Polymerized ionic liquid diblock copolymer as an ionomer and anion exchange membrane for alkaline fuel cells

Abstract

Alkaline fuel cells have the potential to provide sustainable portable energy without high-cost platinum if robust, chemically stable anion exchange polymers can be discovered. In this study, a polymerized ionic liquid (PIL) diblock copolymer, poly(MMA-b-MUBIm-HCO3), composed of an ionic liquid monomer, (1-[(2-methacryloyloxy)undecyl]-3-butylimidazolium bicarbonate) (MUBIm-HCO3), and a non-ionic monomer, methyl methacrylate (MMA), was produced via anion exchange metathesis from the precursor bromide conducting PIL block copolymer, poly(MMA-b-MUBIm-Br), at two PIL compositions (20.0 and 37.9mol%). Prior to anion exchange, the precursor block copolymer was synthesized via the reverse addition fragmentation chain transfer (RAFT) polymerization technique. Non-porous, dense membranes fabricated from this PIL block copolymer were highly conductive, transparent, flexible, and water insoluble. Membrane electrode assemblies were fabricated with this polymer as both the solid-state membrane separator and the ionomer in the catalyst layers using three different techniques: Painted Gas Diffusion Layer (GDL), Air Spray GDL, and Decal Transfer. Alkaline fuel cell (AFC) performance was measured as a function of fuel cell operating conditions, MEA fabrication technique, membrane thickness, and ionomer in different anion exchanged forms. AFC maximum power density of approximately 30mWcm−1 was obtained for H2/O2 fuel, 25psig (172kPa) back pressure, 50μm thick membrane using the Painted GDL MEA fabrication technique. For the first time, these results demonstrate the feasibility of using PIL block copolymers as the membrane and ionomer in alkaline fuel cells.