Semi-solid symmetrical redox flow batteries

Abstract

A redox flow battery includes a semi-solid catholyte including a conjugated heterocyclic carbenium compound and a first electroconductive active carbon; and a semisolid anolyte including a conjugated heterocyclic carbenium compound and a second electroconductive active carbon, wherein the first oxidation state is a higher oxidation state than the second oxidation state. A redox flow battery includes a semi-solid catholyte including a radical dication of a conjugated heterocyclic carbenium compound and a first electroconductive active carbon; and a semi-solid anolyte including a neutral radical of the conjugated heterocyclic carbenium compound and a second electroconductive active carbon.

Description

SEMI-SOLID SYMMETRICAL REDOX FLOW BATTERIESCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of and priority to U.S. Provisional Application No. 63 / 674,584, filed July 23, 2024, which is incorporated herein by reference in its entirety.FIELD

[0002] This technology relates to redox flow batteries. More particularly, this technology relates to semi-solid organic redox flow batteries utilizing conjugated heterocyclic carbenium compounds or organic redox active compounds (e.g., anthraquinones and anthracenes) as the catholyte and anolyte.BACKGROUND

[0003] After many years of intensive use of coal and oil combustion as main energy sources, humanity is increasingly oriented towards the use of electricity. Efficient storage of electricity-compatible with various applications-remains a challenge. Lithium ion-based battery, long dedicated to smartphones and small devices, has been a potential short-term solution. Their use in bigger applications, such as in the car industry, could lead to a scarcity of their raw materials (Li, Co, rare-earth), and result in a very significant increase of cost.

[0004] To overcome this problem and prepare for the future, several sustainable approaches have been considered in the Energy Storage Systems (ESSs) field. One of them is the development of redox flow batteries (RFBs). The energy is stored in liquid electrolyte solutions which flow through a battery of electrochemical cells during charge and discharge. The “redox” term refers to chemical reduction and oxidation reactions involved.

[0005] These redox flow batteries have several advantages over previously presented systems. Power conversion is separated from energy storage, thus allowing for independent power and energy sizing. This separation from energy storage allows for virtually unlimited ESS capacity and are only limited by the tanker size and the electrolyte concentration. In redox flow battery systems, the redox reactions are totally reversible, meaning that the same cell is used to operate as converter of electricity into chemical energy and vice-versa. From an infrastructure point of view, the redox flow battery system is relatively easy to develop. The setup requires only two tanks each provided with a pump and a cell provided with an ion exchange membrane between two electrodes. Therefore, redox flow battery systems have very few wear parts, and the equipment maintenance costs are extremely reduced. Lastly, there is a clear separation between the two electrolyte storage, which prevents selfdischarge and the battery lifetime is mainly chemically dependent.

[0006] However, there are several points concerning redox flow battery systems that remain to be improved. Currently the energy density provided by the RFBs is insufficient for mobile applications. Parameters such as solubility and temperature of electrolytes remain crucial. Also, the cost of these EESs remains high due to their poor presence in the energy market.

[0007] Historically, the RFB systems were first used in France in 1933 with a vanadium- based electrolyte. Today, vanadium RFBs still are the most marketed flow batteries, due to a number of advantages they present on other chemistries (V at both electrodes, no crosscontamination issues, and water-based solution). However, vanadium is costly, and these vanadium-based RFBs have a relatively low energy density. Furthermore, the capital cost of a vanadium-based RFB is attributed to the cost of the membrane materials, which are used to prepare the exchange membrane that separates the two poles of the battery. Such membranes are developed to be permeable only to anions, and are based on cationic functionalized polymers. This type of material is subjected to significant electrical charge stress over time, which impacts the longevity of the RFB. While metal coordination complexes appeared to be the most stable electrolyte, the critical technical and economic limitations associated with these complexes, such as low solubility, inferior electrochemicalactivity, and high costs, have motivated researchers to explore cheaper and easier to synthesize compounds.

[0008] Redox-active organic materials (ROMs) are a promising alternative option for improving current RFB systems as ROMs possess: I) the molecular diversity, II) structural tailorability, and III) natural abundance that make them electrolytes of choice. Thus, there have been several RFB systems developed with redox-active organic materials. An important feature of these RFB systems is a one nitrogen-containing aromatic scaffold that is very soluble and highly tunable. However, the most known redox-active organic based RFB system still lacks high efficiency, robustness, and a large open circuit potential (OCV). This disclosure addresses the need for improved redox-active organic material based RFB systems.SUMMARY

[0009] Provided in one aspect, is a redox flow battery that includes a semi-solid catholyte including a conjugated heterocyclic compound in a first oxidation state and a first electroconductive active carbon; and a semi-solid anolyte including a conjugated heterocyclic compound in a second oxidation state and a second electroconductive active carbon; wherein the first oxidation state is a higher oxidation state than the second oxidation state.

[0010] In some embodiments, the conjugated heterocyclic compound in the first oxidation state is a conjugated heterocyclic cationic compound, and / or wherein the conjugated heterocyclic compound in the second oxidation state is a conjugated heterocyclic cationic compound.

[0011] In another aspect, a redox flow battery is provided that includes a semi-solid catholyte including a conjugated heterocyclic carbenium compound and a first electroconductive active carbon; and a semi-solid anolyte including the conjugated heterocyclic carbenium compound and a second electroconductive active carbon. In some embodiments, the conjugated heterocyclic carbenium compound in the catholyte comprises a radical dication and / or wherein the conjugated heterocyclic carbenium compound in theanolyte comprises a neutral radical.

[0012] In another aspect, a redox flow battery is provided that includes a semi-solid catholyte including a compound of Formula I and a first electroconductive active carbon; and a semi-solid anolyte including the compound of Formula I and a second electroconductive active carbon; wherein the compound of Formula (I) is represented by the following structure:wherein: X is -4, -3, -2, -1, 0, +1, +2, +3, or +4; each Rla, Rlb, Rlc, Rld, R2a, R2b, R2c, R2d, R3ap3b, R3C,ancj p3d in(iepen(ienly H, halide, CF3, CBn, CI3, NH2, C1-C12 alkyl, C1-C4 alkoxy, C1-C4 alkylamino, C1-C4 dialkyl amino, NO2, CN, CO2R, or Ar1; or R2aand R3dtogether form -X1-; or Rlaand R2dtogether form -X2-; or Rldand R3atogether form -X3-; or Rlaand Rlbtogether with atoms to which they are attached to form a phenyl; or R2cand R2dtogether with atoms to which they are attached to form a phenyl; each X1, X2and X3is independently O, NR4a, PR4a, CR4aR4b, or SiR4aR4b; each R4aand R4bis independently H, halide, CF3, C1-C12 alkyl, C1-C4 alkoxy, C1-C4 alkylamino, C1-C4 dialkyl amino, Ar3, -L- Ar3, -L-Z, or -L2-Z2; each Y is independently H, halide, OR5a, NR5aR5b, PR5aR5b, NO2, CN, CF3, CO2R, N3, or Ar2; each R5a, and R5bis independently H, CF3, C1-C12 alkyl, C1-C4 alkoxy, C1-C4 alkylamino, C1-C4 dialkyl amino, Ar4, -L1- Ar4, or -i -Z1; each L and L1is independently C1-C12 alkylene, C1-C12 heteroalkylene, or arylene; each L2is independently C1-C12 alkylene; Z and Z1are each independently -N(R6a)3W or a moiety comprising a conjugated heterocyclic carbenium; each R6ais independently C1-C12 alkyl; each W is independently tetrafluoroborate, hexafluorophosphate, perchlorate, tetrarylborate, trifluoromethanesulfonate, oxalatob orate, oxalate, phosphate, bis- trifluoromethanesulfonimide, halide, hydroxide, carbonate, bicarbonate, sulfate, hydrogensulfate, or sulfite; Z2is each independently -(OCH2CH2O)nCH3; n is each independently 1 to 20; each R is independently C1-C12 alkyl or aryl; Ar1, Ar2, Ar3,and Ar4are each independently unsubstituted or substituted phenyl or unsubstituted or substituted heteroaryl; each Ar1, Ar2, Ar3’ and Ar4is independently substituted with 0 to 5 substituents; the substituents are each independently selected from the group consisting of halide, CF3, NH2, C1-C4 alkyl, C1-C4 alkoxy, C1-C4 alkylamino, C1-C4 dialkyl amino, NO2, CN, or aryl.

[0013] In some embodiments, the conjugated heterocyclic compound in the catholyte has a first oxidation state and the conjugated heterocyclic compound in the anolyte has a second oxidation state, and wherein the first oxidation state is a higher oxidation state than the second oxidation state. In some embodiments, the compound of Formula I in the catholyte comprises a radical dication and / or wherein the compound of Formula I in the anolyte comprises a neutral radical. In some embodiments, the conjugated heterocyclic compound in the catholyte is encapsulated or immobilized within the first electroconductive active carbon. In some embodiments, a supporting electrolyte is encapsulated or immobilized with the catholyte within the first electroconductive active carbon. In some embodiments, the encapsulation or immobilization is achieved by ball milling the conjugated heterocyclic compound, the first electroconductive active carbon, and the supporting electrolyte.

[0014] In some embodiments, the conjugated heterocyclic compound in the anolyte is encapsulated or immobilized within the second electroconductive active carbon. In some embodiments, a supporting electrolyte is encapsulated or immobilized with the anolyte within the second electroconductive active carbon. In some embodiments, the encapsulation or immobilization is achieved by ball milling the conjugated heterocyclic compound, the second electroconductive active carbon, and the supporting electrolyte.

[0015] In some embodiments, the first or second electroconductive active carbon comprises carbon black, mesoporous carbon, bio-sourced carbon, carbon nanotubes, graphene, graphite, carbon nanofiber, carbon aerogel, or carbon nanodots. In some embodiments, the first electroconductive active carbon and the second electroconductive active carbon comprise the same material. In some embodiments, the first electroconductive active carbon and the second electroconductive active carbon comprise different material.

[0016] In some embodiments, a weight ratio of the compound to the second electroconductive active carbon in the anolyte is about 1 :9 to 9: 1. In some embodiments, a weight ratio of the compound to the second electroconductive active carbon in the anolyte is about 1 :9. In some embodiments, a weight ratio of the compound to the first electroconductive active carbon in the catholyte is about 1 :9 to 9: 1. In some embodiments, a weight ratio of the compound to the first electroconductive active carbon in the catholyte is about 1 :9.

[0017] In some embodiments, the redox flow batteries may also include a separator disposed between the anolyte and the catholyte. In some embodiments, any of the redox flow batteries also includes a solvent and an electrolyte salt.

[0018] In some embodiments, the electrolyte salt may be a lithium, sodium, potassium, ammonium, alkylammonium or phosphonium salt of tetrafluoroborate, hexafluorophosphate, perchlorate, tetrarylborate, trifluoromethanesulfonate, oxalatob orate, oxalate, phosphate, bis-trifluoromethanesulfonimide, halide; or a mixture of any two or more thereof.

[0019] In some embodiments, the solvent includes a nitrile, an ether, dimethylformamide, water, a halogenated solvent, an ionic liquid, sulfolane, y- valerolactone, acetonitrile, propylene carbonate, or a mixture of any two or more thereof. In some embodiments, the solvent is an ether, dimethylformamide, water, a halogenated solvent, an ionic liquid, sulfolane, y-valerolactone, or a mixture of any one or more of these with acetonitrile, propylene carbonate, or a mixture thereof.

[0020] In another aspect, a method of operating a redox flow battery includes flowing the catholyte through a catholyte compartment and flowing the anolyte through an anolyte compartment, wherein the catholyte and anolyte compartments are separated by a separator and electron transfer from the anolyte to the catholyte is supported.

[0021] In a further aspect, a method of operating a redox flow battery includes, after electron transfer, regenerating the catholyte and / or the anolyte by an external power source.BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG. 1 A illustrates the monitoring during galvanostatic cycling with potential limitation experiment (10 days), according to the examples.

[0023] FIG. IB is a cyclic voltammogram analysis of the initial solution and both tank after cycling, according to the examples.

[0024] FIG. 2A is an illustration of potential electrochemical impedance spectroscopy (insert = zoom) of the carbon felt electrodes both before and after cycling, according to various embodiments.

[0025] FIG. 2B is a scanning electron microscopy (SEM) analysis of the carbon felt electrodes both before and after cycling, according to the examples.

[0026] FIG. 3 A is a cyclic voltammogram analysis in presence of grinded active carbon CF (carbon felt), according to the examples.

[0027] FIG. 3B is an illustration for monitoring of functionalized CF (carbon felt) in full flow RFB loaded with only pure solvent, according to the examples.

[0028] FIG. 4 is a graph of energy density evolution in comparison with the most widespread commercial RFB ( Vanadium), C+Symmetrical Organic Redox, and the development of semi-solid symmetrical organic RFB (SsORFB) depending on the active carbon loading in C1, according to the examples. The C+in this figure is DAOTA+, the structure of which is shown in Examples 1 and 4.

