Comparative study of polymorph nanosheet materials for emerging metal-ion batteries

Doctor of PhilosophyDepartment of Mechanical and Nuclear EngineeringGurpreet SinghRechargeable batteries have attained strategic place in applications involving transportation, microelectronics, and electric power grid in the past 30 years. Yet in a society that strives to achieve both sustainability and economic growth the concern whether lithium and cobalt reserves may supply the future demand of multibillion-dollar industries and emerging markets has risen. To address this concern, research on novel rechargeable batteries composed by earth-abundant elements has re-gained traction recently. As potential candidates for beyond lithium-ion battery (LIB) technologies, both sodium and potassium present low cost, reserves more globally distributed, and redox potentials closer to that of lithium metal. Likewise, from the knowledge consolidated over decades on LIBs, certain lessons learnt can be applied in the study of these emerging alkali metal ion batteries. One of these lessons is that to enable the use of sodium- and potassium-ion battery technologies a comprehensive study of crystal structure and electrochemical processes happening in electrode materials is crucial. In this scenario, a class of materials known as transition metal dichalcogenides (TMDs), whose structure was first determined by Linus Pauling in 1923, has re-gained attention due to layered and wide variety of species and chemistries. To date, approximately 60 species of TMDs are known, in which two thirds present layered structure and polymorphism. Conducted in the 1970s by the 2019 Nobel Prize in Chemistry, M. Stanley Whittingham, research on layered TMDs for electrochemical energy storage applications was shortly abandoned owing to poor stability of TMDs. Upon the increasing interest on layered materials in the 2000s, TMD nanosheets were found to have relatively higher uptake and faster diffusion of Li⁺, Na⁺, and K⁺ in their host structure -- leading to high theoretical capacity and rate capability, respectively. Nevertheless, along with the fascinating properties of TMDs -- some yet to be unveiled – research challenges are also still present. Molybdenum disulfide (MoS₂) is a layered TMD that presents polymorphism, high specific capacity towards sodium-ions and abundant availability on earth. However, MoS₂ as sodium-ion battery (SIB) electrode shows poor cycle stability and fast capacity degradation, due to low electronic conductivity, and low reversibility. To address the stability issue of MoS₂, this thesis explored synthesis of a novel composite material of 2H-MoS₂ functionalized with a thin layer of molecular precursor-derived silicon oxycarbide (SiOC) ceramic as electrode for sodium-ion battery (SIB). The functionalized MoS₂ electrode was able to overcome shortcomings of pristine 2H-MoS₂ electrodes in SIB. The improved stability was attributed to the SiOC, a ceramic material that safeguarded the active material (MoS₂) without compromising sodiation and de-sodiation processes. Moreover, SiOC provided free carbon domains that showed increased electronic conductivity of functionalized MoS₂, as evidenced by the rate capability test. Electrochemical results show that specific capacity of MoS₂-SiOC was 12 times higher than pristine MoS₂ at 200 mA g⁻¹. Later, in view of the larger interlayer spacing and unique electronic properties of some layered telluride-based TMDs, tungsten ditelluride (WTe₂) was selected as host material for studies involving potassium-ion storage. In addition to providing a detailed description of crystal phase of the thermodynamically stable Td phase of WTe₂ at room temperature, this thesis introduces a discussion regarding electrochemical impedance spectroscopy (EIS), a frequency domain analysis that can provide useful information for electrochemical systems. Findings shows that due to higher interlayer spacing and conversion type-reactions – confirmed by ex-situ post-cycling analysis -- Td-WTe₂ showed first cycle specific charge capacity of 3.3 K⁺ stored per WTe₂ molecule, stable capacity of 143 mA h g⁻¹ at 10th cycle number -- outperforming WS₂ and graphite -- reasonable cycling stability, and low charge transfer resistance. This is the first known work in the field to highlight the potential of Td-WTe₂ as potassium-ion battery (KIB) electrode. Td-WTe₂ was also employed as electrode material in a study of diffusivity of Na⁺ and K⁺ in SIB and KIB half-cells, respectively. Although in the literature there are reports that suggest the larger ionic radius of K⁺ (1.33 Å) -- in comparison to Na⁺ (0.97 Å) – lead to an inferior electrochemical performance of KIBs, in this work we demonstrated that KIB outperforms the SIB cell in terms of rate capability and cycling stability. This behavior was explained by Stokes' radius concept of Na⁺ and K⁺ in propylene carbonate (PC) based electrolyte, which explains the higher mobility of K⁺ in the electrolyte medium. These findings corroborate the potential of semimetal TMD electrode materials and highlight how electrolyte medium has implications on electrochemical performance of electrode materials. In summary, the scientific contributions attained in this research work intend to support the current development and understanding of novel sulfide- and telluride-layered TMDs materials for sodium- and potassium-ion batteries, respectively

