Poly(biphenyl piperidinium) Anion Exchange Membranes for Alkaline Water Electrolyzers: The Effect of Nonionic Pendant Groups

The introduction of different nonionic pendant groups in the backbones of polymeric anion exchange membrane (AEM) materials not only induces microphase separated morphology but also greatly impacts the other physicochemical properties of AEMs. Herein, we reported a series of poly-(biphenyl piperidinium) copolymers having different nonionic pendant groups on the backbones, including methyl, phenyl, and bromomethyl, which were derived from the ketone comonomers in the superacid-catalyzed polycondensation. Under similar ion exchange capacity, the PBP-M-35 membrane with methyl pendant groups shows the highest water uptake due to the less steric effect and electronic effect, reaching the highest OH- hydroxide conductivity (50.7 mS/cm at 20 C-degrees in liquid water) than other membranes. In addition to high conductivity, the PBP-M-35 membrane with more water absorption displayed superior alkaline stability, with the retention of a conductivity of 84.5% after 1200 h in 1 M KOH at 80 C-degrees. Consequently, the PBP-M-35 membrane presented a performance of 2000 mA/cm(2) at 1.8 V in a water electrolyzer (with the IrO2 anode and Pt/C cathode in 1 M KOH at 80 C-degrees). Further continuous operation under different conditions suggested that the cell with the PBP-B-30 membrane could operate under Ni-foam electrodes in 1 M KOH at 80 C-degrees for 240 h, and more harsh working conditions (6 M KOH at 80 C-degrees) led to the fast failure of the cell.