Electrodes for electrochemical capacitors based on surface-modified carbon

Abstract

A method for preparing surface-modified carbon comprises adding a carbon material to a solution of a reaction product of an aromatic primary amine and a molar excess of a nitrite source, and recovering the surface-modified carbon having redox-active sites. Also provided are surface-modified carbon materials, electrodes, and capacitors based thereon.

Description

[0001] As early as the 1990s, the modification of carbon materials using diazo chemistry to form covalent bonds between the carbon material surface and various functional groups was reported, see for example US5554739 and US5851280, both in the name of Cabot Corporation.

[0002] Carbon materials used to prepare electrodes for energy storage devices such as electrochemical capacitors and batteries can particularly benefit from surface modification via diazo chemistry to enable the incorporation of redox molecules into materials such as activated carbon and carbon cloth, thereby improving the performance of electrodes made from this form of carbon. In US6,522,522 (Cabot Corporation), work on diazo-mediated carbon surface modification has been extended to electrode fabrication, and further efforts in this area have been reported in EP2886537, Assresahegn et al. [Carbon 92(2015)362-381], Cougnon et al. [Journal of Power Source, 274(2015)551-559], Comte et al. [Journal of Materials Chemistry A3(2015), 6146-6156], US2018 / 0182566, Malka et al. [Journal of the Electrochemical Society 165(14)A3342-A3349(2018) and Journalof the Electrochemical Society 166(6)A1147-A1153(2019)].

[0003] There are different methods for preparing diazonium salts and reacting them with carbon materials. The salts can be formed by reacting primary amines with nitrous acid in an aqueous system (e.g., in NaNO / HCl / H O) or in an organic solvent, for example, with the help of an organic nitrite such as tert-butyl nitrite. As shown in the working examples of US 5,554,729, the salts can be prepared in solution in advance and can be used without separation. Separation and purification of diazonium salts is also possible—see EP 2886537, in which diazonium salts are collected as tetrafluoroborate salts and then electrochemically or chemically grafted onto carbon.

[0004] A concise approach that appears well-suited for large-scale electrode production consists of the in situ synthesis of diazonium salts from primary amine precursors, where the salt formation reaction occurs in the presence of a carbon material, with spontaneous / chemical reduction and covalent grafting onto the carbon material. This approach is schematically illustrated by the following scheme:

[0005]

[0006] (diazotation; spontaneous radical formation; coupling to activated carbon by radical reduction)

[0007] The effectiveness of the synthetic route lies in its simplicity: it involves neither the prior preparation of salts nor grafting induction, such as electrochemical reduction of diazonium.

[0008] The conversion of amines to diazonium can be carried out in a NaNO2 / HCl / H2O system or in an organic medium.

[0009] For example, in US Pat. No. 5,554,739, equimolar amounts of amine and NaNO2 are used, and the cold diazo solution is added to a suspension of carbon material.

[0010] In Example 1 of US Pat. No. 6,522,522, an electrode material is prepared by adding carbon black to a solution of 2-amino-anthraquinone and hydrochloric acid. Sodium nitrite is the last reagent added, i.e., gradually added dropwise to the reaction mixture in the form of an aqueous solution.

[0011] In Journal of Power Sources (2015, supra), carbon was dispersed in acetonitrile, and a primary amine (3,4-dimethoxyaniline; 0.3 equivalents relative to carbon) was added along with an organic nitrite (tert-butyl nitrite, 0.9 equivalents relative to carbon).

[0012] In the Journal of Materials Chemistry A (2015, supra), a primary amine (2-amino-9,10-phenanthrenequinone) was dissolved in acetonitrile, followed by the addition of 1 equivalent of tert-butyl nitrite, the carbon material, and then 2 equivalents of tert-butyl nitrite (in two equal portions over 30 minutes).

[0013] In Example 1 of US2018 / 0182566, an organic nitrite (tert-butyl nitrite) was dissolved in acetonitrile and the solution was added dropwise to a solution of a primary amine (4-aminobenzoic acid) and carbon fiber. The molar ratio of 4-aminobenzoic acid to nitrite was 1:3.

[0014] In the Journal of the Electrochemical Society (2018, supra and 2019, supra), primary amines (2-aminoanthraquinone and 3,4-dimethoxyaniline, respectively) were dissolved in acetonitrile, 1 equivalent of tert-butyl nitrite was added, followed by the carbon material, and finally another equivalent of tert-butyl nitrite.

[0015] It can be seen that despite the simplicity of this method, there are still different ways to control the formation reaction of diazonium salts and their covalent grafting on carbonaceous electrode materials.