[0029] FIG. 5 is an illustration of the synthesis of materials for the slurry, employing a carbocation C+at x% in mass and an activated carbon source, such as Ketjenblack (KB) at l-x% of mass. Controlled milling of these components lead to the formation of the electroactive compound, denoted as C+@KB-x (where x represents the weight percentage of C+), intended for suspension within the SO3RFB, according to the examples. The C+in this figure is DAOTA+, the structure of which is shown in Examples 1 and 4.

[0030] FIGS. 6 A, 6B, 6C, and 6D are figures showing the scanning electron microscopy(SEM) pictures of materials grinded with 3 aluminum balls collected at 30 kV of KB milled for 30 mins (FIG. 6A), KB milled for Ih (FIG. 6B), and for the same duration C+@KB-5 (FIG. 6C), C+@KB-10 (FIG. 6D). Plot shows diameter distribution, according to the examples. The C+in this figure is DA0TA+, the structure of which is shown in Examples 1 and 4.

[0031] FIG. 7A is a figure showing the cyclic voltammetry (CV) of C+and differential pulse voltammetry (DPV) of C+@KB-10 in 0.1M TBAPFe CEECN, according to the examples. The C+in this figure is DAOTA+, the structure of which is shown in Examples 1 and 4.

[0032] FIG. 7B is an illustration of the setup for a semi-solid symmetrical redox flow battery system (SO3RFB) in operation, according to the examples.

[0033] FIG. 8 is a figure showing a plot of charge, discharge capacity (normalized to theoretical capacity), coulombic and energy efficiency versus cycle number for RFB-cell cycling with tanks loaded each with 4 mL of 200mg C+@KB-10 in 0.1M TBAPFe CH3CN, flow 16 mL.min'1per channel a IC-rate for 100 cycles (lOOh, about 4.2 days), where inversion of polarity occurs at cycle 51, according to the examples. The C+in this figure is DAOTA+, the structure of which is shown in Examples 1 and 4.

[0034] FIG. 9 is an illustration of the synthesis of materials for the slurry, employing a redox active organic electrolyte, such as DAOTA+, DPA and DB-134, a supporting electrolyte, such as TBAPFe, and an activated carbon source, such as Ketjenblack (KB). Controlled milling of these components lead to the formation of the electroactive compound, denoted as X@KB&SE intended for suspension within the SO3RFB. DB or DB- 134 = Disperse Blue 134 (DB-134) or (l,4-bis(isopropylamino) anthraquinone). DPA = diphenyl anthracene. DAOTA = the structure of the carbenium compound shown in Example 4.

[0035] FIG. 10A is a figure showing a plot of charge, discharge capacity (normalized to theoretical capacity), coulombic and energy efficiency versus cycle number for RFB-cell cycling with tanks loaded each with 5 mL of 250 mg C+@KB-10&SE in 0.1M TBAPFe in 1 : 1 ratio of CH3CN: y-valerolactone, where the flow rate 8 mL / min per channel, cycled atIC-rate for 100 cycles (100 hours or about 4.2 days).

[0036] FIG. 1 OB is a figure showing the potential controlled electrochemical impedance spectroscopy of C+@KB-10&SE in 0.1M TBAPFe in 1 : 1 ratio of CEECN: y-valerolactone, at a flow rate of 8 mL / min per channel, according to the examples.

[0037] FIG. 11 A is an illustration of the summary of coulombic, voltaic, and energy efficiencies ofnPrDAOTA PF 6 (C+) in acetonitrile, and C+ball milled with and without supporting electrolyte (SE) TBAPFe in equal mole ratio in pure and mixed organic solvents (CEECN, y-valerolactone) to observe the effects of ball milling with SE and solvent have on battery cycling performance, according to the examples.

[0038] FIG. 1 IB is a table summarizing solution resistance measured on the slurry in different solvent via potential controlled electrochemical impedance spectroscopy, according to the examples.

[0039] FIG. 12 is a cyclic voltammogram in acetonitrile of 9,10 diphenyl anthracene (DPA, top), disperse blue anthraquinone (DB-134, middle), and a planar carbenium ion DAOTA+(C+, bottom) , according to the examples.

[0040] FIG. 13 A is a graph of the plot of charge, discharge capacity (normalized to theoretical capacity), coulombic and energy efficiency versus cycle number for RFB-cell cycling with tanks loaded each with 5 mL of 250 mg DPA@KB-10&SE in 0.1M TBAPFe in 1 : 1 ratio of CEECN: y-valerolactone. The flow rate 8 mL / min per channel, cycled at 1C- rate for 24 cycles (24 hours or about 1 day), according to the examples. DPA = diphenyl anthracene.

[0041] FIG. 13B is a figure showing the potential controlled electrochemical impedance spectroscopy of DPA@KB-10&SE in 0.1M TBAPFe in 1 : 1 ratio of CEECN: y- valerolactone, where the flow rate 8 mL / min was used per channel, according to the examples. DPA = diphenyl anthracene.

[0042] FIG. 14A is a figure showing the plot of charge, discharge capacity (normalized to theoretical capacity), coulombic and energy efficiency versus cycle number for RFB-cellcycling with tanks loaded each with 5 mL of 250 mg DB-134@KB-10&SE in 0.1M TBAPFe in 1 : 1 ratio of CH3CN: y-valerolactone, at a flow rate of 8 mL / min per channel, cycled at IC-rate for 12 cycles (12 hours, about 0.5 day), according to the examples. DB = Disperse Blue 134 (DB-134) or (l,4-bis(isopropylamino) anthraquinone).

[0043] FIG. 14B is a figure showing the potential controlled electrochemical impedance spectroscopy of DB-134@KB-10&SE in 0.1M TBAPFe in 1 : 1 ratio of CH3CN: - valerolactone, at a flow rate of 8 mL / min per channel before and after RFB cycling, according to the examples. DB = Disperse Blue 134 (DB-134) or (l,4-bis(isopropylamino) anthraquinone).DETAILED DESCRIPTION

[0044] Various embodiments are described hereinafter. It should be noted that the specific embodiments are not intended as an exhaustive description or as a limitation to the broader aspects discussed herein. One aspect described in conjunction with a particular embodiment is not necessarily limited to that embodiment and can be practiced with any other embodiment s).

[0045] As used herein, “about” will be understood by persons of ordinary skill in the art and will vary to some extent depending upon the context in which it is used. If there are uses of the term which are not clear to persons of ordinary skill in the art, given the context in which it is used, “about” will mean up to plus or minus 10% of the particular term.

[0046] The use of the terms “a” and “an” and “the” and similar referents in the context of describing the elements (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein may be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g.,“such as”) provided herein, is intended merely to better illuminate the embodiments and does not pose a limitation on the scope of the claims unless otherwise stated. No language in the specification should be construed as indicating any non-claimed element as essential.

[0047] In general, “substituted” refers to an alkyl, alkenyl, alkynyl, aryl, or ether group, as defined below (e.g., an alkyl group) in which one or more bonds to a hydrogen atom contained therein are replaced by a bond to non-hydrogen or non-carbon atoms. Substituted groups also include groups in which one or more bonds to a carbon(s) or hydrogen(s) atom are replaced by one or more bonds, including double or triple bonds, to a heteroatom. Thus, a substituted group will be substituted with one or more substituents, unless otherwise specified. In some embodiments, a substituted group is substituted with 1, 2, 3, 4, 5, or 6 substituents. Examples of substituent groups include: halogens (i.e., F, Cl, Br, and I); hydroxyls; alkoxy, alkenoxy, alkynoxy, aryloxy, aralkyloxy, heterocyclyloxy, and heterocyclylalkoxy groups; carbonyls (oxo); carboxyls; esters; urethanes; oximes; hydroxylamines; alkoxyamines; aralkoxyamines; thiols; sulfides; sulfoxides; sulfones; sulfonyls; sulfonamides; amines; N-oxides; hydrazines; hydrazides; hydrazones; azides; amides; ureas; amidines; guanidines; enamines; imides; isocyanates; isothiocyanates; cyanates; thiocyanates; imines; nitro groups; nitriles (i.e., CN); and the like.

[0048] As used herein, “alkyl” groups include straight chain and branched alkyl groups having from 1 to about 20 carbon atoms, and typically from 1 to 12 carbons or, in some embodiments, from 1 to 8 carbon atoms. As employed herein, “alkyl groups” include cycloalkyl groups as defined below. Alkyl groups may be substituted or unsubstituted. Examples of straight chain alkyl groups include methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, and n-octyl groups. Examples of branched alkyl groups include, but are not limited to, isopropyl, sec-butyl, t-butyl, neopentyl, and isopentyl groups. Representative substituted alkyl groups may be substituted one or more times with, for example, amino, thio, hydroxy, cyano, alkoxy, and / or halo groups such as F, Cl, Br, and I groups. As used herein the term haloalkyl is an alkyl group having one or more halo groups. In some embodiments, haloalkyl refers to a per-haloalkyl group.

[0049] The term “alkylene” refers to a saturated linear divalent hydrocarbon moiety or a branched saturated divalent hydrocarbon moiety. Exemplary alkylene groups include, butare not limited to, methylene, ethylene, propylene, butylene, pentylene, 2-methylpropylene, and the like.

[0050] The term “heteroalkylene” refers to an alkylene group as defined herein in which one or more chain atoms or hydrogen atoms are replaced with a heteroatom such as O, N, P, or S. Exemplary heteroalkylenes include, but are not limited to, polyethylene glycol derived heteroalkylenes such as PEG2 (i.e, 2 molecules of ethylene glycols are linked), PEG3, 2-m ethoxy ethylene, 2 -hydroxy ethyl, 2,3 -dihydroxypropyl, etc.

[0051] Cycloalkyl groups are cyclic alkyl groups such as, but not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl groups. In some embodiments, the cycloalkyl group has 3 to 8 ring members, whereas in other embodiments the number of ring carbon atoms range from 3 to 5, 6, or 7. Cycloalkyl groups may be substituted or unsubstituted. Cycloalkyl groups further include polycyclic cycloalkyl groups such as, but not limited to, norbornyl, adamantyl, bornyl, camphenyl, isocamphenyl, and carenyl groups, and fused rings such as, but not limited to, decalinyl, and the like. Cycloalkyl groups also include rings that are substituted with straight or branched chain alkyl groups as defined above. Representative substituted cycloalkyl groups may be monosubstituted or substituted more than once, such as, but not limited to: 2,2-; 2,3-; 2,4-; 2,5-; or 2,6-disubstituted cyclohexyl groups or mono-, di-, or tri -substituted norbornyl or cycloheptyl groups, which may be substituted with, for example, alkyl, alkoxy, amino, thio, hydroxy, cyano, and / or halo groups.

[0052] Alkenyl groups are straight chain, branched or cyclic alkyl groups having 2 to about 20 carbon atoms, and further including at least one double bond. In some embodiments alkenyl groups have from 1 to 12 carbons, or, typically, from 1 to 8 carbon atoms. Alkenyl groups may be substituted or unsubstituted. Alkenyl groups include, for instance, vinyl, propenyl, 2-butenyl, 3-butenyl, isobutenyl, cyclohexenyl, cyclopentenyl, cyclohexadienyl, butadienyl, pentadienyl, and hexadienyl groups among others. Alkenyl groups may be substituted similarly to alkyl groups. Divalent alkenyl groups, i.e., alkenyl groups with two points of attachment, include, but are not limited to, CH-CH=CH2, C=CH2, or C=CHCH3.

[0053] As used herein, “aryl” or “aromatic,” groups are cyclic aromatic hydrocarbons that do not contain heteroatoms. Aryl groups include monocyclic, bicyclic and polycyclic ring systems. Thus, aryl groups include, but are not limited to, phenyl, azulenyl, heptalenyl, biphenylenyl, indacenyl, fluorenyl, phenanthrenyl, triphenylenyl, pyrenyl, naphthacenyl, chrysenyl, biphenyl, anthracenyl, indenyl, indanyl, pentalenyl, and naphthyl groups. In some embodiments, aryl groups contain 6-14 carbons, and in others from 6 to 12 or even 6- 10 carbon atoms in the ring portions of the groups. The phrase “aryl groups” includes groups containing fused rings, such as fused aromatic-aliphatic ring systems (e.g., indanyl, tetrahydronaphthyl, and the like). Aryl groups may be substituted or unsubstituted.

[0054] As used herein, “arylene” refers to a bivalent group derived from an arene where a hydrogen atom has been removed from two ring carbon atoms.

