1,721,012 research outputs found
Towards a Simplified Electrochemical Method of Assessing Cations Transference Numbers of Electrolytes
No full textA simplified method is presented to extract the transport parameters of a liquid electrolyte solution from an experiment in a four-electrode cell. By observing that both polarisation and relaxation tend exponentially to a finite value with the same time constant, it becomes possible to precisely evaluate the limiting voltage attained upon polarisation though no steady state can be reached in practice, and use this input to evaluate the cation transference number as a function of the thermodynamic factor. This procedure simplifies the data analysis by avoiding complete fitting of the polarisation with a complicated numerical model. Such approach can favour the deployment of the four-electrode method to evaluate electrolyte transport parameters, which are crucial for the development of better performing batteries.Funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (Grant Agreement No. 715087). We thank the Spanish Agencia Estatal de Investigacion Severo Ochoa Programme for Centres of Excellence in R&D (CEX2019-000917-S). R.D. acknowledges support of the Beatriu de Pinos postdoctoral programme of the Government of Catalonia's Secretariat for Universities and Research of the Ministry of Economy and Knowledge (2017 BP 00187). We thank Charles Delacourt and Mohammad Farkhondeh for useful discussion.With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).Peer reviewe
Post-Li batteries: promises and challenges
No full textCurrent societal challenges in terms of energy
storage have prompted an intensification in the
research aiming at unravelling new high energy
density battery technologies. These would have the
potential of having disruptive effects in the world
transition towards a less carbon-dependent energy
economy through transport, both by electrification
and renewable energy integration. Aside from
controversial debates on lithium supply, the
development of new sustainable battery chemistries
based on abundant elements is appealing, especially
for large-scale stationary applications. Interesting
alternatives are to use sodium, magnesium or calcium
instead of lithium. While for the Na-ion case, fast
progresses are expected as a result of chemical
similarities with lithium and the cumulated Li-ion
battery know-how over the years, for Ca and Mg
the situation is radically different. On the one hand,
the possibility to use Ca or Mg metal anodes would
bring a breakthrough in terms of energy density; on
the other, development of suitable electrolytes and
cathodes with efficient multivalent ion migration are
bottlenecks to overcome.Funding from the European Union’s Horizon 2020 research and innovation programme is
acknowledged, both from the European Research Council (A. Ponrouch ERC-2016-STG, CAMBAT grant
agreement no. 715087) and FETOPEN-1-2016-2017 (CARBAT, grant agreement no. 766617).
Acknowledgements. Authors acknowledge ALISTORE-ERI members and NAIADES (H2020, 646433) partners
for helpful discussions and are grateful to Fanny Barde (Toyota Motor Europe) and M. Elena Arroyo-de
Dompablo for fruitful collaboration. Authors are grateful to Ministry of Science, Innovation and Universities
for support through MAT2017-86616-R and ‘Severo Ochoa’ Programme for Centres of Excellence in R&D
(SEV-2015-0496).Peer reviewe
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
Aqua-tri-fluorido-boron-1,3-dioxolan-2-one (1/2)
No full textThe crystal structure of the co-crystal of aqua-tri-fluorido-boron with two ethyl-ene carbonate (systematic name: 1,3-dioxolan-2-one) mol-ecules, BF3H2O·2OC(OCH2)2, was determined by low-temperature single-crystal X-ray diffraction. The co-crystal crystallizes in the ortho-rhom-bic space group P212121 with four formula units per unit cell. The asymmetric unit consists of an aqua-tri-fluorido-boron mol-ecule and two ethyl-ene carbonate mol-ecules, connected by O-H⋯O=C hydrogen bonds. This crystal structure is an inter-esting example of a superacidic BF3H2O species co-crystallized with an organic carbonate.Funding for this research was provided by: European
Research Council (ERC) (StG HiPeR-F and StG CAMBAT)
(grant agreement Nos. 950625 and 715087); Marie Skłodowska-Curie Actions (COFUND-2016 DOC-FAM) under
the European Union’s Horizon 2020 research and innovation
programme (grant No. 754397); Jozˇef Stefan Institute Director’s Fund; Slovenian Research Agency (grant No. N1-0189);
Spanish Ministry for Economy, Industry and Competitiveness
Severo Ochoa Programme for Centres of Excellence in R&D
(contract No. CEX2019-000917-S).With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).Peer reviewe
Electrolytes and Interfaces in Calcium and Magnesium Rechargeable Batteries
Full text linkEl desenvolupament d’una nova generació de bateries (post Li) tindrà, durant els propers anys, un impacte important en la transició de combustibles fòssils a noves fonts d’energia renovables. Dels diferents conceptes de bateries d’aquesta pròxima generació, destaquen els que utilitzen metalls divalents com elèctrodes negatius (especialment Ca i Mg), atesa la seva combinació de baix potencial estàndard de reducció i la seva gran abundància. El desenvolupament de bateries de Ca i Mg metall s’ha vist històricament obstaculitzat a causa de la limitada opció d’electròlits orgànics que permetin la deposició i dissolució reversible del metall, una condició necessària per a un funcionament continu i estable de l’elèctrode metàl·lic. En aquesta tesi es presenten alguns esforços en optimitzar electròlits orgànics per a l’electrodeposició de Ca, amb certs paral·lelismes a l’aplicació en el cas del Mg. En aquest treball, la formulació de l’electròlit, que es basa en una barreja de sal, dissolvent i additius, s’estudia des de tres punts de vista complementaris: la preparació de les sals de Ca, les propietats fisicoquímiques dels electròlits obtinguts i l’avaluació del seu rendiment electroquímic, que inclou també la possible descomposició de l’electròlit per reducció i la formació d’una capa de passivació a l’elèctrode. Tot i que els tres punts de vista estan separats en diferents capítols, no estan realment aïllats, i les interaccions es discuteixen al llarg d’aquest document. En particular, la solvatació del catió apareix com un paràmetre físic de vital importància que afecta els tres punts de vista: està