[0016] We have now discovered that by carefully selecting reaction conditions, namely by mixing the carbon material with a solution of the reaction product of an aromatic primary amine and an excess of nitrite, the degree of grafting of redox molecules onto carbon materials via diazo chemistry can be increased. Specifically, the aromatic primary amine is reacted with a molar excess of a nitrite source in solution, which is then mixed with the carbon material. Due to the presence of excess nitrite, the amount of unreacted amine is minimized, resulting in the elimination of amine adsorption on the carbon surface, making the surface accessible for covalent grafting of diazo.

[0017] Experimental work performed in support of this application demonstrates that the proposed process permutations lead to favorable results. As shown below, 2-aminoanthraquinone, a common benchmark for studying diazo chemistry to improve electrode performance [see also US Pat. No. 6,522,522 and Journal of the Electrochemical Society (2018, supra)], was combined with activated carbon in an organic solvent. In the experimental work reported below, a nitrite source was provided to the reaction mixture in two different ways: before the addition of the carbon material, an excess of nitrite relative to 2-aminoanthraquinone was present in the reaction mixture; and before the addition of the carbon material, an equimolar amount of nitrite relative to 2-aminoanthraquinone was present in the reaction mixture; after the addition of the carbon material, the remaining amount of nitrite was added to the reaction mixture.

[0018] In the studies reported below, the total amount of nitrite was three times the molar amount of 2-aminoanthraquinone. The excess nitrite was either 1) added entirely to the 2-aminoanthraquinone solution before the addition of carbon, or 2) added sequentially to the solution in three equal portions at 30-minute intervals, with the carbon added after the first portion of nitrite. The order in which the reactants were added to the reaction vessel was as follows:

[0019] 1) 2-aminoanthraquinone → 3 eq. nitrite → carbon material

[0020] 2) 2-aminoanthraquinone → 1 eq. nitrite → carbon material → 1 eq. nitrite → 1 eq. nitrite

[0021] The product consisting of the surface-modified carbon material was collected and tested by thermogravimetric analysis (TGA) to determine the change in mass with respect to temperature and to measure the amount of quinone derivative grafted onto the carbon surface by the method described above. Figure 1The results presented in show that the grafting level is enhanced when nitrite is present in excess in the reaction mixture before the addition of the carbon material. The same trend is observed independent of the reaction medium (water or organic).

[0022] Therefore, one aspect of the present application is a method for preparing surface-modified carbon, comprising adding a carbon material to a solution of a reaction product of an aromatic primary amine and a molar excess of a nitrous acid source, and recovering the surface-modified carbon with redox-active sites.

[0023] The aromatic primary amine participating in the reaction has the formula (RED) n -Ar-(NH2) m ,in:

[0024] Ar represents an aromatic or conjugated system containing one or more rings;

[0025] m is 1 or 2;

[0026] RED represents a functional group capable of undergoing redox reactions, optionally in protected form, wherein RED is attached to one or more rings of Ar or forms part of these rings;

[0027] n is the number of RED groups in the primary aromatic amine (1≤n≤5, eg, n=1, 2, or 3).

[0028] The surface-modified carbon is recovered from the reaction mixture, the protecting groups (if present) are removed, and the product is processed and formed into electrodes that can be assembled to construct energy storage devices as described below.

[0029] The formation reaction of diazonium salt and grafting onto carbon can be carried out in the acidic environment of water, by inorganic nitrite source, such as alkali metal nitrite, for example sodium nitrite or potassium nitrite, thereby original position produces nitrous acid to drive reaction. Acidic environment is produced by strong inorganic acid (for example hydrochloric acid, sulfuric acid and nitric acid). Preferred system is NaNO2 / HCl aqueous solution. Reaction is carried out well under the temperature (for example room temperature) in the range of pH value in 0 to 6 (for example 0 to 3) and 10 to 70 ℃. In order to complete grafting, the reducing agent that can discharge nitrogen (N2) and produce corresponding aryl radical from diazonium ion is also present in the reaction mixture.

[0030] Alternatively, the salt formation reaction and grafting onto the carbon occur in a non-aqueous system, i.e., in an organic solvent. Suitable organic solvents are inert solvents capable of dissolving the amine and the organic nitrite. Polar aprotic solvents such as acetonitrile, acetone, dimethylformamide, dioxane, and dioxolane can be used. The nitrite source is an alkyl nitrite, wherein the alkyl group is a linear or branched C2-C7 chain, such as ethyl nitrite, tert-butyl nitrite, and isoamyl nitrite. In organic systems, the diazo reduction to the corresponding aryl radical occurs spontaneously, i.e., no applied potential or chemical reducing agent is required to force the diazo reduction and grafting.

