The ionic conductivity of the STz25 and STz30 membranes was measured at room temperature within the KOH concentration range of 5-25 wt%, as shown in Figure and, respectively. However, due to the extensive swelling observed for the STz30 membrane in the lower concentration range, the ion conductivity was recorded in 15-25 wt% KOH. The STz30 membrane showed higher ion conductivity compared to STz25, due to the higher electrolyte uptake. The ion conductivity followed same trend as the electrolyte uptake, and decreased as the concentration of the surrounding KOH solution increased. For STz30, the room temperature conductivity reached 91 mS cm -1 in 15 wt% KOH, which decreased to 62 mS cm -1 in 25 wt% KOH. For STz25, the ion conductivity dropped from 47 mS cm -1 to 21 mS cm -1 as the KOH concentration increased from 5 to 25 wt%. For comparison, the ion conductivity of m-PBI in 15 wt% KOH at room temperature is around 70 mS cm -1 . The conductivity dependence on temperature for STz25 and STz30 in 15 wt% KOH is