Redox flow battery

Abstract

The present invention relates to dioxygen tolerant redox flow batteries (RFBs), methods of making RFBs in the presence of dioxygen and methods of charging and / or discharging RFBs in the presence of dioxygen and uses thereof. The RFB includes an 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 wherein the two or more heteroarylene groups are conjugated within the redox-active unit. And at least a portion of the redox-active unit is present as a complex formed from a monoreduced form of the redox-active unit, and wherein molecular dioxygen (O2) is dissolved in the electrolyte. The RFB of the present invention can be operated in the presence of dioxygen so that there is no need to create strict dioxygen-free conditions by purging, sealing, and flowing inert gases through the RFB.

Description

[0001] The work that led to this application has received funding from the European Union's Horizon 2020 research and innovation programme (European Research Council grant agreements 726470 and 835073 and Marie Sklodowska-Curie grant agreement 706425).

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims priority to and the benefit of GB 2300538.2, filed on January 13, 2023 (13.01.2023), the contents of which are incorporated by reference in their entirety. Technical Field

[0004] The present invention relates to a redox flow battery (RFB) tolerant to dioxygen, a method for preparing 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 Art

[0005] RFB is a type of electrochemical storage device in which energy is stored in a liquid electrolyte rather than a solid electrode material. This feature allows the capacity of the RFB to be expanded in a cost-effective manner simply by changing the size of the electrolyte reservoir. Their layout can also be flexible because the electrochemical cell components and the electrolyte reservoir can be located in separate locations. Therefore, RFB is a promising method for large-scale energy storage such as power grid or grid storage. RFB can provide an important form of grid storage that smooths the energy fluctuations of intermittent renewable energy sources such as solar and wind.

[0006] During battery operation, electrolytes (called cathode electrolyte and anolyte) flow through electrochemical cells where they undergo redox reactions, thereby storing or releasing charge. The electrolytes are then stored in their reduced or oxidized states in an electrolyte reservoir. The electrolytes contain redox-active species that promote reduction or oxidation.

[0007] Among redox-active materials, those based on organic molecules offer both significant cost benefits compared to existing chemistries (e.g., zinc- or vanadium-based electrolytes) and good energy density.

[0008] Viologens (4,4'-bipyridinium compounds) are organic redox-active species that typically provide good water solubility, negative potential, and electrochemical stability under neutral conditions, which are required for RFBs. Acidic or alkaline conditions can also be used to dissolve organic redox-active species.

[0009] Viologens have been shown to be redox-active species for RFBs in various 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.) to provide redox-active species for RFB electrolytes.

[0010] 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 issue raised about such RFBs is that redox-active species degrade due to association at high concentrations (see Kwabi et al.). It is believed that the redox-active species undergo intermolecular association (e.g., dimerization) and / or electrolyte-electrode association, which contributes to degradation. However, it is desirable to operate RFBs at high concentrations of redox-active molecules in the electrolyte to maximize energy density, but doing so is believed to promote degradation.

[0011] At concentrations above approximately 0.1 mM in aqueous environments, reduced viologen organic redox-active species may form assembled structures such as π-dimers, σ-dimers, and charge-transfer complexes. Dimer formation has previously been linked to capacity fading (Kwabi et al.). Therefore, the design of viologen redox-active species and electrolytes seeks to inhibit this dimerization process.

[0012] Side reactions with dioxygen are also particularly problematic. Redox-active species in the electrolyte may exist in the RFB system during cell cycling in the form of mono- and di-radicals, 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 di-radicals in RFB systems are known to readily transfer electrons to dissolved dioxygen, leading to the formation of reactive oxygen species (ROS) (Bird et al.).

[0013] To suppress dioxygen-mediated side reactions, RFBs are circulated under strict dioxygen-free conditions. For example, gaseous dioxygen is removed from the headspace above the electrolyte in the electrochemical cell and electrolyte reservoir, and dissolved dioxygen is removed from the electrolyte itself. In the preparation of known RFBs, dissolved dioxygen is typically removed by purging the electrolyte with an inert gas. During preparation, the headspace is also purged with an inert gas and then sealed to isolate it from air during operation. During operation, the electrolyte headspace can also be placed under a positive pressure inert gas flow to remove any dioxygen generated during operation.

[0014] Sensitivity to dioxygen is particularly problematic for aqueous electrolytes. In water, dioxygen can be generated in situ by cycling the RFB at a voltage outside the stability window of water (e.g., an open circuit voltage greater than about 1.23V). Therefore, most aqueous RFBs to date have been cycled at an open circuit voltage below 1.23V to avoid in situ generation of dioxygen by the splitting of water (Perry et al.). This maximum operating voltage is very low compared to many common battery technologies (e.g., lithium-ion batteries), which have an operating voltage of approximately 3 to 4V per cell. This limits the energy density and electrical efficiency of RFBs. High currents are typically required to compensate for the low voltage, which reduces efficiency.

[0015] All viologen RFB cycling studies to date have been conducted in a strictly air-free environment. Viologen RFBs are known to be sensitive to dioxygen molecules, and therefore dioxygen is removed from the RFB by purging. The removal of dioxygen is a common practice in RFB preparation and operation.

[0016] However, the additional steps required to keep RFBs free of dioxygen make their manufacture and operation complex and costly. This is a significant barrier to large-scale adoption of RFBs. Relatedly, the low voltage required to avoid in-situ dioxygen generation in aqueous RFBs hinders large-scale adoption due to limited energy density compared to higher voltage systems.

[0017] Therefore, there is a need for RFBs, particularly RFB organic electrolytes, that can be used in the presence of dioxygen without compromising performance. Summary of the Invention

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

[0019] In general, the present invention relates to a RFB comprising an electrolyte comprising:

[0020] 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

[0021] Molecular dioxygen (O2) dissolved in the electrolyte.

[0022] Complexation of the reduced form of the organic redox-active molecule provides dioxygen tolerance to the redox-active species by providing a competitive pathway with the degradation reaction of dioxygen. This in turn provides dioxygen tolerance to the RFB.

[0023] In a general aspect of the present invention, there is provided a redox flow battery comprising an electrolyte comprising:

[0024] 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 in the electrolyte is present as a complex formed from a single reduced form of the redox-active unit, and

[0025] Molecular dioxygen (O2) dissolved in the electrolyte.

[0026] In a first aspect of the present invention, there is provided a redox flow battery, the redox flow battery comprising an electrolyte, the electrolyte comprising:

[0027] 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 in the electrolyte is present as a complex formed from a single reduced form of the redox-active unit, and

[0028] molecular dioxygen (O2) dissolved in the electrolyte;

[0029] 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 intramolecularly complexed redox-active units.

[0030] In some embodiments, a redox flow battery is provided, the redox flow battery comprising an electrolyte comprising:

[0031] 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 single reduced form of the organic redox-active molecule, and

[0032] Molecular dioxygen (O2) dissolved in the electrolyte.

[0033] In some embodiments, the complex is a dimer, such as a homodimer, formed from a single reduced form of the organic redox-active molecule.

[0034] In some embodiments, the organic redox-active molecule comprises a redox-active unit of formula (IA):

[0035]

[0036] in:

[0037] -A- and -B- are each independently C 5-10 arylene;

[0038] Each -L- is independently selected from C 5-14 Arylene, bond, C 2-6 Alkenylene, C 2-4 Alkynylidene, wherein the C 5-14 Arylene and C 2-4 Alkenylene is optionally substituted with one or more -R C group substitution;

[0039] -L 1 - independently selected from a bond, C 1-6 Alkylene, C 5-14 Arylene, -N(H)-, and -(CH2O) a1 -(C2H4O) a2 -(C3H6O) a3 -(CH2C(O)) a4 -, wherein said C 1-6 Alkylene and C 5-14 Arylene is optionally substituted by one or more -R D group substituted, and

[0040] 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;

[0041] When present, -R A 、-R B 、-R C and -R D Each of is a hydrophilic group;

[0042] X is one or more counteranions;

[0043] n is 2 to 4;

[0044] a and b are independently 1 to 5;

[0045] c and d are independently 1 to 5;

[0046] Two or more of -A-, -B-, and -L- are C 5-10 heteroarylene; and

[0047] m is 1 or greater.

[0048] In some embodiments, the organic redox-active molecule has formula (IB):

[0049]

[0050] Among them -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 (IA).

[0051] In some embodiments, the organic redox-active molecule has formula (IC):

[0052]

[0053] in:

[0054] -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 (IA);

[0055] R P is the polymer repeating unit;

[0056] p is 2 or greater.

[0057] In some embodiments, the organic redox-active molecule has formula (ID):

[0058]

[0059] in:

[0060] -A-, -B-, -L-, -RA 、-R B 、-R C , X, a, b, c and n are as defined for Formula (IA); and

[0061] q is 1 to 5.

[0062] In some embodiments, the organic redox-active molecule has formula (I):

[0063]

[0064] in:

[0065] -A- and -B- are each independently C 5-10 arylene;

[0066] Each -L- is independently selected from C 5-14 Arylene, bond, C 2-6 Alkenylene, and C 2-4 Alkynylidene, wherein the C 5-14 Arylene and C 2-6 The alkenylene group is optionally substituted by one or more groups -R C replace;

[0067] When present, -R A and -R B and -R C At least one of is independently a hydrophilic group;

[0068] X is one or more counteranions;

[0069] n is 2 to 4;

[0070] Each of a, b, and c is independently 1 to 5; and

[0071] Two or more of -A-, -B-, and -L- are C 5-10 Heteroarylene.

[0072] In some embodiments, the organic redox-active molecule has formula (II):

[0073]

[0074] Among them, -L-, -R A 、-R B , X, n, a, b and c are as defined for formula (I).

[0075] In some embodiments, the organic redox-active molecule is a viologen or an extended viologen.

[0076] Traditionally, recombination (such as dimerization) has been attributed to capacity fade and is associated with precipitation of reduced electrolyte molecules, for example due to electrolyte-electrode interactions. Precipitation at RFB electrodes is also known to lead to electrode degradation. Therefore, known organic redox-active molecules and electrolytes have been actively designed to prevent dimerization, thereby avoiding capacity fade and solubility issues.

[0077] However, the present inventors have identified that the use of such complexation (e.g., dimerization) in the presence of dioxygen can minimize the capacity decay of RFBs. The redox-active molecules and electrolyte conditions developed by the inventors ensure both an increased tendency for complexation of the reduced form of the electrolyte material and a retention of solubility of the associated free radical complexes in the electrolyte. This has been achieved by providing a redox-active material having a conjugated heteroaromatic system and a solubilizing group (e.g., a hydrophilic group), such as an organic redox-active material of the formula shown above (which can be a viologen or an extended viologen material).

[0078] Without wishing to be bound by theory, it is believed that the complex acts to stabilize the redox-active species through free radical pairing by providing charge transfer interactions as well as steric protection and multiple resonance structures. Furthermore, free radical pairing effectively reduces the free radical concentration while maintaining the oxidation state of the species unchanged.

[0079] In addition to recombination, the inventors also identified a wide singlet-triplet energy gap (E ST ) stabilizes the redox-active species of dioxygen via intramolecular electron pairing. ST shows that the singlet state is energetically favorable and the large negative E ST This means that the more reactive triplet state is inaccessible at typical operating temperatures.

[0080] Thus, in some embodiments, the doubly reduced form of the organic redox-active molecule has a mass fraction of less than 0 kcal mol -1 (0kJ mol -1 ), preferably -6.0 kcal mol -1 (-25.1 kJ mol -1 ) or smaller singlet-triplet energy gap (EST).

[0081] Stability and high E achieved through compounding ST Combinations have been achieved by providing a redox-active material having a conjugated heteroarene system and a solubilizing group (e.g., a hydrophilic group), such as an organic redox-active material of formula (I) or (II) described herein (which can be a viologen or extended viologen material).

[0082] A dioxygen-tolerant electrolyte has several advantages for RFBs. For example, it allows the preparation and circulation of RFBs in the presence of dioxygen, eliminating the need to create strict dioxygen-free conditions. This can reduce the cost of producing and operating RFBs by eliminating the need to purge, seal, and flow inert gas through the RFBs.

[0083] In addition, by making the redox active material tolerant to dioxygen, it is also possible to cycle RFBs based on aqueous electrolytes at higher voltages. As explained above, cycling at voltages above the stability window of water (i.e., 1.23 V or higher) is possible without causing degradation mediated by dioxygen generated in the electrolyte. Due to the higher voltage, the energy density and electrical efficiency of the battery cell can be increased.

[0084] The above advantages remove various obstacles that have previously hindered the large-scale adoption of RFBs. The present invention provides a promising method for large-scale adoption of RFBs such as grid-scale batteries.

[0085] In a second aspect of the present invention, there is provided a method for preparing a redox flow battery, the method comprising:

[0086] preparing an electrolyte by combining an organic redox-active molecule with a liquid carrier, wherein the organic redox-active molecule comprises a redox-active unit having two or more heteroarylene groups, and the two or more heteroarylene groups are conjugated within the redox-active unit;

[0087] adding the electrolyte to the redox flow battery, wherein molecular dioxygen (O2) is dissolved in the electrolyte, and

[0088] reducing the organic redox-active molecule to provide a mono-reduced form of the redox-active unit, the mono-reduced form forming a complex,

[0089] 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 intramolecularly complexed redox-active units.

[0090] In some embodiments, the method comprises:

[0091] An electrolyte is prepared 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,

[0092] adding the electrolyte to the redox flow battery, wherein molecular dioxygen (O2) is dissolved in the electrolyte, and

[0093] The organic redox-active molecule is reduced to provide a mono-reduced form of the organic redox-active molecule, which forms a complex.

[0094] 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.

[0095] 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 comprising:

[0096] 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

[0097] molecular dioxygen (O2) dissolved in the electrolyte;

[0098] The method comprises:

[0099] reducing the redox-active unit to provide a complex formed from a mono-reduced form of the redox-active unit, and / or

[0100] oxidizing the doubly reduced form of the redox-active unit to provide a complex formed from the mono-reduced form of the redox-active unit,

[0101] 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 intramolecularly complexed redox-active units.

[0102] In some embodiments, the redox flow battery includes an electrolyte comprising:

[0103] An organic redox-active molecule comprising two or more heteroarylene groups, wherein the two or more heteroarylene groups are conjugated, and

[0104] Molecular dioxygen (O2) dissolved in the electrolyte,

[0105] The method comprises:

[0106] reducing the organic redox-active molecule to provide a complex formed from a mono-reduced form of the organic redox-active molecule, and / or

[0107] The doubly reduced form of the organic redox-active molecule is oxidized to provide a complex formed from the mono-reduced form of the organic redox-active molecule.

[0108] In a fifth aspect of the present invention, there is provided the use of a redox flow battery for charging and / or discharging in the presence of molecular dioxygen, the redox flow battery comprising an electrolyte comprising:

[0109] 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 single reduced form of the redox-active unit, and

[0110] molecular dioxygen (O2) dissolved in the electrolyte;

[0111] 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 intramolecularly complexed redox-active units.

[0112] In some embodiments, the redox flow battery includes an electrolyte comprising:

[0113] 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 single reduced form of the organic redox-active molecule, and

[0114] Molecular dioxygen (O2) dissolved in the electrolyte.

[0115] In some embodiments of the second to fifth aspects, the organic redox-active molecule comprises a unit of formula (IA) as defined above.

[0116] In some embodiments of the second to fifth aspects, the organic redox-active molecule has formula (IB) as defined above.

[0117] In some embodiments of the second to fifth aspects, the organic redox-active molecule has formula (IC) as defined above.

[0118] In some embodiments of the second to fifth aspects, the organic redox-active molecule has formula (ID) as defined above.

[0119] In some embodiments of the second to fifth aspects, the organic redox-active molecule has formula (I) as defined above. In some embodiments of the second to fifth aspects, the organic redox-active molecule has formula (II) as defined above.

[0120] In some embodiments of the second to fifth aspects, the organic redox-active molecule is a viologen or an extended viologen substance.

[0121] In some embodiments of the second to fifth aspects, the complex is a dimer, such as a homodimer, formed from a single reduced form of the organic redox-active molecule. BRIEF DESCRIPTION OF THE DRAWINGS

[0122] The present invention is described with reference to the drawings listed below.

[0123] Figure 1 Compound 1 was synthesized using activated carbon-supported palladium as a catalyst. 1 H NMR spectrum.

[0124] Figure 2 Comparison between classical hydrocarbon diradicals and bispyridinium diradicals (a). (b) Schematic representation of compounds 10-19. (c) DFT-calculated redox potential values ​​and tabulated experimental meta-position Hammett constant values ​​(σ) for the R-group introduced into the pyridinium nitrogen. m ). The trend lines indicate the least squares linear fits obtained for the first redox event and the second redox event. (d) Solubility of compounds 10-19 versus the first reduction potential. Solid circles indicate electrochemically reversible compounds. Hollow circles indicate electrochemically irreversible compounds. The shaded area indicates compounds with a reduction potential lower than that of any bipyridinium electrolyte characterized by an unsubstituted core reported to date. The dotted line (grey) indicates the lowest reduction potential achieved by substituted or unsubstituted bipyridinium RFB electrolytes, (e) Compounds 10-19 according to their corresponding singlet-triplet energy gap (E ST ) values ​​sorted.

[0125] FIG3 is coupled in situ NMR and EPR spectroscopy of full cells with 10 mM (a) 10, (e) 11, (i) 13 in 100 mM NaCl and 20 mM 4-hydroxy-TEMPO in 100 mM NaCl over time for one full charge-discharge cycle. -2The current was measured using a 0.5 V (10, 11, and 13) cutoff voltage, 1.90 V (10), 1.95 V (11), and 2.00 V (13) cutoff voltages, and a 1 h potential hold at the corresponding cutoff values. NMR (b, f, j) and EPR (c, g, k) spectra were collected during the charge-discharge cycle. (d, h, l): Oxidation states of 10, 11, and 13 and their corresponding NMR proton assignments. Chloride counterions have been omitted for clarity. The proton assignments e* indicate that the protons e undergo rapid hydrogen-deuterium exchange, reducing their intensity and limiting observations by NMR.

[0126] Figure 4 Coupled in situ NMR and EPR spectroscopy of 17 and 18 are shown. Voltage versus time for a full cell of 10 mM (a) 17, (e) 18 in 100 mM NaCl and 20 mM 4-hydroxy-TEMPO in 100 mM NaCl for one full charge-discharge cycle. 2 mA cm -2 Current. Cutoff voltages of 0.5 V (17 and 18), 1.75 V (17), and 1.85 V were used, and a potential hold of 1 h was applied at the corresponding cutoff values. NMR (b, f) and EPR (c, g) spectra were collected during the charge-discharge cycle. (d, h): Oxidation states of 17 and 18 and their corresponding NMR proton assignments. Chloride counterions were omitted for clarity.

[0127] Figure 5 Coupled in situ NMR and EPR spectroscopy of 1 mM 11 is shown. Voltage versus time for a full cell of 1 mM (a) 11 in 100 mM NaCl and 2 mM 4-hydroxy-TEMPO in 100 mM NaCl for one full charge-discharge cycle. 0.2 mA cm -2 . Cutoff voltages of 0.5 V and 1.95 V were used, and a potential hold of 1 h was applied at the respective cutoff values. NMR (b) and EPR (c) spectra were collected during the charge-discharge cycle. EPR spectral features indicate the presence of ultratrace 4-OH-TEMPO crossovers. (d) Structure of 11 and its corresponding NMR proton assignment.

[0128] Figure 6 Performance characteristics of 17 and 18 are shown. Voltage versus discharge capacity of full cells of 10 mM (a) 17 and (b) 18 in 100 mM NaCl and 20 mM 4-hydroxy-TEMPO in 100 mM NaCl over five full charge-discharge cycles. 2 mA cm was used in all cases. -2Cutoff voltages of 0.5 V (17 and 18), 1.75 V (17), and 1.85 V (18) were used, and a potential hold of 1 h was applied at the corresponding cutoff values.

[0129] Figure 7 Figure 5 shows the normalized discharge capacity versus cycle number of 17 and 18 at 10 mM concentration. The Coulombic efficiencies of 17 and 18 are 78.6 ± 0.3 and 79.7 ± 2.8, respectively.

