alloy AA 6063 studied in situ by X-ray reflectivity and electrochemical impedance spectroscopy. We observe that the anodic oxide layer grows linearly with the anodization potential and that the thicknesses are similar for all samples. However, the thicknesses obtained from X-ray reflectivity are higher than that obtained from electrochemical impedance spectroscopy. We attribute the higher thicknesses to an outer porous oxide layer, which is not detected by electrochemical impedance spectroscopy. Both, electrochemical impedance spectroscopy and X-ray reflectivity suggests that a more heterogeneous and rough oxide is formed on AA 6063 due to the influence of the alloying elements and intermetallic particles during the growth.
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| 10. |
- Evertsson, Jonas
(författare)
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Protective and Nanoporous Alumina Films Studied in situ by X-ray and Electrochemical Methods
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, the studies of native and anodic oxides on both aluminum model single crystal surfaces as well as on aluminum alloys found in applications are presented. The focus has been on the characterization in situ as the oxide is growing by an electrochemical process called anodization. For the investigations, a combination of various X-ray scattering and spectroscopy methods, as well as electrochemical methods were used. In addition, scanning electron microscopy and atomic force microscopy were used for ex situ characterization after the oxide growth.From thickness measurements of native oxide films, it was found that the film was thicker on the aluminum alloys than on the pure aluminum single crystal surfaces. It was also found that the thicknesses obtained from the electrochemical impedance spectroscopy were thinner than from X-ray reflectivity and X-ray photoelectron spectroscopy. The anodic oxide film was studied during anodization in sodium sulfate and citrate buffer solutions using a combination of X-ray reflectivity and electrochemical impedance spectroscopy. It was found with both techniques that the film thickness increased with anodization potential, but the thicknesses obtained from electrochemical impedance spectroscopy were thinner. The difference was attributed to a porous layer that is difficult to determine with impedance spectroscopy. It was also found that the electrochemical resistance of the oxide was less on the alloys than on the pure aluminum single crystals, which was partly attributed to the alloying elements. Finally, it was found that the anodic oxides formed in the buffer solution were less rough than the oxides formed in the sodium sulfate solutions. Generally, the approach provides the possibility of studying both the electrochemical and structural properties of anodic oxides, which in the future also can be used for corrosion studies of aluminum materials as well as other materials.The growth of self-ordered nanoporous anodic aluminum oxides was studied using grazing-incidence transmission small-angle X-ray scattering by which the interpore distance between the pores, domain size of ordered pores and thickness of the oxide could be followed during the anodization process. In 0.3 M sulfuric acid at 25 V and 0.3 M oxalic acid at 40 V the interpore distance and domain length increased with time, where the final interpore distance and domain length were larger in the case of oxalic acid at 40 V. In both electrolytes it was found that the single crystal orientation did not significantly influence the interpore distance or the domain length. However, it was found that the orientation had a strong influence on the growth rate, especially during anodization in oxalic acid. The electrodeposition of tin into the pores of the oxides was also studied with X-ray fluorescence and grazing-incidence transmission small-angle X-ray scattering, and it was possible to follow the increase of tin in the pores during the deposition. Generally, the method and the approach provides a tool for high statistical and temporal investigations during the growth as well as during possible applications of the nanoporous oxides, which is not obtained with standard microscopy methods that are classically used for studies of these systems.
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| 11. |
- Evertsson, Jonas, et al.
