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High-temperature polymer-electrolyte membrane fuel cells (HT-PEMFCs) are a very important type of fuel cells since they operate at 150–200 °C, making it possible to use hydrogen contaminated with CO. However, the need to improve the stability and other properties of gas-diffusion electrodes still impedes their distribution. Self-supporting anodes based on carbon nanofibers (CNF) are prepared using the electrospinning method from a polyacrylonitrile solution containing zirconium salt, followed by pyrolysis. After the deposition of Pt nanoparticles on the CNF surface, the composite anodes are obtained. A new self-phosphorylating polybenzimidazole of the 6F family is applied to the Pt/CNF surface to improve the triple-phase boundary, gas transport, and proton conductivity of the anode. This polymer coating ensures a continuous interface between the anode and proton-conducting membrane. The polymer is investigated using CO2 adsorption, TGA, DTA, FTIR, GPC, and gas permeability measurements. The anodes are studied using SEM, HAADF STEM, and CV. The operation of the membrane–electrode assembly in the H2/air HT-PEMFC shows that the application of the new PBI of the 6F family with good gas permeability as a coating for the CNF anodes results in an enhancement of HT-PEMFC performance, reaching 500 mW/cm2 at 1.3 A/cm2 (at 180 °C), compared with the previously studied PBI-O-PhT-P polymer. [ABSTRACT FROM AUTHOR]

Abstract: A new thermally stable polybenzimidazole film has been synthesized by nucleophilic aromatic substitution, transformed into a complex with phosphoric acid and tested as a proton-conductive membrane. [Copyright &y& Elsevier]

The efficient use of renewable energy sources requires development of new electrocatalytic materials for electrochemical energy storage systems, particularly fuel cells. To increase durability of high temperature polymer electrolyte fuel cell (HT-PEMFC), Pt/carbon black based catalysts should be replaced by more durable ones, for example Pt/carbon nanofibers (CNF). Here, we report for the first time the quantitative ascorbic acid assisted deposition of Pt onto electrospun polyacrylonitrile-based CNF composite materials. The effect of their subsequent post-treatment at various temperatures (250 and 500 °C) and media (vacuum or argon-hydrogen mixture) on the Pt/C catalyst morphology is investigated. All obtained samples are thoroughly studied by high resolution electron microscopy, and Pt electrochemically active specific surface area was evaluated by cyclic voltammetry. [ABSTRACT FROM AUTHOR]

Semi-ladder high-molecular polynaphthoylenebenzimidazoles (PNBI) were synthesized through polyaminonaphtoyleneimide (PANI) formation and thermal cyclization at 350 °C. The structures of PANIs and PNBIs were confirmed by NMR, GPC and FTIR. Polymer films were obtained from PANI pre-polymer by solution-cast technique. After thermal cyclization, the PNBI films exhibit excellent mechanical properties: tensile strength of 95–174 MPa, Young's modulus of 1.5–2.4 GPa and elongation at break of 10–50%. The PNBIs are located near the upper bound of the 1991 Robeson diagram for O 2 /N 2 , H 2 /N 2 and H 2 /CH 4 gas pairs, while the PNBI with a hexafluoroisopropylidene bridge (PNBI-4) overcomes it for CO 2 /CH 4 , approaching the upper bound of the 2008 Robeson diagram. A peculiarity of the synthesized polymers is lower gas diffusion coefficients and higher gas solubility coefficients, which are close to polypyrrolones and PIM family polymers. The higher PNBI diffusion selectivity identifies them as organic molecular sieves, as confirmed by the specific surface area of PNBI-4, which is close to PIM-1. The data obtained allows to classify the studied PNBIs as unexpected PIM relatives. The synthesized PNBIs are polymer molecular sieves and, unexpectedly, belong to the polymer of intrinsic microporosity family. [Display omitted] • The PNBI gas transport properties have been obtained. • The studied PNBIs lie on the upper bounds of the 1991 Robeson diagrams. • PNBI-4 is higher than the upper bound on the 1991 Robeson diagram for CO 2 /CH 4. • PNBI-4 is approaching the upper bound of the 2008 Robeson diagram for CO 2 /CH 4. • PNBI-4 possesses a microporous structure similar to the one of PIM-1. [ABSTRACT FROM AUTHOR]

