Preparation And Properties Of Sulfonated Poly(Arylene Ether Ketone Sulfone)S Containing Carboxylic Acid Groups For Proton Exchange Membrane Material

Proton exchange membrane fuel cell (PEMFC) has been widely studied due to its very simple steps, rapid startup time, high efficiency and pollution-free. Proton exchange membrane (PEM) is the heart of PEMFC and its performance directly affects the applications of PEMFC. Nowadays, the most widely used commercially available PEM materials is Nafion. It has a lot of advantages such as good chemical stability, high proton conductivity under low temperatures and excellent mechanical stability. However, the high cost, poor proton conductivity under high temperatures and high methanol permeability have limited its futher development. Therefore, it is a goal for the majority of scientists to develop some good comprehensive performance and relatively cheap cost polymer material.Sulfonated poly(arylene ether ketone sulfone)s are one of the most promising alternative PEM materials due to their good thermal stability, chemical stability and low cost as compared to Nafion membrane. However, it still has a fatal flaw which is that when the degree of sulfonation (DS) is too high, although the proton conductivity can reach a higher level, the membranes may be excessive swelling resulting in a sharp increase in methanol crossover and poor dimensional stability. So, it is necessary to modify this type of material in order to improve the overall performance.In this paper, sulfonated poly(arylene ether ketone sulfone) membranes containing carboxylic acid groups (C-SPAEKS) with different degrees of sulfonation were synthesized by the nucleophilic aromatic substitution reactions. After a series of tests, the membranes exhibited a good dimensional stability and thermal stability. The methanol permeability coefficient of C-SPAEK-20 (1.21×10-7 cm2 s-1) and C-SPAEKS-80 (9.15×10-7 cm2 s-1) membrane were much lower than that of Nafion 117 membrane (22.9×10-7 cm2 s-1). Moreover, the proton conductivity of C-SPAEKS-80 membrane (0.119 S cm-1) was higher than that of Nafion(?) 117 membrane (0.095 S cm-1) at 80℃In order to improve the methanol resistance of the membranes, C-SPAEKS/PVA crosslinked membrane was prepared. After crosslinking, the water uptake, swelling ratio, thermal stability and methanol crossover were improved greatly. The swelling ratio of C-SPAEKS/PVA-40 membrane was 8.1, which was lower than that of C-SPAEKS membrane (13.9). The methanol permeability coefficient of C-SPAEKS/PVA-40 membrane was 2.21×10-7 cm2 s-1 and it is much lower than C-SPAEKS membrane (24.17×10-7cm2s-1).In order to reduce the methanol permeation as well as increased the ptoton conductivity of the membranes, sulfonated PVA and C-SPAEKS/SPVA crosslinked membranes were prepared. The crosslinked membranes exhibited good thermal property, mechanical performance and lower methanol permeability coefficients. The introduction of SPVA greatly reduced methanol permeability coefficients of the membranes. The methanol permeability coefficients of all the crosslinked membranes were below 10×10-7 cm2 s-1 Therefore, the crosslinked membranes are alternative PEM materials for DMFC applications.