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Diglyme as a promoter for the electrochemical formation of quaternary graphite intercalation compounds containing two different types of solvents
Get PDFCo intercalation using ether based electrolytes renders graphite as a promising anode material in sodium ion batteries SIBs . While most research on electrochemical solvent co intercalation in graphite has focused on linear ethers such as mono , di , tri , tetra , and penta glyme, we herein investigate the possibility of reversible electrochemical co intercalation with alternative sol vents, especially cyclic ethers tetrahydrofuran THF and 1,3 dioxolane DOL , which show no signs of co intercalation on their own. We demonstrate, however, that this reaction becomes feasible when incorporating diethylene glycol dimeth yl ether 2G, diglyme as an additive. Operando X ray diffraction and ex situ ss NMR techniques are employed comprehensively to understand the co intercalation reaction of these cyclic ethers, along with Na glymes, into graphite during cycling. When using these mixed electrolytes i. e., THF 2G and DOL 2G, the voltage profiles changes compared to the pure glyme based electrolyte, while showing comparable specific capacities and good long term durability. Overall, we propose that even trace amounts of diglyme prompt the co intercalation of THF and DOL into graphite layers. This leads to the formation of quaternary graphite intercalation compounds q GICs , expand ing beyond the realm of ternary graphite intercalation com pounds t GIC
Elucidating the Complex Oxidation Behavior of Phosphorus Impurities at the Pt Aqueous H3PO3 Interface in HT PEMFCs by a Combination of X ray Spectroscopies
No full textHigh temperature polymer electrolyte membrane fuel cells HT PEMFCs , employing polybenzimidazole PBI membranes doped with concentrated phosphoric acid H3PO4 , are an attractive choice for a micro stationary clean electric energy source. Due to the high operation temperature 120 180 C , HT PEMFCs offer distinct advantages over their lowertemperature counterparts, including the possibility of operation with reformers, enhanced resistance against CO poisoning, and potential for combined heat and electricity generation. Among the challenges associated with HT PEMFCs, the H3PO4 electrolyte may undergo reduction during the fuel cell operation, leading to the formation of phosphorus impurities with a lower oxidation state, such as phosphorus oxo acids H3PO3 . Recent studies indicate that the H3PO3 may strongly adsorb on the state of the art Pt catalysts on both electrodes in the HT PEMFCs, and thus, adversely influence the O2 reduction reaction ORR . During HT PEMFCs operation, the H3PO3 that is formed on the anode might be transported to the cathode and poison Pt catalysts on the cathode. Such catalyst poisoning will significantly limit the ORR, thereby decreasing the HT PEMFCs performance. Therefore, comprehensive investigations of the Pt H3PO3 interaction and its oxidation behavior under relevant HT PEMFCs conditions e.g., at elevated temperatures and under positive potentials similar to the cathode are necessary for an insight driven optimization of HT PEMFCs. Yet, literature on the interaction of H3PO3 with Pt and the oxidation behavior of H3PO3 are currently extremely scarce. This dissertation aims to unravel the interaction between Pt catalysts and H3PO3 and to elucidate its complex oxidation behavior through the combination of in situ X ray spectroscopies, electrochemical methods, and other complementing characterizations such as chromatography. To investigate the interaction at the Pt aqueous H3PO3 interface, in situ ambient pressure hard X ray photoelectron spectroscopy AP HAXPES combined with the dip andpull configuration was performed at the electrode aqueous electrolyte interface at room temperature and open circuit potential OCP conditions. For further insights into the Pt H3PO3 interactions, the stability of aqueous H3PO3 with and without the presence of Pt catalysts was assessed by using ion exchange chromatography IEC , gas chromatography GC , and X ray photoelectron spectroscopy XPS . Results from these experiments show that even though theoretically aqueous H3PO3 is considered thermodynamically unstable, in the absence of O2, on its own aqueous H3PO3 is stable for at least a week. This can be attributed to the fact that on its own H3PO3 exists in a highly stable and less reactive tetrahedral tautomeric form. However, upon contact with Pt, Pt immediately catalyzes the oxidation of aqueous H3PO3 to H3PO4. Likely, H3PO3 adsorbs on the Pt surface in the highly reactive pyramidal tautomeric form, thus the H3PO3 is more susceptible to react with H2O leading to the formation of H3PO4 and H2. To unravel the complex oxidation behavior of aqueous H3PO3 at conditions relevant to HT PEMFCs operation, in situ P K edge X ray absorption near edge structure spectroscopy XANES measurements were conducted. Several preliminary experiments are conducted to ensure a comprehensive understanding and accurate interpretation of the in situ P Kedge XANES dataset. First, the acquisition of the P K edge XANES and complementary P L2,3 edge XANES of a well understood set of reference phosphorus P containing compounds with a wide range of oxidation states and chemical environments was performed. This enabled the collection of reference XANES spectral fingerprints associated with different chemical environments. .
