Development and characterization of graphene oxide doped composite electrolytes for proton exchange membrane fuel cells

Fuel cells are electrochemical systems that convert chemical energy directly into electrical energy. Among the fuel cell types, proton exchange membrane fuel cells (PEMFC) draw attention as alternative energy sources that are suitable for use in many environmentally friendly and highly energy efficient applications. While the widely used commercial Nafion membrane exhibits superior proton conductivity under fully humidified, water-saturated operating conditions, the decrease in proton conductivity above 80℃ prevents the use of Nafion for large-scale applications. In these operating conditions, aromatic polymer matrices such as polyether ether ketone (PEEK), polybenzimidazole (PBI) and polysulfone (PSF) are of interest as proton exchange membrane alternatives with their superior thermomechanical stability at high temperatures. The low ionic conductivity of pure polymer matrices makes them unsuitable for use in fuel cell applications. Therefore, they must be converted to the ion-conducting form by various methods such as sulfonation and chloromethylation. Especially sulfonated polyether ether ketone (SPEEK) has attracted attention as a good alternative with its affordable cost, superior thermal/mechanical strength and high chemical stability and has been the subject of many studies in the literature. In recent years, the hydrophilic graphene oxide (GO) molecule, with its unique structure, has attracted attention with its use and efficiency in many application areas. The presence of functional groups in the GO structure helps to retain more water and improve proton conductivity. In addition, functionalization of the structure by processes such as sulfonation makes it suitable for polymer matrices as an inorganic filler. In this study, the performance of polymer electrolyte membranes produced by adding GO with different ratios to the SPEEK polymer matrix with a certain degree of sulfonation (DS) for fuel cell applications was evaluated. Structural, thermal and morphological characterizations of polymer electrolyte membranes are performed by FT-IR, TGA and SEM analysis, respectively, and proton conductivity of the membranes is evaluated.