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Jens Oluf Jensen - One of the best experts on this subject based on the ideXlab platform.
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Gel Electrolytes of Covalent Network Polybenzimidazole and Phosphoric Acid by Direct Casting
Macromolecular Materials and Engineering, 2017Co-Authors: Andreas Kirkebæk, Dirk Henkensmeier, David Aili, Jens Oluf JensenAbstract:Polybenzimidazole membranes imbibed with phosphoric acid can support high proton conductivity at 120–200 °C, and have therefore emerged as the state-of-the-art electrolytes for fuel cells operating in this temperature range. This work presents a novel and operationally simple methodology for preparing mechanically robust covalent network Polybenzimidazole membranes containing up to 95 wt% phosphoric acid. Diamino-terminal pre-polymers of different chain lengths are first prepared, followed by addition of a trifunctional carboxylic acid. The crude solutions are cast and subsequently heat treated at up to 230 °C, yielding free-standing membranes of networked Polybenzimidazole with high proton conductivity at up to 180 °C and encouraging fuel cell performance.
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long term durability of ht pem fuel cells based on thermally cross linked Polybenzimidazole
Journal of Power Sources, 2017Co-Authors: Tonny Sondergaard, Hans Aage Hjuler, Qingfeng Li, David Aili, Lars Nilausen Cleemann, Hans Becker, Thomas Steenberg, Larisa Seerup, Jens Oluf JensenAbstract:Abstract Long-term durability of high temperature polymer electrolyte membrane fuel cells based on thermally cross-linked Polybenzimidazole membranes was studied and compared with reference membranes based on linear Polybenzimidazole. The test was conducted at 160 °C under constant load currents of 200 mA cm −2 for periods of 1000, 4400, and 13,000 h. Extensive beginning-of-life (BoL) and end-of-test (EoT) characterisation was carried out, and disturbance of the steady state operated cells was minimised by limiting in-line diagnostics to the low-invasive technique of electrochemical impedance spectroscopy (EIS). Up until the operating time of 9200 h, the cell equipped with the cross-linked membrane showed an average degradation rate of 0.5 μV h −1 , compared to 2.6 μV h −1 for the reference membrane, though parallel tests for a shorter period of time showed deviations, likely due to malfunctioning contact between layers or cell components. For the full test period of 13,000 h, the average voltage decay rate was about 1.4 and 4.6 μV h −1 for cells equipped with cross-linked and linear Polybenzimidazole membranes, respectively. EIS and post-test analysis revealed that the cross-linked membrane showed better stability in terms of area specific resistance due to improved acid retention characteristics.
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Amino‐Functional Polybenzimidazole Blends with Enhanced Phosphoric Acid Mediated Proton Conductivity as Fuel Cell Electrolytes
Macromolecular Chemistry and Physics, 2016Co-Authors: David Aili, Chao Pan, Jens Oluf Jensen, Katja Jankova, Irakli Javakhishvili, Junyoung Han, Søren Hvilsted, Niels J BjerrumAbstract:A novel amino‐functional Polybenzimidazole copolymer is synthesized from isophthalic acid, 3,3′‐diaminobenzidine, and new a multifunctional monomer, obtained by coupling of 2,4‐dinitrophenyl with 1,3‐diaminopropane followed by mild and clean reduction with hydrazine hydrate. Blends of the new polymer with conventional Polybenzimidazole afford mechanically robust membranes showing enhanced phosphoric acid uptake, increased proton conductivity, and improved fuel cell performance.
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heterogeneous anion conducting membranes based on linear and crosslinked koh doped Polybenzimidazole for alkaline water electrolysis
Journal of Membrane Science, 2013Co-Authors: David Aili, Jens Oluf Jensen, Qingfeng Li, Martin Kalmar Hansen, Richard Fulgence Renzaho, Erik Christensen, Niels J BjerrumAbstract:Abstract Polybenzimidazole is a highly hygroscopic polymer that can be doped with aqueous KOH to give a material with high ion conductivity in the 10−2 S cm−1 range, which in combination with its low gas permeability makes it an interesting electrolyte material for alkaline water electrolysis. In this study membranes based on linear and crosslinked Polybenzimidazole were evaluated for this purpose. Extensive characterization with respect to spectroscopic and physicochemical properties during aging in 6 mol L−1 KOH at 85 °C for up to 176 days indicated structural stability of the high molecular weight specialty polymer, however, with limitations with respect to hydrolytic stability. The gradual decay of the average molecular weight resulted in a severe deterioration of the mechanical properties over time. Membranes based on crosslinked Polybenzimidazole showed better stability than the membranes based on their linear counterpart. The technical feasibility of the membranes was evaluated by the preliminary water electrolysis tests showing performance comparable to that of commercially available cell separators with great potential of further improvement.
