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- Bertrand, Philippe, et al.
(författare)
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Passivation Layer and Cathodic Redox Reactions in Sodium-Ion Batteries Probed by HAXPES
- 2017
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In this presentation, we will present a recent example on electrode/electrolyte interfaces of materials for energy storage devices using hard X-rays photoelectron spectroscopy (HAXPES). A nondestructive analysis was made through the electrode/electrolyte interface of the first electrochemical cycle to ensure access to information not only on the active material, but also on the passivation layer formed at the electrode surface and referred to as the solid permeable interface (SPI). [1] While electrode/electrolyte study has been performed widely on Li-ion battery, not so much attention as been addressed to the Na-ion technology so far. We will focus in this presentation to NaxCo2/3Mn2/9Ni1/9O2, a novel intercalation material that could be be used as cathode in Na-ion batteries. [2] During a typical charge/discharge cycle (i.e. extraction/insertion of Na+ ions), the oxidation state of the various transition metals in the compound changes in a reversible way. A step by step analysis of the first electrochemical cycle was carried out by HAXPES providing unique information on the oxidation state of Ni, Co and Mn as well as a very interesting insight into the passivation layer present at the surface of the electrode, which results from the degradation of the electrolyte components upon reaction. This investigation shows the role of the SPI and the complexity of the redox reactions. [3] [1] B. Philippe, M. Hahlin, K. Edström, T. Gustafsson, H. Siegbahn, H. Rensmo, J. Electrochem. Soc, 2016, 163, A178-A191[2] S. Doubaji, M. Valvo, I. Saadoune, M. Dahbi, K.Edström, J. Power Sources, 2014, 266, 275-281[3] S. Doubaji, B. Philippe, I. Saadoune, M. Gorgoi, T. Gustafsson, A. Solhy, M. Valvo, H. Rensmo, K. Edström, ChemSusChem, 2016, 9, 97-108
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| 2. |
- Chernysheva, Ekaterina, et al.
(författare)
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Band alignment at Ag/ZnO(0001) interfaces : A combined soft and hard x-ray photoemission study
- 2018
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Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 97:23
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Tidskriftsartikel (refereegranskat)abstract
- Band alignment at the interface between evaporated silver films and Zn- or O-terminated polar orientations of ZnO is explored by combining soft and hard x-ray photoemissions on native and hydrogenated surfaces. Ultraviolet photoemission spectroscopy (UPS) is used to track variations of work function, band bending, ionization energy, and Schottky barrier during silver deposition. The absolute values of band bending and the bulk position of the Fermi level are determined on continuous silver films by hard x-ray photoemission spectroscopy (HAXPES) through a dedicated modeling of core levels. Hydrogenation leads to the formation of similar to 0.3 monolayer of donorlike hydroxyl groups on both ZnO-O and ZnO-Zn surfaces and to the release of metallic zinc on ZnO-Zn. However, no transition to an accumulation layer is observed. On bare surfaces, silver adsorption is cationic on ZnO(000 (1) over bar)-O [anionic on ZnO(0001)-Zn] at the earliest stages of growth as expected from polarity healing before adsorbing as a neutral species. UPS and HAXPES data appear quite consistent. The two surfaces undergo rather similar band bendings for all types of preparation. The downward band bending of V-bb,(ZnO-O) = -0.4 eV and V-bb,(ZnO-Zn) = -0.6 eV found for the bare surfaces is reinforced upon hydrogenation (V-bb,(ZnO-O+H) = -1.1 eV, V-bb,(ZnO-Zn+H) = -1.2 eV). At the interface with Ag, a unique value of band bending of -0.75 eV is observed. While exposure to atomic hydrogen modulates strongly the energetic positions of the surface levels, a similar Schottky barrier of 0.5-0.7 eV is found for thick silver films on the two surfaces.
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| 4. |
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| 5. |
- Doubaji, Siham, et al.
