Molecular engineering of organic electroactive materials for redox flow batteries

Abstract

With high scalability and independent control over energy and power, redox flow batteries (RFBs) stand out as an important large-scale energy storage system. However, the widespread application of conventional RFBs is limited by the uncompetitive performance, as well as the high cost and environmental concerns associated with the use of metal-based redox species. In consideration of advantageous features such as potentially low cost, vast molecular diversity, and highly tailorable properties, organic and organometallic molecules emerge as promising alternative electroactive species for building sustainable RFBs. This review presents a systematic molecular engineering scheme for designing these novel redox species. We provide detailed synthetic strategies for modifying the organic and organometallic redox species in terms of solubility, redox potential, and molecular size. Recent advances are then introduced covering the reaction mechanisms, specific functionalization methods, and electrochemical performances of redox species classified by their molecular structures. Finally, we conclude with an analysis of the current challenges and perspectives on future directions in this emerging research field.

Cation‐Anion Redox Switching in an All‐Ferrocene Salt

“…Investigations into ferrocene compounds as redox active materials continue to grow . Recently, attention has turned to the use of ferrocenes as possible components in redox flow battery (RFB) applications, arising from the desire to produce new chemical compounds for the low cost and scalable storage of energy. Among transition metal‐based compounds, ferrocenes have many notable properties as RFB components, ranging from their relative low cost and ease of synthesis to their stabilities and electrochemical reversibility in a variety of media.…”

A Long Cycle Life, Self‐Healing Zinc–Iodine Flow Battery with High Power Density

“…[1] Although much work has focused on the development of FB technologies,l ow energy densities,h igh cost have hindered their further commercialization. [2][3][4] Even though the recent development of non-aqueous systems has increased voltage output, [5] energy densities,the FBs are currently significantly limited by the low solubility. [6] Regarding the energy density, zinc-based aqueous FBs are very appealing because of the low cost of zinc and the elimination of electrolyte volume.…”

Dithiolene Complexes of First‐Row Transition Metals for Symmetric Nonaqueous Redox Flow Batteries

“…[1,2] Ap romising candidate for grid-scale energy storage is the redox flow battery (RFB) technology,w hereby solutions of electroactivem aterials are pumped to/frome xternal tanks to the electrode interface for charging/discharging. [11] Metal-ligandc oordination complexes are good candidates for nonaqueous RFBelectrolytes as they can be stable in multiple oxidation states and have high solubility in organic solvents.F urthermore, careful choice of metal ion as well as modification of the ligand scaffold (e.g.,s olubilizing groups, denticity,d onorg roups) can allow for fine tuning of the desired properties for RFB applications. [6][7][8][9][10] Acetonitrile (MeCN) is an attractive solvent for nonaqueous RFBs, andi st he main solvento f choice here, owing to its wide ( % 5V)e lectrochemical window as well as low viscosity (0.34 vs. 0.89 MPa sfor water) and moderate dielectric constant(35.9 vs. 78.4 for water).…”