Anion-Tunable Properties and Electrochemical Performance of Functionalized Ferrocene Compounds

Abstract

We report a series of ionically modified ferrocene compounds for hybrid lithium-organic non-aqueous redox flow batteries, based on the ferrocene/ferrocenium redox couple as the active catholyte material. Tetraalkylammonium ionic moieties were incorporated into the ferrocene structure, in order to enhance the solubility of the otherwise relatively insoluble ferrocene. The effect of various counter anions of the tetraalkylammonium ionized species appended to the ferrocene, such as bis(trifluoromethanesulfonyl)imide, hexafluorophosphate, perchlorate, tetrafluoroborate, and dicyanamide on the solubility of the ferrocene was investigated. The solution chemistry of the ferrocene species was studied, in order to understand the mechanism of solubility enhancement. Finally, the electrochemical performance of these ionized ferrocene species was evaluated and shown to have excellent cell efficiency and superior cycling stability.

Feasibility of a Supporting‐Salt‐Free Nonaqueous Redox Flow Battery Utilizing Ionic Active Materials

“…In both cases, the plateauso bserved during cycling occur at the potentials expected based on the CVs ( Figure 3) and demonstrate that only the desired redox couples are accessed.F urthermore, the resultsa re consistent with those reported in the literature. [15,20] Fc1N112-BF 4 exhibits no detectable capacity fade over the ten cycles (Figure 4a), which is in agreement with prior reports. [16,20] CVs beforea nd after the bulk electrolysis experiment ( Figure S5) show little to no evidenceo fd egradation.C onversely,[ Fe(bpy) 3 ](BF 4 ) 2 exhibits capacity decay over the course of the experiment owing to the irreversibility of the negative couple.…”

“…For this study,w es elected iron(II) tris(2,2'-bipyridine) tetrafluoroborate ([Fe(bpy) 3 ](BF 4 ) 2 ;s ee Figure S1 ai nt he Supporting Information) [24] and ferrocenylmethyl dimethyl ethyl ammonium tetrafluoroborate (Fc1N112-BF 4 ,F igure S1 b) [15,16] as model ionic redox-active species to demonstrate the salt-free cell concept. The lack of viable NAqRFB chemistries, especially those with the characteristics necessary for the demonstration of as alt-free device, drove our selections.…”

A Halogen Bonding 1,3‐Disubstituted Ferrocene Receptor for Recognition and Redox Sensing of Azide

“…Very recently, XB motifs have been successfully integrated into redox‐active receptor structural frameworks containing ferrocene, diquat and tetrathiafulvalene and were demonstrated to enhance the electrochemical sensing of halides in comparison to HB analogues. Ferrocene, in particular, has been the redox‐active motif of choice due to its chemical stability, wide synthetic repertoire, favourable voltammetric properties and facile integration into sensitive electrochemical devices . Herein, we describe the synthesis of a novel XB 1,3‐bis‐iodotriazole ferrocene receptor and demonstrate its capability of selectively binding and redox sensing of azide (Figure ).…”

Characterization of Structural and Electronic Transitions During Reduction and Oxidation of Ru(acac)3 Flow Battery Electrolytes by using X‐ray Absorption Spectroscopy

“…When cycled at 0.8 m concentrations, however, significant capacity fade occurred during the first 20 cycles . The same group recently reported reduced capacity fade for the same complex at 1.2 m for 500 cycles in a static cell . The cause of the fade, in most cases, has not been investigated and consequently is not well understood.…”

“…[34] The same group recently reported reduced capacity fade for the same complexa t1 .2 m for 500 cycles in as tatic cell. [16] The cause of the fade, in most cases, has not been investigated and consequently is not well understood.A lthough cyclic voltammetry (CV) of these metallo-organic and organicc omplexes often demonstrates promising fundamental attributes, none possess sufficient cycle lives, in particulara tt he high concentrationsn eededf or commercial applications.…”