A novel high proton conductivity hydrogen bond self-assembly proton exchange membrane with liquid crystal properties

Abstract

The proton exchange membrane crafted from side-chain sulfonated poly(ether ether ketone) has garnered considerable attention because of its notable separation of hydrophilic and hydrophobic phases. Addressing the increase of its proton conductivity is a critical technical challenge that demands more investigation. To address this issue, this work developed a novel proton exchange membrane (LCI_H-AF/CSC) with liquid crystal properties using liquid crystal grafted aramid fiber (LCI_H-AF) and a self-assembly method involving hydrogen bonding with side-chain sulfonated poly(ether ether ketone) (CSC). Nonetheless, the random distribution of fillers inside the matrix leaded in inferior proton conductivity, which limited its performance. Using polarized microscopy (POM), this work verified that the membranes have lyotropic liquid crystal properties, with a liquid crystal phase that ranges from 1 wt% to 3 wt% when LCI_H-AF were added. Within the CSC matrix, the LCI_H-AF were orderly arranged, creating a structured channel for effective proton transfer. Due to the double intermolecular hydrogen bond between the amino group from aramid fiber and the sulfonic acid group in the CSC, LCI_H-AF/CSC exhibited high proton conductivity and mechanical stability. Notably, 3 % LCI_H-AF/CSC had a strong proton conductivity (584.4 mS/cm, 80 °C) that is five times more than that of CSC. Furthermore, the 3 % LCI_H-AF/CSC membranes had excellent endurance, even after 60 days of testing at 80 °C, the membranes remained stable. This design greatly improved the performance of the membrane, making it an excellent candidate for proton exchange membranes.