| 1. |
- Ciosek Högström, Katarzyna
(författare)
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The Complex Nature of the Electrode/Electrolyte Interfaces in Li-ion Batteries : Towards Understanding the Role of Electrolytes and Additives Using Photoelectron Spectroscopy
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The stability of electrode/electrolyte interfaces in Li-ion batteries is crucial to the performance, lifetime and safety of the entire battery system. In this work, interface processes have been studied in LiFePO4/graphite Li-ion battery cells. The first part has focused on improving photoelectron spectroscopy (PES) methodology for making post-mortem battery analyses. Exposure of cycled electrodes to air was shown to influence the surface chemistry of the graphite. A combination of synchrotron and in-house PES has facilitated non-destructive interface depth profiling from the outermost surfaces into the electrode bulk. A better understanding of the chemistry taking place at the anode and cathode interfaces has been achieved. The solid electrolyte interphase (SEI) on a graphite anode was found to be thicker and more inhomogeneous than films formed on cathodes. Dynamic changes in the SEI on cycling and accumulation of lithium close to the carbon surface have been observed. Two electrolyte additives have also been studied: a film-forming additive propargyl methanesulfonate (PMS) and a flame retardant triphenyl phosphate (TPP). A detailed study was made at ambient and elevated temperature (21 and 60 °C) of interface aging for anodes and cathodes cycled with and without the PMS additive. PMS improved cell capacity retention at both temperatures. Higher SEI stability, relatively constant thickness and lower loss of cyclable lithium are suggested as the main reasons for better cell performance. PMS was also shown to influence the chemical composition on the cathode surface.The TPP flame retardant was shown to be unsuitable for high power applications. Low TPP concentrations had only a minor impact on electrolyte flammability, while larger amounts led to a significant increase in cell polarization. TPP was also shown to influence the interface chemistry at both electrodes.Although the additives studied here may not be the final solution for improved lifetime and safety of commercial batteries, increased understanding has been achieved of the degradation mechanisms in Li-ion cells. A better understanding of interface processes is of vital importance for the future development of safer and more reliable Li-ion batteries.
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| 2. |
- Mattsson, Andreas, 1976-
(författare)
-
Formic acid adsorption and photodecomposition on rutile TiO2 (110) : An in situ infrared reflection absorption spectroscopy study
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- TiO2 based photocatalysis is an emerging green nanotechnology that can be used forremoval of pollutants from water and air. It has had an increased research interest, bothfrom an application and fundamental point of view, during the last decades. Despite thismany elementary processes that occur on the photocatalyst surface are not fullyunderstood and are thus limiting our ability to purposefully manufacture more efficientphotocatalytic materials.In this licentiate thesis, the adsorption geometry and photodecomposition of formicacid on differently prepared rutile TiO2 (110) surfaces were investigated. The surface wasprepared by repeated cycles of Argon ion sputtering and annealing. By modifying thisprocedure either reduced, stoichiometric or oxylated surfaces have been obtained. Thesedifferent surfaces are all well-ordered as evident from the obtained low energy electrondiffraction pattern. In addition, a totally disordered surface was also prepared by Argonsputtering alone. Grazing incidence infrared reflection-absorption spectroscopy (IRRAS)employing polarized light with different azimuthal orientations of the TiO2 single crystalwas used to investigate the binding geometry of formic acid (HCOOH) on the surface.Upon adsorption of formic acid on the TiO2 surface, the molecule is deprotonatedresulting in a formate (HCOO-) and a hydrogen (H+) molecule on the surface. The formatemolecules are mainly bridge-bonded to the Ti5c surface atoms with their molecular axisalong the [001] direction. A minority of the formate species was found to adsorb throughhydroxylated oxygen vacancies (or protonated oxygen atoms) and therefore have differentorientations on the surface. For the disordered surface, it was found that the orientation ofthe formate adsorbates are more or less random since no changes in the IRRAS spectraare seen for the different directions of the single crystal. The adsorption geometry for thedisordered surface is also changed, as seen in the shift of the peak positions in the IRRASspectra. This changed adsorption geometry is attributed to exposures of Ti3+ atoms on thesurface, and is a result of the Ar ion sputtering.Irradiation of the HCOO/TiO2 systems by UV light (365 nm, 2 mW/cm2) showed onlya small change in formate coverage after 100 minutes of illumination. The decrease waslargest on the disordered surface and miniscule on the ordered surface. These results werecompared with those obtained on rutile nanoparticles at ambient conditions. Thecomparison shows that the adsorption geometry for the nanoparticles is similar to that ofthe ordered single crystal surfaces and that the photodecomposition rate is about a factorof 30 higher on the nanoparticles than on the disordered surface. This difference isexpected as the single crystal experiments were performed in vacuum, where the supplyof O2 electron acceptors and OH/H2O donors from the gas phase is limited.These results shows that the rutile TiO2 (110) surface is a good model system forfundamental studies of nanoparticle systems and that the presence of hydroxylated oxygenvacancies and protonated oxygen atoms are important for the reactivity of the TiO2surface and must be included in the description of surface reactions on rutile surfaces.
