New blend nanocomposite membranes based on PBI/sulfonated poly(ether keto imide sulfone) and functionalized quantum dot with improved fuel cell performance at high temperatures

In this work, we reported the synthesis of a sulfonated poly(ether keto imide sulfone) (SPEKIS) using a novel aromatic diol containing nitrogen heterocycles and sulfonic monomer. New nanocomposite blend membranes were prepared using obtained SPEKIS and polybenzimidazole (PBI) with the incorporation of zinc sulfide (ZnS) functionalized quantum dots (FQDs) having both -COOH and NH₂ groups with a solution-casting method and were used as proton exchange membranes. The SPEKIS and ZnS FQDs were used for the first time in the preparation of new nanocomposite blend membranes based on PBI. The purpose of this study is to investigate the effect of SPEKIS and ZnS FQDs on the PBI membrane performance in proton conductivity, mechanical and chemical stability, and fuel cell performance. The result displayed that the phosphoric acid doping content and proton conductivity of the PBI-SPEKIS-ZnS FQDs blend nanocomposite membranes enhanced which can be attributed to interactions of thiazole rings and -SO₃H group of SPEKIS, NH₂ and -COOH groups of ZnS FQDs, N-H groups of PBI, and phosphoric acid with each other. The best membrane performance (the best proton conductivity) of the prepared nanocomposite blend membranes was obtained at 162 mS/cm at 7% relative humidity and 180°C. The power density of the PBI-SPEKIS blend membranes (SPEKIS/PBI: 24 wt%) was obtained 0.55 W/cm² while this parameter for the PBI-SPEKIS-ZnS FQDs blend nanocomposite membranes (SPEKIS/PBI: 24 and 3 wt% of ZnS FQDs) obtained 0.67 W/cm² in 7% RH, 0.5 V, and 180°C. These outcomes highlighted the point that the prepared nanocomposite membranes of this research have valuable properties to be considered as a capable sample for the high-temperature fuel cell with enhanced performance. Highlights: Zinc sulfide (ZnS) functionalized quantum dots (FQDs) due to having both -COOH and NH₂ groups are one of the best promising nanoparticles for proton exchange membrane fuel cells. Interactions of thiazole rings and -SO₃H group of sulfonated poly(ether keto imide sulfone) (SPEKIS), N-H and -COOH of ZnS FQDs, and N-H groups of PBI increase the proton conductivity. The SPEKSI/PBI/ZnS FQDs nanocomposite blend membranes show the best fuel cell performance (a power density of 0.67 W/cm² at 180°C and 7% RH).