[0055] Heteroalkyl group include straight and branched chain alkyl groups as defined above and further include 1, 2, 3, 4, 5, or 6 heteroatoms independently selected from oxygen, sulfur, and nitrogen. Thus, heteroalkyl groups include 1 to 12 carbon atoms, 1 to 10 carbons or, in some embodiments, from 1 to 8, or 1, 2, 3, 4, 5, or 6 carbon atoms, or any range therein (e.g., 1-4). Examples of heteroalkyl groups include, but are not limited to, -(CH2CH2O)I-5CH3, -(CH2)I-6O(CH2)I-6 CH3, -(CH2)i-6NRa(CH2)i-6 CH3, -(CH2)I-6S(CH2)I-6 CH3, -(CH2)I-6O(CH2)I-6O(CH2)I-6 CH3, -(CH2)I-6NRa(CH2)i-6NRa(CH2)i-6CH3, -(CH2)I-6O(CH2)I-6O(CH2)I-6O(CH2)I-6CH3, -(CH2)i-6NRa(CH2)i-6NRa(CH2)i-6NRa(CH2)i-6CH3, with the total number of carbon atoms in the heteroalkyl group being 1 to 12 and Rais a hydrogen or a substituted or unsubstituted alkyl, alkenyl, aryl or aralkyl group. Other examples of heteroalkyl groups include, but are not limited to, groups having different heteroatoms in a single group. Such examples of heteroalkyl groups include, but are not limited to, -(CH2)I-6S(CH2)I-6O(CH2)I-6, -(CH2)I-6NTG(CH2)I-6)O(CH2)I-6, -(CH2)i-6O(CH2)I-6NRa(CH2)i-6S(CH2)i-6, -(CH2)i-6NRa(CH2)i-6O(CH2)i-6S(CH2)i-6, with the total number of carbon atoms in the heteroalkyl group being 1 to 12. In some embodiments, heteroalkyl groups include, but are not limited to, polyoxyethylene groups, such as - (OCH2CH2-)I-SCH3, for example, -O(CH2)2O(CH2)2OCH3, -O(CH2)2O(CH2)2O(CH2)2OCH3, - O(CH2)2O(CH2)2O(CH2)2O(CH2)2OCH3.

[0056] Aralkyl groups are substituted aryl groups in which an alkyl group as defined above has a hydrogen or carbon bond of the alkyl group replaced with a bond to an aryl group as defined above. In some embodiments, aralkyl groups contain 7 to 14 carbon atoms, 7 to 10 carbon atoms, e.g., 7, 8, 9, or 10 carbon atoms or any range therein (e.g., 7- 8). Aralkyl groups may be substituted or unsubstituted. Substituted aralkyl groups may be substituted at the alkyl, the aryl or both the alkyl and aryl portions of the group. Representative substituted and unsubstituted alkaryl groups include but are not limited to alkylphenyl such as methylphenyl, (chloromethyl)phenyl, chloro(chloromethyl)phenyl, or fused alkaryl groups such as 5-ethylnaphthalenyl.

[0057] Heterocyclyl groups are non-aromatic ring compounds containing 3 or more ring members, of which one or more is a heteroatom such as, but not limited to, N, O, and S. In some embodiments, the heterocyclyl group contains 1, 2, 3 or 4 heteroatoms. In some embodiments, heterocyclyl groups include mono-, bi- and tricyclic rings having 3 to 16 ring members, whereas other such groups have 3 to 6, 3 to 10, 3 to 12, or 3 to 14 ring members. Heterocyclyl groups encompass partially unsaturated and saturated ring systems, such as, for example, imidazolinyl and imidazolidinyl groups. The phrase also includes bridged polycyclic ring systems containing a heteroatom such as, but not limited to, quinuclidyl. The phrase also includes heterocyclyl groups that have other groups, such as alkyl, oxo or halo groups, bonded to one of the ring members, referred to as “substituted heterocyclyl groups.” Heterocyclyl groups include, but are not limited to, aziridinyl, azetidinyl, pyrrolidinyl, imidazolidinyl, pyrazolidinyl, thiazolidinyl, tetrahydrothiophenyl, tetrahydrofuranyl, dioxolyl, pyrrolinyl, piperidyl, piperazinyl, morpholinyl, thiomorpholinyl, tetrahydropyranyl, and tetrahydrothiopyranyl groups. Representative substituted heterocyclyl groups may be mono-substituted or substituted more than once, such as, but not limited to, morpholinyl groups, which are 2-, 3-, 4-, 5-, or 6-substituted, or disubstituted with various substituents such as those listed above. The heteroatom(s) may also be in oxidized form, if chemically possible.

[0058] Heteroaryl groups are aromatic ring compounds containing 5 or more ring members, of which, one or more is a heteroatom such as, but not limited to, N, O, and S. Heteroaryl groups include, but are not limited to, groups such as pyrrolyl, pyrazolyl,triazolyl, tetrazolyl, oxazolyl, isoxazolyl, thiazolyl, pyridinyl, pyridazinyl, pyrimidinyl, pyrazinyl, thiophenyl, benzothiophenyl, furanyl, imidazolyl, benzofuranyl, indolyl, azaindolyl (pyrrolopyridinyl), indazolyl, benzimidazolyl, imidazopyridinyl (azabenzimidazolyl), pyrazolopyridinyl, triazolopyridinyl, benzotriazolyl, benzoxazolyl, benzothiazolyl, benzothiadiazolyl, imidazopyridinyl, isoxazolopyridinyl, thianaphthyl, purinyl, xanthinyl, adeninyl, guaninyl, quinolinyl, isoquinolinyl, tetrahydroquinolinyl, quinoxalinyl, and quinazolinyl groups. Heteroaryl groups include fused ring compounds in which all rings are aromatic such as indolyl groups and include fused ring compounds in which only one of the rings is aromatic, such as 2,3-dihydro indolyl groups. The phrase “heteroaryl groups” includes fused ring compounds and also includes heteroaryl groups that have other groups bonded to one of the ring members, such as alkyl groups, referred to as “substituted heteroaryl groups.” Representative substituted heteroaryl groups may be substituted one or more times with various substituents such as those listed above. The heteroatom(s) may also be in oxidized form, if chemically possible.

[0059] The term “halogen” or “halo” as used herein refers to bromine, chlorine, fluorine, or iodine. In some embodiments, the halogen is fluorine. In other embodiments, the halogen is chlorine or bromine. The term “halide” as used herein refers to the anion of a halogen, such as bromide, chloride, fluoride, and iodide. In some embodiments, the halide is chloride or iodide.

[0060] The terms “alkoxy” refers to a substituted or unsubstituted alkyl group bonded to an oxygen atom, such as a moiety of the formula -ORa, wherein Rais alkyl as defined herein. Examples include but are not limited to methoxy and ethoxy. Representative substituted alkoxy groups may be substituted one or more times with substituents such as those listed above, such as methoxymethyl and fluoromethoxy.

[0061] The term “alkylamino” refers to a moiety of the formula -NHRa, where Rais alkyl as defined herein.

[0062] The term “dialkyl amino” refers to a moiety of the formula -NRaRb, wherein Raand Rbare independently alkyl as defined herein.

[0063] Disclosed herein are semi-solid (slurry) redox flow battery systems that include conjugated heterocyclic carbenium compounds or organic redox active compounds (e.g., anthraquinones and anthracenes) as both the anolyte and catholyte and electroconductive active carbon, wherein such compounds are redox active compounds that can reversibly be reduced and oxidized. This disclosure reports the use of a slurry electrolyte in which a stable carbocation is deposited on a conductive material. The mixture is suspended in a solvent used as electrolyte for organic redox flow batteries (RFBs). The components of the slurry battery closely resemble those of traditional solution-based flow batteries, including electrolyte reservoirs, electrodes, separators, and the battery framework. The primary distinction lies in the dispersion state of the active material (from solution to suspension) and the conductive electrode (from porous carbon felt in solution-based RFBs to none, in order to prevent filtration and sedimentation of the redox-active material). By substituting solution-based electrolytes with stable, non-settling alternatives, the dispersed redox-active materials slurry redox flow batteries disclosed herein exhibit the benefits of flow batteries with the high energy-density of solid redox-active materials.

[0064] As shown in the Examples, by substituting solution-based electrolytes with stable, non-settling alternatives, the semi solid organic redox flow batteries disclosed herein exhibit the benefits of flow batteries with the high energy-density of solid redox-active materials. For instance, semi-solid organic redox flow battery as disclosed herein with a slurry molarity of 12M, constituting less than 20% in mole of solvent, exhibited an energy density of 370Wh / L, rivaling lithium batteries (about 400Wh / L).

[0065] As described herein, the semi-solid catholyte and a semi solid anolyte of the redox flow battery each comprise the active compound (a conjugated heterocyclic compound or an organic redox active compound, such as anthraquinone and anthracene) and electroconductive active carbon. The electroconductive active carbon may be carbon particles as illustrated in Example 1. The electroconductive active carbon (e.g., carbon black, such as Ketjenblack EC-600JD) may also be mechanically functionalized by ballmilling the electroconductive active carbon with the active compound as illustrated in Example 2. Also Example 3 shows that ball milling the electrolyte, the active carbon, andan electrolyte salt together provides higher energy efficiency, columbic efficiency, and cyclability (See FIG. 11 A).

[0066] A redox flow battery includes a semi-solid catholyte comprising a conjugated heterocyclic compound in a first oxidation state and a first electroconductive active carbon; and a semi-solid anolyte comprising a conjugated heterocyclic compound in a second oxidation state and a second electroconductive active carbon; wherein the first oxidation state is a higher oxidation state than the second oxidation state. In this context, “higher oxidation state’ refer to a state that is both positive and larger.

[0067] In some embodiments, the conjugated heterocyclic compound in the first oxidation state is a conjugated heterocyclic cationic compound, and / or wherein the conjugated heterocyclic compound in the second oxidation state is a conjugated heterocyclic cationic compound.

[0068] Provided in one aspect is a redox flow battery including: a semi-solid catholyte including a conjugated heterocyclic carbenium compound and a first electroconductive active carbon; and a semi-solid anolyte including of the conjugated heterocyclic carbenium compound and a second electroconductive active carbon. In some embodiments, the conjugated heterocyclic carbenium compound in the catholyte comprises a radical dication and / or wherein the conjugated heterocyclic carbenium compound in the anolyte comprises a neutral radical. “Same compound” as used herein refers to two different species, such as the radical dication and neutral radical, while having different oxidation states / charges, have the same atomic components and structure of the cathodic and anodic species.

[0069] Provided in another aspect is a redox flow battery including: a semi-solid catholyte including a compound of Formula I and a first electroconductive active carbon; and a semisolid anolyte including the compound of Formula I and a second electroconductive active carbon; wherein the compound of Formula (I) is represented by the following structure disclosed herein. In some embodiments, the compound of Formula I in the catholyte comprises a radical dication and / or wherein the compound of Formula I in the anolyte comprises a neutral radical.

[0070] Provided in another aspect is a redox flow battery that includes a semi-solid catholyte comprising an organic redox active compound and first electroconductive active carbon; and a semi-solid anolyte comprising an organic redox active compound and second electroconductive active carbon. Such organic redox active compounds comprise a fused aromatic ring and is a compound of Formula (II) or Formula (III) as disclosed herein.

[0071] While the carbon felt and carbon black were used as non-limiting examples, any electroconductive active carbon materials comprising carbon black, mesoporous carbon, bio-sourced carbon, carbon nanotubes, graphene, graphite, carbon nanofiber, carbon aerogel, or carbon nanodots are suitable. In some embodiments, the first electroconductive active carbon and the second electroconductive active carbon comprise the same material. In some embodiments, the first electroconductive active carbon and the second electroconductive active carbon comprise different material.

[0072] In some embodiments, the conjugated heterocyclic compound in the catholyte is encapsulated or immobilized within the first electroconductive active carbon. In some embodiments, a supporting electrolyte is encapsulated or immobilized with the catholyte within the first electroconductive active carbon. In some embodiments, the encapsulation or immobilization is achieved by ball milling the conjugated heterocyclic compound, the first electroconductive active carbon, and the supporting electrolyte. The supporting electrolyte encapsulated or immobilized with the catholyte may be any one of the electrolyte salts described herein.

[0073] In some embodiments, the compound in the anolyte is encapsulated or immobilized within the second electroconductive active carbon. In some embodiments, a supporting electrolyte is encapsulated or immobilized with the anolyte within the second electroconductive active carbon. In some embodiments, the encapsulation or immobilization is achieved by ball milling the conjugated heterocyclic compound, the second electroconductive active carbon, and the supporting electrolyte. The supporting electrolyte encapsulated or immobilized with the anolyte may be any one of the electrolyte salts described herein.

[0074] In some embodiments, the compound and second electroconductive active carbon in the anolyte are present in a weight ratio of about 1 :9 to 9: 1. In some embodiments, the compound and second electroconductive active carbon in the anolyte are present in a weight ratio of about 1 :9. In some embodiments, a weight ratio of the compound to the first electroconductive active carbon in the catholyte is about 1 :9 to 9: 1. In some embodiments, a weight ratio of the compound to the first electroconductive active carbon in the catholyte is about 1 :9.Heterocyclic Carbenium Compounds

[0075] These conjugated heterocyclic carbenium ions are easily prepared from successive double S\Ar reactions between tris(2,6-dimethoxyphenyl)carbenium ion and primary amines at moderate-to-high temperatures with methanol elimination. These stable carbenium salts are of particular interest because: 1) they are among the most stable carbocation in the literature, including under mild acidic or basic aqueous conditions; 2) the stepwise and temperature dependence of the synthesis allows versatility by using aliphatic or aromatic amines, and forming unsymmetrical ions; 3) they can be functionalized via C-H borylation, and / or metal-catalyzed cross-coupling; and 4) the negative counterions can be exchanged to affect the physical and chemical properties of the salts. Not only are these conjugated heterocyclic carbenium compounds also highly fluorescent with large extinction coefficients and long fluorescence life times, these conjugated heterocyclic carbenium compounds are redox active species with three stable redox states: carbodi cation, carbocation, and neutral carboradical.