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| 3. |
- Josefsson, Ida, 1984-
(författare)
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Structure and dynamics in solution – the core electron perspective
- 2015
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is based on theoretical studies of the molecular and electronic structure of solvated ions and molecules. Very detailed information of the system can be obtained from theoretical calculations, but a realistic model is dependent on an accurate computational method. Accurate calculations of core level electronic spectra, and evaluation of the modeling against experiments, are central parts of this work. The main tools used for characterization of the systems are high-level quantum chemistry and molecular dynamics simulations. Molecular components in solutions are involved in many key processes converting sunlight into chemical or electrical energy. Transition metal complexes, with their pronounced absorption in the visible light region of the electromagnetic spectrum, are core components in various energy conversion applications, and the iodide/triiodide redox couple is a commonly used electrolyte. The local structure of the electronic valence in transition metal complexes and the details of the solvation mechanisms of electrolyte solutions are investigated through the combination of computational modeling and core level spectroscopy. The studies of model systems show that interactions between the solute and solvent are important for the electronic structure, and knowledge of the details in model systems studied can be relevant for energy conversion applications. Furthermore, high-level quantum chemistry has been applied for interpreting time-resolved spectra, where the electronic structure of a metal complex is followed during a photoinduced chemical reaction in solution.With advanced modeling in combination with recent experimental developments, more complex problems than previously addressed can be dissected.
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| 4. |
- Källquist, Ida
(författare)
-
Interfaces in Li-ion batteries seen through photoelectron spectroscopy
- 2019
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- To accommodate the need for greener energy solutions renewable energy sources aswell as reliable energy storage is a prerequisite. For the latter, high energy densitybatteries with long-term cycling stability are necessary. The cycling properties of abattery is to a large extent dependent on the functionality of the battery interfaces. Assuch, there is a need to understand the reactions occurring between the electrode andelectrolyte, and to limit those that are detrimental to the battery performance. Thetopic of this thesis is these interfaces in Li-ion batteries seen through photoelectronspectroscopy (PES).PES is due to its surface and chemical sensitivity one of the most suitable techniquesto study battery interfaces. In this thesis, PES is used to follow the oxidationstate and chemical environment of different atoms to understand the reactions occurringin the battery. This work uses a combination of soft and hard X-ray photoelectronspectroscopy as well X-ray absorption spectroscopy (XAS) to investigate the degradationmechanisms in high energy density cathode materials. The materials investigatedare in the class of Li-rich disordered rock-salts (DRS) and provide very highinitial capacities, but unfortunately lacks in cycling stability. In this thesis it is shownthat the reason for this is an unstable surface, possibly related to the occurrence ofanionic redox in the material, leading to breakdown of both electrolyte and electrodematerial. In addition, it is shown that the interface stability can be improved by choosingtransition metals that promotes the DRS structure and thus increases the chemicalstability of the material and long term cycling of the battery.Even though ex situ measurements provide many insights into the properties ofbattery interphases, there is still a need for operando measurement to completely answerthe puzzling question of their full functionality. In this thesis first steps towardsoperando measurements are taken by identifying the measurements conditions necessaryto probe a battery electrolyte with ambient pressure photoelectron spectroscopy(APPES) and a thorough characterization of a typical battery electrolyte is performed.The results show that the liquid can be stabilized by using the solvent as ambient gas,and also that care should be taken to avoid radiation damage when synchrotron lightis used. For the electrolyte characterization it is shown that a salt enrichment of particularlyLi+ and ionic fluoride is found at the droplet surface. These results are crucialto be able to single out contributions from the interphase in future operando measurements.When the method of operando APPES has matured and can be performed routinely,this could possibly be the key needed to understand how the interfaces in batteriescan be controlled to unlock the potential of stable high capacity materials infuture batteries.
