Composite electrolytes based on ammonium salt of 12-phosphotungstic acid and calixarene

The physicochemical properties of composite solid electrolytes based on ammonium salt of 12-phosphotungstic acid and calixarene[4]sulfonic acid, which are thermally stable up to 200 °C, with calixarene content from 0 to 100 mol% were investigated. The proton conductivity and the activation energy of the conductivity were found to exhibit two types of behavior. At calixarene content below 50 mol% the proton conductivity of electrolytes is determined by properties of the initial ammonium salt of phosphotungstic acid (2.3 mS/cm at 30 °C and 32% RH), while above 50 mol% the conductivity corresponds to the conductivity of the initial calixarene (8.3 mS/cm at 30 °C and 32% RH). To describe such systems, the percolation theory was used. The obtained percolation threshold at 50 vol% is in a good agreement with the experimental data. The observed behavior was explained on the basis of the results obtained with the help of differential scanning calorimetry, scanning electron microscopy and impedance spectroscopy in wide range of temperature (from +70 to −70 °C).