[0031] The first step of the method is to dissolve the aromatic primary amine in the above-mentioned aqueous or organic medium. The aromatic primary amine has the formula (RED) n -Ar-(NH2) m The aromatic nucleus Ar comprises one or more aromatic rings, including heteroaromatic rings. When two or more rings are present in Ar, these rings may be fused together to form a polycyclic aromatic system or may be bridged. Thus, formula (RED) n -Ar-(NH2) m The aromatic primary amines include:

[0032] -RED n Group-substituted aniline;

[0033] - a conjugated polycyclic ring consisting of fused six-membered rings, carrying an amine functional group and (RED) x group substitutions, such as quinones, for example, quinones derived from naphthalene (naphthoquinone), anthracene (anthraquinone), and phenanthrene (phenanthrenequinone);

[0034] - aromatic polycyclic rings consisting of fused six-membered and five-membered heteroaromatic rings, such as nitrogen- or oxygen-containing aromatic rings, such as pyridine or pyrimidine rings fused to imidazole rings, carrying amine functional groups and (RED) n Group substitution, or (RED) n Ar is incorporated as part of the ring system;

[0035] Amino-substituted biphenyl-related systems having a linker attached to the phenyl ring.

[0036] Now turn to (RED) n The definition of functional groups, which ultimately explain the redox active sites in surface-modified electrode carbon materials, RED represents the redox group attached to the ring carbon atom, such as:

[0037] =O (oxo group);

[0038] -OH (hydroxy), or a protected hydroxy group, such as -OP1, where P1 represents a hydroxy protecting group, such as an alkyl group (e.g., methyl), -Si(R1)3, where R1 is an alkyl group, especially a methyl group. That is, the hydroxy group can be protected in the form of the corresponding methyl ether -OCH3, trimethylsilyl ether -O-Si(CH3)3, or -OCH2OCH3 (wherein the hydroxy group is protected as a methoxymethyl ether);

[0039] -SH (thiol) or protected thiol,

[0040] -C(O)OH or a salt thereof, such as an alkali metal salt thereof, or a protected carboxylic acid -C(O)OP2, wherein P2 represents a carboxylic acid protecting group, for example, the acid can be protected as an alkyl ester, specifically a methyl ester;

[0041] -SO3H or a salt thereof, for example an alkali metal salt thereof;

[0042] It should be noted that when two or more RED groups are present in an aromatic primary amine, these groups may be the same or different. x -Ar-(NH2) n Starting material.

[0043] A type (RED) used in this application n -Ar-(NH2) m Compounds by (RED) n The carbon surface is composed of substituted anilines, which are capable of incorporating redox-active groups such as thiols, sulfonic acids, and carboxylic acids onto the carbon surface (in the scheme shown below, the carbon surface is represented by a "comb-like" structure):

[0044]

[0045] Above (RED) n The grafting of substituted anilines onto carbon surfaces via the diazo route proceeds efficiently in organic solvents. For example, these aniline derivatives are very soluble in acetonitrile.

[0046] Another preferred type for this application is (RED) n -Ar-(NH2) m Compound (OP1) nThe present invention relates to a substituted aniline composition (i.e., Ar is a benzene ring, m=1, and RED is a protected form). We have found that one or more hydroxyl groups can be grafted onto the carbon surface, for example, up to three hydroxyl groups per aromatic ring with the help of suitable protecting groups. For example, by protecting the hydroxyl groups as corresponding ethers, such as methyl ether. The method is illustrated below, starting from (commercially available) 3,4,5-trimethoxyaniline. Grafting onto the carbon surface via the diazo route occurs in an organic solvent (e.g., acetonitrile), followed by isolation of the surface-modified carbon and cleavage of the protecting groups to generate the hydroxyl redox functional groups, as shown below:

[0047]

[0048] Another preferred type for this application is (RED) n -Ar-(NH2) m Compound (OP1) n1 -(COOP2) n2 -Ar-(NH2) m Composition, wherein Ar represents a benzene ring, for example (OP1) n1 -(COOP2) n2 Substituted aniline, wherein OP1 is a protected hydroxyl group, COOP2 is a protected carboxylic acid, and n1 and n2 are independently 1 or 2. For example, commercially available (OH) n1 -(COOH) n2 The substituted aniline is treated in an organic solvent to protect the hydroxyl group as a silyl ether (e.g., using the reagent (R1)3Si-Cl, e.g., wherein R1 is methyl, to protect the hydroxyl group as a trimethylsilyl ether, such that P1 is preferably -Si(CH3)3), and to protect the carboxylic acid as an alkyl ester (e.g., using a suitable alcohol, such as methanol, to form the corresponding methyl ester, such that P2 is preferably -CH3). The protection reactions can be carried out sequentially with the isolation and purification of the intermediate after the first protection reaction. However, a more convenient method consists of a one-pot synthesis in which the starting material (OH) n1 -(COOH) n2 Substituted anilines react with (R1)3Si-Cl and R1OH (R1 is independently alkyl) to provide the corresponding protected aniline derivatives:

