Alginate-tungsten trioxide-reduced graphene-based membranes for PEM fuel cells operating above the boiling point of water

This study reports the fabrication and characterization of novel high-temperature proton exchange membranes composed of sodium alginate reinforced with tungsten trioxide-reduced graphene (WO₃-rG) nanocomposites, polyethylene glycol (PEG), and ionic liquids (ILs). The pristine sodium alginate (SA) membrane was first modified with varying concentrations of WO₃-rG to enhance its proton conductivity, mechanical characteristics, and thermal stability. The PEG was incorporated to improve flexibility and membrane hydration, along with diethylmethylammonium methanesulfonate ([DEMA][OMs]) IL. Additionally, characterization techniques were conducted, including proton conductivity (at ambient and elevated temperatures), swelling ratio, ion exchange capacity (IEC), water uptake, Fourier transform infrared (FTIR) spectroscopy, and tensile testing, to evaluate the membrane performance. The results show that the 3.23 wt% PEG/WO₃-rG/SA membrane exhibited the highest proton conductivity at room temperature, reaching 2.33 × 10^-1 S cm^-1 at 25 °C, while the IL/PEG/WO₃-rG/SA formulation demonstrated the most stable conductivity profile at elevated temperatures, maintaining 3.88 × 10^-3 S cm^-1 at 145 °C. In addition, the IL/PEG/WO₃-rG/SA membrane showed an excellent IEC of 1.65 meq g^-1 and remarkable mechanical flexibility, with an elongation at break exceeding 768%. Therefore, these findings confirm the positive role of WO₃-rG, IL, and PEG in the membrane's structure and enhancing its functional properties, as well as improving its flexibility. The work showed that the IL/PEG/WO₃-rG/SA composite is a promising candidate for high-temperature proton exchange membrane (HT-PEM) fuel cell applications, especially those operating above the boiling point of water.