Redox flow battery

Abstract

The present invention relates to a dioxygen-tolerant redox flow battery (RFB), a method for making an RFB in the presence of dioxygen, and a method for charging and / or discharging an RFB in the presence of dioxygen, and uses thereof. The RFB includes an electrolyte, which includes an organic redox-active molecule including redox-active units having two or more heteroarylene groups, the two or more heteroarylene groups being conjugated within the redox-active units, at least a portion of which exist as a complex formed from a one-electron reduced form of the redox-active units, and molecular dioxygen (O2) dissolved in the electrolyte. The RFB of the present invention can be operated in the presence of dioxygen, eliminating the need for purging, sealing, and creating a strict dioxygen-free environment by flowing an inert gas through the RFB.

Description

[Technical Field]

[0001] The research leading to this application has received funding from the European Union's Horizon 2020 research and innovation programme (European Research Council grant agreements no. 726470 and 835073, and Marie Sklodowska-Curie grant agreement no. 706425).

[0002] Related Applications This application claims priority to and the benefit of UK Patent Application No. 2300538.2, filed on 13 January 2023 (13.01.2023), the contents of which are incorporated by reference in their entirety.

[0003] The present invention relates to a dioxygen tolerant redox flow battery (RFB), a method for making an RFB in the presence of dioxygen, and a method for charging and / or discharging an RFB in the presence of dioxygen, and uses thereof. [Background technology]

[0004] RFBs are a type of electrochemical storage device in which energy is stored in a liquid electrolyte rather than in solid electrode materials. This feature allows the capacity of RFBs to be increased cost-effectively by simply changing the size of the electrolyte reservoir. Their layout can also be made more flexible because the electrochemical cell components and the electrolyte reservoir can be located at separate locations. RFBs are therefore a promising approach for large-scale energy storage, such as power network or grid storage. RFBs can provide an important form of grid storage to smooth out energy fluctuations from intermittent renewable energy sources such as solar and wind.

[0005] During battery operation, electrolytes, known as catholyte and anolyte, flow through the electrochemical cell where they undergo redox reactions to store or release charge. The electrolytes are then stored in their reduced or oxidized states in the electrolyte reservoir. The electrolytes contain redox-active species that promote reduction or oxidation.

[0006] Among redox-active species, those based on organic molecules offer both substantial cost benefits over existing chemistries (eg, zinc or vanadium-based electrolytes) and good energy density.

[0007] Viologens (4,4'-bispyridinium compounds) are organic redox-active species that often provide good aqueous solubility, negative potential, and electrochemical stability under neutral conditions, as required for RFBs. Acidic or basic conditions may also be used to solubilize organic redox-active species.

[0008] Viologens have been demonstrated as RFB redox-active species in a variety of single and double electron pairs (DeBruler et al., Beh et al., Luo et al.). They have also been incorporated into larger organic materials such as organic polymers (Janoschka et al.) and polypeptides (Nguyen et al.), providing redox-active species in RFB electrolytes.

[0009] A common problem with RFBs (e.g., viologen-based RFBs) is the degradation of redox-active species in the electrolyte due to parasitic side reactions during cell cycling. One proposed problem with such RFBs is the degradation of redox-active species due to association at high concentrations (see Kwabi et al.). Redox-active species undergo intermolecular association (e.g., dimerization) and / or electrolyte-electrode association, which are thought to contribute to degradation. However, while it is desirable to operate RFBs with high concentrations of redox-active molecules in the electrolyte to maximize energy density, doing so is thought to accelerate degradation.

[0010] Above a concentration of about 0.1 mM in an aqueous environment, assembled structures can be formed among reduced viologen organic redox-active species, such as π-dimers, σ-dimers, and charge-transfer complexes. Dimer formation has previously been linked to capacity fade (Kwabi et al.). Therefore, the design of viologen redox-active species and electrolytes was sought to suppress such dimerization processes.

[0011] Furthermore, side reactions with dioxygen are particularly problematic. Redox-active species in the electrolyte can exist as mono- and diradicals in the RFB system during cell cycling, which can transfer electrons to dissolved dioxygen to form reactive dioxygen species (such as peroxides, superoxides, and hydroxyl radicals). These reactive dioxygen species participate in parasitic side reactions during cell cycling. Specifically, viologen mono- and diradicals in the RFB system are known to readily transfer electrons to dissolved dioxygen, leading to the formation of reactive oxygen species (ROS) (Bird et al.).

[0012] To suppress dioxygen-mediated side reactions, RFBs are cycled under strict dioxygen-free conditions. For example, gaseous dioxygen is excluded from the headspace above the electrolyte in the electrochemical cell and electrolyte reservoir, and dissolved dioxygen is removed from the electrolyte itself. During fabrication of known RFBs, dissolved dioxygen is typically removed by purging the electrolyte with an inert gas. The headspace is also purged with an inert gas during fabrication and then air-sealed during operation. The electrolyte headspace may also be placed under a positive flow of inert gas during operation to remove dioxygen generated during operation.

[0013] Sensitivity to dioxygen is particularly problematic for aqueous electrolytes. In water, dioxygen can be generated in situ by cycling the RFB at voltages outside the stability window of water (e.g., open-circuit voltages above approximately 1.23 V). As a result, most aqueous RFBs to date are cycled at open-circuit voltages below 1.23 V to avoid in situ generation of dioxygen through water splitting (Perry et al.). This maximum operating voltage is very low compared to many common battery technologies (e.g., lithium-ion batteries), which operate at approximately 3–4 V per cell. This limits the energy density and electrical efficiency of RFBs. High currents are often required to compensate for the low voltage, which reduces efficiency.

[0014] All viologen RFB cycle research to date has been conducted in a strict air-free environment. It is well known that viologen RFBs are sensitive to dioxygen molecules, and therefore dioxygen is removed from the RFB by purging. Dioxygen removal is common in RFB construction and operation.

[0015] However, the additional steps required to keep RFBs dioxygen-free make their manufacture and operation complex and expensive, which is a major barrier to their large-scale adoption. Relatedly, the low voltages required to avoid in situ dioxygen generation for aqueous RFBs also hinder large-scale adoption, as energy density is limited compared to higher voltage systems. [Prior art documents] [Patent documents]

[0016] [Patent Document 1] U.S. Patent Application Publication No. 2020 / 016891 [Patent Document 2] International Publication No. 2021 / 055275 [Patent Document 3] International Publication No. 2023 / 046710 [Patent Document 4] U.S. Patent Application Publication No. 2022 / 0384834 [Patent Document 5] U.S. Patent Application Publication No. 2022 / 0020990 [Patent Document 6] U.S. Patent Application Publication No. 2022 / 0190374 [Patent Document 7] Chinese Patent No. 112500329 [Patent Document 8] International Publication No. 2022 / 236241 Summary of the Invention [Problem to be solved by the invention]

[0017] Thus, there is a need for RFBs, and particularly RFB organic electrolytes, that can be used in the presence of dioxygen without adversely affecting performance. [Means for solving the problem]

[0018] In its most general form, the present invention provides a redox flow battery (RFB) that contains molecular dioxygen (O2) dissolved in an electrolyte. The RFB can be cycled in the presence of dioxygen, such as in air.

[0019] In general, the present invention relates to an RFB including an electrolyte, the electrolyte comprising: an organic redox active molecule, wherein at least a portion of the organic redox active molecule is present as a complex formed from a reduced form of the organic redox active molecule; and It contains molecular dioxygen (O2) dissolved in an electrolyte.

[0020] Complexation of the reduced form of the organic redox-active molecule provides a competing pathway for the decomposition reaction with dioxygen, rendering the redox-active species dioxygen-tolerant, which in turn renders the RFB dioxygen-tolerant.

[0021] In one general aspect of the invention, there is provided a redox flow battery comprising an electrolyte, the electrolyte comprising: an organic redox-active molecule comprising a redox-active unit having two or more heteroarylene groups, wherein the two or more heteroarylene groups are conjugated within the redox-active unit, and at least a portion of the redox-active units in the electrolyte are present as complexes formed from one-electron reduced forms of the redox-active units; and A redox flow battery is provided that includes molecular dioxygen (O2) dissolved in an electrolyte.

[0022] In a first aspect of the present invention, there is provided a redox flow battery comprising an electrolyte, the electrolyte comprising: an organic redox-active molecule comprising a redox-active unit having two or more heteroarylene groups, wherein the two or more heteroarylene groups are conjugated within the redox-active unit, and at least a portion of the redox-active units in the electrolyte are present as complexes formed from one-electron reduced forms of the redox-active units; and molecular dioxygen (O2) dissolved in an electrolyte, Redox flow batteries are provided wherein the complex is an intermolecular complex of redox active units, such as a homodimer, an intramolecular complex of redox active units, or the complex is a combination of intermolecular and intramolecular complex redox active units.

[0023] In some embodiments, a redox flow battery is provided that includes an electrolyte, the electrolyte comprising: an organic redox-active molecule comprising two or more heteroarylene groups, wherein the two or more heteroarylene groups are conjugated and at least a portion of the organic redox-active molecule exists as a complex formed from a one-electron reduced form of the organic redox-active molecule; and It contains molecular dioxygen (O2) dissolved in an electrolyte.

[0024] In some embodiments, the complex is a dimer, such as a homodimer, formed from a one-electron reduced form of an organic redox active molecule.

[0025] In some embodiments, the organic redox active molecule comprises a redox active unit of formula (lA):

[0026] [ka]

[0027] (Wherein -A- and -B- each independently represent C 5-10 is arylene; -L- is independently C 5-14 Arylene, bond, C 2-6 Alkenylene, C 2-4 alkynylene, C 5-14 Arylene and C 2-4 Alkenylene is a group consisting of one or more -R C optionally substituted with a group; -L 1 - is an independent bond, C 1-6 Alkylene, C 5-14 Arylene, -N(H)-, and (CHO) a1 -(C2H4O) a2 -(C3H6O) a3 -(CHC(O)) a4 - selected from C 1-6 Alkylene and C 5-14 An arylene may be one or more -R D optionally substituted with a group, wherein a1, a2, a3, and a4 are each independently selected from 0 to 12, and the sum of a1, a2, a3, and a4 is 1 to 12; -R A , -R B , if exists -R C and -R D each of which is a hydrophilic group; X is one or more counteranions; n is 2 to 4; a and b are independently 1 to 5; c and d are independently 1 to 5; Two or more of -A-, -B- and -L- are C 5-10 is heteroarylene; m is 1 or greater).

[0028] In some embodiments, the organic redox active molecule is of formula (1B):

[0029] [ka]

[0030] (In the formula, -A-, -B-, -L-, -L 1 -, -R A , -R B , -R C , -R D , X, a, b, c, d, n and m are as defined for formula (lA).

[0031] In some embodiments, the organic redox active molecule is of formula (lC):

[0032] [ka]

[0033] (In the formula, -A-, -B-, -L-, -L 1 -, -R A , -R B , -R C , -R D , X, a, b, c, d, n and m are as defined for formula (lA); R p is a polymer repeat unit; p is 2 or greater).

[0034] In some embodiments, the organic redox active molecule is of formula (lD):

[0035] [ka]

[0036] (In the formula, -A-, -B-, -L-, -R A , -R B , -R C, X, a, b, c and n are as defined for formula (lA); q is 1 to 5).

[0037] In some embodiments, the organic redox active molecule is of formula (I):

[0038] [ka]

[0039] (Wherein -A- and -B- each independently represent C 5-10 is arylene; -L- is independently C 5-14 Arylene, bond, C 2-6 Alkenylene and C 2-4 alkynylene, C 5-14 Arylene and C 2-6 Alkenylene can be one or more -R C optionally substituted with a group; -R A and -R B If the list exists, -R C at least one of is independently a hydrophilic group; X is one or more counteranions; n is 2 to 4; a, b, and c each independently represent 1 to 5; Two or more of -A-, -B- and -L- are C 5-10 Heteroarylene).

[0040] In some embodiments, the organic redox active molecule is of formula (II):

[0041] [ka]

[0042] (In the formula, -L-, -R A , -R B , X, n, a, b and c are as defined for formula (I).

[0043] In some embodiments, the organic redox active molecule is a viologen or an extended viologen.

[0044] Traditionally, complex formation, such as dimerization, has been attributed to capacity fade and has been associated with, for example, the deposition of reduced electrolyte molecules upon electrolyte-electrode interaction. Deposition at RFB electrodes is also known to cause electrode degradation. As a result, known organic redox-active molecules and electrolytes have been actively designed to inhibit dimerization to avoid capacity fade and solubility issues.

[0045] However, the present inventors have recognized that this complexation (e.g., dimerization) can be used to minimize capacity fade of RFBs in the presence of dioxygen. The redox-active molecules and electrolyte conditions developed by the inventors ensure that the propensity of the reduced form of the electrolyte material for complexation is increased and the associated radical complex maintains solubility in the electrolyte. This is accomplished by providing redox-active species with solubilizing groups (e.g., hydrophilic groups), such as conjugated heteroarylene systems and organic redox-active species of the formula shown above, which may be viologen or extended viologen species.

[0046] Without being bound by theory, it is believed that the complexes act to stabilize the redox-active species through radical pair formation by providing charge-transfer interactions, as well as steric protection and multiple resonance structures. Furthermore, radical pair formation effectively reduces the radical concentration while keeping the oxidation state of the species unchanged.

[0047] In addition to complex formation, the inventors have demonstrated a wide singlet-triplet gap (E ST We also found that the redox-active species, which are two-electron reduced to dioxygen, are stabilized through intramolecular electron pairing. ST indicates that the singlet state is energetically favored, and a large negative E ST means that the more reactive triplet state is inaccessible at typical operating temperatures.

[0048] Thus, in some embodiments, the two-electron reduced form of the organic redox active molecule has a kinetic energy of 0 kcal mol -1 Less than (0 kJ mol -1 ), preferably -6.0 kcal mol -1 (-25.1kJ mol -1 ) or less singlet-triplet energy gap (E ST )

[0049] Stabilization by complexation and large E ST The combination of is achieved by providing a redox active species having a conjugated heteroarylene system and a solubilizing group (e.g., a hydrophilic group), such as an organic redox active species of formula (I) or (II) described herein, which may be a viologen or extended viologen species.

[0050] A dioxygen-tolerant electrolyte has various advantages for RFBs. For example, it allows RFBs to be made and cycled in the presence of dioxygen, eliminating the need for RFBs to be made strictly dioxygen-free. By no longer needing to purge, seal, and flush the RFB with inert gas, the cost of making and operating an RFB can be reduced.

[0051] Furthermore, by making the redox-active species dioxygen-tolerant, it is possible to cycle RFB-based aqueous electrolytes at higher voltages. As previously mentioned, it is possible to cycle at voltages beyond the stability window of water (i.e., 1.23 V or greater) without incurring degradation mediated by dioxygen generated in the electrolyte. Higher voltages can result in increased cell energy density and electrical efficiency.

[0052] The above advantages remove various barriers that previously hindered the large-scale adoption of RFBs. The present invention provides a promising approach for the large-scale adoption of RFBs, such as grid-scale batteries.

[0053] In a second aspect of the present invention, there is provided a method of making a redox flow battery, comprising the steps of: forming an electrolyte by combining an organic redox active molecule with a liquid carrier, the organic redox active molecule comprising a redox active unit having two or more heteroarylene groups, the two or more heteroarylene groups being conjugated within the redox active unit; adding an electrolyte to the redox flow battery, wherein molecular dioxygen (O2) is dissolved in the electrolyte; reducing the organic redox active molecule to provide a one-electron reduced form of the redox active unit that forms the complex; Methods are provided wherein the complex is an intermolecular complex of redox active units, such as a homodimer, an intramolecular complex of redox active units, or the complex is a combination of intermolecular and intramolecular complex redox active units.

[0054] In some embodiments, the method comprises: forming an electrolyte by combining an organic redox active molecule with a liquid carrier, wherein the organic redox active molecule comprises two or more heteroarylene groups, and the two or more heteroarylene groups are conjugated; adding an electrolyte to the redox flow battery, wherein molecular dioxygen (O2) is dissolved in the electrolyte; reducing the organic redox active molecule to provide a one-electron reduced form of the organic redox active unit that forms the complex.

[0055] In a third aspect of the present invention, there is provided a redox flow battery obtained or obtainable by the method of the second aspect.

[0056] In a fourth aspect of the present invention, there is provided a method of charging and / or discharging a redox flow battery in the presence of molecular dioxygen, the redox flow battery comprising an electrolyte, the electrolyte comprising: an organic redox-active molecule comprising a redox-active unit having two or more heteroarylene groups, wherein the two or more heteroaryl groups are conjugated within the redox-active unit; and It contains molecular dioxygen (O2) dissolved in an electrolyte, The method is reducing the redox active unit to result in a complex formed from the one-electron reduced form of the redox active unit; and / or oxidizing the two-electron reduced form of the redox active unit to provide a complex formed from the one-electron reduced form of the redox active unit; Methods are provided wherein the complex is an intermolecular complex of redox active units, such as a homodimer, an intramolecular complex of redox active units, or the complex is a combination of intermolecular and intramolecular complex redox active units.

[0057] In some embodiments, the redox flow battery comprises an electrolyte, the electrolyte comprising: an organic redox-active molecule comprising two or more heteroarylene groups, wherein the two or more heteroaryl groups are conjugated; and It contains molecular dioxygen (O2) dissolved in an electrolyte, The method is: reducing the organic redox active molecule to result in a complex formed from the one-electron reduced form of the organic redox active molecule; and / or The method includes oxidizing the two-electron reduced form of the organic redox active molecule to provide a complex formed from the one-electron reduced form of the organic redox active molecule.

[0058] In a fifth aspect of the present invention there is provided a use of a redox flow battery for charging and / or discharging a redox flow battery comprising an electrolyte in the presence of molecular dioxygen, the electrolyte comprising: an organic redox-active molecule comprising a redox-active unit having two or more heteroarylene groups, wherein the two or more heteroarylene groups are conjugated within the redox-active unit, and at least a portion of the redox-active unit exists as a complex formed from a one-electron reduced form of the redox-active unit; and It contains molecular dioxygen (O2) dissolved in an electrolyte, Use is provided wherein the complex is an intermolecular complex of redox active units such as a homodimer, an intramolecular complex of redox active units, or the complex is a combination of intermolecular and intramolecular complex redox active units.

[0059] In some embodiments, the redox flow battery comprises an electrolyte, the electrolyte comprising: an organic redox active molecule comprising two or more heteroarylene groups, wherein the two or more heteroarylene groups are conjugated and at least a portion of the organic redox active molecule exists as a complex formed from a one-electron reduced form of the organic redox active molecule; and It contains molecular dioxygen (O2) dissolved in an electrolyte.

[0060] In some embodiments of the second through fifth aspects, the organic redox active molecule comprises a unit of formula (lA), as defined above.

[0061] In some embodiments of the second through fifth aspects, the organic redox active molecule is of formula (1B), as defined above.

[0062] In some embodiments of the second through fifth aspects, the organic redox active molecule is of formula (lC), as defined above.

[0063] In some embodiments of the second through fifth aspects, the organic redox active molecule is of formula (lD), as defined above.

[0064] In some embodiments of the second through fifth aspects, the organic redox active molecule is of formula (I), as defined above. In some embodiments of the second through fifth aspects, the organic redox active molecule is of formula (II), as defined above.

[0065] In some embodiments of the second through fifth aspects, the organic redox active molecule is a viologen or extended viologen species.

[0066] In some embodiments of the second through fifth aspects, the complex is a dimer, such as a homodimer, formed from the one-electron reduced form of the organic redox active molecule.