[0049] (OH) n1 -(COOH) n2 Substituted anilines

[0050] (OSi(R1)3) n1 -(COOR1) n2 Substituted anilines

[0051] After adding excess (R1)3Si-Cl and R1OH, a one-pot synthesis is carried out in an organic solvent such as acetonitrile, anhydrous tetrahydrofuran and dimethylformamide to form a protected aniline derivative. The protected aniline derivative is separated from the reaction mixture (e.g., by concentration and filtration) and purified by crystallization. Then the purified (OP1) n1 -(COOP2) n2 The substituted aniline is subjected to a diazonium salt formation reaction according to the present application, for example by dissolving in an organic solvent, reacting with an excess of nitrite and grafting onto carbon. The carbon is separated and the protecting groups are cleaved to restore the hydroxyl and carboxylic acid redox-active functional groups by the following techniques, ultimately yielding the desired surface-modified carbon product, as shown below:

[0052]

[0053] Another useful type (RED) n -Ar-(NH2) m Compounds include amino-substituted quinones where the RED is provided by a keto functionality incorporated into the quinone system (the redox activity is due to the interconversion between the quinone-hydroquinone pair). n -Ar-(NH2) m Preferred are amino-substituted anthraquinones (9,10-anthraquinone and isomers) and amino-substituted phenanthrenequinones (e.g., 2,7-diaminophenanthrene-9,10-dione). The grafting of the latter is shown in the figure below; it performs well in organic solvents such as acetonitrile.

[0054]

[0055] Another type (RED) n -Ar-(NH2) m It consists of an amino-substituted biphenyl-based system 2HN-C6H5-Z-C6H5-NH2, where Z represents a linker that binds a redox-active moiety such as a disulfide. An example is shown below:

[0056]

[0057] Amino-substituted heterocyclic aromatic compounds, for example, composed of fused six-membered and five-membered heterocyclic rings, having the ∼N=CH-NH~ structural motif as part of the ring system, such as purines:

[0058]

[0059] (the amino group can be attached at position 2 or 6 of the purine), and the corresponding conjugated derivatives of amino-substituted heterocyclic aromatic compounds in which the -CH= group in the fused six-membered aromatic ring is replaced by a -C(O)- functional group, such as 6-keto derivatives of purine, form another class of useful compounds that can be grafted onto carbon via the diazo route:

[0060]

[0061] The above amino-substituted heterocyclic aromatic compounds readily form diazonium salts in aqueous HCl solution.

[0062] Turning to the method according to the present application, the above (RED) n -Ar-(NH2) m The parent material (optionally in protected form) is dissolved in an acidic aqueous medium or an organic solvent.Then, nitrite is excessively added to the aqueous solution / non-aqueous solution of the aromatic primary amine.The minimum excess is approximately 1 % by mole (1.01 molar equivalent nitrite sources), for example at least 10 % by mole (1.10 molar equivalent nitrite sources), and preferably even significantly higher excess, up to 50 % by mole (1.50 molar equivalent nitrite sources), up to 100 % by mole (2.0 molar equivalent nitrite sources).Preferred excess is 100 to 200 % by mole, for example, adds 2 to 3 molar equivalent nitrite sources.

[0063] As previously mentioned, when the reaction is carried out in an acidic aqueous solution, such as in hydrochloric acid, a reducing agent is beneficial in promoting the reduction of diazonium ions to nitrogen (N2) and aryl radicals. Therefore, a reducing agent can be added to the aqueous reaction mixture (e.g., a solution of an aromatic primary amine in NaNO2 / HCl / H2O), such as metals such as iron, zinc, copper, and nickel, which can be added to the solution in the form of a powder or the like. As an alternative to using a metal reducing agent, reducing agents such as hypophosphorous acid (H3PO2) and ascorbic acid can be considered.

[0064] The last reagent to be added is the carbon material to be modified. Suitable carbon materials that can be surface modified by this application include activated carbon, carbon fibers, carbon cloth, and graphite powder. The carbon matrix should primarily comprise sp2 hybridized carbon, which has as large a surface area as possible and is free of heteroatoms or metal contaminants. For example, a carbon matrix with a surface area of 1500-2000 m 2 / g Activated carbon cloth. Carbon materials and (RED) n -Ar-(NH2) m The mass ratios are 10:0.1 to 0.1:10, such as 1:3-3:1, 2:1-1:2, and about 1:1.

