Aromatic Copolymers Containing Ammonium-Functionalized Oligophenylene Moieties as Highly Anion Conductive Membranes

Abstract

The synthesis and properties of anion conductive aromatic copolymers containing oligophenylene moieties as a scaffold for quaternized ammonium groups are reported. Our new hydrophilic components consist of a chemically robust oligophenylene main chain modified with a high density of ionic groups. A partially fluorinated oligo(arylene ether) was employed as a hydrophobic block. The targeted copolymers (QPE-bl-9) were synthesized via nickel-mediated coupling polymerization, followed by chloromethylation, quaternization, and ion exchange reactions. QPE-bl-9 provided tough, bendable membranes by solution casting. The resulting membrane with the highest ion exchange capacity (IEC = 2.0 mequiv g–1) exhibited high hydroxide ion conductivity (138 mS cm–1) in water at 80 °C. Reasonable alkaline stability of QPE-bl-9 membrane was confirmed in 1 M KOH aqueous solution for 1000 h at 40 °C. A noble metal-free fuel cell with QPE-bl-9 used as the membrane and electrode binder was successfully operated. A maximum power density of 510 mW cm–2 was achieved at a current density of 1.20 A cm–2 with hydrazine as the fuel and O2 as the oxidant.