[0067] The present invention will now be described with reference to the figures listed below. [Brief explanation of the drawings]

[0068] [Figure 1] FIG. 1 is a 1H NMR spectrum of compound 1 synthesized using palladium on activated carbon as a catalyst. [Figure 2] Figure 2 shows (a) a comparison of conventional diradical hydrocarbons and bispyridinium diradicals, (b) a schematic diagram of compounds 10–19, and (c) the linear correlation obtained between DFT-calculated redox potential values ​​and tabulated experimental meta-Hammett constant values ​​(σm) for the R groups introduced at the pyridinium nitrogen. The trend lines show the least-squares linear fits obtained for the first and second redox events. (d) Plot of solubility versus first reduction potential for compounds 10–19. Filled circles indicate electrochemically reversible compounds. Open circles indicate electrochemically irreversible compounds. The shaded area indicates compounds with reduction potentials below that of any bispyridinium electrolyte featuring an unsubstituted core reported to date. The dashed line (gray) indicates the lowest reduction potential reached by substituted or unsubstituted bispyridinium RFB electrolytes. (e) Voltammograms for compounds 10–19 ordered by their respective singlet-triplet gap (EST) values. [Figure 3]Figure 3. Coupled in situ NMR and EPR spectroscopy of 10 mM (a) 10, (e) 11, and (i) 13 in 100 mM NaCl and 20 mM 4-hydroxy-TEMPO in a 100 mM NaCl full cell as a function of time during one full charge-discharge cycle. A current of 2 mA cm was used. Cutoff voltages of 0.5 V (10, 11, and 13), 1.90 V (10), 1.95 V (11), and 2.00 V (13) were used, with a 1 h potential hold applied at each cutoff value. NMR (b, f, j) and EPR (c, g, k) spectra collected during the charge-discharge cycle. (d, h, l) Oxidation states and respective NMR proton assignments of 10, 11, and 13. Chloride counterions are omitted for clarity. The proton assignment e* indicates that proton e undergoes rapid hydrogen-deuterium exchange, reducing its intensity and limiting its observation by NMR. [Figure 4] Figure 4 shows the coupling in situ NMR and EPR spectroscopy for 17 and 18. The voltage of 10 mM (a) 17 and (e) 18 in 100 mM NaCl and 20 mM 4-hydroxy-TEMPO in a 100 mM NaCl full cell as a function of time during one full charge-discharge cycle. A current of 2 mA cm was used. Cutoff voltages of 0.5 V (17 & 18), 1.75 V (17), and 1.85 V were used, with a 1 h potential hold applied at each cutoff value. NMR (b, f) and EPR (c, g) spectra taken during the charge-discharge cycle. (d, h) Oxidation states of 17 and 18 and their respective NMR proton assignments. Chloride counterions are omitted for clarity. [Figure 5]Figure 5 shows the coupled in situ NMR and EPR spectroscopy for 11 at 1 mM. (a) Potential of 11 at 1 mM in 100 mM NaCl and 2 mM 4-hydroxy-TEMPO in a 100 mM NaCl full cell as a function of time during one full charge-discharge cycle. A current of 0.2 mA cm-2 was used. Cutoff voltages of 0.5 V and 1.95 V were used, with a 1 h potential hold applied at each cutoff value. NMR (b) and EPR (c) spectra taken during the charge-discharge cycle. Features in the EPR spectrum indicate the presence of an ultra-trace amount of 4-OH-TEMPO crossover. (d) Structure of 11 and its respective NMR proton assignments. [Figure 6] Figure 6 shows the performance characteristics of 17 and 18. Voltage vs. discharge capacity during five full charge-discharge cycles for (a) 17 and (b) 18 in 100 mM NaCl and 20 mM 4-hydroxy-TEMPO in a 100 mM NaCl full cell. A current of 2 mA cm was used in all cases. Cutoff voltages of 0.5 V (17 & 18), 1.75 V (17), and 1.85 V (18) were used, with a 1 h potential hold applied at each cutoff value. [Figure 7] Figure 7 shows the normalized discharge capacity versus cycle number for 17 and 18 at 10 mM concentration. The coulombic efficiencies for 17 and 18 were 78.6±0.3 and 79.7±2.8, respectively. [Figure 8]Figure 8 shows the reduced bispyridinium compounds, their performance characteristics, and dimerization tendency. (a) Radical concentration profiles for 10, 11, and 13 during charging derived from spin counting based on the EPR data shown in Figure 2. (b) Spectroelectrochemical data for 10, 11, and 13 at 1 mM concentration. (c) Voltage vs. discharge capacity during five full charge-discharge cycles for 10 mM 10, 11, and 13 in 100 mM NaCl and 20 mM 4-hydroxy-TEMPO in a 100 mM NaCl full cell. A current of 2 mA cm was used in all cases. For compound 11, voltage vs. discharge capacity data during five full charge-discharge cycles for 5 mM and 1 mM full cells of 11 are overlaid. 5 mM 11 in 100 mM NaCl and 10 mM 4-hydroxy-TEMPO in a 100 mM NaCl full cell was cycled at a current of 1 mA cm. 1 mM of 11 in 100 mM NaCl and 2 mM 4-hydroxy-TEMPO in a 100 mM NaCl full cell was cycled at a current of 0.2 mA cm-2. Cutoff voltages of 0.5 V (10, 11, & 13), 1.90 V (10), 1.95 V (11), and 2.00 V (13) were used with a 1 h potential hold applied at each cutoff value. (d) Discharge capacity vs. cycle number for 11 at concentrations of 10 mM, 5 mM, and 1 mM. (e) Normalized discharge capacity vs. cycle number for 10, 11, and 13 at 10 mM concentration. [Figure 9]Figure 9 shows the effect of dioxygen on the viologen redox process and its suppression via π-dimerization. (a) Operando online electrochemical mass spectrometry (OEMS) of 1 mM 11 in 100 mM NaCl and 2 mM 4-hydroxy-TEMPO in a 100 mM NaCl H-cell during one full charge-discharge cycle in an atmosphere of 1% O in Ar. A current of 0.2 mA was used. A 2 h potential hold was applied at 1.95 V after 8 h of charge. (b) Voltage, normalized discharge capacity, and Coulombic efficiency of 25 mM 11 in 500 mM NaCl and 50 mM 4-hydroxy-TEMPO in a 500 mM NaCl full cell cycled 6 times in N, 5 times in air, and 10 times in N. A current of 5 mA cm was used. (c) Voltage, normalized discharge capacity, and Coulombic efficiency of 50 mM H-cells in 500 mM NaCl and 100 mM 4-hydroxy-TEMPO in a 500 mM NaCl full cell cycled 6 times in N, 5 times in air, and 10 times in N. A current of 5 mA cm was used. (d) OEMS of a 50 mM H-cell exposed to a 2 h potential hold at 1.95 V in 1% O in Ar and 20% O in Ar atmospheres, respectively, for the 1 mM H-cell described in Figure 4a. A current of 1.55 mA was used in both cases. (e) Voltage, normalized discharge capacity, and Coulombic efficiency of 250 mM 11 and 250 mM 4-hydroxy-TEMPO in a 1 M NaCl full cell cycled 5 times in N2 at a current density of 20 mA cm-2, 15 times in air at a current density of 20 mA cm-2, 111 times in air at a current density of 40 mA cm-2, 5 times in air at a current density of 20 mA cm-2, and 200 times in air at a current density of 30 mA cm-2. Blocking voltages of 0.5 V and 1.65 V were used. [Figure 10] Figure 10 shows the effect of dioxygen on the viologen redox process for compound 17 and its inhibition via π-dimerization. Voltage, normalized discharge capacity, and coulombic efficiency of 50 mM of 17 in 500 mM NaCl and 100 mM 4-hydroxy-TEMPO in a 500 mM NaCl full cell cycled five times in N, five times in air, and eight times in N. A current of 5 mA cm was used. [Figure 11] Figure 11 shows repeated cycling of 17 at high concentrations, illustrating the air resistance of 17. The voltage, normalized discharge capacity, and Coulombic efficiency of 250 mM 17 and 250 mM 4-hydroxy-TEMPO in a 1 M NaCl full cell cycled 5 times in N2 at a current density of 20 mA cm-2, 15 times in air at a current density of 20 mA cm-2, 67 times in air at a current density of 40 mA cm-2, 5 times in air at a current density of 20 mA cm-2, and 100 times in air at a current density of 30 mA cm-2. Blocking voltages of 0.5 V and 1.60 V were used. [Figure 12] Figure 12 shows (A) the voltammograms for compound 10 at a concentration of 1 mM under nitrogen (dashed line), compound 20 at a concentration of 1 mM under nitrogen (dark blue line), and compound 20 at a concentration of 1 mM under air (light blue line). Reversible potentials of -0.147 V and -0.386 V were calculated from the peaks in the voltammograms. (B) shows the H NMR spectrum for compound 20. DETAILED DESCRIPTION OF THE INVENTION

[0069] The present invention provides a redox flow battery (RFB) that includes molecular dioxygen (O2) dissolved in an electrolyte. The RFB can be cycled in the presence of dioxygen, such as in air.

[0070] Generally, the present invention provides an electrolyte for an RFB that includes a redox active species that is tolerant to molecular dioxygen. The redox active species is configured to form a complex with its one-electron reduced form, resulting in improved tolerance to molecular dioxygen.

[0071] More specifically, the present invention relates to an RFB comprising an electrolyte, the electrolyte comprising: an organic redox active molecule, wherein at least a portion of the organic redox active molecule is present as a complex formed from a reduced form of the organic redox active molecule; and It contains molecular dioxygen (O2) dissolved in an electrolyte.

[0072] In a first aspect of the present invention, there is provided a redox flow battery comprising an electrolyte, The electrolyte is an organic redox-active molecule comprising redox-active units having two or more heteroarylene groups, wherein the two or more heteroarylene groups are conjugated within the redox-active units, and at least a portion of the redox-active units in the electrolyte are present as complexes formed from one-electron reduced forms of the redox-active units; and molecular dioxygen (O2) dissolved in the electrolyte; Redox flow batteries are provided wherein the complex is an intermolecular complex of redox active units, such as a homodimer, an intramolecular complex of redox active units, or the complex is a combination of intermolecular and intramolecular complex redox active units.

[0073] In some embodiments, the complex is a dimer.

[0074] In some embodiments, the organic redox active molecule is of formula (I):

[0075] [ka]

[0076] (Wherein -A- and -B- each independently represent C 5-10 is arylene; -L- is independently C 5-14 Arylene, bond, C 2-6 Alkenylene, C 2-4 alkynylene, C 5-14 Arylene and C 2-4 Alkenylene is a group consisting of one or more -R C optionally substituted with a group; -R A and -R B If the list exists, -R C at least one of is independently a hydrophilic group; X is one or more counteranions; n is 2 to 4; a, b, and c each independently represent 1 to 5; Two or more of -A-, -B- and -L- are C 5-10 Heteroarylene).

[0077] In some embodiments, the organic redox active molecule is of formula (II):

[0078] [ka]

[0079] (In the formula, -L-, -R A , -R B , X, n, a, b and c are as defined for formula (I).

[0080] In some embodiments, the organic redox active molecule is a viologen or an extended viologen.

[0081] The present invention achieves dioxygen tolerance by providing redox active species that are one-electron reduced and have an increased tendency to complex, such as dimerization (e.g., by using an extended aromatic core), and that have improved aqueous solubility of the redox active species complex (e.g., by using a hydrophilic adduct). In known systems, the one-electron reduced form of the redox active species is prone to side reactions. However, it has now been found that complex formation (e.g., dimerization) of the redox active species competes with and limits degradation through side reactions.

[0082] Certain organic redox active species are known.

[0083] Tang et al. describe viologen, phenyl-extended viologen, and methyl-substituted phenyl-extended viologen as redox-active species for RFB electrolytes. All of the described RFBs are operated in a dioxygen-free environment. This can be seen by the absence of dioxygen in Tang et al.'s voltammograms (see Figures 2 and S9). Furthermore, the absence of dioxygen is evident from the high Coulombic efficiency of approximately 95-100% (see Table S2).

[0084] Tang et al. further teach that viologens have a tendency to dimerize, which is thought to promote degradation through side reactions and precipitation of redox-active species during reduction. This causes capacity fade during cell cycling. Dimerization is said to increase at high concentrations of redox-active species, so the concentration of redox-active species in the electrolyte is kept low at 10 mM. Tang et al. focus on redox-active species that tend to dimerize due to steric or electronic constraints. Methylated viologen electrolytes are preferred because they do not dimerize due to higher steric hindrance. Therefore, Tang et al. do not describe RFBs containing dimerized redox-active species where dioxygen is present in the electrolyte and / or electrolyte reservoir.

[0085] Luo et al. (and corresponding U.S. Patent Application Publication No. 2020 / 016891) describe 4,4'-(thiazolo[5,4-d]thiazol-2,5-diyl)bis(1-(3-(trimethylammonio)propyl)pyridin-1-ium) tetrachloride. The thiazolo[5,4-d]thiazole-extended viologen was tested as a redox-active species for RFB electrolytes. The described RFB is operated in a dioxygen-free environment.

[0086] Thiazolo[5,4-d]thiazole-extended viologen electrolytes showed poorer capacity retention and energy efficiency at higher concentrations, which was attributed to increased electrolyte-electrolyte interactions and dimerization. Luo et al. report that the improved π-conjugation provided by the thiazolo[5,4-d]thiazole core is important for the electrolyte's performance.

[0087] Luo et al. comment on the dioxygen insensitivity of the reduced 2+ form of the thiazolo[5,4-d]thiazole-extended viologen redox-active species. The demonstrated stability is said to be due to the π-conjugation provided by the thiazolo[5,4-d]thiazole core. The literature does not test the viologen electrolyte during cell cycling or in any other oxidation states, nor does it provide a redox flow cell in which the electrolyte and / or electrolyte reservoir are free of molecular dioxygen.

[0088] Beh et al. describe an RFB that uses viologen redox active species. The described RFB is operated in a dioxygen-free environment. Beh et al. confirm that when operated in air, the viologen redox active species exhibits a very rapid decline in discharge capacity and poor coulombic efficiency (see Figure S5 of Beh et al.).

[0089] WO 2021 / 055275 relates to a 2,5-dimercapto-1,3,4-thiadiazole-based electrolyte for redox flow batteries. The example electrolytes tested contain heteroarylene groups separated by one or more sulfur atoms, and thus there is no conjugation between the heteroarylene groups. The electrolytes are described as dimerizing upon oxidation through the formation of S-S covalent bonds (see the structures in paragraphs

[0005] and

[0031] ). This contrasts with the preferred σ or π dimerization that occurs for the reduced species of the present invention.

[0090] WO 2023 / 046710 relates to viologen electrolytes using various end groups (see Figure 2). D2 does not describe the dimerization of viologen electrolytes. D2 also does not describe the air stability of viologens. It is well known that RFBs containing standard viologen anolytes require an oxygen-free atmosphere for operation (see, for example, Janoschka et al. and Luo et al.). Beh et al. also show that this type of compound is air-unstable.

[0091] U.S. Patent Application Publication Nos. 2022 / 0384834 and 2022 / 0020990 describe RFB electrolyte compositions containing TEMPO-based redox-active species, standard viologens, extended viologens, or mixtures of these components. Preferred embodiments relate to viologens with TEMPO groups appended thereto (see Examples 3, 4, 6, and 7). These compounds differ from the preferred redox-active species of the invention. The literature does not describe the dimerization of viologen species and the oxygen tolerance of RFB electrolytes.

[0092] US Patent Application Publication No. 2022 / 0020990 explains that organic RFBs must be kept oxygen-free.

[0093] U.S. Patent Application Publication No. 2022 / 0190374 describes a viologen electrolyte for RFB, in which the end groups are intended to lower the viologen melting point. The document does not describe the preferred redox-active species of the invention. The document explains that the electrolyte was purged with nitrogen gas, and nitrogen was maintained in the cell headspace when conducting CV tests (see paragraph

[0059] ). There is no mention of oxygen resistance or dimerization of the redox-active species.

[0094] Chinese Patent No. 112500329 describes a TEMPO and viologen RFB electrolyte. The literature suggests that when used in rock salt cavity batteries, where atmospheric exposure is essentially limited, cycling the electrolyte in an inert atmosphere is not necessary (see paragraph

[0028] ). This is believed to be achieved by using TEMPO to react with reactive oxygen species (ROS). TEMPO can quench ROS and, when present in the anolyte, can improve air tolerance. However, the preferred redox-active species of the present invention are not mentioned in the literature, nor is dimerization of the redox-active species described. It is believed that the dimerization of the redox-active species of the invention provides oxygen stability without the need for a sacrificial electrolyte component to consume ROS, such as TEMPO.

[0095] WO 2022 / 236241 describes viologen as an anolyte for RFB. Paragraphs

[0102] and

[0106] describe the oxygen sensitivity of the reduced viologen form of the compound. The relevant literature document explains that the cells were tested in an oxygen-free glove box (see Sullivan et al.). The literature does not describe the preferred redox-active species of the present invention, nor does it describe dimerization of the redox-active species.

[0096] Redox flow battery The RFB may be a full flow battery or a hybrid flow battery.

[0097] An RFB may contain multiple electrochemical cells, typically arranged in parallel.

[0098] Electrochemical cells are typically assembled into stacks, which may be connected in series or parallel, preferably parallel.

[0099] An RFB typically includes an electrochemical cell and an electrolyte reservoir in fluid communication with the cell, with an electrolyte provided in each of the cell and the reservoir.

[0100] The battery headspace is generally adjacent to the electrolyte and may be located within the electrolyte reservoir or the electrochemical cell.

[0101] The RFB includes an electrochemical cell, an electrolyte reservoir, and an electrolyte. Typically, the RFB includes a fluid circuit for circulating the electrolyte between the electrochemical cell and the electrolyte reservoir. In other words, the electrochemical cell and the electrolyte reservoir may be in fluid communication. The RFB may include a pump for circulating the electrolyte between the electrochemical cell and the electrolyte reservoir. The type of pump is not particularly limited. A piston, peristaltic, or rotary pump may be used.

[0102] As known to those skilled in the art, the pump may circulate the electrolyte at any suitable rate. The flow rate will depend on the size of the RFB and the total volume of the electrolyte. The flow rate may be equal to about 25-150% of the total electrolyte volume per minute. For example, for 30 ml of electrolyte, the flow rate may be 7.5-45 ml / min. Larger volumes of electrolyte may have lower flow rates.

[0103] A redox reaction occurs within the electrode, storing or releasing charge from the electrolyte through oxidation or reduction, which is then returned to the electrolyte reservoir to store the oxidized / reduced electrolyte.

[0104] The RFB comprises an electrolyte containing redox active species, as described below.

[0105] The redox active species may be present in the electrolyte at a concentration of 50 mM or more, preferably 250 mM, more preferably 500 mM, and even more preferably 1 M or more. The redox active species may be present in the electrolyte at a concentration of 2 M or less, preferably 1.8 M or less, and even more preferably 1.6 M or less. The redox active species may be present in the electrolyte at a concentration of 50 mM to 2 M, preferably 250 mM to 1.8 M, more preferably 500 mM to 1.6 M, and even more preferably 1 M to 1.5 M.

[0106] In some embodiments, the redox active species may be present in the electrolyte at a concentration of 50 mM or more, preferably 150 mM or more, and more preferably 250 mM or more. The redox active species may be present in the electrolyte at a concentration of 50 mM to 250 mM.

[0107] An RFB typically contains two electrolytes known as a catholyte and an anolyte. The anolyte and catholyte each contain redox-active species. Preferably, the redox-active species of the present invention are contained in the anolyte.

[0108] Any suitable redox active species may be used in the catholyte. In some embodiments, the catholyte may include a ferrocene-based redox active species, a TEMPO-based redox active species, or a thiourea species. Preferably, the catholyte is a TEMPO-based redox active species, such as 4-hydroxy-TEMPO.

[0109] A mixture of different redox active species may be used in each electrolyte. Preferably, at least one of the redox active molecules has the typical properties described herein.

[0110] The electrolyte may further comprise a supporting electrolyte. The supporting electrolyte is typically present at a higher concentration, such as 2-fold higher, 5-fold higher, or 10-fold higher than the redox-active species. Alternatively, the supporting electrolyte is present at the same or lower concentration than the redox-active species. Typically, the supporting electrolyte is present at a concentration of 100 mM or more, preferably 1 M or more. The supporting electrolyte may be a metal salt, such as NaCl.

[0111] The electrolyte may be an organic electrolyte (e.g., the solvent is an organic solvent) or an aqueous electrolyte (e.g., the solvent is water). Preferably, the electrolyte is an aqueous electrolyte.

[0112] Preferably, the electrolyte is an aqueous organic electrolyte, the redox-active species is an organic molecule, and the solvent is water. In some embodiments, the solvent is predominantly water, such as 90% or more by weight of water, preferably 95% or more by weight, more preferably 98% or more by weight, and even more preferably 99% or more by weight, based on the mass of the solvent. Complex formation, such as π-dimerization, of the redox-active species is enhanced in aqueous solution, which is believed to further enhance the stability of the redox-active species of the present invention to dioxygen.

[0113] The RFB includes an electrolyte reservoir, which is a means for containing and storing electrolyte.

[0114] The electrolyte reservoir may have a headspace above the electrolyte, which is in contact with the electrolyte. This may be referred to as the electrolyte reservoir headspace. The reservoir headspace typically contains gas. The reservoir headspace is usually necessary to account for expansion and changes in the volume of the electrolyte during operation of the RFB.

[0115] In embodiments in which the RFB comprises a catholyte and an anolyte, the RFB may include an anolyte reservoir, a catholyte reservoir, an anolyte fluid circuit configured to allow the anolyte to circulate between the electrochemical cell and the anolyte reservoir, and a catholyte fluid circuit configured to allow the catholyte to circulate between the electrochemical cell and the catholyte reservoir.

[0116] Electrochemical cells typically include electrodes, an electrolyte, and a separator. The cell may be formed from a frame with electrodes (e.g., a cathode and an anode) on either side of the separator to form the electrochemical cell.

[0117] The RFBs may each include one or more electrochemical cells (eg, assembled in a stack).

[0118] The electrochemical cell may have a headspace above the electrolyte, which may be referred to as the electrolyte cell headspace. The headspace typically contains a gas. A cell headspace is usually required to account for the expansion and change in volume of the electrolyte during operation of the RFB.

[0119] The anolyte and catholyte typically flow on opposite sides of a membrane or separator in an electrochemical cell, and the two sides of the cell may be referred to as the anolyte side and catholyte side, respectively, of the electrochemical cell.

[0120] The membrane or separator allows for the exchange of ions between the anolyte and catholyte sides of the electrochemical cell. The membrane or separator may be an ionically conductive polymer. Preferably, the membrane or separator is selective for favoring electrolyte ions over redox-active molecular ions present in the electrolyte. This reduces crossover of redox-active electrolyte species, which can reduce the capacity of the RFB.

[0121] Typical membrane or separator materials include fluorinated or perfluorinated polymers. Separators such as dialysis membranes, microporous hydrocarbon polymers, and polymers of intrinsic micropore (PIM) and polyaromatic ionomers with pendant ionic functional groups may also be used, if desired, especially when solvated polymer species or particles are utilized as redox-active species. Ceramic membranes, such as those that are conductive to single ions, may also be used.

[0122] Examples of suitable fluorinated or perfluorinated polymers include sulfonated tetrafluoroethylene copolymers such as Nafion (Dupont), e.g., Nafion 115, 117, and 212. Examples of dialysis membranes include cellulose-based dialysis membranes. Examples of microporous hydrocarbon polymers include microporous polypropylene or polyethylene. Examples of PIMs include Tröger's base-based PIMs and dibenzodioxin-based PIMs, such as those containing amidoxime groups. Examples of anion exchange membranes include 120 μm thick, <10 Å pore size membranes (Selemion, Japan).

[0123] Alternatively, membrane-free flow batteries are known. In a typical membrane-free flow battery, the catholyte and anolyte solutions pass through the electrochemical cell with little to no mixing. This can be achieved, for example, using an immiscible electrolyte system or a laminar flow system.

[0124] Typically, electrodes are located on either side of an electrochemical cell. The electrode located on the catholyte side of the cell may be referred to as the positive electrode, and the electrode located on the anolyte side of the cell may be referred to as the negative electrode. Redox reactions occur at the interfaces between the catholyte and the positive electrode, and between the anolyte and the negative electrode. In RFBs, the electrodes do not participate in the redox reactions, but provide the active surface for the redox reactions to occur.

[0125] Preferably, the electrodes have high conductivity, a high specific surface area, and good stability over the operating potential range of the flow battery. Preferably, the electrodes have good resistance to corrosion by the electrolyte.

[0126] The electrodes preferably have a good affinity for the electrolyte. For aqueous electrolytes, the electrodes are preferably hydrophilic. For organic electrolytes, the electrodes are preferably hydrophobic. For electrolytes (e.g., anolytes) of the present invention, the electrodes (e.g., negative electrodes) are preferably hydrophobic.

[0127] Preferably, the electrode is a carbon-based material. Carbon-based materials are typically hydrophobic, thus providing good affinity to organic electrolytes. For example, the carbon-based material is preferably not treated, for example, not oxygen-treated, to preserve the electrode's hydrophobicity. Examples of carbon-based electrodes include carbon felt, carbon paper, and graphite felt, preferably carbon felt or carbon felt.

[0128] The positive and negative electrode materials may be the same or different.

[0129] The electrochemical cell may include current collectors to collect the charge generated in the electrochemical cell. Typically, one current collector is located on the catholyte side of the electrochemical cell (the positive current collector) and is electrically connected to the positive electrode, and one current collector (the negative current collector) is located on the anolyte side of the electrochemical cell and is electrically connected to the negative electrode. The current collectors are typically electrically connected to an external circuit.

[0130] Typical current collector materials include metals such as aluminum, steel, gold and copper. Preferably, the current collector material is aluminum, steel or copper.

[0131] In another embodiment, the RFB is a hybrid flow battery. A hybrid flow battery is a battery in which one of the electrolytes is in a different state, e.g., a solid or gas, compared to a liquid electrolyte. The hybrid RFB may be a flow liquid, flow metal, or flow gas battery. For example, redox-active molecules may be deposited as a solid layer on or at one electrode during use. In such cases, the liquid electrolyte flows across the surface of a solid electrode in an electrochemical cell. The liquid electrolyte may be either a catholyte or an anolyte, and the solid electrode may be either a cathode or an anode, as appropriate. Preferably, the liquid electrolyte is an anolyte.

