Redox flow batteries (RFBs) are promising technologies for application in both grid-scale power station and electric vehicles owing to their flexible architecture decoupling power and energy^{1, 2}. The development of aqueous RFBs has been strongly hindered by low energy density, limited cell voltage and rapid capacity fading, which largely can be attributed to the poor solubility of electroactive species, small voltage window of water and limited ion selectivity capability of membrane¹. Chalcogenide has been reported to have high solubility in nonaqueous environment with high charge/discharge reversibility, which makes it a promising anolyte candidate for aqueous RFBs^3-5. However, it is found that these sulfur-based RFBs have been challenged by their poor cycle life and rate capability, owing to the strong shuttle phenomenon and slow kinetics of polysulfide reaction^{3, 5}. It is critical to manipulate the competition between diffusion/crossover and the rate of electrochemical reaction of soluble active species in order to improve cycle life of RFBs.

In this work, we exploited a composite-based ion-exchange membrane for chalcogenide-iodide RFBs. We evaluated the effectiveness of various membrane compositions and will discuss the role of each component in the membrane toward long-life operation. We applied UV-vis spectroscopy to probe the active reaction species involved in the RFB operation. In addition, we will discuss the use of complexing agent for polysulfide species to increase the energy density (molar electron number per molecule) and energy efficiency (higher reaction kinetics) of the chalcogenide-iodide RFBs.

Acknowledgement:

This work was fully supported by a grant from the Research Grant Council of the Hong Kong Special Administrative Region, China under NSFC/RGC Joint Research Scheme 2018/19 Project No. N_CUHK435/18.

Reference:

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