(författare)
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Self-organization of porous anodic alumina films studied in situ by grazing-incidence transmission small-angle X-ray scattering
- 2018
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Ingår i: RSC Advances. - 2046-2069. ; 8:34, s. 18980-18991
-
Tidskriftsartikel (refereegranskat)abstract
- Self-ordered porous anodic alumina (PAA) films are studied extensively due to a large number of possible applications in nanotechnology and low cost of production. Whereas empirical relationships between growth conditions and produced oxides have been established, fundamental aspects regarding pore formation and self-organization are still under debate. We present in situ structural studies of PAA films using grazing-incidence transmission small-angle X-ray scattering. We have considered the two most used recipes where the pores self-organize: 0.3 M H2SO4 at 25 V and 0.3 M C2H2O4 at 40 V. During anodization we have followed the evolution of the structural parameters: average interpore distance, length of ordered pores domains, and thickness of the porous oxide layer. Compared to the extensively used ex situ investigations, our approach gives an unprecedented temporal accuracy in determination of the parameters. By using of Al(100), Al(110) and Al(111) surfaces, the influence of surface orientation on the structural evolution was studied, and no significant differences in the interpore distance and domain length could be observed. However, the rate of oxide growth in 0.3 M C2H2O4 at 40 V was significantly influenced by the surface orientation, where the slowest growth occurs for Al(111). In 0.3 M H2SO4 at 25 V, the growth rates were higher, but the influence of surface orientation was not obvious. The structural evolution was also studied on pre-patterned aluminum surfaces. These studies show that although the initial structures of the oxides are governed by pre-patterning geometry, the final structures are dictated by the anodization conditions.
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| 12. |
- Harlow, Gary S., et al.
(författare)
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Observing growth under confinement : Sn nanopillars in porous alumina templates
- 2019
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Ingår i: Nanoscale Advances. - : Royal Society of Chemistry (RSC). - 2516-0230. ; 1:12, s. 4764-4771
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Tidskriftsartikel (refereegranskat)abstract
- Using a micro-focused high-energy X-ray beam, we have performed in situ time-resolved depth profiling during the electrochemical deposition of Sn into an ordered porous anodic alumina template. Combined with micro-diffraction we are able to follow the variation of the structure at the atomic scale as a function of depth and time. We show that Sn initially deposits at the bottom of the pores, and forms metallic nanopillars with a preferred [100] orientation and a relatively low mosaicity. The lattice strain is found to differ from previous ex situ measurements where the Sn had been removed from the porous support. The dendritic nature of the pore bottom affects the Sn growth mode and results in a variation of Sn grain size, strain and mosaicity. Such atomic scale information of nano-templated materials during electrodeposition may improve the future fabrication of devices.
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| 13. |
- Kiefer, Johannes, et al.
(författare)
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Infrared spectroscopy as molecular probe of the macroscopic metal-liquid interface
- 2017
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Ingår i: Applied Sciences (Switzerland). - : MDPI AG. - 2076-3417. ; 7:12
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Tidskriftsartikel (refereegranskat)abstract
- Metal-liquid interfaces are of the utmost importance in a number of scientific areas, including electrochemistry and catalysis. However, complicated analytical methods and sample preparation are usually required to study the interfacial phenomena. We propose an infrared spectroscopic approach that enables investigating the molecular interactions at the interface, but needing only minimal or no sample preparation. For this purpose, the internal reflection element (IRE) is wetted with a solution as first step. Second, a small plate of the metal of interest is put on top and pressed onto the IRE. The tiny amount of liquid that is remaining between the IRE and the metal is sufficient to produce an IR spectrum with good signal to noise ratio, from which information about molecular interactions, such as hydrogen bonding, can be deduced. Proof-of-concept experiments were carried out with aqueous salt and acid solutions and an aluminum plate.
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| 14. |
- Linpé, Weronica, et al.
(författare)
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The State of Electrodeposited Sn Nanopillars within Porous Anodic Alumina from In-situ X-ray Observations
- 2019
-
Ingår i: ACS Applied Nano Materials. - : American Chemical Society (ACS). - 2574-0970. ; 2:5, s. 3031-3038
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Tidskriftsartikel (refereegranskat)abstract
- Porous anodic alumina (PAA) can be used as a template for controlled electrodeposition and growth of nano-structures, it is also essential for long-lasting decorative coloring of aluminum. We have investigated the deposition of Sn nanopillars into PAA in-situ, with Grazing transmission small angle X-ray scattering, X-ray fluorescence and X-ray absorption near edge structure spectroscopy. An accumulation of Sn could be detected in the pores during the electrodeposition. From the X-ray absorption near edge structure spectroscopy measurements we could conclude that the deposited Sn was primarily in the metallic state. Ex-situ scanning electron microscopy cross-section measurements show Sn nanopillars inside the PAA.
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| 15. |
- Lundblad, Jonas, et al.
