چكيده به لاتين
In this study, chemical durability improvement of sulfonated poly (ether ether ketone) (SPEEK) nanocomposite membranes by using some nanoparticles as catalysts for decomposition of degradation agents was investigated. The Pt-Cs2.5H0.5PW12O40, ceria, zirconia, and ceria-zirconia (CZ) mixed oxide nanoparticles were synthesized and used as additives into the membranes. The synthesized nanoparticles were characterized by XRD and SEM. The nanocomposite membranes with different loading of different nanoparticles were prepared by solution casting method. The prepared membranes (SPEEK-Pt-Cs2.5H0.5PW12O40, SPEEK-ZrO2, SPEEK-CeO2, and SPEEK-CZ) were evaluated by FESEM-EDX, IEC, proton conductivity measurements, mechanical tests, TGA, water uptake, hydrolytic stability, and chemical stability in Fenton solution. Then, the membrane electrode assembly (MEA) with different nanocomposite membranes were prepared and the performance tests in the fuel cell test station were performed. Finally, the open circuit voltage (OCV) test in the harsh condition (90oC, 30% RH for 230 h) as accelerated degradation test was performed for different MEAs for chemical durability investigation. Twelve kinds of SPEEK membranes with different DS (40%-89%) were prepared and their physicochemical and electrochemical properties were studied to find an optimum range of degree of sulfonation (DS) because DS has a significant effect on the physicochemical and electrochemical properties of SPEEK. The membranes with the DS higher than 69% showed poor dimensional stability and low chemical stability. The membranes with the DS lower than 60% showed good mechanical and chemical stability but low proton conduction. The results showed that the moderate DS membrane (DS∼65%) had acceptable mechanical, thermal, electrochemical, and chemical stability and used as reference membrane in this work. The prepared SPEEK-Pt-Cs2.5H0.5PW12O40 showed a uniform distribution of nanoparticles in the polymer matrix. The accelerated degradation test showed the nanocomposite membrane with 15% of Pt-Cs2.5H0.5PW12O40 had better chemical durability (8% voltage loss) than pure SPEEK membrane (24% voltage loss). The recombination of crossover hydrogen and oxygen on the platinum surface, decreasing of the gas crossover, and decomposition of the free radicals were the main effects of Pt-Cs2.5H0.5PW12O40 to improve the membrane durability. The prepared SPEEK-ZrO2 and SPEEK-CeO2 membranes showed a decrease in IEC, an increase in water uptake, a decrease in proton conductivity, mechanical and thermal stability improvements, hydrolytic and chemical stability improvements than pure SPEEK membrane with increasing the loading of ZrO2 and CeO2 into the membranes. The fuel cell performance results have not shown a significant change up to 5% of ZrO2 for nanocomposite membranes and results were almost the same as pure SPEEK membrane. The 230 h accelerated degradation test results showed the different SPEEK-ZrO2 nanocomposite membranes had better durability than pure SPEEK. The OCV decay rate was 0.52 mV h-1 for pure SPEEK membrane and 0.14 mV h-1 for SPEEK-10%ZrO2 membrane. The results showed ZrO2 nanoparticles improved the different properties of SPEEK membrane. The fuel cell performance results have also not shown a significant change up to 5% of CeO2 for nanocomposite membranes. The OCV decay rate during the OCV test was 0.09 mV h-1 for SPEEK-10%CeO2 membrane. The results showed CeO2 improved the different properties of SPEEK membrane. The results also showed SPEEK-CeO2 nanocomposite membranes had better chemical durability than SPEEK-ZrO2. The results also showed an improvement in the durability of SPEEK-CZ nanocomposite membranes and the OCV decay rate was 0.04 mV h-1 that this stability was higher than all different SPEEK-CeO2 and SPEEK-ZrO2 nanocomposite membranes.
