Development of ion exchange membranes for electrochemical applications using PET waste bottles

This research presents two innovative strategies for transforming PET bottles into proton exchange membranes (PEMs) and anion exchange membranes (AEMs) for electrochemical applications. By repurposing PET waste, these approaches support sustainability and the circular economy by reducing reliance on virgin polymer materials. In the first approach, chemical modification was applied to the structure of PET bottles by introducing sulfonic functional groups, which enhance the electrochemical properties of the PEM. The sulfonation synthesis process was optimized, and structural characterization was performed using NMR and FTIR analysis. The PET-sulfonated membrane (PET-S MEM) was prepared via the solution casting technique and tested at ARCO Technology for fuel cell applications. The optimized PET-S MEM exhibited a 157 mS/cm conductivity, comparable to the commercial Nafion 212 membrane (181 mS/cm). For membrane electrode assembly (MEA) testing, the PET-S MEM achieved a power density of 354 mW/cm² in a single-cell setup, compared to 605.4 mW/cm² for Nafion 212. These studies highlight the potential of PET-S MEM for PEM as a viable fluorine-free alternative to Nafion, offering a more sustainable and environmentally friendly option for fuel cell applications. The second approach focused on developing PET-based AEMs by introducing cationic functional groups, followed by methylation and OH⁻ exchange. The resulting material was optimized and underwent a series of characterizations. The membrane was prepared using the casting technique, like the PEM preparation. The optimized AEM exhibited an ionic conductivity of 53 mS/cm and maintained alkaline stability for 432 hours in 1M KOH at 80°C. Functionalized TiO₂ (F-TiO₂) nanoparticles were incorporated into the PET-based AEM to further enhance electrochemical performance, increasing conductivity to 126 mS/cm at 80°C, twice that of membranes without TiO₂. The composite membrane also demonstrated excellent stability, retaining 92.2% of its conductivity after 20 days in 2M KOH at 80°C. This modification significantly improved both conductivity and stability, making the membrane a strong candidate for electrochemical applications. This innovative approach transforms waste PET bottles into advanced technologies, providing a key step forward in circular economy solutions.