## 9 Application of Derivatives of Styrene in Membrane of Fuel Cells
### Styrene-Ethylene-Butylene-Styrene (SEBS)
The membrane's crystallinity reaches 20% at 80 \({}^{\circ}\)C after hydrogenation of the 1,4-butadiene units, improving ion transport pathways. On the other hand, the crosslinked polystyrene in the membrane forms high ion clusters due to its hydrophilic nature. With improved crosslinking and hydrophilic groups, the membrane reduces swelling to 12%. Moreover, AEM shows values of water uptake and hydroxide conductivity of approximately 80% and 81 \(\times\) 10\({}^{-3}\) S cm\({}^{-1}\) at a temperature of 80 \({}^{\circ}\)C. The polystyrene availability in the membrane enhances the ion exchange capacity value and its value reaches 1.48 mmol g\({}^{-1}\) when tested with SEBS1401 based AEM. When tested in AEMFC, the membrane with SBS1401 delivers  
Figure 6: (**a**) Graphs of different temperature vs. (**a**) water uptake (**b**) swelling ratio (**c**) hydroxide conductivity; (**d**) temperature dependence graphs of different SEBS-based membranes from 50 to 70%; (**e**) ion conduction retention for AEM after dipping in NAOH solution of concentration 2 M at a temperature of 60 \({}^{\circ}\)C for different time intervals; (**f**) performance curves consist of SEBS-based membrane with different amounts [122]. a power density and current density values of 320 mW cm\({}^{-2}\) and 860 mA cm\({}^{-2}\), respectively. This proves that the SEBS-based AEM results indicate that the proposed method can develop high-performance SEBS-based AEMs, suitable for fuel cell applications. In another example, [PERSON] and his colleague scientists [125] prepared a triblock copolymer of SEBS-based AEM for AEMFC using Poly(styrene-b-(ethylene-co-butylene)-b-styrene) (PSBEBS) for crosslinking and functionalization purpose. SEBS was first converted into chloromethylated SEBS, then quaternization and crosslinking with tertiary amines were carried out. The -CH\({}_{2}\) spacer group alters the membrane's morphology and improves ionic channels. Thus, the ionic conductivity of SEBS-based membranes improves, and as the spacer group length increases from -CH\({}_{2}\) to -CH\({}_{12}\), methanol permeability decreases, confirming its effectiveness. The spacer groups in the modified membrane also increase strength by tightening the polymer chains. Moreover, these changes greatly improve the membrane's chemical and thermal stability. The properties of the synthesized membrane are further improved by adding nanoparticles such as graphene oxide. With 0.5% graphene oxide, the modified membrane shows ion conductivity value and selectivity values of 2.0 \(\times\) 10\({}^{-2}\) S cm\({}^{-1}\) and 7.6 \(\times\) 10\({}^{4}\) S s cm\({}^{-3}\) at a temperature of 60 \({}^{\circ}\)C which shows its superior resistance against methanol permeability. [PERSON] and his colleague scientists [126] synthesized the polymer copolymerized with SEBS to make AEM for fuel cell application. Two polymers named p-triphenylpiperidine and 1,1,1-trifluoroacetone were synthesized and attached to a fluorine group in their polymer chains which boost the phase separation [Figure 7a]. Moreover, the addition of fluorine helps in the construction of ionic channels within the membrane and further improves the ion conductivity. The results show 5, 10, and 15% PTP contents in the polymer studied. The fluorine contents in the AEM increase the dimensional stability and mechanical strength of the membrane. Poly(triphenylpiperidine) (PIP) cations in the membrane improve the hydroxyl ion conduction in the membrane and hydrophobic phase in the membrane protects from the fuel crossover. As a result, the membrane shows a more stable structure and protects against changes that happen during increasing temperature [Figure 7b,c]. The SEBS-based membrane with 15% PTP shows a tensile strength value and elongation of 38.79 MPa and 183.09% at a temperature of 80 \({}^{\circ}\)C and relative humidity value of 100%. With better ionic channels, the membrane shows an ion conductivity value of 102.02 mS cm\({}^{-1}\) at a temperature of 80 \({}^{\circ}\)C [Figure 7b].