Expansion of the operational temperature range for polymer-electrolyte membrane fuel cells (PEMFCs) above 200 °C significantly reduces hydrogen purification requirements. Here, we report a hybrid composite of poly(2,5-benzimidazole) (ABPBI) and CsH2PO4, doped with H3PO4, as a PEM for PEMFC operation at >200 °C up to 250 °C and beyond. The optimal ratio of ABPBI repeating units to CsH2PO4 is 1:1 (mol/mol). Materials are extensively characterized by elemental analysis, scanning electron microscopy, HAADF STEM, elemental mapping, electrochemical impedance spectroscopy, proton conductivity, mechanical testing, and Fourier transform infrared spectroscopy. It is suggested that PEMFCs with the extended operational temperature range (>220 °C) might be categorized as ultrahigh-temperature polymer-electrolyte membrane fuel cells (UT-PEMFCs).

Developing effective approaches for the synthesis of nanomaterials with enhanced properties for applications in high-temperature hydrogen recovery and gas separation technology is a challenging task. Nanoporous polymer films hold significant potential for a diverse range of applications owing to their distinctive characteristics, such as high surface area, adjustable pore size, and selectivity for chemical interactions. The study presents a two-stage method (enabling less toxic solvents) for the production of nanoporous films of heat-resistant and highly permeable fluorine-containing polynaphthoylenebenzimidazole (or polybenzimidazobenzophenanthroline) (PNBI-6F), produced from polymer solutions in DMSO and N-MP. Nanoporosity of the samples is revealed by the CO2 adsorption method. It has been determined that the selection of the solvent can influence the characteristics and structure of the nanoporous polymer matrix. The gas transport properties of the films in the temperature range 20-250 degrees C have also been examined. All of the obtained nanoporous PNBI-6F films retain their mechanical properties at the maximum temperature for an extended period of time. The XRD and DMA methods and gas transport properties unexpectedly reveal a unique two-state behavior with distinct activation energies for gas permeability for each state. The initial state is characterized by lower gas permeability and free volume upon initial heating below 150 degrees C. A second state, which is metastable and characterized by an increase in gas permeability and free volume, occurs above 150 degrees C and persists in the sample over a prolonged period of time after cooling. Overcoming high-temperature gas separation challenges for H2-CO2 mixtures is essential for improving current hydrogen recovery processes and for better purification of reformed hydrogen. Therefore, it is important that the obtained gas transport characteristics significantly exceed the upper bound of the 2008 H2-CO2 Robeson diagram. The obtained results suggest the application of the nanoporous material in high-temperature hydrogen recovery technology.

Ion exchange membranes with high monovalent ion selectivity are essential for extracting valuable components from natural and waste waters. One of the approaches to their fabrication is the creation of nanostructured materials with ion-conducting channels. In this study, materials based on cardo polybenzimidazole (PBI-O-PhT) containing Zn2+, Cr3+ and Cu2+ ions were obtained and used for the first time for electrodialysis separation. The formation of crosslinked structure due to metal-benzimidazole coordination bonds was demonstrated. The obtained metal-polymer membranes have ionic conductivity comparable to commercial ones, reaching 0.32 mS cm-1, and high values of nitrate ion transport numbers (99.2 %). It is shown that the obtained membranes achieve incredibly high values of selectivity coefficients for anion separation. The highest and most stable values were obtained for the copper-containing membrane PBI/Cu-50, which are P(NO3/SO4) = 729, P(Cl/SO4) = 109 and P(NO3/Cl) = 6.66.

For the first time, hollow fiber polynaphthoylenebenzimidazole (PNBI) membranes were obtained by a two-stage acid-free method through a precursor fiber made of poly(o-aminophenylene)naphthoylenimide (PANI-O) by its subsequent heat treatment, leading to the formation of PNBI. The gas separation characteristics of such fiber at room temperature for H2, He, O2 and CO2 were studied by an integral method. It was shown that PNBI is one of the most promising polymers for the manufacture of thermally stable gas separation membranes with high productivity.

Interphase boundary interactions are essential for high-temperature polymer electrolyte membrane fuel cell membrane electrode assembly (MEA) operation. Interactions between the self-phosphorylating polybenzimidazole (PBI)-6F coating on a carbon nanofiber electrode and the self-phosphorylating proton-conducting membrane during MEA operation would improve the cell performance. The presented approach represents a novel path for the development of a PBI membrane-based MEA.

