Structure and properties of sulfonated poly(arylene ether)s with densely sulfonated segments containing mono-, di- and tri-tetraphenylmethane as proton exchange membrane

Abstract

Multiple factors affecting the sulfonated poly (arylene ether) proton exchange membrane materials are worthy of being systematically explored. In order to investigate the variation of membrane materials based on ion exchange capacity (IEC) and hydrophilic segment length, three series of dense sulfonated poly (arylene ether)s (mt-SPAE-y, dt-SPAE-y and tt-SPAE-y) containing mono-, di- and tri-sulfonated tetraphenylmethane structural units were synthesized. Each series contains three sulfonated copolymers with different IEC values. Small angle X-ray scattering and transmission electron microscopy results show that increasing the IEC value is conducive to the aggregation of hydrophilic ion clusters, while the growth of hydrophilic segment length helps to the formation of larger hydrophilic ion clusters. Both variations favor the construction of connected hydrophilic ion channels. Based on the highest IEC value and the longest hydrophilic segment length, the tt-SPAE-1.94 membrane forms a connected hydrophilic channel that allows it to exhibit the highest proton conductivity and lowest activation energy of the proton conductivity. Good thermal properties, mechanical properties and oxidation resistance lay the foundation for the durability of the membrane in fuel cells. Finally, the tt-SPAE-1.94 membrane was used for membrane electrode assembly at 80 °C and 95% relative humidity, exhibiting a power density of 418 mW cm−2 in H2/air fuel cell test. In summary, both the increase in the IEC value and the length of the hydrophilic segment contribute to the formation of good hydrophilic-hydrophobic phase morphology, thereby enhancing the macroscopic properties of the sulfonated poly (arylene ether) proton exchange membrane material. The results prove that these three series of membranes show outstanding prospects in actual fuel cell operation and have considerable research value.