1,721,059 research outputs found
MASS TRANSPORT ISSUES IN LOW PLATINUM LOADING CATALYST LAYERS FOR POLYMER FUEL CELLS
No full textState of art cathode catalyst layers for polymer electrolyte fuel cells require the use of Platinum based catalysts to promote the sluggish oxygen reduction reaction, with a Platinum loading of approximately 0.2 mg cm-2. The main goal of research in long term deals with the necessity to reduce the Platinum loading that still impacts the cost of the system. Even though this topic has been researched intensively, low Platinum catalyst layers present mass transport limitations that strongly affect performance. In the present work mass transport overpotential in low Platinum polymer fuel cells is investigated with the aid of a quasi 2D single cell continuum based model
The influence of the carbon support and platinum particle size on degradation of cathode for low platinum-loading catalyst layer
No full textWe demonstrated the ability to control the platinum particle size in the synthesis of carbon supported Pt (Pt/C) electrocatalyst with reactive spray deposition technology (RSDT). The degradation of Pt cathode with loading of 0.1 mg/cm2 in membrane electrode assembly (MEA) under simulated drive cycles (30000 triangular wave cycles between 0.6 and 1.0 Vrhe) showed similar electrochemical surface area (ECSA) at the end of life (EOL), regardless of the initial Pt particle size or carbon support type. However, it is possible to reduce the loss of ECSA using a gradient catalyst layer consisting of a 6 um layer with Pt particles of 5 nm toward the membrane and another 6 μm layer with Pt particles of 2 nm toward the GDL. Microscopy studies suggested that the gradient catalyst layer have less Pt loss% into the electrolyte, thereby maintained higher ECSA at EOL
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
Investigation of the hydrodynamic response of cells in drop on demand piezoelectric inkjet nozzles
No full textModelling analysis of low platinum polymer fuel cell degradation under voltage cycling: Gradient catalyst layers with improved durability
No full textImproving the durability of polymer electrolyte membrane fuel cells with low platinum loading is a crucial step in the development of next generation electric vehicles. In this work a simplified model of nanoparticle growth is spatially solved across the catalyst layer and combined with a PEMFC model to analyze the heterogeneity of degradation that is induced by accelerated stress test for electrocatalyst durability, which mimics the degradation due to load cycling. The model is calibrated and later validated by analyzing experimental data collected on cathode catalyst layers with 0.1 mg cm(-2) platinum loading and average particle size ranging from 2 nm to 5 nm. Non-uniform degradation is observed in the catalyst layer consequently to the formation of a platinum depleted region next to the membrane, which, according to the model, results from diffusion and precipitation of dissolved platinum into the membrane. Performance of catalyst layers with gradient structure is simulated to get insight into the degradation of non-uniform catalyst layers and results are compared to experimental data. It is concluded that gradient catalyst layers mitigate performance degradation because evolve towards more uniform distribution of active surface and improve transport loss due to low-roughness factor and Ohm loss in the catalyst layer
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
Ultra-low Pt loading catalyst layers for PEMFC using reactive spray deposition technology
No full textReactive spray deposition technology (RSDT) is a cost-effective method for producing high performance proton exchange membrane fuel cell (PEMFC) membrane electrode assemblies (MEAs). In this study, we used the RSDT process to deposit catalyst-coated membrane (CCM) with Pt supported on Ketjen Black (KB), multi-wall carbon nanotube (MWCNT) and reducedgraphene oxide (rGO) with ultra-low Pt loading in order to elucidate the influence of the support and Pt dispersion on the catalyst perfromance. The electrochemically active surface area (ECSA), activity for oxygen reduction reaction (ORR) and PEMFC performance are investigated and compared. © The Electrochemical Society
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
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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