## 9 Application of Derivatives of Styrene in Membrane of Fuel Cells
### Polystyrene
Moreover, the sbPA-based polymer membrane shows no irreversible weight loss, indicating that the membrane containing phosphonic groups or polystyrene begins to degrade only at temperatures up to 400 \({}^{\circ}\)C. With hydrophilic groups, the sbPA polymer membrane with spacer shows conductivity around 1.1 mS cm\({}^{-1}\) at a temperature of 120 \({}^{\circ}\)C [Figure 4d] and under 20% RH which are two times higher values than sbPA polymer membrane without spacer. [PERSON] and his colleague scientists [116] developed a membrane using bacterial cellulose and PSSA polymer using radical polymerization of sodium 4-styrenesulfonate, and in this process, PEGDA was used as a crosslinking agent to bind two polymers. Afterwards, the hybrid polymer was converted into acid form by sulfonation process. The results show that bacterial cellulose nanofiber make a network in the membrane and provide mechanical strength to the structure of the membrane. When tested at a high temperature of 140 \({}^{\circ}\)C, the membrane structure is sustained while at this temperature, Nafion or pure PSSA polymer have membrane meltdown. The sulfonic groups on the membrane form an ionic cluster and help to create ionic channels for a smooth pathway. Ultimately, the IEC capacity of the modified membrane containing PSSA and PEGDA in an amount of 83 wt.% reaches a value of 2.25 mmol g\({}^{-1}\) for a composite with 83 wt.% PSSA/PEGDA. Moreover, through plane ion conductivity, it delivers a value ranging from approximately 0.042 S cm\({}^{-1}\) to 0.1 S cm\({}^{-1}\) when tested under a humidity value from 60% to 98% relative humidity (RH) at a temperature of 94 \({}^{\circ}\)C. These conductivity values are higher than values of Nafion or PSSA polymer membrane. These results demonstrate that this kind of multidimensional modified membrane shows great potential for the application in electronic devices such as PEMFC, DMFC, and AEMFC. To further enhance the properties of polystyrene sulfonic acid, its copolymerization of hydrophilic polymers has been studied, such as in PVP and imidazole. The resulting copolymer is easily soluble in organic solvents, facilitating the production of physically and electrochemically stable membranes. For example, [PERSON] and his colleague scientists [117] synthesized poly(styrene sulfonic acid-co-vinylpyridine) or NaSS-4 VP by free radical polymerization and converted it into membrane by crosslinking with haloalkyl. The membrane exhibits high strength and flexibility due to interaction between sulfonic groups of polystyrene sulfonic acid and nitrogen groups of pyridine. Moreover, the acid-base interactions within the membrane enhance its thermal and oxidative stability. The synthesized polymer membrane exhibits reduced swelling and a stable porous structure at high temperatures, ensuring long-term durability and efficient proton conduction during fuel cell operation. Ultimately, an amount of 90.3% crosslinked polymer membrane shows a proton conductivity value of 71 mS cm\({}^{-1}\) at a temperature and RH value of 30 \({}^{\circ}\)C and 90%, respectively, which are superior to that of the Nafion 117 membrane. However, the presence of more free water in the membrane increases methanol crossover, with values 16% higher than those of the Nafion 117 membrane under the same conditions. Despite high fuel crossover, the synthesized polymer membrane exhibits a selectivity value of 3.38 \(\times\) 10\({}^{5}\) S cm\({}^{-3}\) s which is five times superior to that of the Nafion 117. In another example, [PERSON] and his colleagues [118] synthesized a poly(styrene sulfonic acid-co-1-vinylimidazole-co-styrene) terpolymer through traditional free radical polymerization and mixed it with PVC in order to obtain a polymer blend membrane. The sulfonic acid groups of polystyrene and the imidazole groups of vinylimidazole provide a strong mechanical structure through their interactions, while the hydrophobic nature of polystyrene ensures long-term structural stability.