###### Abstract  
The proton exchange membrane (PEM) is a critical component of fuel cells, responsible for controlling the flow of protons while minimizing fuel crossover through its channels. The commercial membrane commonly used in fuel cells is made of Nafion, which is expensive and prone to swelling when in contact with water. To address these limitations, various polymers have been explored as alternatives to replace the costly Nafion membrane. Styrene, a versatile and cost-effective material, has emerged as a promising candidate. It can be modified into different forms to meet the requirements of a fuel cell membrane. The aromatic rings in styrene can copolymerize with hydrophilic functional groups, enhancing water (H\({}_{2}\)O) uptake, proton conductivity, and ion exchange capacity (IEC) of the membrane. Additionally, the hydrophobic nature of styrene helps maintain the structural integrity of the membrane's channels, reducing excessive swelling and minimizing fuel crossover. The flexible aromatic chains in styrene facilitate the attachment of hydrophilic functional groups, such as sulfonic groups, further improving the membrane's ion conductivity, IEC, thermal stability, mechanical strength, and oxidative stability. This review article explores the application of styrene and its derivatives in fuel cell membranes, with a focus on proton exchange membrane fuel cells (PEMFCs), direct methanol fuel cells (DMFCs), and anion exchange membrane fuel cells (AEMFCs). p 11 -  
chemical energy into electrical energy by using oxygen and fuel, and as a product, heat and water are produced. Compared to traditional devices, fuel cells provide high efficiency, are eco-friendly, and provide a continuous supply of energy with an uninterrupted fuel supply. There are several types of fuel cells [13]. Some are listed below while others are detailed in supplementary data. Fuel cells come in a variety of forms:  
* Proton exchange membrane fuel cells (PEMFCs);
* Anion exchange membrane fuel cells (AEMFCs);
* Phosphoric acid fuel cells
* Solid acid fuel cells
* Alkaline fuel cells
* Molten carbonate fuel cells
* Microbial fuel cells (MFCs)
* Solid oxide fuel cells (SOFCs)
* Zinc-Air fuel cells (ZAFCs)
* Direct methanol fuel cells (DMFCs)  
Among these fuel cells, proton exchange membrane fuel cells (PEMFCs) are lightweight, high-efficiency power generation devices with a simple structure, making them ideal for transportation and aviation applications [14; 15; 16] [Figure 1]. They consist of an anode, cathode, and a separator that facilitates proton flow while preventing fuel crossover [17; 18; 19]. PEMFCs are categorized into low-temperature PEMFCs (LTPEMFCs), which use Nafion membranes and operate at 80-100 \({}^{\circ}\)C [20; 21; 22], requiring full hydration for proton conduction, and high-temperature PEMFCs (HTPEMFCs), which use Polybenzimidazole (PBI) membranes doped with phosphoric acid and operate at 100-160 \({}^{\circ}\)C without the need for hydration [23; 24; 25; 26]. LTPEMFCs are susceptible to CO poisoning from hydrogen fuel impurities, while HTPEMFCs are more resistant to CO and can tolerate hydrogen with up to 10 ppm CO. Despite their differences, both types offer high power density and efficiency, with HTPEMFCs providing additional advantages in high-temperature and impurity-tolerant operations [27; 28; 29]. The direct methanol fuel cell is another power production device that converts chemical energy produced from methanol fuel to electrical energy. It is simple in design, portable, and used in different transportation and military equipment [30; 31]. Methanol fuel offers high energy density, easy storage and handling, and cost effectiveness, making it ideal for fuel cell applications. Its liquid form and compatibility with existing infrastructure simplify its use, while its renewable production potential provides environmental benefits, making it a practical alternative to hydrogen and other fuels. Its structure is similar to PEMFCs  
Figure 1: Typical schematic diagram of PEMFC working principle.