[0065] After the addition of the carbon material, the reaction mixture is held for a period of time, such as at least 2 hours. The surface-modified carbon is then separated from the reaction mixture, such as by filtration, treated in an organic solvent (e.g., DMF, methanol, and acetone) to remove excess reagents (i.e., to remove adsorbed molecules), and dried.

[0066] As mentioned above, in some cases, molecules are grafted onto carbon in an electrochemically inert form. That is, protected derivatives lacking redox activity are used in the synthesis / grafting step. Therefore, the grafted molecule needs to be converted into a redox-active compound, for example, by removing the protecting groups. A typical example is a redox-active hydroxy-substituted aromatic compound that is loaded onto carbon in a protected form, i.e., as an etherified derivative. That is, (OP1) n -Ar-NH2 (e.g., methoxy-substituted aniline) is used in the grafting step and subsequently converted to the redox-active (HO) n -Ar grafted portion.

[0067] This transformation can be achieved chemically (eg with the aid of a deprotecting agent capable of cleaving the protecting group) or electrochemically.

[0068] After the surface-modified carbon is isolated from the reaction mixture, the grafted molecule is converted to its active form by chemically removing the protecting groups. The surface-modified carbon is suspended in an inert organic solvent such as dichloromethane, and the cleavage of the protecting groups is accomplished with the aid of a suitable reagent. For example, dealkylation can be achieved with boron tribromide (sold as a dichloromethane solution) in dichloromethane, which cleaves methoxy groups to form hydroxyl groups at room temperature; silyl ethers are deprotected using a fluoride source such as nBu4NF (tetrabutylammonium fluoride; TBAF) or KF.

[0069] Under the conditions reported in the Journal of Power Sources (2015, supra), the grafted molecules are converted to their redox-active forms by electrochemically removing the protecting groups, for example, converting ether groups to hydroxyl groups. That is, in a three-electrode setup consisting of the working electrode, the surface-modified carbon is used as the working electrode (and, if necessary, shaped with the help of a binder and an additive to increase conductivity), with excess activated carbon serving as the counter electrode and, for example, a saturated calomel electrode (SCE) serving as the reference electrode. (OP1) n -Ar grafted part (e.g. P1 is CH3) to redox active (HO) nIrreversible conversion of the Ar-grafted moiety was achieved in 1-10 M sulfuric acid or 1-10 M HCl electrolyte solutions at scan rates ranging from 1 mV / s to 10 mV / s within a ΔV range of 0-1 V vs SCE. The dual electrode with well-defined mass balance and voltage windows can also be used to oxidize large quantities of species on a commercial scale.

[0070] The surface-modified carbons described herein having redox-active compounds covalently bound to the surface can be used as electrode materials for electrochemical capacitors. Cyclic voltammograms measured in concentrated hydrochloric acid, sulfuric acid, and potassium hydroxide electrolyte solutions (recorded at various rates from 2 mV / s to 20 mV / s) using a three-electrode setup with the surface-modified carbon as the working electrode, the unmodified carbon as the counter electrode, and a saturated calomel electrode (SCE) as the reference electrode demonstrate the effect of the grafted molecules, altering the electrical double layer (EDL) capacitor behavior to incorporate the faradaic contribution of the redox molecules on the surface. The voltammograms were recorded showing peaks indicating the presence of distinct redox sites, for example, for:

[0071] 1) Trihydroxybenzene grafted carbon electrode material:

[0072]

[0073] 3) 9,10-Phenanthrenequinone grafted carbon electrode materials:

[0074]

[0075] 3) 1,9-dihydro-6H-purine-6-one grafted carbon electrode materials:

[0076]

[0077] 4) 2-Hydroxybenzoic acid grafted carbon electrode materials:

[0078]

[0079] Therefore, the present application also relates to carbon materials (e.g., activated carbon, carbon fibers, carbon cloth, and graphite powder) surface-modified with the molecules described herein, in particular the variants 1), 2), 3), and 4) just mentioned above, as well as electrodes comprising such carbon.

[0080] The present application also relates to surface-modified carbons having the above-mentioned molecules, such as 1), 2), 3) and 4) variants, wherein thermogravimetric analysis of a sample of the surface-modified carbon under a nitrogen atmosphere at a heating rate of 10 or 20°C per minute until the temperature reaches 450°C shows a weight loss of at least 15%, for example, at least 20%; 20% to 30%, 30% to 40%, 40% to 50%, 50% to 60%, 60% to 70%, 70% to 80%, 80% to 90%, or 90% to 100%, indicating a high loading of the grafted molecules to the carbon material.

