1,721,001 research outputs found
Guidelines and numerical analysis for the rational design of 3D manufactured solid oxide fuel cell electrodes
No full textThe recent growth of 3D printing has opened the scope for designing microstructures for solid oxide fuel cell (SOFC) electrodes with improved power density and lifetime. This technique can introduce structural modifications of the electrode/electrolyte interface at a scale which is larger than the particle size but smaller than the cell size, such as the insertion of dense electrolyte pillars in the order of 5-100 um.
This study presents some guidelines and sets the minimum requirements for the rational design of 3D printed electrodes based on an electrochemical numerical model and approximated analytical solutions for functional layers with negligible electronic resistance. Results show that this structural modification enhances the power density only when the effective ionic conductivity factor keff of the composite electrode is smaller than 0.5. The maximum performance improvement can be straightforwardly predicted analytically as a function of keff only. A design study on a wide range of pillar shapes indicates that improvements in electrochemical performance are achieved by any chosen structural modification capable to provide ionic conduction farther from the electrolyte up to a characteristic thickness (typically ~10-40 um) without removing electrochemically active volume at the electrolyte interface. The best performance improvements are reached in the limit of thin ( ~80 um) pillars when the composite electrode domain is optimised for maximum three-phase boundary (TPB) density, pointing towards the design of scaffold electrodes with well-defined geometry and fractal structures
Validation of a physically-based solid oxide fuel cell anode model combining 3D tomography and impedance spectroscopy
No full textThis study presents a physically-based model for the simulation of impedance spectra in solid oxide fuel cell (SOFC) composite anodes. The model takes into account the charge transport and the charge-transfer reaction at the three-phase boundary distributed along the anode thickness, as well as the phenomena at the electrode/electrolyte interface and the multicomponent gas diffusion in the test rig. The model is calibrated with experimental impedance spectra of cermet anodes made of nickel and scandia-stabilized zirconia and satisfactorily validated in electrodes with different microstructural properties, quantified through focused ion beam SEM tomography. Besides providing the material-specific kinetic parameters of the electrochemical hydrogen oxidation, this study shows that the correlation between electrode microstructure and electrochemical performance can be successfully addressed by combining physically-based modelling, impedance spectroscopy and 3D tomography. This approach overcomes the limits of phenomenological equivalent circuits and is suitable for the interpretation of experimental data and for the optimisation of the electrode microstructure
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
Simulation of the electrochemical impedance response of SOFC anodes: from the microstructural reconstruction to the physically-based modelling
No full textIn this contribution, a combination of experimental and modelling techniques are integrated and applied to link the electrode microstructure to the performance and degradation of SOFC anodes. Symmetric anodes made of scandia-stabilized zirconia and nickel were fabricated with 30, 40 and 50% vol. of Ni. The impedance response of the samples was measured at 600-800°C in 50-100% wet H2. The microstructure of the electrodes was reconstructed from FIB-SEM tomography for the evaluation of the effective properties. This information was fed to a physically-based model that takes into account the main transport and reaction phenomena occurring within the electrode. Impedance spectra were simulated and fitted with a reduced number of material-specific electrochemical parameters, which showed a clear dependence on temperature and did not vary in different samples (Fig. 1). The same approach was used to decouple the microstructural contribution to performance of infiltrated electrodes [1].
The study reveals that the coupling among microstructural characteristics, impedance and degradation can be methodically addressed to gain a fundamental understanding and to provide design indications to improve the performance and the lifetime of electrodes
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
Electrochemical simulation of Solid Oxide Fuel Cell electrodes: an integrated approach to address the microstructure-performance correlation
Full text linkUnderstanding the complex interplay between electrode microstructure and electrochemical performance is one of the key aspects for the optimization of Solid Oxide Fuel Cells (SOFC). Physically-based modelling, at different levels of sophistication, can provide a valuable insight in order to help the interpretation of experimental data and provide design indications to improve electrode stability and performance. In this contribution we summarize the different modelling approaches used in our group, ranging from physically-based equivalent circuits, continuum conservation models and 3D models solved within the reconstructed electrode microstructure. When necessary, these models are coupled with percolation theory, packing algorithms and tomographic techniques. Special focus is given to the application of the models to interpret impedance spectra and their thorough validation under different conditions. Examples include the application of the models to electrodes with different microstructures, the study of the degradation mechanisms of Ni-infiltrated anodes as well as impedance simulations in real microstructures (Figure 1). Results reveal that coupling physically-based modelling, impedance spectroscopy and 3D tomography is a promising approach to gain a fundamental understanding of the phenomena occurring at different length scales in SOFC electrodes, allowing for interpreting and planning experiments as well as to design more stable and more efficient electrodes
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
Model-based design and 3D characterization of a SOFC electrode microstructure
No full textThe characterization of SOFC performance and reliability has conventionally relied on bulk parameter measurements, such as fuel cell impedance and other electrochemical parameters. These bulk parameters, however, have increasingly been correlated with the porous microstructure of the electrodes but have yet to be fully linked to the degradation of the micro- and nanostructure of the electrodes during use.
In this work, a design led approach to electrode manufacture is implemented. A Ni-ScSZ scaffold was first produced using tape casting and characterised using FIB-SEM tomography in order to quantify the TPB density as well as the tortuosity of the phases. This initial microstructure was also used as an input in a physically-based electrochemical model to predict impedance. The electrode was then incorporated into a symmetrical cell and tested at 610°C to compare its performance to the one predicted by the physical model as well as to examine the degradation of the anode with time. The comparison allowed for a critical assessment of the assumptions of the electrochemical model and for the prediction of better performance with different phase fractions. This approach allows for a seminal pass at manufacturing electrodes with desired specific performance requirements using a predictive model
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
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