[0132] Dioxygen as referred to herein refers to molecular oxygen (O2).

[0133] In a conventional RFB, dioxygen is removed from the electrolyte by, for example, purging with an inert gas and / or air-sealing the RFB. During operation of a conventional RFB, dioxygen is removed from the electrolyte, electrolyte headspace, and / or electrolyte reservoir using positive inert gas pressure.

[0134] In the present invention, the RFB can be operated in the presence of dioxygen. The electrolyte, electrolyte headspace, and / or electrolyte reservoir contain dioxygen during operation of the RFB. Preferably, the anolyte, anolyte headspace, and / or anolyte reservoir contain dioxygen during operation. During operation refers to the period during which the RFB is cycled (i.e., during charging and / or discharging).

[0135] Operation in this context refers to charging and / or discharging the RFB without significant electrolyte degradation, typically by oxygen-mediated processes. In other words, the RFB operates in the absence of aggressive dioxygen, for example, with high coulombic efficiency and good capacity retention despite the fact that dioxygen is dissolved in the electrolyte.

[0136] Preferably, dioxygen is not removed from the RFB during operation, e.g., the RFB is not air-sealed and / or the RFB is not under a positive pressure of inert gas.

[0137] In some embodiments, dioxygen is not removed from the RFB during fabrication of the RFB, e.g., dioxygen is not purged from the electrolyte during fabrication.

[0138] Dioxygen can be generated ex situ, for example from the atmosphere, and dissolved into the electrolyte via the electrolyte headspace. Dioxygen can also be generated in situ, such as from the electrolyte itself. For example, in an aqueous electrolyte cycle at open circuit voltages above about 1.23 V, water is typically split to produce dioxygen in the electrolyte.

[0139] Some known RFBs have been described for cycling at voltages above about 1.23 V, but this typically caused rapid degradation of the electrolyte when organic redox species were used in the electrolyte. For this reason, known systems remove molecular dioxygen from the electrolyte using periodic purging and / or a constant positive flow of an inert gas through the electrolyte and cell. The present invention instead tolerates molecular dioxygen in the electrolyte and therefore does not require purging or flow of this inert gas.

[0140] Dioxygen is typically present in the electrolyte (e.g., anolyte) at a partial pressure equivalent to a concentration of 1% by volume or greater, preferably 10% by volume or greater, more preferably 15% by volume or greater, and even more preferably about 20% by volume or greater. Preferably, dioxygen is present in the electrolyte (e.g., anolyte) at a partial pressure equivalent to the amount of dioxygen present in atmospheric air.

[0141] In some embodiments, the electrolyte is in contact with the battery headspace, and the battery headspace comprises molecular dioxygen. In some such embodiments, the battery headspace comprises molecular dioxygen at a concentration of 1% by volume or greater, preferably 10% by volume or greater, more preferably 15% by volume or greater, and even more preferably 20% by volume or greater.

[0142] The concentration of dioxygen in the headspace is measured at a temperature of 20° C. and a pressure of 1 to 2 bar, preferably 1 to 1.5 bar, more preferably 1 to 1.2 bar. Typically, the concentration of dioxygen is measured at a temperature of 20° C. and a pressure of about 1 bar.

[0143] In some embodiments, the molecular dioxygen (in terms of partial pressure) dissolved in the electrolyte is greater than the volume concentration of molecular dioxygen in the cell headspace. A higher concentration of dioxygen in the electrolyte than in the headspace indicates molecular dioxygen generated in the electrolyte (e.g., by in situ electrolysis of water).

[0144] Redox active species The redox active species is present in the electrolyte, preferably the anolyte of the RFB.

[0145] A redox active species is a species that can be reduced or oxidized, which means losing or gaining electrons. Redox active species are suitable for use in redox flow batteries to store and release charge through the reduction and oxidation of the redox active species. Typically, RFBs charge and discharge by cycling the redox active species between the non-reduced form, the one-electron reduced form (+1 electron), and the two-electron reduced form (+2 electrons).

[0146] The one-electron reduced form of a redox-active species is the form produced by one-electron reduction (gain of one electron per molecule) compared to the unreduced species. The two-electron reduced form is the form produced by two-electron reduction (gain of two electrons per molecule) compared to the unreduced species. Typically, the two-electron reduced form is produced by a further one-electron reduction of the one-electron reduced form.

[0147] The discussion of redox active species encompasses all forms of the redox active species (e.g., unreduced, one-electron reduced, and two-electron reduced). Where necessary, different forms of the redox active species are specified.

[0148] The redox-active species is an organic redox-active molecule. Organic molecules are typically molecules containing carbon-hydrogen and carbon-carbon bonds. Organic molecules may contain heteroatoms such as halo, oxygen, nitrogen, and sulfur, among others.

[0149] The organic redox-active molecule comprises a redox-active unit having two or more heteroarylene groups, where the two or more heteroarylene groups are conjugated within the redox-active unit. Conjugation typically refers to π-conjugation, where three or more p-orbitals share electrons to form a conjugated π-system. The heteroarylene groups may be directly conjugated, i.e., a p-orbital on one heteroarylene group shares electrons with an adjacent p-orbital on another heteroarylene group. Alternatively, the heteroarylene groups may be indirectly conjugated, i.e., one heteroarylene group shares electrons with another heteroarylene group via a p-orbital or p-orbitals of an intermediate group.

[0150] Each organic redox-active molecule may have one or more redox-active units. A redox-active unit refers to two or more conjugated heteroarylene groups that can be reduced to produce a one-electron reduced form and a two-electron reduced form, as described herein. The redox-active unit is preferably of formula (1A):

[0151] In some embodiments, two or more heteroarylene groups are symmetric. Two or more heteroarylene groups may be symmetric with respect to a plane between the heteroarylene groups. In some embodiments, two or more heteroarylene groups and any intermediate groups are also symmetric. Two or more heteroarylene groups may be symmetric with respect to a plane intersecting the intermediate group.

[0152] In some embodiments, two or more heteroarylene groups are different. Thus, two or more heteroarylene groups are not symmetrical about the plane between the heteroarylene groups. In some embodiments, any intermediate group (-[L] c - etc.) are also not symmetrical about the plane between the heteroarylene groups.

[0153] The two or more heteroarylene groups may include two or more pyridinylene groups.

[0154] Two or more heteroarylene groups may be joined by a linker -[L] c - may be connected by -. Each -L- is independently a bond, C 2-6 Alkenylene, C 2-4 Alkynylene and C 5-14 arylene, C 2-6 Alkenylene and C 5-14 An arylene is a group consisting of one or more groups R c optionally substituted with ; if present, R c is a hydrophilic group, and c is independently 1 to 5. -[L] c - Preferences for are as described herein.

[0155] Preferably, two or more heteroarylene groups are linked by a single linker [L] c are connected by.

[0156] In some embodiments, two or more pyridinylene groups are linked by a linker [L] c may be connected by [L] c The preferred groups are as described herein. Preferably, two or more pyridinylene groups are linked by a single linker [L]. c are connected by.

[0157] The organic redox active molecule is preferably of formula (I), more preferably of formula (II). Formulas (I) and (II) are as described below. Preferably, the organic redox active molecule is a viologen or an extended viologen.

[0158] The redox-active species form a complex. The complex is formed by complexation, which typically occurs through non-covalent interactions between individual instances of two or more conjugated heteroarylene groups. These may also be referred to as redox-active units.

[0159] Typically, the complexes are intermolecular complexes of redox-active units, such as homodimers. The complexes may also be intramolecular complexes of redox-active units. The complexes may also be a combination of intermolecular and intermolecularly complexed redox-active units.

[0160] Complexes may form between similar redox active units. Additionally or alternatively, complexes may form between different redox active units.

[0161] A redox active molecule may contain one or more redox active units. Complexes may form between similar redox active molecules. Additionally or alternatively, complexes may form between different redox active molecules.

[0162] Complex formation is preferably achieved by electron-covalent interactions, preferably electron-covalent non-covalent interactions, and preferably is not primarily electrostatic (e.g., resulting from ionic interactions between anionic and cationic groups).

[0163] A complex may refer to an intermolecular complex between two redox-active units or molecules (i.e., between two separate molecules). Additionally, or alternatively, a complex may refer to an intramolecular complex between two redox-active units of the same redox-active molecule (i.e., between portions of the same molecule).

[0164] A complex may refer to a heterogeneous complex between two different redox-active molecules or units, or between two different redox-active units of the same redox-active molecule. Additionally, or alternatively, a complex may refer to a homogeneous complex between two of the same redox-active molecules or units, or between two of the same redox-active units of the same redox-active molecule (e.g., two identical redox-active units of a polymeric redox-active molecule).

[0165] The complex may be formed between two or more redox active units, such as three or more, such as four or more redox active units. Thus, the complex may be a dimer, trimer, tetramer, or oligomer. The complex may be formed between two, three, or four redox active units, such as two or three redox active units, such as two redox active units.

[0166] A complex may form between two or more redox active molecules, such as three or more, such as four or more redox active molecules. Thus, the complex may be a dimer, trimer, tetramer, or oligomer. A complex may form between two, three, or four redox active molecules, such as two or three redox active molecules, such as two redox active molecules. A complex may be a dimer, such as a homodimer.

[0167] The redox active species may dimerize to form dimers, in particular the one-electron reduced forms of organic redox active molecules may dimerize to form dimers.

[0168] The redox active species may dimerize to form homodimers, and in particular the one-electron reduced forms of organic redox active molecules may dimerize to form homodimers.

[0169] Dimerization may refer to dimerization between two redox active species (i.e., between two separate molecules). Additionally, or alternatively, dimerization may refer to intramolecular dimerization between two portions of a redox active species (i.e., between portions of the same molecule).

[0170] In particular, homodimerization may refer to dimerization between two of the same redox-active species (i.e., between two but separate molecules). Additionally, or alternatively, homodimerization may refer to intramolecular homodimerization between two counterparts of the redox-active species (i.e., between counterparts of the same molecule, such as two repeat units of a polymer). For example, in a molecule having multiple viologen units, intramolecular homodimerization may refer to dimerization between the viologen units within the molecule.

[0171] Typically, the complex is formed reversibly, so that the one-electron reduced species exists in equilibrium between the uncomplexed and complexed species. comp In this context, K comp is the equilibrium constant for the formation of a one-electron reduced complex of a redox-active species.

[0172] K comp is 0.1mM -1 or more, preferably 0.2 mM -1 or more, more preferably 0.5 mM -1 or more, more preferably 1 mM -1 That is all. Preferably, K comp is 0.2 to 80 mM -1 , more preferably 10 to 80 mM -1 is.

[0173] K comp may be measured at a temperature of 20°C using the method described in the Examples section.

[0174] The complex may be a σ-complex or a π-complex. Preferably, the homodimer is a π-complex.

[0175] σ-complexes may be formed by the interaction of two or more p-orbitals of a redox active species, such as the p-orbital systems of two or more heteroarylene groups.

[0176] The π-complex may be formed by the interaction of two or more conjugated π systems of the redox-active species, such as the conjugated π systems of two or more heteroarylene groups. Preferably, the π-complex is supported by π-π stacking.

[0177] The complex may be formed by the interaction of multiple centers of the redox-active species. That is, the electrons involved in the complex formation may be shared between multiple atomic centers in the redox-active molecule. The electrons involved in the complex formation are preferably delocalized, such as delocalized π electrons. Thus, the complex formation is a multi-center complex formation, preferably a multi-center π-π complex formation.

[0178] Typically, the one-electron reduced form exists in equilibrium between the monomeric and dimeric species. This is known as K d In this context, K d is the equilibrium constant for dimerization, such as the one-electron reduced homodimerization of redox-active species.

[0179] K d is 0.1mM -1 or more, preferably 0.2 mM -1 or more, more preferably 0.5 mM -1 or more, more preferably 1 mM -1 Preferably, K d is 0.2 to 80 mM -1 , more preferably 10 to 80 mM -1 is.

[0180] K d may be measured at a temperature of 20°C using the method described in the Examples section.

[0181] If the organic redox-active molecule contains multiple redox-active units, K d is the K for each redox activity unit d It may also refer to.

[0182] A dimer, such as a homodimer, may be a σ-dimer or a π-dimer. Preferably, the homodimer is a π-dimer.

[0183] σ-dimers may be formed by orbital interaction on two of the redox active species, such as the p-orbital systems of two or more heteroarylene groups.

[0184] The π-dimer may be formed by the interaction of conjugated π systems on two of the redox-active species, such as the conjugated π systems of two or more heteroarylene groups. Preferably, the π-dimer is supported by π-π stacking.

[0185] Homodimers may be formed by the interaction of multiple centers of redox-active species. That is, the electrons involved in the dimerization may be shared between the centers of multiple atoms in the molecule. The electrons involved in the dimerization are preferably delocalized, such as delocalized π electrons. Thus, the homodimerization is multi-center homodimerization, preferably multi-center π-π homodimerization.

[0186] Dimerization typically occurs through non-covalent interactions between two or more conjugated heteroarylene groups. Dimerization is preferably through electron-covalent interactions, preferably electron-covalent non-covalent interactions. Dimerization is preferably not primarily due to electrostatic interactions (e.g., resulting from ionic interactions between anionic and cationic groups).

[0187] Preferably, in the compounds of formula (I), the non-covalent interactions are between the groups -A-, -B- and -[L] of each molecule. c -, more preferably between the groups -[L] c - is between.

[0188] Complexation (e.g., dimerization) of monoreduced species can affect the solubility of the reduced electrolyte and the kinetics of electron transfer, both intermolecular and interfacial (electrode-electrolyte). Certain organic redox-active molecules resist precipitation during dimerization, and thus dimerization provides a viable mechanism for dioxygen tolerance.

[0189] The two-electron reduced form of an organic redox-active molecule may exist in a singlet or triplet form. This refers to the spin relationship of the electrons in the two-electron reduced species. The singlet form refers to a molecule in which each electron has another electron with an opposite (anti-correlated) spin. The triplet form refers to a molecule in which the two unpaired electrons have the same (correlated) spin.

[0190] Preferably, the two-electron reduced form of the redox active species thermodynamically favors the singlet conformation.

[0191] The energy difference between the two-electron reduced singlet and triplet states of a redox-active species is E ST It can be quantified using a negative E ST indicates that the singlet state is energetically favored, while a positive E ST indicates that the triplet state is energetically favored. Preferably, E for the two-electron reduced species ST is negative.

[0192] In some embodiments, the two-electron reduced form of the organic redox active molecule has a molecular weight of 0 kcal mol -1 (0 kJ mol -1 ), preferably less than -6.0 kcal mol -1 (-25.1kJ mol -1 ) or less singlet-triplet energy gap (E ST )

[0193] In some embodiments, the two-electron reduced form of the organic redox active molecule has a molecular weight of −30.0 kcal mol -1 (-125.5kJ mol -1 )~0 kcal mol -1 (0 kJ mol -1 ), preferably -30.0 kcal mol -1 (-125.5kJ mol -1 )~-6.0 kcal mol -1 (-25.1kJ mol -1 )EST It has.

[0194] If the organic redox-active molecule contains multiple redox-active units, E ST refers to the respective redox active units.

[0195] The two-electron reduced forms of organic redox-active molecules may exist in open-shell or closed-shell structures, which refer to the number of unpaired electrons in the molecular orbitals. Open-shell structures refer to species that have one or more unpaired electrons, such as π electrons. Closed-shell structures refer to structures that have no unpaired electrons, such as π electrons.

[0196] Preferably, the two-electron reduced redox active species thermodynamically favors a closed-shell conformation, the singlet form typically being a closed-shell conformation.

[0197] The closed-shell structure may be a Kekulé structure. A Kekulé structure has a closed-shell structure that does not have an unpaired π electron. Preferably, the two-electron reduced redox active species thermodynamically supports a Kekulé structure.

[0198] The singlet and / or closed-shell structure of the two-electron reduced form facilitates the enhancement of the electrochemical reversibility of the redox-active species. -1 (0 kJ mol -1 ) or less, preferably -6.0 kcal mol -1 (-25.1kJ mol -1 ) below E ST In this case, the two-electron reduced form favors the singlet state and thus tends to exhibit electrochemical redox reversibility. E ST If σ is more negative than σ, the species is likely to exhibit electrochemical redox reversibility, which is favorable for RFB cell cycling.

[0199] Specific K supporting dimerization and redox reversibility d and E ST The value can be determined by formula (1), where Y is 15 to 30. (1) Y≦3.64 * ln(K d )-EST

[0200] K d and E ST is defined as above. K that satisfies Eq. d and E ST A range of values ​​of represents a redox active molecule with a good degree of dioxygen tolerance (by dimerization) as well as electrochemical redox reversibility (by supporting a singlet closed shell conformation).

[0201] Regarding equation (1), (K d )(mM -1 ) is the equilibrium constant for the formation of the one-electron reduced form of an organic redox-active molecule at a temperature of 20 °C, E ST (kcal mol -1 ) is a two-electron reduced form of an organic redox-active molecule.

[0202] Y may be 15 to 30. Preferably, Y is 20 to 25, and more preferably 21 to 24.

[0203] For example, 0.28 mM -1 K d and -27.9 kcal mol -1 (-116.7kJ mol -1 )E ST For a redox active species having -1 K d and -12.3 kcal mol -1 (-51.5kJ mol -1 )E ST For a redox active species having -1 K d and -8.0 kcal mol -1 (-33.5kJ mol -1 )E ST For a redox active species with , then Y is 23.76.

[0204] The organic redox-active molecule comprises two or more heteroarylene groups, and the two or more heteroarylene groups are conjugated. References herein to organic redox-active molecules refer to the non-reduced form of the organic redox-active molecule.

[0205] In some embodiments, the organic redox active molecule is a viologen (4,4'-bispyridinium compound) or an extended viologen (4,4'-bispyridinium with a linker between the pyridinium groups).

[0206] In some embodiments, the organic redox active molecule comprises a redox active unit of formula (lA):

[0207] [ka]

[0208] (Wherein -A- and -B- each independently represent C 5-10 is arylene; -L- is independently C 5-14 Arylene, bond, C 2-6 Alkenylene, C 2-4 alkynylene, C 5-14 Arylene and C 2-4 Alkenylene is a group consisting of one or more -R C optionally substituted with a group; -L 1 - is an independent bond, C 1-6 Alkylene, C 5-14 Arylene, -N(H)-, and (CHO) a1 -(C2H4O) a2 -(C3H6O) a3 -(CHC(O)) a4 - selected from C 1-6 Alkylene and C 5-14 An arylene may be one or more -R D optionally substituted with a group, a1, a2, a3, and a4 are each independently selected from 0 to 12, and the sum of a1, a2, a3, and a4 is 1 to 12; -RA , -R B , if exists -R C and -R D each of which is a hydrophilic group; X is one or more counteranions; n is 2 to 4; c and d are independently 1 to 5; a and b are independently 1 to 5; Two or more of -A-, -B- and -L- are C 5-10 is heteroarylene; m is 1 or greater).

[0209] In some embodiments, the redox active species is polymeric and comprises multiple units of formula (lA). In such embodiments, m is 2 or greater, such as 10 or greater, 50 or greater, or 100 or greater. In some embodiments, m is 2-200, such as 10-100.

[0210] The units of formula (lA) may be arranged as a linear, branched, dendritic or cyclic polymer. Preferably, the units of formula (lA) are arranged as a linear or branched polymer, such as a linear polymer.

[0211] In some embodiments, -L 1 - is a bond and d is 1. In such an embodiment, -A-[L] C The -B- units are directly connected.

[0212] In some embodiments, -L 1 -C independently 1-6 Alkylene, -N-, -(CHO) a1 -(C2H4O) a2 -(C3H6O) a3 -(CHC(O)) a4 - and C 5-14 In such embodiments, -A-[L] is selected from arylene. c -B- units are not directly connected.

[0213] Linker - [L 1 ] d - is a d group -L 1 -, and d is 1 to 5. Preferably, d is 1 to 4, more preferably 1 to 3, and even more preferably 1 or 2. In some embodiments, d is 1.

[0214] In some embodiments, -L 1 -C independently 1-6 Alkylene and -(CHO) a1 -(C2H4O) a2 -(C3H6O) a3 -(CHC(O)) a4 Thus, -A-[L] C The -B- units are not π-conjugated.

[0215] -L 1 - is C 1-6 It may be alkylene. 1-6 Alkylene is a divalent alkyl group having 1 to 6 carbon atoms forming an alkylene chain. The alkylene chain may be linear or branched. For example, the alkylene group may be selected from methylene, ethylene, propylene, including n-propylene and i-propylene, butylene, pentylene, or hexylene. Preferably, C 1-6 Alkylene is C alkylene such as C3 alkylene 1-3 C of alkylene etc. 1-4 It is alkylene.

[0216] -L 1 - is -(CH2O) a1 -(C2H4O) a2 -(C3H6O) a3 -(CHC(O)) a4 The group -(CH2O) a1 -(C2H4O) a2 -(C3H6O) a3 -(CHC(O)) a4 -R N is a polyglycol chain.

[0217] Repeating unit -(CHO) a1- is a methylene glycol repeating unit. The number of repeating units a1 is typically 0 to 12. In some embodiments, a1 is 0. In other embodiments, a1 is 1 to 12, preferably 2 to 6.

[0218] Repeating unit - (C2H4O) a2 - is an ethylene glycol repeating unit. The number of repeating units a2 is typically 0 to 12. In some embodiments, a2 is 0. In other embodiments, a2 is 1 to 12, preferably 2 to 6.

[0219] Repeating unit - (C3H6O) a3 - is a propylene glycol repeating unit. The number of repeating units a3 is typically 0 to 12. In some embodiments, a3 is 0. In other embodiments, a3 is 1 to 12, preferably 2 to 6.

[0220] -(CHC(O)) a4 - is an acetyl repeat unit. N is terminal C 1-6 The number of repeating units a4 is typically 0 to 12. In some embodiments, a4 is 0. In other embodiments, a4 is 1 to 12, preferably 2 to 6.

[0221] Typically, a1, a2, a3, and a4 are each independently selected from 0 to 12, and the sum of a1, a2, a3, and a4 is 1 to 12. Preferably, a1, a2, a3, and a4 are each independently selected from 0 to 6, and the sum of a1, a2, a3, and a4 is 2 to 6.

[0222] -L 1 - is C 5-14 It may be arylene. 5-14An arylene is a divalent aromatic group having 5 to 14 carbon atoms that forms an aryl ring or a fused aryl ring. For example, the arylene group may be a 5-membered arylene group such as thiophene, a 6-membered arylene group such as phenylene or pyridine, a 10-membered arylene group such as naphthylene, or a 14-membered arylene group such as anthracenylene. The arylene may be a carboarylene or heteroarylene.

