2.5.3. Current–voltage curves
The details of the method used to obtain the current–voltage (I–V) characteristic curves of the membranes are described in our previous paper. 28 Briefly, first, the membranes were equilibrated in the test solution for 24 h. All membranes were characterized using 0.5 M NaCl and 0.3 M Na2SO4 solutions as the test and electrode rinsing solutions, respectively. The test cell was connected to a HSPY-120-01 (Hanshengpuyuan Technology Co. Ltd., China) DC power supply via two Ti-coated ruthenium oxide electrodes. The current was incrementally increased and the changes in trans-membrane potential were recorded periodically (every 30-40 s) using a multimeter connected to Ag/AgCl electrodes.