C-substituted pyridinium redox materials and methods

Abstract

The present disclosure generally relates to pyridinium redox materials for various uses, such as electrolytes in electrochemical devices, for example, in redox flow batteries. The pyridine may be a bipyridinium, such as a 4,4 '-bipyridinium, in some aspects. In certain cases, such anolytes may be useful in electrochemical devices, for example, in a battery such as a flow battery. In some embodiments, the electrolyte may be based on a C-substituted 4,4'- bipyridinium, e.g., acting as an anolyte. Other aspects are generally directed to electrolytes such C-substituted pyridiniums, methods of making or using such C-substituted pyridiniums, kits involving such C-substituted pyridiniums, or the like.

Description

[0001] C-SUBSTITUTED PYRIDINIUM REDOX MATERIALS AND METHODS

[0002] RELATED APPLICATIONS

[0003] This application claims the benefit of U.S. Provisional Patent Application Serial No. 63 / 674,375, filed July 23, 2024, entitled “C-Substituted Pyridinium Redox Materials and Methods,” by Sullivan, et al., incorporated herein by reference in its entirety.

[0004] FIELD

[0005] The present disclosure generally relates to pyridinium redox materials for various uses, such as in electrochemical batteries and redox flow batteries.

[0006] BACKGROUND

[0007] As dispatchable fossil fuel power generation is replaced with intermittent solar and wind energy, energy storage is needed to stabilize the grid and time-shift renewable generation to meet demand. This has economic, reliability, and emission implications. Lithium-ion batteries currently dominate new installations due to their manufacturing at scale and operational knowhow, in part from the electric vehicle market. However, lithium-ion systems have fire safety concerns, supply chain constraints, and short duration configuration, limiting their value in the booming grid market. Thus, alternative solutions are needed to address electric grid sustainability at scale.

[0008] Aqueous flow batteries are a promising technology for stationary grid energy storage. Unlike conventional solid-state batteries (i.e., lithium ion), these systems decouple power (kW) and capacity (kWh) components. Redox active species are dissolved in water to serve as the anolyte (liquid anode) and catholyte (liquid cathode) and stored in electrolyte reservoirs. These electrolytes are pumped through a power cell stack where the species are reduced and oxidized at current collector surfaces (the anode and cathode) while separated by a membrane, charging and discharging electricity to and from the grid. Although numerous specific systems exist, flow battery archetypes are intrinsically more scalable and fire-safe for stationary applications.

[0009] Vanadium flow batteries are the most mature flow battery technology, having been heavily researched by NASA in the 1970s and deployed commercially since the early 2000s. However, their commercial progress has been stunted by their performance limitations and lithium-ion battery competition. Additionally, the raw vanadium electrolyte materials have a volatile supply chain with economics that are not able to compete with lithium-ion products. Thus, lower cost electrolyte materials are needed for widespread market impact.

[0010] Aqueous organic redox-active materials have been researched extensively for the past decade. As an alternative to inorganic species, like vanadium, these systems utilize water-soluble organic species that undergo reversible redox reactions. Most of these molecules comprise aromatic conjugation systems that are able to stabilize electrons and holes. Viologens are one such class of anolytes based on 4,4 ’-bipyridine cores with substitutions at both 1 -position N- pyridyl groups, resulting in di-cationic pyridinium salts in the fully oxidized state. However, improvements in aqueous organic redox-active materials, such as bipyridium redox materials, are still needed.

[0011] SUMMARY

[0012] The present disclosure generally relates to pyridinium redox materials for various uses, such as in electrochemical devices, for example, as electrolytes in redox flow batteries. The subject matter of the present disclosure involves, in some cases, interrelated products, alternative solutions to a particular problem, and / or a plurality of different uses of one or more systems and / or articles.

[0013] For instance, some aspects are generally directed to C-substituted bipyridinium redox materials, for example, for use as an anolyte in redox flow battery, or for other applications. In one set of embodiments, the bipyridinium may be a 4,4’ -bipyridinium compound. Other bipyridiniums are contemplated as well. The pyridiniums, in some embodiments, may have anionic, cationic, and or charge-neutral substitutions, for example, A-substitutions and / or C- substitutions. In some embodiments, e.g., when bearing negative ionically charged moieties, such anolytes may serve various purposes. This includes, for example, pairing with proton or cation ion-exchange membrane. In some embodiments, when bearing positive ionically charged moieties, such anolytes may serve other purposes. This includes, for example, pairing with anion ion-exchange membranes. In addition, in certain embodiments, such anolytes may potentially improve system energy density, power density, and cycling stability.

[0014] One aspect is generally drawn to an electrochemical device. In one set of embodiments, the device comprises an anode compartment containing an anolyte, the anolyte comprising a redox-active pyridinium comprising a C-substitution on the pyridyl ring of the pyridinium, wherein the C-substitution comprises at least two carbon atoms; a cathode or a cathode compartment containing a catholyte; and a membrane or separator between the anode compartment and the cathode compartment.

[0015] The device, in another set of embodiments, may comprise an anode compartment containing an anolyte, the anolyte comprising a redox-active pyridinium having a C-substitution on the pyridyl ring in a 3 position and / or a 5 position of the pyridinium; a cathode or a cathode compartment containing a catholyte; and a membrane or separator between the anode compartment and the cathode compartment.

[0016] In yet another set of embodiments, the device comprises an anode compartment containing an anolyte, the anolyte comprising a redox-active 4,4’ -bipyridinium having a C- substitution on the pyridyl ring in a 3 position and / or a 5 position; of the pyridinium, wherein the C-substitution is comprises at least two carbon atoms; a cathode or a cathode compartment containing a catholyte; and a membrane or separator between the anode compartment and the cathode compartment.

[0017] In addition, certain aspects are generally drawn to a composition. In one set of embodiments, the composition comprises a pyridinium comprising a C-substitution on the pyridyl ring of the pyridinium, wherein the C-substitution comprises at least two carbon atoms. In another set of embodiments, the composition comprises a pyridinium having a C-substitution on the pyridyl ring in a 3 position and / or a 5 position of the pyridinium. In still another set of embodiments, the composition comprises a 4,4’ -bipyridinium having a C-substitution on the pyridyl ring in a 3 position and / or a 5 position of the pyridinium, wherein the C-substitution is comprises at least two carbon atoms.

[0018] In another aspect, the present disclosure encompasses methods of making one or more of the embodiments described herein, for example, a C-substituted 4,4’ -bipyridinium, or other compounds such as any of those described herein. In still another aspect, the present disclosure encompasses methods of using one or more of the embodiments described herein, for example, a C-substituted 4,4’ -bipyridinium, or other compounds such as any of those described herein.

[0019] Other advantages and novel features of the present disclosure will become apparent from the following detailed description of various non-limiting embodiments of the disclosure when considered in conjunction with the accompanying figures.

[0020] BRIEF DESCRIPTION OF THE DRAWINGS Non-limiting embodiments of the present disclosure will be described by way of example with reference to the accompanying figures, which are schematic and are not intended to be drawn to scale. In the figures, each identical or nearly identical component illustrated is typically represented by a single numeral. For purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment of the disclosure shown where illustration is not necessary to allow those of ordinary skill in the art to understand the disclosure. In the figures:

[0021] Figs. 1A-1B illustrate a non-limiting example of a battery charging and discharging, in accordance with one embodiment;

[0022] Fig. 2 is a schematic of a flow battery, in another embodiment;

[0023] Figs. 3A-3B illustrate various 4,4’ -bipyridiniums, in other embodiments;

[0024] Fig. 4 illustrates various pyridiniums with C-substituents, in some embodiments;

[0025] Fig. 5 illustrates various C-substituted 4,4’ -bipyridines, in certain embodiments;

[0026] Figs. 6A-6C illustrate certain C-substituted pyridine reactions, in various embodiments;

[0027] Fig. 7 illustrates various pyridiniums with anionic N-substituents, in certain embodiments;

[0028] Fig. 8 illustrates various pyridiniums with cationic A-substituents, in certain embodiments;

[0029] Fig. 9 illustrates various pyridiniums with charge-neutral N-substituents, in certain embodiments;

[0030] Fig. 10 illustrates various extended pyridiniums, in certain embodiments;

[0031] Fig. 11 illustrates various tripyridines, in some embodiments;

[0032] Fig. 12 illustrates l,l-dextrosil-3,3-dimethyl-4,4-bipyridine, in accordance with one embodiment;

[0033] Fig. 13 illustrates l,l-dextrosil-3-methyl-4,4-bipyridine, in accordance with another embodiment

[0034] Figs. 14A-14D illustrates cyclic voltammetry of certain bipyridiniums, in yet other embodiments;

[0035] Fig. 15 illustrates a charge-discharge curve for a C-substituted pyridinium, in still another embodiment. DETAILED DESCRIPTION

[0036] The present disclosure generally relates to pyridinium redox materials for various uses, such as electrolytes in electrochemical devices, for example, in redox flow batteries. The pyridinium may be a bipyridinium, such as a 4,4 ’-bipyridinium, in some aspects. In certain cases, such anolytes may be useful in electrochemical devices, for example, in a battery such as a flow battery. In some embodiments, the electrolytes may be based on a C-substituted 4,4’- bipyridinium, e.g., acting as an anolyte. Other aspects are generally directed to electrolytes containing such C-substituted pyridiniums, methods of making or using such C-substituted pyridiniums, kits involving such C-substituted pyridiniums, or the like.