[0076] The redox states of the heterocyclic carbenium compounds are illustrated in the below Scheme. Neutral radical (C") and radical dication (C++') can lose and gain an electron respectively to form the carbocation (C+), resulting in the battery discharge and generation of electricity (Scheme 1; steps with dashed arrows). Alternately, the carbocation (C+) can gain or lose an electron to convert to the neutral radical (C") or radical dication (C++') respectively, resulting in battery charge (Scheme A; steps with solid arrows).Scheme A

[0077] Their stability, reduction and oxidation potential, solubility in organic solvent, and tunability via simple organic transformation make these compounds ideal candidates to be tested as the anolyte and catholyte for RFBs.

[0078] The conjugated heterocyclic carbenium compounds disclosed herein are compounds of Formula I. The compound of Formula (I) is represented by the following structure:wherein:X is -4, -3, -2, -1, 0, +1, +2, +3, or +4; each Rla, Rlb, Rlc, Rld, R2a, R2b, R2c, R2d, R3a, R3b, R3c, and R3dis independently H, halide, CF3, CBrs, CI3, NH2, C1-C12 alkyl, C1-C4 alkoxy, C1-C4 alkylamino, C1-C4 dialkyl amino, NO2, CN, CO2R, or Ar1; or R2aand R3dtogether form -X1-; or Rlaand R2dtogether form -X2-; or Rldand R3atogether form -X3-; or Rlaand Rlbtogether with atoms to which they are attached to form a phenyl; or R2Cand R2dtogether with atoms to which they are attached to form a phenyl; each X1, X2and X3is independently O, NR4a, PR4a, CR4aR4b, or SiR4aR4b; each R4aand R4bis independently H, halide, CF3, C1-C12 alkyl, C1-C4 alkoxy, C1-C4 alkylamino, C1-C4 dialkyl amino, Ar3, -L- Ar3, -L-Z, or -L2-Z2;each Y is independently H, halide, 0R5a, NR5aR5b, PR5aR5b, NO2, CN, CF3, CO2R, N3, or Ar2; each R5a, and R5bis independently H, CF3, C1-C12 alkyl, C1-C4 alkoxy, C1-C4 alkylamino, C1-C4 dialkyl amino, Ar4, -L1- Ar4, or -i -Z1; each L and L1is independently C1-C12 alkylene, C1-C12 heteroalkylene, or arylene; each L2is independently C1-C12 alkylene;Z and Z1are each independently -N(R6a)3W or a moiety comprising a conjugated heterocyclic carbenium; each R6ais independently C1-C12 alkyl; each W is independently tetrafluoroborate, hexafluorophosphate, perchlorate, tetrary lb orate, trifluoromethanesulfonate, oxalatob orate, oxalate, phosphate, bis- trifluoromethanesulfonimide, halide, hydroxide, carbonate, bicarbonate, sulfate, hydrogen sulfate, or sulfite;Z2is each independently -(OCFhCFhOjiiCFh; n is each independently 1 to 20; each R is independently C1-C12 alkyl or aryl;Ar1, Ar2, Ar3,and Ar4are each independently unsubstituted or substituted phenyl or unsubstituted or substituted heteroaryl; each Ar1, Ar2, Ar3,and Ar4is independently substituted with 0 to 5 substituents; the substituents are each independently selected from the group consisting of halide, CF3, NH2, C1-C4 alkyl, C1-C4 alkoxy, C1-C4 alkylamino, Ci- C4 dialkyl amino, NO2, CN, or aryl.

[0079] In some embodiments, wherein: X is -4, -3, -2, -1, 0, +1, +2, +3, or +4; each Rla, Rlb, Rlc, Rld, R2a, R2b, R2C, R2d, R3a, R3b, R3c, and R3dis independently H, halide, CF3, CBn, CI3, NH2, C1-C12 alkyl, C1-C4 alkoxy, C1-C4 alkylamino, C1-C4 dialkyl amino, NO2, CN, CO2R, or Ar1; or R2aand R3dtogether form -X1-; or Rlaand R2dtogether form -X2-; or Rldand R3atogether form -X3-; or Rlaand Rlbtogether with atoms to which they are attached to form a phenyl; or R2cand R2dtogether with atoms to which they are attached to form a phenyl; each X1, X2and X3is independently O, NR4a, PR4a, CR4aR4b, or SiR4aR4b; each R4aand R4bis independently H, halide, CF3, C1-C12 alkyl, C1-C4 alkoxy, C1-C4 alkylamino, Ci- C4 dialkyl amino, Ar3, -L- Ar3, -L-Z, or -L2-Z2; each Y is independently H, halide, OR5a, NR5aR5b, PR5aR5b, NO2, CN, CF3, CO2R, N3, or Ar2; each R5a, and R5bis independently H,CF3, C1-C12 alkyl, C1-C4 alkoxy, C1-C4 alkylamino, C1-C4 dialkyl amino, Ar4, -L1- Ar4, or -L1-1; each L and L1is independently C1-C12 alkylene, C1-C12 heteroalkylene, or arylene; each L2is independently C1-C12 alkylene; Z and Z1are each independently a moiety comprising a conjugated heterocyclic carbenium; Z2is each independently - (OCFbCFbOjnCHs; n is each independently 1 to 20; each R is independently C1-C12 alkyl or aryl; Ar1, Ar2, Ar3,and Ar4are each independently unsubstituted or substituted phenyl or unsubstituted or substituted heteroaryl; each Ar1, Ar2, Ar3,and Ar4is independently substituted with 0 to 5 substituents; the substituents are each independently selected from the group consisting of halide, CF3, NH2, C1-C4 alkyl, C1-C4 alkoxy, C1-C4 alkylamino, Ci- C4 dialkyl amino, NO2, CN, or aryl.

[0080] In some embodiments, the compound of Formula I is a compound of Formula la,Formula lb, or Formula Ic:

[0081] In some embodiments, X is -4, -3, -2, -1, 0, 1, 2, 3, or 4. In some embodiments, each X1, X2, and X3is independently O or NR4a. In some embodiments, X1is O or NR4a. In some embodiments, X2is O or NR4a. In some embodiments, X3is O or NR4a.

[0082] In some embodiments, each R4ais independently C1-C12 alkyl, C1-C4 alkoxy, C1-C4 alkylamino, C1-C4 dialkyl amino, Ar3, -L-Ar3, -L-Z, or -L2-Z2. In some embodiments,each R4ais independently C1-C12 alkyl, C1-C4 alkoxy, C1-C4 alkylamino, C1-C4 dialkyl amino, Ar3, -L-Ar3, or -L-Z. In some embodiments, R4ais C1-C12 alkyl. In some embodiments, R4ais C1-C4 alkoxy. In some embodiments, R4ais C1-C4 alkylamino. In some embodiments, R4ais C1-C4 dialkyl amino. In some embodiments, R4ais Ar3. In some embodiments, R4ais -L-Ar3. In some embodiments, R4ais -L-Z. In some embodiments, R4ais -L2-Z2.

[0083] In some embodiments, each R4ais independently methyl, ethyl, propyl, butyl, pentyl, hexyl, -(CH2)-N(Me)2, -(CH2)2-N(Me)2, -(CH2)3-N(Me)2, -(CH2)3-N(Me)2, - (CH2)4-N(Me)2, -(CH2)2-Ar3, -(CH2)3-Ar3, -(CH2)3-Ar3, or -(CH2)4-Ar3; and Ar3is 2- pyridinyl. In some embodiments, R4ais methyl, ethyl, propyl, butyl, pentyl, or hexyl. In some embodiments, R4ais -(CH2)-N(Me)2, -(CH2)2-N(Me)2, -(CH2)3-N(Me)2, -(CH2)3- N(Me)2, or -(CH2)4-N(Me)2. In some embodiments, R4ais -(CH2)2-Ar3, -(CH2)3-Ar3, - (CH2)3-Ar3, or -(CH2)4-Ar3. In some embodiments, Ar3is pyridinyl, such as 2-pyridinyl. In some embodiments, R4ais -(CH2)-(OCH2CH2O)nCH3; wherein n is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20. In some embodiments, R4ais -(CH2)2- (OCH2CH2O)nCH3; wherein n is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20. In some embodiments, R4ais -(CH2)3-(OCH2CH2O)nCH3; wherein n is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20. In some embodiments, R4ais - (CH2)4-(OCH2CH2O)nCH3; wherein n is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20. In some embodiments, R4ais -(CH2)3-(OCH2CH2O)nCH3; wherein n is 1.

[0084] In some embodiments, each Rlb, Rlc, R2b, R2c, R3b, and R3cis independently H; R2aand R3dtogether form -O-; each Y is independently H; Rlaand R2dtogether form -NR4a-; Rldand R3atogether form -NR4a-; and each R4ais -CH2-CH2-CH3 or -CH2-CH2-CH2-CH3..

[0085] In some embodiments, Rlaand R2dtogether form -NR4a- and Rldand R3atogether form -NR4a-; each R4ais-L-Z; and each L independently C1-C12 alkylene; each Z independently -N(R6a)3W; each R6ais independently C1-C12 alkyl; and each W is independently tetrafluoroborate, hexafluorophosphate, perchlorate, tetrarylborate, trifluoromethanesulfonate, oxalatob orate, oxalate, phosphate, bis- trifluoromethanesulfonimide, halide, hydroxide, carbonate, bicarbonate, sulfate, hydrogen sulfate, or sulfite.

[0086] In some embodiments, each Rlb, Rlc, R2b, R2c, R3b, and R3cis independently H; R2aand R3dare each methoxy; each Y is independently H; Rlaand R2dtogether form -NR4a-; and Rldand R3atogether form -NR4aeach R4ais -CH2-CH2-N(Me)3W or -CH2-CH2-CH2- N(Me)3W; and each W is independently tetrafluoroborate, hexafluorophosphate, perchlorate, tetrarylborate, trifluoromethanesulfonate, oxalatoborate, oxalate, phosphate, bis-trifluoromethanesulfonimide, halide, hydroxide, carbonate, bicarbonate, sulfate, hydrogen sulfate, or sulfite. In some embodiments, W is independently hexafluorophosphate or trifluoromethanesulfonate.

[0087] In some embodiments, each Rlb, Rlc, R2b, R2c, R3b, and R3cis independently H; R2aand R3dtogether form -O-; each Y is independently H; Rlaand R2dtogether form -NR4a-; Rldand R3atogether form -NR4aeach R4ais -CH2-CH2-N(Me)3W or -CH2-CH2-CH2- N(Me)3W; and each W is independently tetrafluorob orate, hexafluorophosphate, perchlorate, tetrarylborate, trifluoromethanesulfonate, oxalatoborate, oxalate, phosphate, bis-trifluoromethanesulfonimide, halide, hydroxide, carbonate, bicarbonate, sulfate, hydrogen sulfate, or sulfite. In some embodiments, W is independently hexafluorophosphate or trifluoromethanesulfonate.

[0088] In some embodiments, Y is an electron-withdrawing substituent. In some instances, the additional of an electron withdrawing, such as NO2, improves the stability to oxygen and also adds a reduction potential, allowing the storage of more than one electron per molecule. In some embodiments, the compound of Formula I has one, two, or three Y groups, where Y is NO2. In some embodiments, Y is an electron donating substituent. In some embodiments, each Y is independently H or NO2. In some embodiments, each Y is H. In some embodiments, Y is NO2. In some embodiments, Y is NR5aR5bwith each R5aand R5bis independently C1-C12 alkyl. In some embodiments, Y is N(Me)2.

[0089] In some embodiments, Rlaand R2dare each C1-C4 alkoxy. In some embodiments, Rlais C1-C4 alkoxy, such as methoxy or ethoxy. In some embodiments, R2dis C1-C4 alkoxy, such as methoxy or ethoxy.

[0090] In some embodiments, Rldand R3aare each C1-C4 alkoxy. In some embodiments, Rldis C1-C4 alkoxy, such as methoxy or ethoxy. In some embodiments, R3ais C1-C4 alkoxy, such as methoxy or ethoxy.

[0091] In some embodiments, each Rla, Rlb, Rlc, Rld, R2a, R2b, R2c, R2d, R3a, R3b, R3c, and R3dis independently H. In some embodiments, each Rlb, Rlc, R2b, R2c, R3b, and R3cis independently H. In some embodiments, Rlbis H. In some embodiments, Rlcis H. In some embodiments, R2bis H. In some embodiments, R2cis H. In some embodiments, R3bis H.

