1,721,016 research outputs found
Metal oxide nanofiber-based electrodes in solid oxide fuel cells
No full textMetal oxide nanofiber (MONF)-based electrodes are currently at the cutting edge of research for application in solid oxide fuel cells (SOFCs), especially in intermediate temperature–solid oxide fuel cells (IT-SOFCs). Mixed ionic-electronic conductors (MIECs) have been widely investigated as cathode materials for IT-SOFCs. Compared to pure electronic conductors, MIECs present good coking resistance, redox stability, and high catalytic activity at intermediate operating temperature. In addition, the manufacturing technique is also being refined. One-dimensional materials—such as nanotubes, nanowires, nanorods, and NFs—have gained significance due to their high surface area and mechanical properties. Electrospinning is the method of choice for NF preparation since, compared to other available methods, it is cost effective, simple, and reproducible. An overview of innovative NF-based electrodes for application in IT-SOFCs, is reported here. Electrochemical results are critically examined and discussed, with reference to the electrode architecture
Electrochemical study of symmetrical intermediate temperature - solid oxide fuel cells based on La0.6Sr0.4MnO3 / Ce0.9Gd0.1O1.95 for operation in direct methane / air
No full textLa0.6Sr0.4MnO3 (LSM), which is considered a state-of-the-art solid oxide fuel cell (SOFC) cathode, is investigated for application as an anode in direct methane intermediate temperature - solid oxide fuel cells (IT-SOFCs). Ce0.9Gd0.1O1.95 (CGO) is used as the electrolyte. The characterized electrode is a composite LSM/CGO, prepared in two different configurations: LSM crushed electrospun nanofibers / GDC powders, and LSM powders / GDC powders. The electrodes are tested in both air and direct methane conditions. At 815 °C, the polarization resistance Rp = 1.6 Ωcm2 in air, and Rp = 0.15 Ωcm2 in methane. Since perovskite-type manganites may show poor stability in reducing atmosphere, electrode stability is investigated. It is found that LSM shows a reversible modification of the crystal structure, assuming a Ruddlesden-Popper (RP) structure when exposed to methane. The RP structure is expected to be more stable compared to the LSM single perovskite. Furthermore, the composite electrode is expected to benefit from the presence of CGO, which is stable in reducing conditions
Impact of the Oxygen Vacancies of the LSCF (La0.6Sr0.4Co0.2Fe0.8O3–δ) Perovskite on the Activation Energy of the Oxygen Reduction/Evolution Reaction
No full textLa0.6Sr0.4Co0.2Fe0.8O3–δ (LSCF) perovskites, in the form of in–house electrospun nanofibers and commercial powders, have been tested through synchrotron x–ray diffraction and electrochemical impedance spectroscopy in the 800–1200 K range. The former analyses make it possible to evaluate the oxygen vacancies (OV) concentration, and the latter allows to assess the electrokinetics of the oxygen reduction/evolution reaction. Equivalent circuit modeling is carried out to identify the basic electrochemical processes and evaluate the associated polarization resistance Rp. One high-frequency process and two intermediate-frequency processes are recognized. For all electrochemical processes, OV concentration and Rp behave similarly with temperature in both nanofiber and granular electrodes. This led to the proposal of a new equation. For each electrochemical process, it was shown that the activation energy is the sum of an intrinsic electrochemical activation energy, plus the formation energy of OVs. For the LSCF perovskites tested in this work, the intrinsic electrochemical activation energy was found to be independent of the preparation procedure and crystal structure. In contrast, the OV formation energy was found to be strongly dependent on the preparation procedure and crystal structure, with values ranging between 0.5 and 24.1 kJ mol−1. A complete set of data is provided, which can be useful for future simulation studies
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
Synthesis and electrochemical characterization of La<sub>0.6</sub>Sr<sub>0.4</sub>Co<sub>0.2</sub>Fe<sub>0.8</sub>O<sub>3–δ</sub> / Ce<sub>0.9</sub>Gd<sub>0.1</sub>O<sub>1.95</sub> co-electrospun nanofiber cathodes for intermediate-temperature solid oxide fuel cells
No full textSynthesis and electrochemical characterization of composite cathodes, formed from a mixture of La0.6Sr0.4Co0.2Fe0.8O3–δ (LSCF) and Ce0.9Gd0.1O1.95 (GDC) nanofibers, is reported. The electrodes are obtained by simultaneous electrospinning of the two precursor solutions, using apparatus equipped with two spinnerets working in parallel. Results of electrochemical testing carried out through electrochemical impedance spectroscopy (EIS) are presented and discussed. The results suggest that the electrochemical reaction takes place in an electrode region close to the electrode/current collector interface and that the oxygen ions then flow along the ionic conducting path of the GDC fibers. At 650 °C, the polarization resistance is Rp = 5.6 Ω cm−2, in line with literature values reported for other IT-SOFC cathodes.</p
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
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