Artificial Bipolar Redox-Active Molecule for Symmetric Nonaqueous Redox Flow Batteries

Abstract

We synthesize a covalently linked bipolar molecule 1-(2-(4methoxy-2,5-dimethylphenoxy) ethyl)-1′-methyl-[4,4′-bipyridine]-1,1′-diium hexafluorophosphate (VIODAMB) and apply this new compound to a nonaqueous organic redox flow battery (NAORFB) as both the anolyte and catholyte. We demonstrate that this symmetrical electrolyte can mitigate the cross-contamination issue in the flow battery. The compound exhibits an enhanced solubility of 0.66 M in acetonitrile. The flow cell delivers a capacity retention rate of 80% and an energy efficiency of 85% over 35 cycles at a current density of 1.5 mA cm −2 in the cycling test.

Low Viscosity, High Concentration Pyridinium Anolytes for Organic Nonaqueous Redox Flow Batteries

“…Pyridiniums were derivatized by either varying the N-substituent or modifying the 4-aryl ring, and the library was selected to contain sufficient steric and electronic variation at both positions to elucidate broader structure−property relationships for this class of pyridinium ROMs. Variation of the 4-aryl ring was limited to either all hydrogen (i.e., the parent unmodified phenyl ring) (1, 3, 4, 5, 7, 18), 4-methyl (2,8,9,10,11,13,15,21,22), 2,4-dimethyl (12,19,20), or 4methoxy (6,14,16,17,23) substituents; however, variation of the N-substituent represents a wider range of functionality, including flexible butyl or oligoether chains and sterically hindering aryl rings with either electron-donating or -withdrawing substituents. The breadth of substituent variations spanning across all 23 compounds is particularly valuable in revealing the less predictable combined effects of electron density and sterics in the 4-position and N-position.…”

“…This improved solubility is important, because NRFB energy storage capacity is directly proportional to ROM concentration. Despite the recent advancements in identifying and developing numerous classes of ROMs that exhibit promising electrochemical stability and low reduction potentials (or high oxidation potentials), many suffer from high dynamic viscosity (>10 mPa·s) and low conductivity (<5 mS cm –1 ) at concentrations that would be sufficiently high for practical operation (>0.5 M). − In the context of an NRFB, highly viscous ROM solutions limit flow rates and cause pressure drop across the flow field (both of which limit mass transport, and thus limit charge/discharge rates), while poorly conductive solutions result in high overpotentials and low storage efficiency. − Therefore, there remains a need to identify classes of ROMs that demonstrate moderate viscosities and conductivities at elevated concentrations.…”

A Flexible Six-in-One Microsensor Embedded in a Vanadium Redox Flow Battery for Long-Term Monitoring

“…The polyelectrolyte membrane is considered as the key component of VRFB devices and has a long cycle life in practical applications [ 8 ]. Since vanadium ions are used on both sides of the VRFB, vanadium ions with different valence states are used as anolytes and catholytes, and the capacity regeneration process is simple and cross-contamination can be eliminated [ 9 , 10 , 11 , 12 ]. The high-power density VRFB is characterized by its exquisite structure and significantly lower system cost, and its commercial application is increasingly important [ 13 ].…”

Ester-Substituted Bispyridinylidenes: Double Concerted Two-Electron Bipolar Molecules for Symmetric Organic Redox Flow Batteries

“…Broadly speaking, there are two different kinds of bipolar molecules that have previously been studied for organic redox flow batteries. One is artificial, − where independent anolyte and catholyte materials are connected together by an inert linker chain (such as methylene, glycol, etc. ), such that the low and high redox potential units are discrete and largely have the properties of their respective unbridged parent structures.…”