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| 5. |
- Massel, Felix, 1986-
(författare)
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Anion redox processes in novel battery cathode materials investigated by soft X-ray spectroscopy
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents experimental investigations of the electronic structure of emerging and novel cathode materials used in lithium- and sodium-ion batteries. The investigated materials include a range of oxide materials containing the elements nickel and manganese. Central goals are to find fundamental explanations for favorable, respectively, unfavorable electrochemical cycling behavior and to arrive at a better understanding of the roles that the different elemental constituents of the compounds play. The experiments are based on the application of X-ray Absorption Spectroscopy (XAS) and Resonant Inelastic X-ray Scattering (RIXS) in the soft X-ray region and have been performed at synchrotron radiation facilities such as The Advanced Light Source (USA), The Swiss Light Source (Switzerland) and SPring-8 (Japan). XAS and RIXS of spinel LiNi0.44Mn1.56O4 at the O K-edge as well as the Ni and Mn L-edges were measured for two different crystal structures, namely, transition-metal-ordered and -disordered, respectively. The results show that both Ni and O contribute strongly as redox centers for the charge compensation during electrochemical cycling. The Ni L-RIXS spectra show evidence of a more stable Ni--O bond in the disordered material. In the layered manganese oxide materials Li[Li0.2Ni0.2Mn0.6]O2, Na0.67[Mg0.28Mn0.72]O2, and Na0.78[Li0.25Mn0.75]O2, as well as the disordered Li1.9Mn0.95O2.05F0.95 one observes that reversible O redox leads to two distinct features in O K-RIXS. Both features resonate in a narrow incident energy range suggesting that localized O hole states are formed, one close to the elastic peak and the other as a strong emission peak at an energy loss of about 8 eV. These features appear reversibly on the voltage plateau of the charge-discharge curve and can be used to identify a certain type of O redox reactions.The work also includes investigations that compare two different compositions of the structurally related material Li2MnO3 grown epitaxially as thin films. Evidence is found for anionic activity during the initial cycle that is of a different kind than the above as no evidence for localized O holes is found. Instead, excess Li in the transition metal layer is shown to lead to a more rapid loss of covalency in the Mn--O bonds.In short, this work presents some of the first explorations into the role of different types of anionic redox centers in cathodes, by means of XAS and RIXS thereby also demonstrating the utility and power of synchrotron based techniques for gaining atomic-level understanding of battery electrode materials.
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| 6. |
- Oscarsson, Johan, 1984-
(författare)
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Towards Mixed Molecular Layers for Dye-Sensitized Solar Cells : A Photoelectron Spectroscopy Study
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The increasing demand for renewable energy has led to substantial research on different solar cell technologies. The dye-sensitized solar cell (DSC) is a technology utilizing dye molecules for light absorption. Dye molecules are adsorbed to a mesoporous semiconductor surface and after light absorption in the dye, charge separation occurs at this interface. Traditionally, DSCs have used layers of single dye species, but in recent efforts to enhance power conversion efficiency, more complex molecular layers have been designed to increase the light absorption. For example, the most efficient DSCs use a combination of two dye molecules, and such dye co-adsorption is studied in this thesis.A key to highly efficient DSCs is to understand the dye/semiconductor interface from a molecular perspective. One way of gaining this understanding is by using an element specific, surface sensitive technique, such as photoelectron spectroscopy (PES).In this thesis, PES is used to understand new complex dye/semiconductor interfaces. Dyes adsorbed to semiconductor surfaces are analyzed using PES in terms of geometric and electronic surface structure. The investigations ultimately target the effects of co-adsorbing dyes with other dyes or co-adsorbents.PES shows that Ru dyes can adsorb in mixed configurations to TiO2. Co-adsorption with an organic dye affects the configuration of the Ru dyes. As a consequence, shifts in energy level alignment and increased dye coverage are observed. The dyes are affected at a molecular level in ways beneficial for solar cell performance. This is called collaborative sensitization and is also observed in todays most efficient DSC.Dye molecules are generally sensitive to high temperatures and the substantial decrease in power conversion efficiency after heat-treatment can be understood using PES. Furthermore, comparing two mesoscopic TiO2 morphologies used in DSCs show differences in trap state density in the band gap, explaining the photovoltage difference in DSCs comprising these morphologies. Using mixed molecular layers on NiO results in significant improvements of p-type DSC power conversion efficiency. PES shows that changed adsorption configuration contribute to this effect.This thesis shows that PES studies can be used to obtain insight into functional properties of complex DSC interfaces at a molecular level.