The most environmentally safe method of PBI synthesis is reported and applied in the high proton conductivity membrane production for high temperature polymer electrolyte membrane fuel cell. [Display omitted] • Breakthrough PBI synthesis for HT-PEMFC proton-conducting membrane is suggested. • The environmentally safe method of PBI synthesis is developed. • The membrane was successfully tested in HT-PEM fuel cell. • Extremely low hydrogen crossover through the membrane at 180 °C was registered. The article presents a new environmentally safe synthetic approach towards durable polybenzimidazole proton-conducting membrane via polyamidation at ambient conditions and subsequent thermal heterocyclization of films cast from reaction solution followed by phosphoric acid doping. The method avoids exhausts, acid waste and inorganic salts, compared with the existing methods and technologies, allowing to minimize the negative environmental impact related to the process. The membrane possesses an excellent proton conductivity of 105 mS cm−1 and good mechanical properties and has been successfully tested in high temperature polymer electrolyte membrane fuel cells. An extremely low hydrogen crossover through the membrane of 0.040 mA cm−2 at 180 °C has been registered compared with quite high 4–5 mA cm−2 for Celazole® m -PBI. [ABSTRACT FROM AUTHOR]

New PIM-1 copolymers with 2,3,6,7-anthracenetetrayl moiety have been synthesized as fine powders from 2,3,6,7-tetrahydroxy-9,10-di(p -fluorophenyl)anthracene monomer in DMSO, with crystal structure of the monomer as well as its precursors and the product of its model side crosslinking reaction being determined using X-ray diffraction. The microporosity and surface characteristics of the copolymers powders have been measured. As-cast membrane from the copolymer with 5 mol% of the monomer synthesized revealed promising gas separation properties as compared with original PIM-1. [ABSTRACT FROM AUTHOR]

Nitrile groups of model [1,4]benzodioxino[2,3 -b ]oxanthrene- 6,13-dicarbonitrile were transformed into quinazoline moieties by heterocyclization with benzanilides. The procedure was extended for PIM-1 modification to obtain gas separation membranes with promising permeability and selectivity. [ABSTRACT FROM AUTHOR]

Different polyheteroarylenes, such as m-polybenzimidazole, polyphenylene oxide, polymer of intrinsic microporosity (PIM-1) and poly(N-phenylene-benzimidazole) were electrospun to obtain self-supporting polymer nanofiber mats. The mats after heat treatment, which contains stabilization in air at 250-350 °C and pyrolysis at 900-1000 °C under vacuum, convert into carbon nanofiber paper, a material which is suitable for Pt nanoparticle deposition. The possibility of usage of the obtained carbonized nanocomposites as entire gas diffusion electrodes for high temperature polymer electrolyte membrane fuel cell is shown. [ABSTRACT FROM AUTHOR]

A new clean method - reductive heterocyclization of bis( o-nitoanilines) in formic acid/water media with hydrogen on Pd/C catalyst - was used to obtain new bis(benzimidazole) monomers. The monomers were involved in nucleophilic aromatic substitution reaction with 4,4′-diflourodiphenylsulphone for the synthesis of poly(N-phenylenebenzimidazoles) - a novel type of high performance polymers from the polybenzimidazole family. The obtained polymers were characterized by NMR, FTIR, GPC, TGA and TMA data. [ABSTRACT FROM AUTHOR]

Polymer of intrinsic microporosity (PIM-1) is characterized by a developed microporous structure. Needle-free Nanospider™ electrospinning of the PIM-1 solution with subsequent pyrolysis either under vacuum or in argon-hydrogen medium (7 vol% H 2) at 900–1200 °C results in PIM-1 based carbon nanofibers (CNF) self-supporting mats. The samples were thoroughly characterized by N 2 and CO 2 adsorption using the BET, BJH, Dubinin-Radushkevich (DR), NLDFT and GCMC methods, CO 2 uptake, and by Raman spectroscopy, elemental analysis, electrical conductivity, SEM. Since the N 2 adsorption is found to be inapplicable, the presence of microporosity in the CNF is confirmed by CO 2 adsorption (273 K) by the DR, NLDFT and GCMC methods. The CNF reach micropore specific surface area of 919 m2 g−1, micropore volume of 0.257 cm3 g−1 and CO 2 uptake of 4.01 mmol g−1, which is higher than for initial PIM-1. Pt/PIM-1 CNF self-supporting mat, was successfully tested as anode for HT-PEM fuel cell. Carbon dioxide adsorption method unveils PIM-1 carbon nanofiber microporosity exceeding PIM-1 microporosity. [Display omitted] • Electrospun PIM-1 carbon nanofibers are mostly ultramicroporous. • Microporosity characteristics of PIM-1 CNF exceed the ones for PIM-1. • PIM-1 CNF specific surface area reaches 919 m2 g−1 • CO 2 uptake for PIM-1 CNF is higher than for PIM-1. • Pt/PIM-1 CNF mats can be used as anodes in HT-PEM fuel cell. [ABSTRACT FROM AUTHOR]