[0130] Figure 8 The reduced bispyridinium compounds, their performance characteristics and dimerization tendency are shown. (a) Based on Figure 2 (b) EPR data showing the free radical concentration characteristics of 10, 11, and 13 during the charge process obtained from spin counting. (c) EPR data showing the free radical concentration characteristics of 10, 11, and 13 during the charge process obtained from spin counting. (d) Spectroscopic electrochemical data of 10, 11, and 13 at 1 mM concentration. Bands assigned to the mono-reduced and π-dimer species are shown. (e) Voltage versus discharge capacity of a full cell of 10 mM 10, 11, and 13 in 100 mM NaCl and 20 mM 4-hydroxy-TEMPO in 100 mM NaCl over five full charge-discharge cycles. 2 mA cm was used in all cases. -2 For compound 11, the voltage and discharge capacity data for five full charge-discharge cycles of 5 mM and 1 mM 11 full cells were superimposed. Full cells of 5 mM 11 in 100 mM NaCl and 10 mM 4-hydroxy-TEMPO in 100 mM NaCl were charged at 1 mA cm -2 A full cell of 1 mM 11 in 100 mM NaCl and 2 mM 4-hydroxy-TEMPO in 100 mM NaCl was cycled at 0.2 mA cm -2 Cycling at 10 mM and 20 mM currents. 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, and a 1 h potential hold was applied at the corresponding cutoff values. (d) Discharge capacity of 11 at 10 mM, 5 mM, and 1 mM concentrations as a function of cycle number. (e) Normalized discharge capacity of 10, 11, and 13 at 10 mM concentration as a function of cycle number.

[0131] Figure 9 shows the effect of dioxygen on the redox process of viologen and its inhibition by π-dimerization. (a) Operando online electrochemical mass spectrometry (OEMS) of an H-cell of 1 mM 11 in 100 mM NaCl and 2 mM 4-hydroxy-TEMPO in 100 mM NaCl during one full charge-discharge cycle in an atmosphere of 1% O2 in Ar. A current of 0.2 mA was used. After charging for 8 h, a potential hold of 2 h was applied at 1.95 V. (b) Voltage, normalized discharge capacity, and coulombic efficiency of a full cell of 25 mM 11 in 500 mM NaCl and 50 mM 4-hydroxy-TEMPO in 500 mM NaCl cycled 6 times in N2, 5 times in air, and 10 times in N2. A 5 mA cm -2 (c) Voltage, normalized discharge capacity, and coulombic efficiency of a full cell of 50 mM 11 in 500 mM NaCl and 100 mM 4-hydroxy-TEMPO in 500 mM NaCl cycled 6 times in N2, 5 times in air, and 10 times in N2. 5 mA cm -2 (d) relative to Figure 4 OEMS of 1 mM H-cell as described in (a), OEMS of 50 mM H-cell subjected to a 2 h potential hold at 1.95 V in an atmosphere of 1% O2 in Ar and 20% O2 in Ar, respectively. A current of 1.55 mA was used in both cases. (e) At 20 mA cm -2 The current density was 20 mA cm-1 and the -2 The current density was 40 mA cm-1 and the -2 The current density was 20 mA cm-1 and the cycle was repeated 111 times in air. -2 The current density was 5 cycles in air and 30 mA cm -2 Voltage, normalized discharge capacity, and coulombic efficiency of a full cell of 250 mM 11 and 250 mM 4-hydroxy-TEMPO in 1 M NaCl cycled 200 times in air at a current density of 1.5 V. Cutoff voltages of 0.5 V and 1.65 V were used.

[0132] Figure 10 The effect of dioxygen on the redox process of viologen and its inhibition by π-dimerization of compound 17 are shown. The voltage, normalized discharge capacity and coulombic efficiency of a full cell of 50 mM 17 in 500 mM NaCl and 100 mM 4-hydroxy-TEMPO in 500 mM NaCl were cycled 5 times in N2, 5 times in air and 8 times in N2. The 5 mA cm-2 of current.

[0133] Figure 11 Repeated cycling of 17 at high concentrations is shown, illustrating the air tolerance of 17. At 20 mA cm -2 The current density was 20 mA cm-1 and the -2 The current density was 40 mA cm-1 and the -2 The current density was 20mAcm and the cycle was 67 times in air. -2 The current density was 5 cycles in air and 30 mA cm -2 Voltage, normalized discharge capacity, and coulombic efficiency of a full cell of 250 mM 17 and 250 mM 4-hydroxy-TEMPO in 1 M NaCl cycled 100 times in air at a current density of 1.5 V. Cutoff voltages of 0.5 V and 1.60 V were used.

[0134] Figure 12 (A) shows the voltammograms of 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). The reversible potentials of -0.147 V and -0.386 V were calculated from the peaks in the voltammograms. (B) shows the voltammograms of compound 20. 1 H NMR spectrum. DETAILED DESCRIPTION

[0135] The present invention provides a redox flow battery (RFB) comprising molecular dioxygen (O2) dissolved in an electrolyte. The RFB can circulate in the presence of dioxygen, such as in air.

[0136] In general, the present invention provides an electrolyte for RFBs, comprising a redox-active material that tolerates molecular dioxygen. The redox-active material is configured to complex in its mono-reduced form, which provides improved tolerance to molecular dioxygen.

[0137] More specifically, the present invention relates to a RFB comprising an electrolyte comprising:

[0138] 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

[0139] Molecular dioxygen (O2) dissolved in the electrolyte.

[0140] In a first aspect of the present invention, there is provided a redox flow battery, the redox flow battery comprising an electrolyte, the electrolyte comprising:

[0141] 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 in the electrolyte is present as a complex formed from a single reduced form of the redox-active unit, and

[0142] molecular dioxygen (O2) dissolved in the electrolyte;

[0143] 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 intramolecularly complexed redox-active units.

[0144] In some embodiments, the complex is a dimer.

[0145] In some embodiments, the organic redox-active molecule has formula (I):

[0146]

[0147] in:

[0148] -A- and -B- are each independently C 5-10 arylene;

[0149] Each -L- is independently selected from C 5-14 Arylene, bond, C 2-6 Alkenylene and C 2-4 Alkynylidene, where C 5-14 Arylene and C 2-6 The alkenylene group is optionally substituted by one or more groups -R C replace;

[0150] When present, -R A and -R B and -R C At least one of is independently a hydrophilic group;

[0151] X is one or more counteranions;

[0152] n is 2 to 4;

[0153] Each of a, b, and c is independently 1 to 5; and

[0154] Two or more of -A-, -B-, and -L- are C 5-10Heteroarylene.

[0155] In some embodiments, the organic redox-active molecule has formula (II):

[0156]

[0157] Among them, -L-, -R A 、-R B , X, n, a, b and c are as defined for formula (I).

[0158] In some embodiments, the organic redox-active molecule is a viologen or an extended viologen.

[0159] The present invention achieves dioxygen tolerance by providing redox-active materials with an increased tendency to complex, such as dimerize, in a mono-reduced form (e.g., by using an extended aromatic core) and improved water solubility of the redox-active material complex (e.g., by using a hydrophilic appendage). In known systems, the mono-reduced form of the redox-active material is susceptible to side reactions. However, it has now been discovered that complexing (e.g., dimerization) of the redox-active material competes with the side reactions, thereby limiting degradation through side reactions.

[0160] Some specific organic redox-active substances are known.

[0161] Tang et al. describe viologen, phenyl-extended viologen, and methyl-substituted phenyl-extended viologen as redox-active species for RFB electrolytes. All RFBs described operate in a dioxygen-free environment. This can be seen from the absence of dioxygen in the voltammograms of Tang et al. (see Figure 2 and Figure S9). In addition, the absence of dioxygen is evident from the high Coulombic efficiencies of approximately 95% to 100% (see Table S2).

[0162] Tang et al. also teach about the dimerization tendency of viologen, as it is believed that it promotes degradation through side reactions and leads to precipitation of redox-active species during the reduction process. This leads to capacity decay during battery cell cycling. Dimerization is said to increase at high concentrations of redox-active species, and therefore the concentration of redox-active species in the electrolyte is kept below 10 mM. Tang et al. are concerned with 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 in which dioxygen is present in the electrolyte and / or electrolyte reservoir.

[0163] Luo et al. (and corresponding patent application US2020 / 016891) describe 4,4'-(thiazolo[5,4-d]thiazol-2,5-diyl)bis(1-(3-(trimethylammonio)propyl)pyridin-1-ium) tetrachloride. Thiazolo[5,4-d]thiazole-extended viologens were tested as redox-active species for RFB electrolytes. The described RFBs operated in a dioxygen-free environment.

[0164] Thiazolo[5,4-d]thiazole-extended viologen electrolytes show poor capacity retention and energy efficiency at higher concentrations, which is believed to be due to increased electrolyte-electrolyte interactions and dimerization. Luo et al. reported that the improved π-conjugation provided by the thiazolo[5,4-d]thiazole core is important for the performance of the electrolyte.

[0165] Luo et al. reviewed the dioxygen insensitivity of the reduced 2+ form of thiazolo[5,4-d]thiazole-extended viologen redox-active materials. The stability was reportedly attributed to the π-conjugation provided by the thiazolo[5,4-d]thiazole core. The literature did not test the viologen electrolyte during cell cycling or in any other oxidation state, and did not provide a redox flow battery cell in which the electrolyte and / or electrolyte reservoir did not include dioxygen molecules.

[0166] Beh et al. described an RFB using a viologen redox-active material. The described RFB was operated in a dioxygen-free environment. Beh et al. demonstrated that the viologen redox-active material exhibited very rapid discharge capacity degradation and poor Coulombic efficiency when operated in air (see Figure S5 in Beh et al.).

[0167] WO 2021 / 055275 relates to electrolytes based on 2,5-dimercapto-1,3,4-thiadiazole for redox flow batteries. The exemplary electrolytes tested contain heteroarylene groups separated by one or more sulfur atoms, so there is no conjugation between the heteroarylene groups. The electrolytes are described as dimerizing by forming SS covalent bonds upon oxidation (see the structures in paragraphs

[0005] and

[0031] ). This contrasts with the preferred σ or π dimerization that occurs with the reducing substances of the present invention.

[0168] WO 2023 / 046710 relates to viologen electrolytes using various end groups (see Figure 2 D2 does not describe the dimerization of the viologen electrolyte. D2 also does not describe the air stability of the viologen. It is well known that RFBs containing standard viologen anolytes require an oxygen-free operating atmosphere (e.g., see Janoschka et al. and Luo et al.). Beh et al. also showed that this type of compound is unstable to air.

[0169] US2022 / 0384834 and US2022 / 0020990 describe RFB electrolyte compositions comprising TEMPO-based redox-active materials, standard viologens, extended viologens, or mixtures of these components. Preferred embodiments relate to viologens with additional TEMPO groups (see Examples 3, 4, 6, and 7). These compounds differ from the preferred redox-active materials of the present invention. These documents do not describe dimerization of viologen materials or oxygen tolerance of RFB electrolytes.

[0170] US2022 / 0020990 explains that organic RFBs must be kept free of oxygen.

[0171] US2022 / 0190374 describes a viologen electrolyte for RFBs having terminal groups intended to reduce the melting point of viologen. The document does not describe the preferred redox-active materials of the present invention. The document explains that when performing CV testing, the electrolyte solution is purged with nitrogen and the nitrogen is maintained in the cell headspace (see paragraph

[0059] ). There is no description of the oxygen tolerance or dimerization of the redox-active materials.

[0172] CN 112500329 describes TEMPO and viologen RFB electrolytes. The document suggests that the electrolyte does not need to be circulated under an inert atmosphere when used in salt cave cells, where air exposure is inherently limited (see paragraph

[0028] ). This appears to be achieved by using TEMPO to react with reactive oxygen species (ROS). TEMPO can quench ROS and improve air tolerance when present in the anolyte solution. However, the document does not mention the preferred redox active materials of the present invention, and does not describe dimerization of the redox active materials. The dimerization of the redox active materials of the present invention is believed to result in oxygen stability without the need for sacrificial electrolyte components, such as TEMPO, that consume ROS.

[0173] WO 2022 / 236241 describes viologen as an anode electrolyte for RFBs. Paragraphs

[0102] and

[0106] describe the oxygen sensitivity of the reduced viologen form of the compound. The related literature paper explains testing the battery cell in an oxygen-free glove box (see Sullivan et al.). The document does not describe the preferred redox-active materials of the present invention, nor does it describe dimerization of the redox-active materials.

[0174] Redox flow battery

[0175] The RFB can be a full flow battery or a hybrid flow battery.

[0176] An RFB may include a plurality of electrochemical cells, typically arranged in parallel.

[0177] Electrochemical cells are typically assembled into stacks. The stacks can be connected in series or in parallel, and are preferably connected in parallel.

[0178] An RFB typically includes electrochemical cells, an electrolyte reservoir in fluid communication with the cells, wherein an electrolyte is provided in each of the cells and the reservoir.

[0179] The battery headspace is typically present in contact with the electrolyte. The battery headspace may be located in the electrolyte reservoir or in the electrochemical cell.

[0180] The RFB includes an electrochemical cell, an electrolyte reservoir, and an electrolyte. Typically, the RFB includes a flow circuit for circulating the electrolyte between the electrochemical cell and the electrolyte reservoir. In other words, the electrochemical cell and the electrolyte reservoir can be in fluid communication. The RFB can 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 pump, a peristaltic pump, or a rotary pump can be used.

[0181] As known to those skilled in the art, the pump can circulate the electrolyte at any suitable rate. The flow rate will depend on the size of the RFB and the total volume of electrolyte. The flow rate can be equal to about 25%-150% of the total electrolyte volume per minute. For example, for 30 ml of electrolyte, the flow rate can be 7.5 to 45 ml / min. Larger volumes of electrolyte may have lower flow rates.

[0182] Redox reactions occur within the electrodes, storing or releasing charge from the electrolyte through oxidation or reduction. The electrolyte is then returned to the electrolyte reservoir to store the oxidized / reduced electrolyte.

[0183] As described below, the RFB includes an electrolyte containing a redox active material.

[0184] The redox active material may be present in the electrolyte at a concentration of 50 mM or greater, preferably 250 mM or greater, more preferably 500 mM or greater, and even more preferably 1 M or greater. The redox active material 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 material 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.

[0185] In some embodiments, the redox active species may be present in the electrolyte at a concentration of 50 mM or greater, preferably 150 mM or greater, more preferably 250 mM or greater. The redox active species may be present in the electrolyte at a concentration of 50 mM to 250 mM.

[0186] RFBs typically include two electrolytes, referred to as cathode electrolytes and anolytes. The anolyte and cathode electrolyte each contain a redox-active species. Preferably, the redox-active species of the present invention is contained in the anode electrolyte.

[0187] Any suitable redox-active material can be used in the cathode electrolyte. In some embodiments, the cathode electrolyte can include a ferrocene-based redox-active material, a TEMPO-based redox-active material, or a thiourea material. Preferably, the cathode electrolyte is a TEMPO-based redox-active material, such as 4-hydroxy-TEMPO.

[0188] Mixtures of different redox-active species can be used in each electrolyte. Preferably, at least one redox-active molecule has the exemplary properties described herein.

[0189] The electrolyte may further comprise a supporting electrolyte. The supporting electrolyte is typically present at a higher concentration than the redox active substance, such as 2× higher concentration, 5× higher concentration, or 10× higher concentration. Alternatively, the supporting electrolyte is present at the same or lower concentration than the redox active substance. Typically, the supporting electrolyte is present at a concentration of 100 mM or greater, preferably 1 M or greater. The supporting electrolyte may be a metal salt, such as NaCl.

[0190] The electrolyte may be an organic electrolyte (eg, wherein the solvent is an organic solvent) or an aqueous electrolyte (eg, wherein the solvent is water). Preferably, the electrolyte is an aqueous electrolyte.

[0191] Preferably, the electrolyte is an aqueous organic electrolyte in which the redox-active species is an organic molecule and the solvent is water. In some embodiments, the solvent is primarily water, such as 90 wt.% or greater water, preferably 95 wt.% or greater water, more preferably 98 wt.% or greater water, and even more preferably 99 wt.% or greater water, based on the mass of the solvent. It is believed that complexing of the redox-active species (such as π-dimerization) is enhanced in aqueous solution, which further enhances the stability of the redox-active species of the present invention towards dioxygen.

[0192] The RFB includes an electrolyte reservoir. The reservoir is a means of containing and storing electrolyte.

[0193] The electrolyte reservoir may have a headspace above the electrolyte, the headspace being in contact with the electrolyte. This may be referred to as the electrolyte reservoir headspace. The reservoir headspace typically contains a gas. During operation of the RFB, the reservoir headspace is generally required to allow for expansion and changes in the volume of the electrolyte.

[0194] In an embodiment where the RFB includes an anode electrolyte and a cathode electrolyte, the RFB may include an anode electrolyte reservoir, a cathode electrolyte reservoir, an anode electrolyte flow loop configured to allow the anode electrolyte to circulate between the electrochemical cell and the anode electrolyte reservoir, and a cathode electrolyte flow loop configured to allow the cathode electrolyte to circulate between the electrochemical cell and the cathode electrolyte reservoir.

[0195] An electrochemical cell typically includes electrodes, an electrolyte, and a separator. The cell may be formed from a frame to position electrodes (eg, a cathode and an anode) on either side of the separator to form the electrochemical cell.

[0196] Each RFB may include one or more electrochemical cells (eg, assembled in a stack).

[0197] An electrochemical cell may have a headspace above the electrolyte. This may be referred to as the electrolyte cell headspace. The headspace typically contains gas. During operation of an RFB, the cell headspace is generally required to allow for expansion and changes in the volume of the electrolyte.

[0198] The anolyte and catholyte typically flow through opposite sides of a membrane or separator in an electrochemical cell. The two sides of the cell may be referred to as the anolyte side and catholyte side of the electrochemical cell, respectively.

[0199] The membrane or separator allows for ion exchange between the anolyte side and the cathode electrolyte side of the electrochemical cell. The membrane or separator can be an ionically conductive polymer. Preferably, the membrane or separator is selective for supporting electrolyte ions relative to the redox-active molecular ions present in the electrolyte. This reduces crossover of redox-active electrolyte species, which can reduce the capacity of the RFB.

[0200] Typical membrane or diaphragm materials include fluorinated or perfluorinated polymers. Diaphragms such as dialysis membranes, microporous hydrocarbon polymers, intrinsically microporous polymers (PIMs), and polyaromatic ionomers with pendant ionic functional groups can be used as appropriate, particularly when solvated polymeric species or particles are used as the redox-active species. Ceramic membranes, such as those that conduct a single ion, can also be used.

[0201] Examples of suitable fluorinated or perfluoropolymers include sulfonated tetrafluoroethylene copolymers such as Nafion (Dupont), for example 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 those based on Alkali PIMs and dibenzodioxin-based PIMs, such as those containing amidoxime groups. Examples of anion exchange membranes include 120 μm thick Membrane with a pore size of 1.5-2.5 mm (Selemion, Japan).

[0202] Alternatively, membraneless flow batteries are known. In a typical membraneless flow battery, a cathode electrolyte solution and an anolyte electrolyte solution pass through the electrochemical cell with little mixing. This can be achieved, for example, using an immiscible electrolyte system or a laminar flow system.

[0203] Typically, electrodes are located on each side of an electrochemical cell. The electrode located on the cathode electrolyte side of the cell can be referred to as the positive electrode, and the electrode located on the anolyte side of the cell can be referred to as the negative electrode. Redox reactions occur at the interfaces between the cathode electrolyte 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 active surfaces for the redox reactions to occur.

[0204] Preferably, the electrode has high conductivity, high specific surface area and good stability within the operating potential range of the flow battery. Preferably, the electrode has good resistance to corrosion by the electrolyte.

[0205] The electrode preferably has a good affinity for the electrolyte. For aqueous-based electrolytes, the electrode is preferably hydrophilic. For organic-based electrolytes, the electrode is preferably hydrophobic. For the electrolytes of the present invention (e.g., anolyte), the electrode (e.g., anode) is preferably hydrophobic.

