## 2 Materials and Methods
### Membrane Characterization  
To verify the polymerization of the electrolyte monomer and the cross-linking agent introduced into the porous substrate using the pore-filling membrane manufacturing technology applied in this study, Fourier transform infrared spectroscopy (FT-IR) was employed for analysis. For the FT-IR analysis (Spectrum 100, PerkinElmer, Waltham, MA, USA), the pore-filling membrane was cut into 1 \(\times\) 1 cm\({}^{2}\) sections, dried, and measured using the attenuated total reflectance method to obtain spectra. The characteristic peaks in the spectra were then analyzed. The OH\({}^{-}\) conductivity of the membranes was measured in 1.0 M KOH (85%, Junsei Chemical Co., Ltd., Tokyo, Japan) at 60 \({}^{\circ}\)C using a custom-made through-plane clip cell with a potentiostat/galvanostat (SP-150, Bio-Logic Science Instruments, Seyssinet-Pariset, France). Prior to measurement, the AEMs were soaked in 1.0 M KOH for 24 hr. Potentiostatic electrochemical impedance spectroscopy measurements were conducted at frequencies ranging from 100 kHz to 1 Hz with an amplitude of 10 mV. The procedure was repeated at least five times to obtain accurate OH\({}^{-}\) conductivity resistance values [29; 30]. The OH\({}^{-}\) conductivity was calculated as:  
\[Ion\ conductivity:\ \sigma\ \left(\text{mS}\cdot\text{cm}^{-1}\right)=\frac{L}{R \cdot A}\]  
where \(L\) is the thickness of the membranes, \(R\) is the measured impedance of the membranes, and \(A\) is the specific area of the membranes. The IEC of the membranes was measured using the acid-base titration method. Prior to the IEC measurement, the fabricated membrane, with a size of 12 cm\({}^{2}\), was immersed in a 1.0 M KOH solution for 24 h to exchange the Cl\({}^{-}\) ions in the QA functional groups of the membrane with OH\({}^{-}\) ions. After this, the membrane was rinsed several times with D.I. water and then immersed in a 0.01 M HCl (35\(-\)37%, Junsei Chemical Co., Ltd., Tokyo, Japan) solution for 24 h to convert the OH\({}^{-}\) ions in the membrane back to Cl\({}^{-}\) ions. The HCl solutions containing OH\({}^{-}\) ions were titrated using an automatic titrator (848 Tirrino Plus, Metrohm, Herisau, Switzerland) with a 0.01 M NaOH solution. All procedures were conducted at room temperature (RT), and the process was repeated three times to obtain accurate IEC values [29; 30]. The IEC was calculated as:  
\[Ion\ exchange\ capacity\ (IEC):\ \left(\text{meq}\cdot\text{g}^{-1}\right)=\frac{C_{NaOH }\times\left(V_{eq}-V_{blank}\right)}{W_{memb}}\times X\]  
Figure 2: Schematic illustration for the preparation of PFAEMs. where \(W_{memb}\) is the dry weight of the membranes, \(C_{NaOH}\) is the normal concentration of the NaOH solution, and \(V_{eq}\) is the titrated volume of the NaOH solution for samples, \(V_{blank}\) is the titrated volume of the NaOH solution for blanks, and \(X\) is the ratio of total HCl volume to the sampling volume of HCl used for titration. The hydrogen permeability of the PFAEM was evaluated using the membrane and a pair of electrodes. The electrodes were fabricated with Pt/C (Pt 46.4%, TKK TEC10F50E, TANAKA, Tokyo, Japan) and carbon paper (JNT20-A3, JNTG, Gyeonggi-do, Republic of Korea), with a Pt loading of 0.4 mg cm\({}^{-2}\). A graphite single cell with an active area of 9 cm\({}^{2}\) was assembled for the tests. Hydrogen permeability was measured under fully hydrated H\({}_{2}\)/N\({}_{2}\) conditions (0.2/0.2 L min\({}^{-1}\)) at differential pressure using current measurement. The current was measured with an SP-150 potentiostat over a voltage range from 0.1 to 0.8 V at a scan rate of 0.01 V s\({}^{-1}\)[29; 30].