[0081] a surface-modified carbon wherein trihydroxybenzene is grafted onto the carbon, exhibiting a weight loss in TGA of at least 15%, such as at least 20%, such as from 20% to 50%, such as from 15% to 30%, until the temperature reaches 450°C; and

[0082] Surface-modified carbon wherein 9,10-phenanthrenequinone is grafted onto the carbon, showing a weight loss in TGA of at least 20%, such as at least 30%, for example between 30% and 50% (using 2,7-diaminophenanthrene-9,10-dione grafted onto the carbon); forming a particular aspect of the present application.

[0083] Electrodes based on the surface-modified carbon of the present application are prepared by techniques known in the art. There are two main methods for preparing electrodes:

[0084] A monolithic electrode made of activated carbon fiber or cloth without other additives; i.e., the monolithic electrode is punched and formed into a desired size; and

[0085] Composite electrodes, for example, when activated carbon powder is used, a composite paste is prepared using modified carbon powder, a binder (PTFE suspension in water / PVDF, etc.) and, for example, carbon black to improve conductivity.

[0086] For example, to prepare a composite electrode, the components are combined within the following concentration ranges:

[0087] Effective mass (modified carbon of this application): 70%-95%

[0088] Binder (dry weight): 4%-15%

[0089] Conductive additives (carbon black, carbon nanotubes): 0%-20%

[0090] All ingredients are thoroughly mixed with a solvent that dissolves the binder, usually an alcohol (isopropyl alcohol or ethanol) or NMP (n-methylpyrrolidone), to form a homogeneous slurry, which is then partially dried to form a paste-like texture. The composite electrode is then rolled in a roller mill to the desired electrode width.

[0091] The electrodes of the present application can be assembled into an asymmetric electrochemical capacitor for use as an energy storage device. Therefore, the present application also relates to a capacitor comprising a pair of spaced-apart electrodes, a separator disposed in the space between the electrodes and an electrolyte solution (e.g., HCl, H2SO4, or KOH solution), wherein one of the electrodes comprises the surface-modified carbon described herein.

[0092] The experimental results reported below demonstrate that some electrode materials of this application, such as 9,10-phenanthrenequinone-grafted carbon electrodes (obtained using 2,7-diaminophenanthrenequinone, as shown below):

[0093]

[0094] The electrolyte solution performs well in electrochemical capacitors containing salts other than protic acids and hydroxide bases, i.e., salts dissolved in water, such as halide salts such as bromide and chloride salts, such as alkali metal halides (e.g., sodium bromide) or ammonium halides, and other halide metal salts (e.g., divalent halides such as barium chloride), and sulfates such as alkali metal sulfates. The concentration of such electrolyte solutions is >10% by weight, up to and including the saturation limit.

[0095] The capacitor is assembled by methods known in the art, such as symmetrical or asymmetrical capacitors with monolithic / composite electrodes as described above. The electrodes are placed in contact with a current collector (e.g., formed of a carbon sheet, metal foil, or a conductive polymer) or a battery terminal and soaked with an electrolyte solution. Examples of separators placed in the capacitor to separate the two electrodes include cellulose separators (e.g., from NKK), plastics such as high-density polyethylene (HDPE) films, or porous fabrics. The individual cells are tightly closed to allow good contact between each electrode and its current collector and pressed against the separator to form a compact structure with low resistivity. The bipolar configuration in which individual cells are stacked together can be used to increase the output voltage. For example, electrochemical capacitors are described in US5,115,378, US5,581,438, US5,585,999, and US6,522,522, showing an overall double-layer capacitor design suitable for the present application. Example

[0096] The TGA-GC-MS (EI / CI) was performed using a Perkin Elmer Clarus 680 / Clarus SQ 8C instrument. Thermogravimetric analyze To evaluate the thermal stability of the grafted moiety, 6.5 mg of the modified carbon cloth electrode was placed in a TGA oven in an alumina crucible under a nitrogen atmosphere at a heating rate of 10 or 20 °C / min from 25 to 900 °C (equilibrium purge 80 mL / min; sample purge 20 mL / min).

[0097] Cyclic voltammetry (CV) measurements were performed in a BioLogic VSP potentiostat and analyzed using ECLAB software.

[0098] Examples 1-2 (of the present application) and 3-4 (comparative)

[0099] A set of experiments was performed to investigate the effect of the presence of excess nitrite on 2-aminoanthraquinone in the reaction mixture prior to the addition of carbon.

