1,720,963 research outputs found
Ex-situ NMR and Raman studies of H3PO4 and H2O uptake of polybenzimidazole membrane for PEMFC
No full text: Polybenzimidazole (PBI) doped with H3PO4 is the most commonly used membrane mate-rial for high-temperature polymer fuel cells. Despite this fact, only less is known on the chemical equilibria of all species inside the membrane as a function of the com¬position of the ternary system PBI - H3PO4 - H2O. This in¬clu¬des details on the proton transfer pro¬ces-ses, on the dominant conduc¬tion me¬cha¬nisms and on the con¬densation equilibria, lea-ding to the formation of di¬phos¬pho¬ric acid and higher homo¬logues species.
In this study Raman and NMR spectroscopy is used to in¬vestigate the chemical inter¬ac-tions between H3PO4, H2O and PBI vs. the H3PO4 doping level. We could ob¬tain in¬forma-tion on the H-bond formation between H3PO4 and the polymer chains, on tauto¬me¬ric pro-ces¬ses as well as on the presence of not directly bounded H3PO4 at high do¬ping levels [1,2]. Investigations were performed with uncrosslinked and cross¬linked m-PBI and AB-PBI. [1] F. Conti, A. Majerus, V. Di Noto, C. Korte, W. Lehnert, and D. Stolten, Phys. Chem. Chem. Phys. 14, 10022-10026 (2012) [2] F. Conti, S. Willbold, S. Mammi, C. Korte, W. Lehnert, and D. Stolten, New J. Chem. 37, 152-156 (2013)
Spectroscopic investigations of the H3PO4 and H2O uptake of polybenzimidazole membranes for fuel cells
No full textPolybenzimidazole (PBI) doped with H3PO4 is the most commonly used membrane material for high-temperature polymer fuel cells. Proton conductivity is strongly dependent on acid doping and water content (humidity). Despite these facts, only little is known on the chemical equilibria of all species inside the membrane as a function of the composition of the ternary system PBI - H3PO4 - H2O. This includes details on the proton transfer processes, on the dominant conduction mechanisms and on the condensation equilibria, leading to the formation of diphosphoric acid and higher homologues species.
In this study, Raman and NMR spectroscopy is used to investigate the chemical inter¬actions between H3PO4, H2O and PBI vs. the H3PO4 doping level. We obtained information on the H-bond formation between H3PO4 and the polymer chains, on tautomeric processes as well as on the presence of not directly bound H3PO4 at high doping levels. Investigations were performed with uncrosslinked and crosslinked m-PBI and AB-PBI [1-4]. [1] F. Conti, A. Majerus, V. Di Noto, C. Korte, W. Lehnert, D Stolten, Phys. Chem. Chem. Phys. 14, 10022-10026 (2012) [2] F. Conti, S. Willbold, S. Mammi, C. Korte, W. Lehnert, D. Stolten, New J. Chem. 37, 152-156 (2013). [3] A. Majerus, F. Conti, C. Korte, W. Lehnert, D. Stolten, ECS Transaction, in press. [4] G. A. Giffin, F. Conti, S. Lavina, A. Majerus, G. Pace, C. Korte, W. Lehnert, V. Di Noto, Int. J. Hydrogen Energy, submitted
Spectroscopic Investigation of the Acid and Water Uptake of Polybenzimidazole Membranes for Fuel Cells
No full textPolybenzimidazole (PBI) doped with H3PO4 is the most commonly used membrane material for high-temperature polymer fuel cells. Proton conductivity is strongly dependent on acid doping and water content. Despite these facts, only little is known on the chemical equilibria of all species inside the membrane as a function of the composition of the ternary system PBI - H3PO4 - H2O. This includes details on the proton transfer processes, on the dominant conduction mechanisms and on the condensation equilibria, leading to the formation of diphosphoric acid and higher homologues species.
In this study, Raman and NMR spectroscopy is used to investigate the chemical interactions between H3PO4, H2O and PBI vs. the H3PO4 doping level. We have obtained information on the H-bond formation between H3PO4 and the polymer chains, on tautomeric processes as well as on the presence of not directly bound H3PO4 at high doping levels. Investigations were performed with uncrosslinked and crosslinked m-PBI and AB-PBI [1-4]. [1] F. Conti, A. Majerus, V. Di Noto, C. Korte, W. Lehnert, D Stolten, Raman study of the polybenzimidazole–phosphoric acid interactions in membranes for fuel cells, Phys. Chem. Chem. Phys. 14 (2012) 10022. [2] F. Conti, S. Willbold, S. Mammi, C. Korte, W. Lehnert, D. Stolten, Carbon NMR investigation of the polybenzimidazole–dimethylacetamide interactions in membranes for fuel cells, New J. Chem. 37 (2013) 152. [3] A. Majerus, F. Conti, C. Korte, W. Lehnert, D. Stolten, Thermogravimetric and Spectroscopic Investigation of the Interaction between Polybenzimidazole and Phosphoric Acid, ECS Transaction (2013) accepted. [4] G. A. Giffin, F. Conti, S. Lavina, A. Majerus, G. Pace, C. Korte, W. Lehnert, V. Di Noto, A vibrational spectroscopic and modeling study of poly(2,5-benzimidazole) - phosphoric acid interactions, Int. J. Hydrogen Energy (2013) accepted
Spectroscopic Investigation of Acid Doped Polybenzimidazole as Electrolyte Membrane for Fuel Cells
No full textOne fundamental component of a fuel cell (FC) is the electrolyte, which separates the electrocatalytic active sites of the two electrode configurations. Acid-doped poly(2,2’-(m-phenylene)-5,5’-bibenzimidazole) (PBI) polymers have been studied as membrane materials for the use in High Temperature Polymer Electrolyte FCs. [1]
In the present study, we report on a FT-Raman investigation of poly(2,5-benzimidazole) (AB-PBI) polymer membranes doped with various concentrations of ortho-phosphoric acid. Characteristic Raman spectra with three diagnostic regions and specific peaks have been studied [2]. Moreover, we present very recent NMR results on the PBI material [3]. The information is of fundamental importance in order to elucidate the role of H3PO4 in conductivity mechanisms in polybenzimidazoles.
