Carbenium-based organic redox flow battery

Abstract

The redox flow battery includes: a catholyte including a radical dication of a conjugated heterocyclic carbenium compound; and an anolyte including a neutral radical of a conjugated heterocyclic carbenium compound; the conjugated heterocyclic carbenium compound present in the catholyte and the anolyte are the same compound; and the open circuit potential of the redox flow battery is greater than about 2 V. The redox flow battery includes: a catholyte including a conjugated heterocyclic cation compound in a first oxidation state; and an anolyte including a conjugated heterocyclic cation compound in a second oxidation state; the first oxidation state being a more highly oxidized state than the second oxidation state.

Description

Technical Field

[0001] Cross - reference to Related Applications This PCT application claims the benefit of priority to U.S. Provisional Application No. 63 / 014,810, filed Apr. 24, 2020, the entire disclosure of which is hereby incorporated by reference herein.

[0002] This technology relates to redox flow batteries. More particularly, this technology relates to organic redox flow batteries that utilize conjugated cyclic carbenium compounds as catholytes and anolytes.

Background Art

[0003] From the perspectives of economic and environmental power, energy production and storage are particularly worthy of attention. Humanity has intensively used coal and oil combustion as the main energy sources for many years, while the use of electricity has been on the increase. There are still challenges in efficient storage that is electrically compatible for various applications. Lithium - ion batteries, which have been used for a long time, are limited to smartphones and small devices and may be a short - term solution. Using lithium - ion batteries in large - scale applications such as the automotive industry may lead to shortages of raw materials (Li, Co, rare earths) and a significant increase in costs.

[0004] To overcome this problem and prepare for the future, several sustainable approaches have been explored in the field of energy storage systems (ESS). One of them is the development of redox flow batteries (RFB). Energy is stored in a liquid electrolyte that flows through the battery of an electrochemical cell during charge and discharge. The term "redox" refers to the chemical oxidation - reduction reaction involved.

[0005] These redox flow batteries have several advantages over the systems that have been published so far. Since power conversion is separated from energy storage, independent adjustment of the amount of power and energy is possible. This separation from energy storage substantially unbounds the ESS capacity, which is only limited by the size of the tanker and the electrolyte concentration. In a redox flow battery system, the redox reaction is completely reversible, which means that it can operate as a converter that converts electricity into chemical energy or, conversely, chemical energy into electricity using a single cell. The redox flow battery system is relatively easy to develop from an infrastructure perspective. Its installation only requires two tanks equipped with pumps and a cell equipped with an ion exchange membrane between two electrodes. Therefore, the redox flow battery system has very few consumable parts and very low equipment maintenance costs. Finally, since the two electrolyte storage parts are clearly separated, self-discharge is prevented and the battery life mainly depends on the chemical substances. However, there are still some points to be improved regarding the redox flow battery system. Currently, the energy density provided by RFBs is insufficient for automotive applications. Parameters such as the solubility and temperature of the electrolyte are still important. Also, since their presence in the energy market is weak, the costs of these EESs remain high.

[0006] Historically, the RFB system was first used in France in 1933 with a vanadium-based electrolyte. Today, vanadium RFBs are still the most commercially available flow batteries because they have several advantages over other chemicals (voltage (V) at both electrodes, no cross-contamination issues, aqueous solutions). However, vanadium is expensive, and these vanadium-based RFBs have a relatively low energy density. Furthermore, the capital cost of vanadium-based RFBs is tied to the cost of the membrane materials used to prepare the exchange membrane that separates the two electrodes 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 subject to significant charging stress over time that affects the lifespan of the RFB. Metal coordination complexes are thought to be the most stable electrolytes, but these complexes are associated with significant technical and economic limitations such as low solubility, low electrochemical activity, and high cost, driving researchers to search for more affordable and easily synthesized compounds.

[0007] Redox-active organic materials (ROMs) are a promising alternative option for improving current RFB systems. This is because ROMs can be an option as electrolytes due to the following reasons: I) the molecules are diverse, II) the structure can be adapted, and III) they are naturally abundant. Thus, several RFB systems using redox-active organic materials have been developed. An important feature of these RFB systems is a type of nitrogen-containing aromatic backbone that is highly soluble and highly adjustable. However, the most well-known redox-active organic-based RFB systems still cannot be made efficient, are not robust, and cannot increase the open-circuit potential (OCV) significantly. This disclosure addresses the improvements needed for redox-active organic material-based RFB systems. SUMMARY OF THE INVENTION

[0008] The present technology provides a redox flow battery system comprising a conjugated heterocyclic carbenium compound as both anolyte and catholyte. The potential, stability, and solubility of the conjugated heterocyclic carbenium compounds shown herein are readily adjustable, improving the electron density storage and open circuit potential (OVC) of any particular solvent. The redox flow battery system disclosed herein uses one compound as both anolyte and catholyte and is a rare example of a high-performance system with an OCV exceeding 2.0V. By using a conjugated heterocyclic carbenium compound as both anolyte and catholyte, it is also possible to develop a symmetric organic redox flow battery (SORFB). This provides an opportunity to improve the properties of the exchange membrane (EM) separating the two electrodes of the battery and overcome the limitations associated with the aforementioned vanadium-based RFB. Instead of an anion-selective membrane, a simple porous exchange membrane (EM) that allows size-exclusion based selection, particularly based on the EM pore size, may be used. Thus, in another aspect, a symmetric organic redox flow battery (SORFB) comprising a porous exchange membrane as a separator is provided.

[0009] In one aspect, a redox flow battery is provided, the redox flow battery comprising: a catholyte comprising a radical dication of a conjugated heterocyclic carbenium compound; and an anolyte comprising a neutral radical of a conjugated heterocyclic carbenium compound; comprising, wherein the conjugated heterocyclic compounds present in the catholyte and anolyte are the same compound. In some embodiments, the open circuit potential of the redox flow battery exceeds about 1V, 1.5V, or 2V. In some embodiments, the open circuit potential of the redox flow battery exceeds about 2V. In some embodiments, the open circuit potential of the redox flow battery is from about 1V to about 5V, from about 1.5V to about 5V, from about 1.5V to about 3V, from about 2V to about 5V, from about 2V to about 4V, or from about 2V to about 3V.

[0010] In another aspect, a redox flow battery is provided, the redox flow battery comprising: Catholite containing the radical dication of the compound of formula I; and Anolite containing the neutral radical of the compound of formula I; comprising wherein the compound of formula (I) is represented by the following structure:

Chemical formula

[0011] In some embodiments, the compound of formula I is a compound of formula Ia, formula Ib, or formula Ic below.

Chemical formula

[0012] In some embodiments, the compound of formula Ib is the following compound: X 2 and X 3 are each NR 4a ; R 4a are each independently C1-C 12 alkyl, C1-C4 dialkylamino, or -L-Ar 3 ; R1a and R 2d are each C1-C4 alkoxy; R 1b 、R 1c 、R 2b 、R 2c 、R 3b 、and R 3c are each independently H; Y are each independently H or NO2. In some embodiments, the compound of formula Ib is the following compound: X 2 and X 3 are each NR 4a ; R 4a are each independently C1-C 12 alkyl, C1-C4 dialkylamino, -L-Ar 3 , or -L 2 -Z 2 ; R 1a and R 2d are each C1-C4 alkoxy; R 1b 、R 1c 、R 2b 、R 2c 、R 3b 、and R 3c are each independently H, C1-C4 alkylamino, or NO2; Y are each independently H, NO2, or NR 5a R 5b ; R 5a and R 5b are each independently H, CF3, or C1-C 12 alkyl.

[0013] In some embodiments, the compound of formula I is any one of the compounds of the following formula.

Chemical formula

[0014] In some embodiments, the solvent includes a nitrile solvent such as acetonitrile; an ether solvent such as tetrahydrofuran; dimethylformamide; water; a halogenated solvent such as dichloromethane, or an ionic liquid. In some embodiments, the compound of Formula I has photoactivity. In another aspect, a redox flow battery is provided, and the redox flow battery includes: a catholyte including a conjugated heterocyclic cation compound in a first oxidation state; and an anolyte including a conjugated heterocyclic cation compound in a second oxidation state. wherein the first oxidation state has a higher degree of oxidation state than the second oxidation state.

[0015] In some embodiments, the conjugated heterocyclic cation compounds in the catholyte and the anolyte are each independently a compound of Formula I, and the compound of Formula (I) is represented by the following structure:

Chemical formula

[0016] In some embodiments, the compounds of formula I are each independently a compound of formula Ia, formula Ib, or formula Ic below.

Chemical formula

[0017] In some embodiments, the compounds are each independently a compound of formula Ib, wherein: X 2 and X 3 are each NR 4a ; R 4a are each independently C1-C 12 alkyl, C1-C4 dialkylamino, or -L-Ar 3 ; R 1a and R 2d are each C1-C4 alkoxy; R 1b , R 1c , R 2b , R 2c , R 3b and R 3c are each independently H; Each Y is independently H or NO2. In some embodiments, the compound of formula Ib is the following compound: X 2 and X 3 are each NR 4a ; R 4a are each independently C1-C 12 alkyl, C1-C4 dialkylamino, -L-Ar 3 , or -L 2 -Z 2 ; R 1a and R 2d are each C1-C4 alkoxy; R 1b , R 1c , R 2b , R 2c , R 3b and R 3c are each independently H, C1-C4 alkylamino, or NO2; Y is independently H, NO2, or NR 5a R 5b wherein; R 5a and R5b are each independently H, CF3, or C1-C 12 alkyl.

[0018] In some embodiments, the compounds of formula I are each independently any one compound of the following formulae.

Chemical formula

[0019] In some embodiments, the solvent includes a nitrile solvent, an ether solvent, dimethylformamide, water, a halogenated solvent, or an ionic liquid. In some embodiments, the conjugated heterocyclic compounds each independently have photoactivity. In some embodiments, the open circuit potential of the redox flow battery exceeds about 1 V, 1.5 V, or 2 V. In some embodiments, the open circuit potential of the redox flow battery exceeds about 2 V. In some embodiments, the open circuit potential of the redox flow battery is from about 1 V to about 5 V, from about 1.5 V to about 5 V, from about 1.5 V to about 3 V, from about 2 V to about 5 V, from about 2 V to about 4 V, or from about 2 V to about 3 V.

[0020] In another aspect, a method of operating any one of the redox flow battery systems described herein is provided. The method includes flowing catholyte within a catholyte compartment and flowing anolyte within an anolyte compartment, where the catholyte compartment and the anolyte compartment are separated by a porous separator that facilitates electron transport from the anolyte to the catholyte. In some embodiments, the porous separator is a porous membrane. In some embodiments, the method includes regenerating the catholyte and / or the anolyte by an external power source after electron transport. In some embodiments, the step of regenerating the catholyte includes regenerating the catholyte via light-utilizing oxidation. In some embodiments, the step of regenerating the anolyte includes regenerating the anolyte via light-utilizing reduction.

Brief Description of the Drawings

[0021]

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Mode for Carrying Out the Invention

[0022] Hereinafter, various embodiments will be described. It should be noted that a particular embodiment is not intended to be an exhaustive description or limitation of the broad aspects discussed in this specification. One aspect described in connection with a particular embodiment is not necessarily limited to that embodiment and can be implemented in any other embodiment(s). As used in this specification, "about" is understood by those skilled in the art and is somewhat variable depending on the context in which it is used. When using terms that are not clear to those skilled in the art, considering the context in which the term is used, "about" shall mean up to 10% before and after the specific term. The use of the terms "a", "an", and "the", and similar reference words in the context of describing elements (particularly in the context of the following claims), unless otherwise indicated herein or clearly inconsistent with the context, should be construed to include both the singular and the plural. The recitation of numerical ranges herein is merely intended to be a shorthand way of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated herein as if it were individually recited herein. All methods described herein may be performed in any suitable order, unless otherwise indicated herein or clearly inconsistent with the context. The use of any and all examples, or exemplary language (e.g., "such as") provided herein is merely intended to better illuminate embodiments and does not impose a limitation on the claims unless otherwise expressly recited. No language in this specification should be construed as indicating any non-claimed element as essential.

[0023] In general, "substituted" refers to the replacement of one or more bonds to a hydrogen atom in an alkyl, alkenyl, alkynyl, aryl, or ether group (e.g., an alkyl group) as defined below with a bond to a non-hydrogen atom or a non-carbon atom. Substituents also include groups in which one or more bonds to a carbon atom(s) or hydrogen atom(s) are replaced with one or more bonds including a double bond or triple bond to a heteroatom. Thus, unless otherwise specified, substituents will be substituted with one or more substituents. In some embodiments, the substituents are substituted with 1, 2, 3, 4, 5, or 6 substituents. Examples of substituents include: halogen (i.e., F, Cl, Br, and I); hydroxyl group; alkoxy group, alkenoxy group, alkynyloxy group, aryloxy group, aralkyloxy group, heterocyclyloxy group, and heterocyclylalkoxy group; carbonyl (oxo); carboxyl; ester; urethane; oxime; hydroxylamine; alkoxyamine; aralkoxyamine; thiol; sulfide; sulfoxide; sulfone; sulfonyl; sulfonamide; amine; N-oxide; hydrazine; hydrazide; hydrazone; azide; amide; urea; amidine; guanidine; enamine; imide; isocyanate; isothiocyanate; cyanate; thiocyanate; imine; nitro group; nitrile (i.e., CN); and the like. As used herein, an "alkyl" group includes straight-chain and branched alkyl groups having from 1 to about 20 carbon atoms, typically from 1 to 12 carbon atoms, or in some embodiments from 1 to 8 carbon atoms. As employed herein, an "alkyl group" includes cycloalkyl groups as defined below. The alkyl group may or may not be substituted. 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 mono- or more-substituted, for example, with an 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 perhaloalkyl group.

