## 3 Results and Discussion
Furthermore, as shown in Figure 10c, the E3-C10 PFAEM demonstrated higher ohmic overpotential and total  
Figure 9: Chemical stability of PFAEMs: (**a**) variation in ion conductivity of E3-C10 and E3-C11 PFAEMs stored at 4 M KOH and 60 \({}^{\circ}\)C as a function of storage time; (**b**) the decrement of OH\({}^{-}\) conductivity change between BOT and EOT. resistance (\(R_{Total}\), which includes the high frequency resistance (\(R_{HFR}\)) + the charge transfer resistance (\(R_{CTR}\))). Specifically, the \(R_{Total}\) for E3-C10 was 1075 mOhm\(\cdot\)cm\({}^{2}\) at 1.9 V, compared to 856.6 mOhm\(\cdot\)cm\({}^{2}\) for E3-C11 at the same voltage. However, as illustrated in Figure 6, E3-C10 PFAEM exhibits higher OH\({}^{-}\) conductivity (98.7 \(\pm\) 7.0 mS cm\({}^{-1}\)) and IEC (1.57 \(\pm\) 0.026 meq g\({}^{-1}\)) than E3-C11 PFAEM (71.1 \(\pm\) 4.0 mS cm\({}^{-1}\) and 1.54 \(\pm\) 0.038 meq g\({}^{-1}\), respectively). In other words, it can be inferred that other resistance components, such as improper formation of the triple-phase boundary in electrode membrane-electrode interfacial resistance, contributed to the reduced current density observed in the single cell performance of E3-C10. Therefore, the material resistances, including membrane resistance, electrode resistance, and membrane-electrode interfacial resistance, were further investigated using separated resistance components (i.e., \(R_{HFR}\) and \(R_{CTR}\)), as illustrated in Figure 10d. Studies on optimizing the AEM-AEI combination have been conducted using various AEMs and AEIs, as the compatibility between AEM and AEI is crucial for achieving high performance in AEMWE [24; 25]. In other words, the selection of an appropriate AEI as a binder in the electrode is critical due to the influence of the AEM-AEI combination. As shown in Figure 10d, the E3-C10 PFAEM-based single cell exhibited a lower \(R_{HFR}\) compared to the E3-C11 PFAEM-based single cell, which aligns with membrane properties such as OH\({}^{-}\) ion conductivity and IEC. However, \(R_{CTR}\) exhibited the opposite trend. In the context of \(R_{HFR}\), the PFAEMs' performance in terms of OH\({}^{-}\) ion conductivity and IEC was consistent with their performance in water electrolysis. The reduced performance can be inferred as a result of interfacial resistance in \(R_{CTR}\), excluding electrode resistance, as the same electrode was used. Therefore, improvements to the membrane-electrode interfacial resistance should be considered to enhance overall cell performance. The in situ durability of AEMWE with E3-C10 and E3-C11 was evaluated under constant-current conditions at 500 mA cm\({}^{-2}\) with an asymmetric 1.0 M KOH-fed at 60 \({}^{\circ}\)C for 100 h. As shown in Figure 11a, the voltages increased during the constant-current operation. The degradation slopes, calculated from the time-dependent voltage variation, were used to compare membrane stability. The E3-C10 PFAEM exhibited a degradation slope of 1150 \(\mu\)V h\({}^{-1}\), which is lower than that of the E3-C11 PFAEM. As mentioned in the alkaline stability section, when hydroxyl radicals are present, QA groups can degrade through Hofmann elimination, nucleophilic substitution, and E1 elimination, reducing their availability. Furthermore, polymers containing C-O and C=O bonds in ester groups are chemically unstable in AEMs. To investigate the degradation of AEMs, the PFAEMs used in the AEMWE in situ durability test were extracted and analyzed for their IEC. Prior to evaluating the IEC after the in situ durability test, the surfaces of the membranes that contacted both the anode and cathode electrodes were washed several times with D.I. water. Afterwards, the IEC of the PFAEMs was measured. As illustrated in Figure 11b, the E3-C10 and E3-C11 PFAEMs exhibited IEC values of 1.67 \(\pm\) 0.038 and 0.93 \(\pm\) 0.024 meq g\({}^{-1}\), respectively. These results can be used only to observe the degradation trend of the PFAEMs under water-electrolysis operating conditions.