[0223] -L 1 -C 5-14 Arylene, preferably C 5-10 Arylene, more preferably C 5-6 It may be arylene. 1 - is C 5-10 Heteroaryl or C 6-10 It may be carboaryl. Preferably, -L 1 - is phenylene.

[0224] -L 1 When - is alkylene or arylene, the alkylene or arylene group may be one or more -R D Optionally substituted with a -R group. D is an optional substituent. D When present, they may be the same or different. C and -R D If two or more of the following exist, -R C and -R D may be the same or different.

[0225] Typically, adjacent units of formula (lA) are not conjugated. For example, -L 1 - may contain saturated groups that prevent conjugation between adjacent units of formula (lA).

[0226] Dimerization may occur through non-covalent interactions between two or more units of formula (lA) in the same molecule. Preferably, the non-covalent interactions are between -A-, -B- and -[L] in formula (lA). c between one or more - groups, more preferably between -[L] c - Located between the bases.

[0227] -[L 1 ] d The length of the - group may be such that units of formula (lA) in the same molecule can dimerize. 1 ] d The length of the -group may provide sufficient steric freedom to allow adjacent units of formula (lA) to π-dimerize.

[0228] In some embodiments, -[L 1 ] d The length of the - group is 0.5 nm or more, preferably 0.8 nm or more, and more preferably 1.0 nm or more. 1 ] d+- The length of the group can be calculated using the average bond length. For example, -[L 1 ] d The length of the - group is equal to 2 or more -(CH2)- units, preferably 4 or more -(CH2)- units, more preferably 6 or more -(CH2)- units.

[0229] Preferably, the redox active species comprises one unit of formula (lA). In such embodiments, m is 1. More preferably, m is 1 and -L 1 - is a bond and d is 1.

[0230] In some embodiments of the redox active unit of formula (lA), the linker -[L] c - may be joined to multiple -B-. For example, the linker -[L] c may be joined to one -A- and one or more -B- groups, such as one -A- and 2 to 5 -B- groups, such as one -A- and two or three -B- groups. In this way, the linker -[L] c may be conjugated to a total of 2 to 6 -A- and -B- groups, such as 3 or 4 -A- and -B- groups, for a total of 2 to 4 -A- and -B- groups.

[0231] In some embodiments, the organic redox active molecule is of formula (1B):

[0232] [ka]

[0233] -A-, -B-, -L-, -L 1 -, -R A , -R B , -R C , -R D , X, a, b, n and m are as defined for formula (lA); and Two or more of -A-, -B- and -L- are C 5-10 It is heteroarylene.

[0234] -A-, -B-, -L-, -L 1 -, -R A , -R B , -R C , -R D , X, a, b, c, d, n and m are as described herein.

[0235] In some embodiments, the redox active species is polymeric and comprises multiple units of formula (1B). In such embodiments, m is 2 or greater, such as 10 or greater, 50 or greater, or 100 or greater. In some embodiments, m is 2-200, such as 10-100.

[0236] The units of formula (lB) may be arranged as a linear, branched or dendritic polymer. Preferably, the units of formula (lB) are arranged as a linear or branched polymer, such as a linear polymer.

[0237] The units of formula (lB), when present, are -R A and -R B -R group at the end. A and -R B Preferably, both of -R are hydrophilic groups. A and -R B The definition of is set forth in more detail below, as are a and b.

[0238] In some embodiments, L 1 is a bond and d is 1. In such embodiments, -A-[L] c The -B- units are directly connected.

[0239] In some embodiments, the redox active species comprises one or two units of formula (lB): In such embodiments, m is 1 or 2.

[0240] Preferably, m is 1. Particularly preferably, m is 1 and -L 1 - is a bond and d is 1.

[0241] In some embodiments, the organic redox active molecule is of formula (lC):

[0242] [ka]

[0243] (In the formula, -A-, -B-, -L-, -L 1 -, -R A , -R B , -R C , -R D , X, a, b, n and m are as defined for formula (lA) and formula (lB); R p is a polymer repeat unit; p is 2 or greater; Two or more of -A-, -B- and -L- are C 5-10 Heteroarylene).

[0244] -A-, -B-, -L-, -L 1 -, -R A , -R B , -R C , -R D , X, a, b, n and m are as described herein.

[0245] Formula (IC) describes the redox-active molecules of the present invention as pendant polymers. P ] P A-[L] has a pendant group attached thereto. The pendant group is represented by A-[L] C -Contains one or more of the B moieties.

[0246] In formula (lC), m represents the number of repeat units in the pendant group. Typically, m is 1 or greater, such as 2 or greater or 10 or greater. In some embodiments, m is 1 to 20, such as 2 to 10. Preferably, m is 1 or 2.

[0247] The value of p represents the number of repeat units in the polymer backbone. Typically, p is 2 or greater, preferably 10 or greater, more preferably 20 or greater, and even more preferably 50 or greater. In some embodiments, p is 2 to 200, such as 10 to 100.

[0248] R p R may be any suitable polymer repeat unit. p is a polymer repeat unit and may be selected from the group consisting of polyethylene, polypropylene, polystyrene, polyacrylate, polymethacrylate, polyester, polyamide, polyethylene terephthalate, and polysiloxane repeat units. p is a polyethylene or polypropylene repeat unit, such as a polyethylene repeat unit.

[0249] In some embodiments, the organic redox active molecule is of formula (lD):

[0250] [ka]

[0251] (In the formula, -A-, -B-, -L-, -R A , -R B , -R C, X, a, b, n are as defined for formulas (lA) and (lB); q is 1 to 5; Two or more of -A-, -B- and -L- are C 5-10 Heteroarylene).

[0252] -A-, -B-, -L-, -R A , -R B , -R C , -R D , X, a, b, n and q are as described herein.

[0253] The value of q is -[L] c Determines the number of -B- groups attached to -. Typically, q is 1 to 5. In some embodiments, q is 1 to 4, such as 1 to 3. Preferably, q is 1 or 2, such as 1.

[0254] Linker [L] c Linker [L] connects the q groups of -A- and -B- in formula (lD). c contains c L groups, where c is 1 to 5. Preferably, c is 1 to 4, more preferably 1 to 3, and even more preferably 1 or 2. In some embodiments, c is 1.

[0255] -L- is independently C 5-14 Arylene, bond, C 2-6 Alkenylene and C 2-4 alkenylene and arylene are selected from one or more R c The group is optionally substituted.

[0256] When q is 2 or more, -L- is typically C 5-14 Therefore, -L- is C 6-14 Carboarylene or C 5-10 It is heteroarylene.

[0257] Preferably, each -L- is independently C 6-14 Carboarylene, C5-10 Heteroarylene, bond, C2 alkenylene, and C2 alkynylene, more preferably C 6-10 Carboarylene, C 5-6 It is selected from heteroarylene and a bond.

[0258] When -L- is carboarylene, the carboarylene may be independently selected from anthracenylene, naphthylene, and phenylene. Preferably, the carboarylene is selected from naphthylene and phenylene.

[0259] In some embodiments, -[L] c - is phenylene and q is 2. The -A- and two -B- groups may be attached to the phenylene at the 1, 3 and 5 positions.

[0260] When -L- is heteroarylene, the heteroarylene may contain a sulfur or oxygen heteroatom, preferably a sulfur heteroatom. Preferably, when -L- is heteroarylene, the heteroarylene is thiophenylene or furanylene. Preferably, when -L- is heteroarylene, the heteroarylene is thiophenylene.

[0261] Alternatively, in some embodiments, q is 2 or greater, such as 3, and c is 3 or greater, such as 3 or 4, and the -L- groups may be arranged in a cyclic configuration. In some such embodiments, q is 2 to 4, such as 3, and [L] c The group may be a porphyrin group such as porphyrin, porphycene, corrphycene, hemiporphycene or isoporphycene.

[0262] Preferably, each of -A- and -B- in formula (lD) is independently C 5-10 Heteroarylene. C 5-10 Heteroarylene is C 5-6 It may be heteroarylene, preferably C heteroarylene. 5-6Heteroarylene contains one or more nitrogen heteroatoms. More preferably, C6 heteroarylene contains one or more nitrogen heteroatoms, such as one nitrogen heteroatom.

[0263] Nitrogen-containing C6 heteroarylene can be formed by adjacent groups (e.g., -L- and R) at the 1,2, 1,3, or 1,4 positions. A / R B Preferably, the nitrogen-containing C heteroarylene is connected to adjacent groups (e.g., L and R) at the 1,4 positions. A / R B ) is connected.

[0264] In some embodiments, the organic redox active molecule is of formula (I):

[0265] [ka]

[0266] (In the formula, -A- and -B- each independently represent C 5-10 selected from arylene; -L- is independently C 5-14 Arylene, bond, C 2-6 Alkenylene, C 2-4 alkenylene, C 5-14 Arylene and C 2-6 Alkenylene is a group consisting of one or more R C optionally substituted with a group; -R A and -R B If the list exists, -R C at least one of is independently a hydrophilic group; X is one or more counteranions; n is 2 to 4; a, b, and c are independently 1 to 5; Two or more of -A-, -B- and -L- are C 5-10 Heteroarylene).

[0267] In some embodiments, -A- and -B- are the same. Thus, two or more heteroarylene groups are symmetrical.

[0268] In some embodiments, (R A ) a and (R B ) b is the same. Thus, (R A ) a and (R B ) b The group is symmetrical.

[0269] The -A- and -B- groups may be the same, and (R A ) a and (R B ) b The groups may be the same. Thus, the redox active molecule may be symmetrical about the plane between the heteroarylene groups -A- and -B-.

[0270] In some embodiments, two or more heteroarylene groups (-A- and -B-), (R A ) a and (R B ) b group and any intermediate group -[L] c - is a plane between the heteroarylene groups -A- and -B-, preferably an intermediate group -[L] c -, more preferably an intermediate group -[L] c - It is symmetrical with respect to the plane that intersects it.

[0271] In some embodiments, -A- and -B- are different. Thus, the two or more heteroarylene groups are not symmetrical relative to the plane between the heteroarylene groups -A- and -B-.

[0272] In some embodiments, (R A ) a and (R B ) b are different. Thus, (R A ) a and (R B ) bThe group is not symmetrical relative to the plane between the heteroarylene groups -A- and -B-.

[0273] An arylene is a divalent aryl group, such as a divalent carboaryl or a divalent heteroaryl group. An arylene is optionally substituted, such as substituted. In one embodiment, an arylene is unsubstituted.

[0274] C 5-14 The arylene is a divalent aromatic group having 5 to 14 carbon atoms that forms an arylene ring or a fused arylene ring. For example, the arylene group may be a 5-membered arylene group such as thiophene, a 6-membered arylene group such as phenylene or pyridine, a 10-membered arylene group such as naphthalene, or a 14-membered arylene group such as anthracene. The arylene may be a carboarylene or heteroarylene.

[0275] Heteroarylene is a divalent heteroaromatic group that contains at least one ring heteroatom. When fused rings are present, one or more of the rings may contain a ring heteroatom.

[0276] Heteroarylene is optionally substituted, such as substituted. In one embodiment, heteroarylene is unsubstituted. Preferably, when -A- and -B- are heteroarylene, they are monosubstituted, and when -L- is heteroarylene, it is unsubstituted.

[0277] C 5-10 The heteroarylene group is a divalent aryl group having 5 to 10 carbon atoms forming a heteroaryl ring. For example, the heteroarylene group may be a 6-membered heteroarylene group such as pyridinylene, a 5-membered heteroarylene group such as thiophenylene or furanylene, or a 9-membered heteroarylene group such as divalent benzimidazole.

[0278] Carboarylene is a divalent carboaromatic group that contains only carbon atoms in the aryl ring. Carboarylene is optionally substituted, such as substituted. In one preferred embodiment, carboarylene is unsubstituted.

[0279] C 6-14 The carboarylene group is a divalent aryl group having 6 to 14 carbon atoms forming an aryl ring. For example, the carboarylene group may be a 6-membered carboarylene group such as phenylene, a 9-membered carboarylene group such as naphthalene, or a 14-membered carboarylene group such as anthracene.

[0280] Alkenylene is a divalent alkene group. Alkenylene is optionally substituted, including substituted. Preferably, alkenylene is unsubstituted.

[0281] C 2-6 Alkenylene is a divalent alkene group having 2 to 6 carbon atoms that forms an alkene chain. The alkene may be linear or branched. For example, alkenylene may be a 2-membered alkenylene group such as ethylene, a 3-membered alkenylene group such as propylene or arylene, a 4-membered alkenylene group such as buta-1,3-diene, or a 6-membered alkenylene group such as hexa-1,3,5triene or 2-ethylbuta-1,3-diene.

[0282] Alkynylene is a divalent alkyne group. 2-4 Alkynylene is a divalent alkyne group having 2 to 4 carbon atoms that forms an alkyne chain. For example, alkynylene may be a 2-membered alkynylene group such as ethynene, or a 4-membered alkynylene group such as buta-1,3-diynene.

[0283] Typically, -[L] forms the linkage between -A- and -B-. c All atoms (e.g., carbon atoms) in the - group are sp or sp2 hybridized to provide conjugation between the -A- and -B- groups. c Branches that do not directly link -groups may have alternative hybridizations.

[0284] A hydrophilic group is a group that has a good affinity for water. A hydrophilic group typically includes a polar group such as a group capable of hydrogen bonding. A hydrophilic group typically includes one or more heteroatoms such as halo, oxygen, sulfur, nitrogen, or phosphorus. A hydrophilic group may be charged. A hydrophilic group may be attached to an alkylene or arylene group, preferably an alkylene group.

[0285] Preferably, the hydrophilic group is uncharged or is a group having an arylene core (A-[L] C -B-) has the same charge polarization (i.e., anion or cation). For example, if the arylene core is cationic, such as a viologen or extended viologen, the hydrophilic group is preferably uncharged or cationic. In this way, the redox-active species is not zwitterionic, which can cause aggregation and poor solubility.

[0286] The hydrophilic group is -R A and -R B If the list exists, -R C Preferably, the hydrophilic group is one or more of the groups -R A and -R B The descriptions of these groups in this specification apply to hydrophilic groups. A and -R B If the list exists, -R C and -R D The groups are -A-, -B-, -L- and -L- such as carbon or nitrogen atoms. 1 - May be joined at any point on the

[0287] The hydrophilic groups are believed to improve the water solubility of the redox-active species. The hydrophilic groups are placed around the redox-active species to improve water solubility while the conjugated arylene groups are typically poorly water-soluble and are present at the core of the redox-active species. Poorly water-soluble conjugated arylenes have an increased tendency to dimerize when in aqueous solution, while the hydrophilic groups keep the redox-active species in solution and prevent precipitation.

[0288] Multiple -R A , -R B, and if present, -R C When groups are present, each group may be the same or different. For example, -R A or -R B When more than one is present, the -R attached to a heteroatom (e.g., a pyridinylene nitrogen) of -A- or -B- A or -R B are -R attached to the carbon of -A- or -B-, respectively. A or -R B may be different from

[0289] The counter anion is any suitable anion required for charge neutrality of the organic redox active molecule.

[0290] In formula (I), two or more of -A-, -B- and -L- are independently C 5-10 Preferably, each of -A- and -B- is independently C 5-10 It is heteroarylene.

[0291] In some embodiments, C 5-10 Heteroarylene contains one or more heteroatoms each independently selected from oxygen, nitrogen, and sulfur, preferably one heteroatom selected from oxygen, nitrogen, and sulfur. 5-10 The heteroarylene contains nitrogen as the heteroatom.

[0292] C 5-10 Heteroarylene is C 5-6 It may be heteroarylene, preferably C heteroarylene. 5-6 Heteroarylene contains one or more nitrogen heteroatoms. More preferably, C6 heteroarylene contains one or more nitrogen heteroatoms, such as one nitrogen heteroatom.

[0293] Nitrogen-containing C6 heteroarylene can be formed by adjacent groups (e.g., -L- and R) at the 1,2, 1,3, or 1,4 positions. A / R BPreferably, the nitrogen-containing C heteroarylene is connected to adjacent groups (e.g., L and R) at the 1,4 positions. A / R B ) is connected.

[0294] Preferably, C 5-10 Heteroarylene is pyridylene. Preferably, -A- and -B- are both pyridylene.

[0295] The pyridylene may be a pyridyl-1,2-ene, a pyridyl-1,3-ene, or a pyridyl-1,4-ene. Preferably, the pyridylene is a pyridylene having adjacent groups (e.g., L and R) at the 1,4 positions. A / R B More preferably, when -A- and -B- are pyridylenes, the pyridylenes are connected to L at the 4-position and R at the 1-position (i.e., via the nitrogen). A / R B is connected to.

[0296] Typically, two or more of -A-, -B-, and -L- are conjugated, such as -A- and -L-, or -B- and -L-, or -A-, -B-, and -L-. Preferably, -A- and -B- are conjugated. For example, if -L- is a bond, -A- and -B- can be directly conjugated, or if -L- is not a bond, -A-, -B-, and -L- are conjugated.

[0297] Dimerization is typically achieved by non-covalent interactions between two or more conjugated heteroarylene groups. Preferably, the non-covalent interactions are -A-, -B- and -[L] c between groups, more preferably -[L] c -Between the bases.

[0298] In some embodiments, [L] c The length of the group is 0.5 nm or less, such as 0.4 nm or less. In some embodiments, [L] c The length of the group is 0.1 nm or more, such as 0.2 nm or more. [L] cIf the length of the group is about 0.1-0.5 nm, such as 0.2-0.4 nm, [L] c It is believed that the group can provide non-covalent interactions between redox-active molecules to induce dimerization. c The length of the group can be calculated using the average bond length.

[0299] In some embodiments, [L] c The length of the group is 3 to 8 atoms directly connecting the -A- and -B- groups. c The length of the group is 3 to 8 sp2 carbon and / or heteroatoms directly linking the -A- and -B- groups, such as 3 to 6 sp2 carbon and / or heteroatoms directly linking the -A- and -B- groups.

[0300] In some embodiments, the organic redox active molecule is a viologen or extended viologen molecule. -A-

[0301] [ka]

[0302] and -B- is

[0303] [ka]

[0304] is.

[0305] In some further embodiments, the organic redox active molecule comprises a unit of formula (11-A):

[0306] [ka]

[0307] (In the formula, -L-, -L 1 -, -R A, -R B , -R C , -R D , X, n, m, a, b, c and d are as defined above for formulae (I), (lA) and (lB).

[0308] -L-, -L 1 -, -R A , -R B , -R C , -R D , X, n, m, a, b, c and d are as described herein.

[0309] In some further embodiments, the organic redox active molecule comprises a unit of formula (II-B):

[0310] [ka]

[0311] (In the formula, -L-, -L 1 -, -R A , -R B , -R C , -R D , X, n, m, a, b, c and d are as defined above for formulae (I), (lA) and (lB).

[0312] -L-, -L 1 -, -R A , -R B , -R C , -R D , X, n, m, a, b, c and d are as described herein.

[0313] In some embodiments, the organic redox active molecule is of formula (II):

[0314] [ka]

[0315] (In the formula, L, R A , R B , X, n, a, b and c are as defined for formula (I).

[0316] Linker [L] c connects the -A- and -B- groups in formula (I). c connects the pyridinylene groups in formula (II).

[0317] Linker [L] c contains c L groups, where c is 1 to 5. Preferably, c is 1 to 4, more preferably 1 to 3, and even more preferably 1 or 2. In some embodiments, c is 1.

[0318] -L- is independently C 5-14 Arylene, bond, C 2-6 Alkenylene and C 2-4 alkynylene, and alkenylene and arylene are selected from one or more R c The group is optionally substituted.

[0319] When -L- is a bond, the pyridinylene group is directly connected (bi-pyridinylene). The bond refers to a covalent bond.

[0320] -L- is independently C 6-14 Carboarylene or C 5-10 Heteroarylene, bond, C 2-6 Alkenylene and C 2-4 When c is greater than 1, then preferably, each -L- is selected from C 2-6 Not alkenylene, or -L- is C 2-4 It is not alkynylene.

[0321] Preferably, each -L- is independently C 6-14 Carboarylene, C 5-10 Heteroarylene, bond, C2 alkenylene and C2 alkynylene, more preferably C 6-10 Carboarylene, C 5-6It is selected from heteroarylene and a bond.

[0322] In some embodiments, each -L- is independently C 6-10 Carboarylene or C 5-10 Preferably, each -L- is independently selected from naphthylene, anthracenylene, and C 5-10 heteroarylene.

[0323] -L- is C 2-6 When alkenylene, C 2-6 Alkenylene is

[0324] [ka]

[0325] can be independently selected from

[0326] -L- is C 2-4 When alkynylene, C 2-4 Alkynylene is

[0327] [ka]

[0328] can be independently selected from

[0329] -L- is C 5-14 Carboarylene or C 5-14 C such as heteroarylene 5-14 It may also be arylene.

[0330] When -L- is heteroarylene, the heteroarylene contains one or more ring heteroatoms, such as one, two, or three ring heteroatoms, each independently selected from oxygen, nitrogen, and sulfur (O, N(H), and S). The heteroarylene may have only one ring heteroatom selected from oxygen, nitrogen, and sulfur. The heteroarylene may contain two or more heteroatoms selected from oxygen, nitrogen, and sulfur, such as two heteroatoms selected from oxygen, nitrogen, and sulfur. The heteroarylene may be a thiazolene, such as 1,2-thiazolene, 1,3-thiazolene, or 1,4,2-dithiazolene.

[0331] When -L- is heteroarylene, the heteroarylene may contain a sulfur or oxygen heteroatom, preferably a sulfur heteroatom. Preferably, when -L- is heteroarylene, the heteroarylene is thiophenylene or furanylene. Preferably, when -L- is heteroarylene, the heteroarylene is thiophenylene.

[0332] Typically, [L] c The -L- groups therein are arranged in a linear configuration.

[0333] Alternatively, in some embodiments, when c is 3 or greater, such as 3 or 4, the -L- groups may be arranged in a cyclic configuration. c The group may be a porphyrin group such as porphyrin, porphycene, corrphycene, hemiporphycene or isoporphycene.

[0334] When -L- is carboarylene, the carboarylene may be independently selected from anthracenylene, naphthylene, and phenylene. Preferably, the carboarylene is selected from naphthylene and phenylene.

[0335] In some embodiments, -L- is independently selected from a bond and a group selected from anthracenylene, naphthylene, phenylene, and thiophenylene. Preferably, -L- is independently selected from a bond and a group selected from anthracenyl-1,4-ene, anthracenyl-1,6-ene, naphthy-1,8-ene, phenyl-1,4-ene, and thiophenyl-2,5-ene.

[0336] In some embodiments, -L- is a bond, as well as

[0337] [ka]

[0338] are independently selected from the group selected from:

[0339] In some such embodiments, c is 1 or 2.

[0340] In some embodiments, each -L- is independently a bond, and

[0341] [ka]

[0342] is selected from the group selected from

[0343] In some such embodiments, c is 1 or 2.