[0092] In some embodiments, the compound of Formula la is a compound, wherein: X1is each NR4a; each R4ais independently C1-C12 alkyl, C1-C4 dialkyl amino, -L-Ar3, or -L2-Z2; RlaRld, R3a, and R2dare each C1-C4 alkoxy; each Rlb, Rlc, R2b, R2c, R3b, and R3cis independently H, C1-C4 alkylamino, or NO2; each Y is independently H, NO2, orNR5aR5b; and each R5aand R5bis independently H, CF3, or C1-C12 alkyl..

[0093] In some embodiments, X1is each NR4a. In some embodiments, each R4ais C1-C12 alkyl. In some embodiments, each R4ais C1-C4 dialkyl amino. In some embodiments, each R4ais -L-Ar3. In some embodiments, each R4ais -L2-Z2. In some embodiments, RlaRld, R3a, and R2dare each C1-C4 alkoxy. In some embodiments, each Rlb, Rlc, R2b, R2c, R3b, and R3Cis independently H or C1-C4 alkylamino. In some embodiments, each Rlb, Rlc, R2b, R2c, R3b, and R3cis independently H or NO2. In some embodiments, each Y is independently H or NCh. In some embodiments, each Y is independently H, or NR5aR5b. In some embodiments, each R5aand R5bis independently H or C1-C12 alkyl.

[0094] In some embodiments, the compound of Formula lb is a compound, wherein: each R4ais independently C1-C12 alkyl, C1-C4 dialkyl amino, -L-Ar3, or -L2-Z2;X2and X3are each NR4a;Rlaand R2dare each C1-C4 alkoxy; each Rlb, Rlc, R2b, R2c, R3b, and R3cis independently H, C1-C4 alkylamino, or NO2; each Y is independently H, NO2, or NR5aR5b; and each R5aand R5bis independently H, CF3, or C1-C12 alkyl..

[0095] In some embodiments, X2and X3are each NR4a. In some embodiments, each R4ais C1-C12 alkyl. In some embodiments, each R4ais C1-C4 dialkyl amino. In some embodiments, each R4ais -L-Ar3. In some embodiments, each R4ais -L2-Z2. In some embodiments, Rlaand R2dare each C1-C4 alkoxy. In some embodiments, each Rlb, Rlc, R2b, R2C, R3b, and R3cis independently H or C1-C4 alkylamino. In some embodiments, each Rlb,RicR2bR2cR3band R3c is independently H or NO2. In some embodiments, each Y is independently H or NO2. In some embodiments, each Y is independently H, or NR5aR5b. In some embodiments, each R5aand R5bis independently H or C1-C12 alkyl.

[0096] In some embodiments, the compound of Formula lb is a compound, wherein: X2and X3are each NR4a; each R4ais independently C1-C12 alkyl, C1-C4 dialkyl amino, or-L-Ar3;Rlaand R2dare each C1-C4 alkoxy; each Rlb, Rlc, R2b, R2c, R3b, and R3cis independently H; and each Y is independently H or NO2.

[0097] In any of the embodiment described herein, the compound of Formula I may include functional groups that improves the solubility of the compound or the compound in its redox states in an organic solvent, such as CH3CN, sulfolane, or y-valerolactone. These functional groups include oligomeric functionality that can increase solubility, such as PEGyl chains (-(OCFbCFFC^nCHs) as shown in the below compound.

[0098] In some embodiments, the compound of Formula I is a compound of any one of the following:

[0099] In some embodiments, the compound of Formula I is a compound of any one of the following:

[0100] The compounds of Formula I described herein further include a counter anion. Exemplary counter anions of carbocation of Formula I include, but are not limited to, any anion including, but not limited to, halides (e.g., Cl, F, I, and Br), an anion derived from organic compounds such as carboxylates, phosphates, sulfates, etc. In some embodiments, the compound of formula I further includes an anion selected from tetrafluoroborate, hexafluorophosphate, perchlorate, tetrarylborate, trifluoromethanesulfonate, oxalatob orate, oxalate, phosphate, bis-trifluoromethanesulfonimide, halide, anion of an ionic liquid, hydroxide, carbonate, bicarbonate, sulfate, hydrogen sulfate, sulfite; or a mixture of any two or more thereof. In some embodiments, the compound of formula I further comprises an anion selected from tetrafluoroborate, hexafluorophosphate, or a mixture of any two or more thereof.

[0101] In some embodiments, Z and Z1are each independently a moiety including a conjugated heterocyclic carbenium. The moiety including the conjugated heterocyclic carbenium may be a compound of Formula I, including compounds of Formula la, lb, and Ic as described herein. In some instances, when Z and Z1are each independently a moiety including a conjugated heterocyclic carbenium, the resulting compound is a compound that includes two or more conjugated heterocyclic carbeniums. For instance, a compound of Formula lb may be covalently linked by a arylene, alkylene, or heteroalkylene linker toanother compound of Formula lb, or a compound of Formula Ic covalently linked by a arylene, alkylene, or heteroalkylene linker to another compound of Formula Ic.Organic Redox Active Compounds

[0102] The organic redox active compounds disclosed herein are compounds comprising a fused aromatic ring. Such compounds are compounds of Formula II or Formula III.

[0103] The organic redox active compounds described herein may be a compound of Formula (II) represented by the following structure or a salt thereof:wherein: each R1, R2, R3, R4, R6, R7, and R8is independently H, halide, CF3, CBn, CI3, OR9, C1-C12 alkyl, C1-C4 alkoxy, aryl, NO2, CN, CO2R9, NR9R10, C(O)NR9R10, NR9C(O)R10, SO3H, +N R9R10Rn, P(O)OR9OR10or -(CH2CH2O)n-R9;R9, R10and R11are each independently H, C1-C12 alkyl, C1-C4 alkoxy, aryl, or -L-Z; each L is C1-C12 alkylene; each Z is SO3’, P(O)OR12OR13,+NR12R13R14, -(CH2CH2O)n-R12;R12, R13and R14are each independently H, C1-C12 alkyl, C1-C4 alkoxy, or aryl; and each n is an integer from 1 to 20.

[0104] In some embodiments, each R1, R2, R3, R4, R6, and R7is independently H; each R5and R8is NR9R10; and each R9and R10are independently H or C1-C4 alkyl. In some embodiments, each R5and R8is -NH(iPr)2.

[0105] In other embodiments, the organic redox active compounds described herein may be a compound of Formula (III) represented by the following structure or a salt thereof:(Formula III), wherein: each R1, R2, R3, R4, R5, R6, R7, R8, R9, and R10is independently H, halide, CF3, CBn, CI3, OR9, C1-C12 alkyl, C1-C4 alkoxy, aryl, NO2, CN, CO2R9, NR9R10, C(O)NR9R10, NR9C(O)R10, SO3H, +N R9R10Rn, P(O)OR9OR10or -(CH2CH2O)n-R9;R9, R10and R11are each independently H, C1-C12 alkyl, C1-C4 alkoxy, aryl, or -L-Z; each L is C1-C12 alkylene; each Z is SO3’, P(O)OR12OR13,+NR12R13R14, -(CH2CH2O)n-R12;R12, R13and R14are each independently H, C1-C12 alkyl, C1-C4 alkoxy, or aryl; and each n is an integer from 1 to 20.

[0106] In some embodiments, each R1, R2, R3, R4, R5, R6, R7, R8, R9, and R10is independently H. In some embodiments, each R1, R2, R3, R4, R5, R6, R7, and R8is independently H; and each R9and R10is aryl. In some embodiments, each R9and R10is phenyl.

[0107] In some embodiments, the organic redox active compound is one of the following:Additional Components

[0108] In some embodiments, the redox flow battery, such as any one of the redox flow batteries described herein, further includes a separator positioned between the anolyte and the catholyte. In some embodiments, the redox flow battery further comprises a solvent and an electrolyte salt.

[0109] Any one of the redox flow batteries described herein may further include an electrolyte salt. In some embodiments, the electrolyte salt is a lithium, sodium, potassium, ammonium, alkylammonium, or phosphonium salt of tetrafluoroborate, hexafluorophosphate, perchlorate, tetrarylborate, trifluoromethanesulfonate, oxalatob orate, oxalate, phosphate, bis-trifluoromethanesulfonimide, halide; or a mixture of any two or more thereof. In some embodiments, the electrolyte is an alkylammonium salt of tetrafluoroborate, hexafluorophosphate, perchlorate, tetrarylborate, trifluoromethanesulfonate, oxalatob orate, oxalate, phosphate, bis- trifluoromethanesulfonimide, halide; or a mixture of any two or more thereof. In some embodiments, the alkylammonium salt is a tetrabutylammonium salt, tetraethylammonium salt, or a mixture thereof. In some embodiments, the electrolyte salt is tetrabutylammonium hexafluorophosphate, tetrabutylammonium tetrafluorob orate, tetraethylammonium tetrafluorob orate, or a mixture of any two or more thereof.

[0110] Any one of the redox flow batteries described herein may further include a solvent. In some embodiments, the solvent comprises a nitrile solvent, such as acetonitrile; an ether solvent, such as tetrahydrofuran; dimethylformamide; water; a halogenated solvent, such as dichloromethane; an ionic liquid; sulfolane, y-valerolactone; or any of one of these solvents in a mixture of acetonitrile, or propylene carbonate or any mixture thereof. In some embodiments, the solvent comprises a nitrile solvent, such as acetonitrile; an ether solvent, such as tetrahydrofuran; dimethylformamide; water; a halogenated solvent, such as dichloromethane; or an ionic liquid.Methods of Use[OHl] Provided in another aspect is a method of operating the redox flow battery, such as any one of the redox flow batteries described herein, including flowing the catholyte through a catholyte compartment and flowing the anolyte through an anolyte compartment, wherein the catholyte and anolyte compartments are separated by a separator and electron transfer from the anolyte to the catholyte is supported.EXAMPLES

[0112] Example 1. In this Example, the use of a slurry electrolyte in which a stable carbocation,nPrDAOTA[PF6‘] represented as C+in Examples 1-4, is deposited on a conductive material is reported. The mixture was suspended in a medium (i.e., solvent) and used as an electrolyte for organic redox flow batteries (RFBs). The structure ofnPrDAOTA [PF6-] is shown below:

[0113] Previous studies[1]demonstrated that the carbocation (C+) employed exhibited remarkable stability along 300 cycles and capacity retention above 99.84%, along with good energy efficiency (>50%) despite being absent from the solution at the end of cycling in full flow RFB (FIG. 1A).

[0114] It was observed that the content of the Ecreservoir decreased by more than 50% in the region corresponding to its electronic process (FIG. IB), while the content of the Ewreservoir underwent significant degradation, experiencing a 92% reduction in the area associated with its process, resulting in less than 10% of the initial CV's active electroactive material remaining in solution (FIG. IB). However, the cycling monitoring exhibited remarkable stability as mentioned earlier (FIG. 1 A).

[0115] These findings prompted further analysis through in situ potential electrochemical impedance spectroscopy (PEIS) on the carbon-felt electrodes within the RFB cell, and postdisassembling scanning electron microscopy (SEM) analysis on the surface of the electrode's carbon-based material employed (carbon felts, noted CF).

[0116] It was observed initially that the internal resistance of the system decreased during cycling, as evidenced by the PEIS experiment (FIG. 2A, -5% resistance, insert).Furthermore, this diminution in resistance seemed to be related to the formation of a conductive deposit on the CF electrodes (SEM images, FIG. 2B). The more pronounced electron intensity observed on the SEM pictures of CF Ewand Ecafter cycling indicatesimproved conductivity. This enhancement, as observed in this study, translates into an improved stability of C+redox active materials, thereby significantly strengthening the entire system and enabling it to undergo numerous cycles, mostly on the surfaces of electrodes coated with this conductive layer.

[0117] This led to the development of a protocol to assess the feasibility of a system based on the functionality of these CF electrodes. Initially, a first attempt on a C+solution in the presence of a dispersed carbon felt finely grounded, in a ratio of 1 :5 respectively was evaluated. CV analyses proved highly promising, with the entire C+retaining its necessary electrochemical characteristics for the proper functioning of the RFB (two totally reversible mono-electronic redox events, as illustrated in FIG 3 A). This also sidestepped the issue of a secondary reduction process at -2.15V (FIG. 3 A, grey arrow), which had proven problematic in previous studies by acting as a strong base. [2] However, despite these promising results, there was difficulty regarding the size of the CF particles, which were too large to be injected into the RFB cell and the tubing that were using. This issue may be addressed by employing a ball mill in the near future.

[0118] The second approach involved circulating a C+solution within a pre-assembled RFB cell and conducting 50 cycles under normal conditions. Post-cycling CV analysis revealed that some of the electroactive material had disappeared from the solution, indicating its likely deposition on the CF. Subsequently, the cell was rinsed without disassembly, and a solvent-only solution was used to conduct cycles (FIG. 3B). Remarkably, once normalized for functionalized CF quantity of 8% of C+, the system proved capable of achieving 50 cycles with good capacity retention and similar coulombic efficiency to its in-solution parents experience. The lower energy efficiency was attributed to energy losses due to the observed high dilution.

