2.3.6. Ionic Conductivity

The ionic conductivity of the membranes was measured by electrochemical impedance spectroscopy (EIS). A Solartron 1260 equipment (Farnborough, UK) was used as an impedance analyzer with a Solartron 1287 electrochemical interface in a frequency range between 10⁻¹ and 10⁶ Hz. The conductivity cell used consists of two half-cells containing the liquid electrolyte (KOH) connected to each other through a 1.1 cm radius hole where the membrane was placed [33]. The configuration consists of four electrodes, of which two graphite electrodes act as working electrodes and two saturated Ag/AgCl electrodes act as reference electrodes. Electrochemical measurements were made at different concentrations of the liquid electrolyte (between 10⁻⁴ and 10⁻¹ M). Prior to ionic conductivity measurements, the chlorinated membranes were immersed in a 1 M KOH solution for 24 h, and consequently these were measured in OH⁻ form. The ionic conductivity of the membrane was determined using the following equation:

where σ_m (S cm⁻¹) is the ionic conductivity, L (cm) the thickness, A (cm²) the experimental area, and R_m (Ω) is the measured resistance value of the membranes. It was obtained from the impedance plot which was analyzed with the Z-View impedance analyzer software.

The influence of the temperature in the ionic conductivity of the membranes was studied by using a KMF 115 climate chamber (Binder GmbH). Conductivity measurements were made in a temperature range between 30 and 80 °C, using an electrolyte concentration of 10⁻³ M. The activation energy (E_a in kJ·mol⁻¹) was calculated using Arrhenius equation in its linearized form:

where σ, σ_o, R, and T are the conductivity of hydroxide in S·cm⁻¹, the pre-exponential factor, the constant of the ideal gases in J·(mol·K)⁻¹ and the temperature in K, respectively.