## 3 Design Consideration on Radiation-Grafted AEM
### Selection of Polymer Backbone, Irradiation Dose and Dose Rate
The addition of methyl protecting group (i.e., MNVIm) has shown enhancement in alkaline stability, with an ionic conductivity higher than 10 mS cm\({}^{-1}\) at 800 h. To further understand the ionic conductivity channels of AEM in the presence of water [86], [PERSON] et al. [87,88] used the small-angleX-ray scattering technique (SAXS) to investigate the ionic conducting structure of AEMs grafted with 2-methyl-\(N\)-vinulimidazolium and styrene groups at different degrees of grafting under various relative humidity (RH) conditions. SAXS revealed that the mean distance between two ionic clusters was approximately 1.0 nm and the ionic conducting channels were disconnected at relative humidity (RH) < 80%. While in water, the ionic conductivity of these AEMs increased significantly because the ionic conducting channels were well connected. This structural model explained the reason why most power generation of AEMFC reported to date is low because the reduction reaction of water at the cathode will reduce the RH significantly, thus decreasing the ionic conductivity. [PERSON] et al. [89] used SAXS to investigate the morphology changes of quaternized poly(arylene ether) semi-block co-polymer in relation to RH at 40 \({}^{\circ}\)C. SAXS results showed that the peak intensity increased with humidity and a Porod's slope of 4, as shown in Figure 5a, indicating that the periodic structure of hydrophilic domains in the AEM became more pronounced and the hydrophilic domains are in the form of a spherical shape, respectively. The SAXS shape analysis was consistent with the TEM results in Figure 5b. Building on the understanding of their previous work [65], [PERSON] et al. [90] have grafted imidazolium groups with St groups attached in perpendicular orientations onto ETFE (StIm-ETFE), with a total dose of 50 kGy at a dose rate of 10 kGy h\({}^{-1}\), using \(\gamma\)-ray. This molecular design prevents the \(\beta\)-elimination reaction and hydrolysis of imidazolium ring, hence further improving the alkaline durability of ETFE. The grafting time was varied from 40 to 960 min to control the D.O.G. They found that StIm-ETFE with a D.O.G of 18% at 72 min exhibited an ion exchange capacity of 0.54 mmolg\({}^{-1}\) and ionic conductivity of >50 mS cm\({}^{-1}\) at a significantly low water uptake (~10%). The StIm-ETFE membrane showed no sign of degradation over 600 h in 1 M KOH solution at 80 \({}^{\circ}\)C, maintaining its ionic conductivity of 50-60 mS cm\({}^{-1}\). They have also found that there was a critical ion exchange capacity (IEC\({}_{\text{c}}\)) point in the range of 0.7 to 0.8 mmol g\({}^{-1}\), where above this IEC\({}_{\text{c}}\) point, water uptake increased rapidly, contributed to by the switching of \"reverse micelles\" with water domains dispersed in the polymer matrix to \"micelles\" with graft polymer aggregates dispersed in the water matrix. [PERSON] et al. [91] also discovered that the ionic channels were microstructurally different depending on if imidazolium and styrene units were grafted parallelly (AEM1) or perpendicularly (AEM2) onto the ETFE membrane, respectively. The small-angle neutron scattering (SANS) with contrast variation method takes advantage of the inherent difference in scattering density properties between hydrogen and deuterium [92]. Upon hydration in heavy water (D\({}_{2}\)O), the hydrophilic ionic groups form ionic channels provide pathways to transport anion, while the hydrophobic ETFE polymer matrix maintains the membrane integrity by restricting the swelling. SANS revealed that both AEMs have a lamellar structure with alternate stacking between grafted polymer layers and crystalline ETFE layers, as shown in Figure 6. Nevertheless, the ionic channels of these AEMs were distinct from one another. AEM1 shows homogenous distributed  
Figure 5: (**a**) Spherically shaped SAXS profile with a Porod’s slope of 4 and (**b**) its corresponding TEM image. Reprinted with permission from [89].