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| 7. |
- Plogmaker, Stefan
(författare)
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Techniques and Application of Electron Spectroscopy Based on Novel X-ray Sources
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The curiosity of researchers to find novel characteristics and properties of matter constantly pushes for the development of instrumentation based on X-radiation. I present in this thesis techniques for electron spectroscopy based on developments of X-ray sources both in time structure and energy. One part describes a laser driven High-Harmonic Generation source and the application of an off-plane grating monochromator with additional beamlines and spectrometers. In initial experiments, the source is capable of producing harmonics between the 13th and 23rd of the fundamental laser 800 nm wavelength. The intensity in the 19th harmonic, after monochromatization, was measured to be above 1.2·1010 photons/second with a repetition rate of 5 kHz. The development of a chopper system synchronized to the bunch clock of an electron storage ring is also presented. The system can be used to adjust the repetition rate of a synchrotron radiation beam to values between 10 and 120 kHz, or for the modulation of continuous sources. The application of the system to both time of flight spectroscopy and laser pump X-ray probe spectroscopy is shown. It was possible to measure triple ionization of Kr and in applied studies the valence band of a laser excited dye-sensitized solar cell interface. The combination of the latter technique with transient absorption measurements is proposed.The organic molecule maleic anhydride (MA) and its binding configuration to the three anatase TiO2 crystals (101), (100), (001) has been investigated by means of Xray Photoelectron Spectroscopy (XPS) and Near Edge X-ray Absorption Fine structure Spectroscopy (NEXAFS). The results provide information on the binding configuration to the 101 crystal. High Kinetic Energy Photoelectron Spectroscopy was used to investigate multilayers of complexes of iron, ruthenium and osmium. The benefit of hard X-rays for ex-situ prepared samples is demonstrated together with the application of resonant valence band measurements to these molecules.
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| 8. |
- Svanström, Sebastian, 1990-
(författare)
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The life and death of perovskites : Interfacial function and degradation of lead halide perovskites studied by photoelectron spectroscopy
- 2021
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lead halide perovskite solar cells are a promising new technology which could soon see widespread commercial application but is partly held back by poor long-term stability. In this thesis, photoelectron spectroscopy (PES) is used to study the dynamical processes at the surface or interfaces of lead halide perovskite materials. Some of these processes are responsible for the different types of degradation while others are essential for the function of the solar cell. The work includes a range of lead perovskite compositions with the general formula APbX3, in which A is a monovalent cation, and often organic (e.g. formamidinium or methylammonium), and X is a halide anion, typically Br- or I-. The compositions can also include mixtures of cations at the A and anions at the X site.Part of this thesis is dedicated to investigating the degradation of the perovskite surface in response to both intense visible light and X-ray irradiation. The results show that intense illumination induces the decomposition of the perovskite into metallic lead, halide gas and organic halide salt, but also indicate how this process can be suppressed by the addition of small amounts of Cs+ ions and by adjusting the relative amounts of halides. A different process, induced by the X-ray radiolysis of the organic cation, is shown to consume rather than form metallic lead.Another part of this thesis is dedicated to the investigation of the reactions at the interfaces between the perovskite and silver, copper or SnOx. The results show that both copper and silver react rapidly with the perovskite forming metal halides and that the metal can diffuse into the perovskite. Copper is particularly reactive, leading to the formation of two new compounds and the bulk degradation of the perovskite. The SnOx is significantly more stable but material intermixing results in the formation of a thin interface layer that may hinder charge extraction. Finally, a method for measuring both interfacial photovoltage and band alignment in a fully functional perovskite solar cell using hard X-ray photoelectron spectroscopy (HAXPES) is demonstrated. The results showcase the design considerations for the samples and the measurement setup and the potential of this technique. In summary, this thesis shows the suitability of PES for studying both the function and degradation of surfaces and interfaces of complex dynamical systems. It serves as a guide for future studies by highlighting challenges and possibilities faced when working with these systems.
