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Cathode materials for solid oxide electrolysis cells
No full textThe cathode in solid oxide electrolysis cells is the electrode at which water and carbon dioxide can be split into hydrogen, carbon monoxide, and oxygen ions. The state-of-the-art material is a Ni cermet, as developed for solid oxide fuel cells. This electrode shows promising electrolysis rates and compatibility with adjacent cell components, and a basic understanding of its electrode processes has also been gained. However, stability issues have recently triggered a search for alternative materials. Electronically conducting oxides, with or without activation by submicron-scale electrocatalysts, are of interest because of their stability in high water contents, as described in the last part of this chapter
Cathode materials for protonic ceramic fuel cells: Bulk defect chemistry and surface reaction kinetics
Get PDFFuel cells based on ceramic proton conductors receive growing interest because these electrolytes offer a higher ionic conductivity compared to oxide ion conductors, in particular at 300-600 °C. To extend the oxygen reduction reaction to water beyond the three-phase boundary, cathode materials for such cells should have a certain proton conductivity. Since the perovskites considered as cathode material exhibit perceptible oxygen vacancy, proton and hole concentrations, proton uptake can occur by water incorporation (acid-base reaction) and by hydrogen incorporation (redox reaction) [1]. The presence of three mobile carriers can lead to a complex two-fold stoichiometry relaxation kinetics, requiring four diffusion coefficients for complete description [1,2].
The different regimes of proton uptake are explored by thermogravimetry (pH2O changes in different pO2) for perovskites such as La0.5Sr0.5FeO3- and Ba0.5Sr0.2Fe0.8Zn0.2O3- (BSFZ). The obtained maximum proton concentrations are significantly lower than in BaZrO3 electrolyte materials at same T and pH2O [3]. The proton mobility in BSFZ extracted from the transient behavior is comparable to that in BaZrO3 electrolytes. Correlations between cation composition and amount of incorporated protons are discussed.
The kinetics of oxygen reduction to water is measured by impedance spectroscopy at dense thin-film BSFZ microelectrodes on proton-conducting Ba(Zr,Y)O3 as substrate. The dependence of surface reaction resistance on electrode area demonstrates that the proton conductivity of BSFZ in the range of » 10-3 S/cm at 400 °C [4] indeed suffices to transport protons from the Ba(Zr,Y)O3- electrolyte through the dense BSFZ film to the gas interface. The reduction of O2 to water can in principle proceed without oxygen incorporation into the cathode material. The values of the pO2 and pH2O dependence of the effective rate constant indicate that molecular oxygen species participate in the rate determining step, and that protonated oxygen species appear only after this step [5].
[1] D. Poetzsch, R. Merkle, J. Maier, Adv. Funct. Mater. 25 (2015) 1542
[2] R. Merkle, R. Zohourian, J. MAier, Solid State Ionics (2016) doi:10.1016/j.ssi.2015.12.011
[3] D. Poetzsch, R. Merkle, J. Maier, Farad. Disc. 182 (2015) 129
[4] R. Merkle, D. Poetzsch, J. Maier,ECS Transact, 66(2) (2015) 95
[5] D. Poetzsch, R. Merkle, J. Maier, J. Electrochem. Soc. 162 (2015) F93
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
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