Electrotransport and thermal properties of tetrabutylammonium hydrogen sulfate

Abstract

The thermal properties and conductivity of quaternary ammonium compound Bu4NHSO4 were firstly investigated. Tetrabutylammonium hydrogen sulfate is thermally stable up to 260 °C, followed by slow decomposition. It was shown that the enthalpy of Bu4NHSO4 melting is −48.4 J/g. The conductivity of Bu4NHSO4 changes in a wide range: from 10−8 S/cm at 60 °C to 10−2 S/cm in the melt. The conductivity of the melt (165–180 °C) is higher than 10−2 S/cm with activation energy of conductivity 0.5 eV, while activation energy at lower temperatures (50–125 °C) is equal to 0.8 eV. The most important factors affecting the conductivity of the compound are structural characteristics, the nature of the bonding of sulfate tetrahedra, and the energy of hydrogen bonds. The crystal structure of Bu4NHSO4 consists of sulfate tetrahedra pairwise linked into isolated dimers by strong hydrogen bonds with significant distances for proton transfer. It hinders the formation of conductivity pathways.