1,721,004 research outputs found
Exploring 3d-metal compounds based on carboxylate polyanions (oxalates, malonates and carbonates) as positives electrode for Li/Na ions batteries
No full textDans cette thèse, nous avons exploré toute une palette de composés à base de métaux de transition et de polyanions carboxylates (oxalates, malonates et carbonates) préparés via des procédés éco-efficaces. La synthèse du composé oxalate de fer (III) (Fe2(C2O4)3·4H2O) dont nous en avons élucidé pour la première fois la structure cristalline en combinant les techniques de diffraction des rayons X et neutrons, fait l'objet de la première partie de cette étude. Ce composé cristallise dans une maille triclinique (P -1) et il présente des propriétés électrochimiques intéressantes (98 mAh/g à 3.35 V vs. Li+/Li0). Dans cette quête pour de meilleurs matériaux, nous avons exploré la famille des oxalates Na2M2(C2O4)3·2H2O, dont la synthèse avait été déjà rapportée, mais sans qu'aucune activité électrochimique ne puisse être détectée. En revanche, le remplacement du groupement oxalate par un groupement malonate nous a permis d’obtenir pour la première fois plusieurs membres de la famille (Na2M(H2C3O4)2·nH2O (n=0, 2), M= Mn, Fe, Co, Ni, Zn et Mg) dont nous avons résolu leurs structures cristallines correspondantes. Cependant, comme dans le cas des oxalates, ces phases ne dévoilent aucune activité électrochimique vis-à-vis du lithium, bien qu'elles présentent des propriétés magnétiques intéressantes. Enfin nous avons conclu ce travail par la synthèse de composés appartenant à la famille des fluorocarbonates KMCO3F (M= Ca et Mn) en utilisant la voie tout solide. La phase au calcium, déjà rapportée dans la littérature, a fait l'objet d'une étude en température qui nous a permis de mettre en évidence pour la première fois la formation d'une phase haute température (KCaCO3F-HT), pour T≥320°C, dont nous avons résolu la structure. Finalement, l'utilisation du Mn au lieu du Ca a conduit à l'obtention d'une nouvelle phase (KMnCO3F) qui cristallise dans une maille hexagonale (P -6 c 2)This thesis has focused on the exploration of new compounds based on 3d-metal and carboxylate polyanions (oxalates, malonates and carbonates) prepared through different sustainable synthetic approaches. In the first part, we report a new synthetic route to prepare the iron (III) oxalate compound (Fe2(C2O4)3·4H2O) and solve its crystal structure through combined X-ray and neutron powder diffraction. The compound crystallizes within a triclinic cell (P-1) and exhibits attractive electrochemical properties (98 mAh/g at 3.35 V vs. Li+/Li0). Motivated by this finding we pursued our quest for new positive electrode materials. We prepared by hydrothermal synthesis single crystals of sodium 3d-metal oxalates Na2M2(C2O4)3·2H2O, which are widely investigated in the literature for their magnetic properties. Unfortunately, these phases are electrochemically inactive versus lithium. Thereafter, we extended the synthesis towards the malonate family and we reported for the first time several members (Na2M(H2C3O4)2·nH2O (n= 0, 2), M= Mn, Fe, Co, Ni, Zn et Mg). These systems present rich crystal chemistry together with interesting antiferromagnetic properties but as in the case of the oxalates, they are not electrochemically active versus lithium. Finally, we synthesized two members of fluorocarbonates compounds KMCO3F (M= Ca and Mn) using solid state process. We succeeded in the preparation of the calcium member, already reported in the literature and we identified for the first time a phase transition at 320°C. The crystal structure of the high temperature phase (KCaCO3F-HT) was solved using neutron powder diffraction. A new manganese phase (KMnCO3F) was synthesized using the same technique and its crystal structure was solved by combining TEM, XR and neutrons powder diffraction techniques. This compound crystallizes within a hexagonal unit cell (P -6 c 2
Biomineralization of manganese oxides for electrochemical energy storage
No full textNous avons étudié la capacité d’une souche bactérienne à produire par biominéralisation un matériau capable de stocker de l’énergie. L’étude s’est portée sur la culture dans différentes conditions de la souche Pseudomonas putida MnB1, une bactérie Mn-oxydante, capable de produire un oxyde de manganèse par oxydation du Mn2+. En conditions planctoniques (agitation du milieu de culture), la souche bactérienne a la capacité d’oxyder de façon optimale le Mn2+ ajouté dans la solution et conduit à la précipitation d’un oxyde de manganèse MnO2 lamellaire de type birnessite. Les tests électrochimiques réalisés pour cette birnessite biogénique indiquent que ce minéral possède une activité électrochimique d’intercalation des ions lithium et présente une capacité électrochimique proche de la capacité théorique d’un MnO2. La texture produite par biominéralisation permet un maintien des performances électrochimiques et cette propriété intéressante nous a conduit à vouloir l’exploiter en produisant une électrode en une seule étape. Pour cela nous avons produit un biofilm biominéralisé avec la souche Pseudomonas putida directement sur un collecteur de courant. Il est alors possible de former une électrode en une seule étape, composée d’un biofilm avec oxydes de manganèse et ayant une activité électrochimique. L’absence d’agitation, nécessaire à la formation de ce biofilm, entraine une diminution de l’activité d’oxydation de la bactérie et donc une diminution de la précipitation du Mn2+ dans le biofilm. L’optimisation des conditions de cultures (ie. température de