Iv. I. Ponomarev

Synthesis and molecular-mass characteristics of some cardo poly(benzimidazoles)

The GPC procedure for analyzing molecular mass characteristics of cardo poly(benzimidazoles) has been developed. In most cases, the reaction between 4,4′-oxydibenzene-1,2-diamine and 4,4′-(3-oxo-1,3-dihydroisobenzofuran-1,1-diyl)dibenzoic acid in Eaton’s reagent is accompanied by formation of a microgel. Depending on the synthesis conditions (temperature, duration of heating, and content of phosphorus pentoxide in the reaction mixture), polymers with both unimodal and bimodal molecular mass distributions can be prepared. Formation of the microgel fraction is observed for many representatives of poly(benzimidazoles) of various chemical structures. Based on the experimental evidence, the most probable pathway is suggested for the branching side reaction of poly(benzimidazoles) during their synthesis in Eaton’s reagent.

Design of electrodes based on a carbon nanofiber nonwoven material for the membrane electrode assembly of a polybenzimidazole-membrane fuel cell

23 The creation of electrodes for hydrogen–air fuel cells with a polymer electrolyte membrane is a com plex challenge, both fundamental, and scientific and technical. Increase in the fuel cell efficiency directly depends on the quality of the electrodes. Whereas the heart of such a fuel cell is usually believed to be a pro ton conducting membrane, the drive of the fuel cell should be considered to be carbon gas diffusion elec trodes (GDEs) containing nanosized platinum parti cles as an electrocatalyst. Approaches to designing GDEs are quite versatile, but generally reduce to the application of a catalytic ink (aqueous dispersions of perfluoropolymers and electrocatalysts (Pt/C)) to a carbon paper or tissue with a perfluorinated hydro phobic microporous layer [1, 2].

Composites based on cardo polybenzimidazole and hydrated silicon dioxide for phosphoric acid fuel cells

Phosphoric acid-doped composites based on cardo polybenzimidazole and hydrated silicon dioxide have been synthesized. The effect of synthesis conditions on the properties of the resulting composites has been investigated. The silicon dioxide-modified membranes have a higher proton conductivity. Hydrated silicon dioxide substantially suppresses phosphoric acid washout from the hybrid membranes exposed to water vapor. The diffusion permeability of the composite membranes has been measured in solutions of various salts. Some membranes samples have been tested under fuel cell operation conditions.

Hybrid membranes based on polybenzimidazole and hydrated zirconia

Hybrid membranes based on polybenzimidazole and hydrated zirconia doped with phosphoric acid have been synthesized. The effect of synthesis conditions on the properties of the resulting materials has been studied. It has been shown that the modification of the membranes makes it possible to increase their proton conductivity. The introduction of hydrated zirconia decreases the amount of phosphoric acid leached out from the membrane exposed to water vapor. The diffusion permeability of composite membranes in solutions of various salts has been studied. Model tests of some samples under fuel cell operating conditions have been performed.

Chemical modification of cardo poly(benzimidazole) using “click” reaction for membranes of high-temperature hydrogen fuel cells

Phosphonethylated poly(benzimidazole)s (PEP BIs) were obtained for the first time in the Nesmey anov Institute of Organoelement Compounds, Rus sian Academy of Sciences, by the polymer analogous reaction of high molecular weight PBI–O–PT poly mer [3] via the reaction with O,O diethyl vinylphos phonate [4] (Scheme 1) and successfully studied in the construction of the membrane electrode block (MEB) of the hydrogen HTFC.

Synthesis and studies of polybenzimidazoles for high-temperature fuel cells

A number of polybenzimidazoles (PBIs) were synthesized and tested in real fuel cells. The possibility of introducing phosphoric groups in PBIs was studied. The phosphorylated and fluorine-containing PBIs obtained by click reactions were investigated.

Electrospun nanofiber pyropolymer electrodes for fuel cells on polybenzimidazole membranes

After the deposition of Pt on their surface, the carbon nanofiber materials synthesized by sequential oxidation and pyrolysis of electrospun nanofiber mats based on polyacrylonitrile are used as the gas-diffusion electrodes for high-temperature hydrogen–air fuel cells on a polybenzimidazole (PBI) proton-conducting membranes. In contrast to the traditional methods of electrode preparation in which the catalyst (Pt) nanoparticles are localized on the surface of carbon black which is applied as “ink” on the conducting support (carbon paper or tissue), in this study the Pt nanoparticles are being deposited and developed on the surface carbon nanofibers to form a combined gas-diffusion material. In the tests, the resulting electrodes demonstrate good efficiency within hydrogen-air fuel cells on the PBI membrane.

Molecular Mass Characteristics and Solution Behavior of Some Cardo Polybenzimidazoles

The behavior of dilute solutions of cardo polybenzimidazoles based on 3,3′4,4′-tetraaminodiphenyl ether; 3,3′,4,4′-tetraaminodiphenyl sulfone; and 4,4′-diphenylphthalidedicarboxylic acid in solvents of various natures has been studied by the methods of dynamic light scattering, sedimentation, and viscometry. All of the polymers have been found to contain a microgel fraction. For each fraction, the diffusion coefficient and the particle size are determined. The experimental characteristics of macromolecules correspond to the conformational rigidity calculated by a computer simulation procedure.

Development of methanol–air fuel cells with membrane materials based on new sulfonated polyheteroarylenes

New proton-conducting membranes were synthesized from sulfonated polynaphthoyleneimide (SPNI) and polytriazole (SPTA), which are of interest for use in portable methanol fuel cells. The membrane electrode assembly (MEA) based on SPNI and SPTA showed power and voltage-current characteristics comparable to those of MEA based on Nafion®-117. The direct and reverse polarization curves coincided almost completely in shape, indicating that the obtained characteristics are stable. At a voltage of 0.3 V and a temperature of 40°С, the current density and power density reached 68 mA cm–2 and 20.5 mW cm–2, respectively.

Development of hydrogen–air fuel cells with membranes based on sulfonated polyheteroarylenes

Proton-conducting membranes based on sulfonated polynaphthoyleneimide (PNI) and polytriazole (PTA) are synthesized that can be used in portable hydrogen–air fuel cells (HAFC). Membrane–electrode assemblies (MEAs) based on sulfonated PNI and PTA membranes in individual HAFC manifested power and voltammetric characteristics exceeding the characteristics of MEA based on the commercial Nafion-212 membrane. Thus, the current density of 320 mA cm–2 and the power density of 160 mW cm–2 are obtained at the room temperature with no pressure or gas humidification at the voltage of 0.5 V. Also activity of the oxygen electroreduction Pt–Fe/C (30 wt % of metals in total) catalyst synthesized on the basis of coordination compounds is tested in MEA HAFC. It is shown that the values of power for MEAs with the cathodic Pt–Fe/C catalyst at the voltage of 0.5 V, at the room temperature, without additional pressure and gas humidification considerably exceed the corresponding values for MEAs with the commercial E-TEK 20% Pt/C catalyst.