[0037] In certain aspects, pyridinium redox materials such as those described herein may be used as electrolytes in various redox-driven electrochemical devices, such as batteries, fuel cells, supercapacitors, or the like. In some cases, the electrochemical device may be a battery, such as a flow battery. A flow battery may be a battery having liquids present on separate sides of a membrane (e.g., separating an anode compartment from a cathode compartment), where ions can flow through the membrane from one liquid to the other, while electrons flow around the membrane, e.g., through an external circuit, and can be harnessed for power. In some cases, the membrane may be an ion-selective membrane, such as an anion-selective membrane or a cationselective membrane. In some embodiments, one, or both liquids may flow, e.g., from a reservoir, past the membrane, or through the device. In some cases, one or both liquids may be recirculated, e.g., to and from the reservoir. In some embodiments, the electrolyte may be static without flow inside one or more compartments in the battery. In some embodiments, one or both of the liquids may be aqueous, e.g., using water as a solvent, e.g., as in an aqueous electrolyte.

[0038] In some embodiments, the battery may be a flow battery. A flow battery, or a redox flow battery, is a type of electrochemical device where chemical energy is provided by chemical components dissolved in liquids that are present on separate sides of a membrane, such as an ion selective membrane. As discussed, ions can flow through the membrane while electrons flow around the membrane, e.g., through an external circuit. In some cases, liquids may flow on one or both sides of the membrane, e.g., pumped to and / or from a reservoir. In some cases, the liquids may be static without flow inside one or more compartments in the battery. The energy capacity of the battery can be controlled by controlling the volume of liquid within the reservoir. The liquid on the anode side is called the anolyte, while the liquid on the cathode side is called the catholyte, both generally referred to as the electrolyte.

[0039] Redox-active chemical species may be present within the electrolyte solutions in a battery (e.g., in a flow battery or static battery), where they can function as the anode and cathode electrolytes in some embodiments. The electrolyte in the anode compartment may be referred to as the anolyte, while the electrolyte in the cathode compartment may be referred to as the catholyte. During discharge of the electrochemical device, electrons flow from the anolyte to the catholyte (e.g., through a load). Oxidation (loss of electrons) occurs in the anolyte within the anode compartment, while reduction (gain of electrons) occurs in the catholyte within the cathode compartment. The electrons may flow from the anolyte, to an anode current collector, through an electrical circuit, to a cathode current collector, to the catholyte. In addition, to balance charge, cations (positively charged ions) may flow across the ion-exchange membrane from the anode compartment to the cathode compartment, or anions (negatively charged ions) may flow across the ion-exchange membrane from the cathode compartment to the anode compartment. During charging, this process is reversed. Electrons move from the catholyte to the anolyte (typically requiring energy to cause the electrons to flow in that direction). Reduction (gain of electrons) occurs in the anolyte within the anode compartment, while oxidation (loss of electrons) occurs in the catholyte within the cathode compartment. The electrons may flow from the catholyte, to a cathode current collector, through an electrical circuit, to an anode current collector, to the anolyte. In addition, to balance charge, cations (positively charged ions) flow across the ion-exchange membrane from the cathode compartment to the anode compartment, or anions (negatively charged anions) flow across the ion-exchange membrane from the anode compartment to the cathode compartment. In some cases, the liquid within the cathode may flow to and / or from a cathodic reservoir, and / or the liquid within the anode may flow to and / or from an anodic reservoir. In some cases, one or more liquid pumps may be used to cause liquid flow to occur. In some cases, the electrochemical or battery device may be a hybrid design, meaning that one of the anolyte or catholyte has liquid flow while the other is a static electrode / electrolyte material (e.g., zinc or iron deposition anode, sulfur cathode, or intercalation-based electrodes) or utilizes a gas flow (e.g., hydrogen as an anode or oxygen as a cathode). A non-limiting schematic diagram of a battery is shown in Fig. 1 , as an illustrative nonlimiting example. Fig. 1A shows a battery 10 in discharging mode. In anode compartment 20, an anolyte having a charge state n (i.e., An) is oxidized to produce an electron (e ) and a more positively charged state (An+1). The electrons may be collected by anode current collector 25, and can flow through load 40 to reach cathode current collector 35 in cathode compartment 30. In cathode compartment 30, the electrons from cathode current collector 35 may reduce the catholyte (having a charge state Cm+1) to produce a catholyte with a more negatively charged state m (i.e., Cm). In addition, counter-cations M+may flow from anode compartment 20 to cathode compartment 30 across ion exchange membrane 50, for example, which may be selectively permeable to the counter-cations. In these examples, n and m may independently be any suitable value, indicating a charge state, depending on the anolyte and the catholyte. For instance, n and m may independently be -3, -2, -1, 0, 1, 2, 3, etc.

[0040] Fig. IB shows battery 10 in charging mode, where these processes are essentially reversed. Electrons are pumped from the catholyte to the analyte via energy source 45, which inputs energy into the system to be stored in the battery. In anode compartment 20, the electrons combine with anolyte (having a charge state An+1) to produce an anolyte having a more negatively charged state (An), while the catholyte (having a charge state Cm) in cathode compartment 30 releases electrons to produce a more positively charged state (Cm+1). Countercations M+also can flow from cathode compartment 30 to anode compartment 20 across ion exchange membrane 50.

[0041] In some embodiments, for example, when battery 10 is a flow battery, one or both compartments may have fluid flowing therethrough. For example, as is shown in battery 10 in Fig. 2, pump 27 may recirculate a fluid containing the anolyte between anode compartment 20 and anode reservoir 22, and / or pump 37 may recirculate a fluid containing the catholyte between cathode compartment 30 and cathode reservoir 32.

[0042] A variety of redox species can be used as anolytes or catholytes in a battery, such as a flow battery, including inorganic species (e.g., sulfide / polysulfide, Zn / ZnX2 (X=I, Br, Cl), Cr2+ / Cr3+, V2+ / V3+, V4+ / V5+), organic species (e.g., viologens, anthraquionones, phenazines, thiolate, TEMPOs), metal-organic species (e.g., ferro / ferricyanide, metal-bipyridines, metal- polyaminocarboxylates), and halogen species. TEMPO derivatives, such as any of those described in US Pat. Apl. Ser. No. 63 / 552,006, filed February 9, 2024 (incorporated herein by reference in its entirety), and other nitroxyl radical derivatives, may be used in certain embodiments. Additional non-limiting examples of suitable redox species include any of those described in US Pat. Apl. Pub. Nos. 2022 / 0363663 and 2023 / 0006250.

[0043] In one aspect, certain embodiments relate to redox-active pyridiniums with at least one pyridyl core with a substitution at the carbon 2, 3, 5, and / or 6 positions. As used herein, these are to be referred to as “C-substituted” pyridiniums. The C-substituent may be any organic group, including any of those described herein, such as those bearing positive, negative, or neutral ionic charge. In some embodiments, the pyridinium may be a C-substituted bipyridinium. For example, a 4,4 ’-bipyridinium. In some embodiments, one or more of the pyridyl nitrogens may be A-substituted to form cationic pyridiniums. The A-substituent may be any organic group, including any of those described herein, such as those bearing positive, negative, or neutral ionic charge. The overall charge of the conjugated pyridinium core may, in some embodiments, be dynamic during electrochemical charge / discharge cycling. For example, the overall charge may become more negative (i.e., fewer cationic charges) as the pyridinium is reduced.

[0044] Fig. 3 A shows an example of a general, non-limiting schematic of a C-substituted 4,4’- bipyridinium and the associated redox mechanisms. In any of the molecular structures described herein, Ri and R2 may independently be A-substitutions, each at the 1 -position, which may be any organic group, including any of those described herein, such as those bearing positive, negative, or neutral ionic charge. Ri and R2 may be identical or different functionalization.

[0045] In any of the molecular structures described herein, Rnand Rmrepresent any number of C-substitutions at the 2, 3, 5, and / or 6 positions of one or both of the pyridyl rings, and these may independently be any organic group, including any of those described herein, such as those bearing positive, negative, or neutral ionic charge. For example, there may be 0, 1, 2, 3, or 4 Rngroups, and / or 0, 1, 2, 3, or 4 Rmgroups present, and each Rnor Rmmay independently be the same or different. At least one C-substitution may be present on at least one of the pyridyl rings. For example, Rnmay represent a single functionalization while Rmmay not exist, or vice versa. In some embodiments, more than one C-substituent may be on the same pyridyl ring at different positions with identical or different functionalization. For example, Rnmay represent more than one functionalization on the same pyridyl ring at different positions. In some embodiments, both pyridyl rings may bear a C-substituent of identical or varying functionalization. For example, Rnmay represent one or more substituents at different positions with identical or varying functionalization, and Rmmay similarly represent one or more substituents at different positions with identical or varying functionalization. In this context, when an R functionalization is present, that R represents a moiety other than hydrogen. The Rnand Rmgroups may be identical (e.g., symmetrically arranged) or different. Non-limiting examples of such compositions are shown in Fig. 3B.

[0046] In some embodiments, the C-substituted pyridinium may undergo an electron reduction. A non-limiting example is the 4,4 ’-bipyridinium shown in Fig. 3A. In some embodiments, the C- substituted 4,4’ -bipyridinium may undergo a two-step redox process with each step composing a one-electron transfer at different formal potentials. In some embodiments, the pyridinium may only undergo only the first one-step, one-electron redox process, for example inside an electrochemical battery. In other embodiments, the pyridinium material may undergo the full two-step, two-electron (total) redox process, for example inside an electrochemical battery. In some embodiments, undergoing only the first one-electron process may improve the electrochemical capacity stability of the device, while in some embodiments, undergoing the full two-electron process may increase the power and energy density of the device. In some embodiments, depending on the position and identity of the C-substituents, the two-electron reductions may occur at close or the same formal potential, such as in a one-step, two-electron redox process. In some embodiments, the C-substituted pyridinium molecule may have an electrochemical reversible redox process, for example, as in a rechargeable electrochemical battery.