[0024] The term "alkylene" refers to a saturated straight-chain divalent hydrocarbon moiety or a branched saturated divalent hydrocarbon moiety. Examples of alkylene groups include, but are not limited to, methylene, ethylene, propylene, butylene, pentylene, 2-methylpropylene, etc. The term "heteroalkylene" refers to an alkylene group as defined herein in which one or more chain atoms or hydrogen atoms are substituted with a heteroatom such as O, N, P, or S. Examples of heteroalkylene include, but are not limited to, heteroalkylenes derived from polyethylene glycol such as PEG2 (i.e., two molecules of ethylene glycol are linked), PEG3, 2-methoxyethylene, 2-hydroxyethyl, 2,3-dihydroxypropyl, etc. The cycloalkyl group is a cyclic alkyl group such as a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, and a cyclooctyl group, but is not limited thereto. In some embodiments, the cycloalkyl group has 3 to 8 ring members, and in other embodiments, the number of cyclic carbon atoms ranges from 3 to 5, 6, or 7. The cycloalkyl group may or may not be substituted. The cycloalkyl group further includes polycyclic cycloalkyl groups such as a norbornyl group, an adamantyl group, a bornyl group, a camphenyl group, an isocamphenyl group, and a carenyl group, and fused rings such as decalinyl, but is not limited thereto. The cycloalkyl group also includes rings substituted with the linear or branched alkyl groups defined above. Representative substituted cycloalkyl groups may be mono-substituted or di-substituted or more, for example, but not limited to: 2,2-; 2,3-; 2,4-; 2,5-; or 2,6-disubstituted cyclohexyl groups, or mono-substituted, di-substituted, or tri-substituted norbornyl or cycloheptyl groups, which may be substituted, for example, with an alkyl group, an alkoxy group, an amino group, a thio group, a hydroxy group, a cyano group, and / or a halo group.

[0025] The alkenyl group is a linear, branched, or cyclic alkyl group having 2 to about 20 carbon atoms and further includes at least one double bond. In some embodiments, the alkenyl group has 1 to 12 carbon atoms, typically 1 to 8 carbon atoms. The alkenyl group may or may not be substituted. Examples of the alkenyl group include a vinyl group, a propenyl group, a 2-butenyl group, a 3-butenyl group, an isobutenyl group, a cyclohexenyl group, a cyclopentenyl group, a cyclohexadienyl group, a butadienyl group, a pentadienyl group, and a hexadienyl group. The alkenyl group may be substituted in the same manner as the alkyl group. Examples of the divalent alkenyl group, i.e., the alkenyl group having two attachment points, include CH-CH=CH2, C=CH2, or C=CHCH3, but are not limited thereto. As used herein, an "aryl" or "aromatic" group is a cyclic aromatic hydrocarbon that does not contain heteroatoms. Aryl groups include monocyclic, bicyclic, and polycyclic ring systems. Thus, aryl groups include, but are not limited to, phenyl, azulenyl, heptalenyl, biphenylylenyl, indacenyl, fluorenyl, phenanthrenyl, triphenylenyl, pyrenyl, naphthacenyl, chrysenyl, biphenyl, anthracenyl, indenyl, indanyl, pentalenyl, and naphthyl groups. In some embodiments, an aryl group contains 6 to 14 carbon atoms in the ring portion of the group, and in other embodiments 6 to 12, or 6 to 10 carbon atoms. The term "aryl group" includes groups containing fused rings such as fused aromatic-aliphatic ring systems (e.g., indanyl, tetrahydronaphthyl, etc.). An aryl group may or may not be substituted. As used herein, "arylene" refers to a divalent group derived from an arene from which two ring carbon atoms have been removed.

[0026] A heteroalkyl group includes the straight-chain and branched-chain alkyl groups defined above and further includes 1, 2, 3, 4, 5, or 6 heteroatoms independently selected from oxygen, sulfur, and nitrogen. Thus, a heteroalkyl group contains 1 to 12 carbon atoms, 1 to 10 carbon atoms, or in some embodiments, 1 to 8 carbon atoms, or 1, 2, 3, 4, 5, or 6 carbon atoms, or any range therebetween (e.g., 1 to 4) of carbon atoms. Examples of heteroalkyl groups include, but are not limited to, -(CH2CH2O) 1‐5 CH3, -(CH2) 1‐6 O(CH2) 1‐6 CH3, -(CH2) 1‐6 NR a (CH2) 1‐6 CH3, -(CH2) 1‐6 S(CH2) 1‐6 CH3, -(CH2) 1‐6 O(CH2) 1‐6 O(CH2) 1‐6 CH3, -(CH2) 1‐6 NR a(CH2) 1‐6 NR a (CH2) 1‐6 CH3, -(CH2) 1‐6 O(CH2) 1‐6 O(CH2) 1‐6 O(CH2) 1‐6 CH3, -(CH2) 1‐6 NR a (CH2) 1‐6 NR a (CH2) 1‐6 NR a (CH2) 1‐6 CH3 is included, the total number of carbon atoms of the heteroalkyl group is 1 to 12, and R a is hydrogen, or a substituted or unsubstituted alkyl group, alkenyl group, aryl group, or aralkyl group. Other examples of the heteroalkyl group include, but are not limited to, groups having different heteroatoms in one group. Examples of such heteroalkyl groups include, but are not limited to, -(CH2) 1‐6 S(CH2) 1‐6 O(CH2) 1‐6 , -(CH2) 1‐6 NR a (CH2) 1‐6 )O(CH2) 1‐6 , -(CH2) 1‐6 O(CH2) 1‐6 NR a (CH2) 1‐6 S(CH2) 1‐6 , -(CH2) 1‐6 NR a (CH2) 1‐6 O(CH2) 1‐6 S(CH2) 1‐6 are included, and the total number of carbon atoms in the heteroalkyl group is 1 to 12. In some embodiments, the heteroalkyl group is -(OCH2CH2 -) 1‐5 CH3, for example, -O(CH2)2O(CH2)2OCH3, -O(CH2)2O(CH2)2O(CH2)2OCH3, -O(CH2)2O(CH2)2O(CH2)2O(CH2)2OCH3, -O(CH2)2O(CH2)2O(CH2)2O(CH2)2O(CH2)2OCH3 are included, but are not limited thereto. An aralkyl group is a substituted aryl group in which a hydrogen or carbon bond of the alkyl group defined above is substituted with a bond to the aryl group defined above. In some embodiments, the aralkyl group contains 7 to 14 carbon atoms, 7 to 10 carbon atoms, for example, 7, 8, 9, or 10 carbon atoms, or any range thereof (e.g., 7 to 8) carbon atoms. The aralkyl group may or may not be substituted. The substituted aralkyl group may be substituted in the alkyl part, aryl part, or both the alkyl part and the aryl part of the group. Representative substituted and unsubstituted aralkyl groups include, but are not limited to, alkylphenyls such as methylphenyl, (chloromethyl)phenyl, chloro(chloromethyl)phenyl, or condensed aralkyl groups such as 5-ethylnaphthalenyl.

[0027] A heterocyclyl group is a non-aromatic cyclic compound containing three or more ring members, one or more of which are heteroatoms such as N, O, and S, but are not limited thereto. In some embodiments, the heterocyclyl group contains 1, 2, 3, or 4 heteroatoms. In some embodiments, the heterocyclyl group includes monocyclic, bicyclic, and tricyclic rings having 3 to 16 ring members, while other such groups have 3 to 6, 3 to 10, 3 to 12, or 3 to 14 ring members. The heterocyclyl group includes, for example, partially saturated and saturated ring systems such as imidazolinyl and imidazolidinyl groups. This term also includes, but is not limited to, bridged polycyclic ring systems containing heteroatoms such as quinuclidyl. This term also includes heterocyclyl groups having other groups such as an alkyl group, an oxo group, or a halo group attached to one of the ring members, which are referred to as "substituted heterocyclyl groups". Examples of 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 di- or more substituted. For example, a di-substituted, tri-substituted, tetra-substituted, penta-substituted, or hexa-substituted morpholinyl group, or a morpholinyl group di-substituted with various substituents as described above, may be mentioned, but are not limited thereto. Also, the heteroatom(s) may be in an oxidized form if chemically possible. A heteroaryl group is an aromatic ring compound containing 5 or more ring members, and one or more of its ring members are heteroatoms such as N, O, and S, but are not limited thereto. Examples of the heteroaryl group include, but are not limited to, a pyrrolyl group, a pyrazolyl group, a triazolyl group, a tetrazolyl group, an oxazolyl group, an isoxazolyl group, a thiazolyl group, a pyridinyl group, a pyridazinyl group, a pyrimidinyl group, a pyrazinyl group, a thiophenyl group, a benzothiophenyl group, a furanyl group, an imidazolyl group, a benzofuranyl group, an indolyl group, an azaindolyl (pyrrolopyridinyl) group, an indazolyl group, a benzimidazolyl group, an imidazopyridinyl (azabenzimidazolyl) group, a pyrazolopyridinyl group, a triazolopyridinyl group, a benzotriazolyl group, a benzoxazolyl group, a benzothiazolyl group, a benzothiadiazolyl group, an imidazopyridinyl group, an isoxazolopyridinyl group, a thianaphthyl group, a purinyl group, a xanthinyl group, an adeninyl group, a guanylinyl group, a quinolinyl group, an isoquinolinyl group, a tetrahydroquinolinyl group, a quinoxalinyl group, and a quinazolinyl group. The heteroaryl group includes a condensed ring compound in which all rings are aromatic such as an indolyl group, and also includes a condensed ring compound in which only one ring such as a 2,3-dihydroindolyl group is aromatic. The term "heteroaryl group" includes a condensed ring compound, and also includes a heteroaryl group in which another group is bonded to one of the ring members such as an alkyl group, which is referred to as a "substituted heteroaryl group". Representative substituted heteroaryl groups may be mono-substituted or more with various substituents as listed above. Also, the heteroatom(s) may be in an oxidized form if chemically possible.

[0028] As used herein, the term "halogen" or "halo" refers to bromine, chlorine, fluorine, or iodine. In some embodiments, the halogen is fluorine. In other embodiments, the halogen is chlorine or bromine. As used herein, the term "halide" refers to an anion of a halogen such as bromide, chloride, fluoride, and iodide. In some embodiments, the halide is chloride or iodide. The term "alkoxy" refers to a substituted or unsubstituted alkyl group bonded to an oxygen atom, such as the moiety of the formula -OR a wherein R a is alkyl as defined herein. Examples include, but are not limited to, methoxy and ethoxy. Representative substituted alkoxy groups may be mono- or more substituted with substituents such as those listed above, such as methoxymethyl and fluoromethoxy. The term "alkylamino" refers to the moiety of the formula -NHR a wherein R a is alkyl as defined herein. The term "dialkylamino" refers to the moiety of the formula -NR a R b wherein R a and R b are each independently alkyl as defined herein.

[0029] Disclosed herein is a redox flow battery system that includes conjugated heterocyclic carbenium compounds as both anolytes and catholytes. These conjugated heterocyclic carbenium compounds are redox-active compounds that can be reversibly reduced and oxidized to provide an open-circuit potential (the potential difference between oxidation and reduction) higher than 2 V. Also, by using the same compound for both the catholyte and the anolyte, cross-contamination and a decrease in battery life associated with current redox flow battery systems can be avoided. Further, the conjugated heterocyclic carbenium compounds disclosed herein also have photoactivity and enable the preparation of a redox flow battery system that is charged photocatalytically. These conjugated carbene cations are formed by the sequential double S of tris(2,6-dimethoxyphenyl)carbenium ion and a primary amine NIt can be easily prepared by removing methanol at medium to high temperatures from the Ar reaction. The reasons why these stable carbocation salts are particularly interesting are as follows: 1) they are the most stable carbocations in the literature even under weakly acidic or basic aqueous solution conditions; 2) due to the stepwise and temperature-dependent synthesis, versatility is brought about by using aliphatic or aromatic amines or forming asymmetric ions; 3) they can be functionalized via C-H borylation reactions and / or cross-coupling with metal catalysts; and 4) the negative counterions can be exchanged to affect the physical and chemical properties of the salts. In addition, these conjugated heterocyclic carbocation compounds are highly fluorescent, have a high extinction coefficient, and a long fluorescence lifetime. Moreover, these conjugated heterocyclic carbocation compounds are redox-active species with three stable redox states: carbodication, carbocation, and neutral carboradical.