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| 9. |
- Hahlin, Maria, 1975-
(författare)
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Electronic and Molecular Surface Structures of Dye-Sensitized TiO2 Interfaces
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The dye-sensitized solar cell is a promising solar cell technology. In these systems the key process for light to electricity conversion is molecular in nature and is initiated in dye molecules adsorbed at a semiconducting surface. This thesis focuses on the electronic and molecular surface structure of the dye/TiO2 interface, and the experimental results were obtained from surface sensitive X-ray based electron spectroscopic methods. Two families of dyes, triarylamine based organic dyes and ruthenium based inorganic dyes, were investigated. The effect of dye structural modications on the interfacial properties was studied, such as the surface concentrations, dye molecular surface orientation, molecular interactions, and energy level matching. Also, the impact of additional parameters such as the incorporation of coadsorbents and the solvents used for dye sensitization were studied and complementary photoelectrochemical characterization was used to demonstrate functional properties corresponding to changes in the molecular layers. The experiments provided information on how specic structural modications change the frontier electronic structure. The results also showed that the adsorption of the organic dye leads to submolecular electronic changes, and that the dye surface orientations in general favor effcient energy conversion. Moreover, effects of solvents and coadsorbents, on both energy level matching between the dye and the TiO2 substrate and the surfacemolecular structure were quantied.
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| 10. |
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| 11. |
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| 12. |
- Johansson, Erik, 1977-
(författare)
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Interfaces in Dye-Sensitized Oxide / Hole-Conductor Heterojunctions for Solar Cell Applications
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nanoporous dye-sensitized solar cells (DSSC) are promising devices for solar to electric energy conversion. In this thesis photoelectron spectroscopy (PES), x-ray absorption spectroscopy (XAS) and photovoltaic measurements are used for studies of the key interfaces in the DSSC.Photovoltaic properties of new combinations of TiO2/dye/hole-conductor heterojunctions were demonstrated and their interfacial structures were studied. Three different types of hole-conductor materials were investigated: Triarylamine derivatives, a conducting polymer and CuI. The difference in photocurrent and photovoltage properties of the heterojunction due to small changes in the hole-conductor material was followed. Also a series of dye molecules were used to measure the influence of the dye on the photovoltaic properties. Differences in both the energy-level matching and the geometric structure of the interfaces in the different heterojunctions were studied by PES. This combination of photovoltaic and PES measurements shows the possibility to link the interfacial electronic and molecular structure to the functional properties of the device.Three effective dyes used in the DSSC, Ru(dcbpy)2(NCS)2, Ru(tcterpy)(NCS)3 and an organic dye were studied in detail using PES and XAS and resonant core hole decay spectroscopy. The results gave information of the frontier electronic structure of the dyes and how the dyes are bonded to the TiO2 surface.Finally, the hole-conductor mechanism in a conducting polymer was investigated theoretically using semi-empirical and ab-initio methods.
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| 13. |
- Karlsson, Patrik, 1976-
(författare)
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Surface Science Studies of Metal Oxides Formed by Chemical Vapour Deposition on Silicon
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- For an electronic device well-designed interfaces are critical for the performance. Studies of interfaces down to an atomic level are thus highly motivated both from a fundamental and technological point of view. In this thesis, a surface science approach has been employed to study the formation of interfaces in systems relevant for transistor and solar cell applications. Surface science methodology entails ultra high vacuum environment, single crystalline surfaces, submonolayer control of deposited material, surface sensitive spectroscopy and atomic resolution microscopy.The primary experimental method for characterization is electron spectroscopy. This is a family of very powerful experimental techniques capable of giving information on the atomic level. Additionally, studies have been performed using scanning tunnelling microscopy. Combined these two methods can provide an atomic level characterisation of the geometric and electronic properties of the surface.The emphasis of this work is placed on ultra thin TiO2 and ZrO2 films grown on silicon substrates by means of ultra-high vacuum metal-organic chemical vapour deposition. ZrO2 has also been grown on SiC and FeCrAl. Deposition has been performed with different process parameters. The interface region of each film has been characterised. The band alignment, a most important issue with regard to the development of new transistor devices, for the ZrO2/Si(100) system has been explored. Decomposition pathways of the metal organic precursors have been studied in detail. Changing process parameters is shown to alter both the precursor decomposition pathway and the nature of the interface region, thus opening the possibility to tailor the material function.The titanium dioxide films grown in situ have shown to be excellent models of nanostructured electrode materials. In this spirit, interfaces of model systems for the solid-state dye-sensitized solar cell have been studied. Links between device performance and interface structure have been elucidated.
