1,720,966 research outputs found
Development of new molecular systems and innovative materials for regenerative photoelectrochemical cells
No full textWith the increasing world demand of renewable energy sources, the exploitation of solar energy became a priority in the global race for a sustainable future. Dye-sensitized solar cells (DSSC) were recognized to hold great potential for a relatively cheap and easy-to-scale approach to direct solar-to-electrical power conversion. Their transparency, versatile design and wide color palette offers unique structural and architectural possibilities in the emerging field of building integration.
Purpose of this thesis is to contribute to the DSSC technology improvement, aiming at higher efficiencies and making progress towards the comprehension of these devices operative mechanisms. The approach followed consisted in analyzing and modifying the different DSSC components: the sensitized photoanode, the counter electrode and the electronic mediator, contributing all together to the overall device performance.
After describing the DSSC functioning principles in chapter 1 and the employed characterization techniques in chapter 2, in chapter 3 the efforts put in the photoanodic component improvement are presented. A passivation method was tested, consisting in a treatment of the titanium dioxide semiconductor surface with commercially available silanes. The investigation outcome, based on electrochemical and photoelectrochemical analyses, was a significant abatement of the recombination process involving the photoinjected electrons in TiO2 and the electronic mediator oxidized form, event that constitutes the main limit in DSSC containing common ruthenium sensitizers and cobalt redox couples. Subsequently a new category of β–monosobstituted porphyrin dyes was photoelectrochemically and photophysically characterized. Making a comparison with analogous porphyrinic structures in the well-known meso-substituted form, the β–substituted resulted in slightly higher performances, with the advantage of a simpler synthetic route.
In chapter 4, attention was focused on another fundamental DSSC component, that is the electronic mediator. First, a quenching study was conducted in solution, by means of spectroscopic techniques, combining differently charged ruthenium sensitizers and cobalt mediators, aiming at a better understanding of the role electrostatic interactions could have in the charge transfer mechanisms involved in the oxidized sensitizer regeneration by cobalt mediators in DSSC. In particular, interesting results were obtained with a negatively charged cobalt complex, in association with a hexacationic ruthenium complex. This redox mediator was further studied in operative devices, anchoring the sensitizer to the TiO2 surface, through photoelectrochemical methods, leading to results that are consistent with the importance of electrostatic interactions between molecules involved in electron transfer processes responsible for DSSC functioning.
The efforts put into the DSSC cathodic counterpart improvement are reported in chapter 5. A way to enhance the conductive polymer PEDOT adhesion to the fluorine doped tin oxide (FTO) covered electrode surface was explored. EDOT, the starting monomer for this well-known cathodic material, that can be electropolymerized directly on the conductive glass base, was synthetically modified with siloxane terminal groups. This, together with the silanization of the surface itself, led to decreased charge transfer resistance at the polymer/conductive glass interface, hence to improved cell efficiencies. Finally, an interesting category of carbon nanomaterials, called single-walled nanohorns, was investigated as cathodic substrate for DSSC employing cobalt based redox mediators. The good efficiency and stability characteristics observed make this material suitable as a viable alternative to the already consolidated counter electrodes materials like platinum and PEDOT.Nell’ambito della crescente richiesta di sorgenti di energia rinnovabile, lo sfruttamento dell’energia solare si è posto al centro della corsa globale verso un futuro sostenibile. Le celle solari sensibilizzate a colorante (Dye-Sensitized Solar Cells) hanno mostrato elevato potenziale per un approccio alla conversione elettrica dell’energia solare relativamente economico e facilmente realizzabile su ampia scala. La trasparenza, il design versatile e l’ampia gamma di colori disponibili per questi dispositivi offrono possibilità uniche nell’ambito dell’integrazione architettonica.
Scopo di questa tesi è di contribuire allo sviluppo della tecnologia DSSC, puntando a migliorare le efficienze ottenibili e la comprensione dei meccanismi operativi di cella. L’approccio seguito è consistito nell’analizzare e modificare i diversi componenti delle DSSC: il fotoanodo sensibilizzato, il controelettrodo e il mediatore elettronico, i quali contribuiscono tutti insieme al globale funzionamento della cella.