[0206] Preferably, the electrode is a carbon-based material. Carbon-based materials are typically hydrophobic and therefore provide good affinity for organic electrolytes. The carbon-based material is preferably not treated, for example, without oxygen treatment, to retain the hydrophobicity of the electrode. Examples of carbon-based electrodes include carbon felt, carbon paper, and graphite felt, preferably carbon felt or carbon felt.

[0207] The positive electrode material and the negative electrode material may be the same or different.

[0208] An electrochemical cell may include a current collector to collect the charge generated in the electrochemical cell. Typically, one current collector is positioned on the cathode electrolyte side of the electrochemical cell (positive current collector) and electrically connected to the positive electrode, and one current collector (negative current collector) is positioned on the anode electrolyte side of the electrochemical cell and electrically connected to the negative electrode. The current collector is typically electrically connected to an external circuit.

[0209] Typical current collector materials include metals such as aluminum, steel, gold and copper. Preferably, the current collector material is aluminum, steel or copper.

[0210] In an alternative embodiment, the RFB is a hybrid flow battery. A hybrid flow battery is a battery in which one electrolyte is in a different state, such as a solid or gas electrolyte compared to a liquid electrolyte. The hybrid RFB can be a flow-liquid battery, a flow-metal battery, or a flow-gas battery. For example, during use, the redox-active molecules can be precipitated as a solid layer on or in conjunction with one electrode. In this case, the liquid electrolyte flows over the surface of the solid electrode in the electrochemical cell. The liquid electrolyte can be a cathode electrolyte or an anolyte, and the solid electrode can be a cathode or an anode, as the case may be. Preferably, the liquid electrolyte is an anolyte.

[0211] As referred to herein, dioxygen refers to molecular oxygen (O2).

[0212] In a conventional RFB, dioxygen is removed from the electrolyte, for example, by purging the RFB with an inert gas and / or sealing the RFB from air.During operation of a conventional RFB, a positive pressure of inert gas is used to remove dioxygen from the electrolyte, the electrolyte headspace, and / or the electrolyte reservoir.

[0213] In the present invention, the RFB can be operated in the presence of dioxygen. During operation of the RFB, the electrolyte, electrolyte headspace, and / or electrolyte reservoir comprise dioxygen. Preferably, during operation, the anolyte, anolyte headspace, and / or anolyte reservoir comprise dioxygen. During operation refers to the cycling (i.e., charging and / or discharging) of the RFB.

[0214] Operation in this context refers to the charging and / or discharging of the RFB, typically without significant degradation of the electrolyte due to oxygen-mediated processes. In other words, the RFB operates as if no dioxygen is present, e.g., with high coulombic efficiency and good capacity retention, despite the presence of dioxygen dissolved in the electrolyte.

[0215] Preferably, dioxygen is not removed from the RFB during operation. For example, the RFB is not sealed from air and / or the RFB is not under a positive pressure of an inert gas.

[0216] In some embodiments, dioxygen is not removed from the RFB during the preparation of the RFB. For example, dioxygen is not purged from the electrolyte during the preparation process.

[0217] The dioxygen can originate from outside the electrolyte, such as from the atmosphere, and dissolve into the electrolyte through the electrolyte headspace. The dioxygen can also originate from inside the electrolyte, such as from the electrolyte itself. For example, in aqueous electrolytes cycled at open circuit cell voltages exceeding about 1.23 V, water typically decomposes to generate dioxygen in the electrolyte.

[0218] Although some known RFBs are described as cycling at voltages exceeding about 1.23 V, this typically results in rapid degradation of the electrolyte when organic redox species are used in the electrolyte. For this reason, known systems use periodic purges and / or a constant positive pressure inert gas flow through the electrolyte and cell to remove any molecular dioxygen from the electrolyte. In contrast, the present invention tolerates molecular dioxygen in the electrolyte, and therefore does not require such purges or inert gas flows.

[0219] Dioxygen is typically present in the electrolyte (e.g., the anode electrolyte) at a partial pressure relative 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 about 20% by volume. Dioxygen is preferably present in the electrolyte (e.g., the anode electrolyte) at a partial pressure equivalent to the abundance of atmospheric dioxygen.

[0220] In some embodiments, the electrolyte contacts the cell headspace, which comprises molecular dioxygen. In some such embodiments, the cell 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.

[0221] The dioxygen concentration in the headspace is measured at a pressure of 1-2 bar, preferably 1-1.5 bar, more preferably 1-1.2 bar and a temperature of 20° C. Typically, the dioxygen concentration is measured at a pressure of about 1 bar and a temperature of 20° C.

[0222] In some embodiments, the molecular oxygen dissolved in the electrolyte (based on partial pressure equivalents) 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 that molecular dioxygen is being generated in the electrolyte (e.g., due to in situ electrolysis of water).

[0223] Redox-active substances

[0224] The redox active species is present in an electrolyte, preferably the anode electrolyte of the RFB.

[0225] A redox-active substance is a substance that can be reduced or oxidized (i.e., lose or gain electrons). Redox-active substances are suitable for use in redox flow batteries to store and release charge through the reduction and oxidation of the redox-active substance. Typically, RFBs discharge and charge by cycling the redox-active substance between an unreduced form, a singly reduced form (+1 electron), and a doubly reduced form (+2 electrons).

[0226] The mono-reduced form of a redox-active substance is a form produced by a mono-reduction (gaining one electron per molecule) compared to the unreduced substance. The doubly-reduced form is a form produced by a doubly-reduced (gaining two electrons per molecule) compared to the unreduced substance. Typically, the doubly-reduced form is prepared by further mono-reduction of the mono-reduced form.

[0227] Discussion of redox-active species encompasses all forms of the redox-active species (eg, unreduced forms, singly reduced forms, and doubly reduced forms). Different forms of the redox-active species are specified where necessary.

[0228] Redox-active substances are organic redox-active molecules. Organic molecules are typically molecules containing carbon-hydrogen bonds and carbon-carbon bonds. Organic molecules may include heteroatoms such as halogens, oxygen, nitrogen, and sulfur.

[0229] Organic redox-active molecules comprise a redox-active unit having two or more heteroarylene groups, wherein the two or more heteroarylene groups are conjugated within the redox-active unit. Conjugation typically refers to π conjugation, wherein three or more p-orbitals share electrons to form a conjugated π system. The heteroarylene groups can be directly conjugated, in other words, the p-orbital on one heteroarylene group shares electrons with the adjacent p-orbital on another heteroarylene group. Alternatively, the heteroarylene groups can be indirectly conjugated, in other words, one heteroarylene group shares electrons with another heteroarylene group via one or more p-orbitals of an intermediate group.

[0230] Each organic redox-active molecule can 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 mono-reduced form and a di-reduced form, as described herein. The redox-active unit preferably has formula (IA).

[0231] In some embodiments, the two or more heteroarylene groups are symmetrical. The two or more heteroarylene groups can be symmetrical about the plane between the heteroarylene groups. In some embodiments, the two or more heteroarylene groups and any intermediate groups are symmetrical. The two or more heteroarylene groups can be symmetrical about the plane intersecting the intermediate groups.

[0232] In some embodiments, the two or more heteroarylene groups are different. In this way, the two or more heteroarylene groups are not symmetrical about the plane between the heteroarylene groups. In some embodiments, any intermediate group (such as -[L] c -) are not symmetrical about the plane between the heteroarylene groups.

[0233] The two or more heteroarylene groups may contain two or more pyridylene groups.

[0234] The two or more heteroarylene groups may be connected by a linker -[L] c - connection. Each -L- is independently selected from a bond, C 2-6 Alkenylene, C 2-4 Alkynylidene and C 5-14 Arylene, wherein the C 2-6 Alkenylene and C 5-14 The arylene group is optionally substituted by one or more groups R C substituted; wherein when present, R C is a hydrophilic group, and c is independently 1 to 5. -[L] c -Preferred options are as described herein.

[0235] Preferably, the two or more heteroarylene groups are linked by a single linker [L] c connect.

[0236] In some embodiments, two or more pyridylene groups can be linked by a linker [L] c Connect. [L] c Preferably, the two or more pyridylene groups are linked by a single linker [L] c connect.

[0237] The organic redox-active molecule preferably has formula (I), more preferably formula (II). Formulas (I) and (II) are described below. Preferably, the organic redox-active molecule is a viologen or an extended viologen.

[0238] Redox-active species form complexes. Complexes are formed by recombination. Recombination typically occurs through non-covalent interactions between two or more independent instances of conjugated heteroarylene groups. These can be referred to as redox-active units.

[0239] Typically, the complex is an intermolecular complex of the redox-active unit, such as a homodimer. The complex can also be an intramolecular complex of the redox-active unit. The complex can further be a combination of intermolecular and intramolecular complexed redox-active units.

[0240] Complexes can be formed between similar redox-active units. Additionally or alternatively, complexes can be formed between different redox-active units.

[0241] A redox-active molecule can comprise one or more redox-active units. Complexes can be formed between similar redox-active molecules. Additionally or alternatively, complexes can be formed between different redox-active molecules.

[0242] Complexation preferably occurs via electron sharing interactions, preferably electron sharing non-covalent interactions. Complexation is preferably not primarily electrostatic interactions (e.g., arising from ionic interactions between anionic and cationic groups).

[0243] Complex can refer to an intermolecular complex between two redox-active units or redox-active molecules (i.e., between two separate molecules). Additionally or alternatively, complex can refer to an intramolecular complex between two redox-active units of the same redox-active molecule (i.e., between parts of the same molecule).

[0244] A complex can 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 can refer to a homogeneous complex between two identical redox-active molecules or units or between two identical redox-active units of the same redox-active molecule (e.g., two identical redox-active units of a polymeric redox-active molecule).

[0245] Complexes can be formed between two or more redox-active units, such as three or more, such as four or more redox-active units. In this way, the complex can be a dimer, trimer, tetramer, or oligomer. Complexes can be formed between two, three, or four redox-active units, such as two or three redox-active units, such as two redox-active units.

[0246] A complex can be formed between two or more redox-active molecules, such as three or more, such as four or more redox-active molecules. In this way, the complex can be a dimer, trimer, tetramer, or oligomer. A complex can be formed between two, three, or four redox-active molecules, such as two or three redox-active molecules, such as two redox-active molecules.

[0247] The complex may be a dimer, such as a homodimer.

[0248] The redox-active species can dimerize to form a dimer. In particular, the mono-reduced form of the organic redox-active molecule can dimerize to form a dimer.

[0249] The redox-active species can dimerize to form homodimers. In particular, the mono-reduced form of the organic redox-active molecule can dimerize to form a homodimer.

[0250] Dimerization can refer to dimerization between two redox-active species (ie, between two separate molecules). Additionally or alternatively, dimerization can refer to intramolecular dimerization between two portions of a redox-active species (ie, between portions of the same molecule).

[0251] In particular, homodimerization can refer to dimerization of two identical redox-active species (i.e., between two identical but separate molecules). Additionally or alternatively, homodimerization can refer to intramolecular homodimerization between two corresponding portions of a redox-active species (i.e., between corresponding portions of the same molecule, such as two repeating units of a polymer). For example, in a molecule having multiple viologen units, intramolecular homodimerization can refer to dimerization between viologen units within the molecule.

[0252] Typically, the complex is formed reversibly and thus the mono-reduced species exists in equilibrium between the uncomplexed species and the complexed species. This can be expressed in terms of K comp Quantitative. In this context, K comp is the equilibrium constant for the complexation of the mono-reduced forms of the redox-active species.

[0253] K comp Can be 0.1mM -1 or greater, preferably 0.2 mM -1 or greater, more preferably 0.5 mM -1 or greater, even more preferably 1 mM -1 or greater. Preferably, K comp 0.2 to 80 mM -1 , more preferably 10 to 80 mM -1 .

[0254] K can be measured at a temperature of 20°C using the method described in the Examples section. comp .

[0255] The complex may be a σ-complex or a π-complex. Preferably, the homodimer is a π-complex.

[0256] σ-complexes can be formed by the interaction of orbitals on two or more redox-active species, such as the p orbital systems of two or more heteroarylenes.

[0257] The π-complex can be formed by the interaction of conjugated π systems on two or more redox-active species, such as conjugated π systems of two or more heteroarylenes. Preferably, the π-complex is supported by π-π stacking.

[0258] Complexes can form through the interaction of multiple centers of a redox-active species. That is, the electrons involved in the complex can be shared among multiple atomic centers of the redox-active molecule. The electrons involved in the complex are preferably delocalized, such as delocalized π electrons. In this way, the complex is a multi-center complex, preferably a multi-center π-π complex.

[0259] Typically, the single reduced form exists in equilibrium between monomeric and dimeric species. This can be expressed in terms of K d Quantitative. In this context, K d is the equilibrium constant for dimerization, such as homodimerization, of a monoreduced form of a redox-active species.

[0260] K d Can be 0.1mM -1 or greater, preferably 0.2 mM -1 or greater, more preferably 0.5 mM -1 or greater, even more preferably 1 mM -1 or greater. Preferably, K d 0.2 to 80 mM -1 , more preferably 10 to 80 mM -1 .

[0261] K can be measured at a temperature of 20°C using the method described in the Examples section. d .

[0262] In the case of organic redox-active molecules containing multiple redox-active units, K d Can refer to the K per redox active unit d .

[0263] The dimer, such as a homodimer, may be a σ-dimer or a π-dimer. Preferably, the homodimer is a π-dimer.

[0264] σ-dimers can be formed by the interaction of orbitals on two redox-active species, such as the p orbital systems of two or more heteroarylenes.

[0265] The π-dimer can be formed by the interaction of conjugated π systems on two redox-active species, such as conjugated π systems of two or more heteroarylenes. Preferably, the π-dimer is supported by π-π stacking.

[0266] Homodimers can be formed by the interaction of multiple centers of the redox-active species. That is, the electrons involved in dimerization are shared between multiple atomic centers of the molecule. The electrons involved in dimerization are preferably delocalized, such as delocalized π electrons. In this way, the homodimerization is multi-center homodimerization, preferably multi-center π-π homodimerization.

[0267] Dimerization typically occurs through non-covalent interactions between two or more conjugated heteroarylenes. Dimerization preferably occurs through electron-sharing interactions, preferably electron-sharing non-covalent interactions. Dimerization is preferably not primarily electrostatic (e.g., generated by ionic interactions between anionic and cationic groups).

[0268] Preferably, in the compounds of formula (I), non-covalent interactions are between the groups -A-, -B- and -[L] c -, more preferably -[L] c -between.

[0269] Complexation of single-reduced species (such as dimerization) may affect the solubility of the reduced electrolyte and the electron transfer kinetics both intermolecularly and at the interface (electrode-electrolyte). Certain organic redox-active molecules also resist precipitation during dimerization, and thus dimerization provides a viable mechanism for dioxygen tolerance.

[0270] Doubly reduced forms of organic redox-active molecules can exist in either singlet or triplet states. This is related to the spin relationships of the electrons in the doubly reduced species. The singlet state refers to molecules in which for every electron, there is another electron with opposite (anticorrelated) spin. The triplet state refers to molecules with two unpaired electrons, each with the same (correlated) spin.

[0271] Preferably, the doubly reduced form of the redox-active species thermodynamically favors the singlet structure.

[0272] The energy difference between the singlet and triplet states of the doubly reduced form of a redox-active species can be expressed using E ST To quantify. Negative E ST shows that the singlet state is energetically favorable, while the positive E ST This indicates that the triplet state is energetically favorable. Preferably, the E ST It is negative.

[0273] In some embodiments, the di-reduced form of the organic redox-active molecule has a mass fraction of less than 0 kcalmol -1 (0kJ mol -1 ), preferably -6.0 kcal mol -1 (-25.1 kJ mol-1 ) or smaller singlet-triplet energy gap (E ST ).

[0274] In some embodiments, the doubly reduced form of the organic redox-active molecule has a relative humidity of -30.0 kcal mol -1 (-125.5 kJ mol -1 ) to 0 kcal mol -1 (0kJ mol -1 ), preferably -30.0 kcal mol -1 (-125.5 kJ mol -1 ) to -6.0 kcal mol -1 (-25.1 kJ mol -1 ) of E ST .

[0275] In the case of organic redox-active molecules comprising multiple redox-active units, E ST Refers to each redox active unit.

[0276] The doubly reduced form of an organic redox-active molecule can exist in either an open-shell or closed-shell configuration. This is related to the number of unpaired electrons in the molecular orbital. An open-shell configuration refers to a substance with one or more unpaired electrons, such as π electrons. A closed-shell configuration refers to a structure with no unpaired electrons, such as π electrons.

[0277] Preferably, the doubly reduced redox-active species is thermodynamically favored in a closed shell structure. The singlet form is typically a closed shell structure.

[0278] The closed-shell structure may be a Kekulé structure. A Kekulé structure has a closed-shell structure without unpaired π electrons. Preferably, the doubly reduced redox-active material thermodynamically favors the Kekulé structure.

[0279] The singlet state and / or closed shell structure of the doubly reduced form contribute to improved electrochemical reversibility of redox-active materials. In particular, at 0 kcal mol -1 (0kJ mol -1 ) or less, preferably -6.0 kcal mol -1 (-25.1 kJ mol -1 ) or smaller E ST Under these conditions, the doubly reduced form favors the singlet state and thus tends to show electrochemical redox reversibility. ST The more negative, the more likely the material will exhibit electrochemical redox reversibility, which is beneficial for RFB cell cycling.

[0280] Specific K favors dimerization and redox reversibility d and E ST The value can be quantified by equation (1), where Y is 15 to 30.

[0281] (1)Y≤3.64*ln(K d )-E ST

[0282] K d and E ST As defined above. K that satisfies the equation d and E ST The range of values ​​represents redox-active molecules with an excellent degree of dioxygen tolerance (by virtue of dimerization) and electrochemical redox reversibility (by favoring singlet closed-shell structures).

[0283] For equation (1), (K d )(mM -1 ) is the equilibrium constant for the formation of the mono-reduced form of the organic redox-active molecule measured at a temperature of 20°C, and E ST (kcal mol -1 ) is the doubly reduced form of an organic redox-active molecule.

[0284] Y may be 15 to 30. Preferably, Y is 20 to 25, more preferably 21 to 24.

[0285] For example, for K d 0.28mM -1 And E ST -27.9 kcal mol -1 (-116.7 kJ mol -1 ) of the redox active species, then Y is 23.28. Alternatively, for K d 11mM -1 And E ST -12.3 kcal mol -1 (-51.5 kJmol -1 ) of the redox active species, then Y is 21.03. In addition, for K d 76mM -1 And E ST -8.0 kcal mol -1 (-33.5 kJ mol -1 ) of the redox active species, then Y is 23.76.

[0286] The organic redox-active molecule comprises two or more heteroarylene groups, wherein the two or more heteroarylene groups are conjugated. Descriptions of organic redox-active molecules herein refer to the unreduced form of the organic redox-active molecule.

[0287] 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).

[0288] In some embodiments, the organic redox-active molecule comprises a redox-active unit of formula (IA):

[0289]

[0290] in:

[0291] -A- and -B- are each independently C 5-10 arylene;

[0292] Each -L- is independently selected from C 5-14 Arylene, bond, C 2-6 Alkenylene, C 2-4 Alkynylidene, wherein the C 5-14 Arylene and C 2-4 Alkenylene is optionally substituted with one or more -R C group substitution;

[0293] -L 1 - independently selected from a bond, C 1-6 Alkylene, C 5-14 Arylene, -N(H)-, and -(CH2O) a1 -(C2H4O) a2 -(C3H6O) a3 -(CH2C(O)) a4 -, wherein said C 1-6 Alkylene and C 5-14 Arylene is optionally substituted by one or more -R D group substituted, and

[0294] 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,

[0295] When present, -R A 、-R B 、-R C and -R D Each of is a hydrophilic group;

[0296] X is one or more counteranions;

[0297] n is 2 to 4;

[0298] c and d are independently 1 to 5;

[0299] a and b are independently 1 to 5;

[0300] Two or more of -A-, -B-, and -L- are C 5-10 heteroarylene; and

[0301] m is 1 or greater.

[0302] In some embodiments, the redox-active species is polymeric and comprises a plurality of units of formula (IA). 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 to 200, such as 10 to 100.

[0303] A plurality of units of formula (IA) may be arranged in a linear, branched, dendritic or cyclic polymer. Preferably, a plurality of units of formula (IA) are arranged in a linear or branched polymer, such as a linear polymer.