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Cross-Linked Polybenzimidazole Membranes for Fuel Cells
Chemistry of Materials, 2007Co-Authors: Qingfeng Li, Pernille Precht Noyé, Chao Pan, Jens Oluf Jensen, Niels J BjerrumAbstract:Polybenzimidazole membranes have been covalently cross-linked after casting. The membranes exhibit much-improved chemical stability and mechanical strength. This allows the membrane to be doped at higher acid levels and therefore possess higher proton conductivity and potentially increased durability in fuel cells.
Niels J Bjerrum - One of the best experts on this subject based on the ideXlab platform.
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Amino‐Functional Polybenzimidazole Blends with Enhanced Phosphoric Acid Mediated Proton Conductivity as Fuel Cell Electrolytes
Macromolecular Chemistry and Physics, 2016Co-Authors: David Aili, Chao Pan, Jens Oluf Jensen, Katja Jankova, Irakli Javakhishvili, Junyoung Han, Søren Hvilsted, Niels J BjerrumAbstract:A novel amino‐functional Polybenzimidazole copolymer is synthesized from isophthalic acid, 3,3′‐diaminobenzidine, and new a multifunctional monomer, obtained by coupling of 2,4‐dinitrophenyl with 1,3‐diaminopropane followed by mild and clean reduction with hydrazine hydrate. Blends of the new polymer with conventional Polybenzimidazole afford mechanically robust membranes showing enhanced phosphoric acid uptake, increased proton conductivity, and improved fuel cell performance.
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heterogeneous anion conducting membranes based on linear and crosslinked koh doped Polybenzimidazole for alkaline water electrolysis
Journal of Membrane Science, 2013Co-Authors: David Aili, Jens Oluf Jensen, Qingfeng Li, Martin Kalmar Hansen, Richard Fulgence Renzaho, Erik Christensen, Niels J BjerrumAbstract:Abstract Polybenzimidazole is a highly hygroscopic polymer that can be doped with aqueous KOH to give a material with high ion conductivity in the 10−2 S cm−1 range, which in combination with its low gas permeability makes it an interesting electrolyte material for alkaline water electrolysis. In this study membranes based on linear and crosslinked Polybenzimidazole were evaluated for this purpose. Extensive characterization with respect to spectroscopic and physicochemical properties during aging in 6 mol L−1 KOH at 85 °C for up to 176 days indicated structural stability of the high molecular weight specialty polymer, however, with limitations with respect to hydrolytic stability. The gradual decay of the average molecular weight resulted in a severe deterioration of the mechanical properties over time. Membranes based on crosslinked Polybenzimidazole showed better stability than the membranes based on their linear counterpart. The technical feasibility of the membranes was evaluated by the preliminary water electrolysis tests showing performance comparable to that of commercially available cell separators with great potential of further improvement.
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Cross-Linked Polybenzimidazole Membranes for Fuel Cells
Chemistry of Materials, 2007Co-Authors: Qingfeng Li, Pernille Precht Noyé, Chao Pan, Jens Oluf Jensen, Niels J BjerrumAbstract:Polybenzimidazole membranes have been covalently cross-linked after casting. The membranes exhibit much-improved chemical stability and mechanical strength. This allows the membrane to be doped at higher acid levels and therefore possess higher proton conductivity and potentially increased durability in fuel cells.