[0100] The experiment of Example 1 was carried out in an organic system:

[0101] Dissolve 0.5g of 2-aminoanthraquinone (2.2mmol) in 350ml of ACN until the amine derivative is completely dissolved. Add 3eq of tert-butyl nitrite (0.69g, 1ml of a 90% solution). After 5 minutes, add 1eq of activated carbon cloth. Stir the reaction mixture for 24 hours; then filter and wash with equal parts of acetonitrile, DMF, acetone, and methanol. Dry the modified carbon at 100°C for 4 hours.

[0102] The experiment of Example 2 was carried out in an aqueous system:

[0103] Dissolve 0.5g of 2-aminoanthraquinone (2.2mmol) in 400ml of 2M HCl until the amine derivative is completely dissolved. Add 3eq of sodium nitrite (0.455g). After 5 minutes, add 1eq of activated carbon cloth. Stir the mixture for 24 hours; then filter the reaction mixture and wash with equal parts of acetonitrile, DMF, acetone, and methanol. Dry the modified carbon at 100°C for 4 hours.

[0104] The experiment of Example 3 was carried out in an organic system:

[0105] 0.5 gr of 2-aminoanthraquinone (2.2 mmol) was dissolved in 350 ml of ACN until the amine derivative was completely dissolved. 1 eq of tert-butyl nitrite, 0.23 gr (0.33 ml of a 90% solution) was added, followed by 1 eq of activated carbon. The reaction mixture was stirred for 30 minutes, and then 1 eq of tert-butyl nitrite, 0.23 gr (0.33 ml of a 90% solution) was added and stirred for 30 minutes. Then, 1 eq of tert-butyl nitrite, 0.23 gr (0.33 ml of a 90% solution) was added and stirred for 24 hours. The reaction mixture was filtered and washed with equal parts of acetonitrile, DMF, acetone, and methanol. The modified carbon was dried at 100°C for 4 hours.

[0106] The experiment of Example 4 was carried out in an aqueous system:

[0107] Dissolve 0.5 gr of 2-aminoanthraquinone (2.2 mmol) in 400 ml of 2M HCl until the amine derivative is completely dissolved. Add 1 eq of sodium nitrite (0.15 gr), followed by 1 eq of activated carbon. Stir the mixture for 30 minutes, add another 1 eq of sodium nitrite (0.15 gr), stir the mixture for 30 minutes, add another 1 eq of sodium nitrite (0.15 gr), stir the mixture for 24 hours. Filter the reaction mixture and wash with equal parts of acetonitrile, DMF, acetone, and methanol. Dry the modified carbon at 100°C for 4 hours.

[0108] Next, each sample was placed in a thermogravimetric analyzer, which showed a thermogravimetric curve of mass versus temperature. Figure 1 Thermogravimetric analysis of the carbon grafting reaction was performed using a 20°C / min temperature control system (under nitrogen). The mass loss is due to the elimination and / or decomposition of the grafted quinone derivative from the carbon surface and is therefore indicative of the level of grafting achieved for each sample (i.e., the greater the percentage weight loss, the better the grafting process). The thermogravimetric curves demonstrate the beneficial effect of excess nitrite present in the reaction mixture prior to carbon addition on increasing the grafting of 2-aminoanthraquinone onto the carbon, achieving increases of >14 wt%.

[0109] Examples 5A and 5B

[0110] Surface modification of carbon using 3,4,5-trimethoxyaniline

[0111]

[0112] A: Dissolve 0.8 gr 3,4,5-trimethoxyaniline (4.4 mmol) in 300 ml ACN until the amine derivative is completely dissolved. Add 3 eq tert-butyl nitrite, 1.35 gr (1.05 ml of a 90% solution). After 5 minutes, add 1 eq activated carbon. Stir the mixture for 24 hours. Divide the activated carbon cloth into two parts and dry. Suspend one part of the modified activated carbon in 150 ml DCM. Add 40 ml of a 1 M BBr3 solution in DCM (3 x 3 eq) and stir at room temperature for 48 hours. Add 80 ml of methanol in batches, filter and wash three times with water, and wash with equal parts of acetonitrile, DMF, acetone and methanol. Dry the modified carbon at 100°C for 4 hours.