In seguito alla descrizione dei principi di funzionamento delle DSSC nel capitolo 1 e delle tecniche di caratterizzazione usate nel capitolo 2, nel capitolo 3 sono presentati gli sforzi tesi al miglioramento della componente fotoanodica. È stato considerato il trattamento della superficie fotoanodica con silani disponibili in commercio, come metodo di passivazione nei confronti del fenomeno di ricombinazione che coinvolge gli elettroni fotoiniettati nel biossido di titanio e la forma ossidata del mediatore. Analisi di tipo elettrochimico e fotoelettrochimico ne hanno rivelato un significativo abbattimento, in presenza del trattamento a base di silani. Successivamente, una nuova categoria di sensibilizzatori costituiti da porfirine β–monosostituite, è stata caratterizzata dal punto di vista fotoelettrochimico e fotofisico. Facendo un confronto con strutture porfiriniche analoghe, nella più nota forma meso-sostituita, quella β-sostituita ha prodotto prestazioni leggermente maggiori, con il vantaggio di un procedimento sintetico più semplice.
Nel capitolo 4 si è focalizzata l’attenzione su un’altra componente fondamentale delle DSSC, quale il mediatore elettronico. Uno studio di spegnimento degli stati eccitati è stato condotto in soluzione, combinando sensibilizzatori di rutenio e mediatori di cobalto differentemente carichi, con l’obiettivo di razionalizzare l’importanza delle interazioni elettrostatiche tra le specie coinvolte nei processi di trasferimento elettronico responsabili del funzionamento delle DSSC. Risultati degni di nota si sono ottenuti impiegando come mediatore un complesso di cobalto carico negativamente, in associazione con un sensibilizzatore di rutenio esacationico, sistema che è stato ulteriormente studiato in cella tramite metodi fotoelettrochimici, ancorando il sensibilizzatore al TiO2.
Gli sforzi impiegati nello sviluppo della parte catodica delle DSSC sono riportati nel capitolo 5. Inizialmente, è stato messo a punto un metodo per aumentare l’adesione del polimero conduttore PEDOT alla base elettrodica di vetro conduttore, che consiste nel modificare sinteticamente il monomero di partenza, EDOT, con gruppi terminali silossanici, permettendo così la produzione per via elettrochimica di un film di PEDOT stabilmente accoppiato alla superficie del catodo, che mostra migliore stabilità meccanica e ridotta resistenza al trasferimento di carica all’interfaccia polimero/vetro conduttore, fornendo dunque maggiori efficienze in cella. Infine, una categoria di nanomateriali a base di carbonio, chiamati single-walled nanohorns, è stata investigata come substrato catodico per DSSC impieganti mediatori elettronici a base di cobalto, mostrando buone caratteristiche di efficienza e stabilità che li rendono una valida alternativa a materiali catodici il cui impiego è già consolidato, quali platino e PEDOT
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
Coda
No full textThe text closes the publication, highlighting the fruitful disciplinary exchanges between film and music studies when it comes to explore the remediation of opera. It proposes a brief literature review and it identifies the areas of inquiry that the publication has tried to frame as well as those that are still to be developed
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
A viable surface passivation approach to improve efficiency in cobalt based dye sensitized solar cells
No full textA successful general strategy for improving the electron collection efficiency in Dye Sensitized Solar Cells
based on common Ru(II) complexes like Z907 and kinetically fast redox mediators based on the
[Co(bpy)3]3+/2+ couples was investigated.
The post-treatment of the dyed photoanode with commercially available tri-alkoxy silanes was effective
in screening the TiO2 surface by electron recapture involving Co(III), but, interestingly, silanes
endowed with relatively short propyl chains like aminopropyl-triethoxysilane (APTS) and trimethylammoniumpropyl-
trimethoxysilane (TMAS) bearing a cationic charge, proved to be more effective than
longer and more sterically hindered C16 chains in suppressing the dark current. In the best cases (TMAS
and APTS), the siloxane treatment resulted in overall improvements of the cell efficiency of the order of
respectively 600% and 500% by comparison with the untreated photoanode based on the Z907 Ru(II) Dye.
This approach may represent a viable procedure for improving the electron collection efficiency in cobalt
mediated DSSCs even without the use of highly sterically hindered dyes specifically designed to work in
conjunction with kinetically fast metal based mediators
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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