Anion Conductive Aromatic Copolymers from Dimethylaminomethylated Monomers: Synthesis, Properties, and Applications in Alkaline Fuel Cells

A novel series of anion conductive aromatic copolymers were synthesized from preaminated monomers (2,5-, 3,5-, or 2,4-dichloro- N, N -dimethylbenzylamine), and their properties were investigated for alkaline fuel cell applications. The targeted copolymers (QPE- bl -11a, -11b, and -11c) were synthesized via nickel-mediated Ullmann coupling polymerization, followed by quaternization and ion exchange reactions. Unlike the conventional method involving chloromethylation or bromination, this method provided copolymers with well-defined chemical structure. The hydrophilic components of the copolymers were composed of chemically stable phenylene main chain modified with high-density ammonium groups. Oligo(arylene ether sulfone ketone)s were employed as a hydrophobic block. QPE- bl -11a gave tough and bendable membranes by solution casting. The obtained membrane with the highest ion exchange capacity value (IEC = 2.47 mequiv g –1 ) showed high hydroxide ion conductivity (130 mS cm –1 ) in water at 80 °C. The QPE- bl -11a membrane showed reasonable alkaline stability in 1 M KOH aqueous solution for 1000 h at 60 °C. A platinum-free fuel cell was successfully operated with hydrazine as a fuel, the QPE- bl -11a as a membrane, and an electrode binder. The maximum power density of 380 mW cm –2 was achieved at a current density of 1020 mA cm –2 with O 2 .