Impedance spectroscopy was used to study proton conductivity changing of pre-dried sulfonated perfluorinated and hydrocarbon (polynaphtoleimide) membranes over time during their hydration. For this purpose, commercial perfluorinated membranes Nafion 212, Nafion 211, Gore 18 and hydrocarbon co-polynaphthoyleneimide (co-PNIS) membranes with different hydrophobicity blocks (ODAS/MDAC and ODAS/MDOT) synthesized in this work were used. It was found that the proton conductivity steady state values of Gore 18 membrane were established faster in humidity atmosphere after its drying than for other membranes studied in this work. This membrane demonstrates also better characteristics with cyclic humidity changes from 35 to 75

A new unique two-stage method for spinning hollow polynaphthoylenebenzimidazole (PNBI) fibers has been proposed. Polyacrylonitrile (PAN) fiber having a porous morphology was coated with poly(o-aminophenylene)- naphthoylenimide (PANI-O) precursor to form a composite fiber with a core–shell structure and subsequently this composite fiber precursor was heat treated in air. The inner PAN fiber underwent oxidative cyclization, accompanied by its high shrinkage, while the PANI-O shell, due to heterocyclization, turned into a PNBI-O shell, and the inner space of the hollow fiber was only partially filled with cyclized PAN.

A new type of polybenzimidazole-based proton exchange composite membrane, poly(2,5-benzimidazole) (ABPBI)–CsH2PO4, was obtained. The possibility of application of the composite membrane in a hydrogen–air fuel cell operating at 160–250 °C was demonstrated. In the fuel cell tests, the maximum power density reached ~400 mW/cm2 at 250 °C. The resulting data along with high open circuit voltage (0.92–0.95 V) indicate high quality and low hydrogen crossover of the membrane.

High-temperature polymer-electrolyte membrane fuel cells (HT-PEMFCs) operate at 150-200 degrees C, making it possible to use hydrogen contaminated with carbon monoxide. However, the main drawback for their distribution is the need to improve stability of membrane-electrode assembly components, especially cathodes. The cathodes based on carbon nanofiber (CNF) mat are free-standing (self-supporting), and are prepared using the method of electrospinning from a polyacrylonitrile solution containing Zr and Ni salts, followed by the stabilization and pyrolysis steps. The composite Zr, Ni-containing Pt/CNF cathodes are obtained after Pt nanoparticle deposition on the CNF surface. A novel self-phosphorylating polybenzimidazole (PBI-6F) was deposited to the surface of Pt/CNF to improve the triple-phase boundary. Substitution of OMe-groups and hydrophobic nature of CF3-groups lead to improvements in proton conductivity and gas transport of the cathode as well as proton-conducting contacts between cathode and membrane. The materials are studied using N-2 and CO2 gas adsorption, TEM, HAADF STEM. The operation of the H-2/air HT-PEMFC shows that the application of the PBI-6F-covered PBI-6F/Pt/CNF cathode results in an enhancement of HT-PEMFC performance, compared with the uncovered Pt/CNF cathode, providing similar to 20% increase in maximum power density.

Polynaphthoylenebenzimidazoles (PNBI) with keto-(PNBI-CO) and sulfonic (PNBI-SO2) bridge groups were obtained by solid-state polycyclization of polyaminoimides (PANI) synthesized by polycondensation of 1,4,5,8-naphthalenetetracarboxylic acid dianhydride with 3,3`,4,4`-tetraaminobenzophenone and 3,3`,4,4`-tetraaminodiphenylsulfone in N-methylpyrrolidone, respectively. The polycondensation process and resulting chemical structure of PANI and PNBI were controlled by 1H NMR, 13C NMR and IR spectroscopy. It is shown that the temperature of solid-state polycyclization change makes it possible to obtain polymers of several of cyclization degrees. The experimental values of the gas permeability and diffusion coefficients for He, H2, N2, O2, CO2, CH4 were obtained. The gas solubility coefficients and the ideal selectivity for various gas pairs were calculated. It has been established that, in terms of the permeability-selectivity ratio, completely cyclized PNBIs occupy a more favorable position compared to incompletely cyclized ones. This result is important for polymer and a method selection to develop a selective layer of new composite membranes. The gas transport characteristics achieved for competely cyclized PNBI-SO2, as well as the film-forming properties, along with the very high thermal stability of polymers of this polymer class, are interest of further expanding the range of PNBI obtained, as well as the prospects for such new polymers using of in various gas separation processes.