The Behavior of the Intercalant AlCl4 Anion during the Formation of Graphite Intercalation Compound An X ray Absorption Fine Structure Study
Get PDFThis work aims to study the insertion of AlCl4 anion in the crystalline structure of oriented pyrolytic graphite PG at the point of view of the anion itself. The electronic and atomic structures of the anion at different intercalation stages are studied. In particular double edge bicolor X ray absorption spectroscopy at the Al and ClK edges is carried out, highlighting a contraction of the anion bonding at the highest intercalation degree obtained electrochemically stage 3 , while the electronic population changes for both the edges upon cycl
Advancements in X ray spectrometry techniques for enhanced material characterization theoretical validation and applications across material systems
No full textStructural studies of an abasic site DNA damage repair and DNA interstrand cross link formation
No full textDNA damage refers to any alteration or modification in the DNA structure that deviates from its natural state. Abasic site Ap site is one of the most common DNA lesions resulting from spontaneous depurination depyrimidination or enzymatic base excision. When left unrepaired it can lead to a cascade of genetic mutations, potentially causing diseases like cancer. Understanding DNA repair mechanisms is vital for medical research and applications. Bacterial MutM is a DNA repair glycosylase, removing DNA damage generated by oxidative stress and preventing mutations and genomic instability. MutM belongs to the Fpg Nei family of procaryotic enzymes, sharing structural and functional similarities with their eukaryotic counterparts, such as NEIL1 NEIL3. Here, I present two crystal structures of MutM from pathogenic Neisseria meningitidis MutM holoenzyme and MutM bound to DNA. The free enzyme exists in an open conformation, while upon binding to DNA, both the enzyme and DNA undergo substantial structural changes and domain rearrangement. One of the DNA lesion repaired by MutM is the Ap site, which, if not repaired, may spontaneously lead to the formation of an abasic site interstrand crosslink Ap ICL with an adjacent adenine in the opposite strand. NEIL3 glycosylase is known to remove Ap ICL. With a .