[0304] In some embodiments, -L 1 - is a bond and d is 1. In such embodiments, -A-[L] c -B- units are directly connected.

[0305] In some embodiments, -L 1 - independently selected from C 1-6 Alkylene, -N-, -(CH2O) a1 -(C2H4O) a2 -(C3H6O) a3 -(CH2C(O)) a4 - and C 5-14 In such embodiments, -A-[L] c -B- units are not directly connected.

[0306] Connector-[L 1 ] d - contains d groups -L 1 -, wherein d is 1 to 5. Preferably, d is 1 to 4, more preferably 1 to 3, even more preferably 1 or 2. In some embodiments, d is 1.

[0307] In some embodiments, -L 1 - independently selected from C 1-6 Alkylene and -(CH2O) a1 -(C2H4O) a2 -(C3H6O) a3-(CH2C(O)) a4 In this way, -A-[L] c The -B- unit is not π-conjugated.

[0308] -L 1 - can be C 1-6 Alkylene. C 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 may be selected from methylene, ethylene and propylene, including n-propylene and isopropylene, butylene, pentylene or hexylene. Preferably, C 1-6 Alkylene is C 1-4 Alkylene, such as C 1-3 Alkylene, such as C3 alkylene.

[0309] -L 1 - can be -(CH2O) a1 -(C2H4O) a2 -(C3H6O) a3 -(CH2C(O)) a4 . Group -(CH2O) a1 -(C2H4O) a2 -(C3H6O) a3 -(CH2C(O)) a4 -R N It is a polyethylene glycol chain.

[0310] Repeating unit -(CH2O) a1 - is a methylene glycol repeating unit. The number of repeating units a1 is typically 0-12. In some embodiments, a1 is 0. In other embodiments, a1 is 1 to 12, preferably 2 to 6.

[0311] Repeating unit -(C2H4O) a2 - is an ethylene glycol repeating unit. The number of repeating units a2 is typically 0-12. In some embodiments, a2 is 0. In other embodiments, a2 is 1 to 12, preferably 2 to 6.

[0312] Repeating unit -(C3H6O) a3 - is a propylene glycol repeating unit. The number of repeating units a3 is typically 0-12. In some embodiments, a3 is 0. In other embodiments, a3 is 1 to 12, preferably 2 to 6.

[0313] -(CH2C(O)) a4 - is an acetyl repeating unit. -R N It is the terminal C 1-6The number of repeating units a4 is typically 0-12. In some embodiments, a4 is 0. In other embodiments, a4 is 1 to 12, preferably 2 to 6.

[0314] 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.

[0315] -L 1 - can be C 5-14 Arylene. C 5-14 An arylene group is a divalent aromatic group having 5 to 14 atoms forming an aryl ring or a fused aryl ring. For example, an 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 anthrylene. An arylene group may be a carboarylene group or a heteroarylene group.

[0316] -L 1 - can be C 5-14 Arylene, preferably as C 5-10 Arylene, more preferably C 5-6 Arylene. -L 1 - can be C 5-10 Heteroaryl or C 6-10 Preferably, -L 1 - is phenylene.

[0317] In-L 1 - is an alkylene or arylene group, the alkylene or arylene group is optionally replaced by one or more -R D Replace. -R D is an optional substituent. D In the case of -R, they may be the same or different. c and -R D In the case of -R C and -R D Can be the same or different.

[0318] Typically, adjacent units of formula (IA) are not conjugated. For example, -L 1 - may contain saturated groups which prevent conjugation between adjacent units of formula (IA).

[0319] Dimerization can occur through non-covalent interactions between two or more units of formula (IA) in the same molecule. Preferably, the non-covalent interactions occur between the groups -A-, -B- and -[L] c-, more preferably -[L] c -between.

[0320] Group-[L 1 ] d - may be of such length that the units of formula (IA) in the same molecule can dimerize. 1 ] d The length of - may provide sufficient spatial freedom to allow adjacent units of formula (IA) to π-dimerize.

[0321] In some embodiments, the group -[L 1 ] d - has a length of 0.5 nm or greater, preferably 0.8 nm or greater, more preferably 1.0 nm or greater. The group -[L 1 ] d+- The length of can be calculated using the average bond length. For example, the group -[L 1 ] d - corresponds to a length of 2 or more -(CH2)- units, preferably 4 or more -(CH2)- units, more preferably 6 or more -(CH2)- units.

[0322] Preferably, the redox active material comprises one unit of formula (IA). In such embodiments, m is 1. Even more preferably, m is 1, -L 1 - is a key and d is 1.

[0323] In some embodiments of the redox-active unit of Formula (IA), the linker -[L] c - can be attached to multiple -B-. For example, the linker -[L] c can be attached to one -A- and one or more -B- groups, such as one -A- and two to five -B- groups, such as one -A- and two or three -B- groups. In this manner, the linker -[L] c Attachment may be to a total of two to six -A- and -B- groups, such as a total of two to four -A- and -B- groups, such as three or four -A- and -B- groups.

[0324] In some embodiments, the organic redox-active molecule has formula (IB):

[0325]

[0326] in:

[0327] -A-, -B-, -L-, -L 1 -、-R A 、-R B 、-RC 、-R D , X, a, b, n and m are as defined for Formula (IA); and

[0328] Two or more of -A-, -B-, and -L- are C 5-10 Heteroarylene.

[0329] -A-, -B-, -L-, -L 1 -、-R A 、-R B 、-R C 、-R D Preferred options for x, a, b, c, d, n and m are as described herein.

[0330] In some embodiments, the redox-active species is polymeric and comprises a plurality of units of formula (IB). 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 to 200, such as 10 to 100.

[0331] A plurality of units of formula (IB) may be arranged in a linear, branched, or dendritic polymer. Preferably, a plurality of units of formula (IB) are arranged in a straight-chain or branched polymer, such as a linear polymer.

[0332] When present, multiple units of formula (IB) are separated by a group -R A and -R B Terminate. -R A and -R B Preferably, they are all hydrophilic groups. A and -R B and the definitions of a and b.

[0333] In some embodiments, L 1 is a bond and d is 1. In such embodiments, -A-[L] c -B- units are directly connected.

[0334] In some embodiments, the redox-active species comprises one or two units of formula (IB). In such embodiments, m is 1 or 2.

[0335] Preferably, m is 1. Particularly preferably, m is 1, -L 1 - is a key and d is 1.

[0336] In some embodiments, the organic redox-active molecule has formula (IC):

[0337]

[0338] in:

[0339] -A-, -B-, -L-, -L 1 -、-R A 、-R B 、-R C 、-R D , X, a, b, n and m are as defined for Formula (IA) and Formula (IB);

[0340] R P is the polymer repeating unit;

[0341] p is 2 or greater; and

[0342] Two or more of -A-, -B-, and -L- are C 5-10 Heteroarylene.

[0343] -A-, -B-, -L-, -L 1 -、-R A 、-R B 、-R C 、-R D Preferred options for X, a, b, n and m are as described herein.

[0344] Formula (IC) describes the redox-active molecule of the present invention as a side chain polymer. The polymer backbone (composed of [R P ] p (denoted by) having a side group attached. The side group comprises one or more A-[L] c -Part B.

[0345] In the context of formula (IC), m represents the number of repeat units in the side 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.

[0346] The p value represents the number of repeating 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.

[0347] R P R can be any suitable polymer repeating unit. P is a repeating unit of a polymer and may be selected from polyethylene, polypropylene, polystyrene, polyacrylate, polymethacrylate, polyester, polyamide, polyethylene terephthalate, and polysiloxane repeating units. Preferably, R P is a polyethylene or polypropylene repeating unit, such as a polyethylene repeating unit.

[0348] In some embodiments, the organic redox-active molecule has formula (ID):

[0349]

[0350] in:

[0351] -A-, -B-, -L-, -R A 、-R B 、-R C , X, a, b, n are as defined for formulas (IA) and (IB);

[0352] q is 1 to 5; and

[0353] Two or more of -A-, -B-, and -L- are C 5-10 Heteroarylene.

[0354] -A-, -B-, -L-, -R A 、-R B 、-R C 、-R D Preferred options for x, a, b, n and q are as described herein.

[0355] The q value determines the attachment to -[L] c 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.

[0356] Connector [L] c Connects the group -A- and q -B- groups in formula (ID). Linker [L] c Contains c groups L, wherein c is 1 to 5. Preferably, c is 1 to 4, more preferably 1 to 3, even more preferably 1 or 2. In some embodiments, c is 1.

[0357] Each -L- is independently selected from C 5-14 Arylene, bond, C 2-6 Alkenylene and C 2-4 Alkyne, wherein the alkenylene and arylene are optionally replaced by one or more R C Group substitution.

[0358] In the case where q is 2 or greater, -L- is typically C 5-14 Thus, -L- can be C 6-14 Carbon arylene or C 5-10 Heteroarylene.

[0359] Preferably, each -L- is independently selected from C 6-14 Carbon arylene, C 5-10Heteroarylene, bond, C2 alkenylene, and C2 alkynylene, more preferably C 6-10 Carbon arylene, C 5-6 Heteroarylene and bond.

[0360] In the case where -L- is a carboarylene group, the carboarylene group may be independently selected from anthracene, naphthylene and phenylene. Preferably, the carboarylene group is selected from naphthylene and phenylene.

[0361] In some embodiments, -[L] c - is phenylene, and q is 2. -A- and two -B- groups may be attached to the phenylene at the 1, 3, and 5 positions.

[0362] In the case where -L- is a heteroarylene, the heteroarylene may contain a sulfur or oxygen heteroatom, preferably a sulfur heteroatom. Preferably, in the case where -L- is a heteroarylene, the heteroarylene is a thienylene or furylene. Preferably, in the case where -L- is a heteroarylene, the heteroarylene is a thienylene.

[0363] 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 the group [L] c It may be a porphyrin group, such as porphyrin, porphycene, porphycene, hemiporphycene or isoporphycene.

[0364] Preferably, each of -A- and -B- in formula (ID) is independently C 5-10 Heteroarylene. C 5-10 Heteroarylene can be C 5-6 Heteroarylene, preferably C6 heteroarylene. Preferably, C 5-6 The heteroarylene group contains one or more nitrogen as heteroatoms. More preferably, the C6 heteroarylene group contains one or more nitrogen as heteroatoms, such as one nitrogen as heteroatom.

[0365] The nitrogen-containing C6 heteroarylene group can be linked to adjacent groups (eg, -L- and R-) at the 1,2, 1,3, or 1,4 positions. A / R B Preferably, the nitrogen-containing C6 heteroarylene group is connected to the adjacent groups (eg, L and R) at the 1,4 positions. A / R B ).

[0366] In some embodiments, the organic redox-active molecule has formula (I):

[0367]

[0368] in:

[0369] -A- and -B- are each independently selected from C 5-10 arylene;

[0370] Each -L- is independently selected from C 5-14 Arylene, bond, C 2-6 Alkenylene, C 2-4 Alkynylidene, wherein the C 5-14 Arylene and C 2-6 The alkenylene group is optionally substituted by one or more R C group substitution;

[0371] When present, -R A and -R B and -R C At least one of is independently a hydrophilic group;

[0372] X is one or more counteranions;

[0373] n is 2 to 4;

[0374] a, b and c are independently 1 to 5; and

[0375] Two or more of -A-, -B-, and -L- are C 5-10 Heteroarylene.

[0376] In some embodiments, -A- and -B- are the same. In this manner, two or more heteroarylene groups are symmetrical.

[0377] In some embodiments, (R A ) a and (R B ) b In this way, the group (R A ) a and (R B ) b It is symmetrical.

[0378] The groups -A- and -B- may be identical, and the group (R A ) a and (R B ) b In this manner, the redox-active molecule can be symmetrical about the plane between the heteroarylene groups -A- and -B-.

[0379] In some embodiments, two or more heteroarylene groups (-A- and -B-), a group (R A ) a and (RB ) b and any intermediate group -[L] c - With respect to the plane between the heteroarylene groups -A- and -B-, preferably with the intermediate group -[L] c - intersecting planes, more preferably only with the intermediate group -[L] c -Symmetrical about intersecting planes.

[0380] In some embodiments, -A- and -B- are different. In this manner, the two or more heteroarylene groups are not symmetrical about the plane between the heteroarylene groups -A- and -B-.

[0381] In some embodiments, (R A ) a and (R B ) b In this way, the group (R A ) a and (R B ) b There is no symmetry about the plane between the heteroarylene-A- and -B- groups.

[0382] Arylene is a divalent aromatic group, such as a divalent carboaryl or a divalent heteroaryl group. Arylene is optionally substituted, such as substituted. In one embodiment, arylene is unsubstituted.

[0383] C 5-14 An arylene group is a divalent aromatic group having 5 to 14 atoms forming an arylene group or a fused arylene group. 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 group may be a carboarylene group or a heteroarylene group.

[0384] A heteroarylene group is a divalent heteroaromatic group containing at least one ring heteroatom. In the case of fused rings, one or more of these rings may contain a ring heteroatom.

[0385] 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.

[0386] C 5-10 Heteroarylene is a divalent aromatic radical having 5 to 10 atoms forming one or more heteroaryl rings. For example, the heteroarylene can be a 6-membered heteroarylene, such as pyridylene; or a 5-membered heteroarylene, such as thienylene or furylene; or a 9-membered heteroarylene, such as a divalent benzimidazole.

[0387] Carboarylene is a divalent carbon aromatic group, i.e., contains only carbon in the aryl ring. Carboarylene is optionally substituted, such as substituted. In a preferred embodiment, carboarylene is unsubstituted.

[0388] C 6-14 Carboarylene is a divalent aromatic radical having 6 to 14 atoms forming one or more aromatic rings. For example, the carboarylene can be a 6-membered carboarylene, such as phenylene; or a 9-membered carboarylene, such as naphthalene; or a 14-membered carboarylene, such as anthracene.

[0389] Alkenylene is a divalent alkene group. Alkenylene is optionally substituted, such as substituted. Preferably, alkenylene is unsubstituted.

[0390] C 2-6 An alkenylene group is a divalent olefin group having 2 to 6 carbon atoms that forms an olefin chain. The olefin can be linear or branched. For example, the alkenylene group can be a 2-membered alkenylene group, such as ethylene; a 3-membered alkenylene group, such as propylene or allylene; a 4-membered alkenylene group, such as buta-1,3-diene; or a 6-membered alkenylene group, such as hexa-1,3,5-triene or 2-ethylbuta-1,3-diene.

[0391] Alkynylene is a divalent alkyne radical. 2-4 Alkyne is a divalent alkyne group having 2 to 4 carbon atoms forming an alkyne chain. For example, the alkynylene group may be a 2-membered alkynylene group, such as acetylene, or a 4-membered alkynylene group, such as buta-1,3-diyne.

[0392] Typically, the group -[L] forming the link between -A- and -B- c All atoms in - (e.g., carbon atoms) are sp or sp2 hybridized to provide conjugation between the groups -A- and -B-. c -The branches may have alternative hybridizations.

[0393] Hydrophilic groups are groups that have a good affinity for water. Hydrophilic groups typically include polar groups, such as groups that can form hydrogen bonds. Hydrophilic groups typically include one or more heteroatoms, such as halogen, oxygen, sulfur, nitrogen, phosphorus. Hydrophilic groups can be charged. Hydrophilic groups can be attached to alkylene or arylene groups, preferably alkylene groups.

[0394] Preferably, the hydrophilic group is uncharged or has a charge that is similar to the arylene core (-A-[L] c -B-) the same charge polarization (i.e., anionic or cationic). For example, in the case where the arylene core is cationic (such as viologen or extended viologen), the hydrophilic group is preferably uncharged or cationic. In this way, the redox-active species is not zwitterionic, which may lead to aggregation and poor solubility.

[0395] The hydrophilic group is preferably a group -R A and -R B One or more of and (where present) -R C Preferably, the hydrophilic group is a group -R A and -R B The description of these groups herein applies to hydrophilic groups. A and -R B and (where present) -R C and -R D Can be attached to -A-, -B-, -L- and -L 1 - any point on the molecule, such as a carbon atom or a nitrogen atom.

[0396] Hydrophilic groups are believed to improve the water solubility of redox-active materials. Hydrophilic groups are placed at the periphery of the redox-active material to enhance water solubility, while conjugated arylene groups, which typically have poor water solubility, are present at the core of the redox-active material. Conjugated arylene groups with poor water solubility have an increased tendency to dimerize in aqueous solution, while hydrophilic groups keep the redox-active material in solution, preventing precipitation.

[0397] In the presence of multiple-R A 、-R B and (where present) -R C In the case of groups, each group may be the same or different. For example, in the presence of two or more -R A or -R B In the case of -A- or -B-, each -R A or -R B -R may be different from the carbon attached to -A- or -B- A or -R B .

[0398] The counteranion is any suitable anion required for charge neutrality of the organic redox-active molecule.

[0399] 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 Heteroarylene.

[0400] In some embodiments, C 5-10 The heteroarylene group contains one or more heteroatoms each independently selected from oxygen, nitrogen and sulfur, preferably one heteroatom selected from oxygen, nitrogen and sulfur. 5-10 Heteroarylene groups contain nitrogen as a heteroatom.

[0401] C 5-10 Heteroarylene can be C 5-6 Heteroarylene, preferably C6 heteroarylene. Preferably, C 5-6 The heteroarylene group contains one or more nitrogen as heteroatoms. More preferably, the C6 heteroarylene group contains one or more nitrogen as heteroatoms, such as one nitrogen as heteroatom.

[0402] The nitrogen-containing C6 heteroarylene group can be linked to adjacent groups (eg, -L- and R-) at the 1,2, 1,3, or 1,4 positions. A / R B Preferably, the nitrogen-containing C6 heteroarylene group is connected to the adjacent groups (eg, L and R) at the 1,4 positions. A / R B ).

[0403] Preferably, C 5-10 Heteroarylene is pyridinylene. Preferably, -A- and -B- are both pyridinylene.

[0404] The pyridinylene group may be a pyridin-1,2-ene, a pyridin-1,3-ene or a pyridin-1,4-ene. Preferably, the pyridinylene group is attached to the adjacent groups (e.g., L and R) at the 1,4 position. A / R B More preferably, when -A- and -B- are pyridylene, the pyridylene is linked to L at the 4-position and to R at the 1-position. A / R B (i.e., via nitrogen).

[0405] Typically, two or more of -A-, B-, and -L- are conjugated, such that -A- and -L-; or -B- and -L-; or -A-, B-, and -L- are conjugated. Preferably, -A- and -B- are conjugated. For example, where -L- is a bond, -A- and -B- can be directly conjugated, or where -L- is not a bond, -A-, -B-, and -L- are conjugated.

[0406] Dimerization typically occurs through non-covalent interactions between two or more conjugated heteroarylene groups. Preferably, the non-covalent interaction groups -A-, -B- and -[L] c -, more preferably -[L] c -between.

[0407] In some embodiments, the group [L] c The length of is 0.5 nm or less, such as 0.4 nm or less. In some embodiments, the group [L] c The length of is 0.1 nm or more, such as 0.2 nm or more. When the group [L]c When the length is about 0.1 to 0.5 nm, such as 0.2 to 0.4 nm, it is considered that the group [L] c Can provide non-covalent interactions between redox-active molecules leading to dimerization. Group [L] c The length can be calculated using the average bond length.

[0408] In some embodiments, the group [L] c The length of [L] can be 3 to 8 atoms directly connecting the groups -A- and -B-. Preferably, the group [L] c The length of is 3 to 8 sp2 carbons and / or heteroatoms directly connecting the groups -A- and -B-, such as 3 to 6 sp2 carbons and / or heteroatoms directly connecting the groups -A- and -B-.

[0409] In some embodiments, the organic redox-active molecule is a viologen or an extended viologen molecule. In some embodiments:

[0410] -A-Yes and

[0411] -B-Yes

[0412] In some additional embodiments, the organic redox-active molecule comprises units of formula (II-A):

[0413]

[0414] Among them, -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), (IA) and (IB).

[0415] -L-, -L 1 -、-R A 、-R B 、-R c 、-R D Preferred options for x, n, m, a, b, c and d are as described herein.