[0344] Preferably, -L- is

[0345] [ka]

[0346] where c is 1 or 2, -L- is a bond,

[0347] [ka]

[0348] and then c is 1.

[0349] In one embodiment, -L- is not thiazolo[5,4-d]thiazole.

[0350] Group-R A , -R B , -R C and -R D are -A-, -B-, -L- and -L 1 - is a substituent of the group -R A and -R B The number of is defined by a and b, respectively. c and -R d is an optional substituent. A , -R B , -R C and -R D When present, they may be the same or different.

[0351] Group-R A , -R B and -R C are substituents of -A-, -B- and -L-, respectively. A and -R B The number of is defined by a and b respectively. C is an optional substituent. A , -R B and -R c When present, they may be the same or different. For example, -R A or -R B When more than one is present, the -R attached to a heteroatom (e.g., a pyridinylene nitrogen) of -A- or -B- A or -R B is -R attached to the carbon of -A- or -B- A or -R B may be different from

[0352] -R A and -R B , and if present -R C and -R D Each of the -N(R N )2, -N + (R N )3, -P + (R N )3, -OH, -C(O)OH, -NHC(NH)NH2, -NHC(O)NH2 and halogen, optionally substituted with one or more groups selected from 1-6 Alkyl, -(CH2) n -N(R N )2, -(CH2) n -N + (R N )3, -(CH2) n -P + (R N )3, -(CH2) n -OH, -(CH2) n -C(O)OH, -(CH2) n -NHC(NH)NH2, -(CH2) n -NHC(O)NH2 and -(CH2) n -C optionally substituted with one or more groups selected from halogen 5-14 aryl, where n is 0 to 6, and -(CH2O) a1 -(C2H4O) a2 -(C3H6O) a3 -(CHC(O)) a4 -R N (In the formula, a1, a2, a3, and a4 are each independently selected from 0 to 12, the sum of a1, a2, a3, and a4 is 1 to 12, and R N is H or C 1-6 alkyl) may be independently selected from

[0353] R N is preferably methyl such as methyl or C such as ethyl 1-6 R is alkyl. N C 1-6When it is alkyl, it may be optionally substituted, such as monosubstituted. 1-6 The alkyl may be substituted, such as monosubstituted with -NH2 and -OH, -C(O)OH, -NHC(NH)NH2, -NHC(O)NH2 or halogen.

[0354] Preferably, R N C 1-6 When it is alkyl, it is unsubstituted, such as methyl, or unsubstituted, such as ethyl.

[0355] C 1-6 Alkyl is -N(R N )2, -N + (R N )3, -P + (R N )3, -OH, -C(O)OH, -NHC(NH)NH2, -NHC(O)NH2 and halogen. 1-6 Alkyl is -N + (R N )3, -P + (R N )3, -OH, -C(O)OH, -NHC(NH)NH2, -NHC(O)NH2 and halogen.

[0356] C 5-14 Aryl is -(CH2) n -N(R N )2, -(CH2) n -N + (R N )3, -(CH2) n -P + (R N )3, -(CH2) n -OH, -(CH2) n -C(O)OH, -(CH2) n -NHC(NH)NH2, -(CH2) n -NHC(O)NH2 and -(CH2) n -halogen (wherein n is 0 to 6). 5-14Aryl is -(CH2) n -N + (R N )3, -(CH2) n -P + (R N )3, -(CH2) n -OH, -(CH2) n -C(O)OH, -(CH2) n -NHC(NH)NH2, -(CH2) n -NHC(O)NH2 and -(CH2) n -halogen (wherein n is 0 to 6).

[0357] C 5-14 The aryl is preferably substituted on the side opposite the point of attachment to -A- or -B-. For example, C 5-14 When aryl is phenylene, the substitution is preferably at the 4-position. For example, -R A and -R B Ha-N + -N such as (CH3)3 + (R N ) may be phenyl substituted at the 3 and 4 positions.

[0358] -R A and -R B , and if present -R C are, respectively, -N(R N )2, -N + (R N )3, -P + (R N )3, -OH, -C(O)OH, -NHC(NH)NH2, -NHC(O)NH2 and halogen, optionally monosubstituted with a group selected from 1-6 Alkyl, -(CH2) n -N(R N )2, -(CH2) n -N + (R N )3, -(CH2) n -P + (R N )3, -(CH2) n -OH, -(CH2) n-C(O)OH, -(CH2) n -NHC(NH)NH2, -(CH2) n -NHC(O)NH2 and -(CH2) n -C optionally monosubstituted with a group selected from halogen 5-14 aryl, where n is 0 to 6, and -(CH2O) a1 -(C2H4O) a2 -(C3H6O) a3 -(CHC(O)) a4 -R N (In the formula, a1, a2, a3, and a4 are each independently selected from 0 to 12, the sum of a1, a2, a3, and a4 is 1 to 12, and R N is C 1-6 alkyl) can be independently selected from

[0359] -R A and -R B , and if present -R C and -R D One or each of 1-6 It may be alkyl. 1-6 Alkyl is a monovalent alkyl group having 1 to 6 carbon atoms forming an alkyl chain. The alkyl chain may be linear or branched. For example, the alkyl group may be selected from methyl, ethyl, and propyl, including n-propyl and i-propyl, butyl, pentyl, or hexyl. Preferably, C 1-6 Alkyl is C such as C3 alkyl 1-3 C such as alkyl 1-4 It is alkyl.

[0360] -R A , -R B , -R C and -R D But C 1-6 When it is alkyl, it may be one or more groups, preferably -N(R N )2, N + (R N )3, -P + (R N)3, -OH, -C(O)OH, -NHC(NH)NH2, -NHC(O)NH2, NO2, -OCH3 and halogen. A , R B , R C and R D C 1-6 If it is alkyl, it is -N + (R N )3, -P + (R N )3, -OH, -C(O)OH, -NHC(NH)NH2, -NHC(O)NH2 and halogen. 1-6 Alkyl is -N + (R N )3 and -P + (R N )3, -OH, -C(O)OH, -NHC(NH)NH2, -NHC(O)NH2 and halogen.

[0361] -R A and -R B , and if present -R C One or each of 1-6 It may be alkyl. 1-6 Alkyl is a monovalent alkyl group having 1 to 6 carbon atoms forming an alkyl chain. The alkyl chain may be linear or branched. For example, the alkyl group may be selected from methyl, ethyl, propyl, including n-propyl and i-propyl, butyl, pentyl, or hexyl. Preferably, C 1-6 Alkyl is C such as C3 alkyl 1-3 C such as alkyl 1-4 It is alkyl.

[0362] -R A , -R B and -R C C 1-6 If it is alkyl, it is -N(R N )2, -N + (R N )3, -P + (R N)3, -OH, -C(O)OH, -NHC(NH)NH2, -NHC(O)NH2, NO2, -OCH3 and halogen. A , R B and R c C 1-6 If it is alkyl, it is -N + (R N )3, -P + (R N )3, -OH, -C(O)OH, -NHC(NH)NH2, -NHC(O)NH2 and halogen. 1-6 Alkyl is -N + (R N )3, -P + (R N )3, -OH, -C(O)OH, -NHC(NH)NH2, -NHC(O)NH2 and halogen.

[0363] The substitution may be a terminal substitution.

[0364] The alkyl group may be persubstituted with halogen, such as persubstituted with fluoro (eg, trifluoromethyl).

[0365] Preferably, C 1-6 Alkyl is -N + (R N )3. -N + (R N )3 may be present as a terminal substitution. In one embodiment, C 1-6 Alkyl is -CH2CH2-CH2N + (RN)3.

[0366] -R A and -R B , and if present -R C and -R D One or each of the 5-14 It may be aryl. 5-14The aryl is a monovalent aromatic group having 5 to 14 carbon atoms that forms an aryl ring or a fused aryl ring. For example, the aryl group may be a 5-membered aryl group such as thiophenyl, a 6-membered aryl group such as phenyl or pyridinyl, a 10-membered aryl group such as naphthyl, or a 14-membered aryl group such as anthracenyl. The aryl may be a carboaryl or heteroaryl.

[0367] -R A and -R B , and if present -R C and -R D One or each of 5-14 Aryl, preferably C 5-10 Aryl, more preferably C 5-6 It may be aryl. A and -R B , and if present -R C is C 5-10 Heteroaryl or C 6-10 It may also be carboaryl.

[0368] -R A , -R B , -R C and -R D C 5-14 When it is aryl, it is -N(R N )2, -N + (R N )3, -P + (R N )3, -OH, -C(O)OH, -NHC(NH)NH2, -NHC(O)NH2, NO2, -OCH3 and halogen. A , -R B , -R C and -R D But C 5-14 When it is aryl, it is -(CH2) n -N(R N )2, -(CH2) n -N + (R N )3, -(CH2) n -P + (RN )3, -(CH2) n -OH, -(CH2) n -C(O)OH, -(CH2) n -NHC(NH)NH2, -(CH2) n -NHC(O)NH2 and -(CH2) n -halogen (wherein n is 0 to 6). 5-14 Aryl is -(CH2) n -N + (R N )3, -(CH2) n -P + (R N )3, -(CH2) n -OH, -(CH2) n -C(O)OH, -(CH2) n -NHC(NH)NH2, -(CH2) n -NHC(O)NH2 and -(CH2) n -substituted with one group selected from halogen.

[0369] -R A and -R B , and if present -R c One or each of 5-14 It may be aryl. 5-14 The aryl is a monovalent aromatic group having 5 to 14 carbon atoms that forms an aryl ring or a fused aryl ring. For example, the aryl group may be a 5-membered aryl group such as thiophene, a 6-membered aryl group such as phenyl or pyridine, a 10-membered aryl group such as naphthyl, or a 14-membered aryl group such as anthracene. The aryl may be a carboaryl or heteroaryl.

[0370] -R A and -R B , and if present -R C One or each of 5-14 Aryl, preferably C 5-10 Aryl, more preferably C 5-6 It may be aryl. A and -R B, and if present -R C is C 5-10 Heteroaryl or C 6-10 It may also be carboaryl.

[0371] Furthermore, -R A , -R B and -R C C 5-14 When it is aryl, it is -N(R N )2, -N + (R N )3, -P + (R N )3, -OH, -C(O)OH, -NHC(NH)NH2, -NHC(O)NH2, NO2, -OCH3 and halogen.

[0372] -R A , -R B and -R C C 5-14 When it is aryl, it is -(CH2) n -N + (R N )3, -(CH2) n -P + (R N )3, -(CH2) n -OH, -(CH2) n -C(O)OH, -(CH2) n -NHC(NH)NH2, -(CH2) n -NHC(O)NH2 and -(CH2) n -halogen (wherein n is 0 to 6). 5-14 Aryl is -(CH2) n -N + (R N )3, -(CH2) n -P + (R N )3, -(CH2) n -OH, -(CH2) n -C(O)OH, -(CH2) n -NHC(NH)NH2, -(CH2) n-NHC(O)NH2 and -(CH2) n -substituted with one group selected from halogen.

[0373] In some embodiments, n is 0 to 6, such as 0 to 3. Preferably, n is 0 or 3, such as 3.

[0374] Preferably, C 5-14 Aryl is -(CH2) n -N + (R N )3. -N + (R N )3 may be present as a terminal substitution. In one embodiment, C 5-14 Aryl is -CH2-CH2-CH2-N + (R N )3.

[0375] Further, in one embodiment, C 5-14 Aryl is -N + (R N In a preferred embodiment, C 5-14 Aryl is -(C6H6)-N + (CH3)3, etc. -(C6H6)-N + (R N )3. C 5-14 When aryl is phenyl, it may be substituted at the 4-position.

[0376] -R A and -R B , and if present -R c and -R D One or each of -(CHO) a1 -(C2H4O) a2 -(C3H6O) a3 -(CHC(O)) a4 -R N The group -(CH2O) a1 -(C2H4O) a2 -(C3H6O) a3 -(CHC(O)) a4 -R N is a polyglycol chain.

[0377] -R A and -R B , and if present -R C is -(CHO) a1 -(C2H4O) a2 -(C3H6O) a3 -(CHC(O)) a4 -R N -(CH2O) a1 -(C2H4O) a2 -(C3H6O) a3 -(CHC(O)) a4 -R N The group is a polyglycol chain.

[0378] Repeating unit -(CHO) a1 - is a methylene glycol repeating unit. The number of repeating units a1 is typically 0 to 12. In some embodiments, a1 is 0. In other embodiments, a1 is 1 to 12, preferably 2 to 6.

[0379] Repeating unit - (C2H4O) a2 - is an ethylene glycol repeating unit. The number of repeating units a2 is typically 0 to 12. In some embodiments, a2 is 0. In other embodiments, a2 is 1 to 12, preferably 2 to 6.

[0380] Repeating unit - (C3H6O) as - is a propylene glycol repeating unit. The number of repeating units a3 is typically 0 to 12. In some embodiments, a3 is 0. In other embodiments, a3 is 1 to 12, preferably 2 to 6.

[0381] -(CHC(O)) a4 - is an acetyl repeating unit. The number of repeating units a4 is typically 0 to 12. In some embodiments, a4 is 0. In other embodiments, a4 is 1 to 12, preferably 2 to 6.

[0382] Typically, a1, a2, a3, and a4 are each independently selected from 0 to 12, and the sum of a1, a2, a3, and a4 is 1 to 12. Preferably, a1, a2, a3, and a4 are each independently selected from 0 to 6, and the sum of a1, a2, a3, and a4 is 2 to 6.

[0383] R N is H or C 1-6 is alkyl. -R N C 1-6 If it is alkyl, it is C 1-2 C such as alkyl 1-3 C such as alkyl 1-4 Preferably, -R is alkyl. N is methyl. -R A and -R B , and if present -R C is the polyglycol chain, and R N is preferably H.

[0384] In some embodiments, -R A and -R B are each independently N + (R N )3 or -P + (R N )3 substituted C 1-6 Preferably, -R A and -R B are each independently C 2-4 alkyl, preferably N + (R N )3 or P + (R N ) 3, preferably N + (R N )3 is a C3 alkyl group monosubstituted with .

[0385] In some embodiments, -R A and -R B are each independently -(CH2) n -N + (R N )3 or -(CH2) n -P+ (R N )3 (wherein n is 0 to 6) 5-14 Preferably, -R is aryl. A and -R B are each independently -(CH2) n -N + (R N )3 or -(CH2) n -P + (R N )3, preferably -(CH2) n -N + (R N )3 monosubstituted C 5-14 It is aryl.

[0386] In some embodiments, a and b are independently 1 to 3. Preferably, a and b are both 1.

[0387] In some embodiments, -R C is C 1-6 Alkyl and -(CHO) a1 -(C2H4O) a2 -(C3H6O) a3 -(CHC(O)) a4 -R N Preferably, -R C is C 1-6 Alkyl, preferably C 1-3 Alkyl, more preferably C 1-2 is alkyl. -R C Preferably, -R has low steric bulk so as not to inhibit dimerization of the organic redox molecule. C is methyl or ethyl.

[0388] In some embodiments, [L] c is one or two -R C 1 to 4 -R groups C one or more -R groups, etc. C In other embodiments, -L- is unsubstituted.

[0389] Additionally, in some embodiments, -R D is C 1-6 Alkyl and -(CHO) a1 -(C2H4O) a2 -(C3H6O) a3 -(CHC(O)) a4 -R N Preferably, -R D is C 1-6 Alkyl, preferably C 1-3 Alkyl, more preferably C 1-2 is alkyl. -R D Preferably, -R has low steric bulk so as not to inhibit dimerization of the organic redox molecule. D is methyl or ethyl.

[0390] Furthermore, in some embodiments, [L 1 ] d is one or two R D 1 to 4 R groups D one or more -R groups, etc. D In another embodiment, the -L 1 - is not substituted.

[0391] Typically, a redox active species has a positive charge of n in the unreduced state. When the redox active species is reduced, the one-electron reduced form has a charge of n-1. When the redox active species is reduced by two electrons, the two-electron reduced form has a charge of n-2.

[0392] Generally, n is 2 to 4. Preferably, n is 4.

[0393] Furthermore, the redox active species is typically not a zwitterion. Preferably, the redox active species is one-electron reduced or two-electron reduced, not a zwitterion. The redox active species has a positive charge n of 2 or more in the non-reduced form. This is particularly preferred when the hydrophilic group is positively charged. This is such that the two-electron reduced form of the redox active species retains a neutral or positive charge. When n is 1 or less, the arylene core of the redox active species may exhibit a negative charge in the reduced form, which may impart zwitterion characteristics with a positively charged hydrophilic group. The zwitterion characteristics are believed to increase the tendency for stacking and aggregation in an aqueous environment.

[0394] The redox active species has a counter anion, X, such that the redox active species and counter ion have a net zero charge. The counter anion has an overall charge per redox active molecule of -n.

[0395] X is typically a redox-inactive species. In some embodiments, X is a halide, hexafluorophosphate, p-toluenesulfonate, trifluoromethanesulfonate, methylsulfonate. Preferably, X is Cl. - , Br - In one embodiment, X is Br - is.

[0396] In a further embodiment, the organic redox active molecule is

[0397] [ka]

[0398] wherein X is as defined above. is selected from.

[0399] In some embodiments, the organic redox active molecule is

[0400] [ka]

[0401] wherein X is as defined above. is selected from.

[0402] Preferably, the organic redox active molecule is

[0403] [ka]

[0404] wherein X is as defined above. is selected from.

[0405] Additionally or alternatively, the organic redox active molecule may be

[0406] [ka]

[0407] wherein X is as defined above. may be selected from:

[0408] Fabrication of RFB In a second aspect of the present invention, there is provided a method of making a redox flow battery, comprising the steps of: forming an electrolyte by combining an organic redox active molecule with a liquid carrier, the organic redox active molecule comprising a redox active unit having two or more heteroarylene groups, the two or more heteroarylene groups being conjugated within the redox active unit; adding an electrolyte to the redox flow battery, wherein molecular dioxygen (O2) is dissolved in the electrolyte; reducing the organic redox active molecule to provide a one-electron reduced form of the redox active unit that forms the complex; Methods are provided wherein the complex is an intermolecular complex of redox active units, such as a homodimer, an intramolecular complex of redox active units, or the complex is a combination of intermolecular and intramolecular complex redox active units.

[0409] The organic redox active molecule is as described herein. The organic redox active molecule is preferably of formula (I), more preferably of formula (II). Preferably, the organic redox active molecule is a viologen or an extended viologen.

[0410] Typically, molecular dioxygen is present in the electrolyte. Generally, molecular dioxygen is not removed from the electrolyte and / or cell headspace during cell fabrication. For example, the method does not include a step of purging molecular dioxygen from the electrolyte and / or cell headspace.

[0411] The RFB and the presence of dioxygen in the RFB are as described herein. The description of the RFB itself is also applicable to the method of making the RFB.

[0412] In a third aspect, the present invention also provides an RFB obtained or obtainable by the method of making of the second aspect.

[0413] Charging and / or discharging RFB In a fourth aspect, the present invention provides a method of charging and / or discharging a redox flow battery in the presence of molecular dioxygen, comprising: the redox flow battery comprises an electrolyte; The electrolyte is an organic redox-active molecule comprising a redox-active unit having two or more heteroarylene groups, wherein the two or more heteroaryl groups are conjugated within the redox-active unit; and It contains molecular dioxygen (O2) dissolved in an electrolyte, The method is reducing the redox active unit to result in a complex formed from the one-electron reduced form of the redox active unit; and / or oxidizing the two-electron reduced form of the redox active unit to provide a complex formed from the one-electron reduced form of the redox active unit; Methods are provided wherein the complex is an intermolecular complex of redox active units, such as a homodimer, an intramolecular complex of redox active units, or the complex is a combination of intermolecular and intramolecular complex redox active units.

[0414] RFB, organic redox active molecule, and its one-electron and two-electron reduced forms are as described herein. The organic redox active molecule is preferably of formula (I), more preferably of formula (II). Preferably, the organic redox active molecule is a viologen or an extended viologen.

[0415] Charging is typically accomplished by applying a potential difference across the RFB. Discharging is typically accomplished by providing a means for electron transfer across the RFB. Discharging typically provides power to a load.

[0416] The coulombic efficiency during discharge may be 70% or greater, preferably 75% or greater, more preferably 80% or greater, and even more preferably 85% or greater.

[0417] The discharge capacity retention over 100 charge / discharge cycles may be 80% or more, preferably 85% or more, and more preferably 90% or more.

[0418] The discharge capacity retention compared to cycling in the absence of dioxygen is over 50%.

[0419] The high coulombic efficiency and good capacity retention are believed to be related to the low degree of degradation of the redox-active species and the dioxygen tolerance. The high coulombic efficiency and slight decrease in capacity are believed to indicate that π-dimerization serves as a competing pathway to dioxygen-mediated side reactions, thereby suppressing viologen reactivity with dioxygen. The decrease in discharge capacity compared to the capacity in the absence of dioxygen is acceptable in light of the high coulombic efficiency and low degree of degradation.

[0420] In some embodiments, the step of reducing and / or oxidizing the organic redox active molecule is carried out at a per cell voltage of 1.23 V or greater, preferably 1.5 V or greater. At these high per cell voltages, the aqueous liquid carrier typically undergoes electrolytic splitting of water, which results in molecular dioxygen in the electrolyte. The cell voltage required to cause electrolytic water splitting depends on the pH of the water (Gesser, Applied Chemistry).

[0421] Generally, RFBs with aqueous electrolytes that do not contain dioxygen-tolerant redox-active species cannot be cycled at these higher voltages per cell. Dioxygen is generated in situ in the electrolyte, thus contributing to degradation of the redox-active species. Alternatively, known cells must continually purge the electrolyte using an inert gas to remove any in situ generated dioxygen. In the present invention, the redox-active species are dioxygen-tolerant, and therefore can be cycled at these high voltages without significant degradation of the redox-active species and without purging the electrolyte.

[0422] In some embodiments, the step of reducing and / or oxidizing the organic redox active molecule is carried out at a temperature of 20 mAcm -2 More than 30 mAcm, preferably 30 mAcm -2 More preferably, 40 mAcm -2 A current density of at least 1000 kJ / s is used.

[0423] At these higher current densities, the rate of electron transfer is believed to be such that the redox process can effectively compete with the electron transfer reaction to molecular dioxygen in the electrolyte. As a result, higher current densities kinetically favor the redox of the redox-active species rather than the oxygen side reaction, meaning that the influence of molecular dioxygen is further reduced. In some embodiments, this means that the RFB can be cycled for extended periods in the presence of dioxygen, avoiding the need to purge with an inert gas.

[0424] use In a fifth aspect, the present invention provides a use of a redox flow battery for charging and / or discharging a redox flow battery comprising an electrolyte in the presence of molecular dioxygen, comprising: The electrolyte is an organic redox-active molecule comprising a redox-active unit having two or more heteroarylene groups, wherein the two or more heteroarylene groups are conjugated within the redox-active unit, and at least a portion of the redox-active unit exists as a complex formed from a one-electron reduced form of the redox-active unit; and It contains molecular dioxygen (O2) dissolved in an electrolyte, The use is provided wherein the complex is an intermolecular complex of redox active units such as a homodimer, an intramolecular complex of redox active units, or the complex is a combination of intermolecular and intramolecular complex redox active units.

