Three cobalt-based oxides operating at the Co(III)/Co(II) redox couple have been investigated as potential cathode materials for the intermediate-temperature solid oxide fuel cells (IT-SOFCs). X-ray absorption spectroscopy measurements confirmed that both the oxygen-deficient perovskite Sr[subscript 0.7]Y[subscript 0.3]CoO[subscript 2.65-delta] (SYCO) and the double-perovskite Ba₂[Co][Bi[subscript x]Sc[subscript 0.2]Co[subscript 1.8-x]][subscript O6-delta] (x = 0.1 and 0.2) (BBSC) contain high-spin Co(III) in the bulk at room temperature and thus avoid the thermally driven spin-state crossover of the Co(III) ions usually observed in other cobalt-containing perovskite oxides. Electrochemical characterizations demonstrated that both cobalt oxides operating on the Co(III)/Co(II) redox couple are equally catalytically active for the oxygen reduction reaction as those operating on the Co(IV)/Co(III) redox couple. With an LSGM electrolyte-supported single test cell and NiO+GDC as anode, the maximum power densities Pmax at 800 ºC reach 927 and 1180 mW·cm⁻² for SYCO and BBSC cathodes, respectively. The oxygen-deficient perovskites Sr[subscript 1-x]R[subscript x]CoO[subscript 3-delta] (R = Eu-Ho, Y, x [approximately equal] 0.3) are identified as a new class of cathode materials for IT-SOFCs in this dissertation. On the other hand, the layered Ba2Co9O14 (BCO) containing the low-spin Co(III) at room temperature undergoes a thermally driven spin-state crossover, which has prevented it from being evaluated as the cathode of IT-SOFCs. This problem was overcome by fabrication of a 50-50 wt.% BCO + SDC (Sm[subscript 0.2]Ce[subscript 0.8]O[subscript 1.9]) composite cathode. The addition of SDC not only improved the adhesion to the electrolyte, but also enhanced the electrocatalytic activity for the oxygen reduction reaction. The composite cathode delivers a nearly stable P[subscript max] of ~450 mW·cm-2 at 800 °C in an LSGM electrolyte-supported single test cell. In addition, the electrochemical lithium intercalation process in the monoclinic Nb12O29 was studied with a Li/Nb₁₂O₂₉ half-cell, and the results showed that it can reversibly incorporate a relatively large amount of Li-ions in the voltage window of 2.5-1.0 V at a slow discharge/charge rate while retaining structural integrity. Compared with that of the bare Nb₁₂O₂₉, samples with carbon coating show an improved rate capability. The lithium insertion mechanism into Nb₁₂O₂₉ has also been discussed in terms of sites available to the lithium ions / text

abstract: There is a fundamental attractiveness about harnessing renewable energy in an age when sustainability is an ethical norm. Lithium ion batteries and hydrogen fuels are considered the most promising energy source instead of fossil fuels. This work describes the investigation of new cathode materials and devices architectures for lithium ion batteries, and photocatalysts for their usage in water splitting and waste water treatment. LiCoO2 and LiNi1/3Mn1/3Co1/3O2 were exfoliated into nanosheets using electrochemical oxidation followed by intercalation of tetraethylammonium cations. The nanosheets were purified using dialysis and electrophoresis. The nanosheets were successfully restacked into functional cathode materials with microwave hydrothermal assistance, indicating that new cathodes can be obtained by reassembling nanosheets. This method can pave the way for the synthesis of materials with novel structures and electrochemical properties, as well as facilitate the fabrication of hybrid and composite structures from different nanosheets as building blocks. Paper folding techniques are used in order to compact a Li-ion battery and increase its energy per footprint area. Full cells were prepared using Li4Ti5O12 and LiCoO2 powders deposited onto current collectors consisting of paper coated with carbon nanotubes. Folded cells showed higher areal capacities compared to the planar versions. Origami lithium-ion battery made in this method that can be deformed at an unprecedented high level, including folding, bending and twisting. Spray pyrolysis was used to prepare films of AgInS2 with and without Sn as an extrinsic dopant. The photoelectrochemical performance of these films was evaluated after annealing under a N2 or S atmosphere with different amounts of the Sn dopant. Density Function Theory (DFT) was used to calculate the band structure of AgInS2 and understand the role of Sn doping in the observed properties. Cr(VI) removal was investigated using multiple oxide photocatalyst and additives. The efficiency for Cr(VI) removal using these photocatalysts was investigated in synthetic neutral and alkaline water, as well as in cooling tower blowdown water. While sulfite alone can chemically reduce Cr(VI), sulfite in combination with a photocatalyst resulted in faster and complete removal of Cr(VI) in 10 min using a SO32−/Cr(VI) ratio >35 in pH ∼ 8 solutions. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2016