[1] J. N. Asensio, E. M. Sánchez and P. Gómez- Romero, Chem. Soc. Rev., 2010, 39, 3210-3239.
[2] F. Conti, A. Majerus, V. Di Noto, C. Korte, W. Lehnert, D. Stolten, Phys. Chem. Chem. Phys., 2012, 14, 10022-10026.
[3] F. Conti, S. Willbold, C. Korte, W. Lehnert, S. Mammi, D. Stolten Polymer, 2012, under review
NMR investigations of acid doped polybenzimidazole, an electrolyte membrane for fuel cells
No full textFuel cells (FCs) are devices that convert the chemical energy of their reagents into electrical energy without resorting to a thermal Carnot cycle. Polymer electrolyte membrane FCs (PEMFCs) have raised considerable interest for their high energy conversion efficiency, high power density, ease of assembly, silent operation, and good environmental compatibility. Fuel cells consist mainly of an anode, a cathode and a membrane acting as electrolyte and which allows charges to selectively move between anode and cathode. Acid doped polybenzimidazole (PBI) polymers have become a very promising system for use as membranes in high temperature PEMFCs.
The conductivity in FCs is well known to be directly related to the mobility of the ions through the membrane, which might involve a multi-step proton hopping process (Grotthuss mechanism) or the bulk mobility of a proton carrier.
We report investigations of poly(2,5-benzimidazole) (AB-PBI) doped with phosphoric acid (PA) with different methods of NMR [1]. We have characterized the molecular interactions between the polymer matrix and the acid dopant. Heteronuclear correlation experiments were used to study hydrogen bonding characteristics. We have further studied the dynamics and order in the system at different doping levels and temperatures using 2H-NMR and 1H-Double-quantum spectroscopy. This information is of fundamental importance in order to elucidate the role of phosphoric acid in the conductivity mechanism of polybenzimidazole [2, 3].
[1] F. Conti, S. Willbold, C. Korte, W. Lehnert, D. Stolten, S. Mammi, Chem. Commun. 2012, submitted.
[2] C. E. Hughes, S. Haufe, B. Angerstein, R. Kalim, U. Mähr, A. Reiche, M. Baldus, J. Phys. Chem. B., 2004, 108, 13626-13631.
[3] S. Suarez, S. Greenbaum, The Chemical Record, 2010, 10, 377-393
Raman and NMR study of the interaction Polybenzimidazole – Phosphoric acid in membranes for fuel cells
No full textOne fundamental component of a fuel cell is the electrolyte, which separates the electrocatalytic active sites of the two electrode configurations. Phosphoric acid-doped poly(2,2’-(m-phenylene)-5,5’-bibenzimidazole) (PBI) polymers have been studied as membrane materials for the use in High Temperature Polymer Electrolyte Fuel Cells (HT-PEFC), since they can be used at temperatures as high as 200 °C without humidification. Among the many possible PBI derivatives, a very promising material is poly(2,5-benzimidazole) (AB-PBI) [1]
In the present study, we report on FT-Raman and NMR investigations of AB-PBI and PBI polymer membranes doped with various concentrations of ortho-phosphoric acid. Characteristic Raman and 1D- and 2D-NMR spectra with diagnostic signals have been studied. [2, 3] Ab-initio calculations were carried out using density functional theory methods to analyse the Raman data. The information is of fundamental importance in order to elucidate the role of phosphoric acid in the conductivity mechanism of membranes based on polybenzimidazole.
[1] J.N. Asensio, E.M. Sánchez and P.Gómez- Romero, Chem. Soc. Rev.39 (2010) 3210.
[2] F. Conti, A. Majerus, V. Di Noto, C. Korte, W. Lehnert, D. Stolten, Phys. Chem. Chem. Phys. 14 (28) (2012) 10022.
[3] F. Conti, S. Willbold, C. Korte, W. Lehnert, S. Mammi, D. Stolten, Polymer (2012) submitte
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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