1,720,959 research outputs found
A redox shuttle to facilitate oxygen reduction in the lithium air battery
No full textA novel design of the non-aqueous lithium air cell is presented with a demonstration of a new reaction concept, involving a soluble redox shuttle to catalyse oxygen reduction. In principle, this can relieve the requirement for fast diffusion of molecular oxygen from the air interface to the positive electrode. To demonstrate this concept, ethyl viologen ditriflate was dissolved in BMPTFSI, reduced at a carbon electrode and regenerated by aspiration with oxygen. Useful shuttle behaviour, confirmed by several reduction–oxidation cycles, was observed in the case where the electrolyte contained at least 0.3 M lithium salt. The beneficial effect of the salt was attributed to its critical role in converting superoxide, which would otherwise destroy the shuttle, into the more desirable product of oxygen reduction, lithium peroxide.<br/
An in-situ Raman study of the oxygen reduction reaction in ionic liquids
No full textIn-situ Raman spectroscopy is applied, for the first time, to elucidate the reaction products of oxygen reduction in two types of ionic liquids: 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (C2mimTFSI) and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (Pyr14TFSI). The degradation of C2mimTFSI by superoxide attack is evidenced by the appearance of bands characteristic of amide and carbonate compounds. On the contrary, Pyr14TFSI is found to be resistant towards degradation. It is observed that superoxide is the first product of oxygen reduction in Pyr14TFSI, and the formation of Li2O2 is observed at longer time
Data for: Using polyoxometalates to enhance the capacity of lithium-oxygen batteries
No full textDataset supports:
Abstract
The Keggin-type polyoxometalate α-SiW12O404- increases the discharge capacity and potential of lithium-oxygen batteries, by facilitating the reduction of O2 to Li2O2, as confirmed by in-situ electrochemical pressure measurements and XRD. Compared to organic redox mediators, polyoxometalates have higher chemical and structural stability, which could lead to longer cycling lithium-oxygen batteries.
</span
Soluble redox catalysts to enhance and relocate oxygen reduction and evolution in the lithium-air battery
No full textElectrochemical oxygen reduction in a non-aqueous electrolyte often results in the deposition of an insoluble product on the electrode surface, thereby blocking access of oxygen to the surface for continued reaction. In the presence of a suitable redox shuttle such as viologen, oxygen reduction can occur homogeneously in solution near the air interface. This has the effect of displacing the oxygen reduction reaction some distance away from the electrode surface, which remains active to regenerate the reduced form of the shuttle. A further possibility is mediation of the oxygen reduction reaction in order to favour the formation of lithium peroxide rather than radical products that may degrade the electrolyte. Given a suitable shuttle reagent, this scheme may have several potential advantages, for example:Avoidance of electrode passivation by insoluble lithium oxidesAn increased, chemical driving force for oxygen adsorption into the electrolyteIncreased mass transfer to the electrode surfaceEnhanced kinetics of lithium peroxide formationMinimisation of side reactions that may degrade the electrolyt
Understanding LiOH chemistry in a ruthenium-catalyzed Li-O2 battery
Full text linkNon‐aqueous Li–O2 batteries are promising for next‐generation energy storage. New battery chemistries based on LiOH, rather than Li2O2, have been recently reported in systems with added water, one using a soluble additive LiI and the other using solid Ru catalysts. Here, the focus is on the mechanism of Ru‐catalyzed LiOH chemistry. Using nuclear magnetic resonance, operando electrochemical pressure measurements, and mass spectrometry, it is shown that on discharging LiOH forms via a 4 e− oxygen reduction reaction, the H in LiOH coming solely from added H2O and the O from both O2 and H2O. On charging, quantitative LiOH oxidation occurs at 3.1 V, with O being trapped in a form of dimethyl sulfone in the electrolyte. Compared to Li2O2, LiOH formation over Ru incurs few side reactions, a critical advantage for developing a long‐lived battery. An optimized metal‐catalyst–electrolyte couple needs to be sought that aids LiOH oxidation and is stable towards attack by hydroxyl radicals
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
- …