[0047] C-substituted 4,4’ -bipyridiniums, as discussed herein and in some embodiments, could be considered as viologen derivatives. Viologens are A,V-disubstituted 4,4’-biypridiniums, in which both pyridyl nitrogen atoms are functionalized, e.g., to form dicationic pyridiniums in the oxidized state. Viologens may undergo a two-step reduction process in which electrons are sequentially stored in the bipyridyl conjugation system at separate formal potentials. Viologens, by definition, have only hydrogen as substituents on the 2, 3, 5, and 6 carbon positions, or, in other words, are only substituted at the pyridyl 1 -positions. C-substituted pyridiniums such as those discussed herein may have altered physiochemical, electrochemical, and / or device properties, compared to a pyridinium derivative with identical A-substitutions but without the C- substitutions. For example, the solubility, viscosity, redox potentials, electron transfer kinetics, membrane crossover, chemical stability, oxygen sensitivity, and more may be affected and / or can be tuned with C-substitution.

[0048] In some embodiments, the pyridinium redox molecule may possess a C-substitution or combination of one or more C-substitutions. Examples of C-substitutions (e.g., Rnand / or Rm) include, without limitation, alkyls (e.g., methyl), substituted alkyls (e.g., alkyl alcohols), aldehydes, esters, ethers, amines, carboxylates / carboxylic acids, sulfates / sulfuric acids, sulfonates / sulfonic acids, phosphates / phosphoric acids, phosphonates / phosphonic acids, amides, halogens, cyanos, nitrites, nitrates, or nitros, etc. In some embodiments, the C-substitution may be charge neutral, positive, or negative, and / or the pyridinium redox molecule may possess multiple C-substitutions of the same or different charges, for example, both a neutral and a negative, both a neutral and a positive, or both a negative and a positive, etc. In some embodiments, the C-substituted pyridinium may be a 4,4’ -bipyridinium. Furthermore, in some embodiments, the 4,4’-bopydrinidum may have one or more C-substitution on one of the pyridine rings or on both of the pyridine rings. In some embodiments, the C-substitution may be on any of the carbon positions. For example, in some embodiments of a C-substituted 4,4’- bipyridine, the C-substitution maybe be on one or more of the 2, 3, 5, or 6 positions. In some embodiments, the pyridyl may have the same C-substitution at multiple positions on the same pyridyl ring or may have different C-substitution on the same pyridyl ring. Specific non-limiting examples of pyridyl C-substitutions are shown in Fig. 4.

[0049] In one set of embodiments, the C-substituent (e.g., Rnand / or Rm) comprises one or more positively charged groups. The C-substituent may be, without limitation, alkyl groups (straightchain, branched, and cyclic), substituted alkyls (where one or more hydrogen atoms have been replaced by other atoms or groups), alkenes (straight-chain, branched, and cyclic), substituted alkenes (where one or more hydrogen atoms have been replaced by other atoms or groups), aryl groups (derived from aromatic rings), and substituted aryls (aryl groups further modified with additional functional groups, either to the aromatic ring itself or to substituents on the ring). Other examples include, without limitation, heterocyclic compounds (containing one or more heteroatoms such as nitrogen, oxygen, or sulfur), fused ring systems (where heterocyclic rings are joined to other heterocyclic or aromatic rings), and alkyl halides (where one or more halogen atoms are substituted for hydrogen). In one set of embodiments, the C-substituent (e.g., Rnand / or Rm) comprises one or more charge-neutral groups. Examples include without limitation, alkyl groups (straight-chain, branched, and cyclic), substituted alkyls (where one or more hydrogen atoms have been replaced by other atoms or groups), alkenes (straight-chain, branched, and cyclic), substituted alkenes (where one or more hydrogen atoms have been replaced by other atoms or groups), aryl groups (derived from aromatic rings), and substituted aryls (aryl groups further modified with additional functional groups, either to the aromatic ring itself or to substituents on the ring). Other examples include, without limitation, heterocyclic compounds (containing one or more heteroatoms such as nitrogen, oxygen, or sulfur), fused ring systems (where heterocyclic rings are joined to other heterocyclic or aromatic rings), and alkyl halides (where one or more halogen atoms are substituted for hydrogen). In some embodiments, the substituent may comprise charge-neutral hydrophilic moieties, including but not limited to alcohols, ethers, polyethylene glycols, amines, thiols, cyanos, and acid esters (e.g., sulfates, phosphates, sulfonates, phosphates, carboxylates).

[0050] In one set of embodiments, the C-substituent (e.g., Rnand / or Rm) comprises one or more negatively charged groups. Examples include, but are not limited to, sulfates (ROSO3 ), sulfonates (RSO3 ), phosphates (ROPO32), phosphate esters (ROP(OR’)O2-), phosphonates (RPO32), phosphonates esters (RP(OR’)O2-), and carboxylates (RCOO ). Examples of negatively charged organic substituents include but are not limited to nitrates (RONO2 ), carbamates (RO2CNH2 ), acetates (RCOO ), thiocyanates (RSCN ), isothiocyanates (RNCS ), perchlorates (ROCIO3 ), cyanates (ROCN ), isocyanates (RNCO ), and borates (RB(OR)2-). The backbone structures to which these substituents may be attached may encompass a wide range of organic frameworks. These include, without limitation, alkyl groups (straight-chain, branched, and cyclic), substituted alkyls (where one or more hydrogen atoms have been replaced by other atoms or groups), alkenes (straight-chain, branched, and cyclic), substituted alkenes (where one or more hydrogen atoms have been replaced by other atoms or groups), aryl groups (derived from aromatic rings), and substituted aryls (aryl groups further modified with additional functional groups, either to the aromatic ring itself or to substituents on the ring). Other examples include, without limitation, heterocyclic compounds (containing one or more heteroatoms such as nitrogen, oxygen, or sulfur), fused ring systems (where heterocyclic rings are joined to other heterocyclic or aromatic rings), and alkyl halides (where one or more halogen atoms are substituted for hydrogen). In some embodiments, the identity of the C-substitution may have electronic, electrostatic, and / or steric effects. In some embodiments, the C-substitution may perturbate the redox-active pyridinium properties, including redox kinetics, formal potential, water solubility, solution viscosity, membrane crossover, chemical stability, and synthetic cost. For example, electron donating groups (or “activating” groups) may increase the energy level of the Lowest Occupied Molecular Orbital (LUMO) and make the formal reduction potential more negative voltage, while electron withdrawing groups (or “deactivating” groups) may reduce the energy level of the LUMO and make the formal reduction potential more positive voltage. The terms “electron donating” and “electron withdrawing” are in reference to hydrogen as a baseline, as used in common chemistry practice. Non-limiting examples of electron donating groups include alkyl, amine, hydroxy, etc., and examples of electron withdrawing groups include as nonlimiting examples halogen, carbonyl, cyano, etc. In some embodiments, the C-substitution may have electrostatic effects on the pyridinium redox material. For example, the anionic or cationic charge may influence the solvation shell of the molecular species, altering the solubility and viscosity of the electrolyte. As another example, in some embodiments, through coulombic repulsion effects, an anionic charge may reduce permeability through cation-exchange membranes, and a cationic charge may reduce permeability through anionic-exchange membranes. In some embodiments, the size of the C-substitution may also have steric effects on solubility, viscosity, and membrane exclusion of the pyridinium redox molecule. In some embodiments, the identity of the C-substitution may alter the electron transfer interaction with and the mass transport phenomena to the electrode, impacting redox kinetics.

[0051] In addition to the identity of the C-substitution, in some embodiments, the position of the C-substitution on the pyridine redox species may also affect the molecular properties. In some embodiments, the nitrogen of the pyridyl groups may be considered as the 1 -position. Having the C-substitution on the 2 and / or 6 position on one or more of the pyridyl rings of a 4,4’- bipyridinium redox molecule may, in some embodiments, sterically protect the pyridinium group, altering the chemical stability by inhibiting hydrolysis and other substation or elimination reactions of the pyridyl functionalization. In another example, having the C-substitution on the 3 and / or 5 position of a 4,4’ -bipyridinium redox molecule may, in some embodiments, alter the electrochemical redox behavior of the molecule. However, in some embodiments, by having C- substitution at the 3 and / or 5 position of one or more of the pyridyl rings a 4,4’ -bipyridinium redox molecule, this conformational switch can be sterically altered, which may result in perturbations to the formal reduction potential and the redox kinetics. In some embodiments, the position of the C-substitution on the pyridinium redox molecule may alter the oxygen sensitivity of the reduced molecule, the solvation shell (i.e., solubility and viscosity), or the membrane permeability.