[0425] RFB, organic redox active molecule, and its one-electron and two-electron reduced forms are as described herein. The organic redox active molecule is preferably of formula (I), more preferably of formula (II). Preferably, the organic redox active molecule is a viologen or an extended viologen.

[0426] The charging and / or discharging of the redox flow battery is as described above for the charging and / or discharging method.

[0427] Preferably, the use of the RFB is for charging and / or discharging at a voltage per cell of 1.23V or more, preferably 1.5V or more.

[0428] Preferably, the RFB uses 20 mAcm -2 More than 30 mAcm, preferably 30 mAcm -2 More preferably, 40 mAcm -2 The current density is above this.

[0429] The molecular dioxygen dissolved in the electrolyte is as described above for redox flow batteries.

[0430] Preferably, dioxygen is dissolved in the electrolyte (e.g., anolyte) at a partial pressure equivalent to a concentration of 1% by volume or greater, preferably at a concentration of 10% by volume or greater, more preferably at a concentration of 15% by volume or greater, and even more preferably at a concentration of 20% by volume or greater.

[0431] Other positive aspects All suitable combinations of the above embodiments are expressly disclosed herein as if all such combinations were individually and expressly set forth.

[0432] Various further aspects and embodiments of the present invention will be apparent to those skilled in the art in light of the disclosure herein.

[0433] As used herein, "and / or" is understood to be a specific disclosure of each of the two specified features or components with or without the other. For example, "A and / or B" is understood to be a specific disclosure of each of (i) A, (ii) B, and (iii) A and B, each as individually described herein.

[0434] Unless the context dictates otherwise, the above feature descriptions and definitions are not limited to any particular aspect or embodiment of the invention, but apply equally to all aspects and embodiments described.

[0435] Certain aspects and embodiments of the present invention will now be described, by way of example only, and with reference to the figures described below. [Example]

[0436] The following examples are provided to further illustrate the present invention and are not intended to limit the scope of the invention.

[0437] material 4-Pyridinylboronic acid (97%), potassium carbonate (anhydrous), and sodium chloride (analytical) were purchased from Fisher Scientific. 1,4-Dibromobenzene (>98%), 4,4'-dibromobiphenyl (98%), 2,5-dibromothiophene (96%), 1,4-dibromonaphthalene (98%), 2,6-dibromonaphthalene (97%), 2,7-dibromonaphthalene (99%), 9,10-dibromoanthracene (98%), 2,6-dibromopyridine (98%), 5,5'-dibromo-2,2'-bithiophene (99%), tetrakis(triphenylphosphine)palladium(O) (99.8% (metal basis), Pd (9%) Water (minimum) and palladium on carbon (10 wt%) were purchased from Sigma-Aldrich. N,N-Dimethylformamide (>99%, anhydrous), dichloromethane (>99%), ethyl acetate (>99%), acetonitrile (>99%), diethyl ether (>99%), hydrochloric acid (99%), 4,4'-bipyridine (99%), methyl viologen dichloride hydrate (98%), 4-hydroxy-2,2,6,6-tetramethylpiperidi-1-oxyl (97%), and deuterium oxide (99.9% atomic % D) were purchased from Sigma-Aldrich. Milli-Q water was used to make all non-deuterated aqueous solutions. Materials were used as obtained without further purification.

[0438] Measuring equipment NMR measurements were performed using a 300 MHz Bruker Avance III. EPR measurements were performed using a benchtop EPR (MS5000, Magnettech). UV / Vis spectra were collected using a UV / Vis spectrometer (Horiba, Duetta).

[0439] Synthesis of compounds 1-9 Compounds 1, 2, 3, 4, 5, 6, 7, 8, and 9 (exemplified below) were synthesized via Suzuki-Miyaura coupling. 4-Pyridinylboronic acid (1.25 g, 10 mmol), aryl dibromide (4.2 mmol), and potassium carbonate (2.8 g, 20.4 mmol) were added to a 7:1 mixture of degassed DMF and water (120 mL). Tetrakis(triphenylphosphine)palladium(0) (0.39 g, 0.34 mmol) was added to the reaction mixture and the solution was heated to 100 °C under N for 72 h. The reaction mixture was then cooled to room temperature and filtered. The organic phase was concentrated in vacuo, and the residue was dissolved in CHCl (150 mL) and washed three times with water (50 mL each). Concentrated HCl was then added dropwise to the collected organic phase, resulting in precipitation of the product. The precipitate was collected by filtration and subsequently dissolved in HO. Finally, aqueous NaOH (10 M) was added dropwise to the H2O layer until the pH reached 8–9, resulting in the precipitation of pure products, compounds 1, 2, 3, 4, 5, 6, 7, 8, and 9, respectively.

[0440] Characterization of compounds 1–9 Compound 1 It was characterized by 1 H NMR.

[0441] [ka]

[0442] 1 H NMR (400 MHz, CDCl3) δ [ppm]: 8.70 (dd, J = 4.4, 1.6 Hz, 4H), 7.77 (s, 4H), 7.56 (dd, J = 4.4, 1.6 Hz, 4H).

[0443] [ka]

[0444] 11H NMR (400 MHz, CDCl3) δ [ppm]: 8.77 (dd, J = 4.4, 1.6 Hz, 4H), 7.92 (dd, J = 6.4, 3.2 Hz, 2H), 7.52 (dd, J = 6.4, 3.2 Hz; 2H), 7.49 (s, 2H), 7.48 (dd, J = 4.4, 1.6 Hz, 4H).

[0445]

Chem.

[0446] 1 1H NMR (400 MHz, CDCl3) δ [ppm]: 8.73 (dd, J = 4.4, 1.6 Hz, 4H), 8.16 (s, 2H), 8.05 (d, J = 8.5 Hz, 2H), 7.83 (d, J = 8.5 Hz, 2H), 7.66 (dd, J = 4.4, 1.6 Hz, 4H).

[0447]

Chem.

[0448] 1 1H NMR (400 MHz, CDCl3) δ [ppm]: 8.74 (dd, J = 4.4, 1.6 Hz, 4H), 8.21 (dd, J = 1.6, 0.8 Hz, 2H), 8.02 (d, J = 8.7 Hz, 2H), 7.82 (dd, J = 8.6, 1.8 Hz, 2H), 7.66 (dd, J = 4.4, 1.6 Hz, 4H).

[0449]

Chem.

[0450] 11H NMR (400 MHz, CDCl3) δ [ppm]: 8.89 (dd, J = 4.0, 1.6 Hz, 4H), 7.62 (dd, J = 6.8, 3.2 Hz, 4H), 7.45 (dd, J = 4.0, 1.6 Hz, 4H), 7.40 (dd, J = 6.9, 3.2 Hz, 4H).

[0451]

Chem.

[0452] 1 1H NMR (400 MHz, CDCl3) δ [ppm]: 8.70 (dd, J = 4.4, 1.6 Hz, 4H), 7.77 (s, 8H), 7.57 (dd, J = 4.4, 1.6 Hz, 4H).

[0453]

Chem.

[0454] 1 1H NMR (400 MHz, CDCl3) δ [ppm]: 8.64 (dd, J = 4.4, 1.6 Hz, 4H), 7.55 (s, 2H), 7.51 (dd, J = 4.4, 1.6 Hz, 4H).

[0455]

Chem.

[0456] 1 1H NMR (400 MHz, CDCl3) δ [ppm]: 8.62 (dd, J = 4.4, 1.6 Hz, 4H), 7.48 - 7.44 (m, 6H), 7.25 (s, 2H).

[0457]

Chem.

[0458] 1 H NMR (400 MHz, CDCl3) δ [ppm]: 8.79 (dd, J = 4.0, 1.6 Hz, 4H), 8.08 (dd, J = 4.0, 1.6 Hz, 4H), 7.99 (dd, J = 7.5 Hz, 7.0 Hz, 2H), 7.92 (t, J = 6.0Hz 1H).

[0459] Alternative synthesis of compound 1 Compound 1 was also synthesized using the Pd-C catalytic process for tetrakis(triphenylphosphine)palladium(0) described above. 4-Pyridinylboronic acid (1.72 g, 14 mmol), 1,4-dibromobenzene (1.00 g, 4.2 mmol), and potassium carbonate (3.52 g, 25 mmol) were added to a 1:1 mixture of degassed DMF and water (120 mL). Palladium supported on activated carbon (100 mg) was added to the reaction mixture, which was heated to 100 °C under N for 72 h. The reaction mixture was then cooled to room temperature and filtered. The organic phase was concentrated under vacuum, and the residue was dissolved in CHCl (150 mL) and washed three times with water (50 mL each). Concentrated HCl was then added dropwise to the collected organic phase, resulting in precipitation of the product. The precipitate was collected by filtration and subsequently dissolved in HO. Finally, aqueous NaOH (10 M) was added dropwise to the H2O layer until the pH was about 8-9, resulting in the precipitation of the pure product (89 mg, 9%).

[0460] The NMR spectrum of compound 1 prepared by this method (see Figure 1) showed a product purity of over 99%, higher than that obtained using tetrakis(triphenylphosphine)palladium(0).

[0461] Synthesis of Compounds 10, 11, 12, 13, 15, 16, 17, 18 and Comparative Compounds 14 and 19 Compounds 10, 11, 12, 13, 15, 16, 17, 18, and comparative compounds 14 and 19 (illustrated below) were synthesized via the Anderson-Menschutzkin reaction. (3-Bromopropyl)trimethylammonium bromide (1.00 g, 3.83 mmol) was added to a stirred solution of bipyridine (1.29 mmol) in anhydrous, degassed DMF (50 mL). The reaction mixture was heated to 100 °C and stirred for 48 h. The reaction mixture was then cooled to 0 °C, and the resulting precipitate was filtered and washed with cold DMF (3 × 20 mL), MeCN (3 × 20 mL), and diethyl ether (3 × 20 mL) to obtain the pure product. The isolated bispyridinium salt was loaded onto an ion-exchange column to obtain the corresponding tetrachloride salt. The tetrachloride salt was taken up three times (50 mL each) with water. Upon concentration under vacuum, compounds 10, 11, 12, 13, 14, 17, 18, and 19 were obtained. To obtain a purity of greater than 99.9%, suitable for electrochemical studies, compounds 10, 11, 12, 13, 14, 17, 18, and 19 were triturated six times from water with acetone.

[0462] Characterization of Compounds 10, 11, 12, 13, 15, 16, 17, 18 and Comparatives 14 and 19 Compounds 10, 11 and 17 1 Compounds 12, 13, 15, 16, 18 and comparative compounds 14 and 19 were characterized by H NMR. 1 H and C 13 Characterized by NMR, FTIR and MS. The bromide counterion is omitted from the structure for clarity.

[0463] [ka]

[0464] 11H NMR (400 MHz, D2O) δ [ppm]: 9.22 (d, J = 6.0 Hz, 4H), 8.65 (d, J = 6.0 Hz, 4H), 4.88 (t, J = 7.6 Hz, 4H), 3.63 - 3.59 (m, 4H), 3.22 (s, 18H), 2.75 - 2.67 (m, 4H).

[0465]

Chem.

[0466] 1 1H NMR (400 MHz, D2O) δ [ppm]: 8.99 (d, J = 7.0 Hz, 4H), 8.49 (d, J = 6.9 Hz, 4H), 8.21 (s, 4H), 4.83 - 4.75 (m, 4H), 3.62 - 3.57 (m, 4H), 3.22 (s, 18H), 2.73 - 2.63 (m, 4H).

[0467]

Chem.

[0468] 1 1H NMR (400 MHz, D2O) δ [ppm]: 8.89 (d, J = 6.4 Hz, 4H), 8.39 (d, J = 6.0 Hz, 4H), 8.19 (s, 2H), 4.73 (t, J = 7.7 Hz, 4H), 3.66 - 3.50 (m, 4H), 3.21 (s, 18H), 2.73 - 2.60 (m, 4H).

[0469]

Chem.

[0470] 11H NMR (400 MHz, D2O) δ [ppm]: 9.08 (d, J = 5.2 Hz, 4H), 8.39 (d, J = 5.0 Hz, 4H), 8.04 - 8.01 (m, 2H), 7.85 (s, 2H), 7.79 - 7.75 (m, 2H), 4.87 (t, J = 8.0 Hz, 4H), 3.66 - 3.62 (m, 4H), 3.24 (s, 18H), 2.78 - 2.70 (m, 4H). 13 13C NMR (100 MHz, D2O) δ [ppm]: 157.70, 144.26, 136.31, 130.01, 129.52, 128.42, 127.62, 125.08, 62.47, 57.65, 53.20, 53.16, 53.13, 24.60. MS ESI-MS: m / z [M] 4+ C 32 H 44 Calculated value of C12H18N4: 121.0886, measured value: 121.0888. FTIR ν [cm -1 : 667, 742, 768, 832, 845, 878, 912, 929, 963, 1063, 1120, 1190, 1232, 1313, 1361, 1393, 1426, 1472, 1520, 1558, 1635, 3020, 3370. 80% yield.

[0471]

Chemical Structure

[0472] 1 1H NMR (400 MHz, D2O) δ [ppm]: 8.97 (d, J = 5.0 Hz, 4H), 8.69 (s, 2H), 8.56 (d, J = 5.2 Hz, 4H), 8.36 (d, J = 8.0 Hz, 2H), 8.16 (d, J = 8.0 Hz, 2H), 4.79 - 4.76 (m, 4H), 3.61 - 3.57 (m, 4H), 3.24 (s, 18H), 2.78 - 2.70 (m, 4H).13 C NMR (100 MHz, D2O) δ [ppm]: 156.27, 144.27, 134.06, 133.06, 130.73, 128.82, 125.65, 125.23, 62.46, 57.17, 53.18, 24.56. MS ESI-MS: m / z [M] 4+ C 32 H 44 Calculated value of N4: 121.0886, measured value: 121.0885. FTIR ν [cm -1 ]: 741, 768, 833, 846, 887, 930, 964, 1039, 1065, 1120, 1148, 1190, 1233, 1313, 1361, 1392, 1424, 1472, 1520, 1558, 1636, 1711, 3021, 3367. 89% yield.

[0473]

change

[0474] 1 H NMR (400 MHz, D2O) δ [ppm]: 8.98 (d, J = 5.6 Hz, 4H), 8.75 (s, 2H), 8.56 (d, J = 6.2 Hz, 4H), 8.28 (d, J = 8.8 Hz, 2H), 8.18 (d, J = 8.8 Hz, 2H), 4.79 - 4.76 (m, 4H), 3.61 - 3.59 (m, 4H), 3.22 (s, 18H), 2.72 - 2.64 (m, 4H). 13 C NMR (100 MHz, D2O) δ [ppm]: 156.42, 144.23, 135.64, 132.72, 132.24, 130.21, 129.54, 126.46, 125.63, 62.51, 57.20, 53.15, 24.54. MS ESI-MS: m / z [M] 4+ C 32 H 44Calculated value of N4: 121.0886, Found value: 121.0887. FTIR ν [cm -1 ]: 848, 923, 940, 968, 1057, 1066, 1175, 1241, 1349, 1394, 1409, 1477, 1532, 1559, 1623, 1638, 2901, 2988, 3351, 3661. 85% yield.

[0475] [ka]

[0476] 1 H NMR (400 MHz, D2O) δ [ppm]: 9.23 (d, J = 9.2 Hz, 4H), 8.38 (d, J = 6.0 Hz, 4H), 7.68 -7.61 (m, 8H), 4.96 (t, J = 7.2 Hz, 4H), 3.73 - 3.69 (m, 4H), 3.28 (s, 18H), 2.87 - 2.78 (m, 4H). 13 C NMR (100 MHz, D2O) δ [ppm]: 157.54, 144.69, 132.48, 131.46, 128.06, 127.43, 125.31, 62.56, 57.98, 53.22, 24.72. MS ESI-MS: m / z [M] 4+ C 36 H 46 Calculated value of N4: 133.5925, Found value: 133.5925. FTIR ν [cm -1 ]: 679, 734, 819, 831, 893, 923, 960, 1032, 1109, 1139, 1160, 1183, 1216, 1292, 1341, 1394, 1418, 1448, 1477, 1519, 1559, 1640, 3059, 3121, 3352. 83% yield.

[0477] [ka]

[0478] 1 1H NMR (400 MHz, D2O) δ [ppm]: 8.92 (d, J = 6.0 Hz, 4H), 8.46 (d, J = 5.6 Hz, 4H), 8.16 (d, J = 7.6 Hz, 4H), 8.07 (d, J = 7.2 Hz, 4H), 4.75 (t, J = 7.2 Hz, 4H), 3.59 - 3.56 (m, 4H), 3.21 (s, 18H), 2.70 - 2.62 (m, 4H). 13 13C NMR (100 MHz, D2O) δ [ppm]: 156.41, 144.16, 142.75, 133.38, 128.80, 128.24, 125.20, 62.48, 57.10, 53.08, 24.47. MS ESI-MS: m / z [M] 4+ C 34 H 46 Calculated value of C127.5925, measured value: 127.5925. FTIR ν [cm -1 : 739, 756, 817, 836, 872, 927, 964, 1057, 1066, 1187, 1201, 1231, 1295, 1394, 1404, 1469, 1492, 1525, 1543, 1570, 1603, 1635, 2901, 2989, 3363, 3662. Yield: 81%.

[0479]

Chem.

[0480] 1H NMR (400 MHz, D2O) δ [ppm]: 8.76 (d, J = 6.8 Hz, 4H), 8.26 (d, J = 6.0 Hz, 4H), 8.07 (d, J = 3.6 Hz, 2H), 7.70 (d, J = 3.6 Hz, 2H), 4.66 (t, J = 7.8 Hz, 4H), 3.57 - 3.53 (m, 4H), 3.20 (s, 18H), 2.65 - 2.57 (m, 4H). 13 C NMR (100 MHz, D2O) δ [ppm]: 148.90, 143.94, 142.97, 137.00, 133.22, 128.33, 122.70, 62.47, 56.82, 53.14, 53.11, 53.08, 24.41. MS ESI-MS: m / z [M] 4+ C 30 H 42 Calculated value of N4S2: 130.5707, measured value: 130.5706. FTIR ν [cm -1 ]: 667, 728, 741, 772, 805, 845, 875, 942, 964, 1000, 1048, 1071, 1084, 1118, 1174, 1204, 1225, 1240, 1307, 1330, 1357, 1381, 1407, 1433, 1465, 1492, 1528, 1553, 1628, 3002, 3016, 3041, 3423. 82% yield.

[0481]

change

[0482] 1H NMR (400 MHz, D2O) δ [ppm]: 9.08 (d, J = 5.4 Hz, 4H), 8.90 (d, J = 5.2 Hz, 4H), 8.48 (d, J = 8.0 Hz, 2H), 8.37 (t, 7.5 Hz, 1 H), 4.82 (t, J = 7.6 Hz, 4H), 3.62 - 3.58 (m, 4H), 3.21 (s, 18H), 2.73 - 2.65 (m, 4H). 13 C NMR (100 MHz, D2O) δ [ppm]: 153.88, 150.95, 144.96, 140.36, 125.77, 125.64, 62.54, 57.66, 53.24, 24.64. MS ESI-MS: m / z [M] 4+ C 27 H 41 Calculated value of N5: 108.8335, Found value: 108.8337. FTIR ν [cm -1 ]: 722, 811, 871, 925, 962, 991, 1066, 1099, 1183, 1230, 1293, 1349, 1408, 1451, 1477, 1520, 1568, 1590, 1638, 2494, 2989, 3363, 3671. 76% yield.

[0483] Further synthesis and characterization of compound 20 Compound 20 (illustrated below) was synthesized via the Zinke reaction. First, 4,4'-bipyridine and 1-chloro-2,4-dinitrobenzene (excess amount) were refluxed in ethanol for 72 h. The reaction mixture was then cooled to room temperature and concentrated under vacuum. It was precipitated with diethyl ether and dried to give the corresponding Zinke salt. In the second step, this was reacted with 4-trimethylammonium aniline (excess amount) in ethanol under reflux for 72 h. The crude product was collected by filtration and purified by washing three times with ethanol. 20 was obtained in a purity of >99.9%, suitable for electrochemical studies, by triturating six times with acetone from water.

[0484] [ka]

[0485] Compound 20 1 It was characterized by H NMR, and the NMR is shown in Figure 12C. The chloride counterion is omitted from the structure for clarity.

[0486] Calculated singlet-triplet energy gap Singlet-triplet gap (E ST ) was calculated by taking the difference in free energies obtained for optimized structures for both the singlet and triplet forms of each two-electron reduced compound. Free energy values ​​were calculated from geometry-optimized structures based on DFT performed at the UB3LYP / 6-31++G(d,p) level using the UltraFine integration grid, GD3BJ, and the SMD implicit solvent model as implemented in Gaussian09.

[0487] Bispyridinium compounds are generally known to exhibit closed-shell singlet structures when two-electron reduced. However, as conjugation is increased, a population of thermally accessible triplet diradical states is thought to occur. The accessibility of these triplet diradical states is measured by the difference in Gibbs free energies between the corresponding singlet and triplet states, the "singlet-triplet energy gap," E ST can be predicted using

[0488] E for compounds 10, 11, 12, 13, 17 and 18 ST is E ST =-27.9 kcal mol -1 ~-8.0 kcal mol -1 (Fig. 2e), where more negative values ​​indicate a greater tendency to form closed-shell structures. All compounds had E ST <-6.0 kcal mol -1(10, 11, 12, 13, 17, 18) Voltammetry for these compounds demonstrated reversible redox processes. Homocyclic core electrolytes exhibited more negative potentials than heterocyclic core electrolytes. More conjugated molecules exhibited more negative potentials than less conjugated molecules.

[0489] E for compounds 15 and 16 ST are -5.4 kcal mol -1 and -1.6 kcal mol -1 (Figure 2e). -6.0 kcal mol -1 <E ST <0 kcal mol -1 Higher E ST is believed to cause a loss of redox reversibility when tested using cyclic voltammetry (CV). Without being bound by theory, this is believed to be the result of diradical species generation and subsequent participation in parasitic side reactions (e.g., proton or halide abstraction, σ-dimerization, and cyclization). Because redox activity occurs at the electrode surface, these parasitic side reactions are magnified in CV experiments, causing high local concentrations of diradical species around the electrode that can participate in parasitic side reactions. -6.0 kcal mol -1 <E ST <0 kcal mol -1 E ST It is believed that compounds with the formula (I) exhibit redox reversibility when cycled in an RFB because redox occurs in the bulk electrolyte (as opposed to only at the electrode surface), and therefore the local concentration of diradical species is lower, reducing side reactions. It is also believed that redox reversibility can be increased by cycling the compound at lower temperatures. At lower temperatures, the triplet diradical state is less populated, lowering the diradical concentration and suppressing side reactions.