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polymer electrolyte membrane fuel cells
2000Co-Authors: Niels J Bjerrum, Qingfeng Li, Hans Aage HjulerAbstract:A method for preparing Polybenzimidazole or Polybenzimidazole blend membranes and fabricating gas diffusion electrodes and membrane-electrode assemblies is provided for a high temperature polymer electrolyte membrane fuel cell. Blend polymer electrolyte membranes based on PBI and various thermoplastc polymers for high temperature polymer electrolyte fuel cells have also been developed. Miscible blends are used for solution casting of polymer membranes (solid electrolytes). High conductivity and enhanced mechanical strength were obtained for the blend polymer solid electrolytes. With the thermally resistant polymer, e.g., Polybenzimidazole or a mixture of Polybenzimidazole and other thermoplastics as binder, the carbon-supported noble metal catalyst is tape-cast onto a hydrophobic supporting substrate. When doped with an acid mixture, electrodes are assembled with an acid doped solid electrolyte membrane by hot-press. The fuel cell can operate at temperatures up to at least 200° C. with hydrogen-rich fuel containing high ratios of carbon monoxide such as 3 vol % carbon monoxide or more, compared to the carbon monoxide tolerance of 10-20 ppm level for Nafion®-based polymer electrolyte fuel cells.
David Aili - One of the best experts on this subject based on the ideXlab platform.
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From Polybenzimidazoles to polybenzimidazoliums and polybenzimidazolides
Journal of Materials Chemistry A, 2020Co-Authors: David Aili, Jingshuai Yang, Katja Jankova, Dirk HenkensmeierAbstract:Polybenzimidazoles represent a large family of high-performance polymers containing benzimidazole groups as part of the structural repeat unit. New application areas in electrochemical cells and separation processes have emerged during the last two decades, which has been a major driver for the tremendous development of new Polybenzimidazole chemistries and materials in recent years. This comprehensive treatise is devoted to an investigation of the structural scope of Polybenzimidazole derivatives, Polybenzimidazole modifications and the acid–base behavior of the resulting materials. Advantages and limitations of different synthetic procedures and pathways are analyzed, with focus on homogeneous solution polymerization. The discussion extends to solution properties and the challenges that are faced in connection to molecular weight determination and processing. Methods for Polybenzimidazole grafting or crosslinking, in particular by N-coupling, are reviewed and successful polymer blend strategies are identified. The amphoteric nature of benzimidazole groups further enriches the chemistry of Polybenzimidazoles, as cationic or anionic ionenes are obtained depending on the pH. In the presence of protic acids, such as phosphoric acid, cationic ionenes in the form of protic polybenzimidazoliums are obtained, which dramatically changes the physicochemical properties of the material. Cationic ionenes are also derived by complete N-alkylation of a Polybenzimidazole to the corresponding poly(dialkyl benzimidazolium), which has been intensively explored recently as a new direction in the field of anion exchange membranes. In the higher end of the pH scale in aqueous hydroxide solutions, anionic ionenes in the form of polybenzimidazolides are obtained as a result of deprotonation of the benzimidazole groups. The ionization of the polymer results in dramatically changed physicochemical properties as compared to the pristine material, which is described and discussed. From a technological point of view, performance and stability targets continue to motivate further research and development of new Polybenzimidazole chemistries and energy materials. The overall aim of this review is therefore to identify challenges and opportunities in this area from synthetic chemistry and materials science perspectives to serve as a solid basis for further development prospects.
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Thermally crosslinked sulfonated Polybenzimidazole membranes and their performance in high temperature polymer electrolyte fuel cells
Journal of Membrane Science, 2019Co-Authors: N. Nambi Krishnan, David Aili, Anastasiia Konovalova, Hyun S. Park, Jong Hyun Jang, Hyoung-juhn Kim, Dirk HenkensmeierAbstract:Abstract The degradation pathway of phosphoric acid doped Polybenzimidazole membranes in high temperature polymer electrolyte membrane fuel cells depends on the acid contents. If it is high, creep is discussed as the main reason. If it is low (membranes prepared by solvent evaporation and post-doping), the main cause may be loss of acid due to evaporation, in addition to a process observed at high current densities, at which a net transport of acid to the anode side is observed, which should lead to local softening of the membrane. A common way to stabilize membranes is crosslinking. Here we show that sulfonated para -Polybenzimidazole membranes can be stabilized by curing at 350 °C. In contrast to meta -Polybenzimidazole and sulfonated para -Polybenzimidazole, crosslinked sulfonated para -Polybenzimidazole is insoluble in dimethylacetamide at room temperature and phosphoric acid at 160 °C. At 160 °C and 5% relative humidity the conductivity of crosslinked sulfonated para -Polybenzimidazole and meta -Polybenzimidazole are 214 mS cm −1 and 147 mS cm −1 , respectively. At 600 mA/cm 2 , the voltage decay rate is 16 μV/h, much lower than published for commercial meta -Polybenzimidazole (308 μV/h). Furthermore, the average voltage at 600 mA/cm 2 is 523 mV, while a previously published cured meta -Polybenzimidazole membrane only reaches 475 mV.
