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Sökning: WFRF:(Menon Ashok S.)

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  • Klionsky, Daniel J., et al. (författare)
  • Guidelines for the use and interpretation of assays for monitoring autophagy
  • 2012
  • Ingår i: Autophagy. - : Landes Bioscience. - 1554-8635 .- 1554-8627. ; 8:4, s. 445-544
  • Forskningsöversikt (refereegranskat)abstract
    • In 2008 we published the first set of guidelines for standardizing research in autophagy. Since then, research on this topic has continued to accelerate, and many new scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Accordingly, it is important to update these guidelines for monitoring autophagy in different organisms. Various reviews have described the range of assays that have been used for this purpose. Nevertheless, there continues to be confusion regarding acceptable methods to measure autophagy, especially in multicellular eukaryotes. A key point that needs to be emphasized is that there is a difference between measurements that monitor the numbers or volume of autophagic elements (e.g., autophagosomes or autolysosomes) at any stage of the autophagic process vs. those that measure flux through the autophagy pathway (i.e., the complete process); thus, a block in macroautophagy that results in autophagosome accumulation needs to be differentiated from stimuli that result in increased autophagic activity, defined as increased autophagy induction coupled with increased delivery to, and degradation within, lysosomes (in most higher eukaryotes and some protists such as Dictyostelium) or the vacuole (in plants and fungi). In other words, it is especially important that investigators new to the field understand that the appearance of more autophagosomes does not necessarily equate with more autophagy. In fact, in many cases, autophagosomes accumulate because of a block in trafficking to lysosomes without a concomitant change in autophagosome biogenesis, whereas an increase in autolysosomes may reflect a reduction in degradative activity. Here, we present a set of guidelines for the selection and interpretation of methods for use by investigators who aim to examine macroautophagy and related processes, as well as for reviewers who need to provide realistic and reasonable critiques of papers that are focused on these processes. These guidelines are not meant to be a formulaic set of rules, because the appropriate assays depend in part on the question being asked and the system being used. In addition, we emphasize that no individual assay is guaranteed to be the most appropriate one in every situation, and we strongly recommend the use of multiple assays to monitor autophagy. In these guidelines, we consider these various methods of assessing autophagy and what information can, or cannot, be obtained from them. Finally, by discussing the merits and limits of particular autophagy assays, we hope to encourage technical innovation in the field.
  • Chien, Yu-Chuan, et al. (författare)
  • Development of operando XRD coin cells for lithium-sulfur batteries
  • 2018
  • Konferensbidrag (övrigt vetenskapligt)abstract
    • Lithium-sulfur (Li-S) batteries has been regarded as one of the promising technology for the next generation of rechargeable batteries due to its high theoretical energy density (2600 Wh/kg [1]). Several works [2–7] on operando X-ray diffraction (XRD) of the Li-S system have been published; however, their experimental setups showed one or more of the following drawbacks. First, the amount of electrolyte was often not reported or would be considered too high for a common Li-S cell, which has been demonstrated to have a significant impact on the behavior of the system [8]. Another issue is the non-uniform stack pressure and electron conductivity of the operando cell setup, whose effects were found by both experiments and simulations [9].This work aims to tackle with the above-mentioned issues by modifying commercial coin cells and using X-ray transparent metal, beryllium, as the spacers. By doing so, the electron conductivity and stack pressure can be expected to be uniform throughout the electrodes. The amount of electrolyte can also be precisely controlled since no vacuum-sealing is required for coin cells. A preliminary diffraction pattern obtained with the cell setup can be seen in Fig. 1. With electrochemical properties similar to common Li-S cells, ‘online’ electrochemical characterization techniques, e.g. Intermittent Current Interruption (ICI) method for following cell resistance [10], will be applicable with operando XRD, revealing more information about this complex system.Figure 1 XRD patterns of alpha-S and electrode material in the modified coin cell.References[1] J. Tan, et al., Nanoscale (2017) 19001–19016.[2] J. Nelson, et al., J. Am. Chem. Soc. 134 (2012) 6337–6343.[3] N.A. Cañas, et al., J. Power Sources 226 (2013) 313–319.[4] S. Waluś, et al., Chem. Commun. 49 (2013) 7899.[5] M. a. Lowe, et al., RSC Adv. 4 (2014) 18347.[6] J. Kulisch, et al., Phys. Chem. Chem. Phys. 16 (2014) 18765–18771.[7] J. Conder, et al., Nat. Energy 2 (2017) 1–7.[8] M.J. Lacey, ChemElectroChem (2017) 1–9.[9] O.J. Borkiewicz, et al., J. Phys. Chem. Lett. 6 (2015) 2081–2085.[10] M.J. Lacey, et al., Chem. Commun. 51 (2015) 16502–16505.
