Abstract
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.
Highlights
Increasing demands for clean and renewable energy have been widely promoted
electrochemical impedance spectroscopy (EIS) results showed that the diameter of the semicircle increased when dimethyl sulfoxide (DMSO) was added to the electrolyte due to the formation of a passive layer of DMSO over the zinc surface
The Nyquist plots of the electrolyte containing 20% v/v DMSO were significantly depressed without the straight line, and the semicircle diameter decreased indicating a wide frequency dispersion of the double layer capacitance involved in the oxidation of zinc
Summary
Increasing demands for clean and renewable energy have been widely promoted. This is due to growing energy consumption in modern society enhancing the degree of electrification. Primary zinc-air batteries have been commercialized since the 1930s, several barriers including corrosion, water consumption during cycling, dendrite growth of zinc, electrolyte leakage, zinc oxide precipitation and zincate ion crossover impede the practical application of secondary batteries. These issues are responsible for a decrease in efficiency and poor rechargeable performance[17]. The effect of adding two different types of surfactants including sodium dodecyl sulfate (SDS) of 0.2 mM and Pluronic F-127 of 100 ppm to an alkaline electrolyte on zinc-air battery performance was investigated[32]. Results revealed a specific discharge capacity enhancement of 30% and 24% for the electrolytes containing P127 and SDS, respectively
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