1,720,985 research outputs found
Inductance correction in impedance study of solid oxide fuel cells
No full textA procedure for evaluation and elimination of errors, caused by parasitic inductance and resistance in EIS studies of two solid oxide fuel cells (SOFC) materials: yttria stabilized zirconia (YSZ) electrolyte and lanthanum strontium manganite (LSM)/YSZ composite cathode is presented in this paper. It is shown that for these low impedance systems the parasitic inductance can affect not only the high frequencies but also the middle and low ones. The parasitic errors correction procedure increases significantly the reliability of the electrochemical impedance spectroscopy (EIS) results
Overview of current trends in SOFC materials
No full textBecause of their potential to reduce the environmental impact and geopolitical consequences of the use of fossil fuels, fuel cells have emerged as sustainable power generation systems. Like a combustion engine, a fuel cell uses a chemical fuel as its energy source; but like a battery, the chemical energy is directly converted into electrical energy. In addition to high efficiency and low emissions, fuel cells are attractive for their modular and distributed nature, and zero noise pollution. SOFC single cells and stack systems are multilayer structures consisting of ceramic and metallic materials with different well defined electrical transport properties. All components have to show well-adjusted thermal expansion behaviour, chemical compatibility of material interfaces and chemical stability in the prevailing temperature and gas atmosphere. Performance and long-term stability improvements at affordable costs can be obtained by lowering the operating temperature. This goal requires drastic reduction of electrodes polarisation resistance as well as highly-conducting electrolyte materials. The use of new and nanostructured material and the application of appropriate technologies for the production of optimized microstructure becomes essential for highly efficient SOFCs operating in the medium and low temperature range. A review of state-of-art materials is given together with a perspective presentation of innovative materials and technologies for new types of SOFC
Study of the rate limiting step of the cathodic process in anode supported solid oxide fuel cell
No full textThe oxygen reduction (OR) mechanism at the Sr-doped LaMnO3 (LSM) and yttria stabilized zirconia (YSZ) composite cathode for high temperature solid oxide fuel cells is still uncertain, despite of the great deal of work carried out over the last years about this system. In previous works, we tested a half-cell (with a YSZ electrolyte pellet) in a typical three-electrode configuration: It was observed that the portion of the composite cathode volume involved in the reaction depends on the operating temperature. Moreover we analyzed part of the impedance data by the differential impedance analysis, which does not need a preliminary working hypothesis. The results suggested that significant limitations in the oxygen ion transport occur in the LSM pure material, which are not observed in the composite YSZ/LSM cathode. In this study, we investigate the behavior of the LSM/YSZ system in a Ni/YSZ cermet anode-supported hW-cell with yttria stabilized zirconia a (8YSZ) electrolyte and a screen printed LSM/YSZ composite cathode. The aim is to individuate and characterize the cathodic contribution from the overall impedance response, varying the partial pressure of the reactant gases, to obtain additional information about the OR mechanism from the p(O2) dependence. By a possible interpretation of the oxygen reaction mechanism, a comparative study of the cathode behavior with previous results is performed. Copyright © 2008 by ASME
Redox - Cycling - a tool for artificial electrochemical aging of solid oxide cells
No full textIn this work a procedure for accelerated stress tests of Solid Oxide Cell (SOC) by artificial aging of the anode via redox cycling is presented. This approach eliminates the interrelation of different degradation processes and ensures a clear picture of the anode degradation on the total cell performance. The level of oxidation is monitored in situ on bare anode samples by impedance measurements of the Ni network resistance changes during oxidation/reduction cycling which ensures governing of the oxidation level with high reproducibility by selection of appropriate experimental conditions. Once fixed on bare anode samples, the selected redox cycling regime is further applied in full cell configuration. The developed methodology is evaluated by comparative analysis of current-voltage and impedance measurements of artificially aged and calendar aged button cells. The results for 8 redox cycles are comparable to those obtained for more than 600 hours operation in standard conditions
Electrochemical testing of an innovative dual membrane fuel cell design in reversible mode
No full textSolid oxide fuel Cells (SOFC) are intrinsically reversible which makes them attractive for the development of reversible devices (rSOC). The main hurdles that have to be overcome are the higher degradation in electrolyzer (EL) mode and the slow and difficult switching form mode to mode. This work aims at the development and experimental validation of a concept for rSOC based on a new dual membrane fuel cell (dmFC) design which can overcome the existing problems of the classical SOFC. The kernel of the system is additional chamber - central membrane (CM) for water formation/evacuation in FC mode and injection in El mode. Its optimization in respect of microstructure and geometry in laboratory conditions is carried out on button cells. The electrochemical performance is evaluated based on volt-ampere characteristics (VACs) combined with impedance measurements in different working points. The influence of a catalyst in the water chamber is also examined. The VACs which give integral picture of the cell performance are in excellent agreement with the impedance studies which ensure deeper and quantitative information about the processes, including information about the rate limiting step. The results from the optimization of the water chamber show that the combination of design and material brings to important principle advantages in respect to the classical rSOC – better performance in electrolyzer mode combined with instantaneous switching
Fuel cell e.g. mixed conduction membrane fuel cell, for producing electric energy for stationary applications, has channel whose cross section has minimum size larger than specific value so as to discharge from diaphragm to outside of cell
No full textNOVELTY - The cell (1) has a porous central diaphragm (30) whose surfaces (32, 35) are in contact with an electrolyte (20) and a cathode (50). The electrolyte has material conducting M ions and the diaphragm has material conducting both M and N ions. Rectilinear channels (52) pass through the cathode and connected to the diaphragm and a free surface of the cathode. Minimum size of a cross-section of one of the channels is larger than 20 micrometers so as to enable a product i.e. water, from reaction of the ions to be discharged from the diaphragm to outside the cell through the channels.
USE - Fuel cell e.g. mixed conduction membrane fuel cell, for producing electric energy for stationary applications. Can also be used for long term onboard applications e.g. car.
ADVANTAGE - The minimum size of the cross-section of one of the channels is larger than 20 micrometers so as to enable the product resulting from reaction of the ions to be discharged from the diaphragm to outside the cell through the channels in an efficient manner, thus increasing power density of the fuel cell. The electrolyte and the central membrane are manufactured by using single operation e.g. sintering, so as to simplify manufacturing of the fuel cell and improve mechanical resistance and durability of the assembly
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
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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