[0052] In some embodiments, the C-substituted pyridinium redox molecule is a 4,4’- bipyridinium. Non-limiting specific examples of some commercially available C-substituted 4,4’ -bipyridines are shown in Fig. 5. In some embodiments, the C-substituted 4,4’ -bipyridines can be synthesized from the reaction of C-substituted pyridines shown in Fig. 5 with an identical C-substituted pyridine, a different C-substituted pyridine, or with pyridine (i.e., without a C- substitution). In some embodiments, these C-substituted pyridines can be reacted in the presence of a reducing agent (e.g., NaH) and a catalyst, coupling the pyridyl groups to form the C- substituted 4,4’ -bipyridine (Fig. 6A). In some embodiments, a C-substituted 4,4’ -bipyridine can be produced through reaction modification of a 4,4’ -bipyridine. For example, in some embodiments, 4,4 ’-bipyridine or 4,4’ -bipyridinium itself without any a C-substitution can be reacted with a strong acid, base, or other highly reactive species to substitute a functionalization onto the pyridyl ring in place of a hydrogen (Fig. 6B). In other embodiments, for example, a C- substituted 4,4’ -bipyridine or 4,4 ’-bipyridinium with a leaving group (e.g., halogen) or other reactive group already on the pyridyl ring can be further reacted to substitute or form a different a C-substitution group (Fig. 6C). In some embodiments, the C-substituted 4,4’ -bipyridinium redox molecule can be formed by reaction of pyridiniums with A-substitution (Figs. 6A-6C, top routes), while in other embodiments, the C-substituted pyridines are first reacted and the N- substitution is then incorporated (Figs. 6A-6C bottom routes). In other words, to form a C- substituted 4,4’ -bipyridinium redox molecule, the C-substitutions and N- substitutions can be formed in any order. The C-substituents and the A-substituents may be selected independently, e.g., they may independently have the same or different functionalization groups and / or have the same or different ionic charges, etc.

[0053] In one set of embodiments, the organic A-substituent (e.g., Ri and / or R2) comprises one or more negatively charged groups. Examples include, but are not limited to, sulfates (ROSO3 ), sulfonates (RSO3 ), phosphates (ROPO32), phosphate esters (ROP(OR’)O2-), phosphonates (RPO32), phosphonates esters (RP(OR’)O2-), and carboxylates (RCOO ). Examples of negatively charged organic substituents include but are not limited to nitrates (RONO2 ), carbamates (RO2CNH2 ), acetates (RCOO ), thiocyanates (RSCN ), isothiocyanates (RNCS ), perchlorates (ROCIO3 ), cyanates (ROCN ), isocyanates (RNCO ), and borates (RB(OR)2-). The backbone structures to which these substituents may be attached may encompass a wide range of organic frameworks. These include, without limitation, alkyl groups (straight-chain, branched, and cyclic), substituted alkyls (where one or more hydrogen atoms have been replaced by other atoms or groups), alkenes (straight-chain, branched, and cyclic), substituted alkenes (where one or more hydrogen atoms have been replaced by other atoms or groups), aryl groups (derived from aromatic rings), and substituted aryls (aryl groups further modified with additional functional groups, either to the aromatic ring itself or to substituents on the ring). Other examples include, without limitation, heterocyclic compounds (containing one or more heteroatoms such as nitrogen, oxygen, or sulfur), fused ring systems (where heterocyclic rings are joined to other heterocyclic or aromatic rings), and alkyl halides (where one or more halogen atoms are substituted for hydrogen).

[0054] In some embodiments, for example, in which the pyridinium has an anionic N- substituent, various properties may be enhanced. The anionic charge of the anionic / ' / -substituent may, in certain cases, enhance the water solubility for application in aqueous solution, such as in aqueous flow batteries. The anionic substituent may, in some embodiments, reduce crossover through cation-exchange membranes. The anionic substituent may be, in certain embodiments, an inner salt as the pyridinium cation coordinates with the substituent anion or may have a counter-ion or mixture of counter-ions. The term “inner salt” refers to a molecule which has equal number of cation and anion that electrostatically pair together and result in a product without any additional counter-ions. Counter cations may include, without limitation, proton (H+), potassium (K+), sodium (Na+), lithium (Li+), ammonium (NHC), quaternary ammoniums (NRC), zinc (Zn2+), and iron (Fe2 / 3+), as well as other organic cations, metal cations, or metalorganic cations. Counter anions may include, without limitation, hydroxide (OH ), chloride (Cl ), bromide (Br ), iodide (I ), fluoride (F ), sulfate (SO4 ), phosphate (PO4 ), chlorate (CIO4 ), nitrate (NO2 ), borate (BO3 ), sulfide / polysulfide (e.g., S2 ), and acetate (CH3COO ), as well as other organic anions, metal anions, or metal-organic anions. Specific non-limiting examples of these are shown in Fig. 7. In one set of embodiments, the organic / ' / -substituent (e.g., Ri and / or R2) comprises one or more positively charged groups. Examples include, but are not limited to, quaternary ammoniums (RNR3+), imidazoliums, and pyridiniums. In some embodiments, the quaternary ammonium may be an alkyl or substituted alkyl ammonium. In other embodiments, the quaternary may be cyclic, including but not limited to a l,4-diazabicyclo[2.2.2]octane-l,4-diium group, a aziridinium group, an azetidinium group, a pyrrolidinium group, a piperidinium group, a morpholinium group, or a piperazinium group. In some embodiments, the ammonium may be positively charged due to protonation. The backbone structures to which these substituents may be attached may encompass a wide range of organic frameworks. These include, without limitation, alkyl groups (straight-chain, branched, and cyclic), substituted alkyls (where one or more hydrogen atoms have been replaced by other atoms or groups), alkenes (straight-chain, branched, and cyclic), substituted alkenes (where one or more hydrogen atoms have been replaced by other atoms or groups), aryl groups (derived from aromatic rings), and substituted aryls (aryl groups further modified with additional functional groups, either to the aromatic ring itself or to substituents on the ring). Other examples include, without limitation, heterocyclic compounds (containing one or more heteroatoms such as nitrogen, oxygen, or sulfur), fused ring systems (where heterocyclic rings are joined to other heterocyclic or aromatic rings), and alkyl halides (where one or more halogen atoms are substituted for hydrogen).

[0055] In some embodiments in which the pyridinium has a cationic / V- s LI bsti t Lien t , various properties may be enhanced. The cationic charge may enhance the water solubility for application in aqueous solution, such as in aqueous flow battery, in certain embodiments. In some cases, the cationic substituent may reduce crossover through anion-exchange membranes. The pyridinium may have a counter-anion or mixture of counter- anions in certain embodiments. Counter anions may include, without limitation, hydroxide (OH ), chloride (Cl ), bromide (Br ), iodide (I ), fluoride (F ), sulfate (SO4 ), phosphate (PO4 ), chlorate (CIO4 ), nitrate (NO2 ), borate (BO3 ), sulfide / polysulfide (S2), and acetate (CH3COO ), as well as other organic anions, metal anions, or metal-organic anions. Specific non-limiting examples of these are shown in Fig. 8.

[0056] In one set of embodiments, the organic / / -substituent (e.g., Ri and / or R2) comprises one or more charge-neutral groups. Examples include without limitation, alkyl groups (straightchain, branched, and cyclic), substituted alkyls (where one or more hydrogen atoms have been replaced by other atoms or groups), alkenes (straight-chain, branched, and cyclic), substituted alkenes (where one or more hydrogen atoms have been replaced by other atoms or groups), aryl groups (derived from aromatic rings), and substituted aryls (aryl groups further modified with additional functional groups, either to the aromatic ring itself or to substituents on the ring). Other examples include, without limitation, heterocyclic compounds (containing one or more heteroatoms such as nitrogen, oxygen, or sulfur), fused ring systems (where heterocyclic rings are joined to other heterocyclic or aromatic rings), and alkyl halides (where one or more halogen atoms are substituted for hydrogen). In some embodiments, the substituent may comprise chargeneutral hydrophilic moieties, including but not limited to alcohols, ethers, polyethylene glycols, amines, thiols, cyanos, and acid esters (e.g., sulfates, phosphates, sulfonates, phosphates, carboxylates).

[0057] In some embodiments in which the pyridinium has a charge-neutral N-substituent, various properties may be enhanced. For example, the neutral charge may reduce the solution viscosity for flow applications, such as in aqueous flow battery. The charge-neutral substituent may reduce crossover through size-exclusion membranes in some embodiments. The N- monosubstituted bipyridines with a charge-neutral substituent may have a counter-anion or mixture of counter-anions in some cases. Counter anions may include, without limitation, hydroxide (OH ), chloride (Cl ), bromide (Br ), iodide (I ), fluoride (F ), sulfate (SO4 ), phosphate (PO4 ), chlorate (CIO4 ), nitrate (NO2 ), borate (BO3 ), sulfide / polysulfide (S2), and acetate (CH3COO ), as well as other organic anions, metal anions, or metal-organic anions. Specific non-limiting examples of these are shown in Fig. 9.

[0058] In certain aspects, the pyridinium redox molecules may be bipyridiniums in which at least one C-substitution is present. The bipyridine may be a C-substituted 4,4 ’-bipyridinium. Other redox-active C-substituted bipyridiniums are contemplated in other embodiments, such as, without limitation, 2,4’-bipyridiniums, 3,4’ -bipyridiniums, 2,2’ -bipyridiniums, 2,3’- bipyridiniums, and 3, 3 ’-bipyridiniums (Fig. 3B). In certain embodiments, a mixture of bipyridiniums and / or other pyridiniums such as any of those described herein may be present in the same electrolytes. For example, in some cases, various bipyridine cores with different C- substitutions and / or / ' / -substitutions may be present. As a non-limiting example, C-substituted 4,4’-bipyrindiums with differing C-substitution may be used in tandem, or as another example, a C-substituted 4,4’-bipyrindium may be used in tandem with a C-substituted 3,4’-bipyridinium with identical or differing C-substitution. Similarly, in some embodiments, the / / -substitution could be varied with the C-substitution remaining the same. In some embodiments, the pyridinium redox material may not be a polymer, e.g., the bipyridinium may be a small molecule or monomer that is not covalently linked to a repeating-unit backbone with other bipyridinium cores.