(författare)
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Förord
- 2014
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Ingår i: Svenskt gudstjänstliv. - 2001-5828 .- 0280-9133. ; 89, s. 7-16
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Bokkapitel (refereegranskat)
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| 16. |
- Långberg, Marie, 1988-, et al.
(författare)
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Redefining passivity breakdown of super duplex stainless steel by electrochemical operando synchrotron near surface X-ray analyses
- 2019
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Ingår i: npj Materials Degradation. - Stockholm, : Springer Science and Business Media LLC. - 2397-2106. ; 3:1
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Tidskriftsartikel (refereegranskat)abstract
- Passivity determines corrosion resistance and stability of highly-alloyed stainless steels, and passivity breakdown is commonly believed to occur at a fixed potential due to formation and dissolution of Cr(VI) species. In this work, the study of a 25Cr–7Ni super duplex stainless steel in 1 M NaCl solution revealed that the passivity breakdown is a continuous degradation progress of the passive film over a potential range, associated with enhanced Fe dissolution before rapid Cr dissolution and removal of the oxide. The breakdown involves structural and compositional changes of the passive film and the underlying alloy surface layer, as well as selective metal dissolution depending on the anodic potential. The onset of passivity breakdown occurred at 1000 mV/Ag/AgCl, and Fe dissolved more on the ferrite than the austenite phase. With increasing potential, the passive film became thicker but less dense, while the underlying alloy surface layer became denser indicating Ni and Mo enrichment. Rapid Cr dissolution occurred at ≥1300 mV/Ag/AgCl.
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| 17. |
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| 18. |
- Rullik, Lisa, et al.
(författare)
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Surface oxide development on aluminum alloy 6063 during heat treatment
- 2019
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Ingår i: Surface and Interface Analysis. - : Wiley. - 0142-2421 .- 1096-9918. ; 51:12, s. 1214-1224
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Tidskriftsartikel (refereegranskat)abstract
- We report on the influence of oxygen partial pressure for the development of surface oxides covering the industrial aluminum alloy standard 6063 at temperatures ranging from room temperature to 500° C. Using an array of synchrotron-based techniques, we followed the change in oxide thickness, chemical composition, and the lateral distribution of alloying elements. The impact of the oxygen chemical potential is most visible at high temperatures where the oxide composition changes from mostly Al based to mostly Mg based. This is in stark contrast to the ultra-high vacuum (UHV) conditions where only a partial compositional transition is observed. The microscopy data demonstrate that in the UHV case, Mg segregation onto the surface occurs firstly at grain boundaries at 300° C and secondly at sites over the entire surface at 400° C. Further, the initial oxide thickness is 45 Å, as determined by XPS and XRR, decreases in all observed cases after heating to 300° C. At higher temperatures, however, the oxygen partial pressure highly influences the resulting oxide thickness as evident from our X-ray reflectivity data.
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| 19. |
- Vinogradov, Nikolay A., et al.
(författare)
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Observation of Pore Growth and Self-Organization in Anodic Alumina by Time-Resolved X-ray Scattering
- 2018
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Ingår i: ACS Applied Nano Materials. - : American Chemical Society (ACS). - 2574-0970. ; 1:3, s. 1265-1271
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Tidskriftsartikel (refereegranskat)abstract
- The anodic oxidation of metals such as aluminum and titanium can lead to the development of self-ordering pores. These pores make excellent templates for a range of nanoscale objects with many applications in nanoscience. Theoretical studies on pore formation have proposed several models for the establishment, growth, and ordering of these pores; however, experimental verification has mostly been limited to ex situ measurements. Here we show that the lateral and vertical pore structure can be probed in situ with high precision, using grazing transmission X-ray scattering. By making use of the high flux available at modern synchrotrons and fitting only the difference between scattering patterns we show the nearly real-time evolution of the pore’s arrangement. We observe no dependence on the substrate crystallographic orientation for domain size or pore separation. We do however observe an anisotropy in the oxide growth rate for the different substrate surfaces. This experimental approach can be applied to the study of a large variety of electrochemically produced materials such as magnetic nanowires, novel solar cell designs, and catalysts.
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| 20. |
- Weber, Tim, et al.
