1,720,959 research outputs found
New Alternative Chemistries For Redox Flow Batteries
No full textEnergy storage is considered a crucial enabler for the introduction of Renewable Energy sources, especially intermittent and non-programmable ones (e.g., the sun and the wind) in the energy mix. Among the available emerging technologies, Vanadium Flow Batteries (VFBs) stand out in terms of efficiency, long-term storage and ease of deployment. However, there is still room for improving their performance, scalability, and environmental impact. Thus, this thesis addresses some of the most compelling issues of VFBs, namely: (i) the side reactions in the electrolytes, which might degrade the performance; (ii) the high cost, high toxicity, and low availability of vanadium; (iii) the crossover of active species through the membrane and (iv) the low energy density associated with the low cell voltage and the low solubility of vanadium species.
Firstly, a formalism is implemented to study how the coordination species and their equilibria can influence the operation of a single-cell VFB. The formalism suggests that some of the reactions considered by the formalism can negatively contribute to the charge retention and to the charging of the battery. In particular, during charge, the estimate of the total energy wasted can account for ca. 22% of the total.
Secondly, attempts to substitute vanadium with zinc and iodine (as anodic and cathodic active species, respectively) are pursued to cut costs and to increase the energy density of the device. The main problem faced by Zn-I2 FBs is the uneven and partially irreversible plating of zinc at the anode. In this thesis we explore the development of two sets of innovative electrolyte feeds, wherein both the pH and the chemistry of the redox species are modulated by the introduction of suitable buffers. In the presence of the acetic acid/sodium acetate buffer, battery performance is significantly improved: the energy efficiency rises to 78% from a 70% baseline without the buffer. In the same conditions, the energy efficiency rises to 82% upon the introduction of a tris(hydroxymethyl)aminomethane (Tris) hydrochloric acid buffer.
The crossover of active species through the membrane is among the main causes of VFB performance degradation. To address this issue, “Zip-like” Ion Exchange Membranes (ZIEMs) are obtained by a macromolecular reaction between the cationic and anionic moieties of two different ionomers. It is shown that the resulting formation of ionic interactions between the ionomers cuts by a factor of 50 the crossover of vanadium species in comparison with the pristine ionomers taken separately. Single-cell VFB tests show a retained capacity of 82% after 100 cycles at 50 mA⸱cm-2 (in the same conditions, baseline Nafion 212 retains only 21% of the initial capacity). Hence, ZIEMs can be identified among the best performing IEMs for VFBs.
The last chapter of this thesis covers the implementation of ion-exchange membranes (IEMs) for Non-aqueous Flow Batteries (NFBs). NFBs are considered an interesting alternative to VFBs as organic solvents in principle enable higher cell voltages, thus improving the energy density. However, the currently available IEMs often face an excessive swelling upon immersion in organic solvents. After a first screening, a family of ionomers based on polybenzimidazole (PBI) and Nafion is proposed. It is revealed that the interactions between PBI and Nafion significantly modulate the microstructure of the resulting IEMs, raising the conductivity and curtailing the swelling upon immersion in organic solvents. The best membrane of this family swells by only 7% after 900 hours in a 1:1 v/v ethylene carbonate/propylene carbonate solution. Conductivity tests in the same solvent dissolving a reference tetraethylammonium salt show conductivities in the order of 0.5-0.9∙10-3 S∙cm-1. On these bases, these IEMs can be considered suitable for implementation in NFBs.Energy storage is considered a crucial enabler for the introduction of Renewable Energy sources, especially intermittent and non-programmable ones (e.g., the sun and the wind) in the energy mix. Among the available emerging technologies, Vanadium Flow Batteries (VFBs) stand out in terms of efficiency, long-term storage and ease of deployment. However, there is still room for improving their performance, scalability, and environmental impact. Thus, this thesis addresses some of the most compelling issues of VFBs, namely: (i) the side reactions in the electrolytes, which might degrade the performance; (ii) the high cost, high toxicity, and low availability of vanadium; (iii) the crossover of active species through the membrane and (iv) the low energy density associated with the low cell voltage and the low solubility of vanadium species.
Firstly, a formalism is implemented to study how the coordination species and their equilibria can influence the operation of a single-cell VFB. The formalism suggests that some of the reactions considered by the formalism can negatively contribute to the charge retention and to the charging of the battery. In particular, during charge, the estimate of the total energy wasted can account for ca. 22% of the total.
Secondly, attempts to substitute vanadium with zinc and iodine (as anodic and cathodic active species, respectively) are pursued to cut costs and to increase the energy density of the device. The main problem faced by Zn-I2 FBs is the uneven and partially irreversible plating of zinc at the anode. In this thesis we explore the development of two sets of innovative electrolyte feeds, wherein both the pH and the chemistry of the redox species are modulated by the introduction of suitable buffers. In the presence of the acetic acid/sodium acetate buffer, battery performance is significantly improved: the energy efficiency rises to 78% from a 70% baseline without the buffer. In the same conditions, the energy efficiency rises to 82% upon the introduction of a tris(hydroxymethyl)aminomethane (Tris) hydrochloric acid buffer.
The crossover of active species through the membrane is among the main causes of VFB performance degradation. To address this issue, “Zip-like” Ion Exchange Membranes (ZIEMs) are obtained by a macromolecular reaction between the cationic and anionic moieties of two different ionomers. It is shown that the resulting formation of ionic interactions between the ionomers cuts by a factor of 50 the crossover of vanadium species in comparison with the pristine ionomers taken separately. Single-cell VFB tests show a retained capacity of 82% after 100 cycles at 50 mA⸱cm-2 (in the same conditions, baseline Nafion 212 retains only 21% of the initial capacity). Hence, ZIEMs can be identified among the best performing IEMs for VFBs.
The last chapter of this thesis covers the implementation of ion-exchange membranes (IEMs) for Non-aqueous Flow Batteries (NFBs). NFBs are considered an interesting alternative to VFBs as organic solvents in principle enable higher cell voltages, thus improving the energy density. However, the currently available IEMs often face an excessive swelling upon immersion in organic solvents. After a first screening, a family of ionomers based on polybenzimidazole (PBI) and Nafion is proposed. It is revealed that the interactions between PBI and Nafion significantly modulate the microstructure of the resulting IEMs, raising the conductivity and curtailing the swelling upon immersion in organic solvents. The best membrane of this family swells by only 7% after 900 hours in a 1:1 v/v ethylene carbonate/propylene carbonate solution. Conductivity tests in the same solvent dissolving a reference tetraethylammonium salt show conductivities in the order of 0.5-0.9∙10-3 S∙cm-1. On these bases, these IEMs can be considered suitable for implementation in NFBs
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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