  • Chien, Yu-Chuan, 1990-, et al. (författare)
  • Simultaneous Monitoring of Crystalline Active Materials and Resistance Evolution in Lithium-Sulfur Batteries
  • 2020
  • Ingår i: Journal of the American Chemical Society. - : AMER CHEMICAL SOC. - 0002-7863 .- 1520-5126. ; 142:3, s. 1449-1456
  • Tidskriftsartikel (refereegranskat)abstract
    • Operando X-ray diffraction (XRD) is a valuable tool for studying secondary battery materials as it allows for the direct correlation of electrochemical behavior with structural changes of crystalline active materials. This is especially true for the lithium-sulfur chemistry, in which energy storage capability depends on the complex growth and dissolution kinetics of lithium sulfide (Li2S) and sulfur (S-8) during discharge and charge, respectively. In this work, we present a novel development of this method through combining operando XRD with simultaneous and continuous resistance measurement using an intermittent current interruption (ICI) method. We show that a coefficient of diffusion resistance, which reflects the transport properties in the sulfur/carbon composite electrode, can be determined from analysis of each current interruption. Its relationship to the established Warburg impedance model is validated theoretically and experimentally. We also demonstrate for an optimized electrode formulation and cell construction that the diffusion resistance increases sharply at the discharge end point, which is consistent with the blocking of pores in the carbon host matrix. The combination of XRD with ICI allows for a direct correlation of structural changes with not only electrochemical properties but also energy loss processes at a nonequilibrium state and, therefore, is a valuable technique for the study of a wide range of energy storage chemistries.
  • Chien, Yu-Chuan, 1990-, et al. (författare)
  • Understanding the Impact of Precipitation Kinetics on the Electrochemical Performance of Lithium–Sulfur Batteries by Operando X-ray Diffraction
  • Annan publikation (övrigt vetenskapligt)abstract
    • The complex reaction mechanism of the lithium–sulfur battery system consists of re-petitive dissolution and precipitation of the sulfur-containing species in the positiveelectrode. In particular, the precipitation of lithium sulfide (Li2S) during discharge hasbeen considered a crucial factor for achieving a high degree of active material utiliza-tion. Here, the influence of electrolyte amount, electrode thickness, applied current andelectrolyte salt on the formation of Li2S is systematically investigated in a series ofoperando X-ray diffraction experiments. Through a combination of simultaneous dif-fraction and resistance measurements, the evolution of the intensity from Li2S is di-rectly correlated to the variation in internal resistance and transport properties insidethe positive electrode. The correlation indicates that at different stages, the Li2S precip-itation both facilitates and impedes the discharge process. The kinetic information ofLi2S formation offers mechanistic explanations for the strong impact of different elec-trochemical cell parameters on the performance and thus, directions for holistic optimi-zations to achieve high sulfur utilization.
  • Fritze, Stefan, et al. (författare)
  • Magnetron sputtering of carbon supersaturated tungsten films-A chemical approach to increase strength
  • 2021
  • Ingår i: Materials & design. - : Elsevier BV. - 0264-1275 .- 1873-4197. ; 208
  • Tidskriftsartikel (refereegranskat)abstract
    • Tungsten (W)-based materials attract significant attention due to their superior mechanical properties. Here, we present a chemical approach based on the addition of carbon (C) for increased strength via the combination of three strengthening mechanisms in W thin films. W:C thin films with C concentrations up to-4 at.% were deposited by magnetron sputtering. All films exhibit a body-centred-cubic structure with strong texture and columnar growth behaviour. X-ray and electron diffraction measurements suggest the formation of supersaturated W:C solid solution phases. The addition of C reduced the average column width from-133 nm for W to-20 nm for the film containing-4 at.% C. The column refinement is explained by a mechanism where C acts as re-nucleation sites. The W film is-13 GPa hard, while the W:C films achieve a peak hardness of-24 GPa. The W:C films are-11 GPa harder than the W film, which is explained by a combination of grain refinement strengthening, solid solution strengthening and increased dislocation density. Additional micropillar compression tests showed that the flow stress increased upon C addition, from-3.8 to-8.3 GPa and no brittle fracture was observed.