(författare)
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Extraordinary Stability of IrO2(110) Ultrathin Films Supported on TiO2(110) under Cathodic Polarization
- 2020
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Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; , s. 9057-9062
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Tidskriftsartikel (refereegranskat)abstract
- Down to a cathodic potentials of -1.20 V versus the reversible hydrogen electrode, the structure of IrO2(110) electrodes supported by TiO2(110) is found to be stable by in situ synchrotron-based X-ray diffraction. Such high cathodic potentials should lead to reduction to metallic Ir (Pourbaix diagram). From the IrO2 lattice parameters, determined during cathodic polarization in a H2SO4 electrolyte solution (pH 0.4), it is estimated that the unit cell volume increases by 1% due likely to proton incorporation, which is supported by the lack of significant swelling of the IrO2(110) film derived from X-ray reflectivity experiments. Ex situ X-ray photoelectron spectroscopy suggests that protons are incorporated into the IrO2(110) lattice below -1.0 V, although Ir remains exclusively in the IV+ oxidation state down to -1.20 V. Obviously, further hydrogenation of the lattice oxygen of IrO2(110) toward water is suppressed for kinetic reasons and hints at a rate-determining chemical step that cannot be controlled by the electrode potential.
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| 21. |
- Weber, Tim, et al.
(författare)
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In situ studies of the cathodic stability of single-crystalline IrO2(110) ultrathin films supported on RuO2(110)/Ru(0001) in an acidic environment
- 2020
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 22:40, s. 22956-22962
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Tidskriftsartikel (refereegranskat)abstract
- We investigate with in situ surface X-ray diffraction (SXRD) and X-ray reflectivity (XRR) experiments the cathodic stability of an ultrathin single-crystalline IrO2(110) film with a regular array of mesoscopic rooflike structures that is supported on a RuO2(110)/Ru(0001) template. It turns out that the planarity of the single-crystalline IrO2(110) film is lost in that IrO2(110) oxide domains delaminate at a cathodic potential of -0.18 V. Obviously, the electrolyte solution is able to reach the RuO2(110) layer presumably through the surface grain boundaries of the IrO2(110) layer. Subsequently, the single-crystalline RuO2(110) structure-directing template is reduced to amorphous hydrous RuO2, with the consequence that the IrO2(110) film loses partly its adhesion to the template. From in situ XRR experiments we find that the IrO2(110) film does not swell upon cathodic polarization down to -0.18 V, while from in situ SXRD experiments, the lattice constants of IrO2(110) are shown to be not affected. The rooflike mesostructure of the IrO2(110) flakes remains intact after cathodic polarization to -0.18 V, evidencing that the crystallinity of IrO2(110) is retained. This journal is
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| 22. |
- Weber, Tim, et al.
(författare)
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In Situ Synchrotron-Based Studies of IrO2(110)-TiO2(110) under Harsh Acidic Water Splitting Conditions : Anodic Stability and Radiation Damages
- 2022
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 126:48, s. 20243-20250
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Tidskriftsartikel (refereegranskat)abstract
- In situ stability studies of an IrO2(110)-TiO2(110) model electrode are carried out under acidic water electrolysis conditions, employing synchrotron-based techniques including surface X-ray diffraction (SXRD) and X-ray reflectometry (XRR) with a photon energy of 21.5 keV. These experiments are complemented by ex situ scanning electron microscopy (SEM), scanning tunneling microscopy (STM), and X-ray photoelectron spectroscopy (XPS) experiments. Even at an anodic current density of 250 mA·cm-2during electrochemical water splitting, the IrO2(110)-TiO2(110) model electrode turned out to be stable against Ir dissolution. However, radiation-induced damages of the IrO2(110) film are observed: Part of the IrO2(110) film delaminates upon heavy exposure to the synchrotron beam, while subsequently the uncovered TiO2(110) is subject to further (photon-induced) corrosion. We propose that the X-ray photons induce oxygen vacancy formation by displacing O2-ions of TiO2from regular to interstitial sites, while the potential drop across the TiO2(110) substrate leads to a migration of interstitial O2-ions from interface toward bulk TiO2. This reduction step at the interface between IrO2(110) and TiO2(110) weakens the adhesion of the epitaxially grown IrO2(110) film to the TiO2(110) substrate so that the strained IrO2(110) film is partially delaminated. Higher X-ray photon energies of 60-90 keV mitigate this degradation process.