culture, luminosité et polarisation du support) a permis de sélectionner une condition favorisant la colonisation du biofilm et la précipitation d’oxydes de manganèse lamellaires très texturés. Les résultats électrochimiques de cette électrode optimisée montrent une amélioration du maintien de la capacité électrochimique. Il serait par la suite intéressant d’utiliser ce processus de biominéralisation pour la production d’un matériau d’électrode ternaire (ie. contenant déjà un ion alcalin) afin de former une électrode de batterie complète.In this study, we highlighted the ability of a bacterial strain to produce by biomineralization a material to store electrochemical energy. The study focused on the culture under different conditions of the Pseudomonas putida MnB1 strain, a Mn-oxidising bacterium, with the ability to produce a manganese oxide by Mn2+ oxidation. Under planktonic conditions (agitation of the culture medium), the Mn2+ added to the solution was entirely oxidised by the bacterial strain and led to the precipitation of a birnessite-type lamellar manganese oxide MnO2. The electrochemical tests of this biogenic birnessite indicate that this mineral has an electrochemical activity of intercalation of lithium ions and presents an electrochemical capacity close to the theoretical capacity of MnO2. The texture produced by biomineralization allows good electrochemical performances and this interesting property led us to explore the production of an electrode in a one-step process. For this purpose, we wanted to produce a biomineralized biofilm with the Pseudomonas putida strain directly grown on a current collector. The results show that it is possible to form an electrode in one-step, consisting of a biofilm with manganese oxides and exhibiting electrochemical activity. The absence of agitation, necessary for the formation of this biofilm, induces a decrease of bacterial oxidation rate and therefore a decrease in the precipitation of manganese in the biofilm. Then, the optimisation of the culture conditions (i.e. culture temperature, luminosity and polarisation of the support) made it possible to select a condition promoting the colonisation of the biofilm and the precipitation of highly textured manganese oxides. The electrochemical results of this optimised electrode show an improvement of cyclability. It would be interesting to use this biomineralization process to produce a ternary electrode material (i.e. containing an alkali ion) to form a complete battery electrode
From oxides to polyanionic materials, added values of bacterial biomineralisation for battery materials
No full textL'objectif de cette thèse est l'exploration de la biominéralisation bactérienne en solution aqueuse à température modérée, pour la préparation de matériaux électrochimiquement actifs pour une application en accumulateur au lithium éco-compatible. Dans ce contexte, ce manuscrit est focalisé sur la synthèse de FePO4·nH2O amorphe (FP) assistée par la bactérie S. pasteurii. La paroi bactérienne, en favorisant la nucléation de FP, confère aux particules, une organisation originale dite "bactériomorphe". Bien que le composite obtenu soit non-électroactif, il peut être activé par différents traitements : mécanique, chimique ou thermique. Un chauffage sous air s'est avéré être le plus efficace pour décomposer la matière bactérienne qui isole électriquement le FP. Les performances électrochimiques de ces bactériomorphes sont comparables à celles d'un FP produit sans bactéries mais broyé plusieurs heures. Il s'agit cependant d'un compromis car le chauffage induit aussi une déshydratation entrainant une limitation de la capacité délivrée par FP. Cette déshydratation et ses conséquences électrochimiques sont étudiées par différentes techniques, dont des techniques de microscopie et spectroscopie comme le STXM. Afin de contourner cette nécessité d'activation thermique, l'exploration de la synthèse extracellulaire de MnO2 par l'activité de la bactérie P. putida est initiée. Les résultats préliminaires sont prometteurs car le biominéral est actif électrochimiquement sans aucune activation post-synthèseThis study aimed at exploring a diversity of aqueous bacterial biomineralisation processes at room temperature for the synthesis of electrochemically active materials for an eco-compatible and reliable Li-ion battery application. This thesis is focused on S. pasteurii bacteria assisted synthesis of amorphous FePO4·nH2O (FP). The bacterial wall induces an original organization of FP particles (called "bacteriomorph") by promoting its nucleation. The product is an electrochemically inactive composite but can be activated by multiple treatments: mechanical, chemical or thermal. Heating under air is the most efficient method, as it burns the electrically insulating bacterial matter. Bacteriomorph FP’s electrochemical performances are comparable to those of FP synthesized without bacteria but ground for several hours. This treatment is however a compromise as heating induces dehydration as well, which impairs the reversible capacity of FP. This dehydration and its consequences on electrochemical properties have been studied with multiple tools, including microscopic and spectroscopic techniques, such as STXM. To overpass the thermal activation need, we started the exploration of extracellular synthesis of MnO2 assisted by P. putida. First results are promising as the biomineral is electrochemically active without any post-synthesis activatio
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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