Novel high temperature proton exchange membranes based on functionalized poly(arylene dimethylamino benzene) polymers

The electrolyte membrane is a critical component in high temperature proton exchange membrane fuel cells (HT-PEMFCs). We have developed a new triarylmethane-backboned polymer, poly( p -triphenyl dimethylamino benzene) (PTDB), by using p -triphenyl and 4-(dimethylamino)benzaldehyde as monomers through a one-step straightforward Friedel-Crafts reaction. The presence of tertiary amine groups in PTDB enables strong interaction with phosphoric acid (PA) molecules. To improve PA doping content and proton conductivity, both copolymers containing biphenyl repeat unite and side-chain quaternized polymers are synthesized. Results show that the 3-bromopropyl trimethylammonium bromide grafted membrane (PTDB-QA) outperforms the poly(triphenyl-biphenyl-dimethylamino benzaldehyde) (P(T x % -B y % -DB)) copolymer membranes. After being doped in an 85 wt% PA solution at 80 °C, the PTDB-QA membrane exhibits a PA uptake of 160%, resulting in an anhydrous proton conductivity of 0.054 S cm −1 at 180 °C and mechanical strength of 10.1 MPa at room temperature. Under the H 2 -air condition without any back pressure, the peak power density of a single cell based on PTDB-QA/160%PA reaches 230 mW cm −2 at 160 °C. This work presents a promising new membrane for HT-PEMFC applications. • A novel ether-free polymer PTDB was synthesized for HT-PEM applications. • The properties of PTDB were improved by copolymerization and quaternization. • PTDB-QA/160%PA demonstrated a H 2 -air peak power density of 230 mW cm −2 .