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Gel Electrolytes of Covalent Network Polybenzimidazole and Phosphoric Acid by Direct Casting
Macromolecular Materials and Engineering, 2017Co-Authors: Andreas Kirkebæk, Dirk Henkensmeier, David Aili, Jens Oluf JensenAbstract:Polybenzimidazole membranes imbibed with phosphoric acid can support high proton conductivity at 120–200 °C, and have therefore emerged as the state-of-the-art electrolytes for fuel cells operating in this temperature range. This work presents a novel and operationally simple methodology for preparing mechanically robust covalent network Polybenzimidazole membranes containing up to 95 wt% phosphoric acid. Diamino-terminal pre-polymers of different chain lengths are first prepared, followed by addition of a trifunctional carboxylic acid. The crude solutions are cast and subsequently heat treated at up to 230 °C, yielding free-standing membranes of networked Polybenzimidazole with high proton conductivity at up to 180 °C and encouraging fuel cell performance.
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long term durability of ht pem fuel cells based on thermally cross linked Polybenzimidazole
Journal of Power Sources, 2017Co-Authors: Tonny Sondergaard, Hans Aage Hjuler, Qingfeng Li, David Aili, Lars Nilausen Cleemann, Hans Becker, Thomas Steenberg, Larisa Seerup, Jens Oluf JensenAbstract:Abstract Long-term durability of high temperature polymer electrolyte membrane fuel cells based on thermally cross-linked Polybenzimidazole membranes was studied and compared with reference membranes based on linear Polybenzimidazole. The test was conducted at 160 °C under constant load currents of 200 mA cm −2 for periods of 1000, 4400, and 13,000 h. Extensive beginning-of-life (BoL) and end-of-test (EoT) characterisation was carried out, and disturbance of the steady state operated cells was minimised by limiting in-line diagnostics to the low-invasive technique of electrochemical impedance spectroscopy (EIS). Up until the operating time of 9200 h, the cell equipped with the cross-linked membrane showed an average degradation rate of 0.5 μV h −1 , compared to 2.6 μV h −1 for the reference membrane, though parallel tests for a shorter period of time showed deviations, likely due to malfunctioning contact between layers or cell components. For the full test period of 13,000 h, the average voltage decay rate was about 1.4 and 4.6 μV h −1 for cells equipped with cross-linked and linear Polybenzimidazole membranes, respectively. EIS and post-test analysis revealed that the cross-linked membrane showed better stability in terms of area specific resistance due to improved acid retention characteristics.
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Amino‐Functional Polybenzimidazole Blends with Enhanced Phosphoric Acid Mediated Proton Conductivity as Fuel Cell Electrolytes
Macromolecular Chemistry and Physics, 2016Co-Authors: David Aili, Chao Pan, Jens Oluf Jensen, Katja Jankova, Irakli Javakhishvili, Junyoung Han, Søren Hvilsted, Niels J BjerrumAbstract:A novel amino‐functional Polybenzimidazole copolymer is synthesized from isophthalic acid, 3,3′‐diaminobenzidine, and new a multifunctional monomer, obtained by coupling of 2,4‐dinitrophenyl with 1,3‐diaminopropane followed by mild and clean reduction with hydrazine hydrate. Blends of the new polymer with conventional Polybenzimidazole afford mechanically robust membranes showing enhanced phosphoric acid uptake, increased proton conductivity, and improved fuel cell performance.
Dirk Henkensmeier - One of the best experts on this subject based on the ideXlab platform.
