Effect of a Sulfonated Benzothiadiazole Unit on the Morphology and Ion Conduction Behavior of a Polymer Electrolyte Membrane

From the viewpoint of improving the physical properties of ion conducting membranes, especially proton exchange membranes (PEMs), obtaining well-defined nanochannels using conjugated polymers has attracted a significant amount of attention. This study aims to propose a novel and simple molecular design concept for aromatic random copolymers based on sulfonated benzothiadiazole (SBT) units to induce nanostructuring. Using atomic force microscopy (AFM), it is confirmed that introducing a small amount of the SBT unit in the sulfonated [poly(arylene ether sulfone)] membrane induced significant hydrophilic and hydrophobic domain aggregation. Furthermore, these morphological transformations provided high density of proton carrier density in membrane and enabled effective proton conductivity even under low humidity condition (2.0 mS/cm at 30% RH). These results indicate that the SBT unit is a key trigger for constructing favorable nanostructure for ion transport and improving ion conductivity in the proton exchange membrane.