[0119] This approach facilitates a drastic increase in the energy density of targeted symmetric RFB systems (FIG. 4). For instance, comparing the solution results obtained with 12Wh / L over 3 generations of different active redox compounds, a slurry suspension with only 10% functionalized carbon, at a concentration of 7.5M suspended in a solvent (approximately about 30% in molarity of most organic solvents), could reach 46 Wh / L. With the same concentration, a C+:carbon ratio of 1 : 1 would elevate this value to 74 Wh / L.Additionally, in an aqueous example, for a slurry molarity of 12M, constituting less than 20% in mole of solvent, this energy density could reach 370Wh / L, rivaling lithium batteries (about 400Wh / L).

[0120] Beyond overcoming solubility issues by relying on a suspended compound, this semi-solid symmetrical organic RFB (S3ORFB or slurry) approach presents other advantages, such as increased compound stability as exemplified in FIGS. 3A and 3B and the potential to utilize biologically sourced carbon for greater sustainability.

[0121] Conclusion. This demonstrates the feasibility of functionalizing activated carbon with C+ molecules to develop fully organic symmetric RFBs. This approach no longer relies on a solution containing electrolyte, but rather functionalized particles to provide dispersed redox-active materials slurry redox flow batteries that exhibited the benefits of flow batteries with the high energy-density of solid redox-active materials.

[0122] Example 2. Carbon felt (CF) as support for the SO3RFB electrolyte described herein is a textile material that includes carbon fibers felted together, resulting in a fabric with a significant surface area and excellent electrical conductivity. It is lightweight, flexible, and can withstand high temperatures. However, it is more suited for interfacial interactions with fluid compounds (gas / liquid) rather than chemical functionalization due to its limited surface area.

[0123] The specific surface area of activated carbon is a crucial property that determines its capacity to adsorb various substances to be valuable in applications. A higher surface area provides more adsorption sites, enhancing the effectiveness of activated carbon for functionalization. This necessity prompted the search and identification of an active carbon with an outstanding surface area, such as Ketjenblack EC-600JD (KB). This is a safe electroconductive carbon black known for its excellent mechanical properties, fine particle size (about 37 nm), and exceptionally high surface area (about 1400 m2 / g).[3]KB functionalization with metals and organic molecules has been documented in the literature but has proven inefficient when merely mixing the chemical compound with active carbon.[4'6]Instead, mechanical functionalization of the support necessitates the use of high-energy ball mill to grind the compounds together and achieve the desired electroactivematerials (FIG. 5).[7]

[0124] To illustrate this method of functionalization, various ratios of C+:KB (varying x wt%) were investigated to comprehend the functionalization of electroconductive carbon black, where C+isnPrDAOTA[PF6']. This also allowed for optimizing the energy density of these systems by increasing the C+wt%. Physical and spectroscopic characterization of the C+@KB-x compounds was performed using Scanning Electron Microscopy (SEM) and UV-Visible absorption spectroscopy.

[0125] The high-resolution scanning electron microscopy (SEM) images reveal variations in both surface texture and nanoparticle dimensions of the milled KB, as well as how they are functionalized (FIG. 6).

[0126] When milling KB alone with 3 aluminum balls, an improvement in the homogeneity of particle size distribution with increased griding duration was noted. As depicted in FIG. 6A and FIG. 6B, the average particle size tends to decrease as the milling duration progresses from 30 minutes to 1 hour, dropping from an average size of 93 nm to 72 nm. This milling duration was maintained to study the incorporation of C+on the KB, using mixtures of 5 wt% (FIG. 6C) and 10 wt% (FIG. 6D). Initial observations from the images taken at the same energy power of 30 kV reveal the presence of brighter spots, indicative of the deposition of conductive material, confirming the presence of C+. Additionally, there is a noticeable increase in the average particle size, reaching 204 nm for C+@KB-5 and up to 429 nm for C+@KB-10. This suggests that the addition of more electroactive material to the mixture, with a similar milling duration, tends to increase the particle size.

[0127] The risk of leaching of this new material in solution was examined by suspending half a gram of C+@KB-10 in 10 mL of acetonitrile. After 12 hours of stirring at 1000 rpm, the complete lack of coloration in the solution confirmed the stability of the composite and the absence of surface defunctionalization under standard storage conditions. Additional studies to enhance the understanding of the material's functionalization will be conducted by monitoring absorbance in solid states using an integrating sphere device.

[0128] Through these various characterizations and the results obtained using carbon felt(CF) as a support for this carbenium slurry, the use of this material in electrochemistry was considered. Characterization by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) proved to be inadequate, as the suspension in the static three-electrode system did not provide relevant information (FIG. 7A).

[0129] Despite these results, the previous characterizations of carbenium in solution that we highlighted prompted the evaluation of this new material in suspension within a complete semi-solid symmetrical redox flow battery system (SO3RFB, FIG. 7B).

[0130] The flow cell utilized to evaluate the performance of this novel electroconductive material was designed with bipolar graphite plates featuring a serpentine flow pattern and a Daramic-175 porous membrane serving as the exchange separator between the two sides of the cell. During galvanostatic cycling, electrolyte solutions were circulated through the cell at a rate of 32 mL / min. Charging and discharging were conducted at a constant current rate equivalent to IC-rate until a voltage cutoff of +200 mV above the cell's theoretical energy gap (Egap) of 2.3 V was reached, with a 100% state of charge (SOC) limit applied. The discharge cutoff was set at 0 V, corresponding to 0% SOC. At the interface, the charges generated from the electroactive materials' oxidation state were balanced by the migration of PF6- counter anions through the permeable exchange membrane (X in FIG. 7B). A solution of 200 mg of C+@KB-10 in 4 mL of 0.1 M TBAPFe in acetonitrile was circulated through the cell at 16 mL / min from each reservoir, with the reduction process occurring at the Ewfor the first 50 cycles, followed by oxidation at Ewfor the next 50 cycles (Potential in FIG. 8 insert, reversed at 3000 mins).

[0131] During this test, the SO3RFB underwent 100 cycles (i.e. 100 hours), exhibiting consistent and nearly perfect capacity retention, with an average discharge capacity and coulombic efficiency (CE) of 98% (FIG. 8, square). The observed energy efficiency was also relatively high, averaging 63%, despite being a suboptimized model (FIG. 8, triangle). This indicates a slight energy loss between the charging and discharging sequences, partly due to the heterogeneous nature and preliminary aspect of these results. However, it strongly highlights and validates this approach with consistent capacity retention and a system that systematically achieves 100% charging capacity along with robustness in both polarity.

[0132] Example 3. In this example, encapsulation of the supporting electrolyte within the slurry is tested, where both the carbenium electrolyte and supporting electrolyte are encapsulated onto Ketjenblack (C+@KB-10&SE, FIG. 9) at the same time using ball milling, where C+isnPrDAOTA[PF6']. The electrochemical performance of the slurry C+@KB-10&SE was tested in a 50:50 mixture acetonitrile and y-valerolactone.

[0133] The flow cell utilized to evaluate the performance of this electroconductive material was designed with bipolar graphite plates featuring a serpentine flow pattern and a Daramic-175 porous membrane serving as the exchange separator between the two sides of the cell. During galvanostatic cycling, electrolyte solutions were circulated through the cell at a rate of 32 mL / min. Charging and discharging were conducted at a constant current rate equivalent to IC-rate until a voltage cutoff of +200 mV above the cell's theoretical energy gap (Egap) of 2.1 V was reached, with a 90% state of charge (SOC) limit applied. The discharge cutoff was set at 0 V, corresponding to 0% SOC. At the interface, the charges generated from the electroactive materials' oxidation state were balanced by the migration of PF6- counter anions through the permeable exchange membrane (X in FIG. 7B).

[0134] A slurry containing 500 mg of C+@KB-10&SE, prepared by ball milling 50 mg of C+, 400 mg of Ketjenblack and 50mg of TBAPFe for 60 min using 3 aluminum balls, in 5 mL of a 50:50 mixture acetonitrile and y-valerolactone was circulated through the cell at 16 mL / min from each reservoir, with the reduction process occurring at the Ew.

[0135] FIG. 10A shows that the SO3RFB underwent 100 cycles (i.e. 100 hours), exhibiting consistent and nearly perfect capacity retention, with an average discharge capacity and coulombic efficiency (CE) of 99% (FIG. 10A square). The observed energy efficiency was also relatively high, averaging 70%, (FIG. 10A, triangle). These results strongly highlight and validate the efficiency of a semi-solid organic redox flow battery with consistent capacity retention and a system that systematically achieves 100% charging capacity along with robustness.

[0136] The nature of the solvents (acetonitrile versus g- valerolactone versus a 50:50% mixture) as well as the importance of encapsulating the supporting electrolyte (@KB-10 vs @KB-10&SE) were investigated.

[0137] The electrochemical data are summarized in FIG. 1 IB, which shows that a gain of 10% in energy efficiency is observed when using @KB-10&SE compared to (@KB-10, and an additional 10% is gain when switching from a pure solvent, acetonitrile or y- valerolactone to a 50:50 mixture. These results were explained by the increased conductivity of the slurry (FIG. 1 IB).

[0138] This example demonstrates that a higher energy efficiency, columbic efficiency and cyclability is obtained when the supporting electrolyte is encapsulated with the working electrolyte onto the conductive carbon using ball milling. This Example also demonstrates that a higher energy efficiency, columbic efficiency and cyclability were obtained when 50:50 mixture of acetonitrile and y- valerolactone is used.

[0139] Example 4. In this Example, an electrolyte in slurry form and comprising one or more organic redox compounds (e.g., anthraquinones and anthracenes) were deposited on a conductive material and used as a semi-solid battery. The mixture was suspended in a solvent and used as electrolyte for organic redox flow batteries (RFBs).

[0140] FIG. 12 displays the cyclic voltammogram of the two organic molecules used, 9,10 diphenyl anthracene (DPA, top trace) and the anthraquinone Disperse Blue (DB-134, middle trace), and compare it to the carbenium ion presented in Example 3 (C+, bottom trace). The structure of DPA , DB-134, and C+(also known asnPrDAOTA [PFe']) are shown below.DPA DB-134nPrDAOTA [PFe ].

[0141] The summary of their redox potential vs Ag / AgNCh reference are presented in the following table:

[0142] The flow cell utilized to evaluate the performance of these two novel electroconductive material was designed with bipolar graphite plates featuring a serpentine flow pattern and a Daramic-175 porous membrane served as the exchange separator between the two sides of the cell. During galvanostatic cycling, electrolyte solutions were circulated through the cell at a rate of 32 mL / min. Charging and discharging were conducted at a constant current rate equivalent to IC-rate until a voltage cutoff of +200 mV above the cell's theoretical energy gap (Egap) of 2.1 V was reached, with a 90% state of charge (SOC) limit applied. The discharge cutoff was set at 0 V, corresponding to 0% SOC. At the interface, the charges generated from the electroactive materials' oxidation state were balanced by the migration of PF 6" counter anions through the permeable exchange membrane.

[0143] The following results were obtained with 500 mg of the electrolyte DPA@KB- 10&SE, prepared by ball milling 50 mg of DPA, 400 mg of Ketjenblack and 50 mg of TBAPFe for 60 min using 3 aluminum balls, in 5 mL of a 50:50 mixture acetonitrile and y- valerolactone was circulated through the cell at 16 mL / min from each reservoir, with the reduction process occurring at the Ew.

[0144] FIG. 13A shows that the SO3RFB underwent 24 cycles (i.e. 24 hours), exhibiting consistent and nearly perfect capacity retention, with an average discharge capacity and coulombic efficiency (CE) of 90% (FIG. 13 A, square). The observed energy efficiency was also relatively high, averaging 60%, (FIG. 13 A, triangle). These results strongly highlightand validate the efficiency of a semi-solid organic redox flow battery, using anthracene derivative as the active electrolyte, with consistent capacity retention and a system that systematically achieves 100% charging capacity.

[0145] The following results were obtained with 500 mg of the electrolyte DB134@KB- 10&SE, prepared by ball milling 50 mg of DB134, 400 mg of Ketjenblack and 50mg of TBAPFe for 60min using 3 aluminum balls, in 5mL of a 50:50 mixture acetonitrile and y- valerolactone was circulated through the cell at 16 mL / min from each reservoir, with the reduction process occurring at the Ew.

[0146] FIG. 14A shows that the SO3RFB underwent 100 cycles (i.e. 100 hours), exhibiting consistent and nearly perfect capacity retention, with an average discharge capacity and coulombic efficiency (CE) of 85% (FIG. 14A, square). The observed energy efficiency was also relatively high, averaging 58%, (FIG. 14A, triangle). These results validate the efficiency of a semi-solid organic redox flow battery, using anthraquinone derivative as the active electrolyte, with consistent capacity retention and a system that achieves 100% charging capacity.