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From Polybenzimidazoles to polybenzimidazoliums and polybenzimidazolides
Journal of Materials Chemistry A, 2020Co-Authors: David Aili, Jingshuai Yang, Katja Jankova, Dirk HenkensmeierAbstract:Polybenzimidazoles represent a large family of high-performance polymers containing benzimidazole groups as part of the structural repeat unit. New application areas in electrochemical cells and separation processes have emerged during the last two decades, which has been a major driver for the tremendous development of new Polybenzimidazole chemistries and materials in recent years. This comprehensive treatise is devoted to an investigation of the structural scope of Polybenzimidazole derivatives, Polybenzimidazole modifications and the acid–base behavior of the resulting materials. Advantages and limitations of different synthetic procedures and pathways are analyzed, with focus on homogeneous solution polymerization. The discussion extends to solution properties and the challenges that are faced in connection to molecular weight determination and processing. Methods for Polybenzimidazole grafting or crosslinking, in particular by N-coupling, are reviewed and successful polymer blend strategies are identified. The amphoteric nature of benzimidazole groups further enriches the chemistry of Polybenzimidazoles, as cationic or anionic ionenes are obtained depending on the pH. In the presence of protic acids, such as phosphoric acid, cationic ionenes in the form of protic polybenzimidazoliums are obtained, which dramatically changes the physicochemical properties of the material. Cationic ionenes are also derived by complete N-alkylation of a Polybenzimidazole to the corresponding poly(dialkyl benzimidazolium), which has been intensively explored recently as a new direction in the field of anion exchange membranes. In the higher end of the pH scale in aqueous hydroxide solutions, anionic ionenes in the form of polybenzimidazolides are obtained as a result of deprotonation of the benzimidazole groups. The ionization of the polymer results in dramatically changed physicochemical properties as compared to the pristine material, which is described and discussed. From a technological point of view, performance and stability targets continue to motivate further research and development of new Polybenzimidazole chemistries and energy materials. The overall aim of this review is therefore to identify challenges and opportunities in this area from synthetic chemistry and materials science perspectives to serve as a solid basis for further development prospects.
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Thermally crosslinked sulfonated Polybenzimidazole membranes and their performance in high temperature polymer electrolyte fuel cells
Journal of Membrane Science, 2019Co-Authors: N. Nambi Krishnan, David Aili, Anastasiia Konovalova, Hyun S. Park, Jong Hyun Jang, Hyoung-juhn Kim, Dirk HenkensmeierAbstract:Abstract The degradation pathway of phosphoric acid doped Polybenzimidazole membranes in high temperature polymer electrolyte membrane fuel cells depends on the acid contents. If it is high, creep is discussed as the main reason. If it is low (membranes prepared by solvent evaporation and post-doping), the main cause may be loss of acid due to evaporation, in addition to a process observed at high current densities, at which a net transport of acid to the anode side is observed, which should lead to local softening of the membrane. A common way to stabilize membranes is crosslinking. Here we show that sulfonated para -Polybenzimidazole membranes can be stabilized by curing at 350 °C. In contrast to meta -Polybenzimidazole and sulfonated para -Polybenzimidazole, crosslinked sulfonated para -Polybenzimidazole is insoluble in dimethylacetamide at room temperature and phosphoric acid at 160 °C. At 160 °C and 5% relative humidity the conductivity of crosslinked sulfonated para -Polybenzimidazole and meta -Polybenzimidazole are 214 mS cm −1 and 147 mS cm −1 , respectively. At 600 mA/cm 2 , the voltage decay rate is 16 μV/h, much lower than published for commercial meta -Polybenzimidazole (308 μV/h). Furthermore, the average voltage at 600 mA/cm 2 is 523 mV, while a previously published cured meta -Polybenzimidazole membrane only reaches 475 mV.