Non-aqueous metal-air (Li-O2 and Na-O2) batteries have been emerging as one of the most promising high-energy storage systems to meet the requirements for demanding applications due to their high theoretical specific energy. In the present thesis work, advanced characterization techniques are demonstrated for the exploration of metal-O2 batteries. Prominently, the electrochemical reactions occurring within the Li-O2 and Na-O2 batteries upon cycling are studied by in operando powder X-ray diffraction (XRD). In the first part, a new in operando cell with a combined form of coin cell and pouch cell is designed. In operando synchrotron radiation powder X-ray diffraction (SR-PXD) is applied to investigate the evolution of Li2O2 inside the Li-O2 cells with carbon and Ru-TiC cathodes. By quantitatively tracking the Li2O2 evolution, a two-step process during growth and oxidation is observed. This newly developed analysis technique is further applied to the Na-O2 battery system. The formation of NaO2 and the influence of the electrolyte salt are followed quantitatively by in operando SR-PXD. The results indicate that the discharge capacity of Na-O2 cells containing a weak solvating ether solvent depends heavily on the choice of the conducting salt anion, which also has impact on the growth of NaO2 particles. In addition, the stability of the discharge product in Na-O2 cells is studied. Using both ex situ and in operando XRD, the influence of sodium anode, solvent, salt and oxygen on the stability of NaO2 are quantitatively identified. These findings bring new insights into the understanding of conflicting observations of different discharge products in previous studies. In the last part, a binder-free graphene based cathode concept is developed for Li-O2 cells. The formation of discharge products and their decomposition upon charge, as well as different morphologies of the discharge products on the electrode, are demonstrated. Moreover, considering the instability of carbon based cathode materials, a new type of titanium carbide on carbon cloth cathode is designed and fabricated. With a surface modification by loading Ru nanoparticles, the titanium carbide shows enhanced oxygen reduction/evolution activity and stability. Compared with the carbon based cathode materials, titanium carbide demonstrated a higher discharge and charge efficiency.

Le besoin accru de stockage d'énergie via Li- et batteries Na-ion nécessite une recherche continue de nouveaux matériaux de cathode ayant une densité énergétique plus élevée et étant sûr et durable. Ainsi, nous avons exploré des composés à base de borate capables de réagir avec Li/ Na-ions de manière réversible, soit par le biais de réactions topotactic- ou de conversion. Nous nous sommes concentrés sur les candidats avec des anions polyborate, qui devraient montrer des potentiels redox élevés par rapport aux matériaux à base BO3. Li6CuB4O10 utilisant comme composé modèle, nous avons montré la possibilité d'obtenir des potentiels d'oxydo-réduction de 4.2 et 3.9 V par rapport à Li pour l'α- et ß polymorphes. L'activité redox a été rationalisée par spectroscopie EPR et calculs DFT. Nous révélons en outre la relation structurelle / synthétique entre les deux polymorphes et montrons une conductivité ionique élevée de 1.4 mS / cm à 500 °C pour une forme de HT d'-Li6CuB4O10. De plus, nous avons pu préparer deux pentaborates 3d-métal nouveau sodium Na3MB5O10 (M = Fe, Co). M = Fe, nous avons observé une intercalation Na réversible à un potentiel moyen de 2.5 V par rapport à Na, alors Na3CoB5O10 avéré être inactif électrochimique. Dévier à partir de composés d'insertion / désinsertion classiques, nous avons étudié la électrochimique entraîné la réaction d'un oxyborate bismuth Bi4B2O9 contre Li par des mesures électrochimiques combinées avec XRD et TEM. Nous avons constaté qu'il est possible de faire défiler ce matériau réversible entre 1.7 et 3.5 V avec un potentiel redox d'environ 2.3 V par rapport à Li avec seulement 5% en poids de carbone et une faible polarisation ~ 300 mV. / The increased need of energy storage via Li- and Na-ion batteries requires a continuous search for new cathode materials having higher energy density and being safe and sustainable. Thus, we explored borate based compounds capable of reacting with Li/ Na-ions in a reversible way either through topotactic- or conversion reactions. We focused on candidates with polyborate anions, that are expected to show elevated redox potentials compared to BO3 based materials. Using Li6CuB4O10 as a model compound we showed the possibility to achieve redox potentials of 4.2 and 3.9 V vs Li for the α- and β-polymorphs. The redox activity was rationalized through EPR spectroscopy and DFT calculations. We further reveal the structural/ synthetic relation between the two polymorphs and show a high ionic conductivity of 1.4 mS/cm at 500°C for a HT form of α-Li6CuB4O10. Moreover we were able to prepare two new sodium 3d-metal pentaborates Na3MB5O10 (M = Fe, Co). For M = Fe we observed a reversible Na intercalation at an average potential of 2.5 V vs Na, whereas Na3CoB5O10 turned out to be electrochemical inactive. Deviating from classical insertion/ deinsertion compounds, we studied the electrochemical driven reaction of a bismuth oxyborate Bi4B2O9 versus Li through electrochemical measurements combined with XRD and TEM. We found that it is possible to reversible cycle this material between 1.7 and 3.5 V with an redox potential of ~2.3 V vs Li with only 5wt% carbon and a small polarization ~300 mV. Owing to the complexity of 3d-metal borate chemistry encountered through this PhD, the chances of having a borate based positive electrode for next generation Li-ion batteries is rather slim.