[0030] The redox states of the heterocyclic carbocation compounds are shown in the following scheme. The neutral radical (C·) and the radical dication (C ++ ·) donate and accept electrons respectively to form the carbocation (C + ), and the discharge and power generation of the battery occur (Scheme 1; the process of the red dashed arrow). Alternately, the carbocation (C + ) donates and accepts electrons to be converted into the neutral radical (C·) or the radical dication (C ++ ·) respectively, and the battery is charged (Scheme A; the process of the blue solid arrow). Scheme A

Chemical Structure

[0031] FIG. 1 shows one embodiment of a redox flow battery - Type I RFB. In this embodiment, charging occurs via a current provided by an external energy source such as an ideal renewable energy (e.g., wind, sunlight, etc.) that needs to be stored. In the preliminary experiments disclosed herein, the current is provided by a potentiostat. FIG. 2 shows one embodiment of a redox flow battery - Type II RFB. Type II RFB utilizes the photovoltaic properties of C + wherein, after absorption of visible light, the excited state is oxidized upon losing an electron and can return to catholyte C ++ ·. The electron can move to the cathode and reduce C + to anolyte C·. Furthermore, by using a conjugated complex cyclic carbenium compound as both the anolyte and the catholyte, it is also possible to develop a symmetric organic redox flow battery (SORFB). This provides an opportunity to improve the characteristics of the exchange membrane (EM) separating the two electrodes of the battery and overcome the constraints associated with the aforementioned vanadium-based RFB. In particular, when the anion-selective membrane commonly used in vanadium-based RFB is replaced with a simple porous exchange membrane (EM), size-exclusion-based selection can be performed according to the pore size of the EM. By using the conjugated complex cyclic carbenium compound as both the anolyte and the catholyte, the chemical gradient of the electroactive species is reduced and crossover is reduced. Therefore, compared with VRFB and other RFBs, the risk of leakage of electroactive substances from one electrode to the other electrode of the battery is minimized in SORFB. Even if membrane-penetrating crossover occurs, since SRFB causes self-discharge, the ROM may return to its initial redox state without permanent contamination or electrolyte degradation. Thus, the symmetric RFB may be storable indefinitely without undergoing irreversible side reactions

[29] . Further description of exemplary porous EMs that can perform size-exclusion-based selection according to the pore size of the exchange membrane (EM) is provided herein.

[0032] First Embodiment of Redox Flow Battery In one aspect, a redox flow battery is provided that includes a catholyte containing a radical dication of a conjugated complex cyclic carbenium compound; and an anolyte containing a neutral radical of a conjugated complex cyclic carbenium compound. Here, the conjugated complex cyclic compounds present in the catholyte and the anolyte are the same compound. As used herein, the "same compound" refers to two different species such as a radical dication and a neutral radical that have different oxidation states / charges but the same atomic components and structure of the cathode species and the anode species. In some embodiments, the open-circuit potential of the redox flow battery exceeds about 1V. In some embodiments, the open-circuit potential of the redox flow battery exceeds about 2V. In some embodiments, the open-circuit potential of the redox flow battery is from about 1V to about 5V, from about 1.5V to about 5V, from about 1.5V to about 3V, from about 2V to about 5V, from about 2V to about 4V, or from about 2V to about 3V. In another aspect, there is provided a redox flow battery comprising a catholyte containing a radical dication of a compound of Formula I; and an anolyte containing a neutral radical of a compound of Formula I. Here, the compound of Formula (I) is represented by the following structure disclosed herein.

[0033] The conjugated heterocyclic carbenium compound disclosed herein is a compound of Formula I. The compound of Formula (I) is represented by the following structure:

Chemical formula

[0034] In some embodiments, the compound of formula I is a compound of formula Ia, formula Ib, or formula Ic below.

Chemical formula

[0035] In some embodiments, R 4a are each 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-Ar 3 , -(CH2)3-Ar 3 , -(CH2)3-Ar 3 , or -(CH2)4-Ar 3 ; Ar 3 is 2-pyridinyl. In some embodiments, R 4a is methyl, ethyl, propyl, butyl, pentyl, or hexyl. In some embodiments, R 4a is -(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, R4a is -(CH2)2-Ar 3 、-(CH2)3-Ar 3 、-(CH2)3-Ar 3 、or (CH2)4-Ar 3 is. In some embodiments, Ar 3 is pyridinyl such as 2-pyridinyl. In some embodiments, R 4a is -(CH2)-(OCH2CH2O) n CH3; 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, R 4a is -(CH2)2-(OCH2CH2O) n CH3; 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, R 4a is -(CH2)3-(OCH2CH2O) n CH3; 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, R 4a is -(CH2)4-(OCH2CH2O) n CH3; 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, R 4a is -(CH2)3-(OCH2CH2O) n CH3; wherein n is 1. In some embodiments, Y is an electron-withdrawing substituent. In some examples, the addition of an electron-withdrawing group such as NO2 improves the stability against oxygen, adds a reduction potential, and enables the storage of multiple electrons per molecule. In some embodiments, the compound of formula I has one, two, or three Y groups, and 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 NR 5a R 5b wherein R 5a and R 5b are each independently C1-C 12 alkyl. In some embodiments, Y is N(Me)2. In some embodiments, R 1a and R 2d are each C1-C4 alkoxy. In some embodiments, R 1a is C1-C4 alkoxy such as methoxy or ethoxy. In some embodiments, R 2d is C1-C4 alkoxy such as methoxy or ethoxy.

[0036] In some embodiments, R 1d and R 3a are each C1-C4 alkoxy. In some embodiments, R 1d is C1-C4 alkoxy such as methoxy or ethoxy. In some embodiments, R 3a is C1-C4 alkoxy such as methoxy or ethoxy. In some embodiments, R 1a , R 1b , R 1c , R 1d , R 2a , R 2b , R 2c , R 2d , R 3a , R 3b , R 3c , and R 3dis independently H in each case. In some embodiments, R 1b , R 1c , R 2b , R 2c , R 3b , and R 3c is independently H in each case. In some embodiments, R 1b is H. In some embodiments, R 1c is H. In some embodiments, R 2b is H. In some embodiments, R 2c is H. In some embodiments, R 3b is H. In some embodiments, the compound of formula Ia is the following compound: X 1 is each NR 4a ; R 4a is each independently C1-C 12 alkyl, C1-C4 dialkylamino, -L-Ar 3 , or -L 2 -Z 2 ; R 1a R 1d , R 3a , and R 2d are each C1-C4 alkoxy; R 1b , R 1c , R 2b , R 2c , R 3b , and R 3c are each independently H, C1-C4 alkylamino, or NO2; Y is each independently H, NO2, or NR 5a R 5b , and R 5a and R 5b are each independently H, CF3, or C1-C 12 alkyl. In some embodiments, X 1 is each NR 4a . In some embodiments, R 4a is each C1-C 12 alkyl. In some embodiments, R 4a is each C1-C4 dialkylamino. In some embodiments, R4a are each -L-Ar 3 respectively. In some embodiments, R 4a are each -L 2 -Z 2 respectively. In some embodiments, R 1a R 1d , R 3a , and R 2d are each C1-C4 alkoxy. In some embodiments, R 1b , R 1c , R 2b , R 2c , R 3b , and R 3c are each independently H or C1-C4 alkylamino. In some embodiments, R 1b , R 1c , R 2b , R 2c , R 3b , and R 3c are each independently H or NO2. In some embodiments, Y are each independently H or NO2. In some embodiments, Y are each independently H, or NR 5a R 5b respectively. In some embodiments, R 5a and R 5b are each independently H or C1-C 12 alkyl.

[0037] In some embodiments, the compound of formula Ib is the following compound: X 2 and X 3 are each NR 4a respectively; R 4a are each independently C1-C 12 alkyl, C1-C4 dialkylamino, -L-Ar 3 , or -L 2 -Z 2 respectively; R 1a and R 2d are each C1-C4 alkoxy; R 1b , R 1c , R 2b , R2c , R 3b , and R 3c are each independently H, C1-C4 alkylamino, or NO2; Y are each independently H, NO2, or NR 5a R 5b ; R 5a and R 5b are each independently H, CF3, or C1-C 12 alkyl. In some embodiments, X 2 and X 3 are each NR 4a . In some embodiments, R 4a are each C1-C 12 alkyl. In some embodiments, R 4a are each C1-C4 dialkylamino. In some embodiments, R 4a are each -L-Ar 3 . In some embodiments, R 4a are each -L 2 -Z 2 . In some embodiments, R 1a and R 2d are each C1-C4 alkoxy. In some embodiments, R 1b , R 1c , R 2b , R 2c , R 3b , and R 3c are each independently H or C1-C4 alkylamino. In some embodiments, R 1b , R 1c , R 2b , R 2c , R 3b , and R 3c are each independently H or NO2. In some embodiments, Y are each independently H or NO2. In some embodiments, Y are each independently H, or NR 5a R 5b . In some embodiments, R 5a and R 5b are each independently H or C1-C 12It is alkyl. In some embodiments, the compound of formula Ib is one of the following compounds: X 2 and X 3 are each NR 4a respectively; R 4a are each independently C1-C 12 alkyl, C1-C4 dialkylamino, or -L-Ar 3 respectively; R 1a and R 2d are each C1-C4 alkoxy; R 1b , R 1c , R 2b , R 2c , R 3b and R 3c are each independently H; Y is each independently H or NO2.

[0038] In any of the embodiments described herein, the compound of formula I may contain a functional group that improves the solubility of the compound or its redox state compound in an organic solvent such as CH3CN. These functional groups have oligomeric functionality such as PEGyl chains (-(OCH2CH2O) n CH3) that can improve solubility as shown in the following compounds. This type of molecular engineering has already been proven in recent literature to dramatically improve solubility [30, 31], and the relevance of this approach has been confirmed in recent community reviews

[32] .

Chemical formula

Chemical formula

[0039] The compounds of formula I described herein further include a counter anion. Exemplary counter anions for the carbocations of formula I can be any anion, such as anions derived from organic compounds such as halides (e.g., Cl, F, I, and Br), carboxylates, phosphates, sulfates, etc., but are not limited thereto. In some embodiments, the compounds of formula I further include an anion selected from tetrafluoroborate, hexafluorophosphate, perchlorate, tetraarylborate, trifluoromethanesulfonate, oxalatoborate, oxalate, phosphate, bis-trifluoromethanesulfonimide, halide, anions of ionic liquids, hydroxide, carbonate, bicarbonate, sulfate, hydrogen sulfate, sulfite; or a mixture of any two or more thereof. In some embodiments, the compounds of formula I further include an anion selected from tetrafluoroborate, hexafluorophosphate, or a mixture of any two or more thereof. In some embodiments, the compounds of formula I have photoactivity. In some embodiments, the compounds of formula I are excited by visible light. In some embodiments, the compounds of formula I are excited by wavelengths greater than about 500 nm. In some embodiments, Z and Z 1 are each independently a moiety containing a conjugated heterocyclic carbeneium. The moiety containing a conjugated heterocyclic carbeneium may be a compound of formula I including the compounds of formula Ia, Ib, and Ic described herein. In some examples, when Z and Z 1 are each independently a moiety containing a conjugated heterocyclic carbeneium, the resulting compound is a compound containing two or more conjugated heterocyclic carbeneiums. For example, a compound of formula Ib may be covalently bonded to another compound of formula Ib by an arylene, alkylene, or heteroalkylene linker, or a compound of formula Ic may be covalently bonded to another compound of formula Ic by an arylene, alkylene, or heteroalkylene linker.

[0040] Second Embodiment of a Redox Flow Battery In another aspect, a redox flow battery comprising: a catholyte comprising a conjugated heterocyclic cationic compound in a first oxidation state; and an anolyte comprising a conjugated heterocyclic cationic compound in a second oxidation state; is provided, wherein the first oxidation state has a higher degree of oxidation state than the second oxidation state. In some embodiments, the conjugated heterocyclic compound in the catholyte and the conjugated heterocyclic compound in the anolyte are the same compound, and the same compound refers to two different species having the same atomic components and structure of the cathode species and the anode species but having different oxidation states. In some embodiments, the conjugated heterocyclic compound in the catholyte and the conjugated heterocyclic compound in the anolyte are different compounds. For example, the anolyte contains a carbene having an electron-donating substituent, and the catholyte contains a carbene having an electron-donating substituent. The redox flow battery system may include a multi-electron process involving two, three, four, or more electrons. In some embodiments, the redox flow battery includes two electron processes such as the oxidation of a carbene compound to a radical dication and the reduction of the carbene compound to a neutral radical. In some embodiments, the redox flow battery includes an electron process of four or more electrons, in which different oxidation states / charges are achieved by adding an electron-donating or electron-withdrawing substituent to the conjugated heterocyclic carbene compound.

[0041] The conjugated heterocyclic compound in the catholyte or the anolyte may be any one of the carbene compounds described herein. In some embodiments, the conjugated heterocyclic compounds in the catholyte and the anolyte are each independently a compound of Formula I, and the compound of Formula (I) is represented by the following structure:

Chemical formula

[0042] In some embodiments, the compounds of formula I are each independently a compound of formula Ia, formula Ib, or formula Ic.

Chemical formula

[0043] In some embodiments, the compound of formula Ia is the following compound: X 1 are each NR 4a ; R 4a are each independently C1-C 12 alkyl, C1-C4 dialkylamino, -L-Ar 3 , or -L 2 -Z 2 ; R 1a , R 1d , R 3a , and R 2d are each C1-C4 alkoxy; R 1b , R 1c , R 2b , R 2c , R 3b , and R 3c are each independently H, C1-C4 alkylamino, or NO2; Y are each independently H, NO2, or NR 5a R 5b ; R 5a and R 5b are each independently H, CF3, or C1-C 12 alkyl. In some embodiments, X 1 are each NR4a It is. In some embodiments, R 4a are each C1-C 12 alkyl. In some embodiments, R 4a are each C1-C4 dialkylamino. In some embodiments, R 4a are each -L-Ar 3 It is. In some embodiments, R 4a are each -L 2 -Z 2 It is. In some embodiments, R 1a R 1d R 3a and R 2d are each C1-C4 alkoxy. In some embodiments, R 1b R 1c R 2b R 2c R 3b and R 3c are each independently H or C1-C4 alkylamino. In some embodiments, R 1b R 1c R 2b R 2c R 3b and R 3c are each independently H or NO2. In some embodiments, Y are each independently H or NO2. In some embodiments, Y are each independently H, or NR 5a R 5b It is. In some embodiments, R 5a and R 5b are each independently H or C1-C 12 alkyl.