Exploring Pathogenic Mutations at Phosphorylation Sites through a Peptide Based Proteomics Screen
No full textVisualization of stepwise electrode decomposition in a nail penetrated commercial lithium ion cell using low temperature synchrotron X ray computed tomography
Get PDFThe transition towards zero carbon emissions in power generation hinges on the integration of efficient electrical energy storage systems, with lithium ion batteries LIBs positioned as a pivotal technology. While generally safe, deviations in their operational guidelines due to manufacturing defects or misuse can lead to critical safety concerns, notably thermal runaway TR events. Internal short circuits ISCs are primary initiators of TR within LIBs. For abuse testing, ISCs are often triggered by nail penetration. This study explores the morphological changes and mechanisms underlying ISC induced TR in LIBs using operando synchrotron X ray computed tomography SXCT at subzero temperatures. A novel cryogenic setup was developed to control a stepwise temperature increase in the damaged sample while monitoring electrochemical characteristics and simultaneously enabling acquisition of high resolution SXCT images. The findings reveal that conducting nail penetration at minus 80 amp; 9702;C prevents immediate TR, enabling detailed analysis of subsequent structural and electrochemical behavior during controlled thawing. Thus, the initiation of TR processes at localized ISC sites has been observed, evidenced by voltage fluctuations and morphological changes, such as cathode material cracking and decomposition. These results underscore the importance of temperature control in mitigating TR risks and provide critical insights into the internal dynamics of LIBs under abusive conditions. The developed cryogenic SXCT methodology offers a powerful tool for non destructive, high resolution investigation of battery failure mechanisms, contributing to the enhancement of LIB safet
Dynamics of K2Ni2 SO4 3 governed by proximity to a 3D spin liquid model
Get PDFQuantum spin liquids QSLs have become a key area of research in magnetism due to their remarkable properties, such as long range entanglement, fractional excitations, and topologically protected phenomena. Recently, the search for QSLs has expanded into the three dimensional world, despite the suppression of quantum fluctuations due to high dimensionality. A new candidate material, K2Ni2 SO4 3, belongs to the langbeinite family and consists of two interconnected trillium lattices. Although magnetically ordered, it exhibits a highly dynamical and correlated state. In this work, we combine inelastic neutron scattering measurements with density functional theory DFT , pseudo fermion functional renormalization group PFFRG , and classical Monte Carlo cMC calculations to study the magnetic properties of K2Ni2 SO4 3, revealing a high level of agreement between experiment and theory. We further reveal the origin of the dynamical state in K2Ni2 SO4 3 to be centred around a magnetic network composed of tetrahedra on a trillium lattic
Mechanistic Insights and Technical Challenges in Sulfur Based Batteries A Comprehensive In Situ Operando Monitoring Toolbox
Get PDFBatteries based on sulfur cathodes offer a promising energy storage solution due to their potential for high performance, cost effectiveness, and sustainability. However, commercial viability is challenged by issues such as polysulfide migration, volume changes, uneven phase nucleation, limited ion transport, and sluggish sulfur redox kinetics. Addressing these challenges requires insights into the structural, morphological, and chemical evolution of phases, the associated volume changes and internal stresses, and ion and polysulfide diffusion within the battery. Such insights can only be obtained through real time reaction monitoring within the battery s operational environment, supported by molecular dynamics simulations and advanced artificial intelligence driven data analysis. This review provides an overview of in situ operando techniques for real time tracking of these processes in sulfur based batteries and explores the integration of simulations with experimental data to provide a holistic understanding of the critical challenges, enabling advancements in their development and commercial adoptio
High performance anion exchange membrane water electrolysers using NiX X Fe,Co,Mn catalyst coated membranes with redox active Ni O ligands
No full textRecent efforts in anion exchange membrane water electrolysis AEMWE focus on developing superior catalysts and membrane electrode assemblies to narrow the performance gaps compared with proton exchange membrane water electrolysis PEMWE . Here we present and characterize Ir free AEMWE cells with NiX X amp; 8201; amp; 8201;Fe, Co or Mn layered double hydroxide LDH catalyst coated membranes with polarization characteristics and hydrogen productivities approaching those of acidic PEMWE cells, achieving gt;5 amp; 8201;A amp; 8201;cm amp; 8722;2 at lt;2.2 amp; 8201;V. Operando spectroscopy revealed a correlation between Ni4 centres and redox active O ligands with an O K edge feature, attributed to 3 O ligands in the amp; 947; LDH catalytic phase via density functional theory calculations. This computational experimental study challenges the previously assumed correlation between spectral O K edge features and oxygen evolution reaction performance in Ni based LDH catalysts and provides insights from the molecular to the technological level demonstrating how redox active Ni O species and innovative catalyst coated membrane preparation boost AEMWE performance to values rivalling state of the art PEMWE cell technolog