Dans les années à venir, la production d’Energie devra passer par l’utilisation de moyens plus respectueux de l’environnement tels que les énergies renouvelables. Leur caractère intermittent nécessite cependant la mise en place d’un stockage à grande échelle. Parmi les différentes technologies à disposition, les batteries Na-ion apparaissent comme une solution de choix grâce aux ressources de sodium illimitées. Dans ce contexte, nous nous sommes donc intéressés à la synthèse et la caractérisation de nouveaux matériaux d’électrodes positives pour batteries Na-ion. Les oxydes de métaux de transition et plus particulièrement le système Na-Mn-O a attiré notre attention pour les avantages que procure le manganèse en termes de non toxicité, de faible coût et d’abondance. Les phases Na4Mn2O5, lacunaire en oxygène, et Na2Mn3O7, lacunaire en cation manganèse, montrent des capacités spécifiques intéressantes par l’action de différents phénomènes redox. Na2Mn3O7 peut notamment être réduite, pour former la phase Na4Mn3O7 et oxydée, par l’action de l’activité redox de l’oxygène, donnant des capacités de 160 et 120 mAh/g, respectivement. Dans le but d’élargir l’étude à un métal de transition pouvant être oxydé à un état de valence +V, la phase isoformulaire Na2V3O7 a également été étudiée et un Na+ peut être réversiblement extrait de cette dernière. / N the coming years, the production of Energy will have to go through the use of more environmentally friendly means such as renewable energies. However, their intermittent nature requires the establishment of a large-scale storage. Among the various technologies available, Na-ion batteries appear as a solution of choice thanks to unlimited sodium resources. In this context, we are interested in the synthesis and characterization of new positive electrode materials for Na-ion batteries. The transition metal oxides, and more particularly the Na-Mn-O system, have drawn our attention to the benefits of manganese in terms of non-toxicity, low cost and abundance. The phase Na4Mn2O5 (with oxygen vacancies) and Na2Mn3O7 (with manganese vacancies) show interesting specific capacities by the action of various redox phenomena. Na2Mn3O7 may be reduced, to form the phase Na4Mn3O7 and oxidized, by the action of the oxygen redox activity, giving capacities of 160 and 120 mAh/g, respectively. In order to extend the study to a transition metal that can be oxidized to a +V valence state, Na2V3O7 has also been studied and one Na+ can be reversibly extracted from it.

The aim of this project was to find a recycling route for Prussian white. During the experimental part, one recycling method was tested using sodium hydroxide and from this a method for re-synthesis of Prussian white was conducted as well as a method for re-crystallisation of sodium ferrocyanide. The method that proved most successful was the re-crystallisation of sodium ferrocyanide. Furthermore, the conditions needed to conduct a proper re-synthesis of Prussian white was not available during this research. Therefore, it was not possible to produce Prussian white of the right structure. The analysis was performed through XRD analysis and it was concluded that it is possible to re-crystallise sodium ferrocyanide from Prussian white.

京都大学 / 新制・課程博士 / 博士(人間・環境学) / 甲第24710号 / 人博第1083号 / 新制||人||253(附属図書館) / 2022||人博||1083(吉田南総合図書館) / 京都大学大学院人間・環境学研究科相関環境学専攻 / (主査)教授 内本 喜晴, 教授 田部 勢津久, 教授 吉田 鉄平, 教授 雨澤 浩史 / 学位規則第4条第1項該当 / Doctor of Human and Environmental Studies / Kyoto University / DFAM