[0059] In some embodiments, the pyridinium may be an extended bipyridine comprising at least one C-substituted pyridyl ring. The extended structure may refer to a structure in which a conjugated organic linker connects the two pyridyl cores, e.g., such that there are one or more atoms between the pyridine groups. Non-limiting examples of extended pyridine conjugated linkers include, without limitation, C=C, C=C, N=N, SC4H2 heteroaromatic rings, C6H4 aromatic rings, S2N2C4 heteroaromatic rings, and C2N2O aromatic rings, etc. Additional non-limiting examples of linkers include phenyls, substituted phenyls, thiazolos, chalcogenophenes, oxadiazoles, pyridines, diazines, triazines, pyrimidines, pyrazines, or the like. In certain cases, additional substitutions (e.g., C-substitutions and / or A-substitutions such as any of those described herein) may be included on these aromatic linkers. Without wishing to be bound by any theory, it is believed that with extended conjugated systems between the pyridyl cores, the properties of the pyridinium may be altered, such as the redox mechanism, formal potential, electron kinetics, chemical stability, water solubility, and membrane crossover, etc. Those of ordinary skill in the art will be familiar with techniques for synthesizing extended viologens and other similar structures. In some embodiments, C-substitutions may be incorporated into the extended bipyridine structures as previously described, for example, by coupling C-substituted pyridines with a 4-position extension moiety or by post-modification of an extended bipyridine with a reagent to substitute a functionalization onto a pyridyl carbon. Specific non-limiting examples of such extended structures include those shown in Fig. 10.

[0060] In some cases, tripyridine or higher-order pyridiniums are possible in certain embodiments. For example, in some embodiments, the pyridinium may be a tripyridine in which a single molecular structure comprises three pyridine cores. The pyridyl cores may be covalently linked by a linker that retains the conjugation system between pyridyls. Examples include without limitation phenyls, diazines, triazines, and heteroaromatics, which may be substituted or unsubstituted. In some embodiments, the tripyridine may have one or more C-substitutions, e.g., as described herein. In some embodiments, one, two, or each of the pyridyl rings will have a C- substitution. In some embodiments, there may be one or more than one C-substitution on one or more of the pyridyl rings. The tripyridine may have various anionic, cationic, and uncharged N- substituents or combinations thereof, e.g., as described herein. In some embodiments, tripyridines may exhibit three-electron storage, enhanced energy density, deterred membrane crossover, altered electrochemical and physical properties, or the like. See, e.g., Fig. 11.

[0061] U.S. Provisional Patent Application Serial No. 63 / 674,375, filed July 23, 2024, entitled “C-Substituted Pyridinium Redox Materials and Methods,” by Sullivan, et al., is incorporated herein by reference in its entirety.

[0062] The following examples are intended to illustrate certain embodiments of the present disclosure, but do not exemplify the full scope of the disclosure.

[0063] EXAMPLE 1

[0064] A C-substituted pyridinium redox molecule was synthesized according to the following procedure in this example. 1.84 g (10 mmol) of 3,3’-dimethyl-4,4’-bipyridine was added to 6 mL (22 mmol) of 3-chloro2-hydroxypropyl trimethylammonium chloride (65 wt.% in water; also known as “dextrosil”) in an autoclave reactor. 3,3’-dimethyl-4,4’-bipyridine was chosen as a commercially available C-substituted 4,4’ -bipyridine from Ambeed, and dextrosil was chosen to increase the aqueous anolyte properties of the materials (i.e., water solubility, chemical stability, and membrane compatibility). The solution was then transferred to a stainless-steel autoclave with PTFE liner (100 mL) and heated to 120 °C for 24 hr. After the reaction, DMF (20 mL) was added dropwise to the reaction mixture and stirred to precipitate out the pure product. The off- white product was filtered, washed with acetone, and vacuum dried. A high overall yield of 81 % (4.5 g) was obtained for l,l-dextrosil-3,3-dimethyl-4,4-bipyridine. The 'H NMR (D2O, 400 MHz) of the product is shown in Fig. 12.

[0065] Similarly, another C-substituted pyridinium redox molecule was synthesized according to the following procedure. 1.7 g (10 mmol) of 3-methyl-4, 4’ -bipyridine was added to 6 mL (22 mmol) of 3-chloro2 -hydroxypropyl trimethylammonium chloride (65 wt% in water) in an autoclave reactor. 3-methyl-4,4’-bipyridine was chosen as another commercially available C- substituted 4,4’ -bipyridine from Ambeed, and dextrosil was once again chosen to keep the N- substitution constant. The solution was then transferred to a stainless-steel autoclave with PTFE liner (100 mL) and heated to 120 °C for 24 hr. After the reaction, DMF (20 mL) was added dropwise to the reaction mixture and stirred to precipitate out the pure product. The off-white product was filtered, washed with acetone, and vacuum dried. A high overall yield of 76% (4.2 g) was obtained for l,l-dextrosil-3-methyl-4,4-bipyridine. The ’H NMR of the product is shown in Fig. 13.

[0066] This method is highly adaptable and can be universally applied to produce multitudes of C-substituted 4,4’ -bipyridiniums. For example, various C-substitutued 4,4 ’-bipyridines could be paired with alternative iV-subtituent reagents. Thus, C-substituted 4,4 ’-bipyridiniums of varying size and charge can be produced through the hydrothermal method. Furthermore, a two-step reaction process could also be performed with 1:1 molar equivalent of the 4,4’ -bipyridine to the iV-subtitution reagent to form asymetric C-substituted 4,4’ -bipyridiniums, meaning a C- substituted 4,4’ -bipyridinium with two different functionalizations at the 1 -positions. Therefore, the successful synthesis of l,l-dextrosil-3,3-dimethyl-4,4-bipyridine and l,l-dextrosil-3-methyl- 4,4-bipyridine through the hydrothermal reaction routes demonstrates a path towards producing numerous C-substituted 4,4’-bipyridiniums.

[0067] EXAMPLE 2

[0068] The electrochemical propoerties of the C-substituted 4,4’ -bipyridiniums was then explored in this example. Specifically, cyclic voltamtery (CV) of l,l-dextrosil-3-methyl-4,4- bipyridine and l,l-dextrosil-3,3-dimethyl-4,4-bipyridine were performed and can be compared to l,l-dextrosil-4,4-bipyridine, i.e., the 4,4 ’-bipyridinium without any C-substitution. This provided a controlled analysis of the effects of the C-substitution with the A-substitution remaining constant. The CVs were each taken at 0.1 M concentration of the redox material, with a scan rate of 100 mV / s, with 1 M NaCl support salt in water, and using a glassy carbon working electrode, a platinum wire counter electrode, and a standard calomel reference electrode (+0.241 V vs. SHE). The CV results are shown in Figs. 14A-14D.

[0069] The 1 , 1 -dextrosil-4,4-bipyridine showed two distinct one-electron processes seperated by approximately 400 mV. The first electron reduction was at approximately -0.32 V vs. SHE, and the second electron reduction was at approximately -0.70 V vs. SHE . Without wishing to be bound by any theory, it is believed that after the first reduction process, a radical electron is stored in the aromatic bipyridine system. In addition, it is believed that upon this one-electron reduction, the viologen pyridyls switch from an oblique angle to a planar orientation. Upon the second electron reduction, an the moleulce is double reduced, an electron pair is formed, and the pyridyl rings are hypothesized to switch back from the planar orientation to an oblique angle. This process is reverisble, meaning the 4,4’ -bipyridinium oxidized back to its original state upon the cathodic cycle.

[0070] Interestingly, with l,l-dextrosil-3-methyl-4,4-bipyridine, the second electron reduction formal potential remained unchanged at approximately -0.70 V vs. SHE. However, the first electron reduction shifted significantly towards more negative potential by approximately 200 mV to about -0.5 V vs. SHE compared to that of the l,l-dextrosil-4,4-bipyridine without C- substitution. It is believed that this represented the LUMO of the 4,4 ’-bipyridinium shifting towards higher energy with the inclusion of the methyl functionalization at the 3-position. It is believed, again withuot wishing to be bound by any theory, that this increase in LUMO energy and the more negative formal reduction potential of the first electron process is two-fold. First, the methyl group is donating, meaning that the LUMO will be pushed to higher energy and the reduction process will become more difficult (i.e., occur at more negative potential) due to enthalpic effects. Second, the inclusion of a methyl at the 3-position may sterically hinder the rotation of the 4,4 ’-bipyridine core from an oblique angle to a planar conformation during the one-electron reduction processes, leading to a more negative reductin potential due to entropic effects. The low current signal and the third, smaller peak observed in CV for l,l-dextrosil-3- methyl-4,4-bipyridine may be due to trace impurities in the sample, such as l-dextrosil-3- methyl-4,4-bipyridine with a iV-position that was not fully reacted.

