Proton conductivity and structural properties of tetraethylammonium hydrogen sulfate

The properties of high-temperature phases of Et 4 NHSO 4 and the temperature ranges of their stability were investigated. The sequence of the reversible phase transitions at 147°C and 160°C with the enthalpies of − 3.28 J/g and − 8.99 J/g, respectively, was observed. It was shown that at 160° C the I4 1 /acd phase with the unit cell parameters a = 14.0430(8) Å, c = 25.686(3) Å with higher degree of sulfate tetrahedra disordering was formed. This phase exists up to the melting of Et 4 NHSO 4 , 245°C. The proton conductivity of Et 4 NHSO 4 was determined firstly and the temperature dependence varies widely from 10 −8 S/cm at 90°C up to ~ 10 −2 S/cm at the melting. The conductivity of the Et 4 NHSO 4 is rather low and does not exceed 5*10 −6 S/cm at temperatures below 210°C. The structural closed dimers of hydrogen-bonded sulfate anions at low temperatures hinder the effective proton transfer. Spectral characteristics of room-temperature phase also have been discussed.