Highly conductive mechanically robust high Mw polyfluorene anion exchange membrane for alkaline fuel cell and water electrolysis application

Abstract

New, high molecular weight poly-(fluorene-alt-tetrafluorophenylene) anion exchange membranes were synthesized by a Pd-catalyzed C–H activation method. The synthesized membranes exhibited high OH⁻ conductivity over 100 mS cm⁻¹, and membrane swelling could be suppressed by controlling the side chain length of the polymers. The membranes were flexible with high tensile strengh (25–42 MPa), which is comparable to Nafion 211 and likely because of their high molecular weight (M_w = 170–240 kDa). Conductivity and mechanical flexibility of the membranes did not vary significantly in 8 M NaOH at 80 °C for 168 h. These membranes hold promise for both membrane and solid ionomer materials that can be used in alkaline fuel cells or alkaline water electrolysis devices.