Materials and Systems for Organic Redox Flow Batteries: Status and Challenges

Abstract

Redox flow batteries (RFBs) are propitious stationary energy storage technologies with exceptional scalability and flexibility to improve the stability, efficiency, and sustainability of our power grid. The redox-active materials are the key component for RFBs with which to achieve high energy density and good cyclability. Traditional inorganic-based materials encounter critical technical and economic limitations such as low solubility, inferior electrochemical activity, and high cost. Redox-active organic materials (ROMs) are promising alternative "green" candidates to push the boundaries of energy storage because of the significant advantages of molecular diversity, structural tailorability, and natural abundance. Here, the recent development of a variety of ROMs and associated battery designs in both aqueous and nonaqueous electrolytes are reviewed. The critical challenges and potential research opportunities for developing practically relevant organic flow batteries are discussed.

Bioderived Molecular Electrodes for Next‐Generation Energy‐Storage Materials

“…The solubility of quinones, viologens, flavins, and other natural/biological redox‐active species in acidic or alkaline pH electrolytes make them excellent candidates for organic aqueous flow batteries (schematic shown in Figure ). Compared with inorganic RFB systems, an organic RFB paired with aqueous electrolyte is of low cost, with enhanced power density, improved safety, and environmental benignity . Furthermore, organic species, such as quinones, offer tunability through the attachment of functional groups for improved solubility .…”

A Comparative Review of Electrolytes for Organic‐Material‐Based Energy‐Storage Devices Employing Solid Electrodes and Redox Fluids

“…Interestingly, organic redox materials have shown broad applicability in LIBs, beyond‐Li systems (such as Na + , K + , and multivalent cations including Mg 2+ , Ca 2+ , Zn 2+ , or Al 3+ ), and RFBs . The first two use organic materials as solid electrodes assembled inside the electrochemical cell (Figure ), whereas RFBs store energy by using the electrochemical reactions of organic materials as dissolved species that are transported to reaction sites in the battery by the forced flow of redox electrolytes.…”

Comparison of Quinone‐Based Catholytes for Aqueous Redox Flow Batteries and Demonstration of Long‐Term Stability with Tetrasubstituted Quinones

“…[ 5 ] Compared to inorganic compounds, organic electrolytes hold the promise of near‐limitless availability and (bio)degradability into benign products. [ 6,7 ] One class of redox‐active organic compounds that has attracted much research is quinones, which undergo 2e − /2H + reduction over a wide range of potentials based on their ancillary substitution. [ 8–11 ] It is thus possible to select two quinones with different reduction potentials as the low‐ and high‐potential mediators in a RFB ( Scheme 1 ).…”