(författare)
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Passivation Layer and Cathodic Redox Reactions in Sodium-Ion Batteries Probed by HAXPES
- 2016
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Ingår i: ChemSusChem. - : Wiley. - 1864-5631 .- 1864-564X. ; 9:1, s. 97-108
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Tidskriftsartikel (refereegranskat)abstract
- The cathode material P2-NaxCo2/3Mn2/9Ni1/9O2, which could be used in Na-ion batteries, was investigated through synchrotron-based hard X-ray photoelectron spectroscopy (HAXPES). Nondestructive analysis was made through the electrode/electrolyte interface of the first electrochemical cycle to ensure access to information not only on the active material, but also on the passivation layer formed at the electrode surface and referred to as the solid permeable interface (SPI). This investigation clearly shows the role of the SPI and the complexity of the redox reactions. Cobalt, nickel, and manganese are all electrochemically active upon cycling between 4.5 and 2.0V; all are in the 4+ state at the end of charging. Reduction to Co3+, Ni3+, and Mn3+ occurs upon discharging and, at low potential, there is partial reversible reduction to Co2+ and Ni2+. A thin layer of Na2CO3 and NaF covers the pristine electrode and reversible dissolution/reformation of these compounds is observed during the first cycle. The salt degradation products in the SPI show a dependence on potential. Phosphates mainly form at the end of the charging cycle (4.5V), whereas fluorophosphates are produced at the end of discharging (2.0V).
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| 8. |
- Fondell, Mattis, 1984-, et al.
(författare)
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An HAXPES study of Sn, SnS, SnO and SnO2
- 2014
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Mattis Fondell. - 0368-2048 .- 1873-2526. ; 195, s. 195-199
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Tidskriftsartikel (refereegranskat)abstract
- Hard X-ray photoelectron spectra have been recorded for Sn, SnO2, SnO and SnS. The binding energies of the core levels of elemental Sn from 2s up to, and including, 4d have been determined with least squares fitting and calibrated against an Au 4f standard. For the oxides and the sulphide data on Sn 3p, 3d core levels’ binding energies and relative intensities are presented together with the binding energies of O 1s, S 1s and 2p. This study thus serves as a picture of tin's core level spectra compared to those of some of its oxides and a sulphide taken at photon energies beyond Al Kα and Mg Kα.
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| 9. |
- Fondell, Mattis, 1984-, et al.
(författare)
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HAXPES study of Sn core levels and their plasmon loss features
- 2014
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Ingår i: Results in Physics. - : Elsevier BV. - 2211-3797. ; 4, s. 168-169
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Tidskriftsartikel (refereegranskat)abstract
- Hard X-ray Photoelectron spectra have been recorded for elemental Sn. Electron loss features, prominent in all core level spectra of the metal, are analyzed at several photo energies for the 3p core level. For higher photoelectron kinetic energies the intensity of the plasmonic features follows a simple exponential law. The data and models presented here will aid the modeling of spectra where tin is present and especially if its spectrum overlaps with those from other sources.
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| 10. |
- Fondell, Mattis, 1984-, et al.
(författare)
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Phase control of iron oxides grown in nano-scale cauliflower structures: hematite, maghemite and magnetite
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We demonstrate that iron oxide in the form of hematite, suitable as absorber in photoelectrochemical cells, can be produced by pulsed chemical vapour deposition. By choosing carbon monoxide or nitrogen as carrier gases in the process the phase and granularity of the grown material can be controlled. The choice of carrier gas a ect the decomposition rate of iron pentacarbonyl used as iron precursor. The iron oxide phase is also dependent on the chosen substrate, here fluorine doped tin oxide and crystalline silicon have been used. Regardless of the substrate nitrogen yields hematite, whereas carbon monoxide gives magnetite on Si and maghemite on fluorine doped tin oxide. A combination of Raman spectroscopy, X-ray di raction, and hard X-ray photoelectron spectroscopy were used for characterization of the crystalline phase and chemical composition in the films. Scanning electron microscopy were used to visualise the deposited films’ nano-structure reminiscent of a cauliflower.
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