Fluoride Ion Supported on gamma-Alumina: Characterization and Catalytic Activity

Caesium or potassium fluoride supported on gamma-alumina have been widely used as solid bases and catalysts in organic synthesis, in the presence of the solvent and under heterogeneous conditions. The nature of the active sites on the surface of these solids was not yet fully understood. The aim of the present work is to obtain information regarding the nature and the active sites of the supported metal fluoride, using a series of analytical techniques and chemical reactions. The chemical reactions involve the individual interactions of the Lewis acid sulphur tetrafluoride and its hydrolysis products, thionyl fluoride and sulphur dioxide, the Lewis acid carbonyl fluoride and its hydrolysis product carbon dioxide, and anhydrous hydrogen fluoride with the supported metal fluoride. The interactions of the probe molecules described above with gamma-alumina pretreated with sulphur tetra-fluoride, thionyl fluoride, carbonyl fluoride or anhydrous hydrogen fluoride are also studied. Terminal hydroxyl groups present on the surface of gamma-alumina supported metal fluoride are removed by treatment with sulphur tetra-fluoride, thionyl fluoride or sulphur dioxide then anhydrous hydrogen fluoride. The resulting materials caesium or potassium fluoride supported on gamma-alumina, are catalytically examined, using the chlorofluorination of sulphur tetrafluoride with chlorine monofluoride at room temperature to give sulphur chloride pentafluoride as a model reaction. The reactions described above are studied under heterogeneous conditions at room temperature, using the radiotracers [14C]-carbon [36Cl]-chlorine, [18F]-fluorine and [35S]-sulphur labelled compounds. The experiments carried out using [35S]-sulphur labelled sulphur tetrafluoride, thionyl fluoride or sulphur dioxide show that there is more than one adsorbed species present on the surface of the supported metal fluoride, these are weakly adsorbed molecules of sulphur tetra-fluoride, thionyl fluoride and sulphur dioxide, and permanently retained pentafluorosulphate and fluorosulphite. For each system studied the surface activity is dependent on the metal fluoride loading in the composition range 0.6 - 20.0 mmol g -1, and is at a maximum at 5.5 mmol g The overall uptake of the volatile sulphur containing probe molecules by the supported metal fluoride is in the order SF4> SO2 ~ SOF2. [18F]-Fluorine exchange is observed in the sulphur tetrafluoride/supported metal fluoride system but not in the thionyl fluoride/supported metal fluoride system. [18F]-Fluorine exchange is observed between [18F]-fluorine labelled carbonyl fluoride and the supported metal fluoride. The trifluoromethoxide anion is detected after each reaction. Experiments carried out using [14C]-carbon labelled carbonyl fluoride show that there are two species present on the surface of the supported metal fluoride, weakly adsorbed molecules of carbonyl fluoride and carbon dioxide. The surface activity is at a maximum at 5.5 mmol g -1. The reaction of carbon dioxide and the supported metal fluoride is barely detectable but experiments carried out using [14C]-carbon labelled carbon dioxide confirm that weakly adsorbed carbon dioxide occurs. The uptake of fluorine by calcined gamma-alumina during treatment with sulphur tetrafluoride, thionyl fluoride, carbonyl fluoride or anhydrous hydrogen fluoride, is in the order SF4 ~ SOF2 > COF2 ~ HF. It is found that treatment of gamma-alumina with anhydrous hydrogen fluoride or carbonyl fluoride results in labile surface fluorine. However treatment of calcined gamma-alumina with sulphur tetrafluoride or thionyl fluoride results in at least two forms of surface fluorine being produced one which is not labile and consisted of ca. 40% of the total fluorine present at the surface. Caesium or potassium fluoride supported on gamma-alumina prepared from aqueous or non-aqueous solution and treated with sulphur tetrafluoride, thionyl fluoride or sulphur dioxide then anhydrous hydrogen fluoride are efficient catalysts for the chlorofluorination of sulphur tetrafluoride by chlorine monofluoride. Catalytic activity is at a maximum at 5.5 mmol g -1 and poisoning by chlorine monofluoride appears to be less important than was the case for unsupported caesium fluoride. Catalysts prepared by mixing the two salts in the absence of the solvent or those treated with carbonyl fluoride or anhydrous hydrogen fluoride give very poor yields of sulphur chloride pentafluoride

