## 9 Application of Derivatives of Styrene in Membrane of Fuel Cells  
### Polystyrene  
Polystyrene is one of the derivative of styrene also known as synthetic polymer and it is made from a monomer of styrene. It is widely used in plastic and also present in the form of solid and foam. It is lightweight, rigid in nature, clear or white in color, and easy to mold into any shape. It contains better mechanical strength but is brittle and easy to break when stress is applied. It is hydrophobic in nature and dissolves in solvents like acetone. Its melting temperature is 115 \({}^{\circ}\)C and its density is greater than 1000 kg m\({}^{-3}\)[109]. It has wide application including in fuel cells. Its synthesis is possible on a laboratory level. [PERSON] and his colleague scientists [110] synthesized a polystyrene-contained PE solution and mixed it with different amounts of dual functional graphene oxide in order to make polymer composite membrane for DMFCs. The graphene oxide functionalized with sulfonic and phosphonic groups. A strong \(\pi\)-\(\pi\) interaction between fillers and polymers developed defects free and smooth of the surface of the membrane which facilitated the protection from fuel crossover and the value shrunk to 18.42 \(\times\) 10\({}^{-7}\) cm\({}^{2}\) s\({}^{-1}\). Moreover, the presence of dual functional groups on the composite membrane surface facilitates proton transport through the membrane via vehicular and Groththuss mechanisms, resulting in increased proton conductivity. The exchange of functional groups further enhances the ion exchange capacity (IEC) of the membrane due to the abundance of sulfonic and phosphonic groups on the composite membrane. The high proton conductivity and enhanced IEC create efficient pathways for the membrane to function effectively in fuel cells, enabling the composite membrane to deliver a power density of 78 mW cm\({}^{-2}\) at 25 \({}^{\circ}\)C.  
Styrene is also copolymerized with other polymers to transfer its properties, making the membrane more suitable for fuel cell applications. [PERSON] and his colleague scientists [111] prepared a composite membrane consisting of sulfonated poly(styrene-co-maleic anhydride), poly(ethylene glycol), and silica. PEG was added in the composite membrane with the different amounts of silica nanoparticles. The role of PEG is to adjust the spacing between chemically connected polymer chains and silica nanoparticles, fine-tuning the ionic channels in the membrane. When tested for ion conductivity and IEC, the modified membrane showed no significant advantage over commercial Nafion membranes but exhibited higher mechanical strength. The tortuous pathways in the modified membrane reduce methanol permeability, with values lower than those of the commercial Nafion 117 membrane when tested at temperatures ranging from 30 \({}^{\circ}\)C to 70 \({}^{\circ}\)C. The improved thermal stability, low swelling, and high protection from fuel crossover represents that the membrane is able to apply in a DMFC fuel cell. Polystyrene can be easily modified with sulfonic groups, enhancing its hydrophilic properties [112]. Grafting polystyrene sulfonic acid onto nanoparticles is a common practice to enhance the compatibility of nanoparticles with polymers in composite membranes. Moreover, polystyrene grafting further enhances fuel crossover resistance and improves proton conduction in the composite membrane. [PERSON] and his colleague scientists [113] used covalent grafting to make polystyrene-modified graphene oxide nanoplatelets. Then, the polystyrene sulfonic acid-grafted graphene oxide was mixed with SPEEK polymer to make composite membrane. The barrier attributes of modified graphene nanoplatelets act as a shield against methanol crossover and reduce its value to 5.57 \(\times\) 10\({}^{-7}\) cm\({}^{2}\) s\({}^{-1}\).