[0416] In some additional embodiments, the organic redox-active molecule comprises units of formula (II-B):

[0417]

[0418] Among them, -L-, -L 1 -、-R A 、-RB 、-R c 、-R D , X, n, m, a, b, c and d are as defined above for formulae (I), (IA) and (IB).

[0419] -L-, -L 1 -、-R A 、-R B 、-R c 、-R D Preferred options for x, n, m, a, b, c and d are as described herein.

[0420] In some embodiments, the organic redox-active molecule has formula (II):

[0421]

[0422] Among them, L, R A 、R B , X, n, a, b and c are as defined for formula (I).

[0423] Connector [L] c Connects the groups -A- and -B- in formula (I). Linker [L] c Connecting the pyridylene group in formula (II).

[0424] Connector [L] c Contains c groups L, wherein c is 1 to 5. Preferably, c is 1 to 4, more preferably 1 to 3, even more preferably 1 or 2. In some embodiments, c is 1.

[0425] Each -L- is independently selected from C 5-14 Arylene, bond, C 2-6 Alkenylene and C 2-4 Alkyne, wherein the alkenylene and arylene are optionally replaced by one or more R C Group substitution.

[0426] In the case where -L- is a bond, the pyridylene is directly attached (bi-pyridylene). A bond refers to a covalent bond.

[0427] Each -L- can be independently selected from C 6-14 Carbon arylene or C 5-10 Heteroarylene, bond, C 2-6 Alkenylene and C 2-4 In the case where c is greater than 1, then preferably each -L- is not C 2-6 Alkenylene or each -L- is not C 2-4 Alkynylidene.

[0428] Preferably, each -L- is independently selected from C6-14 Carbon arylene, C 5-10 Heteroarylene, bond, C2 alkenylene, and C2 alkynylene, more preferably C 6-10 Carbon arylene, C 5-6 Heteroarylene and bond.

[0429] In some embodiments, each -L- is independently selected from C 6-10 Carbon arylene or C 5-10 Preferably, each -L- is independently selected from naphthylene, anthracene and C 5-10 Heteroarylene.

[0430] In-L- is C 2-6 In the case of alkenylene, the C 2-6 Alkenylene groups can be independently selected from:

[0431]

[0432] In-L- is C 2-4 In the case of an alkynylene group, the C 2-4 Alkynylenyl groups can be independently selected from:

[0433]

[0434] Each -L- can be a C 5-14 Arylene, such as C 5-14 Carbon arylene or C 5-14 Heteroarylene.

[0435] In the case where -L- is a heteroarylene, the heteroarylene includes 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 include 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 thiazolylene, such as a 1,2-thiazolylene, a 1,3-thiazolylene or a 1,4,2-dithiazolylene.

[0436] In the case where -L- is a heteroarylene, the heteroarylene may contain a sulfur or oxygen heteroatom, preferably a sulfur heteroatom. Preferably, in the case where -L- is a heteroarylene, the heteroarylene is a thienylene or furylene. Preferably, in the case where -L- is a heteroarylene, the heteroarylene is a thienylene.

[0437] Typically, [L] c The -L- groups in the molecule are arranged in a linear configuration.

[0438] Alternatively, in some embodiments, where c is 3 or greater (such as 3 or 4), the -L- groups may be arranged in a cyclic configuration. In some such embodiments, the group [L] c It may be a porphyrin group, such as a porphyrin, a porphyrinene, a porphycene, a hemiporphyrinene or an isoporphyrinene.

[0439] In the case where -L- is a carboarylene group, the carboarylene group may be independently selected from anthracene, naphthylene and phenylene. Preferably, the carboarylene group is selected from naphthylene and phenylene.

[0440] In some embodiments, -L- is independently selected from a bond, and a group selected from anthracene, naphthylene, phenylene, and thiophene. Preferably, -L- is independently selected from a bond, and a group selected from anthracene-1,4-ylidene, anthracene-1,6-ylidene, naphthalene-1,8-ylidene, benzene-1,4-ylidene, and thiophene-2,5-ylidene.

[0441] In some embodiments, -L- is independently selected from a bond, and selected from group.

[0442] In some such embodiments, c is 1 or 2.

[0443] In some embodiments, each -L- is independently selected from a bond, and selected from group.

[0444] In some such embodiments, c is 1 or 2.

[0445] Preferably, where -L- is In the case of , then c is 1 or 2, and -L- is a bond, , then c is 1.

[0446] In one embodiment, -L- is not thiazolo[5,4-d]thiazole.

[0447] Group -R A 、-R B 、-R C and -R D They are -A-, -B-, -L- and -L 1 -Substituents of -. 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 -RD In some cases, they may be the same or different.

[0448] 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 In the case of -R, they may be the same or different. For example, in the presence of two or more -R A or -R B In the case of -R attached to a heteroatom (e.g., pyridylene nitrogen) of -A- or -B- A or -R B -R may be different from the carbon attached to -A- or -B- A or -R B .

[0449] -R A and -R B and (where present) -R C and -R D Each of can be independently selected from:

[0450] C optionally substituted by one or more groups selected from 1-6 Alkyl: -N(R N )2、-N + (R N )3. -P + (R N )3, -OH, -C(O)OH, -NHC(NH)NH2, -NHC(O)NH2 and halogen,

[0451] C optionally substituted by one or more groups selected from 5-14 Aryl: -(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, and

[0452] -(CH2O) a1 -(C2H4O) a2 -(C3H6O) a3 -(CH2C(O)) a4 -R N , 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,

[0453] where R N Is H or C 1-6 alkyl.

[0454] R N C is preferred 1-6 Alkyl, such as methyl or ethyl, such as methyl. In R N It is C 1-6 In the case of an alkyl group, it may be optionally substituted, such as monosubstituted. 1-6 The alkyl group may be substituted, such as monosubstituted, with -NH2, -OH, -C(O)OH, -NHC(NH)NH2, -NHC(O)NH2 or halogen.

[0455] Preferably, in R N It is C 1-6 In the case of an alkyl group, it is unsubstituted, such as unsubstituted methyl or ethyl, such as methyl.

[0456] C 1-6 The alkyl group may be polysubstituted, such as disubstituted or trisubstituted, by groups selected from: -N(R N )2、-N + (R N )3. -P + (R N )3, -OH, -C(O)OH, -NHC(NH)NH2, -NHC(O)NH2 and halogen. Preferably, C 1-6 The alkyl group is monosubstituted with a group selected from: -N + (R N )3. -P + (R N )3, -OH, -C(O)OH, -NHC(NH)NH2, -NHC(O)NH2 and halogen.

[0457] C 5-14 Aryl may be polysubstituted, such as disubstituted or trisubstituted, by groups selected from: -(CH2) n -N(RN )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. Preferably, C 5-14 The aryl group is monosubstituted by a group selected from: -(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.

[0458] C 5-14 The aryl group is preferably substituted opposite the point of attachment to -A- or -B-. 5-14 When the aryl group is phenylene, the substitution is preferably at the 4-position. For example, -R A and -R B Can be -N in 4 bits + (R N )3 Such as -N + (CH3)3 substituted phenyl.

[0459] -R A and -R B and (where present) -R C Each of can be independently selected from:

[0460] C optionally monosubstituted by a group selected from 1-6 Alkyl: -N(R N )2、-N + (R N )3. -P + (R N)3, -OH, -C(O)OH, -NHC(NH)NH2, -NHC(O)NH2 and halogen,

[0461] C optionally monosubstituted by a group selected from 5-14 Aryl: -(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, and

[0462] -(CH2O) a1 -(C2H4O) a2 -(C3H6O) a3 -(CH2C(O)) a4 -R N , 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,

[0463] where R N It is C 1-6 alkyl.

[0464] -R A and -R B and (where present) -R C and -R D One or each of the 1-6 Alkyl. C 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 isopropyl), butyl, pentyl or hexyl. Preferably, C 1-6 Alkyl is C 1-4 Alkyl groups, such as C 1-3 Alkyl, such as C3 alkyl.

[0465] In-R A 、-R B 、-R C and -R D It is C1-6 In the case of an alkyl group, it may be substituted by one or more, preferably one, groups selected from: -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 It is C 1-6 In the case of an alkyl group, it may be substituted by one or more groups selected from: -N + (R N )3. -P + (R N )3, -OH, -C(O)OH, -NHC(NH)NH2, -NHC(O)NH2 and halogen. In one embodiment, C 1-6 The alkyl group is substituted with a group selected from: -N + (R N )3. -P + (R N )3, -OH, -C(O)OH, -NHC(NH)NH2, -NHC(O)NH2 and halogen.

[0466] -R A and -R B and (where present) -R C One or each of the 1-6 Alkyl. C 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 isopropyl), butyl, pentyl or hexyl. Preferably, C 1-6 Alkyl is C 1-4 Alkyl groups, such as C 1-3 Alkyl, such as C3 alkyl.

[0467] In-R A 、-R B and -R C It is C 1-6 In the case of an alkyl group, it may be substituted by one or more groups selected from: -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 It is C 1-6 In the case of an alkyl group, it may be substituted by one or more groups selected from: -N + (R N )3. -P + (R N )3, -OH, -C(O)OH, -NHC(NH)NH2, -NHC(O)NH2 and halogen. In one embodiment, C 1-6 The alkyl group is substituted with a group selected from: -N + (R N )3. -P + (R N )3, -OH, -C(O)OH, -NHC(NH)NH2, -NHC(O)NH2 and halogen.

[0468] The substitution may be a terminal substitution.

[0469] Alkyl groups may be persubstituted by halogen, such as by fluorine (eg, trifluoromethyl).

[0470] Preferably, C 1-6 Alkyl is -N + (R N )3 replaced. -N + (R N ) 3 may exist as a terminal substitution. In one embodiment, C 1-6 Alkyl is -CH2-CH2-CH2-N + (R N )3.

[0471] One or each -R A and -R B and (where present) -R C and -R D Can be C 5-14 Aryl. C 5-14 An aryl group is a monovalent aromatic group having 5 to 14 atoms forming an aryl ring or a fused aryl ring. For example, an aryl group can be a 5-membered aryl group, such as a thienyl group; a 6-membered aryl group, such as a phenyl group or a pyridyl group; a 10-membered aryl group, such as a naphthyl group; or a 14-membered aryl group, such as an anthracenyl group. An aryl group can be a carboaryl group or a heteroaryl group.

[0472] One or each -R A and -R B and (where present) -R Cand -R D Can be C 5-14 Aryl, preferably as C 5-10 Aryl, more preferably C 5-6 Aryl. -R A and -R B and (where present) -R C Can be C 5-10 Heteroaryl or C 6-10 Carboaryl.

[0473] In-R A 、-R B 、-R C and -R D It is C 5-14 In the case of an aryl group, it may be substituted by one or more groups selected from: -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 It is C 5-14 In the case of an aryl group, it may be substituted by one or more groups selected from: -(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. In one embodiment, C 5-14 The aryl group is substituted with a group selected from: -(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.

[0474] -R A and -R B and (where present) -R C One or each of the 5-14 Aryl. C 5-14 An aryl group is a monovalent aromatic group having 5 to 14 atoms forming an aryl ring or a fused aryl ring. For example, an aryl group can 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. An aryl group can be a carboaryl group or a heteroaryl group.

[0475] R A and -R B and (where present) -R C One or each of the 5-14 Aryl, preferably as C 5-10 Aryl, more preferably C 5-6 Aryl. R A and R B and (where present) R C Can be C 5-10 Heteroaryl or C 6-10 Carboaryl.

[0476] In addition, in -R A 、-R B and -R C It is C 5-14 In the case of an aryl group, it may be substituted by one or more groups selected from: -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.

[0477] In-R A 、-R B and -R C It is C 5-14 In the case of an aryl group, it may be substituted by one or more groups selected from: -(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. In one embodiment, C 5-14 The aryl group is substituted with a group selected from: -(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.

[0478] In some embodiments, n is 0 to 6, such as 0 to 3. Preferably, n is 0 or 3, such as 3.

[0479] Preferably, C 5-14 Aryl is -(CH2) n -N + (R N )3 replaced. -N + (R N ) 3 may exist as a terminal substitution. In one embodiment, C 5-14 Aryl is -CH2-CH2-CH2-N + (R N )3 replaced.

[0480] Additionally, in one embodiment, C 5-14 Aryl is -N + (R N )3 is substituted. In a preferred embodiment, C 5-14 Aryl is -(C6H6)-N + (R N )3, such as -(C6H6)-N + (CH3)3. 5-14 In case the aryl group is phenyl, it may be substituted at the 4-position.

[0481] -RA and -R B and (where present) -R C and -R D One or each of the may be -(CH2O) a1 -(C2H4O) a2 -(C3H6O) a3 -(CH2C(O)) a4 -R N . Group -(CH2O) a1 -(C2H4O) a2 -(C3H6O) a3 -(CH2C(O)) a4 -R N It is a polyethylene glycol chain.

[0482] -R A and -R B and (where present) -R C It can be -(CH2O) a1 -(C2H4O) a2 -(C3H6O) a3 -(CH2C(O)) a4 -R N . Group -(CH2O) a1 -(C2H4O) a2 -(C3H6O) a3 -(CH2C(O)) a4 -R N It is a polyethylene glycol chain.

[0483] Repeating unit -(CH2O) a1 - is a methylene glycol repeating unit. The number of repeating units a1 is typically 0-12. In some embodiments, a1 is 0. In other embodiments, a1 is 1 to 12, preferably 2 to 6.

[0484] Repeating unit -(C2H4O) a2 - is an ethylene glycol repeating unit. The number of repeating units a2 is typically 0-12. In some embodiments, a2 is 0. In other embodiments, a2 is 1 to 12, preferably 2 to 6.

[0485] Repeating unit -(C3H6O) a3 - is a propylene glycol repeating unit. The number of repeating units a3 is typically 0-12. In some embodiments, a3 is 0. In other embodiments, a3 is 1 to 12, preferably 2 to 6.

[0486] -(CH2C(O)) a4- is an acetyl repeating unit. The number of repeating units a4 is typically 0-12. In some embodiments, a4 is 0. In other embodiments, a4 is 1 to 12, preferably 2 to 6.

[0487] 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.

[0488] R N Is H or C 1-6 Alkyl. In -R N It is C 1-6 In the case of an alkyl group, it is preferably C 1-4 Alkyl groups, such as C 1-3 Alkyl groups, such as C 1-2 Preferably, -R N Is a methyl group. A and -R B and (where present) -R C In the case of a polyethylene glycol chain, then R N H is preferred.

[0489] In some embodiments, -R A and -R B Each is independently N + (R N )3 or -P + (R N )3 substituted C 1-6 Preferably, -R A and -R B Each is independently N + (R N )3 or P + (R N )3 substituted, preferably by N + (R N )3 monosubstituted C 2-4 Alkyl, preferably C3 alkyl.

[0490] In some embodiments, -R A and -R B Each is independently selected from one or more of -(CH2) n -N + (R N )3 or -(CH2) n -P + (R N )3 group substituted C 5-14Aryl, wherein n is 0 to 6. Preferably, -R A and -R B are each independently selected from -(CH2) n -N + (R N )3 or -(CH2) n -P + (R N )3 is substituted, preferably by -(CH2) n -N + (R N )3 monosubstituted C 5-14 Aryl.

[0491] In some embodiments, a and b are independently 1 to 3. Preferably, a and b are both 1.

[0492] In some embodiments, -R C Selected from C 1-6 Alkyl and -(CH2O) a1 -(C2H4O) a2 -(C3H6O) a3 -(CH2C(O)) a4 -R N Preferably, -R C It is C 1-6 Alkyl, preferably C 1-3 Alkyl, more preferably C 1-2 Alkyl. R C It preferably has low steric bulk so as not to inhibit the dimerization of the organic redox molecule. C It is methyl or ethyl.

[0493] In some embodiments, [L] c By one or more -R C groups, such as one to four -R C groups, such as one or two -R C In other embodiments, -L- is unsubstituted.

[0494] Additionally, in some embodiments, -R D Selected from C 1-6 Alkyl and -(CH2O) a1 -(C2H4O) a2 -(C3H6O) a3 -(CH2C(O)) a4 -R N Preferably, -R D It is C 1-6 Alkyl, preferably C 1-3 Alkyl, more preferably C1-2 Alkyl. -R D It preferably has low steric hindrance so as not to inhibit the dimerization of the organic redox molecule. D It is methyl or ethyl.

[0495] Additionally, in some embodiments, [L 1 ] d By one or more -R D groups, such as one to four -R D groups, such as one or two -R D In other embodiments, -L 1 -Not superseded.

[0496] Typically, the redox-active species has a positive charge n in the unreduced state. When the redox-active species is reduced, the mono-reduced form has a charge of n-1. When the redox-active species is doubly reduced, the doubly reduced form has a charge of n-2.

[0497] Typically, n is 2 to 4. Preferably, n is 4.

[0498] In addition, the redox-active material is typically not zwitterionic. The redox-active material is preferably not zwitterionic in either the mono- or doubly-reduced form. The redox-active material preferably has a positive charge n of 2 or greater in the unreduced form. This is particularly preferred in cases where the hydrophilic group is positively charged. This allows the doubly-reduced form of the redox-active material to retain a neutral or positive charge. In cases where n is 1 or less, the arylene core of the redox-active material can be negatively charged in the reduced form, which can give the positively charged hydrophilic group a zwitterionic character. It is believed that the zwitterionic character increases the tendency to stack and aggregate in aqueous environments.

[0499] The redox active species has a counter anion X such that the redox active species and the counter ion have a net charge of zero. The one or more counter anions have a total charge of the redox active molecule -n.

[0500] X is typically a redox inactive species. In some embodiments, X is a halide, hexafluorophosphate, p-toluenesulfonate, trifluoromethanesulfonate, or methanesulfonate. Preferably, X is a halide such as Cl - or Br - In one embodiment, X is Br - .

[0501] In further embodiments, the organic redox-active molecule is selected from the group consisting of:

[0502]

[0503]

[0504] wherein X is as defined above.

[0505] In some embodiments, the organic redox-active molecule is selected from the group consisting of:

[0506]

[0507]

[0508] wherein X is as defined above.

[0509] Preferably, the organic redox-active molecule is selected from:

[0510]

[0511] wherein X is as defined above.

[0512] Additionally or alternatively, the organic redox-active molecule may be selected from:

[0513]

[0514]

[0515] wherein X is as defined above.

[0516] Preparation of RFB

[0517] In a second aspect of the present invention, there is provided a method for preparing a redox flow battery, the method comprising:

[0518] preparing an electrolyte by combining an organic redox-active molecule with a liquid carrier, wherein the organic redox-active molecule comprises a redox-active unit having two or more heteroarylene groups, and the two or more heteroarylene groups are conjugated within the redox-active unit;

[0519] adding the electrolyte to the redox flow battery, wherein molecular dioxygen (O2) is dissolved in the electrolyte, and

[0520] reducing the organic redox-active molecule to provide a mono-reduced form of the redox-active unit, the mono-reduced form forming a complex,

[0521] 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 intramolecularly complexed redox-active units.

[0522] The organic redox-active molecule is as described herein. The organic redox-active molecule preferably has formula (I), more preferably has formula (II). Preferably, the organic redox-active molecule is viologen or extended viologen.

[0523] Typically, molecular dioxygen is present in the electrolyte. Typically, molecular dioxygen is not removed from the electrolyte and / or the cell headspace during the preparation of the battery cell. For example, the method does not include a step of purging molecular dioxygen from the electrolyte and / or the cell headspace.

[0524] RFB and the presence of dioxygen in RFB are as described herein. The description of RFB itself also applies to the method of preparing RFB.

[0525] In a third aspect, the present invention further provides RFB obtained or obtainable by the preparation method of the second aspect.

[0526] Charging and / or discharging of RFB

[0527] 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, the redox flow battery comprising an electrolyte comprising:

[0528] 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

[0529] molecular dioxygen (O2) dissolved in the electrolyte;

[0530] The method comprises:

[0531] reducing the redox-active unit to provide a complex formed from a mono-reduced form of the redox-active unit, and / or

[0532] oxidizing the doubly reduced form of the redox-active unit to provide a complex formed from the mono-reduced form of the redox-active unit,

[0533] 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 intramolecularly complexed redox-active units.