[0071] With l,l-dextrosil-3,3-dimethyl-4,4-bipyridine, including a methyl group at the 3- position on both pyridyl rings, the first-electron reduction was pushed even more negative by about 500 mV compared to that of the l,l-dextrosil-4,4-bipyridine without C-substitution. In fact, both redox processes appeared to now be superimposed at approximately -0.8 V vs. SHE in a one-step, two-electron process. Once again, it is believed that this represents the LUMO of the 4,4’ -bipyridinium shifting towards higher energy with the inclusion of the additional methyl functionalization at the 3-position, and it is further believed that this increase in LUMO energy and the more negative formal reduction potential of both electron processes is two-fold. First, the additonal methyl group is donating, meaning that the LUMO will be pushed to higher energy and the reduction process will become more difficult (i.e., occur at more negative potential) due to enthalpic effects. Second, the inclusion of a methyl at each 3-position may now effectively sterically inhibit the rotation of the 4,4 ’-bipyridine core from an oblique angle to a planar conformation. As a result of not being able to switch toward a planar conformation to stabilize the one-electron radical, the 4,4’ -bipyridinium now undergoes a one-step, two-electron process as the non-reduced and doubly-reduced states both share an oblique angle and no conformational shift is needed in this redox mechanism. The low current signal and the third, smaller peak observed in CV for 1,1,- dextrosil-3,3-dimethyl-4,4-bipyridine is presumably due to trace impurities in the sample, such as l-dextrosil-3,3-dimethyl-4,4-bipyridine with a / ' / -position that was not fully reacted, which can be addressed through increased reaction temperature and time or through alternative purification methods.

[0072] Overall, this CV example shows that C-substitution significantly altered the electrochemical properties of the pyridinium redox materials, even with the same 4,4-bipyridine core and same / -substitutions. It should also be noted that this also demonstrates the effects of the positioning of the C-substitution on these types of materials. The fact that an inclusion of a single methyl C-substitution at the 3-position shifted the formal potential more negative — by approximately 200 mV — than multiple methyl C-substitions at the 2 and 6 positions appears to show that the potential shift is not only due to the electron donating effects of the methyl group but also due to the steric conformational effects. This can be further observed by the fact that the 3,3-methyl C-substitions pushed the reduction process to a one-step, two-electron process around -0.8 V vs. SHE, a signifcantly more dramatic shift in redox behavior than 2,2-methyl C- substitutions and 2,2,6,6-methyl C-substitutions.

[0073] EXAMPLE 3

[0074] After characterizing the electrochemical behavior of the representative C-substituted pyridinium redox materials in Examples 1 and 2, flow battery characterization was performed in this example on a select species: l,l-dextrosil-3-methyl-4,4-bipyridine. A custom flow battery single-cell device was used with a 4 cm2active area and peristaltic pumps inside a nitrogen glovebox (below 1 ppm O2). Selemion AMVN anion-exchange membrane was used as the separator. Graphite felts with a thickness of 3 mm (GFD 3 EA, SIGRACELL®) were pre-treated at 400 °C in air for 6 h before being used as electrodes on both sides of the cell. The cell was galvanically cycled at 40 mA / cm2with a charging voltage cutoff of 1.40 V as to limit the charging to the first one-electron process and a discharging voltage cutoff of 0.5 V. 10 mL of 2.0 M 4-methylmorpholinium amide TEMPO was used as the catholyte, and 10 mL of 2.0 M, 1- dextrosil-3-methyl-4,4-bipyridine was used as the anolyte. Chloride salts of the anolyte and catholyte redox species were used without any additional supporting salt. Fig. 15 shows the charge-discharge curve for the C-substituted pyridinium. An opencircuit voltage at 50% state-of-charge of approximately 1.25 V was observed. A full cell capacity of 39 Ah / L was utilized with a coulombic efficiency of nearly 100%. The inclusion of the methyl at the 3 -position did not noticeably affect the cycling capacity of the anolyte as the 2.0 M 1,1- dextrosil-3-methyl-4,4-bipyridine was cycled fully without any precipitation, even in the reduced state with fewer positive charge on the bipyridinium redox core. The methyl moiety, meanwhile, increased the output voltage of the full cell to over 1.2 V at 50% state-of-charge. Overall, these RFB results support that C-substituted pyridiniums can be deployed as electrolytes in electrochemical battery devices with modified properties.

[0075] While several embodiments of the present disclosure have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and / or structures for performing the functions and / or obtaining the results and / or one or more of the advantages described herein, and each of such variations and / or modifications is deemed to be within the scope of the present disclosure. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and / or configurations will depend upon the specific application or applications for which the teachings of the present disclosure is / are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the disclosure described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, the disclosure may be practiced otherwise than as specifically described and claimed. The present disclosure is directed to each individual feature, system, article, material, kit, and / or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and / or methods, if such features, systems, articles, materials, kits, and / or methods are not mutually inconsistent, is included within the scope of the present disclosure.

[0076] In cases where the present specification and a document incorporated by reference include conflicting and / or inconsistent disclosure, the present specification shall control. If two or more documents incorporated by reference include conflicting and / or inconsistent disclosure with respect to each other, then the document having the later effective date shall control.

[0077] All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and / or ordinary meanings of the defined terms.

[0078] The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.”

[0079] The phrase “and / or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with “and / or” should be construed in the same fashion, i.e., “one or more” of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the “and / or” clause, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, a reference to “A and / or B”, when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

[0080] As used herein in the specification and in the claims, “or” should be understood to have the same meaning as “and / or” as defined above. For example, when separating items in a list, “or” or “and / or” shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as “only one of’ or “exactly one of,” or, when used in the claims, “consisting of,” will refer to the inclusion of exactly one element of a number or list of elements. In general, the term “or” as used herein shall only be interpreted as indicating exclusive alternatives (i.e. “one or the other but not both”) when preceded by terms of exclusivity, such as “either,” “one of,” “only one of,” or “exactly one of.”

[0081] As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently “at least one of A and / or B”) can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

[0082] When the word “about” is used herein in reference to a number, it should be understood that still another embodiment of the disclosure includes that number not modified by the presence of the word “about.”

[0083] It should also be understood that, unless clearly indicated to the contrary, in any methods claimed herein that include more than one step or act, the order of the steps or acts of the method is not necessarily limited to the order in which the steps or acts of the method are recited.

[0084] In the claims, as well as in the specification above, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” “composed of,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of’ and “consisting essentially of’ shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03.

Claims

CLAIMSWhat is claimed is:

1. An electrochemical device, comprising: an anode compartment containing an anolyte, the anolyte comprising a redoxactive pyridinium comprising a C-substitution on the pyridyl ring of the pyridinium, wherein the C-substitution comprises at least two carbon atoms; a cathode or a cathode compartment containing a catholyte; and a membrane or separator between the anode compartment and the cathode compartment.

2. The electrochemical device of claim 1 , wherein the electrochemical device is a battery.

3. The electrochemical device of claim 2, wherein the electrochemical device is an aqueous battery.

4. The electrochemical device of any one of claims 1-3, wherein the electrochemical device is a flow battery.

5. The electrochemical device of any one of claims 1-3, wherein the electrochemical device is a hybrid flow battery.

6. The electrochemical device of any one of claims 1-3, wherein the electrochemical device is a static-cell battery.

7. The electrochemical device of any one of claims 1-6, wherein the membrane is an ionexchange membrane.

8. The electrochemical device of claim 7, wherein the membrane is a cation-exchange membrane.

9. The electrochemical device of claim 7, wherein the membrane is a proton-exchange membrane.

10. The electrochemical device of claim 7, wherein the membrane is an anion-exchange membrane.

11. The electrochemical device of any one of claims 1-6, wherein the membrane is a sizeexclusion membrane.

12. The electrochemical device of any one of claims 1-11, wherein the redox-active pyridinium is a bipyridine.

13. The electrochemical device of claim 12, wherein the redox-active bipyridine is a 4,4’- bipyridine.

14. The electrochemical device of any one of claims 1-13, wherein the pyridinium comprises pyridines connected by a conjugated organic linker.

15. The electrochemical device of claim 14, wherein the linker is a N=N.

16. The electrochemical device of claim 14, wherein the linker is a C=C.

17. The electrochemical device of claim 14, wherein the linker comprises a phenyl.

18. The electrochemical device of claim 14, wherein the linker comprises a substituted phenyl.

19. The electrochemical device of claim 14, wherein the linker comprises a thiazolo.

20. The electrochemical device of claim 14, wherein the linker comprises a chalcogenophene.

21. The electrochemical device of claim 14, wherein the linker comprises an oxadiazole.

22. The electrochemical device of any one of claims 1-21, wherein the pyridinium is a tripyridinium connected by a conjugated organic linker.

23. The electrochemical device of claim 22, wherein the linker comprises a phenyl.

24. The electrochemical device of claim 22, wherein the linker comprises a substituted phenyl.

25. The electrochemical device of claim 22, wherein the linker comprises a pyridine.

26. The electrochemical device of claim 22, wherein the linker comprises a diazine.

27. The electrochemical device of claim 22, wherein the linker comprises a triazine.

28. The electrochemical device of claim 22, wherein the linker comprises a pyrimidine.

29. The electrochemical device of claim 22, wherein the linker comprises a pyrazine.

30. The electrochemical device of any one of claims 1-29, wherein the C-substitution is in the 2 position.

31. The electrochemical device of any one of claims 1-29, wherein the C-substitution is in the 3 position.

32. The electrochemical device of any one of claims 1-29, wherein the C-substitution is in the 4 position.

33. The electrochemical device of any one of claims 1-29, wherein the C-substitution is in the 5 position.

34. The electrochemical device of any one of claims 1-29, wherein the C-substitution is in the 6 position.

35. The electrochemical device of any one of claims 1-34, wherein the pyridinium comprises at least one C-substitution on each pyridyl ring.

