Effect of ceria loading on performance and durability of sulfonated poly (ether ether ketone) nanocomposite membranes for proton exchange membrane fuel cell applications

Abstract

The addition of ceria nanoparticles can significantly enhance the durability of sulfonated poly (ether ether ketone) (SPEEK) membranes for fuel cell applications. Here, the fuel cell performance and durability of SPEEK/ceria nanocomposite membranes containing different ceria loadings were investigated. Ceria nanoparticles were synthesized via a microwave-assisted gel-combustion method and were characterized by XRD, FESEM, HRTEM, BET, and pore-structure analysis. The SPEEK/ceria nanocomposite membranes (SPEEK-x wt% CeO2; x= 2.5, 5.0, 7.5, and 10.0) were prepared by the solution-casting method and characterized by XRD, DSC, water uptake, proton conductivity, and oxidative stability. The physical, thermal, and chemical analyses showed that the nanocomposite membrane had improved properties over the pure SPEEK membrane. Proton conductivity measurements before and after a 100 h Fenton test confirmed that the SPEEK nanocomposite membranes had superior chemical stability compared to pure SPEEK membranes. Fuel cell performance was evaluated by obtaining polarization curves at different temperatures, and accelerated stress tests (AST) were conducted by holding the cell at open circuit voltage (OCV) at 90 °C and low humidity (30% RH) for 230 h. The nanocomposite membranes showed a lower degradation rate than the pure SPEEK membrane, and the degradation rate decreased with increasing ceria content. The gas crossover, polarization curves, and ohmic resistance before and after AST showed that the SPEEK nanocomposite membranes were extremely stable. XRF measurements indicated that the ceria nanoparticles were highly resistant to migration and leach-out from the SPEEK/ceria nanocomposite membranes, and FESEM images confirmed that the nanocomposite membranes did not undergo significant thinning. The results indicate that SPEEK/ceria nanocomposite membranes are potentially good candidates for proton exchange membrane fuel cells.