Graphical abstract 1,7-Dihydrodiimidazo[4,5- b :4′,5′- e ]pyridine obtained by reductive heterocyclization was N-arylated with 4-fluoronitrobenzene to form two regioisomers in 7 : 3 ratio. This N-arylation is considered as a model reaction for the polymer synthesis. [ABSTRACT FROM AUTHOR]

High strength flame-resistant semi-ladder fibers of the "Lola" family (PNBI) have been obtained by an acid-free and more environmentally friendly method with controlled heating of precursor fibers in an inert atmosphere. The suggested two-step method consists in preparation of a prepolymer (PANI-O) in N-methylpyrrolidone. The prepared PANI-O dopes were additionally modified by introducing a certain part of a non-solvent (ethanol) to smooth the interdiffusion mass-transfer and prepare defectless precursor fibers. A detailed study of the thermal behavior of the PANI-O fibers by DSC and TGA shows that the maximum exothermic effect is observed at 320–370 °C, associated with formation of a ladder structure, i.e., transformation of the PANI-O into the PNBI-O. As a result, after the heat treatment, the flame-resistant PNBI "Lola" family fibers were obtained with an oxygen index of up to 83, tensile strength of ∼500 MPa, relative elongation of ∼5% and elastic modulus of ∼12 GPa. Flame-resistant semi-ladder PNBI fibers were obtained by acid-free environmentally friendly way through PANI-O prepolymer stage. [Display omitted] • PNBI fibers were obtained by an environmentally friendly way. • PNBI fibers were obtained through a PANI-O prepolymer stage. • Ethanol addition leads to defectless pre-polymer fibers by dry-wet spinning. • LOI of 83 for the H 3 PO 4 impregnated PNBI fibers was obtained. • Outstanding mechanical properties were recorded for the obtained PNBI fibers. [ABSTRACT FROM AUTHOR]

A new method for the effective synthesis of high molecular weight polymer of intrinsic microporosity (PIM-1) powder widely employed for gas separation membranes was successfully developed using precipitative polyheterocyclization process in non-toxic DMSO. [ABSTRACT FROM AUTHOR]

Electrospinning of polyacrylonitrile/DMF dopes containing salts of nickel, cobalt, zirconium, cerium, gadolinium, and samarium, makes it possible to obtain precursor nanofiber mats which can be subsequently converted into carbon nanofiber (CNF) composites by pyrolysis at 1000–1200 °C. Inorganic additives were found to be uniformly distributed in CNFs. Metal states were investigated by transmission electron microscopy and X-ray photoelectron spectroscopy (XPS). According to XPS in CNF/Zr/Ni/Gd composites pyrolyzed at 1000 °C, nickel exists as Ni0 and as Ni2+, gadolinium as Gd3+, and zirconium as Zr4+. If CNF/Zr/Ni/Gd is pyrolyzed at 1200 °C, nickel exists only as Ni0. For CNF/Sm/Co composite, samarium is in Sm3+ form when cobalt is not found on a surface. For CNF/Zr/Ni/Ce composite, cerium exists both as Ce4+ and as Ce3+. Composite CNF mats were platinized and tested as cathodes in high-temperature polymer electrolyte membrane fuel cell (HT-PEMFC). Such approach allows to introduce Pt–M and Pt–MOx into CNF, which are more durable compared to carbon black under HT-PEMFC operation. For CNF/Zr/Ni/Gd composite cathode, higher performance in the HT-PEMFC at I >1.2 A cm-2 is achieved due to elimination of mass transfer losses in gas-diffusion electrode compared to commercial Celtec®P1000. [ABSTRACT FROM AUTHOR]

A new approach to the synthesis of polynaphthoylenebenzimidazoles and heat resistant fiber spinning has been developed using an environmentally friendly and energy efficient method, which operates with solutions of pre-polymers based on 3,3',4,4'-tetraaminodiphenyl ether and 1,4,5,8-naphthalenetetracarboxylic acid dianhydride in N-methylpyrrolidone. Rheological properties of polymer reaction solutions and appropriate coagulant mixtures were investigated for further wet spinning process. The coagulation process was investigated through microscopic observation of solution droplets which imitate jet/fiber cross section surrounded with coagulants of different composition. For the case of the most optimal viscoelastic properties of dopes the best coagulant was found to be a ternary mixture ethanol/water/NMP (20/10/70). Fibers were prepared through the wet spinning from pre-polymers of various molecular weight characterized by intrinsic viscosity. As a result, complex yarns were spun, and their morphology was characterized and mechanical properties were measured. The strength of ~300 MPa and elastic modulus of ~2 GPa and elongation at break of ~20% were reached for the best fibers at average diameter of ~20 µm. After heat treatment "Lola-M" fibers do not burn and do not support combustion in open flame. [ABSTRACT FROM AUTHOR]