36. The electrochemical device of any one of claims 1-34, wherein the pyridinium has a C- substitution on only one pyridyl ring.

37. The electrochemical device of any one of claims 1-36, wherein the pyridinium comprises a plurality of C-substitutions on at least one pyridyl ring.

38. The electrochemical device of any one of claims 1-37, wherein the C-substitution is an anionic substituent.

39. The electrochemical device of claim 38, wherein the anionic substituent comprises sulfonate or sulfonic acid.

40. The electrochemical device of claim 38, wherein the anionic substituent comprises sulfate or sulfuric acid.

41. The electrochemical device of claim 38, wherein the anionic substituent comprises phosphonate or phosphonic acid.

42. The electrochemical device of claim 38, wherein the anionic substituent comprises phosphate or phosphoric acid.

43. The electrochemical device of claim 38, wherein the anionic substituent comprises carboxylate or carboxylic acid.

44. The electrochemical device of any one of claims 1-37, wherein the C-substitution is a cationic substituent.

45. The electrochemical device of claim 44, wherein the cationic substituent comprises a protonated ammonium.

46. The electrochemical device of claim 44, wherein the cationic substituent comprises a quaternary ammonium.

47. The electrochemical device of claim 44, wherein the cationic substituent comprises a cyclic ammonium.

48. The electrochemical device of any one of claims 1-37, wherein the C-substitution is a charge-neutral substituent.

49. The electrochemical device of claim 48, wherein the charge-neutral substituent is an alkyl.

50. The electrochemical device of claim 48, wherein the charge-neutral substituent is a branched alkyl.

51. The electrochemical device of claim 48, wherein the charge-neutral substituent is a substituted alkyl.

52. The electrochemical device of claim 48, wherein the charge-neutral substituent is an alkyl alcohol.

53. The electrochemical device of claim 48, wherein the charge-neutral substituent is an ether.

54. The electrochemical device of claim 48, wherein the charge-neutral substituent is an ester.

55. The electrochemical device of claim 48, wherein the charge-neutral substituent is an amide.

56. The electrochemical device of claim 48, wherein the charge-neutral substituent is a nitrite.

57. The electrochemical device of claim 48, wherein the charge-neutral substituent is a nitrate.

58. The electrochemical device of claim 48, wherein the charge-neutral substituent is a nitro.

59. The electrochemical device of claim 48, wherein the charge-neutral substituent is a cyano.

60. The electrochemical device of claim 48, wherein the charge-neutral substituent is an aldehyde.

61. The electrochemical device of claim 48, wherein the charge-neutral substituent is a halogen.

62. The electrochemical device of any one of claims 1-61, wherein the redox-active pyridinium comprises an N- substitution at a pyridyl nitrogen 1 -position.

63. The electrochemical device of claim 62, wherein the redox-active pyridinium comprises an / ' / -substitution at each pyridyl nitrogen 1 -position.

64. The electrochemical device of claim 62, wherein the N- substitution is a cationic substituent.

65. The electrochemical device of claim 64, wherein the N- substitution is a quaternary ammonium.

66. The electrochemical device of claim 64, wherein the N- substitution is a protonated ammonium.

67. The electrochemical device of claim 64, wherein the N- substitution is a cyclic ammonium.

68. The electrochemical device of claim 62, wherein the N- substitution is an anionic substituent.

69. The electrochemical device of claim 68, wherein the N- substitution is a sulfonate or sulfonic acid.

70. The electrochemical device of claim 68, wherein the N- substitution is a phosphonate or phosphonic acid.

71. The electrochemical device of claim 68, wherein the N- substitution is a carboxylate or carboxylic acid.

72. The electrochemical device of claim 62, wherein the N- substitution is a charge-neutral substituent.

73. The electrochemical device of claim 72, wherein the N- substitution is an alkyl.

74. The electrochemical device of claim 72, wherein the N- substitution is a substituted alkyl.

75. An electrochemical device, comprising: an anode compartment containing an anolyte, the anolyte comprising a redoxactive pyridinium having a C-substitution on the pyridyl ring in a 3 position and / or a 5 position of the pyridinium; a cathode or a cathode compartment containing a catholyte; and a membrane or separator between the anode compartment and the cathode compartment.

76. The electrochemical device of claim 75, wherein the electrochemical device is a battery.

77. The electrochemical device of claim 76, wherein the electrochemical device is an aqueous battery.

78. The electrochemical device of any one of claims 75-77, wherein the electrochemical device is a flow battery.

79. The electrochemical device of any one of claims 75-77, wherein the electrochemical device is a hybrid flow battery.

80. The electrochemical device of any one of claims 75-77, wherein the electrochemical device is a static-cell battery.

81. The electrochemical device of any one of claims 75-80, wherein the membrane is an ionexchange membrane.

82. The electrochemical device of claim 81 , wherein the membrane is a cation-exchange membrane.

83. The electrochemical device of claim 81, wherein the membrane is a proton-exchange membrane.

84. The electrochemical device of claim 81 , wherein the membrane is an anion-exchange membrane.

85. The electrochemical device of any one of claims 75-80, wherein the membrane is a sizeexclusion membrane.

86. The electrochemical device of any one of claims 75-85, wherein the redox-active pyridinium is a bipyridine.

87. The electrochemical device of claim 86, wherein the redox-active bipyridine is a 4,4’- bipyridine.

88. The electrochemical device of any one of claims 75-87, wherein the pyridinium comprises pyridines connected by a conjugated organic linker.

89. The electrochemical device of claim 88, wherein the linker is a N=N.

90. The electrochemical device of claim 88, wherein the linker is a C=C.

91. The electrochemical device of claim 88, wherein the linker comprises a phenyl.

92. The electrochemical device of claim 88, wherein the linker comprises a substituted phenyl.

93. The electrochemical device of claim 88, wherein the linker comprises a thiazolo.

94. The electrochemical device of claim 88, wherein the linker comprises a chalcogenophene.

95. The electrochemical device of claim 88, wherein the linker comprises an oxadiazole.

96. The electrochemical device of any one of claims 75-95, wherein the pyridinium is a tripyridinium connected by a conjugated organic linker.

97. The electrochemical device of claim 96, wherein the linker comprises a phenyl.

98. The electrochemical device of claim 96, wherein the linker comprises a substituted phenyl.

99. The electrochemical device of claim 96, wherein the linker comprises a pyridine.

100. The electrochemical device of claim 96, wherein the linker comprises a diazine.

101. The electrochemical device of claim 96, wherein the linker comprises a triazine.

102. The electrochemical device of claim 96, wherein the linker comprises a pyrimidine.

103. The electrochemical device of claim 96, wherein the linker comprises a pyrazine.

104. The electrochemical device of any one of claims 75-103, wherein the C-substitution is in the 3 position.

105. The electrochemical device of any one of claims 75-103, wherein the C-substitution is in the 5 position.

106. The electrochemical device of any one of claims 75-105, wherein the redox-active pyridinium comprises two C-substitutions on the pyridyl ring.

107. The electrochemical device of any one of claims 75-106, wherein the redox-active pyridinium comprises two C-substitutions on the pyridyl ring in the 3-position and the 5- position.

108. The electrochemical device of any one of claims 75-107, wherein the pyridinium comprises at least one C-substitution on each pyridyl ring.

109. The electrochemical device of any one of claims 75-107, wherein the pyridinium has a C- substitution on only one pyridyl ring.

110. The electrochemical device of any one of claims 75-109, wherein the pyridinium comprises a plurality of C-substitutions on at least one pyridyl ring.

111. The electrochemical device of any one of claims 75-110, wherein the C-substitution is an anionic substituent.

112. The electrochemical device of claim 111, wherein the anionic substituent comprises sulfonate or sulfonic acid.

113. The electrochemical device of claim 111, wherein the anionic substituent comprises sulfate or sulfuric acid.

114. The electrochemical device of claim 111, wherein the anionic substituent comprises phosphonate or phosphonic acid.

115. The electrochemical device of claim 111, wherein the anionic substituent comprises phosphate or phosphoric acid.

116. The electrochemical device of claim 111, wherein the anionic substituent comprises carboxylate or carboxylic acid.

117. The electrochemical device of any one of claims 75-110, wherein the C-substitution is a cationic substituent.

118. The electrochemical device of claim 117, wherein the cationic substituent comprises a protonated ammonium.

119. The electrochemical device of claim 117, wherein the cationic substituent comprises a quaternary ammonium.

120. The electrochemical device of claim 117, wherein the cationic substituent comprises a cyclic ammonium.

121. The electrochemical device of any one of claims 75-110, wherein the C-substitution is a charge-neutral substituent.

122. The electrochemical device of claim 121, wherein the charge-neutral substituent is an alkyl.

123. The electrochemical device of claim 122, wherein the charge-neutral substituent is a methyl.

124. The electrochemical device of claim 121, wherein the charge-neutral substituent is a branched alkyl.

125. The electrochemical device of claim 121, wherein the charge- neutral substituent is a substituted alkyl.

126. The electrochemical device of claim 121, wherein the charge-neutral substituent is an alkyl alcohol.

127. The electrochemical device of claim 121, wherein the charge- neutral substituent is an ether.

128. The electrochemical device of claim 121, wherein the charge- neutral substituent is an ester.

129. The electrochemical device of claim 121, wherein the charge- neutral substituent is an amide.

130. The electrochemical device of claim 121, wherein the charge-neutral substituent is a nitrite.

131. The electrochemical device of claim 121, wherein the charge- neutral substituent is a nitrate.

132. The electrochemical device of claim 121, wherein the charge-neutral substituent is a nitro.

133. The electrochemical device of claim 121, wherein the charge-neutral substituent is a cyano.

134. The electrochemical device of claim 121, wherein the charge-neutral substituent is an aldehyde.

135. The electrochemical device of claim 121, wherein the charge-neutral substituent is a halogen.

136. The electrochemical device of any one of claims 75-135, wherein the redox-active pyridinium comprises an N- substitution at a pyridyl nitrogen 1 -position.

