| Summary: | Rechargeable zinc−air batteries are deemed as the most feasible alternative to replace lithium−ion batteries in various applications. Among battery components, separators play a crucial role in the commercial realization of rechargeable zinc−air batteries, especially from the viewpoint of preventing zincate (Zn(OH)<sub>4</sub><sup>2−</sup>) ion crossover from the zinc anode to the air cathode. In this study, a new hydroxide exchange membrane for zinc−air batteries was synthesized using poly (2,6-dimethyl-1,4-phenylene oxide) (PPO) as the base polymer. PPO was quaternized using three tertiary amines, including trimethylamine (TMA), 1-methylpyrolidine (MPY), and 1-methylimidazole (MIM), and casted into separator films. The successful synthesis process was confirmed by proton nuclear magnetic resonance and Fourier-transform infrared spectroscopy, while their thermal stability was examined using thermogravimetric analysis. Besides, their water/electrolyte absorption capacity and dimensional change, induced by the electrolyte uptake, were studied. Ionic conductivity of PPO−TMA, PPO−MPY, and PPO−MIM was determined using electrochemical impedance spectroscopy to be 0.17, 0.16, and 0.003 mS/cm, respectively. Zincate crossover evaluation tests revealed very low zincate diffusion coefficient of 1.13 × 10<sup>−8</sup>, and 0.28 × 10<sup>−8</sup> cm<sup>2</sup>/min for PPO−TMA, and PPO−MPY, respectively. Moreover, galvanostatic discharge performance of the primary batteries assembled using PPO−TMA and PPO−MPY as initial battery tests showed a high specific discharge capacity and specific power of ~800 mAh/g<sub>Zn</sub> and 1000 mWh/g<sub>Zn</sub>, respectively. Low zincate crossover and high discharge capacity of these separator membranes makes them potential materials to be used in zinc−air batteries.
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