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| 14. |
- Källquist, Ida
(författare)
-
Combining Electrochemistry and Photoelectron Spectroscopy for the Study of Li-ion Batteries
- 2021
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis photoelectron spectroscopy (PES) is combined with electrochemistry to investigate the electrochemical processes that occur at the electrode/electrolyte interfaces in lithium-ion batteries (LIBs). LIB systems are studied by the use of both ex situ PES, where electrodes are electrochemically pre-cycled and subsequently measured by PES, and operando PES, where electrodes are cycled during PES measurements. Ex situ PES is used to determine the main degradation mechanisms of a novel high capacity material, Li2VO2F. The capacity fade seen for Li2VO2F. is found to be related to an irreversible oxidation of the active material at high voltages, and a continuous surface layer formation at low voltages. To decrease the capacity fading three strategies for optimizing the interface are investigated. The results show that a surface coating of AlF3 most efficiently can mitigate electrolyte reduction, while boron containing electrolyte additives and transition metal substitution more successfully limit the oxidation of the active material. A large part of the work performed in this thesis has been devoted towards developing a methodology suitable for conducting operando ambient pressure photoelectron spectroscopy (APPES) measurements on LIB systems. A general connection between the theory of PES and electrochemistry is made, where in particular a model suitable for interpreting operando APPES results on solid/liquid interfaces is suggested. The model is further developed for the specific case of LIB interfaces. The results from the operando studies show that the kinetic energy shifts of the liquid electrolyte measured by APPES can be correlated to the electrochemical reactions occurring at the interface. If no charge transfer occurs, the kinetic energy shift is proportional to the applied voltage. During charge transfer the behavior is more complex, and the kinetic energy shifts are related to the change in chemical potential of the working electrode. In summary, this thesis exemplifies how both ex situ and operando PES are highly useful techniques for the study of LIB battery interfaces. The possibilities of both techniques are highlighted, and important considerations for an accurate interpretation of the PES results are also discussed.
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| 15. |
- Källquist, Ida, et al.
(författare)
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Probing Electrochemical Potential Differences over the Solid/Liquid Interface in Li-Ion Battery Model Systems.
- 2021
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 13:28, s. 32989-32996
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Tidskriftsartikel (refereegranskat)abstract
- The electrochemical potential difference (Δμ̅) is the driving force for the transfer of a charged species from one phase to another in a redox reaction. In Li-ion batteries (LIBs), Δμ̅ values for both electrons and Li-ions play an important role in the charge-transfer kinetics at the electrode/electrolyte interfaces. Because of the lack of suitable measurement techniques, little is known about how Δμ̅ affects the redox reactions occurring at the solid/liquid interfaces during LIB operation. Herein, we outline the relations between different potentials and show how ambient pressure photoelectron spectroscopy (APPES) can be used to follow changes in Δμ̅e over the solid/liquid interfaces operando by measuring the kinetic energy (KE) shifts of the electrolyte core levels. The KE shift versus applied voltage shows a linear dependence of ∼1 eV/V during charging of the electrical double layer and during solid electrolyte interphase formation. This agrees with the expected results for an ideally polarizable interface. During lithiation, the slope changes drastically. We propose a model to explain this based on charge transfer over the solid/liquid interface.
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| 16. |
- Mahrov, Boriss, 1977-
(författare)
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Studies of Semiconductors Modified with Nanoscale Light Absorbers for Solar Cell Application
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Recently, materials such as hole conductors (CuI, CuSCN) and light absorbers (Ru-complexes, CuInS2) have been actively investigated for application in nanocrystalline solar cells. In this thesis combinations of these materials have been studied.In the first part of the thesis, various methods were applied to characterize the electronic structure and photoconversion mechanism of the dye molecule Ru(dcbpyH2)2(NCS)2 when combined with materials for the use in photovoltaic devices. Specifically, the adsorption and electronic structure of the dye molecules adsorbed to semiconductors were investigated by means of photoelectron spectroscopy. The results indicate a chemical bond between the dye molecules and the hole conductors (CuI, CuSCN) via the NCS- groups. In addition, preparation of a TiO2/Ru-dye/CuI solid state model system was studied in situ. These experiments showed a partial breaking of the TiO2-dye bond caused by CuI evaporation. Photovoltage measurements were also performed. These investigations showed a shift in the light absorption threshold of the dye molecules adsorbed onto the hole conductors (CuI and CuSCN), indicating new defect states at the dye/CuSCN interface. Also, charge accumulation and transport in solar cells with CuSCN were compared to liquid electrolyte cells. Measurements showed that the lifetime and transport time of electrons in solar cells with CuSCN are much shorter than in electrolyte cells.In the second part of the thesis, the deposition of CuInS2 onto various metal oxides by spray pyrolysis has been studied with x-ray diffraction and photoelectron spectroscopy. The measurements showed that the morphologies of the substrates play a significant role in the formation of CuInS2 layers. Also, the presence of CdS at TiO2 has a positive influence on the formation of CuInS2.