[0534] RFB, organic redox-active molecules, and their mono- and di-reduced forms are as described herein. The organic redox-active molecule preferably has formula (I), more preferably formula (II). Preferably, the organic redox-active molecule is viologen or extended viologen.

[0535] Charging is typically performed by applying a potential difference across the RFB. Discharging is typically performed by providing a means for electron transfer across the RFB. Discharging typically provides power to a load.

[0536] The coulombic efficiency during discharge may be 70% or greater, preferably 75% or greater, more preferably 80% or greater, and still more preferably 85% or greater.

[0537] The discharge capacity retention rate over 100 charge and discharge cycles may be 80% or greater, preferably 85% or greater, more preferably 90% or greater.

[0538] Compared with the cycle in the absence of hydrogen oxygen, the discharge capacity retention ratio was 50% or more.

[0539] The high Coulombic efficiency and good capacity retention are believed to be related to the low degradation and dioxygen tolerance of the redox-active species. The high Coulombic efficiency and small capacity drop suggest that π-dimerization acts as a competing pathway for dioxygen-mediated side reactions, suppressing the reactivity of viologen with dioxygen. Given the high Coulombic efficiency and low degradation, the reduction in discharge capacity compared to the capacity in the absence of dioxygen is acceptable.

[0540] In some embodiments, the step of reducing and / or oxidizing the organic redox-active molecule is performed at a single cell voltage of 1.23 V or greater, preferably 1.5 V or greater. At these high single cell voltages, the aqueous liquid carrier typically undergoes electrolytic decomposition of water. This provides molecular dioxygen in the electrolyte. The cell voltage required to induce electrolytic water decomposition depends on the pH of the water (Gesser, Applied Chemistry).

[0541] Typically, RFBs with aqueous electrolytes that do not contain redox-active materials that tolerate dioxygen cannot be cycled at these higher single cell voltages. Dioxygen is generated in situ in the electrolyte and thus contributes to the degradation of the redox-active materials. Alternatively, known cells must continuously purge the electrolyte with an inert gas to remove any dioxygen generated in situ. In the present invention, the redox-active materials are tolerant to dioxygen—and therefore can be cycled at these higher voltages without significant redox-active material degradation and without purging the electrolyte.

[0542] In some embodiments, the step of reducing and / or oxidizing the organic redox-active molecule uses 20 mA cm -2 or greater, preferably 30 mA cm -2 or greater, more preferably 40 mA cm -2 or greater current density.

[0543] At these higher current densities, it is believed that the rate of electron transfer is such that the redox process can effectively compete with the electron transfer reaction of dioxygen molecules in the electrolyte. Therefore, the higher current density kinetically favors the redox of the redox-active species over the oxygen side reaction, which means that the impact of molecular dioxygen is further reduced. In some embodiments, this means that the RFB can be cycled for long periods of time in the presence of dioxygen, thereby avoiding the need to purge with an inert gas.

[0544] use

[0545] In a fifth aspect, the present invention provides the use of a redox flow battery for charging and / or discharging in the presence of molecular dioxygen, the redox flow battery comprising an electrolyte comprising:

[0546] 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 single reduced form of the redox-active unit, and

[0547] molecular dioxygen (O2) dissolved in the electrolyte;

[0548] 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 intramolecularly complexed redox-active units.

[0549] RFB, organic redox-active molecules, and their mono- and di-reduced forms are as described herein. The organic redox-active molecule preferably has formula (I), more preferably formula (II). Preferably, the organic redox-active molecule is viologen or extended viologen.

[0550] Charging and / or discharging of the redox flow battery is as described above with respect to the charging and / or discharging methods.

[0551] Preferably, the RFB is used for charging and / or discharging at a single cell voltage of 1.23 V or greater, preferably 1.5 V or greater.

[0552] Preferably, at 20 mA cm -2 or greater, preferably 30 mA cm -2 or greater, more preferably 40 mA cm -2 or greater current density using RFB.

[0553] Molecular dioxygen dissolved in the electrolyte is as described above for redox flow batteries.

[0554] Preferably, dioxygen is dissolved in the electrolyte (e.g., anode electrolyte) at a partial pressure relative to a concentration of 1 vol% or greater, preferably at a concentration of 10 vol% or greater, more preferably at a concentration of 15 vol% or greater, and even more preferably at a concentration of about 20 vol%.

[0555] Other preferences

[0556] Every compatible combination of the above-described embodiments is expressly disclosed herein, as if each combination were individually and specifically enumerated.

[0557] Various other aspects and embodiments of the present invention will be apparent to those skilled in the art in view of this disclosure.

[0558] When used herein, "and / or" will be taken as specific disclosure of each of the two specified features or components with or without the other. For example, "A and / or B" will be taken as specific disclosure of each of (i) A, (ii) B, and (iii) A and B, as if each were individually set forth herein.

[0559] Unless the context dictates otherwise, the descriptions and definitions of the features set out above are not limited to any particular aspect or embodiment of the invention and apply equally to all aspects and embodiments described.

[0560] Certain aspects and embodiments of the present invention will now be described by way of example and with reference to the above-identified drawings.

[0561] Example

[0562] The following examples are provided to further illustrate the present invention and are not intended to limit the scope of the invention.

[0563] Material

[0564] 4-Pyridylboronic 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(0) (99.8% (metal basis), Pd 9% min), 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-tetramethylpiperidinyl 1-oxide (97%), and deuterium oxide (99.9%, atomic % D) were purchased from Sigma-Aldrich. Milli-Q water was used to prepare all non-deuterated aqueous solutions. Materials were used as received without further purification.

[0565] Measuring equipment

[0566] 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).

[0567] Synthesis of compounds 1 to 9

[0568] By Suzuki-Miyaura coupling (Suzuki-Miyaura coupling) synthetic compound 1,2,3,4,5,6,7,8 and 9 (shown in the figure below).4-pyridylboronic acid (1.25g, 10mmol), aryl dibromide (4.2mmol) and potassium carbonate (2.8g, 20.4mmol) are added in the 7:1 mixture of degassed DMF and water (120ml).Tetrakis (triphenylphosphine) palladium (0) (0.39g, 0.34mmol) is added in the reaction mixture, and N2, solution is heated to 100 ℃ and continues 72h.After this, reaction mixture is cooled to room temperature and filtered.Organic phase is concentrated under vacuum, and resistates is dissolved in CH2Cl2 (150mL) in and washed with water three times (each 50mL).Then concentrated HCl dropwise adds in the organic phase collected, causes product precipitation.Collect precipitate by filtration, and then it is dissolved in H2O. Finally, aqueous NaOH solution (10 M) was added dropwise to the H 2 O layer until the pH was 8-9, resulting in the precipitation of pure products of compounds 1, 2, 3, 4, 5, 6, 7, 8, and 9, respectively.

[0569] Characterization of compounds 1 to 9

[0570] pass 1 The compounds were characterized by H NMR.

[0571]

[0572] 1 H NMR (400MHz, 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).

[0573]

[0574] 1 H NMR (400MHz, 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).

[0575]

[0576] 1H NMR(400MHz,CDCl3)δ[ppm]:8.73(dd,J=4.4,1.6Hz,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)。

[0577]

[0578] 1 H 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=4.4,1.6Hz,4H)。

[0579]

[0580] 1 H 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)。

[0581]

[0582] 1 H 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)。

[0583]

[0584] 1 H 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)。

[0585]

[0586] 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).

[0587]

[0588] 1 H NMR (400MHz, 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 = 6.0 Hz 1H).

[0589] Alternative synthesis of compound 1

[0590] In contrast to above-mentioned tetrakis (triphenylphosphine) palladium (0), Pd-C catalytic method is also used to synthesize compound 1.4-pyridylboronic acid (1.72g, 14mmol), 1,4-dibromobenzene (1.00g, 4.2mmol) and potassium carbonate (3.52g, 25mmol) are added to the 1:1 mixture of degassed DMF and water (120ml). Activated carbon-supported palladium (100mg) is added to the reaction mixture, and the solution is heated to 100 DEG C for 72h under N2. After this, the reaction mixture is cooled to room temperature and filtered. The organic phase is concentrated under vacuum, and the residue is dissolved in CH2Cl2 (150mL) and washed with water three times (each 50mL). Then concentrated HCl is added dropwise to the organic phase collected, causing product precipitation. Precipitate is collected by filtration, and then it is dissolved in H2O. Finally, aqueous NaOH (10 M) was added dropwise to the H2O layer until the pH was approximately 8-9, resulting in the precipitation of the pure product (89 mg, 9%).

[0591] Compound 1 prepared by this method (see Figure 1 ) revealed products exceeding 99% purity - higher than those obtained using tetrakis(triphenylphosphine)palladium(0).

[0592] Synthesis of compounds 10, 11, 12, 13, 15, 16, 17, 18 and comparative compounds 14 and 19

[0593] Compound 10, 11, 12, 13, 15, 16, 17, 18 and comparison compounds 14 and 19 (shown in the figure below) are synthesized by Anderson / Menshutkin reaction. (3-Bromopropyl) trimethylammonium bromide) (1.00 g, 3.83 mmol) is added to a stirred solution of bipyridine (1.29 mmol) in anhydrous and degassed DMF (50 mL). The reaction mixture is heated to 100 ° C and stirred for 48 h. After this, the reaction mixture is cooled to 0 ° C, and the resulting precipitate is filtered and washed with cold DMF (3 × 20 mL), MeCN (3 × 20 mL) and ether (3 × 20 mL) to obtain pure product. In order to obtain the corresponding tetrachloride salt, the separated bipyridinium salt is loaded onto an ion exchange column. Three portions of water (each 50 mL) are used to collect the tetrachloride salt. After concentration under vacuum, compounds 10, 11, 12, 13, 14, 17, 18, and 19 were obtained. To obtain a purity exceeding 99.9% suitable for electrochemical studies, compounds 10, 11, 12, 13, 14, 17, 18, and 19 were triturated six times from water using acetone.

[0594] Characterization of compounds 10, 11, 12, 13, 15, 16, 17, 18 and comparative compounds 14 and 19

[0595] pass 1 Compounds 10, 11, and 17 were characterized by H NMR and 1 H and C 13 NMR, FTIR and MS characterized compounds 12, 13, 15, 16, 18 and comparative compounds 14 and 19. For clarity, the bromide counterion was omitted from the structures.

[0596]

[0597] 1 H NMR (400MHz, 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).

[0598]

[0599] 1H NMR(400MHz,D2O)δ[ppm]:8.99(d,J=7.0Hz,4H),8.49(d,J=6.9Hz,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).

[0600]

[0601] 1 H NMR(400MHz,D2O)δ[ppm]:8.89(d,J=6.4Hz,4H),8.39(d,J=6.0Hz,4H),8.19(s, 2H), 4.73 (t, J = 7.7Hz, 4H), 3.66–3.50 (m, 4H), 3.21 (s, 18H), 2.73–2.60 (m, 4H).

[0602]

[0603] 1 H NMR(400MHz,D2O)δ[ppm]:9.08(d,J=5.2Hz,4H),8.39(d,J=5.0Hz,4H),8.04–8.01(m,2H),7.85(s, 2H),7.79–7.75(m,2H),4.87(t,J=8.0Hz,4H),3.66–3.62(m,4H),3.24(s,18H),2.78–2.70(m,4H). 13 C NMR (100MHz, 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. MSESI-MS: m / z[M] 4+ , C 32 H 44 Calculated value of N4: 121.0886, found: 121.0888. FTIR v[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.

[0604]

[0605] 1 H NMR(400MHz,D2O)δ[ppm]:8.97(d,J=5.0Hz,4H),8.69(s,2H),8.56(d,J=5.2Hz,4H),8.36(d,J=8.0H z,2H),8.16(d,J=8.0Hz,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 (100MHz, 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, found: 121.0885. FTIR v[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.

[0606]

[0607] 1 H NMR(400MHz,D2O)δ[ppm]:8.98(d,J=5.6Hz,4H),8.75(s,2H),8.56(d,J=6.2Hz,4H),8.28(d,J=8.8H z,2H),8.18(d,J=8.8Hz,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 (100MHz, 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. MSESI-MS: m / z[M] 4+ , C 32 H 44Calculated value of N4: 121.0886, found: 121.0887. FTIR v[cm -1 ]:848,923,940,968,1057,1066,1175,1241,1349,1394,1409,1477,1532,1559,1623,1638,2901,2988,3351,3661. 85% yield.

[0608]

[0609] 1 H NMR(400MHz,D2O)δ[ppm]:9.23(d,J=9.2Hz,4H),8.38(d,J=6.0Hz,4H),7.68–7.61 (m,8H),4.96(t,J=7.2Hz,4H),3.73–3.69(m,4H),3.28(s,18H),2.87–2.78(m,4H). 13 CNMR(100MHz,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: 133.5925. FTIR v[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.

[0610]

[0611] 1 H NMR(400MHz,D2O)δ[ppm]:8.92(d,J=6.0Hz,4H),8.46(d,J=5.6Hz,4H),8.16(d,J=7.6Hz,4H),8 .07(d,J=7.2Hz,4H),4.75(t,J=7.2Hz,4H),3.59–3.56(m,4H),3.21(s,18H),2.70–2.62(m,4H). 13C NMR (100MHz, 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 N4: 127.5925, found: 127.5925. FTIR v[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. 81% yield.

[0612]

[0613] 1 H NMR(400MHz,D2O)δ[ppm]:8.76(d,J=6.8Hz,4H),8.26(d,J=6.0Hz,4H),8.07(d,J=3.6Hz,2H),7 .70(d,J=3.6Hz,2H),4.66(t,J=7.8Hz,4H),3.57–3.53(m,4H),3.20(s,18H),2.65–2.57(m,4H). 13 C NMR (100MHz, 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, found: 130.5706. FTIR v[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.

[0614]

[0615] 1 H NMR(400MHz,D2O)δ[ppm]:9.08(d,J=5.4Hz,4H),8.90(d,J=5.2Hz,4H),8.48(d,J=8.0Hz,2H), 8.37(t,7.5Hz,1H),4.82(t,J=7.6Hz,4H),3.62–3.58(m,4H),3.21(s,18H),2.73–2.65(m,4H). 13 C NMR (100MHz, 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: 108.8337. FTIR v[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.

[0616] Additional synthesis and characterization of compound 20

[0617] Compound 20 (shown below) was synthesized by the Zincke reaction. First, 4,4'-bipyridine and 1-chloro-2,4-dinitrobenzene (excess) were refluxed in ethanol for 72 hours. The reaction mixture was then cooled to room temperature and concentrated under vacuum. It was precipitated with diethyl ether and dried to obtain the corresponding Zincke salt. In a second step, it was reacted with 4-trimethylammoniumaniline (excess) in ethanol at reflux for 72 hours. The crude product was collected by filtration and purified by washing with three portions of ethanol. 20, suitable for electrochemical studies, was obtained with a purity exceeding 99.9% by grinding it six times from water with acetone.

[0618]

[0619] pass 1 H NMR characterization of compound 20 showed that Figure 12 C. For clarity, the chloride counterion has been omitted from the structure.

[0620] Calculated singlet-triplet energy gap

[0621] The singlet-triplet energy gap (E) was calculated by using the free energy difference obtained from the optimized structures of both the singlet and triplet forms of the corresponding doubly reduced compounds. ST The free energy values ​​were calculated from the geometry-optimized structures based on DFT performed at the UB3LYP / 6-31++G(d,p) level using an UltraFine integrating grid, GD3BJ, and the SMD implicit solvation model (as implemented in Gaussian 09).

[0622] When doubly reduced, bispyridinium compounds are generally known to exhibit a closed shell singlet structure. However, as conjugation increases, it is believed that population of the thermally accessible triplet diradical state occurs. The Gibbs free energy difference between the corresponding singlet and triplet states ('singlet-triplet energy gap' E) can be used to determine the energy distribution of the diradical. ST ) predict the accessibility of these triplet diradical states.

[0623] E of compounds 10, 11, 12, 13, 17 and 18 ST Range E ST = -27.9 kcal mol -1 to -8.0 kcal mol -1 ( Figure 2 e), where the more negative the value, the greater the tendency to form a closed shell structure. ST <-6.0 kcal mol -1 (10, 11, 12, 13, 17, 18). For these compounds, voltammetry indicates a reversible redox process. Homocyclic electrolytes exhibit more negative potentials than heterocyclic electrolytes. Molecules with greater conjugation also exhibit more negative potentials than less conjugated molecules.

[0624] E of compounds 15 and 16 ST -5.4 kcal mol -1 and -1.6 kcal mol -1 ( Figure 2 e). When tested using cyclic voltammetry (CV), -6.0 kcal mol -1 <E ST <0 kcal mol -1The higher EST of is believed to result in a loss of redox reversibility. Without wishing to be bound by theory, this is believed to be the result of the generation of diradical species and their subsequent participation in parasitic side reactions (e.g., proton or halide abstraction, σ-dimerization, and cyclization). These parasitic side reactions are amplified in CV experiments because redox activity occurs on the electrode surface - resulting in high local concentrations of diradical species around the electrode that can participate in parasitic side reactions. It is believed that when cycling in the RFB, E ST -6.0 kcal mol -1 <E ST <0 kcal mol -1 Compounds with this capacity will exhibit redox reversibility because redox occurs in the bulk electrolyte solution (as opposed to only at the electrode surface), resulting in lower local concentrations of diradical species and reduced side reactions. It is also believed that redox reversibility can be enhanced by cycling the compound at lower temperatures. At lower temperatures, the triplet diradical state is less populated, reducing the diradical concentration and suppressing side reactions.

[0625] Comparison of E of compounds 14 and 19 ST 3.6 kcal mol -1 and 2.3 kcal mol -1 (See Figure 2 e). At these higher E ST >0kcal mol -1 Under these conditions, the compounds are believed to adopt a non-Kekulé (or open shell) double-reduction structure and thus possess a ground-state triplet diradical. Notably, the first and second redox events of compounds 14 and 19 are very close (see Figure 2 e), so that they immediately form a double-reduction open-shell state after being reduced. Therefore, comparative compounds 14 and 19 have irreversible redox properties.

[0626] E ST The value is also related to the separation between the first and second redox events, with more negative E ST The values ​​correspond to wider energy gaps between redox events.

[0627] Electrochemical Characterization: No Dioxygen Electrolyte

[0628] Cyclic voltammetry

[0629] Cyclic voltammetry experiments were performed at 25°C in a 0.1 M NaCl solution under N2 purge using a Metrohm Eco Chemie Autolab PGSTAT12 potentiostat operating on GPES 4.9 software. A three-electrode configuration was used with a 3 mm or 1.6 mm glassy carbon working electrode, a platinum counter electrode, and a RE-5B Ag / AgCl BASI reference electrode. Before each measurement, the glassy carbon electrode was polished using a 0.05 μm alumina-H2O slurry on a polishing cloth. A 20 mV s -1 CVs were performed at a scan rate of 1 mM concentration of the corresponding compound.

[0630] By cyclic voltammetry (CV), compounds 10, 11, 12, 13, 17, and 18 exhibited reversible potentials spanning from -0.35 to -0.82 V vs. standard hydrogen electrode (SHE) for the first reduction (see Figure 2 d). Compounds 10, 11, and 17 exhibit reversible potentials of -0.35 V and -0.68 V, -0.76 V, and -0.56 V and -0.67 V, respectively. However, notably, compounds 12 and 13 have first redox potentials of -0.77 V and -0.82 V, respectively—which are very negative and are believed to be the most negative first redox potentials to date for any pyridinium RFB electrolyte with unsubstituted core features.

[0631] Viologen derivatives whose doubly reduced structures can adopt a Kekulé structure (e.g., 12, 13) are believed to be more likely to have reversible potentials. Compounds that exhibit a lower degree of conjugation are also believed to have more reversible redox potentials.

[0632] Compounds 15 and 16 showed similarly negative first reduction potentials as 12 and 13, however, as discussed above, under CV conditions, due to the small negative E ST , the redox of compounds 15 and 16 is electrochemically irreversible. It is believed that cycling in a redox flow battery cell and / or at lower temperatures will lead to reversible redox of compounds 15 and 16.

[0633] In contrast, the comparative compounds 14 and 19 had no reversible potential, which is believed to be due to the positive E ST .