<p>The Li-ion battery has, from its commercialisation in the early 1990's, now become the most widely used power source for portable low-power electronics: laptops, cellular phones and MP3-players are a few examples. To further develop existing and find new electrode materials for these batteries, it is vital to understand the lithium insertion/extraction mechanisms taking place during battery operation. In this thesis, single-crystal X-ray diffraction has been used to investigate lithium insertion/extraction mechanisms in the cathode materials V₆O₁₃ and LiFePO₄. A novel single-crystal electrochemical cell for <i>in situ</i> single-crystal X-ray diffraction studies has also been developed.</p><p>The phases Li₃V₆O₁₃ and Li_3+xV₆O₁₃, 0<x<1, both contain a disordered lithium ion. A low-temperature study of Li_3.24V₆O₁₃ (at 95 K) shows that this disorder is static rather than dynamic; the lithium ion is equally distributed above and below an inversion centre in the centrosymmetric V₆O₁₃ host structure. Short-range-ordering between this disordered lithium ion and the lithium ion inserted into Li₃V₆O₁₃ gives rise to solid-solution behaviour not observed earlier in the Li_xV₆O₁₃ system. A model is proposed for the lithium insertion mechanism up to the end-member composition Li₆V₆O₁₃.</p><p>Lithium has also been electrochemically extracted from LiFePO₄ single crystals. On the basis of the shapes of the LiFePO₄ and FePO₄ reflections, it is concluded that FePO₄ is formed at the crystal surface and that the LiFePO₄/FePO₄ interface propagates into the crystal. This is in agreement with an earlier proposed model for lithium extraction from LiFePO₄ particles.</p><p>Initial experiments with the newly developed single-crystal electrochemical cell for <i>in situ</i> single-crystal X-ray diffraction demonstrate that it is possible to insert lithium into a single crystal of V₆O₁₃ and then collect single-crystal X-ray diffraction data. The method needs further development but promises to become a powerful tool for studying lithium insertion/extraction mechanisms.</p>

<p>This thesis addresses the electronic structure of vanadium and copper oxides using soft X-ray absorption (SXA) spectroscopy and resonant inelastic X-ray scattering (RIXS) at high brightness synchrotron radiation sources. In RIXS incident photons, tuned to the energy of specific absorption resonances, are inelastically scattered leaving behind a low energy valence excitation in the system studied. Effects of electron localization are reflected by the occurrence of low-energy excitations in form of dd- and charge-transfer excitations that are modelled by cluster calculations. Band-like states are dominating when the intermediate core excited state is delocalized.</p><p>RIXS at V 2p and O 1s resonances has been used to study the electronic structure of the monovalent vanadium oxides VO₂ and V₂O₃, and of the mixed valence compounds, NaV₂O₅ and V₆O₁₃. For NaV₂O₅ and V₆O₁₃ significant contributions from localized low-energy excitations reflect the partly localized character of their valence band electronic structure, whereas VO₂ and V₂O₃ appear mostly as band-like. Effects of carrier doping are addressed for the case of Mo doping into VO₂ and reveal a quasi-rigid band behavior. In the cases of VO₂ and V₆O₁₃ the temperature dependent metal-insulator transition could be monitored by following the spectral evolution of bands originating from V 3d and V 3d - O2p hybridized states. For Na₂V₃O₇ nanotubes it was possible to selectively probe states from the apical and the basal oxygen sites of VO₅ pyramids that constitute these nanotubes. Furthermore, the RIXS technique has been demonstrated to be highly valuable in characterizing the charge transfer processes that accompany lithium insertion into vanadium oxide battery cathodes. Finally, for insulating cuprates RIXS at O 1s, Cu 3p and Cu 3s resonances has been recorded at high-resolution for the detailed investigation of crystal field excitations.</p>

<p>Proton exchange membrane fuel cells and lithium polymer batteries are important as future power sources in electronic devices, vehicles and stationary applications. The development of these power sources involves finding and characterising materials that are well suited r the application.</p><p>The materials investigated in this thesis are the perfluorosulphonic ionomer Nafion^TM(DuPont) and metal oxides incorporated into the membrane form of this material. The ionomer is used as polymer electrolyte in proton exchange membrane fuel cells (PEMFC) and the metal oxides are used as cathode materials in lithium polymer batters (LPB).</p><p>Crystallinity in cast Nafion films can be introduced by ion beam exposure or aging. Spectroscopic investigations of the crystallinity of the ionomer indicate that the crystalline regions contain less water than amorphous regions and this could in part explain the drying out of the polymer electrolyte membrane in a PEMFC.</p><p>Spectroscopic results on the equilibrated water uptake and the state of water in thin cast ionomer films indicate that there is a full proton transfer from the sulphonic acid group in the ionomer when there is one water molecule per sulphonate group.</p><p>The LPB cathode materials, lithium manganese oxide and lithium cobalt oxide, were incorporated <i>in situ</i> in Nafion membranes. Other manganese oxides and cobalt oxides were incorporated <i>in situ</i> inside the membrane. Ion-exchange experiments from HcoO₂to LiCoO₂within the membrane were also successful.</p><p>Fourier transform infrared spectroscopy, Raman spectroscopy and X-ray diffraction were used for the characterisation of the incorporated species and the Nafion film/membrane.</p>