[0490] E for comparative compounds 14 and 19 ST are 3.6 kcal mol -1 and 2.3 kcal mol -1 (See Figure 2e). These higher EST >0 kcal mol -1 At this point, the compounds are believed to adopt a non-Kekulé (or open-shell) two-electron reduced structure and thus possess a ground-state triplet diradical. Remarkably, the first and second redox events for compounds 14 and 19 are very close together (see Figure 2e), so that they form a two-electron reduced open-shell state immediately after reduction. Consequently, comparative compounds 14 and 19 possess irreversible redox properties.

[0491] E ST The value is related to the degree of separation between the first and second redox events, with a larger negative E ST The values ​​correspond to wider gaps between redox events.

[0492] Electrochemical characterization: Dioxygen-free electrolyte Cyclic Voltammetry Cyclic voltammetry experiments were performed at 25 °C in N2-purged 0.1 M aqueous NaCl solution on a Metrohm Eco Chemie Autolab PGSTAT12 potentiostat running GPES4.9 software. Three electrode configurations were used: a 3 mm or 1.6 mm glassy carbon working electrode, a platinum counter electrode, and an RE-5B Ag / AgCI BASI reference electrode. The glassy carbon electrode was polished before each measurement using 0.05 μm alumina-H2O slurry on an abrasive cloth. CVs were measured at 20 mVs. -1 The scan rate was 100 s, and the concentration of each compound was 1 mM.

[0493] By cyclic voltammetry (CV), compounds 10, 11, 12, 13, 17, and 18 exhibited reversible potentials for the first reduction between −0.35 and −0.82 V vs. the standard hydrogen electrode (SHE) (see Figure 2d). Compounds 10, 11, and 17 exhibited reversible potentials of −0.35 V and −0.68 V, −0.76 V, and −0.56 V and −0.67 V, respectively. Notably, however, compounds 12 and 13 had first redox potentials of −0.77 V and −0.82 V, respectively, which are highly negative and are believed to be the most negative first redox potentials for any pyridinium RFB electrolyte featuring an unsubstituted core to date.

[0494] Viologen derivatives whose two-electron reduced structure can adopt the Kekulé structure (e.g., 12, 13) are likely to have reversible potentials. Compounds that exhibit a lower degree of conjugation are also likely to have more reversible redox potentials.

[0495] Compounds 15 and 16 exhibit similar negative first reduction potentials to 12 and 13, but under the CV conditions discussed above, the redox potentials of 15 and 16 are smaller and more negative than those of 12 and 13. ST Cycling in a redox flow cell and / or at lower temperatures is believed to result in reversible redox for compounds 15 and 16.

[0496] In contrast, comparative compounds 14 and 19 have no reversible potential and exhibit a positive E ST This is thought to be due to the following.

[0497] In situ NMR and EPR of RFB The flow battery was purchased from Scribner Associates. Ultra-high purity sealed graphite flow plates with a serpentine flow pattern were used for both electrodes. Each electrode was 5 cm 2The active area was a carbon felt (SGL). An anion exchange membrane (120 μm, membrane thickness, <10 Å pore size, Selemion, Japan) was placed between the two electrodes. A PTFE frame with a 3 mm membrane thickness was used to mount the electrodes, with 0.7 mm Viton gaskets on both sides of the frame. The current collector was a gold-plated copper plate. Anodized aluminum end plates with reactant input and output ports were used. A Masterflex L / S peristaltic pump (Cole-Parmer, Vernon Hills, IL) was used to pump the mixture at 40 rpm (approximately 20 mL min−1). -1 The electrolyte was circulated through the electrodes at a flow rate of 1000 kJ / cm. A custom-made glassware made of Pyrex® with a gas inlet, outlet, and liquid inlet and outlet was used as the electrolyte reservoir.

[0498] In situ NMR and EPR characterization was performed using a flow battery as described above, two peristaltic pumps, an electrochemical cycler (SP-150, BioLogic SAS), and benchtop EPR (MS5000, Magnettech) and NMR (300 MHz, Bruker Avance III) spectrometers. The battery and EPR spectrometer were placed outside the 5G line of the NMR magnet. Electrolyte was pumped through the flow battery, then through the EPR and NMR magnets, and finally back into the electrolyte reservoir. The flow direction was from the bottom to the top of both magnets. PFA tubing (1 / 16 inch) was used to connect the electrolyte reservoir, the battery, and the EPR and NMR sampling tubes.

[0499] In the anolyte reservoir, the flow cell used 30 mL of 0.01 M test compound in 0.1 M deuterated NaCl solution, unless otherwise noted. In the catholyte reservoir, the flow cell used 50 mL of 0.02 M 4-hydroxy-TEMPO in 0.1 M deuterated NaCl solution, unless otherwise noted. Both reservoirs were purged with N2, degassed for 1 h, and then held under active N2 flow during cycling. The flow cell was galvanostatically charged and discharged five times at room temperature on a portable electrochemical cycler at 10 mA current.

[0500] In situ NMR and EPR spectra were obtained for compounds 10, 11, and 13 while full cells consisting of 10 mM viologen and 20 mM 4-hydroxy-TEMPO in DO were galvanostatically cycled for five full charge-discharge cycles. The second charge-discharge cycle is shown in Figure 3. The voltages for (a) 10, (b) 11, and (c) 13 in 100 mM NaCl and 20 mM 4-hydroxy-TEMPO in a 100 mM NaCl full cell as a function of time during one full charge-discharge cycle. Cutoff voltages of 0.5 V (10, 11, and 13), 1.90 V (10), 1.95 V (11), and 2.00 V (13) were used, with a 1 h potential hold applied at each cutoff value. NMR is shown in Figure 3(b, f, j), and EPR is shown in Figure 3(c, g, k). Spectra were collected during the charge-discharge cycle. The oxidation states and respective NMR proton assignments of 10, 11, and 13 are shown in (d, h, I). The chloride counterions are omitted for clarity. Proton assignments e * indicates that proton e undergoes fast hydrogen-deuterium exchange, reducing its intensity and limiting its observation by NMR.

[0501] Upon charging a full cell containing compound 10, plateaus corresponding to two well-separated one-electron redox events were observed. For compounds 11 and 13, the redox events were sufficiently closely spaced that a single charge and discharge plateau was observed in each case. Starting at 0.50 V vs. 4-hydroxy-TEMPO, the unreduced 10 4+ , 11 4+ and 13 4+ Protons belonging to both the aliphatic and aromatic moieties of the ion result from nearly complete hydrogen-deuterium exchange within the first charge-discharge cycle. 4+ The signal intensity for the proton e of 1 was visible by NMR at a low level.

[0502] Above 0.50 V, all signals except a (terminal quaternary amine proton) disappeared almost immediately with the simultaneous appearance of EPR resonances of the radical 10 3+·, 11 3+· and 13 3+· belongs to.

[0503] At high states of charge (1.90 V, 1.95 V, or 2.00 V for 10, 11, or 13, respectively), the potential was held constant for 1 h.

[0504] During this period, new resonances appeared in the NMR spectra for compounds 10 and 11 that were substantially shifted to lower frequencies relative to those observed in the lower charge states. These features correspond to the diamagnetic, two-electron reduced species 10. 2+ and 11 2+ 10 2+ For the 10 , we observed substantial broadening of all resonances and 2+ This suggests the existence of residual levels of radicals that exist in equilibrium with the hydroxyl group.

[0505] For compound 13, no new resonances were observed during the potential hold. Instead, all NMR resonances were substantially broadened, including a". Furthermore, no radical species were observed by EPR. E for 13 ST Since is small, a population of paramagnetic, thermally accessible triplet states may be responsible for the dramatic NMR line broadening observed. The lack of direct observation of triplet diradicals by EPR suggests that fast singlet-triplet interconversion occurs on the experimental time scale, or at low radical concentrations, resulting in spin pairing of the triplet diradicals to form EPR-silent dimers.

[0506] For compounds 17 and 18, in situ NMR and EPR spectra were obtained while full cells containing both 10 mM viologen and 20 mM 4-hydroxy-TEMPO in DO were galvanostatically cycled for five full charge-discharge cycles, two of which are shown in Figure 4. (a) Voltage of 17, 18 in 100 mM NaCl and 20 mM 4-hydroxy-TEMPO in a 100 mM NaCl full cell as a function of time for one full charge-discharge cycle. 2 mA cm -2A current of 0.5 V (17 & 18), 1.75 V (17), and 1.85 V (18) were used, with cutoff voltages of 0.5 V (17 & 18), 1.75 V (17), and 1.85 V (18) applied with a 1 h potential hold at each cutoff value. NMR (b,f) and EPR (c,g) spectra collected during charge-discharge cycling. (d,h) The oxidation states of 17 and 18 and their respective NMR proton assignments are shown. The chloride counterion is omitted for clarity.

[0507] Heteroatom-based compounds 17 (wide E ST ) and 18 (narrow E ST ) (Figure 4) show that these phenomena are common and that E ST This suggests that two distinct regions of electrochemical performance arise, described by:

[0508] For variable concentration experiments, currents of 1 mA, 5 mA and 10 mA were used for concentrations of 1 mM, 5 mM and 10 mM, respectively.

[0509] For compound 11, in situ NMR and EPR spectra were obtained for a full cell containing 1 mM of viologen in 100 mM NaCl and 2 mM 4-hydroxy-TEMPO in a 100 mM NaCl full cell as a function of time during one full charge-discharge cycle. -2 A current of 1000 kJ / s was used.

[0510] Cut-off voltages of 0.5 V and 1.95 V were used with a 1 h potential hold applied at each cut-off value.

[0511] The results are shown in Figure 5. NMR (b) and EPR (c) spectra taken during charge-discharge cycling. Features in the EPR spectrum indicate the presence of ultra-trace amounts of 4-OH-TEMPO crossover. (d) Structure of 11 and its respective NMR proton assignments.

[0512] Cycle Data Galvanostatic cell cycling was performed using the procedure described above from the in situ NMR / EPR studies. Voltage versus discharge capacity was measured for 10 mM compounds 17 (Figure 6a) and 18 (Figure 6b) in 100 mM NaCl and 20 mM 4-hydroxy-TEMPO in a 100 mM NaCl full cell for 5 full charge-discharge cycles. 2 mA cm -2 Currents of 0.5 V (17 and 18), 1.75 V (17) and 1.85 V (18) were used in all cases. Blocking voltages of 0.5 V (17 and 18), 1.75 V (17) and 1.85 V (18) were used with a 1 h voltage hold applied at each cut-off value.

[0513] Compounds 17 and 18 are shown to have a relatively flat voltage profile over their discharge (see Figure 6). This flat voltage profile is advantageous for energy storage applications, eliminating the need for additional circuitry to increase / decrease voltage or systems that can tolerate variable input voltages.

[0514] The discharge capacities of compounds 17 and 18 are shown to be relatively constant during their first three cycles (see Figure 7). Compound 18 has a capacity retention of about 92% during the first five cycles. Compound 17 has an excellent capacity retention of about 99% during the first five cycles. The closed-shell nature of compound 17 is believed to result in improved capacity retention.

[0515] The coulombic efficiencies for compounds 17 and 18 were also measured at 78.6±0.3 and 79.7±2.8, respectively.

[0516] E about 18 ST is less negative than that for compound 17, it is believed that compound 18 has a higher population of paramagnetic thermally accessible triplet states, which may be responsible for the slightly poorer capacity retention of 18.

[0517] Further cycling data was measured for compounds 10, 11 and 13 and is shown in FIG.

[0518] FIG. 8a shows the radical concentration profiles of 10, 11, and 13 during charging derived from spin counting based on the EPR data shown in FIG. 3 (and discussed above).

[0519] Figure 8b shows spectroelectrochemical data for 10, 11, and 13 at a concentration of 1 mM. Bands assigned to the one-electron reduced and π-dimer species are labeled. UV-Vis spectroelectrochemical studies were performed on compounds 10, 11, and 13. 10 4+ (0.5mM), 11 4+ (0.5mM) and 13 4+ A degassed solution of 0.5 mM HCl was prepared using Schlenk techniques. The solution was transferred to a quartz cuvette (10 mm path length) under N2, and the cuvette was held under a positive flow of N2. The sample was electrochemically reduced using a carbon paper working electrode and a gold counter electrode. Spectral data were acquired using a UV / Vis spectrometer (Horiba, Duetta) immediately after the solution was transferred to the cuvette and electrochemically reduced.

[0520] Figure 8c shows the voltage versus discharge capacity over five full charge-discharge cycles for 10, 11, and 13 in 100 mM NaCl and 20 mM 4-hydroxy-TEMPO in a 100 mM NaCl full cell. -2 A current of 1 mA cm was used in all cases. For compound 11, voltage vs. discharge capacity data over 5 full charge-discharge cycles for 5 mM and 1 mM 11 full cells are overlaid. 5 mM 11 in 100 mM NaCl and 10 mM 4-hydroxy-TEMPO in a 100 mM NaCl full cell was measured at 1 mA cm. -2 1 mM 11 in 100 mM NaCl and 2 mM 4-hydroxy-TEMPO in a 100 mM NaCl full cell was cycled at a current of 0.2 mA cm -2 Cut-off voltages of 0.5 V (10, 11 & 13), 1.90 V (10), 1.95 V (11) and 2.00 V (13) were used with a 1 h potential hold applied at each cut-off value.

[0521] Figure 8(d) shows the discharge capacity versus cycle number for 11 at concentrations of 10 mM, 5 mM, and 1 mM.

[0522] FIG. 8(e) shows the normalized discharge capacity versus cycle number for 10, 11, and 13 at 10 mM concentration.

[0523] Dimerization research In situ DOSY NMR Quasi-2D NMR experiments were performed in flowing electrolytes by direct excitation with a 90° radio frequency pulse. NMR spectra were acquired by collecting eight free induction decays with a 15 s cycling delay. The pulse width for the 90° pulse was 27 μs at 30 W. All spectra were referenced to the water chemical shift at 4.79 ppm. NMR data were processed using TopSpin 3.6.3 (Bruker). EPR data were processed using EasySpin version 5.2.30. Electrochemical data were processed using EC-lab 11.36 (BioLogic).

[0524] The flow was stopped for the acquisition period (12 min) to perform DOSY NMR.

[0525] In situ DOSY NMR experiments were performed on 10, 11, and 13 at 0%, 50%, and 100% SOC (Table 1). This shows a general decrease in diffusivity (D) from 0 to 100% SOC, particularly for compounds 11 and 13, indicating low radical concentrations at all SOCs. These results suggest an increase in the size of the cation upon generation of the monoradical, consistent with the formation of a dimer with twice the molecular weight of the monomer (the decrease in diffusivity is due to the increased molecular weight).

[0526] Compound 10 results in a much smaller decrease in diffusivity, indicating that little or no dimer is formed upon generation of the monoradical.

[0527] [Table 1]

[0528] The presence of the dimer could not be determined directly (both as a result of the high radical concentration, which affected the observation by NMR, and as the known EPR silence of the viologen π-dimer affected the observation by EPR).

[0529] EPR and CV model studies The redox equilibria associated with compounds 10, 11, and 13 were analyzed. The proportionalization equilibrium constant, K c Representing the two one-electron reductions as a propor- tionation equilibrium with

[0530] The difference between redox events is

[0531]

number

[0532] By the proportional equilibrium constant K c and related.

[0533] Proportionation equilibrium of compounds,

[0534]

number

[0535] For , the fit to the experimental radical concentration data is

[0536] K c ≠4

[0537]

number

[0538] K c =4

[0539]

number

[0540] obtained by.

[0541] If n is the number of electrons removed from the system, starting from 100% SOC, then x is the fraction of radicals.

[0542] For the π-dimerization equilibrium, K d The values ​​were estimated as follows: At 50% SOC, the starting concentration of viologen, V o was added to create the reduced species, thereby obtaining the previous result:

[0543]

number

[0544] Initial concentration (V o ) and K in this state of charge c and radical concentration (V 3+· ) is known and the dimerization constant is:

[0545]

number

[0546] It can be calculated as follows.

[0547] This equation was used to fit experimental radical fraction data obtained by the spin-counting EPR-based method, from which the observed propor- tionation equilibrium constant, K, was obtained. c,obs During the fitting, K values ​​of 0.75, 0.021, and 0.0021 were derived. c,obs The values ​​of σ were determined for 10, 11, and 13, respectively (Table 2). However, the fits based on the EPR data were not very good and deviated substantially from the experimental data, especially for compound 13, suggesting the existence of other phenomena not explained by the simple approximation model.

[0548] The formula was also used for CV curve fitting, which gave a much better agreement with the experimental data. c The "exact" K is calculated in terms of the difference between the first and second redox events obtained by CV curve fitting to c Estimate the value of K c,obs The K values ​​for 10, 11, and 13 could be compared. c The value is 3.2 x 10 5 , 1.3 and 2.9 (see Table 2), and K c,obs The values ​​were substantially higher than those shown. This discrepancy indicates that, in addition to the propor- tionation , an addition reaction equilibrium may exist, causing the lower observed radical fractions. The strongest candidate for this is the dimerization equilibrium.

[0549] From the radical concentrations for 10, 11, and 13, K c Deriving the values ​​is an average K of 0.7, 0.2 and 0.002 c Also, the significantly low value of 13 is unreliable because there is a large asymmetry in the radical concentration as a function of SOC, which means that some assumptions may be violated.

[0550] [Table 2]

[0551] Capacity fade rate and coulombic efficiency The capacity fade rate and coulombic efficiency were calculated for 10, 11, 13, 17, and 18 based on five full charge-discharge cycles (see Figures 7 and 8 and the galvanostatic cycle data column). c , K. d and E ST (See Table 2 and EPR and CV modeling studies.) For all compounds, the coulombic efficiencies were within a narrow range (74%-81%), while the values ​​for capacity fade showed a series of trends.

[0552] First, a lower E STExtended viologens with higher E values ​​(e.g., compounds 13 and 18) ST These compounds exhibited significantly higher capacity fade than those with higher capacities (e.g., compounds 11 and 17). Together with the NMR and EPR findings, this may suggest the existence of two distinct regions of electrochemical performance. It may also indicate that the thermally accessible triplet species is associated with a parasitic process, possibly similar in nature to that observed by CV for compounds 14, 15, 16, and 19 (Figure 2 and cyclic voltammetry).

[0553] Second, a higher E ST Among the compounds with high radical concentrations (e.g., compounds 10, 11, and 17) at all charge states, those that exhibit high radical concentrations (e.g., compound 10) also exhibit a greater degree of capacity fade (Figures 8a, 8c, and 8e and galvanostatic cycling data). Collectively, these results suggest that the capacity fade of bispyridinium compounds is primarily related to the formation of open-shell structures, e.g., either monoradicals or diradicals. Thus, all SOCs (low K c , high K d and high E ST ) should correlate with improved capacity retention. c and high E ST The process leads to closed-shell structures, while high K d The process preserves the monoradical as a spin-paired π-dimer, which is now believed to directly contribute to capacity fade.

[0554] Because π-dimerization is a concentration-dependent process that favors a higher degree of dimerization at higher monoradical concentrations, a set of additional RFB operations was performed on compound 11 (i.e., a compound with a high k dCompound (11) was analyzed to determine the extent to which π-dimerization contributes to capacity fade (Figure 8d). As the concentration of 11 increased, both the capacity retention and Coulombic efficiency increased, corresponding to a high degree of π-dimerization. At 10 mM, a Coulombic efficiency of 77% was observed. These decreased slightly to 74% at 5 mM and then dramatically to 18% at 1 mM. Concomitantly, at 10 mM, a capacity fade rate of 0.01% per cycle was obtained, while at 5 mM, they increased sharply to 9.64% per cycle. Even at a Coulombic efficiency of 77%, capacity fade is minimal, whereas at 74%, corresponding to half the concentration (5 mM), it is substantial. However, at a concentration of 1 mM, consistent with a low degree of π-dimerization, a completely different set of charge-discharge characteristics was observed. Instead of the charge processes corresponding to the reduction of 11, a new set of processes emerged with an onset voltage of 0.82 V vs. 4-hydroxy-TEMPO (Figure 5). These processes proceed over much longer timescales than those characteristic of viologen charging, causing both hydroxide accumulation that increases the pH from 7 to 12 and almost complete loss of system capacity within the first charge-discharge cycle, with no evidence of chemical decomposition from in situ NMR or EPR.

[0555] Electrochemical characterization: Dioxygen exposed electrolyte In situ mass spectrometry Online electrochemical mass spectrometry (OEMS) experiments were performed using 1% dioxygen in argon at 1.2 bar using a custom-made H-cell connected to a gas flow system previously described in Zhao et al.

[0556] In situ online electrochemical mass spectrometry of 1 mM 11 in 100 mM NaCl and 2 mM 4-hydroxy-TEMPO in a 100 mM NaCl full cell during one full charge-discharge cycle in an atmosphere of 1% O in Ar. A current density of 0.2 mA was used. A 2 h potential hold was applied at 1.95 V after 8 h of charging.

[0557] This revealed a rapid, steady decrease in dioxygen partial pressure in the headspace above the electrolyte during charging under a continuous flow of 1% O in Ar (Figure 9a). This dioxygen consumption became more evident upon reaching the viologen reduction potential. During the operating phase, no change in hydrogen partial pressure was detected despite operating at a cell voltage (1.23 V) outside the thermodynamic stability window of water. Taken together, these results suggest that the increase in pH during cycling is associated with gaseous dioxygen consumption rather than water splitting, and that reduced viologen species facilitate this process. Based on these findings, a two-electron direct reduction of trace dissolved dioxygen via the peroxide pathway to form hydroxide anions has been proposed as a parasitic process (E = -0.065 V vs. SHE; 0.87 V vs. 4-hydroxy-TEMPO), which is consistent with the previous work (11). 3+· The reduced forms of HCl, HCl, etc., act as redox mediators.

[0558] At higher concentrations, normal viologen redox behavior was restored with no further evidence for charging plateaus corresponding to other processes, although a similar increase in pH was observed. This suggests that oxygen reduction (direct or viologen-mediated) still occurs. The onset of dimerization typically occurs at about 0.1 mM in water, and π-dimerization appears to favor a higher degree of association at higher concentrations of the corresponding monoradicals, thus favoring a higher degree of π-dimerization and hence K. d It was hypothesized that this may contribute to mitigating competitive side reactions between monoradical species and trace impurities such as oxygen during operation.

[0559] OEMS experiments were also performed using a 50 mM H-cell exposed to a 2 h potential hold at 1.95 V under an atmosphere of 1% O in Ar and 20% O in Ar, respectively, compared to the 1 mM H-cell described above. A current of 1.55 mA was used in both cases. Normalized dioxygen consumption is shown in Figure 9d. Dioxygen consumption at the 50 mM concentration is significantly lower than at 1 mM. Dioxygen consumption at 50 mM is only slightly increased in the presence of 20% dioxygen (partial pressure in argon) compared to 1% dioxygen. This revealed that dioxygen consumption per mole of 11 was substantially lower at 50 mM than at 1 mM. This suggests that dimerized electrolyte species (more prevalent at higher concentrations) tolerate the presence of dioxygen up to atmospheric pressure.

