## 3 Design Consideration on Radiation-Grafted AEM
### Selection of Polymer Backbone, Irradiation Dose and Dose Rate
Copyright Elsevier, 2018.  
ions in the ion channels, whereas AEM2 forms ionic clusters (caused by nanophase separation) with a size of ~2.2 nm, which improve the water diffusion and ionic conductivity of the membrane. Nonetheless, high irradiation doses may cause damage to the fluorinated polymer main chains, such as ETFE-based AEMs, leading to mechanical weakening [76]. As such, [PERSON] et al. [70] have attempted to optimize the irradiation process by replacing propan-2-ol diluent with water, and further reduced the irradiation dose from 70 to 30 kGy, and VBC concentration from 20 vol% to 5 vol%. The results showed that ETFE-g-VBC with reduced irradiation dose preserved its high IEC of 2.01 mmol g\({}^{-1}\) and improved mechanical properties with its Young's modulus of 415 MPa, stress at break of 30% and elongation at break of 189%, which were higher than the one irradiated at 70 kGy. The peak power density of AEMFC with ETFE-g-VBC membrane was reported at 1.16 W cm\({}^{-2}\) at 60 \({}^{\circ}\)C.  
Non-fluorinated polymers, with a higher resistance to radiation damage, such as polyethylene (PE), low-density polyethylene (LDPE) and high-density polyethylene (HDPE)-based anion exchange membranes, were proposed as an alternative to EFTE. These non-fluorinated hydrocarbon-based polymers offer several advantages over the fluorinated polymer, such as lower costs, enhanced commercial precursor availability, and more possibilities for recycling the final products (no C-F content) [76]. LDPE-based AEM offers a cheaper alternative to other commercially available materials [64], with promising thermomechanical and chemical stability, as well as durability properties. [PERSON] et al. [93] studied UV-induced grafting of VBC onto LDPE and aminated with 1,4-diazabicyclo(2.2.2)octane (LDPE-g-VBC-DABCO) for electrolysis cell applications. Here, DABCO also functions as cationic crosslinker, which supports the formation of thin sheet anion exchange thermoplastic membrane. Although DABCO contains b-hydrogen atoms, DABCO is highly resistant to alkali degradation through Hofmann elimination because of its rigid cage structure [94]. The LDPE-g-VBC-DABCO membrane was examined in terms of its ionic conductivity, ion exchange capacity, water uptake, electrolytic cell tests, and hydrogen permeability. They found that the electrochemical performance of LDPE-g-VBC-DABCO was comparable with the benchmark commercial membrane at that time, and the electrolysis cell with this membrane was able to produce approximately 30 cc/min of hydrogen at 20 bar, over more than 500 h. It showed that the hydrogen permeation rate of LDPE-g-VBC-DABCO, which was a safety concern in electrolysis applications, was in the range of 10\({}^{-13}\) mol cm\({}^{-1}\) s\({}^{-1}\) kPa\({}^{-1}\). However, the LDPE-g-VBC-DABCO membrane displayed instability due to its low resistance in an alkaline environment. [PERSON] et al. [76] compared the performance of radiation-grafted ETFE-based AEM and LDPE-based AEM. The LDPE-based AEM was able to withstand an irradiation dose of up to 100 kGy without showing mechanical failure, while only an irradiation dose of 30 kGy was used in ETFE-based AEM. It was found that that the C\({}^{-}\) conductivity of radiation-grafted LDPE-based AEM  
Figure 6: Schematic representation of ion channels of (**a**) parallel-grafted (AEM1) and (**b**) perpendicular-grafted (AEM2) ionic polymer into the ETFE polymer matrix. Reprinted with permission from [91]. Copyright Elsevier, 2018. (76 mS cm\({}^{-1}\) at 80 \({}^{\circ}\)C) was slightly higher than that of ETFE-based AEM (60 mS cm\({}^{-1}\) at 80 \({}^{\circ}\)C). However, the elasticity of LDPE-AEM after aging in alkaline at 80 \({}^{\circ}\)C improved drastically, with the elongation at break of LDPE-based AEM at least an order larger than that of ETFE-based AEM. Similarly, [PERSON] et al.