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| 23. |
- Weber, Tim, et al.
(författare)
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Potential-Induced Pitting Corrosion of an IrO2(110)-RuO2(110)/Ru(0001) Model Electrode under Oxygen Evolution Reaction Conditions
- 2019
-
Ingår i: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 9:7, s. 6530-6539
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Tidskriftsartikel (refereegranskat)abstract
- Sophisticated IrO2(110)-based model electrodes are prepared by deposition of a 10 nm thick single-crystalline IrO2(110) layer supported on a structure-directing RuO2(110)/Ru(0001) template, exposing a regular array of mesoscopic rooflike structures. With this model electrode together with the dedicated in situ synchrotron based techniques (SXRD, XRR) and ex situ characterization techniques (SEM, ToF-SIMS, XPS), the corrosion process of IrO2(110) in an acidic environment (pH 0.4) is studied on different length scales. Potential-induced pitting corrosion starts at 1.48 V vs SHE and is initiated at so-called surface grain boundaries, where three rotational domains of IrO2(110) meet. The most surprising result is, however, that even when the electrode potential is increased to 1.94 V vs SHE 60-70% of the IrO2 film still stays intact down to the mesoscale and atomic scale and no uniform thinning of the IrO2(110) layer is encountered. Neither flat IrO2(110) terraces nor single steps are attacked. Ultrathin single-crystalline IrO2(110) layers seem to be much more stable to anodic corrosion than hitherto expected.
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| 24. |
- Zetterberg, Johan, et al.
(författare)
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Spatially and temporally resolved gas distributions around heterogeneous catalysts using infrared planar laser-induced fluorescence.
- 2015
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- Visualizing and measuring the gas distribution in close proximity to a working catalyst is crucial for understanding how the catalytic activity depends on the structure of the catalyst. However, existing methods are not able to fully determine the gas distribution during a catalytic process. Here we report on how the distribution of a gas during a catalytic reaction can be imaged in situ with high spatial (400 μm) and temporal (15 μs) resolution using infrared planar laser-induced fluorescence. The technique is demonstrated by monitoring, in real-time, the distribution of carbon dioxide during catalytic oxidation of carbon monoxide above powder catalysts. Furthermore, we demonstrate the versatility and potential of the technique in catalysis research by providing a proof-of-principle demonstration of how the activity of several catalysts can be measured simultaneously, either in the same reactor chamber, or in parallel, in different reactor tubes.
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| 25. |
- Zhang, Chu, et al.
(författare)
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An in situ sample environment reaction cell for spatially resolved x-ray absorption spectroscopy studies of powders and small structured reactors.
- 2015
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 86:3
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Tidskriftsartikel (refereegranskat)abstract
- An easy-to-use sample environment reaction cell for X-ray based in situ studies of powders and small structured samples, e.g., powder, pellet, and monolith catalysts, is described. The design of the cell allows for flexible use of appropriate X-ray transparent windows, shielding the sample from ambient conditions, such that incident X-ray energies as low as 3 keV can be used. Thus, in situ X-ray absorption spectroscopy (XAS) measurements in either transmission or fluorescence mode are facilitated. Total gas flows up to about 500 mln/min can be fed while the sample temperature is accurately controlled (at least) in the range of 25-500 °C. The gas feed is composed by a versatile gas-mixing system and the effluent gas flow composition is monitored with mass spectrometry (MS). These systems are described briefly. Results from simultaneous XAS/MS measurements during oxidation of carbon monoxide over a 4% Pt/Al2O3 powder catalyst are used to illustrate the system performance in terms of transmission XAS. Also, 2.2% Pd/Al2O3 and 2% Ag - Al2O3 powder catalysts have been used to demonstrate X-ray absorption near-edge structure (XANES) spectroscopy in fluorescence mode. Further, a 2% Pt/Al2O3 monolith catalyst was used ex situ for transmission XANES. The reaction cell opens for facile studies of structure-function relationships for model as well as realistic catalysts both in the form of powders, small pellets, and coated or extruded monoliths at near realistic conditions. The applicability of the cell for X-ray diffraction measurements is discussed.
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