Water soluble ferrocene (Fc) derivatives are promising cathode materials for aqueous organic redox flow batteries (AORFBs) towards scalable energy storage. However, their structure–performance relationship and degradation mechanism in aqueous electrolytes remain unclear. Herein, physicochemical and electrochemical properties, battery performance, and degradation mechanisms of three Fc catholytes, (ferrocenylmethyl)trimethylammonium chloride (C₁-FcNCl), (2-ferrocenyl-ethyl)trimethylammonium chloride (C₂-FcNCl), and (3-ferrocenyl-propyl)trimethylammonium chloride (C₃-FcNCl) in pH neutral aqueous electrolytes were systemically investigated. UV-Vis and gas chromatography (GC) studies confirmed the thermal and photolytic C_x-Cp⁻ ligand dissociation decomposition pathways of both discharged and charged states of C₁-FcNCl and C₂-FcNCl catholytes. In contrast, in the case of the C₃-FcNCl catholyte, the electron-donating 3-(trimethylammonium)propyl group strengthens the coordination between the C₃-Cp⁻ ligand and the Fe³⁺ or Fe²⁺ center and thus mitigates the ligand-dissociation degradation. Consistently, the Fc electrolytes displayed cycling stability in both half-cell and full-cell flow batteries in the order of C₁-FcNCl < C₂-FcNCl < C₃-FcNCl.

中文翻译：

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二茂铁阴极液在水系氧化还原液流电池中循环稳定性的机理见解

水溶性二茂铁 (Fc) 衍生物是用于水性有机氧化还原液流电池 (AORFB) 的有前途的正极材料，可用于可扩展的能量存储。然而，它们在水性电解质中的结构-性能关系和降解机制仍不清楚。本文介绍了三种 Fc 阴极液（二茂铁基甲基）三甲基氯化铵（C ₁ -FcNCl）、（2-二茂铁基乙基）三甲基氯化铵（C ₂ -FcNCl）和（3-二茂铁基丙基）三甲基氯化铵（C ₃ -FcNCl) 在 pH 中性水性电解质中进行了系统研究。UV-Vis 和气相色谱 (GC) 研究证实了C ₁ -FcNCl和C ₂ -FcNCl阴极液的放电和充电状态的热和光解C _x -Cp ^-配体解离分解途径。相反，在C ₃ -FcNCl阴极电解液的情况下，给电子3-(三甲基铵)丙基增强了C ₃ -Cp ^-配体与Fe ³⁺或Fe ^{2+之间的配位}中心，从而减轻配体解离降解。一致地，Fc电解质在半电池和全电池液流电池中均显示出循环稳定性，顺序为C ₁ -FcNCl < C ₂ -FcNCl < C ₃ -FcNCl。