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The present work describes the effects of dimethyl sulfoxide (DMSO) in KOH aqueous electrolyte on the performance of a zinc-air flow battery. Aqueous electrolytes containing 7 M KOH and (0 to 20)% v/v DMSO were studied revealing a critical role of DMSO on the dissolution and deposition of zinc. The anodic zinc dissolution process was studied via cyclic voltammetry, Tafel polarization and electrochemical impedance spectroscopy (EIS). The presence of DMSO showed improved zinc dissolution performance with the highest peak of zinc dissolution being the electrolyte containing 5% v/v DMSO. Tafel analysis demonstrated a significant decrease in polarization resistance and an increase in corrosion rate due to the introduction of DMSO to the electrolyte. This suggests that DMSO has the ability to suspend zinc oxide in the electrolyte, thus preventing passivation of the zinc surface. EIS results revealed that by adding DMSO to the electrolyte, charge transfer resistance increased. This is attributed to the formation of passive layers having arisen from DMSO adsorption, the formation of zincate ions in the vicinity of the zinc surface, and the deposition of discharged products. A difference in Nyquist plots was observed for 20% v/v DMSO/KOH and 0% v/v DMSO/KOH electrolytes implying non-Debye relaxation behavior taking place due to the surface effects. The electrolytes were implemented in a zinc-air flow battery. Maximum power densities of 130 mW/cm2 (5% v/v DMSO) and 125 mW/cm2 (20% v/v DMSO) were obtained and were observed to be about 43% and 28% higher than that of the DMSO-free electrolyte. Results indicated that when 20% v/v DMSO was added to KOH solution, there was 67% zinc utilization efficiency (550 mAh/g) which provided 20% improvement in discharge capacity. Further, the battery with 20% v/v DMSO demonstrated excellent cyclability. Overall, DMSO shows great promise for enhancement of zinc dissolution/deposition in zinc-air batteries.

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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)42−) 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 × 10−8, and 0.28 × 10−8 cm2/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/gZn and 1000 mWh/gZn, respectively. Low zincate crossover and high discharge capacity of these separator membranes makes them potential materials to be used in zinc–air batteries.