## 9 Application of Derivatives of Styrene in Membrane of Fuel Cells
### Polystyrene
Moreover, the hydrophilic functional groups of SPEEK and polystyrene sulfonic acid-grafted graphene oxide attract more water molecules, and the interactions between these functional groups within the membrane capture and retain water, further boosting proton conductivity. With 0.15 wt.% modified graphene oxide nanoplatelets, the composite membrane shows a proton conductivity value of approx. 73 mS cm\({}^{-1}\). With taking advantage of minimum fuel crossover and high proton conductivity, the composite membrane shows apower density value of 170 mW cm\({}^{-2}\) which is more than that of the pristine SPEEK membrane [110 mW cm\({}^{-2}\)] and 50% higher than that of the commercial Nafion 117 membrane [80 mW cm\({}^{-2}\)]. Moreover, the composite membrane is able to deliver stable performance up to 100 h of working in a fuel cell. In another example, [PERSON] and his colleague scientists [114] synthesized SSA and grafted it with cellulose acetate materials. Afterwards, it was converted into membrane by solution casting method [Figure 4a]. Grafting SSA onto cellulose acetate in the membrane increase its thermal stability, mechanical strength, and oxidative stability. The hydrophilic functional groups of polystyrene and cellulose acetate absorb more water molecules, and their interactions strengthen the interior walls of the channels, reducing swelling. High water uptake in the modified cellulose acetate membrane results in high proton conductivity and IEC. As a result, the modified membrane with 1.5 wt.% SSA shows low methanol permeability (5.514 \(\times\) 10\({}^{-7}\) cm\({}^{2}\) s\({}^{-1}\)), proton conductivity (4.77 mS cm\({}^{-1}\)), membrane selectivity of 8.65 \(\times\) 10\({}^{3}\) S s cm\({}^{-3}\), and peak power density of 24.6 mW cm\({}^{-2}\), respectively [Figure 4b]. This high power density stems from the membrane's unique architecture, where the sulfonated polystyrene grafts provide efficient proton-conducting pathways, while the cellulose acetate matrix acts as a barrier to methanol crossover. The shallow ohmic region slope further confirms low membrane resistance, aligning with the high proton conductivity data. Membranes containing phosphonic groups can be easily synthesized using polystyrene as a monomer due to its hydrophobic nature. As an example, [PERSON] and his fellow scientists [115] synthesized a poly(4-(p-styryl)-1-butanephosphonic acid) (sbPA) polymer and diethyl 4-(p-styryl)-1-butanephosphonate which afterwards converted into membrane for PEFC [Figure 4c]. During the synthesis process, the diethyl 4-(p-styryl)-1-butanephosphonate monomer was treated with a phosphonic acid along with an alkylene spacer as a crosslinking agent. Through polymerization, sbPA polymer was synthesized containing phosphonic groups by alkaline spacer. The final step involved deprotection of the alkyl protecting group containing phosphonic acid ester. Due to high molecular mobility, the sbPA polymer membrane with an alkylene spacer exhibits a thermal stability  
Figure 4: (**a**) Chemical structure of polystyrene grafted cellulose acetate. (**b**) Polarization curves for CA@P(SSA)5 grafted membrane and Nafion® 212. (**c**) Sulfonated crosslinked polystyrene (Selemion HSFN). (**d**) Relative humidity dependence of conductivity of sbPA (red circles), sPA (black squares) at 80 \({}^{\circ}\)C temperature [114; 115]. temperature of 170 \({}^{\circ}\)C, while the thermal stability of the sbPA polymer membrane with an alkylene spacer reaches 218 \({}^{\circ}\)C. However, TGA results show that the sbPA polymer membrane begins to degrade at approximately 180 \({}^{\circ}\)C, which is higher than the operating temperature of current PEFCs (100-150 \({}^{\circ}\)C under low humidity conditions).