Interaction of metal complexes with nucleic acid: a thermodynamic and kinetic study, with an eye on photoreactive processes

La Tesis "Interaction of metal complexes with nucleic acids. A thermodynamic and kinetic study, with an eye on photoreactive processes" de Matteo Lari estudia los mecanismos de acción de varias moléculas con ácidos nucleídos. En la primera parte de la Tesis se estudian los efectos Del ion aluminio hacia el ARN, el cual provoca importantes cambios estructurales de ese acido nucleico y favorece su agregación. En la segunda parte se estudia la interacción de complejos metálicos con ADN, como posibles compuestos antitumorales. En particular, estudios de fotoreactividad han revelado que las moléculas sintetizadas incrementan su efecto tras irradiación en la región UV-vis. Además de eso, alguna de esta moléculas tienen una interesante subida de la fluorescencia en presencia de polinucleótidos, y selectividad hacia estructuras no canonícas de ADN, las G-Quadruplex, las cuales incrementan aun más el interés de estas especies como drogas antitumorales.The Thesis "Interaction of metal complexes with nucleic acids. A thermodynamic and kinetic study, with an eye on photoreactive processes" by Matteo Lari regards the study of the mechanisms of action of different kinds of molecules with nucleic acids. The first part of the thesis is centered on the characterization of an aluminium complex and its interaction with RNA, which provokes important structural changes and the formation of aggregates. In the second part, the interaction of metal complexes with DNA is characterized, in the view of their possible use as anticancer drugs. In particular, a focus on their photoreactivity is performed, and it is seen that such complexes enhance their reactivity in the presence of a UV-vis light. In addition, fluorescence enhancement of the complexes is observed by interaction with DNA, and selectivity towards non-canonical DNA structures, the G-Quadruplexes, is found, making these complexes more interesting for anticancer strategy

Advance in Composite Gels

In the last few decades, various composite gels have been developed. In recent years, further advances have been made in the development of novel composite gels with potential applications in various fields. This reprint offers the latest findings of composite gels by experts throughout the world

Molecules in Superfluid Helium Nanodroplets

This open access book covers recent advances in experiments using the ultra-cold, very weakly perturbing superfluid environment provided by helium nanodroplets for high resolution spectroscopic, structural and dynamic studies of molecules and synthetic clusters. The recent infra-red, UV-Vis studies of radicals, molecules, clusters, ions and biomolecules, as well as laser dynamical and laser orientational studies, are reviewed. The Coulomb explosion studies of the uniquely quantum structures of small helium clusters, X-ray imaging of large droplets and electron diffraction of embedded molecules are also described. Particular emphasis is given to the synthesis and detection of new species by mass spectrometry and deposition electron microscopy

Covalent versus ionic bonding in alkalimetal fluoride oligomers

The most polar bond in chemistry is that between a fluorine and an alkalimetal atom. Inspired by our recent finding that other polar bonds (C - M and H - M) have important covalent contributions (i.e., stabilization due to bond overlap), we herein address the question if covalency is also essential in the F - M bond. Thus, we have theoretically studied the alkalimetal fluoride monomers, FM, and (distorted) cubic tetramers, (FM)4, with M = Li, Na, K, and Rb, using density functional theory at the BP86/TZ2P level. Our objective is to determine how the structure and thermo-chemistry (e.g., F - M bond lengths and strengths, oligomerization energies, etc.) of alkalimetal fluorides depend on the metal atom, and to understand the emerging trends in terms of quantitative Kohn-Sham molecular orbital theory. The analyses confirm the extreme polarity of the F - M bond (dipole moment, Voronoi deformation density and Hirshfeld atomic charges), and they reveal that bond overlap-derived stabilization (ca. -6, -6, and -2 kcal/mol) contributes only little to the bond strength (-136, -112, and -114 kcal/mol) and the trend therein along Li, Na, and K. According to this and other criteria, the F - M bond is not only strongly polar, but also has a truly ionic bonding mechanism. Interestingly, the polarity is reduced on tetramerization. For the lithium and sodium fluoride tetramers, the