[0044] In some embodiments, the compound of formula Ib is the following compound: X 2 and X 3 are each NR 4a It is; R 4a are each independently C1-C 12 alkyl, C1-C4 dialkylamino, -L-Ar 3 or -L 2 -Z2 and; R 1a and R 2d are each C1-C4 alkoxy; R 1b , R 1c , R 2b , R 2c , R 3b , and R 3c are each independently H, C1-C4 alkylamino, or NO2; Y are each independently H, NO2, or NR 5a R 5b ; R 5a and R 5b are each independently H, CF3, or C1-C 12 alkyl. In some embodiments, X 2 and X 3 are each NR 4a . In some embodiments, R 4a are each C1-C 12 alkyl. In some embodiments, R 4a are each C1-C4 dialkylamino. In some embodiments, R 4a are each -L-Ar 3 . In some embodiments, R 4a are each -L 2 -Z 2 . In some embodiments, R 1a and R 2d are each C1-C4 alkoxy. In some embodiments, R 1b , R 1c , R 2b , R 2c , R 3b , and R 3c are each independently H or C1-C4 alkylamino. In some embodiments, R 1b , R 1c , R 2b , R 2c , R 3b , and R 3cEach is independently H or NO2. In some embodiments, each Y is independently H or NO2. In some embodiments, each Y is independently H or NR 5a R 5b wherein. In some embodiments, R 5a and R 5b are each independently H or C1-C 12 alkyl. In some embodiments, the compounds are each independently a compound of formula Ib below: X 2 and X 3 are each NR 4a wherein; R 4a are each independently C1-C 12 alkyl, C1-C4 dialkylamino, or -L-Ar 3 wherein; R 1a and R 2d are each C1-C4 alkoxy; R 1b , R 1c , R 2b , R 2c , R 3b and R 3c are each independently H; Each Y is independently H or NO2.

[0045] In some embodiments, the compounds of formula 1 are each independently any one of the compounds of the following formula.

Chemical formula

[0046] In some embodiments, the electrolyte salt is a lithium, sodium, potassium, ammonium, or alkylammonium salt of tetrafluoroboric acid, hexafluorophosphoric acid, perchloric acid, tetraarylboric acid, trifluoromethanesulfonic acid, oxalatoboric acid, oxalic acid, phosphoric acid, bis-trifluoromethanesulfonimide, halide; or a mixture of any two or more thereof. In some embodiments, the electrolyte is a tetrafluoroboric acid, hexafluorophosphoric acid, perchloric acid, tetraarylboric acid, trifluoromethanesulfonic acid, oxalatoboric acid, oxalic acid, phosphoric acid, bis-trifluoromethanesulfonimide, alkylammonium salt of 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 tetrafluoroborate, tetraethylammonium tetrafluoroborate, or a mixture of any two or more thereof. In some embodiments, the solvent includes a nitrile solvent, an ether solvent, dimethylformamide, water, a halogenated solvent, or an ionic liquid.

[0047] In some embodiments, the conjugated heterocyclic cation compound has photoactivity. In some embodiments, the open circuit potential of the redox flow battery exceeds about 1V, 1.5V, or 2V. In some embodiments, the open circuit potential of the redox flow battery is from about 1V to about 5V, from about 1.5V to about 5V, from about 1.5V to about 3V, from about 2V to about 5V, from about 2V to about 4V, or from about 2V to about 3V. In some embodiments, the redox flow battery, such as any one of the redox flow batteries described herein, further includes a separator disposed between the anolyte and the catholyte. In some embodiments, the separator is a porous membrane. In some embodiments, the redox flow battery further includes a solvent and an electrolyte salt. 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, or alkylammonium salt of tetrafluoroboric acid, hexafluorophosphoric acid, perchloric acid, tetraarylboric acid, trifluoromethanesulfonic acid, oxalatoboric acid, oxalic acid, phosphoric acid, bis-trifluoromethanesulfonimide, halide; or a mixture of any two or more thereof. In some embodiments, the electrolyte is a tetrafluoroboric acid, hexafluorophosphoric acid, perchloric acid, tetraarylboric acid, trifluoromethanesulfonic acid, oxalatoboric acid, oxalic acid, phosphoric acid, bis-trifluoromethanesulfonimide, alkylammonium salt of 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 tetrafluoroborate, tetraethylammonium tetrafluoroborate, or a mixture of any two or more thereof.

[0048] Any one of the redox flow batteries described herein may further include a solvent. In some embodiments, the solvent includes a nitrile solvent such as acetonitrile; an ether solvent such as tetrahydrofuran; dimethylformamide; water; a halogenated solvent such as dichloromethane, or an ionic liquid. In another aspect, a method of operating a redox flow battery, such as any one of the redox flow batteries described herein, is provided. The method includes flowing catholyte within a catholyte compartment and flowing anolyte within an anolyte compartment, the catholyte compartment and the anolyte compartment being separated by a porous separator that facilitates electron transport from the anolyte to the catholyte. In some embodiments, the separator is a porous membrane. In some embodiments, after electron transport, the method includes regenerating the catholyte and / or the anolyte by an external power source. In some embodiments, the step of regenerating the catholyte includes regenerating the catholyte via photo-assisted oxidation. In some embodiments, the step of regenerating the anolyte includes regenerating the anolyte via photo-assisted reduction. The redox flow battery system described herein may comprise any type of anode, cathode, and separator known to those skilled in the art. Further, the redox flow battery system described herein may also be used for energy release and / or energy storage.

[0049] In any of the embodiments described herein, the redox flow battery system is a symmetric organic reverse flow battery (SORFB). In some embodiments, the separator or exchange membrane is a porous membrane. Examples of porous membranes include, but are not limited to, the porous polypropylene membrane Celgard® 2500 with a porosity of about 55%, a thickness of about 25 μm, and a pore size (average diameter) of about 0.064 μm, and the porous membrane Daramic® HD plus with a porosity of about 55% and a thickness of about 175 μm. In some embodiments, the porous membrane is Celgard® 2500. In some embodiments, the porous membrane is a porous polypropylene membrane having one or more of the following characteristics: the porosity is at least about 55%, the thickness is at least about 25 μm, and the pore size (average diameter) is at least about 0.064 μm. In some embodiments, the porous membrane is a porous polypropylene membrane having one or more of the following characteristics: the porosity is about 55%, the thickness is about 25 μm, and the pore size (average diameter) is about 0.064 μm. In some embodiments, the porous membrane is Daramic® HD plus. In some embodiments, the porous membrane has one or more of the following characteristics: the porosity is at least about 55%, and the thickness is at least about 175 μm. In some embodiments, the porous membrane has one or more of the following characteristics: the porosity is about 55%, and the thickness is about 175 μm. In some embodiments, the separator or exchange membrane is an anion exchange membrane (AEM). In some embodiments, the efficiency or performance of a symmetric organic redox flow battery (SORFB) having a porous membrane as the exchange membrane is equivalent to or better than that of a symmetric organic redox flow battery (SORFB) having an anion exchange membrane as the exchange membrane. Suitable examples of anion exchange membranes include fluoride anion exchange membranes such as Fumasep® FAP-450 (conductivity in 0.5 M H2SO4 is 9-12 mS cm -1 and the 0.1 / 0.5 mol / kg KCl selectivity at T = 25 is 90-96%, and the proton transport rate is 2500-4500 μmol min-1 cm -2 There is, for example, a fluorinated anion exchange membrane having a thickness of 50 μm, but the present invention is not limited thereto. In some embodiments, the fluorinated anion exchange membrane is Fumasep® FAP-450. In some embodiments, the fluorinated anion exchange membrane has one or more of the following characteristics: the conductivity in 0.5 M H2SO4 is 9-12 mS cm -1 and the KCl selectivity of 0.1 / 0.5 mol / kg at T = 25 is 90-96%, and the proton transport rate is 2500-4500 μmol min -1 cm -2 and the thickness is 50 μm.

[0050] Furthermore, as shown in the examples described herein, based on preliminary results obtained from the study of the H-cell cycle, it has been found that one or more of the following characteristics are related to identifying a conjugated heterocyclic cation compound that is an ideal candidate for the RFB system. - The conjugated heterocyclic cation compound needs to have at least two fully reversible electron processes (symmetry parameter); - The two fully reversible electron processes need to be separated by a voltage difference of at least 2 V (energy density criterion); - The diffusion coefficient of the electron process is D ≧ 5.0×10 -6 cm 2 ·s -1 ; - The heterogeneous electron transport coefficient of the electron process is k 0 ≧ 1.0×10 -2 cm·s -1 ; - In the initial carbocation state, the conjugated heterocyclic cation compound needs to be soluble at ≧ 50 mM (energy density criterion); - In an H-cell, the cyclicity (capacity retention > 90%) of the conjugated heterocyclic cation compound needs to be ≧ 200 cycles. In some embodiments, the conjugated heterocyclic cation compounds described herein exhibit one or more of these characteristics.

Examples

[0051] Example 1. Preliminary Results of an RFB Cell Using Bis-nPr Helicene

Chemical Formula

[0052] Regarding the RFB test: To facilitate understanding and ease comparison with charge and discharge measurements, all the following data are provided with reference to the AgNO3 / Ag electrode.

[0053] DMF Dichloromethane was considered to be an inconvenient solvent for stabilizing the reduced species on a longer time scale than cyclic voltammetry. And due to the high polarity that makes the solubility of C + and C· ++ species and the known stability of C· in solution (over several days) suitable, DMF (dimethylformamide) was selected and investigated. Cyclic voltammetry was performed in a three-electrode electrochemical cell consisting of a carbon working electrode, an AgNO3 / Ag reference electrode (0.01 M AgNO3 in 0.1 M nBu4NPF6 in DMF), and a platinum counter electrode. The glassy carbon disk electrode was polished using aluminum oxide abrasive paper and anhydrous DMF. CV experiments were conducted at a scan rate of 100 mV / s in a 10 mL DMF electrolyte containing 1 mM of the active species (Figure 4). Unfortunately, compared to AgNO3 / Ag, C· generated at 850 mV++ Its formation was not reversible. This was confirmed by the fact that several processes acting during oxidation were shown in the DPV experiment (Figure 5).

[0054] ACN C· species were synthesized (see above) and dissolved in dry ACN in a glove box. No decomposition was observed by ultraviolet-visible (UV-Vis) spectroscopy for several hours. Therefore, ACN was selected as the solvent for further battery tests. Cyclic voltammetry was performed in a three-electrode electrochemical cell consisting of a carbon working electrode, an AgNO3 / Ag reference electrode (0.01 M AgNO3 in 0.1 M nBu4NPF6 in CH3CN), and a platinum counter electrode (Figure 6). The glassy carbon disk electrode was polished using aluminum oxide polishing paper and anhydrous CH3CN. CV experiments were carried out in a CH3CN electrolyte containing 1 mM active species and 0.1 M TBAPF6 at different scan rates of 10, 100, 500 mV / s. The reduction and oxidation processes occur at -1.14 V and 0.98 V with reference to the reference electrode (Figures 7, 8A, 8B). From these measurements, it can be seen that the open circuit potential (OCV) of a once-charged battery is 2.12 V between the two terminals (for a 100% charged solution). Just before the system is completely discharged, the minimum potential is 1.90 V. When measured at different rates (10, 100, 500 mV / s, Figures 8A and 8B) in the oxidation and reduction phenomena, waves that retain their shape appear after 5 cycles, demonstrating the stability of the species formed during the electron process and the reversibility in the selected solvent.

[0055] Conventionally, to report the cycle stability and reversibility of the device, galvanostatic charge / discharge with potential limitation (GCPL) was used. To avoid the overoxidation / overreduction phenomenon of the electrolyte during this research period, the total capacity of the battery was theoretically determined and the charge limit was defined (Figure 9). To account for possible charging losses and to compensate for system-specific overheating and resistance, an additional capacity limited to +1% has been defined. Thus, with an applied current of 5 mA, a load limit of 0.317 mA·h was selected. Hereinafter, the term "discharge" means "reverse current charging". Also, note that in the selected cell configuration, it starts with a battery in an intermediate "half-charged" state. In fact, each part of the cell contains the same neutral C + solution, i.e., half the amount of electroactive material. Therefore, the first charging cycle must be a cycle of capacity Total / 2 (i.e., 0.1585 mA·h) in order to avoid oxidation / reduction phenomena. This first charge and its total discharge (0.317 mA·h) have been removed from the following graph so as not to distort the efficiency of the system and not to artificially increase it.

