## 3 Design Consideration on Radiation-Grafted AEM
### Selection of Polymer Backbone, Irradiation Dose and Dose Rate
They reported that an increase in total irradiation dose from 10 to 20 kGy resulted in an increase in D.O.G. of all the polyethylene membrane because more active sites were formed for VBC monomers to graft onto the polyethylene backbone. The BPI-LDPE-g-VBC membrane showed the highest value of IEC (3.2 med g\({}^{-1}\)) and D.O.G (74.6%) among the listed polyethylene membranes, respectively. The membrane also showed an extremely stable ionic conductivity of 0.11 S cm\({}^{-1}\) in a durability test over a period of 7 months under nitrogen at 80 \({}^{\circ}\)C. The AEMFC based on the BPI-LDPE-g-VBC membrane has demonstrated a peak power density of 608 mW cm\({}^{-2}\) at 50 \({}^{\circ}\)C, with low fuel crossover. In another study, [PERSON] et al. [75] investigated the effect of irradiation dose rate on the degradation of radiation-grafted VBC onto polyethylene-based (LDPE and HDPE) and EFTE-based AEMs and functionalized with TMA, respectively. The polyethylene-based membranes were both prepare via simultaneous irradiation with \(\gamma\)-ray with dose rate ranges from 30 to 2000 kGy h\({}^{-1}\), while ETFE-based membrane was pre-irradiated with electron beam at a dose rate of 400 kGy h\({}^{-1}\). Interestingly, they found that AEMs, regardless of fluorinated or non-fluorinated polymer backbone, that were treated with a high irradiation dose rate (above 400 kGy h\({}^{-1}\)) resulted in a lower loss of IEC (less than 15%) in percentage over a period of 2 months compared to those treated at a low irradiation dose rate (up to 50% loss of IEC). They concluded that polymer subjected to high irradiation dose rate exhausts available oxygen rapidly and prevents any dissolved oxygen from penetrating into the polymer that degrades the polymer through oxidation. Table 2 summarizes and compares the performance of polyethylene-based and ETFE-based AEMs at different irradiation doses and dose rates. In 1996, Shell commercialized a type of aliphatic polyketone (PK), which is a terpolymer of carbon monoxide, ethylene and propylene. This relatively new type of polymer has excellent thermomechanical properties, high chemical stability and high resistance to hydrolysis. Nevertheless, its unique chemical resistance property also contributes to its difficulty to graft chemically. [PERSON] et al. [97] are among the first group that used \(\gamma\)-irradiation to graft VBC onto PK membrane and aminated with TMA (PK-g-VBC-TMA). They have successfully achieved a D.O.G of 98% with a VBC monomer concentration of 70 wt% and at the total irradiation dose of 70 kGy. They found that the performance of PK-g-VBC-TMA outperformed a Nafion 117, which has an ionic conductivity of 78 mS cm\({}^{-1}\), an IEC of 0.8 meg g\({}^{-1}\), water uptake of 24% and swelling ratio of 21%. Both ionic conductivity and the IEC of PK-g-VBC-TMA were recorded as 310 mS cm\({}^{-1}\) and 1.2 meg g\({}^{-1}\), respectively, which was supported by its maximum water uptake of 35%. Although its water uptake was much higher than that of Nafion, the swelling ratio of PK-g-VBC-TMA was comparable to that of Nafion, which indicated that the mechanical strength of PK-g-VBC-TMA has a high potential for commercial applications.