Marek Malinowski

Synthesis and characterization of para- and meta-polybenzimidazoles for high-temperature proton exchange membrane fuel cells

In this article, two polybenzimidazoles (PBIs) were synthesized by the polycondensation reaction of 3,3′-diaminobenzidine with terephthalic acid (p-PBI) or isophthalic acid (m-PBI) for application in high-temperature proton exchange membrane fuel cells. Two kinds of purification (P1, P2) were applied to clean the polymers. The chemical structure of PBI polymers was confirmed using Fourier transform infrared (FTIR) spectroscopy. Polymers after P1 can be soluble and cast into film only from hot sulfuric acid solution (H2SO4), whereas both polymers after P2 were soluble in dimethylacetamide solution. Polymer films cast from H2SO4 were investigated using FTIR. The thermal stabilities of PBIs and PBI films were studied using the thermogravimetric analysis and the first derivative of the TG method. The temperature of 5% weight loss (T 5%) for both PBIs ranges from 136 to 312°C under nitrogen atmosphere, depending on the dicarboxylic acid used and the kind of purification. The PBI films exhibited T 5% at 55°C because of the protonation of nitrogen atom in PBI by hydrogen atom of hydroxyl group in H2SO4. Electrical behavior of the two polymers was tested using electrochemical impedance spectroscopy for gold (Au)/PBI/Au architecture. For both measured polymers, Nyquist plots are presented with fittings based on circuit models.

Synthesis and characterization of two new TiO2-containing benzothiazole-based imine composites for organic device applications

The effect of the presence of titanium dioxide in two new imines, (E,E)-(butane-1,4-diyl)bis(oxybutane-4,1-diyl) bis(4-{[(benzo[d][1,3]thiazol-2-yl)methylidene]amino}benzoate) (SP1) and (E)-N-[(benzo[d][1,3]thiazol-2-yl)methylidene]-4-dodecylaniline (SP2), on the properties and stability of imine:TiO2 composites for organic device applications were examined. The investigated titanium dioxide (in anatase form, obtained via the sol–gel method) exhibited a surface area of 59.5 m2/g according to Brunauer–Emmett–Teller theory, and its structure is a combination of both meso- and microporous. The average pore diameter calculated by the Barrett–Joyner–Halenda method was 6.2 nm and the cumulative volume of pores was 0.117 m3/g. The imine SP1 exhibited columnar organization (Col), while SP2 revealed a hexagonal columnar crystalline phase (Colhk). The imine:TiO2 mixtures in various weight ratio (3:0, 3:1, 3:2, 3:3) showed a lower energy gap and HOMO–LUMO energy levels compared to pure TiO2. This implies that TiO2 provides not only a larger surface area for sensitizer adsorption and good electron collection, but also causes a shift of the imine energy levels resulting from intermolecular interaction. Also the temperature of the phase transition was slightly affected with the increase of TiO2 concentration in imine-based composites. The changes observed in the Fourier transform middle-infrared absorption (FT-MIR) spectra confirmed the significant influence of TiO2 on structural properties of both investigated imines. Similar interactions of oxygen vacancies existing on the TiO2 surface with SP1 and SP2 were observed. The imine:TiO2 mixtures showed good air stability and reusability, which demonstrates its potential for organic device applications.