  • Menon, Ashok S., et al. (författare)
  • A Crystallographic Reinvestigation of Li1.2Mn0.6Ni0.2O2
  • Annan publikation (övrigt vetenskapligt)abstract
    • Despite substantial research interest, the crystallography of the promising Li-ion positive electrode material, Li1.2Mn0.6Ni0.2O2, remains disputed. The dispute is predicated on the description of the cationic arrangement in the structure, and multiple structure models have been proposed. This study attempts to provide a fresh perspective to this debate through a multi-scalar structural characterisation of Li1.2Mn0.6Ni0.2O2. Combining Bragg diffraction, transmission electron microscopy and magnetic measurements with reverse Monte Carlo analysis of total scattering data, a quantitative structural description of Li1.2Mn0.6Ni0.2O2 is developed and the existing single- and multi-phase structural descriptions of this compound have been unified. Furthermore, the merits and drawbacks of each technique is evaluated with respect to the crystallography of Li1.2Mn0.6Ni0.2O2 to explain the factors that have contributed to the lack of clarity pervading the structural description of this material. It is envisioned that a better understanding of the crystallography of Li1.2Mn0.6Ni0.2O2 contributes to harnessing the electrochemical potential of this compound.  
  • Menon, Ashok S., et al. (författare)
  • Influence of Synthesis Routes on the Crystallography, Morphology, and Electrochemistry of Li2MnO3
  • 2020
  • Ingår i: ACS Applied Materials and Interfaces. - : AMER CHEMICAL SOC. - 1944-8244 .- 1944-8252. ; 12:5, s. 5939-5950
  • Tidskriftsartikel (refereegranskat)abstract
    • With the potential of delivering reversible capacities of up to 300 mAh/g, Li-rich transition-metal oxides hold great promise as cathode materials for future Li-ion batteries. However, a cohesive synthesis-structure-electrochemistry relationship is still lacking for these materials, which impedes progress in the field. This work investigates how and why different synthesis routes, specifically solid-state and modified Pechini sol-gel methods, affect the properties of Li2MnO3, a compositionally simple member of this material system. Through a comprehensive investigation of the synthesis mechanism along with crystallographic, morphological, and electrochemical characterization, the effects of different synthesis routes were found to predominantly influence the degree of stacking faults and particle morphology. That is, the modified Pechini method produced isotropic spherical particles with approximately 57% faulting and the solid-state samples possessed heterogeneous morphology with approximately 43% faulting probability. Inevitably, these differences lead to variations in electrochemical performance. This study accentuates the importance of understanding how synthesis affects the electrochemistry of these materials, which is critical considering the crystallographic and electrochemical complexities of the class of materials more generally. The methodology employed here is extendable to studying synthesis-property relationships of other compositionally complex Li-rich layered oxide systems.