[0634] In situ NMR and EPR of RFB

[0635] The flow cell was purchased from Scribner Associates. Ultra-high purity sealed graphite flow plates with a serpentine flow pattern were used for both electrodes. Each electrode consisted of a 5 cm 2 The anion exchange membrane (120 μm thick, The electrodes were positioned between the electrodes (diameter, Selemion, Japan). A 3 mm thick PTFE frame was used to position the electrodes, with a 0.7 mm thick fluororubber gasket on each side of the frame. The current collector was a gold-plated copper plate. Anodized aluminum end plates with reactant inlet / outlet ports were used. A Masterflex L / S peristaltic pump (Cole-Parmer, Vernon Hills, Illinois) was used to pump the electrolyte at 40 rpm (approximately 20 mL min -1 ) was circulated through the electrodes at a flow rate of . A custom glassware made of Pyrex with a gas inlet, outlet, liquid inlet and outlet was used as the electrolyte reservoir.

[0636] Use flow cell as above, two peristaltic pumps, electrochemical cycler (SP-150, BioLogic SAS), desktop EPR (MS5000, Magnettech) and NMR (300MHz, Bruker Avance III) spectrometer to carry out original position NMR and EPR characterization.Battery and EPR spectrometer are positioned outside the 5G line of NMR magnet.Electrolyte is pumped through flow cell, then flows through EPR and NMR magnet, and finally returns to electrolyte reservoir.Flow direction is from the bottom of two magnets to top.PFA pipe (1 / 16 inch) is used to connect electrolyte reservoir, battery and EPR and NMR sampling tube.

[0637] In the anode electrolyte reservoir, unless otherwise specified, the flow battery cell uses 30 mL of 0.01 M test compound in a 0.1 M NaCl deuterated aqueous solution. In the cathode electrolyte reservoir, unless otherwise specified, the flow battery cell uses 50 mL of 0.02 M 4-hydroxy-TEMPO in a 0.1 M NaCl deuterated aqueous solution. Both reservoirs were purged with N2, degassed for 1 h, and then kept under an active N2 flow during the cycling process. At room temperature, the flow battery cell was charged and discharged five times with a constant current of 10 mA on a portable electrochemical cycler.

[0638] For compounds 10, 11, and 13, in situ NMR and EPR spectra were obtained when a full cell consisting of 10 mM viologen and 20 mM 4-hydroxy-TEMPO, all in D2O, was galvanostatically cycled for five full charge-discharge cycles. The second charge-discharge cycle is shown in FIG3 . The voltage of a full cell of 10 mM (a) 10, 11, (i) 13 in 100 mM NaCl and 20 mM 4-hydroxy-TEMPO in 100 mM NaCl over time for 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, and a 1 h potential hold was applied at the corresponding cutoff values. NMR is shown in FIG3 (b, f, j), and EPR is shown in FIG3 (c, g, k). Spectra were collected during the charge-discharge cycle. The oxidation states of 10, 11, and 13 and their corresponding NMR proton assignments are shown in (d, h, l). For clarity, the chloride counterion is omitted. The proton assignment e* indicates that the proton e undergoes rapid hydrogen-deuterium exchange, reducing its intensity and limiting observation by NMR.

[0639] Upon charging of a full cell containing compound 10, plateaus corresponding to two well-separated single-electron redox events were observed. For compounds 11 and 13, the redox events were narrowly spaced such that a single charge and discharge plateau was observed in each case. Starting at 0.50 V vs. 4-hydroxy-TEMPO, a charge plateau assigned to unreduced 10 was observed by NMR. 4+ 、11 4+ and 13 4+ The protons of both the aliphatic and aromatic parts of the ion and the 10 4+ The low signal intensity of the proton e.

[0640] Above 0.50 V, all signals except a (terminal quaternary amine proton) disappear almost immediately, accompanied by the appearance of EPR resonances assigned to radical 10 3+· 、11 3+· and 13 3+· .

[0641] At the high state of charge (1.90 V, 1.95 V, or 2.00 V for 10, 11, or 13, respectively), the potential was kept constant for 1 h.

[0642] During this time period, new resonances appeared in the NMR spectra of compounds 10 and 11 that were significantly shifted to lower frequencies relative to those observed in the low-charge state. These features were assigned to the diamagnetic doubly reduced species 10.2+ and 11 2+ For 10 2+ , significant broadening of all resonances was observed, indicating the presence of residual levels of ions with closed shell ions 10 2+ Balance the presence of free radicals.

[0643] For compound 13, no new resonances were observed during the potential hold. Instead, all NMR resonances were significantly broadened, including a". In addition, no free radical species were observed by EPR. ST The population of a small, paramagnetic, thermally accessible triplet state is likely responsible for the significant NMR line broadening observed. The absence of direct observation of triplet diradicals by EPR suggests either rapid singlet-triplet interconversion or low radical concentrations on the experimental timescale, either intrinsically or as a result of triplet diradical spin pairing to form EPR-silent dimers.

[0644] For compounds 17 and 18, in situ NMR and EPR spectra were obtained when a full cell comprising 10 mM viologen and 20 mM 4-hydroxy-TEMPO, both in D2O, was galvanostatically cycled for five full charge-discharge cycles, with the second full charge-discharge cycle showing Figure 4 Voltage variation over time of a full cell of 10 mM (a) 17, I 18 in 100 mM NaCl and 20 mM 4-hydroxy-TEMPO in 100 mM NaCl for one full charge-discharge cycle. -2 . Cutoff voltages of 0.5 V (17 and 18), 1.75 V (17), and 1.85 V (18) were used, and a potential hold of 1 h was applied at the corresponding cutoff values. NMR (b, f) and EPR (c, g) spectra were collected during the charge-discharge cycle. (d, h): The oxidation states of 17 and 18 and their corresponding NMR proton assignments are shown. Chloride counterions are omitted for clarity.

[0645] Based on heteroatom compound 17 (wide E ST ) and 18 (narrow E ST ) similar NMR and EPR characteristics ( Figure 4 ) show that these phenomena are universal and arise from E ST Two different electrochemical performance modes are depicted.

[0646] For variable concentration experiments, currents of 1 mA, 5 mA, and 10 mA were used for 1 mM, 5 mM, and 10 mM concentrations, respectively.

[0647] For compound 11, in situ NMR and EPR spectra were obtained as a function of time for a full cell (containing 1 mM viologen in 100 mM NaCl and 2 mM 4-hydroxy-TEMPO in 100 mM NaCl) for one full charge-discharge cycle. -2 Cutoff voltages of 0.5 V and 1.95 V were used, and a potential hold was applied at the corresponding cutoff value for 1 h.

[0648] The results are shown in Figure 5 (b) NMR and EPR spectra collected during charge-discharge cycling. EPR spectral features indicate the presence of ultratrace 4-OH-TEMPO crossovers. (d) Structure of 11 and its corresponding NMR proton assignments.

[0649] Circular Data

[0650] Galvanostatic cell cycling was performed using the procedure described above from the in situ NMR / EPR studies. 10 mM compound 17 ( Figure 6 a) and 18( Figure 6 b) and 20 mM 4-hydroxy-TEMPO in 100 mM NaCl were used to measure the voltage as a function of discharge capacity over five full charge-discharge cycles. In all cases, 2 mA cm -2 Cutoff voltages of 0.5 V (17 and 18), 1.75 V (17), and 1.85 V (18) were used, and a potential hold of 1 h was applied at the corresponding cutoff values.

[0651] It shows that compounds 17 and 18 have relatively flat voltage curves during the entire discharge process (see Figure 6 This flat voltage curve is advantageous for energy storage applications and does not require additional circuitry to increase / decrease the voltage or a system that tolerates variable input voltages.

[0652] The discharge capacities of compounds 17 and 18 were shown to be relatively constant over their first three cycles (see Figure 7 Compound 18 had a retention capacity of approximately 92% over the first five cycles. Compound 17 had an excellent capacity retention of approximately 99% over the first five cycles. It is believed that the closed-shell nature of Compound 17 improved the capacity retention.

[0653] The coulombic efficiencies of compounds 17 and 18 were also measured at 78.6 ± 0.3 and 79.7 ± 2.8, respectively.

[0654] Due to the E ST Compared with compound 17 STIt is more negative, so it is believed that compound 18 has a higher paramagnetic thermally accessible triplet population, which may be the reason why the capacity retention of 18 is slightly worse.

[0655] Further cycling data for compounds 10, 11 and 13 are measured and are shown in Figure 8 middle.

[0656] Figure 8 a shows the radical concentration signatures of 10, 11, and 13 during the charging process derived from spin counting based on the EPR data shown in FIG3 (and discussed above).

[0657] Figure 8 b shows the spectroscopic electrochemical data of 10, 11 and 13 at 1 mM concentration. The bands assigned to the mono-reduced and π-dimer species are marked. UV-Vis spectroscopic electrochemical studies were performed on compounds 10, 11 and 13. 10 was prepared using the Schlenk technique. 4+ (0.5mM), 11 4+ (0.5 mM) and 13 4+ The sample was electrochemically reduced using a carbon paper working electrode and a gold counter electrode. After the solution was transferred to the cuvette and electrochemically reduced, a UV / Vis spectrometer (Horiba, Duetta) was used to obtain spectral data.

[0658] Figure 8 c shows the voltage versus discharge capacity of a full cell of 10 mM 10, 11, and 13 in 100 mM NaCl and 20 mM 4-hydroxy-TEMPO in 100 mM NaCl over five full charge-discharge cycles. 2 mA cm -2 For compound 11, the voltage and discharge capacity data for five full charge-discharge cycles of 5 mM and 1 mM 11 full cells were superimposed. Full cells of 5 mM 11 in 100 mM NaCl and 10 mM 4-hydroxy-TEMPO in 100 mM NaCl were charged at 1 mA cm -2 A full cell of 1 mM 11 in 100 mM NaCl and 2 mM 4-hydroxy-TEMPO in 100 mM NaCl was cycled at 0.2 mA cm -2 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, and a potential hold of 1 h was applied at the corresponding cutoff value.

[0659] Figure 8 d shows the discharge capacity of 11 as a function of cycle number at concentrations of 10 mM, 5 mM, and 1 mM.

[0660] Figure 8 e shows the normalized discharge capacity of 10, 11, and 13 at 10 mM concentration as a function of cycle number.

[0661] Dimerization studies

[0662] In situ DOSY NMR

[0663] Pseudo-2D NMR experiments were performed on flowing electrolyte solutions using direct excitation with 90° radio frequency pulses. Each NMR spectrum was acquired by collecting eight free induction decays with a recycle delay of 15 s. The pulse width of the 90° pulses 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).

[0664] The flow was stopped during the acquisition period (12 min) for DOSY NMR.

[0665] In situ DOSY NMR experiments were performed on 10, 11, and 13 at 0%, 50%, and 100% SOC (Table 1). This showed an overall decrease in diffusivity (D) from 0-100% SOC, especially for compounds 11 and 13, which exhibited low radical concentrations at all SOCs. These results indicate that the size of the cation increases after the generation of single radicals, which is consistent with the formation of dimers with a molecular weight twice that of the monomer (the decrease in diffusivity can be attributed to the increase in molecular weight).

[0666] Compound 10 produced a much smaller decrease in diffusivity, indicating that no or little dimer formation occurred after the generation of the single radical.

[0667] Table 1 - Summary of the diffusivities of bispyridinium at different SOCs obtained by in situ DOSY NMR

[0668]

[0669] The presence of the dimer could not be directly determined due to high free radical concentrations (affecting observations by NMR) and the known EPR silencing of viologen π-dimers (affecting observations by EPR).

[0670] EPR and CV modeling studies

[0671] An analysis of the redox balance related to compounds 10, 11, and 13 was performed. The two one-electron reductions were expressed as the normalized equilibrium constant K c The equation for the change of free radical fraction with battery SOC is obtained by performing the normalization balance.

[0672] The difference between redox events and the equilibrium constant K c Related, as follows:

[0673]

[0674] For compounds, return to equilibrium:

[0675]

[0676] The fit to the experimental free radical concentration data was obtained by:

[0677] K c ≠4

[0678]

[0679] K c =4

[0680]

[0681] where n is the number of electrons removed from the system starting from 100% SOC, and x is the fraction of free radicals.

[0682] For the π-dimerization equilibrium, K d The values ​​are estimated as follows. At 50% SOC, an initial concentration of 1 electron equivalent of viologen (V0) was added to produce the reduced species, thus yielding the previous results:

[0683]

[0684] Since the initial concentration (V0) and K c and free radical concentration (V 3+· ), the dimerization constant can therefore be calculated as follows:

[0685]

[0686] This equation was used to fit experimental radical fraction data obtained by EPR-based spin counting methods, thereby extracting the observed normalized equilibrium constant, K c,obs After fitting, it was found that K values ​​of 10, 11, and 13 c,obsThe values ​​were 0.75, 0.021, and 0.0021, respectively (Table 2). However, the fits based on the EPR data were modest at best and deviated significantly from the experimental data, especially for compound 13, suggesting the presence of other phenomena that could not be explained by the simple normalization model.

[0687] The equation was also used for CV curve fitting, thereby obtaining much better agreement with the experimental data. The difference between the first redox event and the second redox event obtained by CV curve fitting was related to K c , we can estimate the 'true' K c value and K c,obs The corresponding K values ​​of 10, 11 and 13 are compared. c The value is 3.2 x 10 5 , 1.3 and 2.9 (see Table 2) - significantly higher than K c,obs This discrepancy suggests that there may be another reaction equilibrium besides normalization that leads to the lower observed radical fraction. The strongest candidate is the dimerization equilibrium.

[0688] Extraction of K from radical concentrations of 10, 11, and 13 c The average K c are 0.7, 0.2, and 0.002. The notably low value of 13 is also unreliable because there is a large asymmetry in the variation of free radical concentration with SOC, which means that some assumptions may be violated.

[0689] Table 2 - Summary of Bipyridinium Equilibrium Data and Coulombic Efficiencies

[0690]

[0691] Capacity fading rate and Coulombic efficiency

[0692] Based on five full charge-discharge cycles (see Figure 7 and Figure 8 and constant current cycle data part) to calculate the capacity decay rate and coulombic efficiency of 10, 11, 13, 17 and 18 and compare them with the corresponding K c , K d and E ST The values ​​are compared to those of Figure 2 (see Table 2 and EPR and CV modeling studies). For all compounds, while the coulombic efficiencies fall within a narrow range (74%-81%), the capacity fade values ​​reveal a range of trends.

[0693] First, relative to E ST Compounds with higher values ​​(e.g., compounds 11 and 17), E STExtended viologens with lower values ​​(e.g., compounds 13, 18) exhibit significantly higher capacity fade. Combined with the findings from NMR and EPR, this is thought to indicate the presence of two distinct electrochemical performance modes. It is also thought to indicate that thermally accessible triplet species are associated with parasitic processes—possibly similar in nature to those observed by CV for compounds 14, 15, 16, and 19 ( Figure 2 and cyclic voltammetry).

[0694] Second, in E ST Among the higher compounds (e.g., compounds 10, 11, 17), those that exhibited high radical concentrations at all states of charge (e.g., compound 10) also exhibited greater capacity fade ( Figure 8 a. Figure 8 c. Figure 8 e and galvanostatic cycling data). Overall, these results indicate that the capacity decay of bispyridinium compounds is mainly related to the formation of open-shell structures (monoradicals or diradicals). Therefore, the process of reducing the radical concentration at all SOCs (low K c , high K d and high E ST ) should be associated with improved capacity retention. Although low K c and high E ST The process will produce a closed shell structure, but the high K d This process retains single radicals as spin-paired π-dimers, which is currently believed to be the direct cause of capacity fading.

[0695] Since π-dimerization is a concentration-dependent process that favors a higher degree of dimerization at higher single radical concentrations, the reaction of compound 11 (i.e., high K d An additional set of RFB runs was performed to determine the extent to which π-dimerization contributes to capacity fade ( Figure 8 d). With increasing concentration of 11 (corresponding to a higher degree of π-dimerization), both capacity retention and coulombic efficiency increase. At 10 mM, a coulombic efficiency of 77% is observed. These drop slightly to 74% at 5 mM and then drop sharply to 18% at 1 mM. At the same time, at 10 mM, a capacity decay rate of 0.01% per cycle is obtained, while at 5 mM, they rise sharply to 9.64% per cycle. Even at a coulombic efficiency of 77%, the capacity decay is small, while at 74%, corresponding to half the concentration (5 mM), the capacity decay is significant. However, at a concentration of 1 mM, consistent with the low degree of π-dimerization, a completely different set of charge-discharge characteristics is observed. Unlike the charging process corresponding to the reduction of 11, a new set of processes with an onset voltage of 0.82 V relative to 4-hydroxy-TEMPO appears ( Figure 5These processes proceed on a much longer timescale than those characteristic of viologen charging and result in both an accumulation of hydroxide that increases the pH from 7 to 12 and an almost complete loss of system capacity within the first charge-discharge cycle, with no evidence of chemical degradation by in situ NMR or EPR.

[0696] Electrochemical Characterization: Dioxygen-Exposed Electrolytes

[0697] In situ mass spectrometry

[0698] On-line electrochemical mass spectrometry (OEMS) experiments were performed using a custom-made H-cell unit connected to the gas flow system previously described in Zhao et al. using 1% dioxygen in argon at 1.2 bar.

[0699] In situ online electrochemical mass spectrometry of a full cell containing 1 mM 11 in 100 mM NaCl and 2 mM 4-hydroxy-TEMPO in 100 mM NaCl during one full charge-discharge cycle in an atmosphere of 1% O2 in Ar. A current density of 0.2 mA was used. After charging for 8 h, a potential hold of 1.95 V was applied for 2 h.

[0700] This revealed a sharp steady-state decrease in the dioxygen partial pressure in the headspace above the electrolyte solution during charging under a continuous flow of 1% O2 in Ar (Figure 9a). This dioxygen consumption became significantly more pronounced once the viologen reduction potential was reached. Despite operating at cell voltages outside the thermodynamic stability window of water (1.23 V), no changes in the hydrogen partial pressure were detected at any stage during operation. Overall, these results suggest that the increase in pH during cycling is associated with the consumption of gaseous dioxygen rather than the decomposition of water, and that the reduced viologen species promote this process. Based on these findings, the two-electron direct reduction of trace dissolved dioxygen to form hydroxide ions via the peroxide pathway is proposed as a parasitic process (E = -0.065 V, relative to SHE; 0.87 V, relative to 4-hydroxy-TEMPO) - in which the reduced form of 11 (such as 11 3+· ) is used as a redox mediator.

[0701] At higher concentrations, the usual viologen redox behavior was restored, and there was no additional evidence for a charge plateau corresponding to other processes, but a similar increase in pH was observed. This suggests that oxygen reduction (whether direct or viologen-mediated) still occurs. Given that the onset of dimerization typically occurs at approximately 0.1 mM in water, and that π-dimerization favors a higher degree of association at higher concentrations of the corresponding monoradical, it is hypothesized that a higher degree of π-dimerization, and therefore K dIt can play a role in mitigating competing side reactions between monoradical species and trace impurities such as oxygen during operation.

[0702] In contrast to the OEMS of the 1 mM H-cell described above, OEMS experiments were also performed using 50 mM H-cells subjected to a 2 h potential hold at 1.95 V in an atmosphere of 1% O2 in Ar and 20% O2 in Ar, respectively. A current of 1.55 mA was used in both cases. The normalized dioxygen consumption is shown in FIG9d. The dioxygen consumption at a concentration of 50 mM was significantly lower than that at a concentration of 1 mM. In the presence of 20% dioxygen (partial pressure in argon), the dioxygen consumption at a concentration of 50 mM increased only slightly compared to 1% dioxygen. This reveals that the dioxygen consumption per mole of 11 at 50 mM is significantly lower than that at 1 mM. This suggests that the dimerized electrolyte species (which are more prevalent at higher concentrations) are tolerant to the presence of dioxygen, even at up to atmospheric partial pressure.

