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Catalysis for sustainable energy conversion and storage
No full textClimate change, pollution, unprecedented population growth, geopolitical tensions and rapid technological development are intrinsically connected to the nature, level and availability of global energy, which shapes present and future aspects of human society. Particularly, in a society where global energetic demand is continuously rising and the awareness of the negative impact of fossil fuels on the environment is becoming widespread, the exploitation of renewable sources for the generation of sustainable energy is highly needed. In this regard one key requirement for an effective deployment and expansion of renewable energy in the global energy market is represented by its ability to conveniently convert and store the energy derived from intermittent sources, in order to guarantee a constant supply to the electric grid. The technologies for the energy conversion and storage present various degrees of maturity, each one having specific advantages and disadvantages depending on the type of application and energetic source.This thesis aims to give a tiny contribution to the complex problem of energy conversion and storage, through the design, characterisation and testing of electrocatalytic materials for water electrolysis, photoelectrochemical water splitting and direct methanol fuel cell. It is expected that the first two processes will play an important role in the future as convenient technologies for the conversion of solar and wind power into chemical energy in the form of hydrogen. The third process is regarded as promising way to convert the renewable chemical energy in the form of methanol into electrical energy.At the core of the research lies the design and development of electrocatalysts, which are directly responsible for lowering the reaction overpotentials and ultimately increasing the overall efficiency of the processes. As such, in this thesis three materials were synthesised using straightforward methodologies and evaluated as electrocatalysts for the alkaline hydrogen evolution, the photoelectrochemical oxygen evolution and the alkaline methanol oxidation. Their performances were directly linked to the morphological and structural properties which in turn significantly affected the nature of active sites. For the first work reported in Chapter 3, a material based on a mixed cobalt nickel sulphide nanoparticles supported onto Ni foam showed high activity toward the hydrogen evolution reaction, with a required small overpotentials of 163 mV at a current density of 10 mA/cm2 in 1.0 M KOH electrolyte. This value compares well with the best existing hydrogen evolution reaction electrocatalysts based on non-noble elements. Moreover the catalyst showed good durability which was tested under chronoamperometric conditions, maintaining an optimal performance for 72 hours. The origin of such high activity was attributed to the existence of an optimal nickel-cobalt sulphide ratio at the surface of the electrode, which was obtained by selecting the appropriate temperature and time of thermal annealing of the material. This optimal presence of the biphasic nickel-cobalt sulphide nanoparticles led to high electrochemically active surface area and small charge transfer resistance, as evidenced by the extensive characterisation analysis carried out on these materials. For the second work reported in Chapter 4, a WO3/Co3O4 photoanode was successfully synthesised via a facile sol-gel method and tested for the photoelectrochemical oxygen evolution. It was found that the degree of crystallinity of the cocatalyst influenced heavily the photoelectrochemical activity towards the oxygen evolution. In particular, a poorly crystalline structure of Co3O4 led to an improvement of up to 40% in photocurrent generation compared to the bare WO3. Interestingly, the highly crystalline Co3O4 significantly suppressed the photocurrent generation, as a result of the creation of an unfavourable band alignment, with a dramatic increase in the charge recombination at the interface. Finally, for the third and last work reported in Chapter 5, ultra-small Pt nanoparticles embedded on a 3D structure composed of CeO2, NiO and Ni foam was synthesised and tested as electrocatalyst for the alkaline methanol oxidation reaction. The generated catalyst showed extremely high activity for the alkaline methanol oxidation, with mass and geometric current density values of 1160 mA/mgPt and 202 mA/cm2, whose values are among the highest ever reported for Pt-based materials. It was demonstrated that the unique morphological architecture and existence of a synergistic effect between Pt and adjacent CeO2 nanoparticles contributed decisively to the observed high performance. Particularly the presence of defective and poorly crystalline CeO2 nanoparticles was beneficial to the efficient oxidative removal of the CO from the Pt active sites which resulted in a higher durability of the electrocatalyst. Moreover, the concomitant presence of the superficial Ni(OH)2 was thought to contribute to the supply of OH species to the Pt, which act as reactants for the CO removal. The most active electrocatalyst was subjected to stability test, retaining 40 % of the initial geometric current density after 6 hours, and quite surprisingly the activity could be totally restored through straightforward CV scans in 1.0 M NaOH electrolyte
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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 highly active hydrogen evolution electrocatalyst based on a cobalt–nickel sulfide composite electrode
Get PDFA novel Co9S8–NixSy/Ni foam composite material was synthesized through the thermal decomposition of a cobalt–thiourea molecular precursor onto a 3D metallic support. The obtained electrode exhibited good activity toward the hydrogen evolution reaction in an alkaline medium, requiring a small overpotential of 163 mV at a current density of 10 mA cm?2, which is one of the lowest ever reported among transition metal sulfide materials
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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