| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 178665 | Electrochemistry Communications | 2016 | 4 Pages |
•Acetyl ferrocene shows promising behaviors as a redox couple for flow batteries.•The solubility is greatly enhanced by acetyl group substitution on ferrocene.•The oxidation potential becomes more positive by acetyl substitution.•Acetylferrocene is chemically and electrochemically stable to give an excellent cycle performance.
As a redox couple for flow batteries, the effects of acetyl group substitution on ferrocene (Fc) are examined on the aspect of solubility, oxidation potential, and chemical/electrochemical stability. The solubility of acetyl ferrocene (AcFc) (0.81 M at 25 °C) is 4 times larger than that for ferrocene (0.2 M) in a propylene carbonate-based electrolyte solution. This is rationalized by a decrease in solute/solute interactions and enhanced solute/solvent interactions resulting from acetyl substitution. The former can be explained by the reduction of molecular symmetry, which leads to a looser molecular packing in the solid state. The melting point, which is another barometer for solute/solute interactions, is also lower for AcFc. The enhanced solute/solvent interactions are due to the addition of a polar acetyl group, which enhances the polar interactions between the acetyl group and propylene carbonate solvent. Meanwhile, the oxidation potential moves to the positive direction (3.65 V vs. Li/Li+ for AcFc and 3.44 V for Fc), which must be due to the introduction of an electron-withdrawing acetyl group. The acetyl ferrocene/acetyl ferrocenium couples are chemically/electrochemically stable at 3.3–4.1 V (vs. Li/Li+). Due to this stability, a Li/AcFc coin-type non-flowing cell shows a reasonably good cycleability and Coulombic efficiency of > 98%.
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