[0703] Constant current circulation in air

[0704] The flow battery cells were assembled as described above. For the 25 mM test, a full cell was assembled from 25 mM 11 (30 mL) in 500 mM NaCl and 50 mM 4-hydroxy-TEMPO (50 mL) in 500 mM NaCl. For the 50 mM test, a full cell was assembled from 50 mM 11 (15 mL) in 500 mM NaCl and 100 mM 4-hydroxy-TEMPO (25 mL) in 500 mM NaCl. 5 mA cm was used in both tests. -2 The current of the two reservoirs was purged with N2, degassed for 1 hour, and then kept under an active N2 flow during the cycling process. The flow cell was charged and discharged with a constant current using a portable potentiostat at room temperature. The cycling sequence consisted of six full charge and discharge cycles, after which the N2 connection was disconnected and the reservoir was opened to the air. After 1 hour, the cell was further cycled five times in air, at which point the reservoir was closed, purged with N2 for 1 hour, and kept under N2 under a positive pressure N2 flow for the next ten cycles. EC-lab 11.36 (BioLogic) was used to process the electrochemical data.

[0705] The results are shown in Figures 9b and 9c. At these concentrations, the cell was subjected to six galvanostatic cycles under N2 at the same current, after which the electrolyte solution was exposed to air for one hour and cycled five more times in air. In both cases, the capacity under N2 was stable. However, after the introduction of air, while the capacity dropped sharply over five cycles in the 25 mM test, it remained almost unchanged in the 50 mM test, although the Coulombic efficiency decreased slightly. This suggests that, while parasitic processes still exist, π-dimerization can serve as a competitive pathway by which the reactivity of viologen with dioxygen can be suppressed. It is believed that the open-shell viologen radical cation transfers electrons to dioxygen, thereby regenerating its unreduced state and forming reactive dioxygen species (i.e., peroxides, superoxides, and hydroxyl radicals) as byproducts (Figure 9). The latter group of species can also be produced by direct reduction of dioxygen at the electrode. π-dimerization is considered a reversible competitive pathway by which viologen can both retain its charge and be further reduced.

[0706] The 25 mM and 50 mM systems exposed to air were further bubbled with N2 for 1 hour and cycled under N2 for an additional ten times. Without wishing to be bound by theory, because capacity fade is associated with parasitic processes based on dioxygen, reintroduction of N2 resulted in capacity recovery—but at a lower rate than the initial decay rate due to the possible accumulation of peroxide species that, upon decomposition, reintroduced dioxygen. According to the proposed mechanism, at 25 mM, capacity steadily recovered over ten cycles, with the recovery rate being lower than the decay rate. At 50 mM, capacity and coulombic efficiency were fully recovered within one cycle, providing evidence for robust air tolerance, which may be further improved at RFB-related concentrations.

[0707] The experiment was repeated with 50 mM compound 17 in full RFB cells ( Figure 10 ). Voltage, normalized discharge capacity, and coulombic efficiency of a full cell of 50 mM 17 in 500 mM NaCl and 100 mM 4-hydroxy-TEMPO in 500 mM NaCl cycled 5 times in N2, 5 times in air, and 8 times in N2. 5 mA cm -2 of current.

[0708] After exposure to air, the capacity retention remained almost unchanged, but the Coulombic efficiency decreased slightly, supporting the idea that while parasitic processes still exist, π-dimerization can serve as a competing pathway by which the reactivity of viologen with dioxygen can be suppressed.

[0709] Another cyclic voltammetry

[0710] Cyclic voltammetry experiments were performed on aqueous solutions of compounds 20 and 10 at 25°C and a concentration of 1 mM in 0.1 M NaCl using a Metrohm Eco Chemie Autolab PGSTAT12 potentiostat operating on GPES 4.9 software. In the case of CVs performed under nitrogen, the solutions were purged with nitrogen. A three-electrode configuration was used with a 3 mm glassy carbon working electrode, a platinum counter electrode, and a RE-5BAg / AgCl BASI reference electrode. Before each measurement, the glassy carbon electrode was polished using a 0.05 μm alumina-H2O slurry on a polishing cloth. A 20 mV s -1 CV was performed at a scan rate of 1.

[0711] The results of compound 20 and compound 10 are shown in Figure 12 In A, voltammograms were obtained for compound 10 under nitrogen (dashed line), 20 under nitrogen (dark blue line), and 20 under air (light blue line).

[0712] As calculated from the voltammogram, compound 20 was found to have reversible reduction potentials of -0.147 V and -0.386 V vs. standard hydrogen electrode (SHE).

[0713] Notably, the voltammograms obtained for compound 20 under nitrogen (dark blue line) and under air (light blue line) are very similar, with similar reduction potentials. This suggests that compound 20 is highly tolerant to the presence of oxygen in solution.

[0714] Extended galvanostatic cycling flow battery cell studies at 250 mM

[0715] Long-term cycling was also tested at much higher electrolyte concentrations (see FIG. 9e and Table 3).

[0716] The flow battery cells were assembled as described above. Full cells were assembled from 250 mM 11 or 17 (12.5 mL) and 250 mM 4-hydroxy-TEMPO in 1 M NaCl (50 mL). In both cases, 20 mA cm -2 (at a flow rate of 40 rpm), 30 mA cm -2 (at a flow rate of 60 rpm) and 40 mA cm -2The current of (at a flow rate of 80 rpm) was measured. Both reservoirs were purged with N2, degassed for 1 h, and then for the first five cycles, maintained under an active N2 flow during the cycling process, after which the nitrogen flow was disconnected and the reservoir was opened to the air. A portable potentiostat was used to perform constant current charge and discharge on the flow cell at room temperature. Electrochemical data were processed using EC-lab 11.36 (BioLogic).

[0717] For compound 11, the -2 The voltage, normalized discharge capacity, and coulombic efficiency were measured for a full cell of 250 mM compound 11 and 250 mM 4-hydroxy-TEMPO in 1 M NaCl cycled 5 times at a current density of 1 Å (see FIG9e and Table 3). The cell was heated in air at 20 mA cm -2 The current density was 40 mA cm in air for 15 cycles. -2 The current density was 20 mA cm in air for 111 cycles. -2 The current density was 30 mA cm-1 for 5 cycles and 30 mA cm-1 for 10 cycles in air. -2 The cell was cycled 200 times at a current density of 1.5 V. Cut-off voltages of 0.5 V and 1.65 V were used.

[0718] For the cycling of compound 17, at 20 mA cm -2 The current density was 20 mA cm-1 and the -2 The current density was 40 mA cm-1 and the -2 The current density was 20 mA cm and the cycle was repeated 67 times in air. -2 The current density was 5 cycles in air and 30 mA cm -2 Voltage, normalized discharge capacity, and coulombic efficiency of a full cell of 250 mM 17 and 250 mM 4-hydroxy-TEMPO in 1 M NaCl cycled 100 times in air at a current density of 1.5 V. Cutoff voltages of 0.5 V and 1.60 V were used.

[0719] Summary of Extended Galvanostatic Cycling Performance of Tables 3-11 and 17

[0720]

[0721] For compound 11 (see Figure 9e and Table 3), although an initial jump in capacity of 12.337% was observed after exposure to air in the first 130 cycles, a slow time decay followed, which increased slightly with current. However, the decay slowed towards the end of this step and stabilized over the next 255 cycles, with a peak at 30 mA cm-1. -2 The value of 1.411% per day (0.021% per cycle, Table 3) was reached. -2 After 111 cycles, the current was switched to 20 mA cm -2 and from 20mAcm -2 No significant loss of capacity was observed upon switching, demonstrating the ability to handle variable power demands as required in real RFB applications.

[0722] Similar results were obtained for compound 17, demonstrating the generality of these performance characteristics (see Figure 11 and Table 3 ).

[0723] It is believed that π-dimerization provides additional stability to dioxygen, thereby inhibiting the viologen-mediated reduction mechanism but not 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 electron transfer rate (k 0,11 =1.98x 10 -2 cm s -1 , k 0,17 =2.8x10 -3 cm s -1 ) and the similar rate of electron transfer to dioxygen (k 0,O2 =8.4x 10 -4 cm s -1 ) is favorable compared to . Therefore, at sufficiently high currents, as used in these tests, electron transfer to the bispyridinium compound is thought to be kinetically favored. Combined with the inhibition of the viologen-mediated reduction pathway through π-dimerization, at such currents, the bispyridinium compound should be preferentially reduced, and the effect of any dioxygen (trace or otherwise) should be negligible—potentially eliminating the need for periodic purging with inert gas.

[0724] In comparison, Beh et al. described the -2 Cycling an unexpanded viologen electrolyte (corresponding to compound 10) at a similar current density to that of , in the presence of dioxygen in the headspace, resulted in a rapid drop in discharge capacity and poor Coulombic efficiency (see Figure S5 of Beh et al.).

[0725] Collectively, these results demonstrate the role of π-dimerization in the capacity fade mechanism and novel dimer-mediated air stability in recovering capacity after initial loss, suggesting that the dimerization reaction is broadly applicable to organic redox flow electrolytes.

[0726] Typically, it can be shown that if the initial coulombic efficiency is 96% or greater, the RFB is cycled in the absence of oxygen. In known systems, the initial coulombic efficiency in the presence of oxygen is typically less than 96% because the oxygen present decreases during initial cell cycling.

[0727] References

[0728] A number of publications are cited above in order to more fully describe and disclose the present invention and the state of the art to which the present invention pertains. The complete citations for these references are provided below. The entirety of each of these references is incorporated herein.

[0729] Beh et al. A neutral pH aqueous organic–organometallic redox flowbattery with extremely high capacity retention. ACS Energy Lett. 2, 639-644 (2017).

[0730] Bird, CL, & Kuhn, ATE Electrochemistry of the viologens. Chem. Soc. Rev. 10, 49-82 (1981).

[0731] DeBruler,C.,et al.Designer two-electron storage viologen anolytematerials for neutral aqueous organic redox flow batteries.Chem 3,961-978(2017)

[0732] Hyman Gesser,Applied Chemistry pp.16(2002)

[0733] Janoschka,T.,et al.An aqueous,polymer-based redox-flow battery usingnon-corrosive,safe,and low-cost materials.Nature 527,78-81(2015)

[0734] Kwabi,D.G.,Ji,Y.&Aziz,M.J.Electrolyte lifetime in aqueous organicredox flow batteries:a critical review.Chem.Rev.120,6467-6489(2020)

[0735] Luo et al.Aπ-conjugation extended viologen as a two-electron storageanolyte for total organic aqueous redox flow batteries.Angew.Chem.Int.Ed.57,231-235(2018)

[0736] Nguyen,T.P.,et al.Polypeptide organic radical batteries.Nature 593,61-66(2021)

[0737] Mike L.Perry.,et al.,ACS Energy Lett.2022,7,2,659–667

[0738] Sullivan et al.,Adv.Energy Mater.2023,13,2203919

[0739] Tang et al.[JACS Au,2022]

[0740] Zhao et al.In situ NMR metrology reveals reaction mechanisms in redoxflow batteries.Nature 579,224-228(2020)

[0741] WO 2021 / 055275

[0742] WO 2023 / 046710

[0743] US 2022 / 0384834

[0744] US 2022 / 0190374

[0745] US 2022 / 0020990

[0746] CN 112500329

[0747] WO 2022 / 236241

Claims

1. A redox flow battery, comprising an 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 in the electrolyte is present as a complex formed from a single reduced form of the redox-active unit, and molecular dioxygen (O2) dissolved in the electrolyte; 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 intramolecularly complexed redox-active units.

2. The redox flow battery of claim 1 , wherein the organic redox-active molecule comprises a redox-active unit of formula (IA): in: -A- and -B- are each independently C 5-10 arylene; Each -L- is independently selected from C 5-14 Arylene, bond, C 2-6 Alkenylene, C 2-4 Alkynylidene, wherein the C 5-14 Arylene and C 2-4 Alkenylene is optionally substituted with one or more -R C group substitution; -L 1 - independently selected from a bond, C 1-6 Alkylene, C 5-14 Arylene, -N(H)-, and -(CH2O) a1 -(C2H4O) a2 -(C3H6O) a3 -(CH2C(O)) a4 -, wherein said C 1-6 Alkylene and C 5-14 Arylene is optionally substituted by one or more -R D group substituted, and 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; When present, -R A 、-R B 、-R C and -R D Each of 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 heteroarylene; and m is 1 or greater.

3. The redox flow battery of claim 2, wherein the organic redox-active molecule has formula (IB): Among them -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 (IA).

4. The redox flow battery according to any one of claims 2 to 4, wherein -L 1 - independently selected from C 1-6 Alkylene, C 5-14 Arylene and -(CH2O) a1 -(C2H4O) a2 -(C3H6O) a3 -(CH2C(O)) a4 -, preferably C 1-6 Alkylene and C 5-14 Arylene. 5 . The redox flow battery according to claim 2 , wherein d is 1 to 4, preferably 1 to 3, more preferably 1 or 2.

6. The redox flow battery of claim 2 or claim 3, wherein the organic redox-active molecule has formula (I): in: -A- and -B- are each independently C 5-10 arylene; Each -L- is independently selected from C 5-14 Arylene, bond, C 2-6 Alkenylene, and C 2-4 Alkynylidene, wherein the C 5-14 Arylene and C 2-6 The alkenylene group is optionally substituted by one or more groups -R C replace; When present, -R A and -R B and -R C At least one of is independently a hydrophilic group; X is one or more counter anions; n is 2 to 4; Each of a, b, and c is independently 1 to 5; and Two or more of -A-, -B-, and -L- are C 5-10 Heteroarylene.

7. The redox flow battery according to any one of claims 2 to 6, wherein each of -A- and -B- is independently C 5-10 Heteroarylene, preferably C 5-6 Heteroarylene, more preferably C6 heteroarylene.

8. The redox flow battery according to any one of claims 2 to 7, wherein each of -A- and -B- is independently a C-atom having one heteroatom selected from oxygen, nitrogen and sulfur, preferably nitrogen and sulfur. 5-10 Heteroarylene.

9. The redox flow battery according to any one of claims 2 to 8, wherein -A-Yes and -B-Yes 10. The redox flow battery according to any one of claims 6 to 9, wherein the organic redox-active molecule has formula (II): Among them, -L-, -R A 、-R B , X, n, a, b and c are as defined for formula (I).

11. The redox flow battery according to any one of claims 2 to 10, wherein each -L- is independently selected from C 6-14 Carbon arylene, C 5-10 Heteroarylene, bond, C2 alkenylene, and C2 alkynylene, more preferably -L- is independently selected from C 6-10 Carbon arylene and C 5-6 Heteroarylene.

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

13. The redox flow battery according to any one of claims 2 to 12, wherein at least one -L- is selected from anthracene, naphthylene, and phenylene.

14. The redox flow battery according to any one of claims 2 to 13, wherein -L- is independently selected from a bond and:

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

16. The redox flow battery of any one of claims 2 to 15, wherein when present, each -R A and -R B And each -R C and -R D Each independently selected from: C optionally monosubstituted by a group selected from 1-6 Alkyl: -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 by a group selected from the following C 5-14 Aryl: -(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, and -(CH2O) a1 -(C2H4O) a2 -(C3H6O) a3 -(CH2C(O)) a4 -R N , 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, wherein each R N are independently H or C 1-6 alkyl.

17. The redox flow battery according to claim 16, wherein -R A and -R B Each is independently + (R N )3 or -P + (R N )3 single substitution such as -N + (R N )3 monosubstituted C 2-4 Alkyl, such as C3 alkyl(propyl), such as n-propyl.

18. The redox flow battery according to claim 16, wherein -R A and -R B Each is independently + (R N )3 single substitution such as -N + (R N )3 monosubstituted C 5-14 Aryl, such as C6 aryl, such as phenyl.

19. The redox flow battery according to any one of claims 16 to 18, wherein each R N It is methyl or ethyl, preferably methyl.

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

21. The redox flow battery of claim 1 , wherein the organic redox-active molecule is selected from the group consisting of: wherein X is as defined for formula (I).

22. The redox flow battery of claim 1 , wherein the organic redox-active molecule is selected from the group consisting of: wherein X is as defined for formula (I).

23. The redox flow battery of claim 2, wherein the organic redox-active molecule has formula (IC): in: -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 (IA); R P is the polymer repeating unit; p is 2 or greater.

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

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

26. The redox flow battery of claim 2, wherein the organic redox-active molecule has formula (ID): in: -A-, -B-, -L-, -R A 、-R B 、-R C , X, a, b, c and n are as defined for Formula (IA); and q is 1 to 5. 27 . The redox flow battery according to claim 26 , wherein q is 1 to 4, preferably 1 to 3, more preferably 1 or 2.

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

29. The redox flow battery of any one of claims 1 to 28, wherein the complex is a π-complex, such as a π-dimer, formed from a mono-reduced form of the organic redox-active molecule.

30. The redox flow battery of any one of claims 1 to 28, wherein the complex is a dimer, such as a homodimer, formed from a mono-reduced form of the organic redox-active molecule.

31. The redox flow battery according to claim 30, wherein the equilibrium constant (K d ) is 0.2 to 80 mM measured at a temperature of 20°C -1 .

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 greater, preferably 150 mM or greater, more preferably 250 mM or greater.

33. The redox flow battery of any one of claims 1 to 32, wherein the doubly reduced form of the organic redox-active molecule has a relative humidity of less than 0 kcal mol -1 (0kJ mol -1 ), preferably -6.0 kcal mol -1 (-25.1 kJmol -1 ) or smaller singlet-triplet energy gap (E ST ).

34. The redox flow battery according to any one of claims 1 to 33, wherein the mono-reduced form of the organic redox-active molecule has an equilibrium constant (K) for the formation of the dimer from the monomer measured at a temperature of 20°C. d )(mM -1 ), and the di-reduced form of the organic redox-active molecule has E ST (kcal mol -1 ), wherein the K d and E ST Satisfying equation (1): (1)Y≤3.64*ln(K d )-HAVE BEEN ST wherein Y is 15 to 30, preferably wherein Y is 20 to 25.

35. The redox flow battery according to any one of claims 1 to 34, wherein the electrolyte contains molecular dioxygen dissolved at a partial pressure corresponding to a concentration of 1 vol% or greater, preferably 10 vol% or greater, more preferably 15 vol% or greater, and even more preferably 20 vol% or greater.

36. The redox flow battery of any one of claims 1 to 35, wherein the electrolyte contacts the cell headspace, the cell headspace comprising molecular dioxygen, preferably at a concentration of 1 vol% or greater, more preferably 10 vol% or greater, even more preferably 20 vol% or greater.

37. A method of preparing a redox flow battery, the method comprising: preparing an electrolyte by combining an organic redox-active molecule with a liquid carrier, wherein the organic redox-active molecule comprises a redox-active unit having two or more heteroarylene groups, and the two or more heteroarylene groups are conjugated within the redox-active unit; adding the electrolyte to the redox flow battery, wherein molecular dioxygen (O2) is dissolved in the electrolyte, and reducing the organic redox-active molecule to provide a mono-reduced form of the redox-active unit, the mono-reduced form forming a complex, 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 intramolecularly complexed redox-active units.

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

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

40. A method of charging and / or discharging a redox flow battery in the presence of molecular dioxygen, the redox flow battery comprising an 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 molecular dioxygen (O2) dissolved in the electrolyte; The method comprises: reducing the redox-active unit to provide a complex formed from a mono-reduced form of the redox-active unit, and / or oxidizing the doubly reduced form of the redox-active unit to provide a complex formed from the mono-reduced form of the redox-active unit, 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 intramolecularly complexed redox-active units.

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

42. The method for preparing a redox flow battery according to claim 37 or 38, or the method for charging and / or discharging a redox flow battery according to claim 40 or 41, wherein the complex is a dimer, such as a homodimer, formed from a single reduced form of the organic redox-active molecule.

43. The method for preparing a redox flow battery according to claim 37, 38 or 42, or the method for 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 molecules is performed at a single cell voltage of 1.23 V or greater, preferably 1.5 V or greater.

44. Use of a redox flow battery for charging and / or discharging in the presence of molecular dioxygen, the redox flow battery comprising an 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 single reduced form of the redox-active unit, and molecular dioxygen (O2) dissolved in the electrolyte; 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 intramolecularly complexed redox-active units.

45. Use according to claim 44, wherein the complex is a dimer, such as a homodimer, formed from a mono-reduced form of the organic redox-active molecule.

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