Alginic acid–imidazole composite material as anhydrous proton conducting membrane

Modeling protic dicationic ionic liquids based on quaternary ammonium, imidazolium or pyrrolidinium cations and bis(trifluoromethanesulfonyl)imide anion: Structure and spectral characteristics

Protic dicationic ionic liquids (PDILs) have attracted growing attention owing to their applications in domains of electrochemistry, proton conducting materials and other diverse areas. In the present work protic dicationic ionic liquids (PDILs) comprising of quaternary ammonium-, imidazolium- or pyrrolidinium-dications and bis(trifluoromethanesulfonyl)imide (Tf₂N‾) anion have been modelled as the dication-(Tf₂N)₂ complexes. Electronic structure, vibrational and ¹H NMR spectra of these complexes have been derived employing the M06-2x density functional theory. Theoretical calculations have shown that the strength of cation-anion binding follows the order: methylpyrrolidinum > quaternary ammonium > butylpyrrolidinium > imidazolium, which can be attributed to number and strength of N-H---O and C-H---O interactions. The dication-(Tf₂N)₂ complexes emerge with signature in frequency up-shift of the characteristic N-H stretching in their infrared spectra. Underlying molecular interactions are unveiled through natural bond orbital analyses, Quantum theory of atoms in molecules (QTAIM) and noncovalent interaction reduced density gradient method. The calculations have shown that cation-anion binding energies increase linearly with kinetic energy density component G(r) in QTAIM analysis and proton affinities in the PDILs. A correlation between change in free energies accompanying the dication-(Tf₂N)₂ complexes and proton affinities has also been established.

Local structure and hydrogen bond characteristics of imidazole molecules for proton conduction in acid and base proton-conducting composite materials

Protons in composite materials of acidic polymers and imidazole molecules transport with rotational motion of imidazole in hydrogen bonds.

Enhanced proton conductivity of proton exchange membrane at low humidity based on poly(methacrylic acid)-loaded imidazole microcapsules

Poly(methacrylic acid)-loaded imidazole microcapsules with high water retention property and significantly enhanced membrane proton conductivity at low humidity.

FT NIR Raman studies of alginic acid-benzimidazole polymer composite

New bio-inspired polymer composites of alginic acid and benzimidazole were created and characterized by FT NIR Raman spectroscopy. The obtained films with 1:0.5, 1:1 and 1:1.5 molar ratio are homogeneous, with good mechanical properties. Raman spectra recorded at room temperature revealed that the obtained films are a new compound with a different molecular structure and physical properties compared with pure substrates: alginic acid and benzimidazole. Raman band related to vibration of COOH entity at 1740 cm(-1) of alginic acid disappears in the alginic acid:benzimidazole composites, in which new Raman band related to COO(-) was found. Additionally, characteristic lines observed in polymer composites which may be associated with vibrations of NH groups, can be attributed to the linking of proton to deprotonated N atom in benzimidazole group. Possibility of such proton exchange is a promising property which might facilitate the application of obtained composites to anhydrous proton conducting electrolytes in fuel cells.

New 2-methylimidazole-dicarboxylic acid molecular crystals: crystal structure and proton conductivity

Three new proton conducting molecular crystals, 2-methylimidazole glutarate, 2-methylimidazole suberate and 2-methylimidazole azelate, were obtained and their structure was determined by the x-ray diffraction method. The structure of the crystals was found to be of layer-type. A hydrogen bond network between the heterocycle, glutaric acid and water molecules was apparent in a single layer of 2-methylimidazole glutarate, whereas chains consisting of two heterocyclic molecules linked with hydrogen bonds with dicarboxylic acid were distinguished in a single layer of 2-methylimidazole suberate and azelate crystals. Thermal stability of the crystals was characterized by differential scanning calorimetry and the electrical conductivity was studied by the impedance spectroscopy method. The maximum conductivity of 2-methylimidazole glutarate pellets amounts to 3.3 × 10(-2) S m(-1) at 325 K, in the case of 2-methylimidazole suberate pellets the maximum conductivity is 2.4 × 10(-4) S m(-1) at 348 K and for 2-methylimidazole azelate pellets the maximum conductivity reaches 6.9 × 10(-4) S m(-1) at 353 K.

Synthesis and proton conductivity of anhydrous dendritic electrolytes

Water soluble PEG cored dendritic hexa-acid which comprises peripheral carboxylic acidic groups were prepared via nucleophilic substitution reactions. Novel anhydrous proton conducting electrolytes were prepared by incorporation of the heterocyclic protogenic solvent imidazole (Im) into PEG cored dendritic hexa acid, (PEG-HA), at several molar ratios of Im to-COOH units of PEG-HA. The complexation of PEG-HA and Im was illustrated by infrared spectroscopy (FT-IR). The materials are thermally stable up to 150 °C as evidenced by thermogravimetry analysis (TGA). Differential scanning calorimetry (DSC) results verified that the organic electrolytes are homogeneous and amorphous. The proton conductivities were characterized by means of AC impedance spectroscopy and a maximum conductivity of 1 × 10−3 S/cm was measured at 120 °C in the anhydrous state.