Organic Electroactive Materials for Aqueous Redox Flow Batteries

Abstract

Organic electroactive materials take advantage of potentially sustainable production and structural tunability compared to present commercial inorganic materials. Unfortunately, traditional redox flow batteries based on toxic redox‐active metal ions have certain deficiencies in resource utilization and environmental protection. In comparison, organic electroactive materials in aqueous redox flow batteries (ARFBs) have received extensive attention in recent years for low‐cost and sustainable energy storage systems due to their inherent safety. This review aims to provide the recent progress in organic electroactive materials for ARFBs. The main reaction types of organic electroactive materials are classified in ARFBs to provide an overview of how to regulate their solubility, potential, stability, and viscosity. Then, the organic anolyte and catholyte in ARFBs are summarized according to the types of quinones, viologens, nitroxide radicals, hydroquinones, etc, and how to increase the solubility by designing various functional groups is emphasized. The research advances are presented next in the characterization of organic electroactive materials for ARFBs. Future efforts are finally suggested to focus on building neutral ARFBs, designing advanced electroactive materials through molecular engineering, and resolving problems of commercial applications.

Quinones for Aqueous Organic Redox Flow Battery: A Prospective on Redox Potential, Solubility, and Stability

“…Since the redox potential is a critical property of redox‐active materials that affects the battery's open‐circuit voltage, there has been significant research ongoing. [ 40 ] If protons or hydroxyl ions are absorbed or released during the redox reaction, the potential is pH‐dependent. The redox potential of the species is significantly influenced by the substituents on its parent structure.…”

Enabling Long-Life Aqueous Organic Redox Flow Batteries with a Highly Stable, Low Redox Potential Phenazine Anolyte

“…7−13 Aqueous organic redox flow batteries (AORFBs) utilize organics dissolving in aqueous solutions as active species in ARFBs and are being explored as a new direction for energy storage systems. 14 These organics consist of earth-abundant elements such as C, H, O, N, P, and S, making AORFBs more promising in terms of cost reduction compared to vanadiumbased ARFBs. 15,16 Since the first report of AORFBs based on 9,10-anthraquinone-2,7-disulfonic acid (AQDS) by Aziz, 17 there has been substantial progress in the development of high-performance AORFBs, marked by the exploration of novel organic compounds and advancements in electrode designs.…”

“…Aqueous organic redox flow batteries (AORFBs) utilize organics dissolving in aqueous solutions as active species in ARFBs and are being explored as a new direction for energy storage systems . These organics consist of earth-abundant elements such as C, H, O, N, P, and S, making AORFBs more promising in terms of cost reduction compared to vanadium-based ARFBs. , Since the first report of AORFBs based on 9,10-anthraquinone-2,7-disulfonic acid (AQDS) by Aziz, there has been substantial progress in the development of high-performance AORFBs, marked by the exploration of novel organic compounds and advancements in electrode designs. − The success of AQDS-based AORFBs has encouraged more researchers to focus on highly soluble and electro-active organic compounds for AORFBs. − Despite progress in the development of AORFBs, many previous reports on this technology are yet to be translated into practical applications due to challenges such as short cycling time (less than 1 month), ,− ,− serious capacity fade (greater than 0.1% per day), ,,,− and low open-circuit voltage (e.g., less than 1 V in al...…”

Exploring the Landscape of Heterocyclic Quinones for Redox Flow Batteries

“…Anthraquinones (AQs) offer a greater degree of charge delocalization and higher chemical stability compared to benzoquinone (BQ) alternatives, and so it not surprising that this class of molecules has been the most extensively explored in both nonaqueous and aqueous electrolytes . Perhaps the most well-known examples are those reported by the Aziz group who explored the effects of different pendant functional groups on the solubility and stability of the AQ-based electrolytes for long-term battery performance. − Modification of anthraquinone and naphthoquinone frameworks with solubilizing groups has been explored extensively, ,− but other electrolytes that operate on the same principle of fused-ring systems for greater chemical and electrochemical stability have also been developed, both within RFBs and within the broader battery literature. For example, annulated rings have been used to prevent degradation by electrophilic or nucleophilic addition to the quinone during cycling .…”