137. The electrochemical device of 136, wherein the redox-active pyridinium comprises an N- substitution at each pyridyl nitrogen 1 -position.

138. The electrochemical device of claim 136 , wherein the / ' / -substitution is a cationic substituent.

139. The electrochemical device of claim 138 , wherein the ^-substitution is a quaternary ammonium.

140. The electrochemical device of claim 138 , wherein the ^-substitution is a protonated ammonium.

141. The electrochemical device of claim 138 , wherein the ^-substitution is a cyclic ammonium.

142. The electrochemical device of claim 136 , wherein the ^-substitution is an anionic substituent.

143. The electrochemical device of claim 142 , wherein the ^-substitution is a sulfonate or sulfonic acid.

144. The electrochemical device of claim 142 , wherein the ^-substitution is a phosphonate or phosphonic acid.

145. The electrochemical device of claim 142 , wherein the ^-substitution is a carboxylate or carboxylic acid.

146. The electrochemical device of claim 136 , wherein the ^-substitution is a charge-neutral substituent.

147. The electrochemical device of claim 146 , wherein the ^-substitution is an alkyl.

148. The electrochemical device of claim 146 , wherein the ^-substitution is a substituted alkyl.

149. An electrochemical device, comprising: an anode compartment containing an anolyte, the anolyte comprising a redoxactive 4,4’ -bipyridinium having a C- substitution on the pyridyl ring in a 3 position and / or a 5 position of the pyridinium, wherein the C-substitution is comprises at least two carbon atoms; a cathode or a cathode compartment containing a catholyte; and a membrane or separator between the anode compartment and the cathode compartment.

150. The electrochemical device of claim 149, wherein the electrochemical device is a battery.

151. The electrochemical device of claim 150, wherein the electrochemical device is an aqueous battery.

152. The electrochemical device of any one of claims 149-151, wherein the electrochemical device is a flow battery.

153. The electrochemical device of any one of claims 149-151, wherein the electrochemical device is a hybrid flow battery.

154. The electrochemical device of any one of claims 149-151, wherein the electrochemical device is a static-cell battery.

155. The electrochemical device of any one of claims 149-154, wherein the membrane is an ion-exchange membrane.

156. The electrochemical device of claim 155, wherein the membrane is a cation-exchange membrane.

157. The electrochemical device of claim 155, wherein the membrane is a proton-exchange membrane.

158. The electrochemical device of claim 155, wherein the membrane is an anion-exchange membrane.

159. The electrochemical device of any one of claims 149-154, wherein the membrane is a size-exclusion membrane.

160. The electrochemical device of any one of claims 149-159, wherein the redox-active pyridinium is a bipyridine.

161. The electrochemical device of claim 160, wherein the redox-active bipyridine is a 4,4’- bipyridine.

162. The electrochemical device of any one of claims 149-161, wherein the pyridinium comprises pyridines connected by a conjugated organic linker.

163. The electrochemical device of claim 162, wherein the linker is a N=N.

164. The electrochemical device of claim 162, wherein the linker is a C=C.

165. The electrochemical device of claim 162, wherein the linker comprises a phenyl.

166. The electrochemical device of claim 162, wherein the linker comprises a substituted phenyl.

167. The electrochemical device of claim 162, wherein the linker comprises a thiazolo.

168. The electrochemical device of claim 162, wherein the linker comprises a chalcogenophene.

169. The electrochemical device of claim 162, wherein the linker comprises an oxadiazole.

170. The electrochemical device of any one of claims 149-161, wherein the pyridinium is a tripyridinium connected by a conjugated organic linker.

171. The electrochemical device of claim 170, wherein the linker comprises a phenyl.

172. The electrochemical device of claim 170, wherein the linker comprises a substituted phenyl.

173. The electrochemical device of claim 170, wherein the linker comprises a pyridine.

174. The electrochemical device of claim 170, wherein the linker comprises a diazine.

175. The electrochemical device of claim 170, wherein the linker comprises a triazine.

176. The electrochemical device of claim 170, wherein the linker comprises a pyrimidine.

177. The electrochemical device of claim 170, wherein the linker comprises a pyrazine.

178. The electrochemical device of any one of claims 149-177, wherein the C-substitution is in the 3 position.

179. The electrochemical device of any one of claims 149-177, wherein the C-substitution is in the 5 position.

180. The electrochemical device of any one of claims 149-179, wherein the redox-active pyridinium comprises two C-substitutions on the pyridyl ring.

181. The electrochemical device of any one of claims 149-180, wherein the redox-active pyridinium comprises two C-substitutions on the pyridyl ring in the 3-position and the 5- position.

182. The electrochemical device of any one of claims 149-181, wherein the pyridinium comprises at least one C-substitution on each pyridyl ring.

183. The electrochemical device of any one of claims 149-181, wherein the pyridinium has a C-substitution on only one pyridyl ring.

184. The electrochemical device of any one of claims 149-183, wherein the pyridinium comprises a plurality of C-substitutions on at least one pyridyl ring.

185. The electrochemical device of any one of claims 149-184, wherein the C-substitution is an anionic substituent.

186. The electrochemical device of claim 185, wherein the anionic substituent comprises sulfonate or sulfonic acid.

187. The electrochemical device of claim 185, wherein the anionic substituent comprises sulfate or sulfuric acid.

188. The electrochemical device of claim 185, wherein the anionic substituent comprises phosphonate or phosphonic acid.

189. The electrochemical device of claim 185, wherein the anionic substituent comprises phosphate or phosphoric acid.

190. The electrochemical device of claim 185, wherein the anionic substituent comprises carboxylate or carboxylic acid.

191. The electrochemical device of any one of claims 149-184, wherein the C-substitution is a cationic substituent.

192. The electrochemical device of claim 191, wherein the cationic substituent comprises a protonated ammonium.

193. The electrochemical device of claim 191, wherein the cationic substituent comprises a quaternary ammonium.

194. The electrochemical device of claim 191, wherein the cationic substituent comprises a cyclic ammonium.

195. The electrochemical device of any one of claims 149-184, wherein the C-substitution is a charge-neutral substituent.

196. The electrochemical device of claim 195, wherein the charge-neutral substituent is an alkyl.

197. The electrochemical device of claim 195, wherein the charge- neutral substituent is a branched alkyl.

198. The electrochemical device of claim 195, wherein the charge-neutral substituent is a substituted alkyl.

199. The electrochemical device of claim 195, wherein the charge- neutral substituent is an alkyl alcohol.

200. The electrochemical device of claim 195, wherein the charge-neutral substituent is an ether.

201. The electrochemical device of claim 195, wherein the charge- neutral substituent is an ester.

202. The electrochemical device of claim 195, wherein the charge-neutral substituent is an amide.

203. The electrochemical device of claim 195, wherein the charge- neutral substituent is a nitrite.

204. The electrochemical device of claim 195, wherein the charge-neutral substituent is a nitrate.

205. The electrochemical device of claim 195, wherein the charge- neutral substituent is a nitro.

206. The electrochemical device of claim 195, wherein the charge-neutral substituent is a cyano.

207. The electrochemical device of claim 195, wherein the charge- neutral substituent is an aldehyde.

208. The electrochemical device of claim 195, wherein the charge-neutral substituent is a halogen.

209. The electrochemical device of any one of claims 149-208, wherein the redox-active pyridinium comprises an N- substitution at a pyridyl nitrogen 1 -position.

210. The electrochemical device of 209, wherein the redox-active pyridinium comprises an N- substitution at each pyridyl nitrogen 1 -position.

211. The electrochemical device of claim 209 , wherein the / ' / -substitution is a cationic substituent.

212. The electrochemical device of claim 211 , wherein the ^-substitution is a quaternary ammonium.

213. The electrochemical device of claim 211 , wherein the ^-substitution is a protonated ammonium.

214. The electrochemical device of claim 211 , wherein the ^-substitution is a cyclic ammonium.

215. The electrochemical device of claim 209 , wherein the ^-substitution is an anionic substituent.

216. The electrochemical device of claim 215 , wherein the ^-substitution is a sulfonate or sulfonic acid.

217. The electrochemical device of claim 215 , wherein the ^-substitution is a phosphonate or phosphonic acid.

218. The electrochemical device of claim 215 , wherein the ^-substitution is a carboxylate or carboxylic acid.

219. The electrochemical device of claim 209 , wherein the ^-substitution is a charge-neutral substituent.

220. The electrochemical device of claim 219 , wherein the ^-substitution is an alkyl.

221. The electrochemical device of claim 219 , wherein the ^-substitution is a substituted alkyl.

222. The electrochemical device of any of claims 1-221, wherein the pyridinium has a structure:

223. The electrochemical device of any of claims 1-221, wherein the pyridinium has a structure:

224. The electrochemical device of any of claims 1-221, wherein the pyridinium has a structure:

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