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High temperature polymer electrolyte membrane fuel cells with Polybenzimidazole-Ce0.9Gd0.1P2O7 and Polybenzimidazole-Ce0.9Gd0.1P2O7-graphite oxide composite electrolytes
Journal of Power Sources, 2018Co-Authors: Bhupendra Singh, N. Nambi Krishnan, Anastasiia Konovalova, Nitika Devi, Avanish Kumar Srivastava, Rajesh Kumar Singh, Sun-ju Song, Dirk HenkensmeierAbstract:Abstract In this work, Polybenzimidazole based composite membranes are fabricated using Polybenzimidazole, Ce0.9Gd0.1P2O7 and graphite oxide by solution casting procedure. The microstructural, mechanical and electrical properties of the phosphoric acid-doped composite membranes are characterized for fuel cell applications. Addition of graphite oxide in the composite leads to improvement in homogeneous dispersion of higher amount, 31 wt%, of Ce0.9Gd0.1P2O7. With the increasing amount of Ce0.9Gd0.1P2O7 in the composite membranes the amount of phosphoric acid loading decreases, but the proton conductivity of the composite membrane is higher than that is reported for the phosphoric acid-doped Polybenzimidazole membranes. At 180 °C, a maximum conductivity of 182 mS cm−1 for Polybenzimidazole/Ce0.9Gd0.1P2O7 membrane with 24 wt% Ce0.9Gd0.1P2O7 and 199 mS cm−1 for Polybenzimidazole/Ce0.9Gd0.1P2O7/graphite oxide membrane with 31 wt% Ce0.9Gd0.1P2O7 is observed. The H2-Air fuel cells operating at 160 °C with ∼250 μm thick Polybenzimidazole/Ce0.9Gd0.1P2O7 electrolyte shows open circuit voltage of 0.938 V and maximum power density of 255 mW cm−2 with 640 mA cm−2 current at 160 °C whereas the corresponding values with ∼200 μm thick Polybenzimidazole/Ce0.9Gd0.1P2O7/graphite oxide membrane are 0.976 V and 307 mW cm−2 with 800 mA cm−2 current, respectively. However, irrespective of the increased conductivity at the higher temperatures, the maximum power density decreases with increasing temperature >160 °C.
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Gel Electrolytes of Covalent Network Polybenzimidazole and Phosphoric Acid by Direct Casting
Macromolecular Materials and Engineering, 2017Co-Authors: Andreas Kirkebæk, Dirk Henkensmeier, David Aili, Jens Oluf JensenAbstract:Polybenzimidazole membranes imbibed with phosphoric acid can support high proton conductivity at 120–200 °C, and have therefore emerged as the state-of-the-art electrolytes for fuel cells operating in this temperature range. This work presents a novel and operationally simple methodology for preparing mechanically robust covalent network Polybenzimidazole membranes containing up to 95 wt% phosphoric acid. Diamino-terminal pre-polymers of different chain lengths are first prepared, followed by addition of a trifunctional carboxylic acid. The crude solutions are cast and subsequently heat treated at up to 230 °C, yielding free-standing membranes of networked Polybenzimidazole with high proton conductivity at up to 180 °C and encouraging fuel cell performance.
Brian C Benicewicz - One of the best experts on this subject based on the ideXlab platform.
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Solution polymerization of Polybenzimidazole
Journal of Polymer Science Part A: Polymer Chemistry, 2016Co-Authors: Kayley Fishel, Alexander Gulledge, Andrew T. Pingitore, Jason P. Hoffman, Warren P. Steckle, Brian C BenicewiczAbstract:Polybenzimidazoles (PBI) are an important class of heterocyclic polymers that exhibit high thermal and oxidative stabilities. The two dominant polymerization methods used for the synthesis of PBI are the melt/solid polymerization route and solution polymerization using polyphosphoric acid as the solvent. Both methods have been widely used to produce high-molecular weight PBI, but also highlight the obvious absence of a practical organic solution-based method of polymerization. This current work explores the synthesis of high-molecular weight meta-PBI in N,N-dimethyl acetamide (DMAc). Initially, model compound studies examined the reactivity of small molecules with various chemical functionalities that could be used to produce 2-phenyl-benzimidazole in high yield with minimal side reactions. 1H NMR and FTIR studies indicated that benzimidazoles could be efficiently synthesized in DMAc by reaction of an o-diamine and the bisulfite adduct of an aromatic aldehyde. Polymerizations were conducted at various polymer concentrations (2-26 wt % polymer) using difunctional monomers to optimize reaction conditions in DMAc which resulted in the preparation of high-molecular weight m-PBI (inherent viscosities up to 1.3 dL g−1). TGA and DSC confirmed that m-PBI produced via this route has comparable properties to that of commercial m-PBI. This method is advantageous in that it not only allows for high-polymer concentrations of m-PBI to be synthesized directly and efficiently, but can be applied to the synthesis of many PBI derivatives. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 1795–1802