  • Menon, Ashok S. (författare)
  • Synthesis–Structure–Property Relationships in Li- and Mn-rich Layered Oxides
  • 2021
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • The commercialisation of Li-ion batteries over the last decade has provided additional impetus for the improvement of existing energy storage technologies. Towards this, a major portion of the global efforts includes exploratory research aimed at the development of new material chemistries. Aligning with this theme, this Thesis explores the synthesis–structure–property relationships in Li- and Mn-rich layered oxides, a cost-effective high-capacity material system that shows promise as a positive electrode material for future Li-ion batteries. The compositional and crystallographic diversity of Li- and Mn-rich layered oxides make them particularly susceptible to synthesis-dependent variations and exacerbates structural characterisation. Therefore, understanding how synthetic variations influence their structural and electrochemical properties is a crucial step in realising their potential as positive electrode materials.Even for simple compositions like Li2MnO3, dissimilar crystallographic ordering and particle morphologies are produced depending on whether a solid-state or sol-gel synthesis approach was implemented. Subsequently, due to the higher degree of structural disorder and larger surface area, the sol-gel sample exhibited higher initial electrochemical capacities. The structural features present in these compounds such as cation site-mixing and stacking faults, manifest over varying crystallographic regimes. Hence, complementary characterisation techniques that probe different structural length scales are necessary for an accurate structural characterisation of these compounds. This factor, together with their complex crystallography, have led to contradictory single- and multi-phase structure models being reported for complex Li- and Mn-rich layered oxides. By using a combination of diffraction, spectroscopic techniques and magnetic measurements it was discovered that Li1.2Mn0.54Ni0.13Co0.13O2 can exist in both single- and multi-phase structural forms if synthesised through sol-gel and solid-state methods, respectively. Further studies following the same theme revealed that when synthesised under common laboratory conditions these compounds are metastable. Here, the composition and synthesis play a critical role in the thermodynamic and kinetic factors affecting the resultant phase, domain structure and degree of cationic order. Finally, to encompass all the structural features contained in Li- and Mn-rich layered oxides, a supercell-based structure model for Li- and Mn-rich layered oxides, using Li1.2Mn0.6Ni0.2O2 as an example, is presented. Summing all the work together from the thesis, a critical evaluation of commonly used characterisation techniques is also provided as a guideline for future research in this field.
  • Menon, Ashok S., et al. (författare)
  • Synthetic Pathway Determines the Nonequilibrium Crystallography of Li- and Mn-Rich Layered Oxide Cathode Materials
  • 2021
  • Ingår i: ACS Applied Energy Materials. - : AMER CHEMICAL SOC. - 2574-0962. ; 4:2, s. 1924-1935
  • Tidskriftsartikel (refereegranskat)abstract
    • Li- and Mn-rich layered oxides show significant promise as electrode materials for future Li-ion batteries. However, an accurate description of its crystallography remains elusive, with both single-phase solid solution and multiphase structures being proposed for high performing materials such as Li1.2Mn0.54Ni0.13Co0.13O2. Herein, we report the synthesis of single- and multiphase variants of this material through sol-gel and solid-state methods, respectively, and demonstrate that its crystallography is a direct consequence of the synthetic route and not necessarily an inherent property of the composition, as previously argued. This was accomplished via complementary techniques that probe the bulk and local structure followed by in situ methods to map the synthetic progression. As the electrochemical performance and anionic redox behavior are often rationalized on the basis of the presumed crystal structure, clarifying the structural ambiguities is an important step toward harnessing its potential as an electrode material.
  • Naylor, Andrew J., et al. (författare)
  • Depth-dependent oxygen redox activity in lithium-rich layered oxide cathodes
  • 2019
  • Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488. ; 7:44, s. 25355-25368
  • Tidskriftsartikel (refereegranskat)abstract
    • Lithium-rich materials, such as Li1.2Ni0.2Mn0.6O2, exhibit capacities not limited by transition metal redox, through the reversible oxidation of oxide anions. Here we offer detailed insight into the degree of oxygen redox as a function of depth within the material as it is charged and cycled. Energy-tuned photoelectron spectroscopy is used as a powerful, yet highly sensitive technique to probe electronic states of oxygen and transition metals from the top few nanometers at the near-surface through to the bulk of the particles. Two discrete oxygen species are identified, On− and O2−, where n < 2, confirming our previous model that oxidation generates localised hole states on O upon charging. This is in contrast to the oxygen redox inactive high voltage spinel LiNi0.5Mn1.5O4, for which no On− species is detected. The depth profile results demonstrate a concentration gradient exists for On− from the surface through to the bulk, indicating a preferential surface oxidation of the layered oxide particles. This is highly consistent with the already well-established core–shell model for such materials. Ab initio calculations reaffirm the electronic structure differences observed experimentally between the surface and bulk, while modelling of delithiated structures shows good agreement between experimental and calculated binding energies for On−.
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