1,721,021 research outputs found
EXAFS studies of carbon supported fuel cells electrocatalysts
No full textCarbon supported Pt, PtRu and PtMo fuel cells catalysts were investigated by means of advanced synchrotron X-ray adsorption spectroscopies (XAS), in particular extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) EXAFS results at both the Pt LIII and Ru K edges for the PtRu/C electrocatalysts have highlighted the interference of the backscattering from secondary metal element, Ru, with that from Pt when the neighbours were at similar distances. The resulting phase cancellation in the EXAFS at about k ~ 10o A-1 gave rise to a splitting of the main peak of the Fourier transform. The extent of intermixing in the alloy could then be related to the extent to which this peak was split. Shortened first shell Pt-Pt coordination distances and decreased first shell coordination numbers provided evidence of the smaller size of carbon supported small platinum particles when modified with Ru or Mo. While the complementary Ru K edge investigation reflected the metallic nature of the Ru at a reducing potential. XAS results at the Mo K edge indicated the presence of Mo oxyhydroxide species at the surface of the particle related to the presence of the redox couple Mo(IV)/MO(VI), as indicated by changes in the XANES feature as function of potential. The performance of proton exchange membrane fuel cells with PtRu and PtMo catalysts on reformate mixes containing up to 100 ppm CO was enhanced over that of Pt. The enhancement of the catalytic activity for the CO electro-oxidation reaction by PtRu/C electroanalysis is thought to arise from an intrinsic mechanism rather than the presence of oxide on the Ru surface. Whereas the Mo oxyhydroxide species are thought to play a significant role of oxidise CO adsorbed species at lower potentials than Pt. Finally, in situ EXAFS investigation of fuel cell electrocatalysts was shown to be sensitive to the surface composition of the metal particles (CO and O) and therefore, may be used to investigate the chemistry of the fuel cell reactions.</p
EXAFS of carbon monoxide oxidation on supported Pt fuel cell electrocatalysts
No full textThe potential dependence of the extended X-ray absorption fine structure (EXAFS) obtained at the Pt LIII absorption edge for a carbon supported Pt electrocatalyst exposed to carbon monoxide is presented. The data have been analyzed using the difference file method to separate the dominant contributions of the Pt neighbors from contributions to the EXAFS from the adsorbed species. The presence of adsorbed CO is clearly observed with a Pt-C distance of 1.85 Å at potentials less than 0.5 V vs RHE. Increasing the potential above 0.5 V resulted first in the removal of the adsorbed CO and at more positive potentials, e.g., 1.05 V, in the formation of an oxide layer, as evidenced by the presence of a Pt-O coordination shell at 2.00 Å. These results demonstrate that in situ EXAFS of supported Pt electrocatalysts may be used to probe adsorbate structures
Unravelling the complexities of CO2 tolerance at PtRu/C and PtMo/C
No full textThe CO2 tolerance exhibited by PtRu/C is known to be greater than that of PtMo/C catalysts in contrast to the trend in CO tolerance. In this manuscript the origins of these differences are investigated in a cyclic voltammetric investigation of the potential dependence of the poisoning of Pt/C, PtRu/C and PtMo/C anode catalyst electrodes in a miniature PEM fuel cell when exposed to pure CO, pure CO2, or 25% CO2 in H2. The results show that the difference in the mechanisms of improved CO tolerance, compared to a Pt/C reference catalyst, of PtRu and PtMo explain the decreased CO2 tolerance of PtMo compared to PtRu; at PtRu the mechanism is intrinsic (water activation at Ru sites), whilst at PtMo the mechanism relies on the turn-over the Mo(IV/VI) redox couple
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
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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