The synthesis of porous organic polymers (POPs) based on a polymer of intrinsic microporosity (PIM), which represent a new class of promising materials, has been studied in detail. These porous systems are formed by precise joining of organic building blocks through covalent bonds in order to create predefined assemblies and can possess a three-dimensional (3D) or 2D-layered structure. The model reactions are considered and porosimetry studies are performed for the resulting POPs.

Polybenzimidazoles (PBI) doped with phosphoric acid are a promising electrolyte for medium-temperature fuel cells. However, to be effective at high temperatures in the presence of acid, the mechanical and conductive properties of the material must be stable and no critical increase in gas permeability is required. This work proposes an approach to improve the properties of PBI-O-PhT-based materials by combining two previously known methods: covalent crosslinking with silane (3-bromopropyl)trimethoxysilane (Si-Br) and doping with silicon oxide (SiO2), including grafted imidazolinpropyl groups (SiO(2)Im). The silanol cross-linked samples exhibited higher stability when tested with Fenton's reagent and retained their morphological integrity even after 360 h of testing. The study shows that covalent crosslinking improves the stability of dopant particles in the membrane matrix and prevents their leaching during acid treatment. Additionally, the incorporation of silicon oxides enhances the proton conductivity of samples with covalent cross-linking and reduces gas permeability compared to the original PBI membrane. Proton conductivity of the covalent cross-linked samples reaches 50 and 55 mS center dot cm(-1) at oxide contents of 5 wt% SiO(2)Im and 10 wt% SiO2, respectively.

This review focuses on the synthesis and investigation of fluorine-free heterocyclic polyheteroarylenes (PHAs) which can be used as proton exchange membranes (PEMs) in hydrogen–air fuel cells at 60–200 °C. Below 100 °C, sulfonated PHAs are typically employed as PEMs. Among them, polynaphthoyleneimides with SO3H substituents have received significant attention. At higher temperatures (>120 °C), polybenzimidazole-based PEMs doped with phosphoric acid exhibit superior performance.

Homogeneous films of polynaftoylenebenzimidazole (PNBI-sigma) were obtained by two-stage synthesis from pre- polymer films by thermal cyclization at 350 degrees C. The presence of micropores in PNBI-sigma films is shown by the method of CO2 2 sorption, the micropore specific surface area is 285 m2/g. 2 /g. Gas permeability of He, H2, 2 , CO2, 2 , CH4, 4 , O2 2 and N2 2 was studied by differential gas chromatographic method in the temperature range of 50-250 degrees C, and the activation energies of permeability were determined. At 250 degrees C, hydrogen permeability coefficient of 220 Barrers and ideal selectivity of 17 for H2/CO2 2 /CO 2 were achieved, which significantly exceeds the values for the upper bound of 2008 Robeson diagram. The analysis of permeability of the components of mixtures of gases H2/CO2 2 /CO 2 and H2/CH4 2 /CH 4 of various compositions at 250 degrees C showed that with a decrease in the concentration of the sorbed component (CO2 2 or CH4) 4 ) a sharp increase in the separation factor is observed. When the composition of the H2/ 2 / CO2 2 mixture is 70/30, the H2/CO2 2 /CO 2 separation factor increases by more than an order of magnitude compared to the selectivity for individual gases while the hydrogen flow is maintained. The obtained experimental data demonstrate the capabilities of PNBI-sigma for high-temperature separation processes, including the separation of industrial hydrogen-containing mixtures.

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.

Polyacrylonitrile and polyheteroarylenes, such as polybenzimidazole (PBI) and a polymer of intrinsic microporosity (PIM-1), have been employed to prepare nanoporous electrospun carbon nanofiber (CNF)-based materials for high-temperature proton-exchange (or polymer-electrolyte) membrane (HT-PEM) fuel cells. The nanoporous CNF mats are obtained by Nanospider (needle-free) electrospinning method from polymer solution followed by pyrolysis at 1500 degrees C to form nanoporous electrospun polymer nanofiber self-supporting mats with micropores (D < 2 nm) and mesopores (D 2-50 nm). The nanoporous CNF samples are extensively characterized by N-2 and CO2 adsorption applying the BET, BJH, Dubinin-Radushkevich (DR), NLDFT, and GCMC methods, CO2 uptake, Raman spectroscopy, elemental analysis, electrical conductivity, electron microscopy, and XPS. The role of the polymer precursor on the obtained values of specific surface area (SSA) and volume for micro- and mesopores is presented and discussed. The PBI-based CNF material reaches a micropore SSA of 919 m(2) g(-1) and CO2 uptake of 4.0 mmol g(-1) derived from CO2 adsorption (273 K) data, and a micropore SSA of 873 m(2) g(-1) according to the t-method derived from N-2 adsorption data. Close values confirm higher accessibility of micropores compared with the case of PIM-based CNF, where the micropore SSA values derived from CO2 and N-2 adsorption data are different and indicate the partial inaccessibility of micropores for low-temperature nitrogen adsorption (77 K). Platinum-decorated CNF mats are successfully tested as electrodes for HT-PEM fuel cells, showing the feasibility of using the mats as cathodes; nevertheless, further optimization is required. For CNF anodes, the HT-PEM fuel cell performance reaches 0.69 V at 0.2 A cm(-2) and 0.53 W cm(-2) at 1.4 A cm(-2) which permits the use of the Pt/CNF mats as anodes.