[0056] Charge-discharge measurements were carried out in a custom-made glass H-cell equipped with a 2 mm fine porous glass frit (pore diameter 4 - 5.5 μm) used as a separator and a reference electrode (0.01 M AgNO3 / Ag in 0.1 M TBAPF6 in CH3CN). C + 10 mL of a 1.2 mM solution (0.1 M TBAPF6) of C was evenly filled into both compartments of the cell. A reticulated vitreous carbon (RVC) electrode (100 pores per inch (ppi), Duocel®) was cut into a rod shape with dimensions of 0.5 cm × 0.5 cm × 4 cm and placed at a depth of about 2 cm in the solution (about 33 cm 2 of active surface per electrode). To eliminate the contamination process, the electrodes were used alone. Next, a "constant current with constant voltage" galvanostat charge (CCCV / GCPL protocol) was applied to the RVC electrodes at a current of |5| mA. In a single electron cycle, the potential boundaries were set at -1.54 V and -0.74 V, and the capacity limit was 90% SOC. On the other hand, the stress test was limited between -1.54 V and 1.38 V, and the capacity limit was 100% SOC (Q max =Q theo ). During the charge-discharge experiment, both cells were continuously stirred at 1000 rpm. In the initial example, single-electron transport was carried out in a charge-discharge cycle at 90% of the theoretical capacity limit (90% state of charge "SOC") (Figure 9), where "constant current with constant voltage" galvanostat charging (CCCV / GCPL protocol) was performed at |5| mA, and the potential boundaries were E ref which were -1.54 V and -0.64 V compared to. A complete cycle corresponds to the charging process followed by the discharging process (Figure 10). During the charge-discharge cycle, two plateaus were observed at approximately -1.0 V and -1.2 V in the E w voltage curve, and these were the electron processes of the C + / C·redox pair process (Figure 11). Quite well, from the monitoring of this test cell in Figure 12, it can be seen that the Coulombic efficiency (CE, green triangles) remains constant and close to 100% throughout the experiment. Furthermore, the capacity Q (red and blue squares) was proven to be excellent by maintaining the initial capacity (Q init ) > 90% over 550 cycles (Figure 12). The battery of the present invention began to decrease in capacity at the 461st cycle. Thereafter, the system had a capacity retention rate decrease of 0.16% per cycle, and at the 800th cycle when the battery was stopped, the value was Q = 0.081 mA.h (i.e., 58% of Q init ). After the 800th cycle, CV analysis was performed at 100 mV / s for each content on each side of the cell (Figure 13).

[0057] n PrDMQA + By analyzing more deeply all the data collected so far for, in the following figure (Figure 12), the following was confirmed: In addition to the Coulombic efficiency (CE, green squares) being perfect throughout the experiment, the cycles of the molecules under the described standard conditions showed impressive values for the energy efficiency (EE, red triangles) representing the efficiency of the electrochemical conversion and the open-circuit voltage efficiency (VE, purple circles) regarding the polarization efficiency within the system. In both examples, EE and VE maintained an efficiency of 60 - 70% during 550 cycles of the cyclability shown by the system. This was an excellent result since it is difficult for most ORFBs to reach a value of 60% at the start of the cycle. Next, from the initial state of this symmetric cell, the potential boundaries were set to 1.38 and -1.54 V compared to E ref and a CCCV galvanostat charging sequence was started at a current of |5| mA (Figure 14). Focusing on the charge-discharge measurements (a figure focusing on the period from 400 s to 1000 s, i.e., one cycle, Figure 15), two different behaviors were shown as the battery charged. During discharge (488 - 718 s), the value of Ewe slowly reached 0.98 V (blue), and it was prominent that the discharge transfer rate was slow. Conversely, during discharge (718 - 898 s), it was confirmed that the -1 V threshold plateau was easily reached, and then it slowly reached the limit value of -1.54 V (blue). Based on the decrease in current intensity (red), it could be assumed that the reduction was efficient. Here, the diffusion of substances in the solution was the limiting factor. By deeply studying the resistivity of the system, diffusion parameters, and optimization of stirring in the cell, these limitations can be easily solved. In the long term, the current intensity, as well as the charging and discharging rates, can be increased.

[0058] Note that throughout the experiment, the discharge threshold of -1.54 V was systematically reached, but it should be noted that, as shown by the blue trace, it slowly reached the value of 1.38 V during 81 cycles. This phenomenon was caused by two factors: one was the deterioration of the surface of the electrode and its support (oxidation of the clamp holding the carbon electrode); the second cause was the change over time of the C· ++ form of the electrolyte. This suddenly appeared after the 80th cycle. These parameters can and will be solved by more reliable electrode research and rational selection, as well as stabilization of this electrolyte by proper functionalization of the suspension arm. Finally, when considering the efficiency of this system, it was found that the efficiency was almost constant and close to 100% over the 81 cycles examined (efficiency for the 81st cycle: 101%, 82nd cycle: 30%, green in Figure 16). These measurement results are preliminary results and will be improved in the near future using more appropriate electrodes. The efficiency was calculated based on the total cell capacity, or the Q charge / discharge of 0.317 mA·h maintained during the test (purple). All of these data indicate the robustness and high reliability of the electrolyte system over chemical stress cycles exceeding 15 hours. From the monitoring of the total capacity of the system during the cycle, it was found that during the experiment, a load of 0.317 mA·h was transmitted to and continuously regenerated in this system (Figure 16). The system begins to lose capacity after the 80th cycle, as shown by the decrease in the blue-violet (Figure 16) plot. And it begins to affect its efficiency from the 81st cycle. Note that when using the conventional "battery" type, the open-circuit voltage of this system is 2.12 V, but it should be noted that only half of the charge used for this study can be utilized. In fact, this battery can only return to the initial state t init (see the first scheme). The study of this cycle shown here is only for obtaining information and for demonstrating the robustness and versatility of this system.

[0059] Example 2. Synthesis and Characterization of Anolight C·Radical Stable neutral organic radicals are open-shell molecules with unpaired electrons occupying the highest molecular orbital (HOMO), which can easily participate in reactions such as hydrogen removal, dimerization, or recombination. [1、2] These molecules have been of interest in the scientific community for decades because they are low-cost, easily synthesized, have diverse structures, and are suitable for applications in catalysis. [3] Furthermore, in recent years, organic radicals have become of particular interest in the development of organic light-emitting diodes (OLEDs) and other material applications. [4] Since Gomberg discovered triphenylmethyl (trityl) radical in 1900[5] , through the basic research on other persistent and stable carbon-based radicals, their electronic structures and stabilities have become clear. Triarylmethyl radicals [6] , cyclopentadienyl radicals [7] , fluorenyl radicals [8] , and anthryl radicals [9] , bulky protecting groups have been used to prevent dimerization, as in the case of. Another approach to overcome the σ-dimerization of radicals is to introduce electron-withdrawing / donating substituents to control the electronic structure. For example, α,α-dicyanomethyl having a nitrogen-based electron donor at the para position of the carboradical has been demonstrated to have kinetic stability. The presence of an electron-withdrawing group α at the radical center helps to contract the spin density at the benzylic position and weaken the intermolecular C-C coupling reactivity

[10] . Furthermore, radicals can be stabilized when incorporated into a large π-conjugated system. This is the case for porphyrinoids

[11] , macrocyclic molecules, and fused π-skeletons

[12] .

[0060] In addition to linear systems, helical organic molecules can be obtained by developing fused π-conjugated systems. The inherent enantiomerism of helical molecules is of great concern for the development of novel organic radicals and their application to optoelectronic and spintronic materials [13、14] . Examples of [n]helicene (n = 4, 5, 6, 7) radicals have been reported only a few times in the literature. In this example, n represents the number of fused aromatic rings

[15] . In most cases, the unpaired electrons in these systems are stabilized through delocalization on the π-conjugated substituents, and the molecules with a larger number of fused aromatic rings show higher stability. Thus, [4]helicene is the least stable among this class of radicals and is a representative of relatively unknown radicals. As far as we know, only four examples of [4]helicene radicals have been reported in the literature, and one of them has not been isolated (Scheme 1a).

[0061] In 1958, Neunhoffer and Haase reported the first [4]helicene radical as the double ortho-bridged radical (I). This radical was of low stability and decomposed readily upon exposure to air.

[16] . Aulmich and co-workers also synthesized a [4]helicene radical (II) with a dimethyl-methylene unit as the bridging group.

[17] . Subsequently, Laursen et al. generated a quinolinoacridinium [4]helicene radical (III) by the in-situ electrochemical reduction of N,N’-dialkyl-1,13-dimethoxyquinacridinium (DMQA + ) and examined it by UV-vis and electron paramagnetic resonance (EPR) spectroscopy.

[18] . The characteristic data of this compound were insufficient to draw conclusions about the electronic structure of this radical species because the EPR spectrum was unresolved and DFT calculations could not be performed. In 2012, Morita and co-workers reported an enantiophenyl [4]helicene neutral radical (IV) stabilized by spin delocalization of the intramolecular π-electron network.

[19] . Recently, Osuka et al. reported air-stable triaryl Ni-porphyrin [4]helicene radicals and their chemically oxidized and reduced products.

[20] . Scheme 1. Literature reports and studies on [4]helicenium radicals

Chem.

[0062] It should be noted that in none of the above studies has the X-ray crystal structure of a pure organic [4]helicene-based neutral radical system been reported. Here, we introduce the facile synthesis and structural tuning of [4]helicene quinacridyl neutral radicals and the first X-ray crystal structure data of such species. The electronic properties of these paramagnetic [4]helicenium-based radicals will be 1The system was systematically studied by 1H NMR spectroscopy, continuous-wave (CW) EPR, electron-nuclear double resonance (ENDOR) spectroscopy, cyclic voltammetry, UV-vis absorption spectroscopy, and density functional theory (DFT) calculations. Similarly, the inventors have shown that introducing an electron-withdrawing -NO2 group into the backbone greatly affects the properties (stability, decomposition products, etc.) of the radical, and further one-electron reduction occurs, reaching the diradical anion form. Furthermore, the stability of all these radicals under aerobic conditions was investigated by UV-vis absorption spectroscopy. It was observed that while most radicals react irreversibly with oxygen molecules, these carboradicals reversibly oxidized to the corresponding carbocation analogs.

[0063] Results and Discussion The precursor helenium cation was synthesized according to the literature protocol

[21] . Tris(2,6-dimethoxyphenyl)methylium tetrafluoroborate (1) was stirred in acetonitrile at 85 °C for 12 h in the presence of the corresponding primary amine. This gave the helenium cations 2-H + , 3 + , and the known 4 + in high yields (Scheme 1a, condition i). Nitration of 2-H + according to the procedure reported by Lacour gave helenium 2-NO2 + (Scheme 2a, condition ii). Finally, the helenium cation 5 + was synthesized in a two-step method (Scheme 2a, condition iii). First, reacting 1 with 1 equiv of 2-(pyridin-2-yl)ethan-1-amine at room temperature for 2 h caused a color change from purple to red, typically forming the known acridinium intermediate S1

[22] . Reacting S1 with an excess of 3-(dimethylamino)-1-propylamine in acetonitrile at 85 °C for 12 h gave 5 + in high yield (Scheme 1a)

[23] . The formation of all [4]heleniums (2 + ~5 + ) was confirmed by 1 H and 13Confirmed by 13C NMR spectroscopy and X-ray crystallography.

[0064] Carbocation 2-H + and 3 + ~5 + of 1 The 1H NMR spectra are well-resolved and sharp at room temperature. At the same temperature, the 2-NO2 + 1 1H NMR spectra show broad and unclear signals in the range of 2.70~2.00 ppm, suggesting the presence of dynamic motion. To resolve the observed broad signals, variable temperature (VT) + 1H NMR spectroscopy of 2-NO2 1 was carried out. Samples were prepared in a non-coordinating solvent (CD2Cl2) and examined in the temperature range of 59.85~-80.15 °C (333~193 K). At room temperature (19.85 °C (293 K)), the aromatic protons are hardly resolved, and the 1 1H NMR spectra indicate that the amino arm is rapidly exchanging. When the temperature is lowered to -80.15 °C (193 K), the dynamic exchange decreases, and the proton signals become sharper and clearer. The six methylene protons of the amino arm are clearly visible at 4.95 and 3.55 ppm, 4.87 and 4.68 ppm, and 1.92 and 1.75 ppm, and it can be confirmed that they are assigned there. Also, by low-temperature correlated spectroscopy (COSY) NMR sequence method, the assignment of these protons was successful. These diastereostopic protons may have been caused by the interaction between the lone pair of nitrogen of one -nPr-NMe2 arm and the C + carbocation center (Scheme 3). Based on these data and the methylene H A‐A’ proton shift, the coalescence temperature is 4.85 °C (278 K), and NMe2-C +The Gibbs free energy change (ΔG) of the interaction was found to be 12.2 kcal / mol. Similarly, by observing the methoxy groups of the helicene structure ([4] at 3.77 ppm and 3.73 ppm at -80.15 °C (193 K)), it was found that at the association temperature of -25.15 °C (248 K), the ΔG of the o-MeOPh partial interconversion energy is 12.6 kcal / mol.

[0065] Scheme 2. Synthesis route

Chemical formula

Chemical formula

[0066] 2 + ~5 +The radical analogues (2·~5·) were synthesized by reducing it with metallic potassium in THF at room temperature overnight (Scheme 1b). The reaction mixture changed from a dark green suspension to a dark purple solution. The insoluble KBF4 salt formed in this process was removed by filtration. THF was removed under vacuum, and the resulting solid was extracted with toluene. Crystallization from a toluene / hexane mixture at -35 °C gave 2·~5· as dark brown crystals in good yield (Scheme 1b). The formation of the radicals 2·~5· was confirmed by the absence of a fluorine signal in the 19 19F NMR spectrum and the observation of characteristic EPR signals (see below). The resulting radicals are remarkably stable under an inert atmosphere at room temperature, both in the solid and solution states, and it is noteworthy that their color and crystallinity are retained indefinitely (for more than several months).