[0147] This Example demonstrates the feasibility of functionalizing activated carbon with organic dyes molecules to develop fully organic symmetric RFBs. This approach no longer relies on a solution containing electrolyte, but rather functionalized particles, thereby overcoming solubility issues, while aiming for energy densities previously inaccessible for RFBs.

[0148] Para. 1. A redox flow battery comprising: a semi-solid catholyte comprising a conjugated heterocyclic compound in a first oxidation state and a first electroconductive active carbon; and a semi-solid anolyte comprising a conjugated heterocyclic compound in a second oxidation state and a second electroconductive active carbon; wherein the first oxidation state is a higher oxidation state than the second oxidation state.

[0149] Para. 2. The redox flow battery of Para 1, wherein the conjugated heterocyclic compound in the first oxidation state is a conjugated heterocyclic cationic compound, and / or wherein the conjugated heterocyclic compound in the second oxidation state is aconjugated heterocyclic cationic compound.

[0150] Para. 3. A redox flow battery comprising: a semi-solid catholyte comprising a conjugated heterocyclic carbenium compound and a first electroconductive active carbon; and a semi-solid anolyte comprising the conjugated heterocyclic carbenium compound and a second electroconductive active carbon.

[0151] Para. 4. The redox flow battery of Para. 3, wherein the conjugated heterocyclic carbenium compound in the catholyte comprises a radical dication and / or wherein the conjugated heterocyclic carbenium compound in the anolyte comprises a neutral radical.

[0152] Para. 5. A redox flow battery comprising: a semi-solid catholyte comprising a compound of Formula I and a first electroconductive active carbon; and a semi-solid anolyte comprising the compound of Formula I and a second electroconductive active carbon; wherein the compound of Formula (I) is represented by the following structure:wherein:X is -4, -3, -2, -1, 0, +1, +2, +3, or +4; each Rla, Rlb, Rlc, Rld, R2a, R2b, R2c, R2d, R3a, R3b, R3c, and R3dis independently H, halide, CF3, CBrs, CI3, NH2, C1-C12 alkyl, C1-C4 alkoxy, C1-C4 alkylamino, C1-C4 dialkyl amino, NO2, CN, CO2R, or Ar1; or R2aand R3dtogether form -X1-; or Rlaand R2dtogether form -X2-; or Rldand R3atogether form -X3-;or Rlaand Rlbtogether with atoms to which they are attached to form a phenyl; or R2Cand R2dtogether with atoms to which they are attached to form a phenyl; each X1, X2and X3is independently O, NR4a, PR4a, CR4aR4b, or SiR4aR4b; each R4aand R4bis independently H, halide, CF3, C1-C12 alkyl, C1-C4 alkoxy, C1-C4 alkylamino, C1-C4 dialkyl amino, Ar3, -L- Ar3, -L-Z, or -L2-Z2; each Y is independently H, halide, OR5a, NR5aR5b, PR5aR5b, NO2, CN, CF3, CO2R, N3, or Ar2; each R5a, and R5bis independently H, CF3, C1-C12 alkyl, C1-C4 alkoxy, C1-C4 alkylamino, C1-C4 dialkyl amino, Ar4, -L1- Ar4, or -i -Z1; each L and L1is independently C1-C12 alkylene, C1-C12 heteroalkylene, or arylene; each L2is independently C1-C12 alkylene;Z and Z1are each independently -N(R6a)3W or a moiety comprising a conjugated heterocyclic carbenium; each R6ais independently C1-C12 alkyl; each W is independently tetrafluoroborate, hexafluorophosphate, perchlorate, tetrary lb orate, trifluoromethanesulfonate, oxalatob orate, oxalate, phosphate, bis- trifluoromethanesulfonimide, halide, hydroxide, carbonate, bicarbonate, sulfate, hydrogen sulfate, or sulfite;Z2is each independently -(OCFkCFhOjiiCFh; n is each independently 1 to 20; each R is independently C1-C12 alkyl or aryl;Ar1, Ar2, Ar3,and Ar4are each independently unsubstituted or substituted phenyl or unsubstituted or substituted heteroaryl; each Ar1, Ar2, Ar3,and Ar4is independently substituted with 0 to 5 substituents; the substituents are each independently selected from the group consisting of halide, CF3, NH2, C1-C4 alkyl, C1-C4 alkoxy, C1-C4 alkylamino, Ci- C4 dialkyl amino, NO2, CN, or aryl.

[0153] Para. 6. The redox flow battery of Para. 5, wherein the conjugated heterocyclic carbenium compound in the catholyte comprises a radical dication and / or wherein the conjugated heterocyclic carbenium compound in the anolyte comprises a neutral radical.

[0154] Para. 7. The redox flow battery of any one of Paras. 3-5, wherein the conjugatedheterocyclic compound in the catholyte has a first oxidation state and the conjugated heterocyclic compound in the anolyte has a second oxidation state, and wherein the first oxidation state is a higher oxidation state than the second oxidation state.

[0155] Para. 8. The redox flow battery of any one of Paras. 1-7, wherein the conjugated heterocyclic compound in the catholyte is encapsulated or immobilized within the first electroconductive active carbon.

[0156] Para. 9. The redox flow battery of any one of Paras. 1-8, wherein a supporting electrolyte is encapsulated or immobilized with the catholyte within the first electroconductive active carbon.

[0157] Para. 10. The redox flow battery of Paras. 9, wherein the encapsulation or immobilization is achieved by ball milling the conjugated heterocyclic compound, the first electroconductive active carbon, and the supporting electrolyte.

[0158] Para. 11. The redox flow battery of any one of Paras. 1-10, wherein the conjugated heterocyclic compound in the anolyte is encapsulated or immobilized within the second electroconductive active carbon.

[0159] Para. 12. The redox flow battery of any one of Paras. 1-11, wherein the conjugated heterocyclic compound in the anolyte is encapsulated or immobilized within the second electroconductive active carbon.

[0160] Para. 13. The redox flow battery of Paras. 12, wherein the encapsulation or immobilization is achieved by ball milling the conjugated heterocyclic compound, the second electroconductive active carbon, and the supporting electrolyte.

[0161] Para. 14. The redox flow battery of any one of Paras. 1-13, wherein the electroconductive active carbon comprises carbon black, mesoporous carbon, bio-sourced carbon, carbon nanotubes, graphene, graphite, carbon nanofiber, carbon aerogel, or carbon nanodots.

[0162] Para. 15. The redox flow battery of any one of Paras. 1-14, wherein a weight ratio of the compound to the second electroconductive active carbon in the anolyte is about 1 :9 to9: 1.

[0163] Para. 16. The redox flow batery of any one of Paras. 1-15, wherein a weight ratio of the compound to the first electroconductive active carbon in the catholyte is about 1 :9 to 9: 1.

[0164] Para. 17. The redox flow batery of any one of Paras. 1-16 further comprising a separator disposed between the anolyte and the catholyte.

[0165] Para. 18. The redox flow batery of any one of Paras. 1-17 further comprising a solvent and an electrolyte salt.

[0166] Para. 19. The redox flow batery of Para. 18, wherein the electrolyte salt is a lithium, sodium, potassium, ammonium, alkylammonium or phosphonium salt of tetrafluoroborate, hexafluorophosphate, perchlorate, tetrarylborate, trifluoromethanesulfonate, oxalatob orate, oxalate, phosphate, bis- trifluoromethanesulfonimide, halide; or a mixture of any two or more thereof.

[0167] Para. 20. The redox flow battery of Paras. 18 or 19, wherein the solvent comprises a nitrile, an ether, dimethylformamide, water, a halogenated solvent, an ionic liquid, sulfolane, y-valerolactone, acetonitrile, propylene carbonate, or a mixture of any two or more thereof.

[0168] Para. 21. A method of operating the redox flow battery of any one of Paras. 1-20 the method comprising: flowing the catholyte through a catholyte compartment and flowing the anolyte through an anolyte compartment, wherein the catholyte and anolyte compartments are separated by a separator and electron transfer from the anolyte to the catholyte is supported.

[0169] Para. 22. The method of Para. 21, wherein after electron transfer, the method comprises regenerating the catholyte and / or the anolyte by an external power source.

[0170] Para. 23. A redox flow battery comprising: a semi-solid catholyte comprising an organic redox active compound and first electroconductive active carbon; anda semi-solid anolyte comprising an organic redox active compound and a second electroconductive active carbon.

[0171] Para. 24. The redox flow battery of Para. 23, wherein the organic redox active compound in the catholyte comprises a fused aromatic ring.

[0172] Para. 25. The redox flow battery of Paras. 23 or 24, wherein the organic redox active compound in the catholyte is a compound of Formula (II) represented by the following structure or a salt thereof:wherein: each R1, R2, R3, R4, R5, R6, R7, and R8is independently H, halide, CF3, CBn, CI3, OR9, Ci- C12 alkyl, C1-C4 alkoxy, aryl, NO2, CN, CO2R9, NR9R10, C(O)NR9R10, NR9C(O)R10, SO3H, +N R9R10Rn, P(O)OR9OR10or -(CH2CH2O)n-R9;R9, R10and R11are each independently H, C1-C12 alkyl, C1-C4 alkoxy, aryl, or -L-Z; each L is C1-C12 alkylene; each Z is SO3’, P(O)OR12OR13,+NR12R13R14, -(CH2CH2O)n-R12;R12, R13and R14are each independently H, C1-C12 alkyl, C1-C4 alkoxy, or aryl; and each n is an integer from 1 to 20.

[0173] Para. 26. The redox flow battery of Para. 24, wherein the organic redox active compound in the catholyte is a compound of Formula (III) represented by the following structure:(Formula III), wherein:each R1, R2, R3, R4, R5, R6, R7, R8, R9, and R10is independently H, halide, CF3, CBn, CI3, OR9, C1-C12 alkyl, C1-C4 alkoxy, aryl, NO2, CN, CO2R9, NR9R10, C(O)NR9R10, NR9C(O)R10, SO3H, +N R9R10Rn, P(O)OR9OR10or -(CH2CH2O)n-R9;R9, R10and R11are each independently H, C1-C12 alkyl, C1-C4 alkoxy, aryl, or -L-Z; each L is C1-C12 alkylene; each Z is SO3’, P(O)OR12OR13,+NR12R13R14, -(CH2CH2O)n-R12;R12, R13and R14are each independently H, C1-C12 alkyl, C1-C4 alkoxy, or aryl; and each n is an integer from 1 to 20.

[0174] Para. 27. The redox flow batery of any one of Paras. 23-26, wherein the organic redox active compound in the catholyte is one of the following:

[0175] Para. 28. The redox flow batery of any one of claims Paras. 23-27, wherein the organic redox active compound in the anolyte comprises a fused aromatic ring.

[0176] Para. 29. The redox flow battery of Para. 28, wherein the organic redox active compound in the anolyte is a compound of Formula (II):wherein: each R1, R2, R3, R4, R5, R6, R7, and R8is independently H, halide, CF3, CBn, CI3, OR9, Ci- C12 alkyl, C1-C4 alkoxy, aryl, NO2, CN, CO2R9, NR9R10, C(O)NR9R10, NR9C(O)R10, SO3H, +N R9R10Rn, P(O)OR9OR10or -(CH2CH2O)n-R9;R9, R10and R11are each independently H, C1-C12 alkyl, C1-C4 alkoxy, aryl, or -L-Z; each L is C1-C12 alkylene; each Z is SO3’, P(O)OR12OR13,+NR12R13R14, -(CH2CH2O)n-R12;R12, R13and R14are each independently H, C1-C12 alkyl, C1-C4 alkoxy, or aryl; and each n is an integer from 1 to 20.

[0177] Para. 30. The redox flow battery of Para. 28, wherein the organic redox active compound in the anolyte is a compound of Formula (III) represented by the following structure:(Formula III), wherein: each R1, R2, R3, R4, R5, R6, R7, R8, R9, and R10is independently H, halide, CF3, CBn, CI3, OR9, C1-C12 alkyl, C1-C4 alkoxy, aryl, NO2, CN, CO2R9, NR9R10, C(O)NR9R10, NR9C(O)R10, SO3H, +N R9R10Rn, P(O)OR9OR10, or -(CH2CH2O)n-R9;R9, R10and R11are each independently H, C1-C12 alkyl, C1-C4 alkoxy, aryl, or -L-Z; each L is C1-C12 alkylene; each Z is SO3’, P(O)OR12OR13,+NR12R13R14, -(CH2CH2O)n-R12;R12, R13and R14are each independently H, C1-C12 alkyl, C1-C4 alkoxy, or aryl; and each n is an integer from 1 to 20.

[0178] Para. 31. The redox flow battery of any one of Paras. 23-27, wherein the organic redox active compound in the anolyte is one of the following:

[0179] Para. 32. The redox flow batery of any one of Paras. 23-31, wherein the organic redox active compound in the catholyte is encapsulated or immobilized within the first electroconductive active carbon.

