1,721,092 research outputs found
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
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 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
Physicochemical investigation of phosphoric acid doped poly(2,5-benzimidazole) as electrolyte membrane for fuel cells
No full textPhosphoric acid doped polybenzimidazole membranes are a promising candidate for use as electrolyte membrane in high temperature polymer electrolyte membrane fuel cells (HT-PEFC). They present high thermal stability and excellent proton conductivity at low humidity [1]. Although polybenzimidazole membranes are routinely doped with phosphoric acid, few studies on the exact nature of the acid inside the membrane have been published. It is not known whether the phosphoric acid is present as ortho- or pyrophosphoric acid at all operating conditions and how it interacts with the membrane at a high operating temperature of 160 °C.
In this study, we investigated cross-linked poly(2,5-benzimidazole) (ABPBI) membranes obtained from FuMA-Tech GmbH which were doped in 85 % phosphoric acid. Conductivity measurements of the doped membrane under dry conditions show a maximum conductivity at 160 °C. At higher temperatures, the conductivity decreases as the dehydration of the orthophosphoric acid to the less conductive pyrophosphoric acid becomes relevant. Thermogravimetric analyses of pure phosphoric acid and doped membranes help to assess the amount of dehydrated phosphoric acid as well as the content of water and phosphoric acid inside the doped membrane. The thermal signals show two distinct weight losses between 30 °C and 200 °C, whose onset varies with the doping level of the membrane. An explanation for this effect, besides limited heat transfer, could be the bonds formed between the phosphoric acid molecules and the imidazole rings of the polymer. While free phosphoric acid molecules, found in pure phosphoric acid or in highly doped membranes, are free to condensate to pyrophosphoric acid molecules as soon as the activation energy is reached, bonded molecules need more energy to first break the bond and then dehydrate.
To further consolidate these results, the structure of the as-received and phosphoric acid doped membranes were analyzed and compared by means of Raman spectroscopy [2]. They confirm the presence of hydrogen bonds between the phosphoric acid and the imidazole group of the membrane, thus supporting the results obtained by thermogravimetric analysis.
[1] Q. Li, J. O. Jensen, R. F. Savinell, and N. J. Bjerrum, Progress in Polymer Science, 34, 449 (2009)
[2] F. Conti, A. Majerus, V. Di Noto, C. Korte, W. Lehnert, and D. Stolten, Phys. Chem. Chem. Phys., 14, 10022 (2012)
SUMMARY
We present a physicochemical investigation of phosphoric acid doped polybenzimidazole membranes, including conductivity measurements, thermogravimetric analysis and Raman spectroscopy
Investigations on the H3PO4-Uptake of Polybenzimidazole type Polymers using RAMAN Spectroscopy — Correlations between Adsorption Process and Electrolyte - Polymer Molecular Interactions
No full textAn important application of phosphoric acid doped polybenzimidazol (PBI) is the use as proton conducting electrolyte membrane in high temperature polymer electrolyte fuel cells (HT-PEFC). At typical operation temperatures of 120 to 200 °C and very low humidity ionic conductivities of 10-1 to 10-2 S cm-1 can be measured.
The H3PO4-doping process of different PBI-type materials were still investigated in se¬ve¬ral experimental studies, e.g. [1,2]. Unfortunately, no general applicable model for the kinetic of the adsorption process available which is able to describe the whole acces¬sible range of doping degrees has been published yet. The correlation between the interactions between H3PO4 molecules and polymer chains, the ad-sorp¬tion iso¬therm as well as the polycondensation equilibria of H3PO4 and the corresponding implications on the pro¬ton conductivity are also not finally illuminated.
We have investigated the ad¬sorption process of H3PO4 on a com¬mer¬cial cross-linked PBI deri¬vative (Fuma¬pem AM-55). A num¬ber of mem¬bra¬nes has been pre¬pared at dif¬fe¬rent do¬ping levels and analysed to elucidate the ad¬sorp¬tion process of H3PO4 as func¬tion of temperature and con¬cen¬tra¬tion. Karl-Fischer-, pH-titration and RAMAN spec¬tro¬scopy are used to cha¬rac¬terise the mem¬branes [3,4]. The ad¬sorp¬tion equi¬li¬bria of the up¬take pro¬cess have been ana¬ly¬sed with dif¬fe¬rent ki¬ne¬tic mo¬dels for own and for lite¬ra¬ture data on non-cross¬lin¬ked m-PBI and AB-PBI. The be¬ha¬viour of all PBI-type poly¬mers can be de¬scri¬bed sa¬tis¬fac¬torily with a BET-like ad¬sorp¬tion iso¬therm. Using the RAMAN data, re-gions in the isotherm can be cor¬re¬la¬ted to the pro¬tonation of the poly¬mer chains, for¬ma¬tion of H-bonds di¬rec¬tly to the chains and to still adsorbed H3PO4 mole¬cules.
[1] Q. Li et al., Solid State Ionics, 2004, 168, 177-185 [2] J. A. Asensio et al., Chem. Soc. Rev., 2010, 39, 3210-3239 [3] F. Conti et al., submitted to Fuel Cells, Jan. 2014 [4] C. Korte et al., to be submitted 201
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
Diagnostic Raman signals of the interaction polybenzimidazole – phosphoric acid in membrane 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). [1-4]
In the present study, we report on a FT-Raman investigation of 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. The information is of fundamental importance in order to elucidate the role of phosphoric acid in the conductivity mechanism of AB-PBI. [5]
Reference:
[1] J. N. Asensio, E. M. Sánchez and P. Gómez- Romero, Chem. Soc. Rev., 2010, 39, 3210-3239.
[2] C. Wannek, B. Kohnen, H.-F. Oetjen, H. Lippert and Mergel J., Fuel Cell, 2008, 8, 87-95.
[3] C. Wannek, W. Lehnert and J. Mergel, J. Power Sources, 2009, 192, 258-266.
[4] K. Wippermann, C. Wannek, H.-F. Oetjen, J. Mergel and W. Lehnert, J. Power Sources, 2010, 195, 2806-2809.
[5] F. Conti, A. Majerus, V. Di Noto, C. Korte, W. Lehnert, D. Stolten, Phys. Chem. Chem. Phys., 2012, 14, 10022-10026
Electrical conductivity and chemical equilibria of the phosphoric acid – water system at HT-PEM fuel cells relevant condition
No full textHigh temperature polymer electrolyte membrane (HT-PEM) fuel cells typically work at 120-200°C and are mainly based on phosphoric acid (PA) swollen basic polymer membranes like phosphoric acid doped polybenzimidazole. An overview can be found in [1-7]. Although PA is a widely used material even outside the field of electrochemical transformers, only little is known about the thermodynamical but also physical properties at temperatures above 100°C. Especially the correlation between different parameters provided from different sources in literature is often demanding due to different experimental approaches.
In this work, an alternative approach is used simulating directly the conditions inside an operational HT-PEM. The obtained physical and thermodynamic data are critically compared to results from other laboratories
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
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