[0067] In addition, the molecules 2·~5· are paramagnetic 1Analysis was also performed by \(^1H\) NMR to examine whether the pendant arms of the molecule have any effect or interaction with the radical system. Due to the remarkable radical properties of these compounds, the aromatic protons of the helicene radical skeleton could not be observed. However, the protons of the substituent arms α (N-CH₂-CH₂-R) and β (N-CH₂-CH₂-R) on the helicene nucleus appear to be consistently broad and shifted at 17 and -7 ppm, respectively, in all radicals. The proton γ (N-CH₂-CH₂-R; R = CH₃, CH₂NMe₂, Py) on the helicene nucleus is not significantly affected by the radical and resonates in the broad but diamagnetic 10 - 0 ppm region. In 2-H·, the γ-proton was observed as a broad band with a width of 4 ppm centered at 5.71 ppm. The electron-withdrawing NO₂ group on 2-NO₂· is also presumed to have an effect of spreading in a band (9 - 2 ppm) centered around 5.71 ppm. The pyridinyl protons (π) of 3· and 5· are distinct at 8.58, 7.38, 6.33, and 6.03 ppm, respectively. In skeleton 5·, the broad signature of the γ-proton at 5.71 ppm is partially hidden by the π-protons. The γ-proton on 4· from the n-propyl group is less affected by the radical system and appears as a broad peak centered at 2.88 ppm. Therefore, the nature of the selected pendant arms seems to have little effect on the radical properties of compounds 2· - 5·. Conversely, substituting the protons of the helicenium nucleus with electron-withdrawing groups induces modification of the electronic structure of the resulting radical 2-NO₂·. This can be utilized in future research to freely modify the electronic structure of these heliceniums.

[0068] X-ray diffraction. By slowly layering DCM / hexane, cationic precursors 2-H + and 2-NO₂ + suitable for X-ray diffraction (XRD) analysis were obtained. 2-H + crystallized in the P-1 triclinic space group, while the nitro-cation (2-NO₂ +) showed the C2 / c monoclinic system. In both structures, the [4] helicenium skeleton is planar along the nitrogen cyclized fragment. Similarly, due to the significant steric hindrance between the o-(MeO)-phenyl moieties, torsion (2-H + : 41.93°, 2-NO2 + : 38.37°) was observed in the solid state (Table 1). The difference in the torsion angles between 2-H + and 2-NO2 + is also evident from the O1-O2 distances of 2.743 Å and 2.659 Å respectively. The two -nPr-NMe2 arms of 2-H + are not constrained and appear to be oriented on the same plane as the carbocation skeleton. As inferred from the VT 1 H NMR spectral analysis, one of the -nPr-NMe2 arms of 2-NO2 + is folded on the carbocation center (C1-N3: 3.194 Å). Also, this phenomenon occurs at the adjacent position of the NO2 group and is considered to be caused by steric hindrance. This interaction shows an increase in the Lewis acidity imparted to the carbocation center by the presence of the m-(NO2) group of 2-NO2 + , resulting in a non-bonding interaction between the lone pair electrons in C1 and N3 in the solid state, which can confirm the interpretation of the VT 1 H NMR spectrum of the present inventors. By slowly diffusing hexane, the neutral radicals 2-H· and 2-NO2· were isolated from the concentrated toluene solution, and crystals having the orthorhombic Pbca and triclinic P-1 space groups were obtained respectively. Since the BF4· counterion was absent, single electron reduction induced by metallic K in THF was confirmed. The distortion of the o-(MeO)-phenyl group is more prominent in 2-H· (45.92°, +3.99°), especially 2-NO2· (52.05°, +13.68°) than its cationic precursor. As a result, the O1-O2 distances of both complexes are similar distances (2-H·: 2.772 Å, and 2-NO2·: 2.773 Å) (Table 1).

[0069] The interatomic distances between the C1-C2, C1-C3, and C1-C4 atoms of 2-H· (1.439, 1.444, and 1.446 Å respectively) are those of the cation 2-H+ (1.406, 1.435, and 1.431 Å) indicates that there is an antibonding interaction between C1 and the surrounding atoms. This interaction, along with the localization of electron density at C1, is supported by DFT calculations (see below). Similarly, the C1–C3 distance (1.429 Å) in 2-NO2· is longer than that in 2-NO2 + (1.413 Å). In contrast, the bond distances in 2-NO2· are shorter than those in 2-NO2 + . For C1–C2, it is 1.423 Å compared to 1.431 Å in 2-NO2 + . For C1–C4, it is 1.438 Å compared to 1.440 Å in 2-NO2 + . For C2–C5, it is 1.408 Å compared to 1.435 Å in 2-NO2 + . This phenomenon is presumably due to the electron-withdrawing NO2 group, and the interatomic distances C–NO2 (from 1.452 Å to 1.444 Å) and N–O (from 1.233 / 1.235 Å to 1.226 / 1.235 Å) are also shorter, indicating a higher degree of delocalization of the electron charge. Finally, in 2-NO2·, the –nPr–NMe2 arm adjacent to the nitro group is out of plane due to the steric hindrance of the NO2 moiety. However, unlike in 2-NO2 + where an interaction is seen between the lone pair of NMe2 and the electron-deficient p-system, NMe2 is oriented away from the electron-rich π-system of the neutral radical molecule. Furthermore, it can be seen that the twist angle of the MeO–Ph group of helicene increases upon transition from the 2 + state to the 2· state. In the case of 2-H, the angle between the two planes formed by the aromatic rings increases slightly from 41.93° to 45.92° (i.e., +3.99°). In the case of 2-NO2 + , noting the twist angle (38.37°) of 2-H + in the carbocation state, an increase of +13.68° (to 52.05°) is observed upon transition to the radical state, indicating the significant influence of the –NO2 group.

[0070]

Table 1

[0071] EPR (ESR), ENDOR, measurements: The X-band EPR spectra of 2-H· and 3·–5· in liquid toluene solution are represented by Gaussian lines centered at g ≈ 2.003, with a width of about 0.76 mT and a low-resolution multi-line hyperfine structure split by about 0.088 mT (see Trace 1 of Fig. 17A showing the spectrum of 2-H· as an example). The g-factor and width of the EPR spectrum of 2-NO2· are the same, but the hyperfine structure is not resolved. 1 For more detailed information about the 1H hyperfine interaction (hfi), continuous-wave electron nuclear double resonance (ENDOR) experiments were carried out (Fig. 17B). The 1H ENDOR spectra of 2-H· and 3·–5· are generally similar, showing three pairs of lines indicated by (a,a’), (b,b’), and (c,c’). Each pair of lines is located at the frequency of ν 1 ± a H / 2, where ν H is the Zeeman frequency of the proton and a H is the hfi constant (which varies depending on the proton). The specific hfi constants estimated for each pair of ENDOR lines are: |a H | ≈ 7.1 MHz (a,a’ lines), |a Ha | ≈ 2.3 MHz (b,b’ lines), and |a Hb | ≈ 0.65 MHz (c,c’ lines). The splitting of 0.088 mT (about 2.5 MHz in frequency units) observed in the EPR spectra of 2-H· and 3·–5· is clearly due to a Hc and a Ha ​Hb It is determined by 1 The H hfi constants were assigned to specific molecular positions by comparing them with DFT predicted values. Figure 18 shows the relevant parts of the molecular structures of 2-H· and 3·-5· (i.e., since the ring system has approximately C2 symmetry with respect to the C1-C## axis, only half of the structure is shown). The calculated results of the spin populations of ring carbon, nitrogen(s), and ## oxygen are shown in purple. The 1 H hfi constant (a H = 1420 ρH [MHz]) is shown in green, and the corresponding experimentally assigned hfi constants are shown in light blue. The assignment of the ENDOR lines is shown in parentheses. Also, using the McConnell equation: a H = (-63 MHz) ρC the spin populations on the adjacent carbon atoms (α-protons) estimated from the experimental a H values are shown in dark blue in Figure 18.

[0072] For radical 2-NO2·, the protons marked with asterisks in Figure 18 are replaced with nitrogen of the NO2 group (only on one side of the molecule, see Scheme 2). As a result of this substitution in spectroscopy, the relative intensity of the (b,b’) lines in the ENDOR spectrum decreased by about 30%, and the (d,d’) and (e,e’) lines corresponding to a H = 6.05 and 5.37 MHz appeared (see Trace 2 in Figure 17B). Such a significant decrease in the intensity of the (b,b’) lines, according to the hfi assignment of the present invention shown in Figure 18, can be explained by the fact that one proton is removed from the a H = 2.3 MHz pool due to the substitution of H with NO2 ((b,b’) lines). Also, two or more protons are “rearranged” from the (b,b’) lines to the new (d,d’) and (e,e’) ENDOR lines. The three protons removed from the a H = 2.3 MHz pool originally consisted of ten protons, explaining the 30% decrease in the intensity of the (b,b’) lines. To assign the protons contributing to the (d,d’) and (e,e’) ENDOR lines, the molecular structure and DFT results are examined. In radical 2-NO2·, due to the steric collision between the NO2 group and the CH2 group bonded to the nearest ring nitrogen, the steric structure of the aromatic ring structure is greatly distorted, and the affected CH2 group reorients. In particular, the entire set of three aromatic rings shown in Fig. 18 acquires a remarkable saddle steric structure with an angle of 38° between the N-CH2 bond and the average plane formed by the N-containing ring (compared with <10° in 2-H· and 3·-5·). At the same time, as a result of the DFT calculation of radical 2-NO2·, the distribution of the spin population was basically the same as that of 2-H· and 3·-5·. Therefore, even considering the specific inaccuracies in the DFT prediction, the hfi constants of 6.05 and 5.37 MHz are most likely assigned to the protons of the methylene group bonded to the ring nitrogen adjacent to the NO2 group in 2-NO2·, and the a H values changing from 2.3 MHz to 6.05 and 5.37 MHz must undoubtedly be concluded to be mostly due to the above-mentioned steric structure changes.

[0073] Electrochemistry: The electrochemical behavior of 2 + to 5 + was investigated by cyclic voltammetry (Fig. 19). Under reduction conditions, in 2 + to 5 + , a complete reversible event was observed around E 1 / 2 = -1.25 V, which corresponds to the reduction to C· of C + (the CV of 4 + is reported by Laursen)

[18] . This event was observed at a lower potential (-1.0 V) in 2-NO2 + , which is consistent with the fact that the skeleton has less electrons due to the presence of the NO2 group. In 2-NO2 + , a second reversible reduction was observed at E 1 / 2 = -1.8 V. In the case of 2-H + and 3 + to 5 + , an irreversible reduction event was observed at E 1 / 2 = -2.3 V, which, as reported by Laursen, is from C· to C- corresponding to reduction to

[18] .

[0074] UV-Vis spectroscopy. To understand the electronic transitions, the UV-visible spectra of the cations and radicals (2 - 5) were examined (Table 2). Radical 2-H· shows sharp absorption bands, which have a maximum absorbance at 392 nm (ε = 15936), a shoulder at 445 nm (ε = 5090), and a broad absorption peak at 558 nm (ε = 6496). Such types of transition bands are not found in Compound IV

[19] , indicating that the inductive effect of the R substituent, which is either on the aryl ring or the bridging nitrogen, is responsible for the radical transition. On the other hand, the cation precursor (2-H + ) shows a sharp peak at 617 nm (ε = 14431), a shoulder at 570 nm (ε = 10526), and broad absorption at 435 nm (ε = 6044)

[34] . However, 2-H· has a blue-shifted absorption band compared to 2-H + , suggesting that the radical character exists in the central atom, the involvement of heteroatoms in the molecular skeleton is reduced, and the conjugation is significantly decreased. The increase in the localization of transitions in the isolated radical results in an increase in the number of transition bands in the visible region of 2-H· compared to 2-H + . Furthermore, the other radicals 3· - 5· show more or less similar transition energies, indicating that the influence of the nitrogen-bridging substituents on the transition energy is negligible. 2-NO2· showed the highest energy in the first transition among all transitions due to the inductive stabilization combining the NO2 group and the N-alkyl bridge

[18] .

Table 2

[0075] To quantify the stability of all radicals in the presence of oxygen, a solution of 2·–5· in CF3-tol prepared in an N2-filled glove box was exposed to air and monitored over time by UV-vis spectroscopy. For radicals 2-H· and 3·–5·, the absorption spectra of the radicals decreased slowly over time (indicated by the arrows), reaching low absorption in a few hours, and the final absorption spectral decay was consistent with that of their cationic forms (see Figure 20). Different from other radicals in this family, these quinacridyl[4]helenium radicals do not undergo oxygen insertion or dimer formation because the two ortho-methoxy groups within the molecule interact to prevent the radical from adopting a completely planar structure. Steric repulsion suppresses delocalization and avoids the formation of dimers or oxo analogues. Instead, complete reversible oxidation to the cationic analogue is observed. The half-life (t [16、17、25] ) of 2-H· was about 27 minutes, 45 minutes for 3·, 47 minutes for 5·, and 57 minutes for 4·. Due to the positive inductive effect of the n-propyl fragment of 4·, compared to other radicals, 4· has a longer half-life. On the other hand, the electron-deficient 2-NO2· radical has a long t 1 / 2 of 271 minutes, indicating that the radical is stabilized by the inductive effects of the nitro group and the n-propyl fragment. The stronger the -I effect of the -NO2 group, the lower the spin density and the loss of reactivity 1 / 2 . Furthermore, the electron-withdrawing -NO2 group reduces the reactivity of the radical towards oxygen molecules, so the oxidation of 2-NO2· to form its cationic analogue is less selective

[26] .

[27] .

[0076] Example 3.C ++ Preliminary results of radical dication supporting that · is a stable catholyte By oxidizing the carbeneium C + precursor with Magic Blue as the oxidizing agent, catholyte C++ as shown in the following scheme was successfully synthesized and isolated. The preliminary EPR spectroscopy measurement results are shown in Figure 21. This work is currently in progress to fully characterize this molecule using X-ray diffraction spectroscopy, UV-Vis spectroscopy, and DFT calculations.

Chem.

