For the STz25 membranes, area swelling in 5 wt% KOH was 20%, which decreased to around 7% when the KOH concentration increased to 15 wt% KOH. Interestingly, the geometric area of the membrane remained unchanged in 20 and 25 wt% KOH. The STz30 membranes showed higher swelling throughout the entire range of KOH concentration range, consistent with the electrolyte uptake trend. The swelling ranged from 56% in a 10 wt% KOH solution to 3% in a 25 wt% KOH solution.