Polymerized ionic liquid diblock copolymer as an ionomer and anion exchange membrane for alkaline fuel cells
By Nykaza, Jacob R.; Benjamin, Rishon; Meek, Kelly M.; Elabd, Yossef A.
Published in Chemical Engineering Science
2016
Abstract
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 37.9 mol%). 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 30 mW cm?1 was obtained for H2/O2 fuel, 25 psig (172 kPa) back pressure, 50 ?m 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.