[0077] Example 4. Preliminary Results of Photocatalytic Activity for Photocharging of Batteries The following scheme shows the photocatalytic activity of the following compounds. Figure 22 shows the corresponding UV-visible spectra, cyclic voltammetry, and excited state potentials of these compounds. Scheme C. Potentials recorded in acetonitrile with respect to the SCF electrode.

Chem.

[0078] Example 5. Evaluation of the Robustness and Cyclability of Active Carbocation Electrolytes Dependent on the Supporting Electrolyte Salt In this example, an H-type cell cycle was used to evaluate the robustness and cyclability of active carbocation electrolytes dependent on the supporting electrolyte salt. The following compounds n PrDMQA + were used.

Chem.

[28] . The system was able to perform 550 cycles before losing 10% of its capacity. The use of the TBABF4 salt, which is slightly more expensive and less robust (stability range is 6.4 V)

[28] , improved this result, and a capacity exceeding 90% of the initial charge could be maintained during 680 cycles. The use of the TEABF4 salt (stability of 6.4 V)

[28] confirmed that the tetrabutylammonium salt is important for the stability of the system. In fact, from the second charging cycle, the capacity retention rate of the model battery decreased rapidly, and a loss exceeding 10% was observed after the 195th cycle.

Table 3

[0079] From these studies, it was found that the lifetime of the system and its capacity maintenance ability are directly and strongly dependent on the nature of the anions and countercations that make up the supporting salt. These results led to the conclusion that it is appropriate to first select the supporting electrolyte, as it results in good performance in terms of its cost and the cycle situation of the galvanostat cycle with potential limitation (GCPL). Therefore, TBAPF6 is a good "model" electrolyte for CH3CN in future investigations. It also seems important to emphasize the remarkable robustness of the redox materials proposed in this specification. Tests in an H-type cell guarantee the primary stability in the evaluation process of a suitable RFB system. In fact, lithium batteries are only tested at a maximum charging rate of 10C and show a 60% loss under these conditions, while the compounds tested were charged and discharged at 33C (i.e., 3.3 times the maximum charging rate of current batteries). This result also shows that in a static system, its capacity retention was maintained for more than 500 cycles under the most severe and stressful conditions.

[0080] Example 6. Evaluation of the Robustness and Cyclability of Active Carbocation Electrolytes Dependent on Supporting Electrolyte Salts This example relates to the design and construction of a highly robust, scalable, and reliable flow redox cell. Examples of non-aqueous, organic-based, and symmetric RFBs are shown in Fig. 23. The RFB cell is a gapless structure commercially available from Fuel Cell Technologies, consisting of a single exchange membrane EM (porous or anion-selective), two metal plates i, two gold-plated current collectors ii, two POCO (registered trademark) graphite serpentine bipolar electrodes iii, two Teflon gaskets iv, and two graphite felts (Sigracet 29AA) v with an area of 5 cm 2 Each. Eight bolts were used to seal the cell. A 2-channel Cole-Parme (Permer) Masterflex peristaltic pump, two electrolyte tanks, and several pump tubes were used to assemble the RFB. To validate the electrolyte as a redox-active material for electrochemical energy storage in symmetric ONRFBs, several aspects were evaluated: - Various DMQA + concentration (which affects not only the energy density but also the viscosity and therefore the efficiency of energy transport within the cell). - current density (affects the charging rate C, fatigue of electroactive materials, and duration of study) - The nature of the membrane EM, anionic (very expensive, accounting for 40% of the deployment costs of VRFB, but already proven as a separator) or porous (4-10 times cheaper, made possible by the symmetry of the system).

[0081] A lot of effort was put into standardizing cuts (carbon felt, membrane, gaskets), connecting all the tubes, calibrating the flow rates, and especially leak testing the whole RFB system to ensure its reliability and reproducibility of the results. After many adjustments and fine tuning, we built a fully assembled RFB system in a dedicated glove box. To obtain preliminary results, C in 0.1M TBAPF6CH3CN per tanker was + 10mL of 1mM solution of the model was used, and the flow rate was 10mL / min per tanker. -1 The EM selected for this evaluation was a porous membrane (Daramic HD plus, 175 μm, provided in bulk by Daramic). To demonstrate the suitability of the compounds described herein, n PrDMQA + is the C used in "real" RFB applications. + The model was run at different current densities (1, 3, 5, 10 mA cm 2 , 5 cycles each) at 100% state of charge (SOC), galvanostatic cycling with potential limiting (GCPL) and constant current constant voltage (CCCV) cycling were performed, and data were recorded at the most stressful conditions (e.g., >10C) that are expected to yield results better than the "normal" region (Figure 24).

[0082] Since the charge and discharge operated normally, the inexpensive porous membrane showed good performance as a separator, proving the reliability of the proof of concept of SONRFB using the porous separator. This also applied to different processing sequences (including >100C errors). 1 mA·cm 2 Then, despite the high C-rate (19C), as evidence of the electrochemical process, the reduction of C at around 2.1V + to C· serves as clear evidence (black trace, Figure 24). Focusing on the results of capacity retention and efficiency along the number of cycles, the results were quite astonishing for the system in its beta version (Figure 25). Along the 19C cycles, which are interpreted as the equilibrium period, the discharge capacity (blue trace, the classical behavior of RFB) slowly increased from 75% to 83%. Subsequently, along the charging rates of 56C, 93C, and 187C, Qdischarge increased to nearly 90%, and CE also approached 90%. Note that omitting the first 5 balance cycles, even when the C-rate state was 5.5 times higher, the values of EE and VE were good (>50%), close to the values observed in the H-type cell with the same compound. This result not only acknowledges the effectiveness of the proposed approach but also highlights that the H-type cell is a very effective test bench system for new compounds before scaling up to a full RFB cell. Furthermore, investigations at a maximum charging rate of 10C, 10-fold concentration, and a minimum of 200 cycles are underway.

[0083] Paragraph 1. A redox flow battery, wherein the redox flow battery comprises: A catholyte comprising a radical dication of a conjugated heterocyclic carbene compound; and An anolyte comprising a neutral radical of a conjugated heterocyclic carbene compound and The redox flow battery, wherein the conjugated heterocyclic compounds present in the catholyte and the anolyte are the same compound.

[0084] Paragraph 2. A redox flow battery, wherein the redox flow battery comprises: A catholyte comprising a radical dication of a compound of Formula I; and An anolyte comprising a neutral radical of a compound of Formula I; comprising The compound of formula (I) is represented by the following structure:

Chemical formula

[0085] Paragraph 3. The compound of formula I is a compound of formula Ia, formula Ib, or formula Ic, redox flow battery according to Paragraph 2.

Chemical formula

[0086] Paragraph 4. X 1 、X 2 、and X 3 is each independently O or NR 4a , redox flow battery according to Paragraph 2.

[0087] Paragraph 5. R 4a is each independently C1-C 12 alkyl, C1-C4 alkoxy, C1-C4 alkylamino, C1-C4 dialkylamino, Ar 3 、-L-Ar 3 、-L-Z, or -L 2 -Z 2 , redox flow battery according to Paragraph 4.

[0088] Paragraph 6. R 4aare each 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-Ar 3 , -(CH2)3-Ar 3 , -(CH2)3-Ar 3 , or -(CH2)4-Ar 3 ; Ar 3 is 2-pyridinyl, the redox flow battery according to paragraph 5.

[0089] Paragraph 7. R 4a are each -(CH2)-(OCH2CH2O) n CH3, -(CH2)2-(OCH2CH2O) n CH3, -(CH2)3-(OCH2CH2O) n CH3, or -(CH2)4-(OCH2CH2O) n CH3; n is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20, the redox flow battery according to paragraph 5.

[0090] Paragraph 8. R 4a are each -(CH2)-(OCH2CH2O) n CH3, -(CH2)2-(OCH2CH2O) n CH3, -(CH2)3-(OCH2CH2O) n CH3, or -(CH2)4-(OCH2CH2O) n CH3; n is 1, the redox flow battery according to paragraph 7.

[0091] Paragraph 9. Y are each independently H or NO2, the redox flow battery according to paragraph 2.

[0092] Paragraph 10. R 1a and R 2dThe redox flow battery according to paragraph 2, wherein each is C1-C4 alkoxy.

[0093] Paragraph 11. The compound of formula Ib is the following compound: X 2 and X 3 are each NR 4a ; R 4a are each independently C1-C 12 alkyl, C1-C4 dialkylamino, -L-Ar 3 or -L 2 -Z 2 ; R 1a and R 2d are each C1-C4 alkoxy; R 1b R 1c R 2b R 2c R 3b and R 3c are each independently H, C1-C4 alkylamino, or NO2; Y is each independently H, NO2, or NR 5a R 5b ; R 5a and R 5b are each independently H, CF3, or C1-C 12 alkyl, the redox flow battery according to paragraph 3.

[0094] Paragraph 12. The compound of formula I is any one of the compounds of the following formula, the redox flow battery according to paragraph 2.

Chemical formula

[0095] Paragraph 13. The redox flow battery according to paragraph 2, wherein the compound of formula I further comprises an anion selected from tetrafluoroborate, hexafluorophosphate, perchlorate, tetrarylborate, trifluoromethanesulfonate, oxalatoborate, oxalate, phosphate, bis-trifluoromethanesulfonimide, halide, anion of ionic liquid, hydroxide, carbonate, bicarbonate, sulfate, hydrogen sulfate, sulfite; or a mixture of two or more of these anions.

[0096] Paragraph 14. The redox flow battery according to paragraph 2, further comprising a separator disposed between the anolyte and the catholyte.

[0097] Paragraph 15. The redox flow battery according to paragraph 14, wherein the separator is a porous membrane.

[0098] Paragraph 16. The redox flow battery according to paragraph 2, further comprising a solvent and an electrolyte salt.

[0099] Paragraph 17. The redox flow battery according to paragraph 16, wherein the electrolyte salt is a lithium, sodium, potassium, ammonium salt or alkylammonium salt of tetrafluoroboric acid, hexafluorophosphoric acid, perchloric acid, tetraarylboric acid, trifluoromethanesulfonic acid, oxalatoboric acid, oxalic acid, phosphoric acid, bis-trifluoromethanesulfonimide, halide; or a mixture of two or more of these.

[0100] Paragraph 18. The redox flow battery according to paragraph 16, wherein the solvent comprises a nitrile solvent, an ether solvent, dimethylformamide, water, a halogenated solvent, or an ionic liquid.

[0101] Paragraph 19. The compound of formula I is a redox flow battery as described in paragraph 1 having photoactivity.

[0102] Paragraph 20. A method of operating a redox flow battery as described in paragraph 2, said method comprising flowing catholyte within a catholyte compartment and flowing anolyte within an anolyte compartment, the catholyte compartment and the anolyte compartment being separated by a porous separator, a method for promoting electron transport from the anolyte to the catholyte.

[0103] Paragraph 21. The method as described in paragraph 20, comprising the step of regenerating the catholyte and / or the anolyte by an external power source after electron transport.

[0104] Paragraph 22. The method as described in paragraph 21, wherein the step of regenerating the catholyte comprises the step of regenerating the catholyte via photo-utilized oxidation.

[0105] Paragraph 23. The method as described in paragraph 21, wherein the step of regenerating the anolyte comprises the step of regenerating the anolyte via photo-utilized reduction.

[0106] Paragraph 24. A redox flow battery, said redox flow battery comprising: A catholyte comprising a conjugated heterocyclic cationic compound in a first oxidation state; and An anolyte comprising a conjugated heterocyclic cationic compound in a second oxidation state; comprising A redox flow battery, wherein the first oxidation state has a higher degree of oxidation state than the second oxidation state.

[0107] Paragraph 25. The conjugated heterocyclic cationic compounds in the catholyte and the anolyte are each independently a compound of formula I, and the compound of formula (I) is represented by the following structure:

Chemical formula

[0108] Paragraph 26. The compound of formula I is each independently a compound of formula Ia, formula Ib, or formula Ic as described in paragraph 25, a redox flow battery.

Chemical formula

[0109] Paragraph 27. X 1 、X 2 、and X 3 are each independently O or NR 4a as described in paragraph 25, a redox flow battery.

[0110] Paragraph 28. R 4a are each independently C1-C 12 alkyl, C1-C4 alkoxy, C1-C4 alkylamino, C1-C4 dialkylamino, Ar 3 、-L-Ar 3 、-L-Z、or -L 2 -Z 2 as described in paragraph 27, a redox flow battery.

[0111] Paragraph 29. R 4a are each 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-Ar 3 、-(CH2)3-Ar 3 、-(CH2)3-Ar 3、 or -(CH2)4-Ar 3 ; Ar 3 is 2-pyridinyl, the redox flow battery described in paragraph 28.

[0112] Paragraph 30. R 4a are each -(CH2)-(OCH2CH2O) n CH3, -(CH2)2-(OCH2CH2O) n CH3, -(CH2)3-(OCH2CH2O) n CH3, or (CH2)4-(OCH2CH2O) n CH3; n is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20, the redox flow battery described in paragraph 28.

[0113] Paragraph 31. R 4a are each -(CH2)-(OCH2CH2O) n CH3, -(CH2)2-(OCH2CH2O) n CH3, -(CH2)3-(OCH2CH2O) n CH3, or -(CH2)4-(OCH2CH2O) n CH3; n is 1, the redox flow battery described in paragraph 30.

[0114] Paragraph 32. Y are each independently H or NO2, the redox flow battery described in paragraph 25.

[0115] Paragraph 33. R 1a and R 2d are each C1-C4 alkoxy, the redox flow battery described in paragraph 25.