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Handbook of Fuel Cells - High‐temperature polybenzimidazol‐based membranes
Handbook of Fuel Cells, 2010Co-Authors: D.c. Seel, Lixiang Xiao, Brian C Benicewicz, T J SchmidtAbstract:High-temperature Polybenzimidazole-based membranes Polybenzimidazole (PBI) is an excellent material for phosphoric acid-doped proton exchange membranes. PBI-based membranes can operate reliably at temperatures above 120 °C, which provides high CO tolerance, fast electrode kinetics, and simplified water and thermal management. PBI membranes prepared by the polyphosphoric acid (PPA) process exhibit improved mechanical properties, proton conductivities, and fuel cell operational characteristics at higher phosphoric acid loading levels compared to the conventionally prepared PBI-based membranes for high-temperature fuel cell applications. Keywords: high-temperature polymer electrolyte membrane (PEM); phosphoric acid (PA); Polybenzimidazole (PBI); PPA process
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high temperature Polybenzimidazole fuel cell membranes via a sol gel process
Chemistry of Materials, 2005Co-Authors: Lixiang Xiao, Eugene Scanlon, L S Ramanathan, Euiwon Choe, Diana F Rogers, Tom Apple, Haifeng Zhang, Brian C BenicewiczAbstract:A sol−gel process is described to produce phosphoric acid (PA)-doped Polybenzimidazole (PBI) films that operate as fuel cell membranes above 150 °C for extended periods of time without the need for feed gas humidification. When solutions of high molecular weight heterocylic polymers such as Polybenzimidazoles in polyphosphoric acid (PPA) were cast into films, a transition from solution state to gel state was observed during the hydrolysis of the solvent from PPA (a good solvent for PBI) to PA (a poor solvent for PBI). The resulting membranes retained high levels of phosphoric acid in the gel structure and exhibited high ionic conductivities and stable mechanical properties at elevated temperatures. Preliminary fuel cell tests have demonstrated the feasibility of such PBI membranes from the sol−gel process for operating a fuel cell at temperatures above 150 °C without any feed gas humidification or pressure requirements for more than 1000 h.
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synthesis and characterization of pyridine based Polybenzimidazoles for high temperature polymer electrolyte membrane fuel cell applications
Fuel Cells, 2005Co-Authors: Lixiang Xiao, Eugene Scanlon, L S Ramanathan, Euiwon Choe, Haifeng Zhang, Tushar Jana, R Chen, S Yu, Brian C BenicewiczAbstract:A series of Polybenzimidazoles (PBIs) incorporating main chain pyridine groups were synthesized from the pyridine dicarboxylic acids (2,4-, 2,5-, 2,6- and 3,5-) and 3,3′,4,4′-tetraaminobiphenyl, using polyphosphoric acid (PPA) as both solvent and polycondensation reagent. A novel process, termed the PPA process, has been developed to prepare phosphoric acid (PA) doped PBI membranes by direct-casting of the PPA polymerization solution without isolation or re-dissolution of the polymers. The subsequent hydrolysis of PPA to PA by moisture absorbed from the atmosphere usually induced a transition from the solution state to a gel-like state and produced PA-doped PBI membranes with a desirable suite of physiochemical properties. The polymer structure characterization included inherent viscosity (I.V.) determination as a measurement of polymer molecular weight and thermal stability assessment via thermogravimetric analysis. Physiochemical properties of the doped membrane were studied by measurements of the PA doping level, ionic conductivity and mechanical properties. The resulting pyridine-based Polybenzimidazole membranes displayed high PA doping levels, ranging from 15 to 25 mol of PA per PBI repeat unit, which contributed to their unprecedented high proton conductivities of 0.1 to 0.2 S cm–1 at 160 °C. The mechanical property measurements showed that the pyridine-based PBI membranes were thermally stable and maintained mechanical integrity even at high PA doping levels. Preliminary fuel cell tests demonstrated the feasibility of the novel pyridine-based PBI (PPBI) membranes from the PPA process for operating fuel cells at temperatures in excess of 120 °C without any external humidification.