A bipolar nitronyl nitroxide small molecule for an all-organic symmetric redox-flow battery

Abstract

An all-organic symmetric redox-flow battery (RFB) that employs nitronyl nitroxide (NN) units as a bipolar redox-active chargestorage material was designed and investigated. An organic molecule possessing two bipolar redox-active NN units connected via a tetraethylene glycol chain was synthesized for this purpose. Owing to the ethylene glycol chain, this molecule demonstrates good solubility in organic solvents. The electrochemical behavior of the obtained compound was investigated via cyclic voltammetry (CV) measurements and it features quasi-reversible redox reactions of the NN + /NN redox couple at E ½ = 0.37 V and the NN/NN − redox couple at E ½ = − 1.25 V versus AgNO 3 /Ag, which led to a promising cell voltage of 1.62 V in a subsequent battery application. A static solution-based battery exhibits a stable charge/discharge performance over 75 consecutive cycles with a high energy efficiency of 82% and an overall energy density of the electrolyte system of 0.67 W h l − 1 . In addition, a pumped RFB test demonstrates an overall energy density of the electrolyte system of 4.1 W h l − 1 and an energy efficiency of 79%.

Research Frontiers in Energy‐Related Materials and Applications for 2020–2030

“…For these reasons, in the future, we foresee a differentiation of storage technologies depending on the final application of the battery system (Figure 2). [61,62] Last but not the least, in recent years different metal-ion chemistries such as Zn-ion, Al-ion, and Mg-ion batteries have been proposed as promising technologies for wearable devices. [55][56][57] Moreover, redox flow batteries are a recent technology that shows encouraging results for its application in the stationary large-scale energy sector.…”

“…2020, 4,1900145 www.advsustainsys.com as Li-sulfur, Li-air, all-solid-state Li-ion, metal-ion (Na-ion, K-ion, Zn-ion, Al-ion, and Mg-ion), redox flow batteries, and allorganic batteries are being developed. [55][56][57][58][59][60][61][62][63][64][65] Among the many post-Li-ion systems that are under current development, here we will focus on Li-S and Li-air because specific advancements in these technologies could enable extremely high energy densities batteries.…”

“…[55][56][57] Moreover, redox flow batteries are a recent technology that shows encouraging results for its application in the stationary large-scale energy sector. [61,62] Last but not the least, in recent years different metal-ion chemistries such as Zn-ion, Al-ion, and Mg-ion batteries have been proposed as promising technologies for wearable devices. [63][64][65] At the same time, the development of theoretically higher energy density technologies, such as Li-S or Li-air systems is most promising for mobility and electronic applications, and all these different technologies should be pursued in parallel.…”

Integrated Saltwater Desalination and Energy Storage through a pH Neutral Aqueous Organic Redox Flow Battery

“…Recently sustainable, structurally tunable redox active organic and organometallic molecules have been increasingly populated as charge storage electrolyte materials in both aqueous [ 19–40 ] and nonaqueous redox flow batteries. [ 41–51 ] We and others have made contributions to the development of pH neutral aqueous organic redox flow batteries (AORFBs) for safe and low cost large‐scale and residential energy storage using sustainable, noncorrosive, nonflammable aqueous redox‐active organic electrolytes and low cost ion exchange membranes. [ 11–14 ] Specifically, pH neutral AORFBs employing water‐soluble, structurally tunable viologen (anolyte), TEMPO (catholyte), ferrocene (catholyte), and ferrocyanide active materials have been extensively demonstrated.…”

Aqueous Symmetrical Redox Flow Batteries Based Upon a pH-Responsive Cobalt Complex

“…17,18 Unlike the more commonly studied asymmetric RFBs, 19 a symmetric RFB would require only a single redox active compound if it has at least three stable oxidation states; 17 such an architecture would eliminate cross-contamination due to crossover of the redox-active species in asymmetric configurations, thus facilitating longterm cyclability. 20,21 Most symmetric RFBs have been developed for non-aqueous systems for reasons of solubility of organic components, and a wider potential window in which to operate. [22][23][24] For aqueous symmetric RFBs, the three stable oxidation states need to be accessible within the potential window of the hydrogen and oxygen evolution reactions.…”