[0116] Paragraph 34. The compounds of formula Ib are each independently the following compounds: X 2 and X 3is each NR 4a and; R 4a is each independently C1-C 12 alkyl, C1-C4 dialkylamino, -L-Ar 3 or -L 2 -Z 2 and; R 1a and R 2d is each C1-C4 alkoxy; R 1b R 1c R 2b R 2c R 3b and R 3c is each independently H, C1-C4 alkylamino, or NO2; Y is each independently H, NO2, or NR 5a R 5b and; R 5a and R 5b is each independently H, CF3, or C1-C 12 alkyl, the redox flow battery according to paragraph 26.

[0117] Paragraph 35. The compound of formula I is each independently any one compound of the following formulas, the redox flow battery according to paragraph 25.

Chemical formula

[0118] Paragraph 36. The conjugated complex cyclic cation compound further includes an anion selected independently from each other from tetrafluoroborate, hexafluorophosphate, perchlorate, tetraarylborate, trifluoromethanesulfonate, oxalatoborate, oxalate, phosphate, bis-trifluoromethanesulfonimide, halide, anion of ionic liquid, hydroxide, carbonate, bicarbonate, sulfate, hydrogen sulfate, sulfite; or a mixture of any two or more thereof, and the redox flow battery described in paragraph 24.

[0119] Paragraph 37. Furthermore, the redox flow battery described in paragraph 24, including a separator disposed between the anolyte and the catholyte.

[0120] Paragraph 38. The separator of the redox flow battery described in paragraph 37 is a porous membrane.

[0121] Paragraph 39. Furthermore, the redox flow battery described in paragraph 24, including a solvent and an electrolyte salt.

[0122] Paragraph 40. The electrolyte salt is a lithium, sodium, potassium, ammonium, or alkylammonium salt of tetrafluoroboric acid, hexafluorophosphoric acid, perchloric acid, tetraarylboric acid, trifluoromethanesulfonic acid, oxalatoboric acid, oxalic acid, phosphoric acid, bis-trifluoromethanesulfonimide, halide; or a mixture of any two or more thereof, and the redox flow battery described in paragraph 39.

[0123] Paragraph 41. The solvent of the redox flow battery described in paragraph 39 includes a nitrile solvent, an ether solvent, dimethylformamide, water, a halogenated solvent, or an ionic liquid.

[0124] Paragraph 42. The redox flow battery described in paragraph 24, wherein the conjugated complex cyclic cation compounds each independently have photoactivity.

[0125] Paragraph 43. The redox flow battery described in paragraph 24, wherein the open circuit potential of the redox flow battery exceeds about 1 V, 1.5 V, or 2 V.

[0126] Paragraph 44. A method of operating the redox flow battery described in paragraph 24, the method including flowing catholyte within a catholyte compartment and flowing anolyte within an anolyte compartment, the catholyte compartment and the anolyte compartment being separated by a porous separator, and promoting electron transport from the anolyte to the catholyte.

[0127] Paragraph 45. The method described in paragraph 44, including a step of regenerating the catholyte and / or the anolyte by an external power source after electron transport.

[0128] Paragraph 46. The method described in paragraph 45, wherein the step of regenerating the catholyte includes a step of regenerating the catholyte via photo-utilized oxidation.

[0129] Paragraph 47. The method described in paragraph 45, wherein the step of regenerating the anolyte includes a step of regenerating the anolyte via photo-utilized reduction.

[0130] Specific embodiments have been illustrated and described, but it should be understood that modifications and changes can be made to the embodiments in accordance with ordinary techniques in the art without departing from the broader aspects of the technology as defined in the following claims. The embodiments exemplified in this specification can be preferably implemented in the absence of elements (singular or plural) and limitations (singular or plural) not specifically disclosed in this specification. Therefore, for example, terms such as "comprising", "including", "containing", etc. shall be construed in an expansive manner without limitation. Also, the terms and expressions adopted in this specification have been used as terms of explanation and are not restrictive. In the use of such terms and expressions, there is no intention to exclude any equivalents of the features shown and explained or a part of such features, but it is recognized that various modifications are possible within the scope of the claimed technology. Further, the expression "consisting essentially of" is understood to include the specifically recited elements and additional elements that do not substantially affect the basic and novel features of the claimed technology. The expression "consisting of" excludes all elements not specified.

[0131] The present disclosure is not limited from the perspective of the specific embodiments described in this application. As will be apparent to those skilled in the art, many modifications and changes can be made without departing from the spirit and scope of the disclosure. In addition to those listed in this specification, functionally equivalent methods and compositions within the scope of the present disclosure will be apparent to those skilled in the art from the foregoing description. Such modifications and changes are intended to fall within the scope of the appended claims. The present disclosure should be limited only by the terms of the appended claims, to the extent of the full equivalents to which such claims are entitled. The present disclosure is not limited to a particular method, reagent, compound, composition, or biological system, and it should be understood that they can naturally be changed. Also, it should be understood that the terms used in this specification are for the purpose of describing only a particular embodiment and are not intended to be limiting. Also, when explaining the features or aspects of the present disclosure from the perspective of a Markush group, it is to be recognized by those skilled in the art that thereby the present disclosure is also explained from the perspective of any individual component of the Markush group or a subgroup of components.

[0132] As will be understood by those skilled in the art, for any and all purposes, particularly from the perspective of providing a written description, all ranges disclosed herein include any and all possible sub-ranges and combinations of sub-ranges. It can be readily recognized from any of the recited ranges that it is fully described and possible to divide the same range into at least equal halves, thirds, fourths, fifths, tenths, etc. As a non-limiting example, each range discussed herein can be readily divided into lower thirds, middle thirds, upper thirds, etc. Also, as will be understood by those skilled in the art, all phrases such as "up to", "at least", "more than", "less than", etc. include the recited numbers and then refer to ranges that can be divided into sub-ranges as described above. Finally, as will be understood by those skilled in the art, ranges include each individual member. All publications, patent applications, published patents, and other documents mentioned in this specification are hereby incorporated by reference as if each individual publication, patent application, published patent, or other document was specifically and individually indicated to be incorporated by reference in its entirety. Definitions contained in the documents incorporated by reference are excluded to the extent they conflict with the definitions in this disclosure. Other embodiments are described in the following claims.

[0133] [References] TIFF0007706472000032.tif158155 TIFF0007706472000033.tif198158 TIFF0007706472000034.tif186156 TIFF0007706472000035.tif183154

Claims

**Claim 1** A redox flow battery, wherein the redox flow battery comprises: a catholyte containing a radical dication of a compound of formula (I); and an anolyte containing a neutral radical of the compound of formula (I); comprising a redox flow battery, wherein the compound of formula (I) is represented by the following structure. 【Chemical Formula 1】 (In the formula, X is from -4 to +4; R 1a 、 R 1b 、 R 1c 、 R 1d 、 R 2a 、 R 2b 、 R 2c 、 R 2d 、 R 3a 、 R 3b 、 R 3c 、 and R 3d are each independently H, a halide, CF 3 、 NH 2 、 C 1 -C 12 alkyl, C 1 -C 4 alkoxy, C 1 -C 4 alkylamino, C 1 -C 4 dialkylamino, NO 2 、 CN, CO 2 R, or Ar 1 ; Or, R 2a and R 3d together form -X 1 -; Or, R 1a and R 2d together form -X 2 -; or, R 1d and R 3a together form -X 3 -; or R 1a and R 1b together with the atom to which it is attached forms phenyl; Or, R 2c and R 2d together with the atom to which it is attached form a phenyl; X 1 , X 2 and X 3 are each independently O, NR 4a , PR 4a , CR 4a R 4b , or SiR 4a R 4b ; R 4a and R 4b are each independently H, a halide, CF 3 , C 1 -C 12 alkyl, C 1 -C 4 alkoxy, C 1 -C 4 alkylamino, C 1 -C 4 dialkylamino, Ar 3 , -L-Ar 3 , -L-Z, or -L 2 -Z 2 ; Y is independently H, a halide, OR 5a , NR 5a R 5b , PR 5a R 5b , NO 2 , CN, CF 3 , CO 2 , N 3 , or Ar 2 ; R 5a and R 5b are each independently H, CF 3 , C 1 -C 12 alkyl, C 1 -C 4 alkoxy, C 1 -C 4 alkylamino, C 1 -C 4 dialkylamino, Ar 4 , -L 1 -Ar 4 , or -L 1 -Z 1 ; L and L 1 are each independently C 1 -C 12 -alkylene, C 1 -C 12 -heteroalkylene, or arylene; L 2 is each independently C 1 -C 12 alkylene; Z and Z 1 are each independently a moiety containing a conjugated cyclic carbenium ion; Z 2 are each independently —(OCH 2 CH 2 O) n CH 3 ; n is each independently from 1 to 20; R is each independently C 1 -C 12 alkyl or aryl; Ar 1 、Ar 2 、Ar 3 、and Ar 4 is each independently unsubstituted or substituted phenyl, or unsubstituted or substituted heteroaryl; Ar 1 、Ar 2 、Ar 3 、and Ar 4 is each independently substituted with 0 to 5 substituents; said substituents are each independently a halide, CF 3 、NH 2 、C 1 -C 4 alkyl, C 1 -C 4 alkoxy, C 1 -C 4 alkylamino, C 1 -C 4 dialkylamino, NO 2 、CN, or aryl (selected from the group consisting of). **Claim 2** The redox flow battery according to claim 1, wherein the compound of formula (I) is a compound of formula Ia, formula Ib, or formula Ic below. 【Chemical 2】 **Claim 3** X 1 , X 2 , and X 3 are each independently O or NR 4a The redox flow battery according to claim 1, wherein **Claim 4** R 4a is each independently C 1 -C 12 -alkyl, C 1 -C 4 -alkoxy, C 1 -C 4 -alkylamino, C 1 -C 4 -dialkylamino, Ar 3 , -L-Ar 3 , -L-Z, or -L 2 -Z 2 The redox flow battery according to claim 3, wherein it is **Claim 5** R 4a is independently methyl, ethyl, propyl, butyl, pentyl, hexyl, -(CH 2 )-N(Me) 2 ,-(CH 2 ) 2 -N(Me) 2 ,-(CH 2 ) 3 -N(Me) 2 ,-(CH 2 ) 3 -N(Me) 2 ,-(CH 2 ) 4 -N(Me) 2 ,-(CH 2 ) 2 -Ar 3 ,-(CH 2 ) 3 -Ar 3 ,-(CH 2 ) 3 -Ar 3 ,-(CH 2 ) 4 -Ar 3 ,-(CH 2 )-(OCH 2 CH 2 O)CH 3 ,-(CH 2 ) 2 -(OCH 2 CH 2 O)CH 3 ,-(CH 2 ) 3 -(OCH 2 CH 2 O)CH 3 or-(CH 2 ) 4 -(OCH 2 CH 2 O)CH 3 ; Ar 3 is 2-pyridinyl, the redox flow battery according to claim 4. **Claim 6** For the compound of formula Ib, in the formula, X 2 and X 3 are each NR 4a respectively; R 4a is each independently C 1 -C 12 -alkyl, C 1 -C 4 -dialkylamino, -L-Ar 3 or -L 2 -Z 2 wherein; R 1a and R 2d are each C 1 -C 4 alkoxy; R 1b 、R 1c 、R 2b 、R 2c 、R 3b 、and R 3c are each independently H, C 1 -C 4 alkylamino, or NO 2 ; Y is independently H, NO 2 , or NR 5a R 5b respectively; R 5a and R 5b are each independently H, CF 3 , or C 1 -C 12 alkyl, a compound, the redox flow battery according to claim 2. **Claim 7** The redox flow battery according to claim 1, wherein the compound of formula (I) is any one of the following compounds. [Chemical Formula 3] **Claim 8** The compound of formula (I) further comprises an anion selected from tetrafluoroborate, hexafluorophosphate, perchlorate, tetraarylborate, trifluoromethanesulfonate, oxalatoborate, oxalate, phosphate, bis-trifluoromethanesulfonimide, halide, an anion of an ionic liquid, hydroxide, carbonate, bicarbonate, sulfate, hydrogen sulfate, sulfite; or a mixture of any two or more thereof. The redox flow battery according to claim 1. **Claim 9** The redox flow battery according to claim 1, further comprising a separator disposed between the anolyte and the catholyte, wherein the separator is a porous membrane. **Claim 10** Furthermore, the redox flow battery according to claim 1, further comprising a solvent and an electrolyte salt. **Claim 11** The electrolyte salt is tetrafluoroboric acid, hexafluorophosphoric acid, perchloric acid, tetraarylboric acid, trifluoromethanesulfonic acid, oxalatoboric acid, oxalic acid, phosphoric acid, bis-trifluoromethanesulfonimide, a halide of lithium, sodium, potassium, ammonium, or alkylammonium salt; or a mixture of any two or more thereof. The redox flow battery according to claim 10. **Claim 12** The solvent comprises a nitrile solvent, an ether solvent, dimethylformamide, water, a halogenated solvent, or an ionic liquid. The redox flow battery according to claim 10. **Claim 13** A method of operating the redox flow battery according to claim 1, the method including the steps of flowing the catholyte within a catholyte compartment and flowing the anolyte within an anolyte compartment, the catholyte compartment and the anolyte compartment being separated by a porous separator, and a method in which electron transport from the anolyte to the catholyte is promoted.

14. The method according to claim 13, including the step of regenerating the catholyte and / or the anolyte by an external power source after the electron transport.

15. The redox flow battery according to claim 1, wherein an open circuit potential of the redox flow battery exceeds 1V.

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