Recent Developments on Electroactive Organic Electrolytes for Non‐Aqueous Redox Flow Batteries: Current Status, Challenges, and Prospects

Abstract

The ever‐increasing threat of climate change and the depletion of fossil fuel resources necessitate the use of solar‐ and wind‐based renewable energy sources. Large‐scale energy storage technologies, such as redox flow batteries (RFBs), offer a continuous supply of energy. Depending on the nature of the electrolytes used, RFBs are broadly categorized into aqueous redox flow batteries (ARFBs) and non‐aqueous redox flow batteries (NARFBs). ARFBs suffer from various problems, including low conductivity of electrolytes, inferior charge/discharge current densities, high‐capacity fading, and lower energy densities. NARFBs offer a wider potential window and range of operating temperatures, faster electron transfer kinetics, and higher energy densities. In this review article, a critical analysis is provided on the design of organic electroactive molecules, their physiochemical/electrochemical properties, and various organic solvents used in NARFBs. Furthermore, various redox‐active organic materials, such as metal‐based coordination complexes, quinones, radicals, polymers, and miscellaneous electroactive species, explored for NARFBs during 2012–2023 are discussed. Finally, the current challenges and prospects of NARFBs are summarized.

Electrochemical C–H Mono-/Multi-Bromination Regulation of N-Sulfonylanilines on a Cost-Effective Carbon Fiber Electrode and Its Prospective Electroactive Molecule Screening

“…Organic electroactive molecules have attracted much attention for their versatile applications, such as the key components for redox flow batteries (RFBs) , and the electroactive molecular beacons (MBs) for electrochemical biosensors. , In RFBs, electroactive molecules are used as redox molecules to bridge the interconversion between chemical energy and electric energy, most of which are scarce and expensive inorganic metal ions, , seriously hindering the development of RFBs. In electrochemical biosensors, methylene blue (MTB) and ferrocene (Fc) are the only two organic electroactive molecules due to their excellent electrochemical response.…”

Studies of the Functionalized α-Hydroxy-p-Quinone Imine Derivatives Stabilized by Intramolecular Hydrogen Bond

“…Quinones represent a class of biologically active compounds with both cytotoxic and cytoprotective effects [3]. Considerable attention to redox-active compounds in general and quinones in particular [4,5] can be explained by growing demands on energy storage devices for portable electronics and renewable energy-powered vehicles [6]. Quinones can potentially be used in different applications connected with energy storage due to their remarkable redox activity: as organic cathode materials for different kinds of rechargeable batteries [7], including redox flow batteries [8] and Zn-ion batteries [9], or as redox mediators in lithium-sulfur batteries [10].…”

Recent Development of Electrolytes for Aqueous Organic Redox Flow Batteries (Aorfbs): Current Status, Challenges, and Prospects

“…Aqueous RFBs (ARFBs), such as Br-polysulfide flow batteries, employ water as the solvent for the solution is presented by Zhang et al [27] Wei et al, published a report about redox-active materials in non-aqueous RFBs (NARFBs) by dissolving in non-aqueous organic solvents such as acetonitrile, ethylene carbonate, and dimethyl acetate. [28,29] Figure 1. Schematic of a typical RFBs.…”

“…In contrast, inorganic RFBs, such as all‐vanadium redox flow batteries (VRFBs), employ inorganic materials as solutes in the solution is reported by Chai et al [26] Additionally, RFBs can be classified as aqueous or non‐aqueous. Aqueous RFBs (ARFBs), such as Br‐polysulfide flow batteries, employ water as the solvent for the solution is presented by Zhang et al [27] Wei et al, published a report about redox‐active materials in non‐aqueous RFBs (NARFBs) by dissolving in non‐aqueous organic solvents such as acetonitrile, ethylene carbonate, and dimethyl acetate [28,29] …”