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| 17. |
- Maibach, Julia, et al.
(författare)
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Probing a battery electrolyte drop with ambient pressure photoelectron spectroscopy
- 2019
-
Ingår i: Nature Communications. - : NATURE PUBLISHING GROUP. - 2041-1723. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- Operando ambient pressure photoelectron spectroscopy in realistic battery environments is a key development towards probing the functionality of the electrode/electrolyte interface in lithium-ion batteries that is not possible with conventional photoelectron spectroscopy. Here, we present the ambient pressure photoelectron spectroscopy characterization of a model electrolyte based on 1M bis(trifluoromethane)sulfonimide lithium salt in propylene carbonate. For the first time, we show ambient pressure photoelectron spectroscopy data of propylene carbonate in the liquid phase by using solvent vapor as the stabilizing environment. This enables us to separate effects from salt and solvent, and to characterize changes in electrolyte composition as a function of probing depth. While the bulk electrolyte meets the expected composition, clear accumulation of ionic species is found at the electrolyte surface. Our results show that it is possible to measure directly complex liquids such as battery electrolytes, which is an important accomplishment towards true operando studies.
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| 18. |
- Mukherjee, Soham, et al.
(författare)
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Entrapped Molecule-Like Europium-Oxide Clusters in Zinc Oxide with Nearly Unaffected Host Structure
- 2023
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Ingår i: Small. - : Wiley-VCH Verlagsgesellschaft. - 1613-6810 .- 1613-6829. ; 19:1
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Tidskriftsartikel (refereegranskat)abstract
- Nanocrystalline ZnO sponges doped with 5 mol% EuO1.5 are obtained by heating metal–salt complex based precursor pastes at 200–900 °C for 3 min. X-ray diffraction, transmission electron microscopy, and extended X-ray absorption fine structure (EXAFS) show that phase separation into ZnO:Eu and c-Eu2O3 takes place upon heating at 700 °C or higher. The unit cell of the clean oxide made at 600 °C shows only ≈0.4% volume increase versus undoped ZnO, and EXAFS shows a ZnO local structure that is little affected by the Eu-doping and an average Eu3+ ion coordination number of ≈5.2. Comparisons of 23 density functional theory-generated structures having differently sized Eu-oxide clusters embedded in ZnO identify three structures with four or eight Eu atoms as the most energetically favorable. These clusters exhibit the smallest volume increase compared to undoped ZnO and Eu coordination numbers of 5.2–5.5, all in excellent agreement with experimental data. ZnO defect states are crucial for efficient Eu3+ excitation, while c-Eu2O3 phase separation results in loss of the characteristic Eu3+ photoluminescence. The formation of molecule-like Eu-oxide clusters, entrapped in ZnO, proposed here, may help in understanding the nature of the unexpected high doping levels of lanthanide ions in ZnO that occur virtually without significant change in ZnO unit cell dimensions.
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| 19. |
- Mukherjee, Soham, et al.
(författare)
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Structure and Electronic Effects from Mn and Nb Co-doping for Low Band Gap BaTiO3 Ferroelectrics
- 2021
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 125:27, s. 14910-14923
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the doping-induced local structural and electronic effects in the recently developed low band gap room temperature ferroelectric Mn-Nb co-doped BaTiO3. Experimental and theoretical Raman spectroscopies are utilized to quantify the Ti off-centering, identified to be the intrinsic origin of ferroelectricity in these systems. Mn and Nb exhibit contrasting doping behaviors that have remarkable effects on BaTiO3 functionality. Jahn-Teller distorted Mn3+ is primarily associated with lowering of the bulk band gap, while charge-compensating Nb5+ off-centers within the O-6 octahedra, creating a polar mode that stabilizes the ferroelectric ground state. The charge neutral aliovalent Mn3+-Nb5+ pair effectively couples to the inherent ferroelectric instability of the BaTiO3 lattice, restoring some spontaneous polarization lost by doping Mn3+ (d(4)) ions at Ti4+ (d(0)) sites.
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