influenciada per la sal i el dissolvent, és responsable de les propietats macroscòpiques (com la conductivitat iònica i la ionicitat), i afecta, alhora, a la dinàmica d’electrodeposició i a la naturalesa de la capa de passivació formada. Per tant, en aquesta tesi es presenten alguns detalls enfocats en la manipulació de l’esfera de solvatació del catió, com una via per optimitzar el funcionament d’un elèctrode de Ca metàl·lic. A més a més, també es presenta un estudi sobre les capes de passivació formades en elèctrodes metàl·lics de calci en funció de la formulació de l’electròlit. S’ha demostrat que la capa de passivació a base de borat, que es produeix in situ per descomposició d’anions o additius, afavoreix l’electrodeposició de calci, en contrast amb una capa de passivació a base de carbonat, que sembla bloquejar totalment els cations de calci. Estudis futurs aclariran de manera més precisa la composició d’aquesta capa basada en borats, i facilitaran el camí per a la utilització de capes de passivació generades artificialment en futures bateries de calci.El desarrollo de una nueva generación de baterías (post Li) tendrá, en los próximos años, un impacto importante en la transición de combustibles fósiles a nuevas fuentes de energía renovables. De los diferentes conceptos de baterías de próxima generación, destacan los que utilizan metales divalentes como electrodos negativos (especialmente Ca y Mg), dada su combinación de bajo potencial estándar de reducción y su gran abundancia. El desarrollo de baterías de Ca y Mg metal se ha visto históricamente obstaculizado debido a la limitada opción de electrolitos orgánicos que permitan la deposición y disolución reversible del metal, una condición necesaria para un funcionamiento continuo y estable del electrodo metálico. En esta tesis se presentan algunos esfuerzos en la optimización de electrolitos orgánicos para la electrodeposición de Ca, con ciertos paralelos a la aplicación en el caso de Mg. La formulación del electrolito, que se basa en una mezcla de sal, disolvente y aditivos, se estudia en este trabajo desde tres puntos de vista complementarios: la preparación de las sales de calcio, las propiedades fisicoquímicas de los electrolitos obtenidos y la evaluación de su rendimiento electroquímico, que incluye también la posible descomposición del electrolito por reducción y la formación de una capa de pasivación en el electrodo. Aunque los tres puntos de vista están separados en diferentes capítulos, no están realmente aislados, y sus interacciones se discuten a lo largo de este documento. En particular, la solvatación del catión aparece como un parámetro físico de vital importancia que afecta los tres puntos de vista: está influenciada por la sal y el disolvente, es responsable de las propiedades macroscópicas (como conductividad iónica e ionicidad), y afecta, a su vez, la dinámica de electrodeposición y a la naturaleza de la capa de pasivación formada. Por lo tanto, en esta tesis se presentan algunos detalles enfocados en la manipulación de la esfera de solvatación del catión, como una vía para optimizar el funcionamiento de un electrodo de Ca metálico. Además, se presenta aquí un estudio sobre las capas de pasivación formadas en electrodos metálicos de calcio, en función de la formulación del electrolito. Se ha demostrado que la capa de pasivación a base de borato, que se produce in-situ por descomposición de aniones o aditivos, favorece la electrodeposición de calcio, en contraste con una capa de pasivación a base de carbonato, que parece bloquear totalmente los cationes de calcio. Estudios futuros elucidarán de manera más precisa la composición de esta capa basada en boratos, y allanarán el camino para la utilización de capas de pasivación generadas artificialmente en futuras baterías de calcio.The development of next-generation batteries (post Li) will have a great impact in the upcoming years of transition from fossil fuels to renewable sources of energy. Among the many next-generation battery concepts, the ones based on divalent metals as negative electrodes stand out (particularly Ca and Mg), given their combination of low standard redox potential and high natural abundance. Development of Ca and Mg metal batteries have been historically hampered, as only a few organic electrolytes allow reversible electroplating/stripping of the metal, which is required for a continuous and stable operation of the metallic negative electrode. In this thesis, some efforts on the optimization of organic electrolytes for Ca metal plating are presented, with parallels to Mg application. The electrolyte formulation, which is based on a mixture of salt, solvent, and additives, is studied in this work from three complementary points of view: preparation of calcium salts, physicochemical properties of the obtained electrolytes, and evaluation of their electrochemical performance, which includes also the possible reductive decomposition of the electrolyte and the formation of a passivation layer on the electrode. Although they are separated in different chapters, these are not isolated parameters, and their interactions are discussed across this document. Particularly, the cation solvation appears as a physical parameter of critical importance from the three points of view: being influenced by salt and solvent choice, it is responsible for the macroscopic properties (as ionic conductivity and ionicity), and affects, in turn, the dynamics of electroplating, and the nature of the passivation layer formed. Therefore, some insides in the cation solvation-shell manipulation are presented as a route to optimize the operation of a Ca metal as the negative electrode. Additionally, a study on the passivation layers formed on metallic calcium electrodes is presented, as a function of the electrolyte formulation. The borate-based passivation layer, which is produced in-situ by anion or additive decomposition, was shown to promote calcium plating in contrast to a carbonate-based passivation layer, which appeared to be fully blocking for Ca2+ cations. Further studies will determine a more precise composition of the borate-based layer and will pave the way for artificially generated passivation layers to be used in future calcium batteries.Universitat Autònoma de Barcelona. Programa de Doctorat en Ciència de Material
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
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