<i>N</i>-ferrocenylphthalimide; A single redox couple formed by attaching a ferrocene moiety to phthalimide for non-aqueous flow batteries

다국어 초록 (Multilingual Abstract)

<P><B>Abstract</B></P> <P> <I>N</I>-ferrocenylphthalimide (FcPI) is prepared by replacing the hydrogen atom at the <I>N</I>-site of phthalimide with a ferrocene moiety. Phthalimide shows irreversible redox reaction due to H atom at the <I>N</I>-site of phthalimide. By replacing H atom of phthalimide with non-detachable functional group, such as alkyl group, redox reaction becomes reversible. Reversibility of redox reaction is requirement for redox couple due to cycling performance in battery system. In this work, electroactive group, not the simple functional group, is introduced to substitute H atom of phthalimide. As an electroactive group, ferrocenyl group has two main benefits. First, the redox reaction of the initial phthalimide with H atom at the <I>N</I>-site becomes reversible at <I>E</I> <SUB>1/2</SUB> = −1.87 V (<I>vs.</I> Fc/Fc<SUP>+</SUP>) with an excellent stability. Second, FcPI is a single redox couple with <I>E</I> <SUB>cell</SUB> = 1.94 V in a non-aqueous electrolyte because the ferrocene moiety in the molecule is also redox-active at <I>E</I> <SUB>1/2</SUB> = 0.07 V (<I>vs.</I> Fc/Fc<SUP>+</SUP>) with stability. A non-flowing coin-type cell employing FcPI as a single redox couple exhibits an excellent Coulombic efficiency of 97.3% and stable cycle performance during the 50<SUP>th</SUP> cycle. Furthermore, rate test realizes fast charge transfer kinetics as voltage efficiency of 96.5–90.1% at 1.0–3.0 <I>C</I>.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A single redox couple, <I>N</I>-ferrocenylphthalimide is proposed by replacing H atom at the <I>N</I>-site of phthalmide with ferrocene. </LI> <LI> <I>N</I>-ferrocenylphthalimide was synthesized and has solubility of 0.3 M in background electrolyte. </LI> <LI> <I>N</I>-ferrocenylphthalimide exhibits increased stability in redox reactions of phthalimide while ferrocene moiety shows the stable redox reaction. </LI> <LI> Stability of <I>N</I>-ferroceneylphthalimide is implemented in cell test with an excellent CE of 97.3%. </LI> <LI> Fast kinetic of the proposed materials is verified by rate test with VE of 96.5–90.1%. </LI> </UL> </P>