[0180] Para. 33. The redox flow batery of any one of Paras. 23-32, wherein a supporting electrolyte is encapsulated or immobilized with the catholyte within the first electroconductive active carbon.

[0181] Para. 34. The redox flow battery of Para. 33, wherein the encapsulation or immobilization is achieved by ball milling the organic redox active compound, the first electroconductive active carbon, and the supporting electrolyte.

[0182] Para. 35. The redox flow batery of any one of Paras. 23-34, wherein the organic redox active compound in the anolyte is encapsulated or immobilized within the second electroconductive active carbon.

[0183] Para. 36. The redox flow battery of any one of Paras. 23-35, wherein the conjugated heterocyclic compound in the anolyte is encapsulated or immobilized within the second electroconductive active carbon.

[0184] Para. 37. The redox flow battery of Para. 36, wherein the encapsulation or immobilization is achieved by ball milling the organic redox active compound, the second electroconductive active carbon, and the supporting electrolyte.

[0185] Para. 38. The redox flow batery of any one of Paras. 23-37, wherein the first or second electroconductive active carbon comprises carbon black, mesoporous carbon, bio sourced carbon, carbon nanotubes, graphene, graphite, carbon nanofiber, carbon aerogel, or carbon nanodots.

[0186] Para. 39. The redox flow battery of any one of Paras. 23-38, wherein a weight ratio of the organic redox active to the second electroconductive active carbon in the anolyte is about 1 :9 to 9: 1.

[0187] Para. 40. The redox flow batery of any one of Paras. 23-39, wherein a weight ratio of the organic redox active to the first electroconductive active carbon in the catholyteis about 1 :9 to 9: 1.

[0188] Para. 41. The redox flow batery of any one of Paras. 23-40 further comprising a separator positioned between the anolyte and the catholyte.

[0189] Para. 42. The redox flow batery of any one of Paras. 23-41 further comprising a solvent and an electrolyte salt.

[0190] Para. 43. The redox flow battery of Para. 42, wherein the solvent comprises a nitrile solvent, an ether solvent, dimethylformamide, water, a halogenated solvent, an ionic liquid, sulfolane, y-valerolactone, or any of one of these solvents in a mixture of acetonitrile, or propylene carbonate or any mixture thereof.

[0191] Para. 44. The redox flow battery of Paras. 42 or 43, wherein the electrolyte salt comprises a lithium, sodium, potassium, ammonium, alkylammonium, or phosphonium salt of tetrafluoroborate, hexafluorophosphate, perchlorate, tetrarylborate, trifluoromethanesulfonate, oxalatob orate, oxalate, phosphate, bis- trifluoromethanesulfonimide, halide, or a mixture of any two or more thereof.

[0192] Para. 45. A method of operating the redox flow battery of any one of Paras. 23-44, the method comprising: flowing the catholyte through a catholyte compartment and flowing the anolyte through an anolyte compartment, wherein the catholyte and anolyte compartments are separated by a separator and electron transfer from the anolyte to the catholyte is supported.

[0193] Para. 46. The method of Para. 45, wherein after electron transfer, the method comprises regenerating the catholyte and / or the anolyte by an external power source.

[0194] Para. 47. The redox flow batery of any one of Paras. 1-20 and 23-44, wherein the first electroconductive active carbon and the second electroconductive active carbon comprise the same material.

[0195] Para. 48. The redox flow battery of Para. 1-20 and 23-44, wherein the first electroconductive active carbon and the second electroconductive active carbon comprise different material.REFERENCES[1] Moutet J., Nowack M. H., Mills D. D., Lozier D. L., Laursen B. W., Gianetti T. L. Planar Carbenium Ions for Robust Symmetrical All Organic Redox Flow Batteries. Mater. Adv. 2023, 4 (19), 4598-4606.[2] Moutet J., Mills D. D., Lozier D. L., Gianetti T. L. Helicenium Ion as Bipolar Redox Material for Symmetrical Fully Organic Pole-less Redox Flow Battery. Batter. Supercaps 2024, 202300519, 1-33.

[0196] While certain embodiments have been illustrated and described, it should be understood that changes and modifications can be made therein in accordance with ordinary skill in the art without departing from the technology in its broader aspects as defined in the following claims.

[0197] The embodiments, illustratively described herein may suitably be practiced in the absence of any element or elements, limitation or limitations, not specifically disclosed herein. Thus, for example, the terms “comprising,” “including,” “containing,” etc. shall be read expansively and without limitation. Additionally, the terms and expressions employed herein have been used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the claimed technology. Additionally, the phrase “consisting essentially of’ will be understood to include those elements specifically recited and those additional elements that do not materially affect the basic and novel characteristics of the claimed technology. The phrase “consisting of’ excludes any element not specified.

[0198] The present disclosure is not to be limited in terms of the particular embodiments described in this application. Many modifications and variations can be made without departing from its spirit and scope, as will be apparent to those skilled in the art.Functionally equivalent methods and compositions within the scope of the disclosure, in addition to those enumerated herein, will be apparent to those skilled in the art from theforegoing descriptions. Such modifications and variations are intended to fall within the scope of the appended claims. The present disclosure is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled. It is to be understood that this disclosure is not limited to particular methods, reagents, compounds, compositions, or biological systems, which can of course vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.

[0199] In addition, where features or aspects of the disclosure are described in terms of Markush groups, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group.

[0200] As will be understood by one skilled in the art, for any and all purposes, particularly in terms of providing a written description, all ranges disclosed herein also encompass any and all possible subranges and combinations of subranges thereof. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a nonlimiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as “up to,” “at least,” “greater than,” “less than,” and the like, include the number recited and refer to ranges which can be subsequently broken down into subranges as discussed above. Finally, as will be understood by one skilled in the art, a range includes each individual member.

[0201] All publications, patent applications, issued patents, and other documents referred to in this specification are herein incorporated by reference as if each individual publication, patent application, issued patent, or other document was specifically and individually indicated to be incorporated by reference in its entirety. Definitions that are contained in text incorporated by reference are excluded to the extent that they contradict definitions in this disclosure.

[0202] Other embodiments are set forth in the following claims.

Claims

WHAT IS CLAIMED IS:

1. A redox flow battery comprising: a semi-solid catholyte comprising a conjugated heterocyclic compound in a first oxidation state and a first electroconductive active carbon; and a semi-solid anolyte comprising a conjugated heterocyclic compound in a second oxidation state and a second electroconductive active carbon; wherein the first oxidation state is a higher oxidation state than the second oxidation state.

2. The redox flow battery of claim 1, wherein the conjugated heterocyclic compound in the first oxidation state is a conjugated heterocyclic cationic compound, and / or wherein the conjugated heterocyclic compound in the second oxidation state is a conjugated heterocyclic cationic compound.

3. A redox flow battery comprising: a semi-solid catholyte comprising a conjugated heterocyclic carbenium compound and a first electroconductive active carbon; and a semi-solid anolyte comprising the conjugated heterocyclic carbenium compound and a second electroconductive active carbon.

4. A redox flow battery comprising: a semi-solid catholyte comprising a compound of Formula I and a first electroconductive active carbon; and a semi-solid anolyte comprising the compound of Formula I and a second electroconductive active carbon; wherein the compound of Formula (I) is represented by the following structure:wherein:X is -4, -3, -2, -1, 0, +1, +2, +3, or +4; each Rla, Rlb, Rlc, Rld, R2a, R2b, R2c, R2d, R3a, R3b, R3c, and R3dis independently H, halide, CF3, CBn, CI3, NH2, C1-C12 alkyl, C1-C4 alkoxy, C1-C4 alkylamino, C1-C4 dialkyl amino, NO2, CN, CO2R, or Ar1; or R2aand R3dtogether form -X1-; or Rlaand R2dtogether form -X2-; or Rldand R3atogether form -X3-; or Rlaand Rlbtogether with atoms to which they are attached to form a phenyl; or R2Cand R2dtogether with atoms to which they are attached to form a phenyl; each X1, X2and X3is independently O, NR4a, PR4a, CR4aR4b, or SiR4aR4b; each R4aand R4bis independently H, halide, CF3, C1-C12 alkyl, C1-C4 alkoxy, C1-C4 alkylamino, C1-C4 dialkyl amino, Ar3, -L- Ar3, -L-Z, or -L2-Z2; each Y is independently H, halide, OR5a, NR5aR5b, PR5aR5b, NO2, CN, CF3, CO2R, N3, or Ar2; each R5a, and R5bis independently H, CF3, C1-C12 alkyl, C1-C4 alkoxy, C1-C4 alkylamino, C1-C4 dialkyl amino, Ar4, -L1- Ar4, or -l -Z1; each L and L1is independently C1-C12 alkylene, C1-C12 heteroalkylene, or arylene;each L2is independently C1-C12 alkylene;Z and Z1are each independently -N(R6a)3W or a moiety comprising a conjugated heterocyclic carbenium; each R6ais independently C1-C12 alkyl; each W is independently tetrafluoroborate, hexafluorophosphate, perchlorate, tetrarylborate, trifluoromethanesulfonate, oxalatob orate, oxalate, phosphate, bis- trifluoromethanesulfonimide, halide, hydroxide, carbonate, bicarbonate, sulfate, hydrogen sulfate, or sulfite;Z2is each independently -(OCH2CH2O)nCH3; n is each independently 1 to 20; each R is independently C1-C12 alkyl or aryl;Ar1, Ar2, Ar3,and Ar4are each independently unsubstituted or substituted phenyl or unsubstituted or substituted heteroaryl; each Ar1, Ar2, Ar3,and Ar4is independently substituted with 0 to 5 substituents; the substituents are each independently selected from the group consisting of halide, CF3, NH2, C1-C4 alkyl, C1-C4 alkoxy, C1-C4 alkylamino, C1-C4 dialkyl amino, NO2, CN, or aryl.

5. The redox flow battery of claim 4, wherein the conjugated heterocyclic compound in the catholyte has a first oxidation state and the conjugated heterocyclic compound in the anolyte has a second oxidation state, and wherein the first oxidation state is a higher oxidation state than the second oxidation state.

6. The redox flow battery of claim 1, wherein the conjugated heterocyclic compound in the catholyte is encapsulated or immobilized within the first electroconductive active carbon.

7. The redox flow battery of claim 6, wherein a supporting electrolyte is encapsulated or immobilized with the catholyte within the first electroconductive active carbon.

8. The redox flow battery of claim 7, wherein the encapsulation or immobilization isachieved by ball milling the conjugated heterocyclic compound, the first electroconductive active carbon, and the supporting electrolyte.

9. The redox flow battery of claim 1, wherein the conjugated heterocyclic compound in the anolyte is encapsulated or immobilized within the second electroconductive active carbon.

10. The redox flow battery of claim 9, wherein a supporting electrolyte is encapsulated or immobilized with the anolyte within the second electroconductive active carbon.

11. The redox flow battery of claim 10, wherein the encapsulation or immobilization is achieved by ball milling the conjugated heterocyclic compound, the second electroconductive active carbon, and the supporting electrolyte.

12. The redox flow battery of claim 1, wherein the first or second electroconductive active carbon comprises carbon black, mesoporous carbon, bio-sourced carbon, carbon nanotubes, graphene, graphite, carbon nanofiber, carbon aerogel, or carbon nanodots.

13. The redox flow battery of claim 1, wherein a weight ratio of the compound to the second electroconductive active carbon in the anolyte is about 1 :9 to 9:1.

14. The redox flow battery of claim 1, wherein a weight ratio of the compound to the first electroconductive active carbon in the catholyte is about 1 :9 to 9: 1.

15. The redox flow battery of claim 1, wherein the first electroconductive active carbon and the second electroconductive active carbon comprise the same material.

16. The redox flow battery of claim 1, wherein the first electroconductive active carbon and the second electroconductive active carbon comprise different material.

17. The redox flow battery of claim 1 further comprising a separator disposed between the anolyte and the catholyte.

18. The redox flow battery of claim 1 further comprising a solvent and an electrolyte salt.

19. The redox flow battery of claim 18, wherein the electrolyte salt is a lithium, sodium, potassium, ammonium, alkylammonium, or phosphonium salt of tetrafluoroborate, hexafluorophosphate, perchlorate, tetrarylborate, trifluoromethanesulfonate, oxalatob orate, oxalate, phosphate, bis-trifluoromethanesulfonimide, halide; or a mixture of any two or more thereof.

20. The redox flow battery of claim 18, wherein the solvent comprises a nitrile, an ether, dimethylformamide, water, a halogenated solvent, an ionic liquid, sulfolane, y- valerolactone, acetonitrile, propylene carbonate, or a mixture of any two or more thereof.

21. A method of operating the redox flow battery of claim 1, the method comprising: flowing the catholyte through a catholyte compartment and flowing the anolyte through an anolyte compartment, wherein the catholyte and anolyte compartments are separated by a separator and electron transfer from the anolyte to the catholyte is supported.

22. The method of claim 21, wherein after electron transfer, the method comprises regenerating the catholyte and / or the anolyte by an external power source.

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