[0560] Galvanostatic cycling in air Flow cells were assembled as described above. For the 25 mM test, a full cell was assembled from 25 mM 11 in 500 mM NaCl (30 mL) and 50 mM 4-hydroxy-TEMPO in 500 mM NaCl (50 mL). For the 50 mM test, a full cell was assembled from 50 mM 11 in 500 mM NaCl (15 mL) and 100 mM 4-hydroxy-TEMPO in 500 mM NaCl (25 mL). 5 mA cm -2 A current of 0.01 V was used in both tests. Both reservoirs were purged with N2, degassed for 1 h, and then held under active N2 flow for the duration of the cycle. The flow cell was galvanostatically charged and discharged at room temperature using a portable potentiostat. The cycling sequence consisted of six full charge-discharge cycles, after which the N2 was stopped and the reservoirs were opened to air. After 1 h, the cell was cycled five more times in air, at which point the reservoirs were closed, purged with N2 for 1 h, and held under positive N2 flow for the next 10 cycles under N2. Electrochemical data were processed using EC-lab 11.36 (BioLogic).

[0561] The results are shown in Figures 9b and 9c. At these concentrations, the cells were galvanostatically cycled six times under N2 at the same current, after which the electrolyte was exposed to air for 1 hour and cycled five more times in air. In both cases, the capacity remained stable under N2. However, upon air introduction, the capacity dropped sharply for five cycles for the 25 mM test, while it remained nearly unchanged for the 50 mM test, with only a slight decrease in Coulombic efficiency. This suggests that while parasitic processes still exist, π-dimerization can be used as a competitive pathway that can suppress viologen reactivity with dioxygen. Open-shell viologen radical cations are thought to transfer electrons to dioxygen, regenerating their non-reduced state and forming reactive dioxygen species (i.e., peroxide, superoxide, and hydroxyl radical) as by-products (Figure 9). The latter set of species can also be generated by direct reduction of dioxygen on the electrode. π-dimerization is thought to be a reversible, competitive pathway by which viologens can both retain their charge and further reduce.

[0562] The 25 mM and 50 mM systems exposed to air were further purged with N for 1 h and cycled an additional 10 times under N. Without being bound by theory, we hypothesize that capacity fade is associated with a dioxygen-based parasitic process, where reintroduction of N results in capacity recovery, albeit at a slower rate than the initial fade, reintroducing dioxygen upon decomposition as a result of the possible accumulation of peroxide species. In accordance with the proposed mechanism, at 25 mM, capacity recovered steadily over the course of 10 cycles of operation, with the recovery rate being slower than the fade rate. At 50 mM, capacity and coulombic efficiency were fully recovered within one cycle, confirming strong air resistance and potentially improving at concentrations relevant to RFB.

[0563] The experiment was repeated with 50 mM of compound 17 in a full RFB cell (Figure 10). Voltage, normalized discharge capacity, and coulombic efficiency of 50 mM of 17 in 500 mM NaCl and 100 mM 4-hydroxy-TEMPO in a 500 mM NaCl full cell cycled 5 times in N2, 5 times in air, and 8 times in N2. -2 A current of 1000 kJ / s was used.

[0564] The capacity remained nearly unchanged upon exposure to air, but the Coulombic efficiency decreased slightly, supporting that while parasitic processes are still present, π-dimerization can be used as a competing pathway that can suppress viologen reactivity with dioxygen.

[0565] Additional cyclic voltammetry Cyclic voltammetry experiments were performed on aqueous solutions of compounds 20 and 10 at 25 °C and 1 mM concentration in 0.1 M NaCl using a Metrohm Eco Chemie Autolab PGSTAT12 potentiostat running GPES4.9 software. When CVs were performed under nitrogen, the solution was purged with nitrogen. A three-electrode configuration was used: a 3 mm glassy carbon working electrode, a platinum counter electrode, and an RE-5B Ag / AgCI BASI reference electrode. The glassy carbon electrode was polished before each measurement using 0.05 μm alumina-H2O slurry on an abrasive cloth. CVs were measured at 20 mVs. -1 The scan was performed using a scan rate of 100 s.p.m.

[0566] The results for compound 20 and compound 10 are shown in Figure 12A. Voltammograms were obtained for compound 10 under nitrogen (dashed line), compound 20 under nitrogen (dark blue line), and compound 20 under air (light blue line).

[0567] As calculated from the voltammograms, compound 20 was found to have reversible reduction potentials of −0.147 V and −0.386 V vs. standard hydrogen electrode (SHE).

[0568] Remarkably, the voltammograms obtained for compound 20 under nitrogen (dark blue line) and air (light blue line) are very similar with similar reduction potentials, suggesting that compound 20 is highly tolerant of the presence of oxygen in solution.

[0569] Extended constant current cycling flow cell study at 250mM Extended cycles were also tested at much higher electrolyte concentrations (see Figure 9e and Table 3).

[0570] The flow cell was assembled as described above. The flow cell was assembled from 250 mM 11 or 17 (12.5 mL) and 250 mM 4-hydroxy-TEMPO in 1 M NaCl (50 mL). 20 mA cm -2 (at a flow rate of 40 rpm), 30 mAcm -2 (at a flow rate of 60 rpm) and 40 mAcm -2 A current of 0.05 V (at a flow rate of 80 rpm) was used in both cases. Both reservoirs were purged with N2, degassed for 1 h, and then held under active N2 flow during cycling for the first 5 cycles, after which the nitrogen flow was stopped and the reservoirs were opened to air. The flow cells were galvanostatically charged and discharged at room temperature using a portable potentiostat. Electrochemical data were processed using EC-lab 11.36 (BioLogic).

[0571] For compound 11, 20 mAcm -2 Measured voltage, normalized discharge capacity, and coulombic efficiency for 250 mM compound 11 and 250 mM 4-hydroxy-TEMPO in a 1 M NaCl full cell cycled five times with N2 at a current density of 20 mA cm (see Figure 9e and Table 3). -2 15 times in air at a current density of 40 mAcm -2 111 times in air at a current density of 20 mAcm -2 5 times in air at a current density of 30 mAcm -2 The electrodes were cycled 200 times in air at a current density of 0.5 V and 1.65 V. Cutoff voltages were used.

[0572] For compound 17 cycles, 20 mAcm -2 5 times in N2 at a current density of 20 mAcm -2 15 times in air at a current density of 40 mAcm -2 67 times in air at a current density of 20 mAcm -2 5 times in air at a current density of 30 mAcm -2Voltage, normalized discharge capacity, and coulombic efficiency of 250 mM 17 and 250 mM 4-hydroxy-TEMPO in 1 M NaCl full cells cycled 100 times in air at a current density of 0.5 V. Blocking voltages of 0.5 V and 1.60 V were used.

[0573] [Table 3]

[0574] For compound 11 (see Figure 9e and Table 3), an initial surge of 12.337% capacity was observed upon exposure to air during the first 130 cycles, followed by a slow transient decay that increased slightly with current. However, towards the end of this step, the decay slowed and stabilized over the next 255 cycles, reaching 30 mA cm -2 At 40 mAcm, a value of 1.411% per day (0.021% per cycle, Table 3) was reached. -2 Even after 111 cycles, the -2 No substantial loss of capacity is observed when switching between , proving the system's ability to handle variable power demands as needed in practical RFB applications.

[0575] Similar results were obtained for compound 17, which demonstrated most of these performance characteristics (see Figure 11 and Table 3).

[0576] It is believed that π-dimerization provides additional stability to dioxygen, allowing suppression of the viologen-mediated reduction mechanism rather than the direct reduction mechanism. The above cycles at 25 mM and 50 mM required the reintroduction of an inert atmosphere to prevent peroxide accumulation. However, the rates of electron transfer (k 0,11 =1.98×10 -2 cms -1 , k 0,17 =2.8×10 -3 cms -1 ) is the same rate for electron transfer to dioxygen (k 0,o2 =8.4×10 -4 cms-1 ) compares favorably. Therefore, at sufficiently high currents, such as those used in these studies, electron transfer to the bispyridinium compound is believed to be kinetically favored. In addition to suppressing the viologen-mediated reduction pathway via π-dimerization, at such currents the bispyridinium compound should be preferentially reduced and the effect of any dioxygen (e.g., trace amounts) should be negligible, potentially obviating the need for periodic purging with inert gas.

[0577] For comparison, Beh et al. reported that dioxygen in the headspace was 40 mAcm -2 described cycling a non-extended viologen electrolyte (corresponding to compound 10) at a similar current density of 10, resulting in a very rapid decline in discharge capacity and low coulombic efficiency (see Figure S5 in Beh et al.).

[0578] Taken together, these results demonstrate the role of π-dimerization in the capacity fade mechanism and novel dimer-mediated air stability, as well as for recovering the initially lost capacity, suggesting that dimerization may be broadly applicable to organic redox flow electrolytes.

[0579] Typically, if the initial coulombic efficiency is 96% or greater, it can be suggested that the RFB be cycled in the absence of oxygen. In known systems, when oxygen is present, the initial coulombic efficiency is typically less than 96% because the oxygen present is reduced during the initial cell cycle.

[0580] (References) A number of publications have been cited above in order to more fully describe and disclose the present invention and the state of the art to which it pertains. Full citations for these references are set forth below. Each of these references is incorporated herein in its entirety by reference.

Claims

1. 1. A redox flow battery comprising an electrolyte, the electrolyte is an organic redox-active molecule comprising redox-active units having two or more heteroarylene groups, the two or more heteroarylene groups being conjugated within the redox-active units, and at least a portion of the redox-active units in the electrolyte are present as complexes formed from one-electron reduced forms of the redox-active units; and molecular dioxygen (O 2 ), A redox flow battery wherein the complex is an intermolecular complex of redox active units such as a homodimer, an intramolecular complex of redox active units, or the complex is a combination of intermolecular and intramolecular complex redox active units.

2. 10. The redox flow battery of claim 1, wherein the organic redox active molecule comprises a redox active unit of formula (IA): 【Chemistry 1】 (Wherein -A- and -B- each independently represent C 5-10 is arylene; -L- is independently C 5-14 Arylene, bond, C 2-6 Alkenylene, C 2-4 alkynylene, 5-14 Arylene and the C 2-4 Alkenylene is a group consisting of one or more -R C optionally substituted with a group; -L 1 - is an independent bond, C 1-6 Alkylene, C 5-14 Arylene, -N(H)-, and (CH 2 O) a1 -(C 2 H 4 O) a2 -(C 3 H 6 O) a3 -(CH 2 C(O)) a4 wherein C is selected from 1-6 Alkylene and the C 5-14 The arylene may be one or more -R D optionally substituted with a group, wherein a1, a2, a3, and a4 are each independently selected from 0 to 12, and the sum of a1, a2, a3, and a4 is 1 to 12; -R A , -R B , if exists -R C and R D each of which is a hydrophilic group; X is one or more counteranions; n is 2 to 4; a and b are independently 1 to 5; c and d are independently 1 to 5; Two or more of -A-, -B- and -L- are C 5-10 is heteroarylene; m is 1 or greater).

3. 3. The redox flow battery of claim 2, wherein the organic redox active molecule is of formula (1B): 【Chemistry 2】 (In the formula, -A-, -B-, -L-, -L 1 -, -R A , -R B , -R C , -R D , X, a, b, c, d, n and m are as defined for formula (lA).

4. -L 1 -C independently 1-6 Alkylene, C 5-14 Arylene and (CH 2 O) a1 -(C 2 H 4 O) a2 -(C 3 H 6 O) a3 -(CH 2 C(O)) a4 -, preferably C 1-6 Alkylene and C 5-14 The redox flow battery according to any one of claims 2 to 4, wherein the compound is an arylene.

5. 6. The redox flow battery according to claim 2, wherein d is 1 to 4, preferably 1 to 3, and more preferably 1 or 2.

6. 4. The redox flow battery of claim 2 or claim 3, wherein the organic redox active molecule is of formula (I): 【Transformation 3】 (Wherein -A- and -B- each independently represent C 5-10 is arylene; -L- is independently C 5-14 Arylene, bond, C 2-6 Alkenylene and C 2-4 alkynylene, Said C 5-14 Arylene and the C 2-6 Alkenylene can be one or more -R C optionally substituted with a group; -R A and -R B If the list exists, -R C at least one of is independently a hydrophilic group; X is one or more counteranions; n is 2 to 4; a, b, and c are each independently 1 to 5; Two or more of -A-, -B- and -L- are C 5-10 Heteroarylene).

7. -A- and -B- each independently represent C 5-10 Heteroarylene, preferably C 5-6 Heteroarylene, more preferably C 6 The redox flow battery according to any one of claims 2 to 6, which is a heteroarylene.

8. Each of -A- and -B- independently has one heteroatom selected from oxygen, nitrogen and sulfur, preferably nitrogen and sulfur. 5-10 The redox flow battery of any one of claims 2 to 7, which is a heteroarylene.

9. -A- 【Chemistry 4】 and -B- is 【Transformation 5】 The redox flow battery according to any one of claims 2 to 8, wherein

10. The redox flow battery of any one of claims 6 to 9, wherein the organic redox active molecule is of formula (II): 【Transformation 6】 (In the formula, -L-, -R A , -R B , X, n, a, b and c are as defined for formula (I).

11. Each -L- is independently C 6-14 Carboarylene, C 5-10 Heteroarylene, bond, C 2 Alkenylene, C 2 alkynylene, more preferably -L- is independently selected from C 6-10 Carboarylene and C 5-6 The redox flow battery according to any one of claims 2 to 10, wherein the heteroarylene is selected from heteroarylene.

12. At least one -L- is C 5-14 The redox flow battery according to any one of claims 2 to 11, wherein the heteroarylene is a heteroarylene, preferably having one heteroatom selected from oxygen, nitrogen, and sulfur, and more preferably the heteroarylene is thiophenylene.

13. 13. The redox flow battery of claim 2, wherein at least one -L- is selected from anthracenylene, naphthylene, and phenylene.

14. -L- independently represents a bond, and 【Transformation 7】 The redox flow battery according to any one of claims 2 to 13, wherein the redox flow battery is selected from the group consisting of:

15. 15. The redox flow battery according to any one of claims 2 to 14, wherein c is 1 or 2, preferably c is 1.

16. -R A and -R B If each of the following exists, then -R C and -R D Each of these independently; -N(R N ) 2 , -N + (R N ) 3 , -P + (R N ) 3 , -OH, -C(O)OH, -NHC(NH)NH 2 , -NHC(O)NH 2 and C optionally monosubstituted with a group selected from halogen 1-6 Alkyl, -(CH 2 ) n -N(R N ) 2 , -(CH 2 ) n -N + (R N ) 3 , -(CH 2 ) n -P + (R N ) 3 , -(CH 2 ) n -OH, -(CH 2 ) n -C(O)OH, -(CH 2 ) n -NHC(NH)NH 2 , -(CH 2 ) n -NHC(O)NH 2 and -(CH 2 ) n -C optionally monosubstituted with a group selected from halogen 5-14 aryl, where n is 0 to 6, and -(CH 2 O) a1 -(C 2 H 4 O) a2 -(C 3 H 6 O) a3 -(CH 2 C(O)) a4 -R N (wherein a1, a2, a3, and a4 are each independently selected from 0 to 12, the sum of a1, a2, a3, and a4 is 1 to 12, and R N are each independently H or C 1-6 alkyl) The redox flow battery according to any one of claims 2 to 15, wherein the redox flow battery is selected from the group consisting of:

17. -R A and -R B are each independently, -N + (R N ) 3 Monosubstituted with -N + (R N ) 3 or -P + (R N ) 3 C monosubstituted n-propyl etc. 3 C such as alkyl (propyl) 2-4 17. The redox flow battery of claim 16, wherein the alkyl group is alkyl.

18. -R A and -R B are each independently, -N + (R N ) 3 Monosubstituted with -N + (R N ) 3 C, such as monosubstituted phenyl 6 C such as aryl 5-14 17. The redox flow battery of claim 16, wherein the compound is aryl.

19. R N and each is methyl or ethyl, preferably methyl.

20. 20. The redox flow battery of any one of claims 2 to 19, wherein a and b are independently selected from 1 to 3, preferably a and b are both 1.

21. the organic redox active molecule 【Transformation 8】 (wherein X is as defined in formula (I)).

2. The redox flow battery of claim 1, wherein the redox flow battery is selected from the group consisting of:

22. the organic redox active molecule 【Chemistry 9】 (wherein X is as defined in formula (I)).

2. The redox flow battery of claim 1, wherein the redox flow battery is selected from the group consisting of:

23. 3. The redox flow battery of claim 2, wherein the organic redox active molecule is of the formula (IC): 【Chemistry 10】 (In the formula, -A-, -B-, -L-, -L 1 -, -R A , -R B , -R C , -R D , X, a, b, c, d, n and m are as defined for formula (lA); R P is a polymer repeat unit; p is 2 or greater).

24. R P 24. The redox flow battery of claim 23, wherein is a repeat unit of a polymer selected from the group consisting of polyethylene, polypropylene, polystyrene, polyacrylate, polymethacrylate, polyester, polyamide, polyethylene terephthalate, and polysiloxane repeat units.

25. The redox flow battery according to claim 23 or 24, wherein p is 2 to 200, preferably 10 to 100.

26. 3. The redox flow battery of claim 2, wherein the organic redox active molecule is of formula (LD): 【Chemistry 11】 (In the formula, -A-, -B-, -L-, -R A , -R B , -R C , X, a, b, c, and n are as defined in formula (lA), and q is 1 to 5).

27. 27. The redox flow battery according to claim 26, wherein q is 1 to 4, preferably 1 to 3, and more preferably 1 or 2.

28. X is a halide, hexafluorophosphate, p-toluenesulfonate, trifluoromethanesulfonate, methylsulfonate, preferably a halide, more preferably Cl ー or Br ー , more preferably Br ー The redox flow battery according to any one of claims 2 to 27,

29. 29. The redox flow battery according to claim 1, wherein the complex is a π-complex such as a π-dimer formed from a one-electron reduced form of the organic redox active molecule.

30. 29. The redox flow battery according to claim 1, wherein the complex is a dimer, such as a homodimer, formed from a one-electron reduced form of the organic redox active molecule.

31. The monomer (K d ) so that the equilibrium constant for the formation of said dimer is 0.2 to 80 mM as measured at a temperature of 20°C. -1 31. The redox flow battery of claim 30, wherein:

32. 32. The redox flow battery of any one of claims 1 to 31, wherein the organic redox active molecule is present at a concentration of 50 mM or more, preferably 150 mM or more, more preferably 250 mM or more.

33. The two-electron reduced form of the organic redox-active molecule is 0 kcal mol -1 (0 kJ mol -1 ), preferably less than -6.0 kcal mol -1 (-25.1kJ mol -1 ) or less singlet-triplet energy gap (E ST 33. The redox flow battery of claim 1, wherein

34. The one-electron reduced form of the organic redox-active molecule is the monomer (K d )(mM -1 ) and the two-electron reduced form of the organic redox active molecule is E ST (kcal mol -1 ) and K d and E ST The redox flow battery of any one of claims 1 to 33, wherein satisfies formula (1): (1)Y≦3.64 * ln(K d )-HAVE BEEN ST (wherein Y is 15 to 30, preferably 20 to 25).

35. 35. The redox flow battery of any one of claims 1 to 34, wherein the electrolyte comprises molecular dioxygen dissolved at a partial pressure equivalent to a concentration of at least 1% by volume, preferably at least 10% by volume, more preferably at least 15% by volume, and even more preferably at least 20% by volume.

36. 36. The redox flow battery of any one of claims 1 to 35, wherein the electrolyte is in contact with a battery headspace, and the battery headspace comprises molecular dioxygen at a concentration of preferably 1% by volume or more, more preferably 10% by volume or more, and even more preferably 20% by volume or more.

37. 1. A method of making a redox flow battery, comprising: forming an electrolyte by combining an organic redox active molecule with a liquid carrier, the organic redox active molecule comprising a redox active unit having two or more heteroarylene groups, the two or more heteroarylene groups being conjugated within the redox active unit; adding the electrolyte to the redox flow battery, 2 ) is dissolved in the electrolyte; reducing the organic redox active molecule to provide a one-electron reduced form of the redox active unit that forms a complex; A method wherein the complex is an intermolecular complex of redox active units such as a homodimer, an intramolecular complex of redox active units, or the complex is a combination of intermolecular and intramolecular complex redox active units.

38. 38. The method of claim 37, wherein the method does not include purging the molecular dioxygen from the electrolyte and / or cell headspace.

39. 39. A redox flow battery obtained or obtainable by the method of claim 37 or 38.

40. 1. A method of charging and / or discharging a redox flow battery in the presence of molecular dioxygen, the redox flow battery comprising an electrolyte; The electrolyte is an organic redox-active molecule comprising a redox-active unit having two or more heteroarylene groups, wherein the two or more heteroaryl groups are conjugated within the redox-active unit; and Molecular dioxygen (O 2 ), The method comprises: reducing the redox active unit to result in a complex formed from the one-electron reduced form of the redox active unit; and / or oxidizing the two-electron reduced form of the redox active unit to provide a complex formed from the one-electron reduced form of the redox active unit; A method wherein the complex is an intermolecular complex of redox active units such as a homodimer, an intramolecular complex of redox active units, or the complex is a combination of intermolecular and intramolecular complex redox active units.

41. 41. The method of claim 40, wherein the coulombic efficiency during discharge is 75% or more, preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more.

42. 42. The method of making the redox flow battery of claim 37 or 38, or the method of charging and / or discharging the redox flow battery of claim 40 or 41, wherein the complex is a dimer, such as a homodimer, formed from a one-electron reduced form of the redox active molecule.

43. 43. The method of making a redox flow battery according to claim 37, 38 or 42, or the method of charging and / or discharging a redox flow battery according to claims 40 to 42, wherein the step of reducing and / or oxidizing the organic redox active molecule is carried out at a voltage per cell of 1.23 V or more, preferably 1.5 V or more.

44. 1. Use of a redox flow battery to charge and / or discharge a redox flow battery comprising an electrolyte in the presence of molecular dioxygen, The electrolyte is an organic redox-active molecule comprising redox-active units having two or more heteroarylene groups, wherein the two or more heteroarylene groups are conjugated within the redox-active units, and at least a portion of the redox-active units exist as complexes formed from one-electron reduced forms of the redox-active units; and Molecular dioxygen (O 2 ), The use wherein the complex is an intermolecular complex of redox active units such as a homodimer, an intramolecular complex of redox active units, or the complex is a combination of intermolecular and intramolecular complex redox active units.

45. 45. The use of claim 44, wherein the complex is a dimer, such as a homodimer, formed from the one-electron reduced form of the organic redox active molecule.

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