关键词: 全钒液流电池电堆, 局部供液不足, 副反应, 电位

Abstract:

In an operating all-vanadium redox flow battery stack, uneven electrolyte flow through each individual electrode is common, if not inevitable. Moreover, localized insufficiencies of liquid supply may become severe in a long-term operation, which not only directly affects overall stack performance, but also exacerbates harmful side reactions (including oxygen evolution, hydrogen evolution, and carbon corrosion). These reactions may in turn lead to blockages and increased resistance. This paper reports a model-based quantitative study of an all-vanadium redox flow battery stack under conditions of local liquid supply shortage. A two-dimensional steady-state simulation was carried out for charge/discharge under galvanostatic operation, focusing on the impact of local fluid supply deficiency on electrode potential and side reactions. The results show that decreased flow rate in one or several electrodes has little effect on the overall voltage of the stack, but that it does cause local sharp changes in current and ion concentrations inside the electrodes. It may also lead to an ultra-high potential gradient, causing seriously deviation of the potential from its normal value. This in turn reduces the uniformity of distribution of the main reaction and intensifies the progress of side reactions on the electrode surface, potentially compromising the energy efficiency and safety of the stacks. Since the rate of side reactions also depends on the material properties of the electrode, this paper provides qualitative conclusions based on representative working conditions. These conclusions allow general guidance to be suggested for the design and testing of flow battery stacks.

Key words: all-vanadium redox flow battery stack, insufficient local liquid supply, side reactions, potential