Abstract:

The urgent need for large-scale, low-cost, and long-term electric energy storage has again aroused people's interest in the research and development of iron-chromium redox flow battery (ICRFB). The efficiency of the ICRFB system can be improved and the operating cost can be reduced by inhibiting the hydrogen evolution side reaction and improving the electrochemical reaction activity of the negative electrode. The deposition of bismuth catalyst is an effective method to improve the performance of the negative electrode. However, there is a lack of systematic understanding and in-depth research on uniform bismuth deposition strategy and the impact of bismuth loading on battery performance. Thus, this paper proposes a slow-release deposition strategy that is realized by dissolving bismuth ions in the positive electrolyte in order to improve the uniformity of catalyst deposition. The ions gradually migrate across the membrane and are deposited on the negative electrode. The effect of deposition rate and loading of bismuth on the performance of an ICRFB was explored by varying the concentration of BiCl₃ in the positive electrolyte. Our results show that the continuous deposition of bismuth significantly and continuously improved due to the coulombic efficiency of the ICRFB because of the accompanied reduction in hydrogen evolution. In addition, the in situ deposition of bismuth also helps to improve the voltage efficiency of the ICRFB, indicating an enhanced reaction activity of Cr²⁺/Cr³⁺. With an initial 10 mmol/L Bi³⁺ in the positive electrolyte, the coulombic, voltage, and energy efficiency reach about 97%, 90%, and 87%, respectively.

Key words: iron-chromium redox flow battery, bismuth catalyst, electrochemical deposition, slow release deposition