Carbon nanofibers are currently used in many applications including electrochemical power sources, particularly, fuel cells. Their properties are highly dependent on the micro- and mesoporous structure. Here we provide a porosimetric analysis of the polyacrylonitrile-based electrospun composite Zr- and Ni-containing carbon nanofiber mats by N2 and CO2 adsorption methods for the first time. It was found that pyrolysis temperature affects specific surface area and volume: the values increase for the sample pyrolyzed at 900 °C compared with the initial stabilized nanofibers (300 °C, air) according to the Dubinin --- Radushkevich, non-local density functional theory (NLDFT) and grand canonical Monte-Carlo methods (GCMC). For higher pyrolysis temperatures (1000 and 1200 °C), the porosimetric parameters decrease compared with the one pyrolyzed at 900 °C. According to the NLDFT and GCMC pore size distribution, the difference for pyrolyzed samples is mostly related to a sharp decrease in the specific surface area for pores with a size of ~ 0.5 nm and an increase for pores at 0.55--0.8 nm compared with the initial stabilized sample. The study demonstrates a way to adjust porosimetric parameters depending on the pyrolysis conditions of the nanofiber mats, since it can improve characteristics of such type of carbon materials in electrochemical devices

Derivatives of naphthalene-diimide (NDI) are among the most studied and popular organic semiconductors showing n-type conductivity. However, the structure and optoelectronic properties of crystalline NDIs N-functionalized with conjugated donors have not been investigated yet. In this study, a novel donor-acceptor compound NDI-Stb bearing one NDI core, as an acceptor, and two stilbene moieties covalently linked via imide positions of NDI, as a donor, was synthesized. A combined experimental and theoretical approach was applied to study the structure and properties of NDI-Stb molecules and its crystals. We found and explained why optical absorption and high-frequency Raman spectra are inherited from those of donor and acceptor moieties, but photoluminescence is determined by the properties of the whole molecule. We resolved the structure of NDI-Stb single crystals and found that strong intermolecular interactions operate along two directions, for which NDI cores stack either on similar cores or on stilbene moieties. These interactions cause suppression of dynamic disorder indicated by a weak low-frequency Raman signal and solid-state luminescence enhancement. Ambipolar charge transport was predicted, and electron transport was experimentally observed in NDI-Stb polycrystalline thin films. The results obtained highlight the potential of using NDIs N-functionalized with conjugated donor moieties in optoelectronic applications, and improve the understanding of structure-property relationships necessary for the rational design of novel donor-acceptor organic semiconductors.

High-temperature polymer-electrolyte membrane fuel cells (HT-PEM FC) are a very important type of fuel cell since they operate at 150–200 °C, allowing the use of hydrogen contaminated with CO. However, the need to improve stability and other properties of gas diffusion electrodes still hinders their distribution. Anodes based on a mat (self-supporting entire non-woven nanofiber material) of carbon nanofibers (CNF) were prepared by the electrospinning method from a polyacrylonitrile solution followed by thermal stabilization and pyrolysis of the mat. To improve their proton conductivity, Zr salt was introduced into the electrospinning solution. As a result, after subsequent deposition of Pt-nanoparticles, Zr-containing composite anodes were obtained. To improve the proton conductivity of the nanofiber surface of the composite anode and reach HT-PEMFC better performance, dilute solutions of Nafion®, a polymer of intrinsic microporosity (PIM-1) and N-ethyl phosphonated polybenzimidazole (PBI-OPhT-P) were used to coat the CNF surface for the first time. These anodes were studied by electron microscopy and tested in membrane-electrode assembly for H2/air HT-PEMFC. The use of CNF anodes coated with PBI-OPhT-P has been shown to improve the HT-PEMFC performance.