Unraveling the coordination behavior and transformation mechanism of Cr3+ in Fe–Cr redox flow battery electrolytes

Xiaojun Zhao , Xinwei Niu , Xinyuan Liu , Chongchong Wu , Xinyu Duan , Zhiqi Ma , Yan Xu , Hao Li , Weijie Yang
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Abstract

Currently, the iron chromium redox flow battery (ICRFB) has become a research hotspot in the energy storage field owing to its low cost and easily-scaled-up. However, the activity of electrolyte is still ambiguous due to its complicated solution environment. Herein, we performed a pioneering investigation on the coordination behavior and transformation mechanism of Cr3+ in electrolyte and prediction of impurity ions impact through quantum chemistry computations. Based on the structure and symmetry of electrostatic potential distribution, the activity of different Cr3+ complex ions is confirmed as [Cr(H2O)5Cl]2+ > [Cr(H2O)4Cl2]+ > [Cr(H2O)6]3+. The transformation mechanism between [Cr(H2O)6]3+ and [Cr(H2O)5Cl]2+ is revealed. We find the metal impurity ions (especially Mg2+) can exacerbate the electrolyte deactivation by reducing the transformation energy barrier from [Cr(H2O)5Cl]2+ (24.38 kcal mol−1) to [Cr(H2O)6]3+ (16.23 kcal mol−1). The solvent radial distribution and mean square displacement in different solvent environments are discussed and we conclude that the coordination configuration limits the diffusivity of Cr3+. This work provides new insights into the activity of electrolyte, laying a fundamental sense for the electrolyte in ICRFB.

Abstract Image

揭示铁-铬氧化还原液流电池电解质中 Cr3+ 的配位行为和转化机制
目前,铁铬氧化还原液流电池(ICRFB)因其成本低、易于规模化生产而成为储能领域的研究热点。然而,由于其复杂的溶液环境,电解质的活性仍不明确。在此,我们开创性地研究了 Cr3+ 在电解质中的配位行为和转化机制,并通过量子化学计算预测了杂质离子的影响。根据静电位分布的结构和对称性,确定了[Cr(H2O)5Cl]2+ >;[Cr(H2O)4Cl2]+ >;[Cr(H2O)6]3+等不同Cr3+配合离子的活性。揭示了 [Cr(H2O)6]3+ 和 [Cr(H2O)5Cl]2+ 之间的转化机制。我们发现金属杂质离子(尤其是 Mg2+)会降低从 [Cr(H2O)5Cl]2+ (24.38 kcal mol-1)到 [Cr(H2O)6]3+ (16.23 kcal mol-1)的转化能垒,从而加剧电解质失活。我们讨论了不同溶剂环境中的溶剂径向分布和均方位移,并得出结论:配位限制了 Cr3+ 的扩散性。这项研究为了解电解质的活性提供了新的视角,为 ICRFB 中的电解质奠定了基础。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
材料导报:能源(英文)
材料导报:能源(英文) Renewable Energy, Sustainability and the Environment, Nanotechnology
CiteScore
13.00
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50 days
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