[0113] B: Dissolve 3 gr of 3,4,5-trimethoxyaniline (16 mmol) in 600 ml of ACN until the amine derivative is completely dissolved. Add 3 eq of tert-butyl nitrite (5 gr (7.1 ml of a 90% solution). After 10 minutes, add 1.3 g of activated carbon. Stir the mixture at room temperature for 24 hours, filter the reaction mixture and wash with equal parts of acetonitrile, DMF, acetone, and methanol. Dry the modified carbon at 100°C for 4 hours to obtain 1.93 gr of modified carbon (48% enrichment). The activated carbon cloth is divided into two parts and dried. Suspend 1 part of the modified activated carbon in 150 ml of DCM. Add 40 ml of a 1 M BBr3 solution in DCM (3 x 3 eq) and stir at room temperature for 48 hours. Add 80 ml of methanol in batches, filter, and wash with water three times, and with equal parts of acetonitrile, DMF, acetone, and methanol. Dry the modified carbon at 100°C for 4 hours.

[0114] Example 6

[0115] Surface modification of carbon using 4-aminobenzenethiol

[0116]

[0117] Dissolve 1 gr of 4-aminobenzenethiol (8 mmol) in 200 ml of ACN until the amine derivative is completely dissolved. Add 3 eq of tert-butyl nitrite (2.46 gr, 3.48 ml of a 90% solution). After 5 minutes, add 2 eq of activated carbon cloth. Stir the mixture at room temperature for 24 hours. Filter the reaction mixture and wash with equal parts of acetonitrile, DMF, acetone, and methanol. Dry the modified carbon at 100°C for 4 hours.

[0118] Example 7

[0119] Surface modification of carbon using 4,4'-disulfanyldiphenylamine

[0120]

[0121] Dissolve 1 gr of 4,4'-dithiodiphenylamine (4 mmol) in 200 ml of ACN until the amine derivative is completely dissolved. Add 3 eq of tert-butyl nitrite (1.23 gr, 1.74 ml of a 90% solution). After 5 minutes, add 2 eq of activated carbon. Stir the mixture at room temperature for 24 hours. Filter the reaction mixture and wash with equal parts of acetonitrile, DMF, acetone, and methanol. Dry the modified carbon at 100°C for 4 hours.

[0122] Example 8

[0123] Surface modification of carbon using 5-amino-2-hydroxybenzoic acid

[0124]

[0125] In a 250ml round-bottomed flask, 3gr aminosalicylic acid (19.5mmol) is dissolved in 100ml anhydrous THF. Slowly add 2.34gr 2.75ml 1.1eq TMSiCl (21.45mmol) and stir 1 hour. Add 60ml methyl alcohol and 2eq TMSiCl 4.95ml 4.2gr (39mmol) and stir 24 hours. Concentrated reaction mixture is also dissolved in DCM / EtOAc / hexane. Wash with water and recrystallize the product from EtOAc / hexane.

[0126] 3.1 gr protected ASA aminosalicylic acid (13 mmol) was dissolved in 250 ml ACN until the ASA was completely dissolved. 3 eq tert-butyl nitrite 4.5 gr (5.4 ml 90% solution) was added and 1 eq activated carbon was added after 5 minutes. The mixture was stirred for 24 hours. The reaction mixture was evaporated and dissolved in 50 ml DCM and 1 eq BBr 3 was added and stirred in an ice bath for 3 hours and at room temperature for 24 hours. The BBr 3 was quenched with 3 eq water / methanol. 1 eq TBAF was added and stirred for 24 hours. The reaction mixture was washed with water and filtered and washed with equal parts of acetonitrile, DMF, acetone and methanol. The ASA-modified carbon was dried at 100° C. for 4 hours.

[0127] Example 9

[0128] Surface modification of carbon using 5-aminoisophthalic acid

[0129]

[0130] Dissolve 1.6g of 5-aminoisophthalic acid (8.8mmol) in 200ml of ACN until the amine derivative is completely dissolved. Add 3eq of tert-butyl nitrite (2.73g) (3.48ml of a 90% solution). After 5 minutes, add 2eq of activated carbon cloth. Stir the mixture for 24 hours, filter the reaction mixture, and wash with equal parts of acetonitrile, DMF, acetone, and methanol. Dry the modified carbon at 100°C for 4 hours.

[0131] Example 10

[0132] Surface modification of carbon using 2,7-diaminophenanthrene-9,10-dione

[0133]

[0134] 3 gr of 2,7-diaminophenanthrene-9,10-dione (13.5 mmol) was dissolved in 350 ml of ACN until the amine derivative was completely dissolved. 3 eq of tert-butyl nitrite (4.2 gr, 6 ml of a 90% solution) was added. After 10 minutes, 1.8 gr of activated carbon cloth was added. The reaction mixture was stirred for 24 hours, filtered, and washed with equal parts of acetonitrile, DMF, acetone, and methanol. The modified carbon was dried at 100°C for 4 hours to obtain 2.6 gr of modified carbon (40% enrichment).

[0135] Example 11

[0136] Surface modification of carbon using 5-amino-2,3-dihydrophthalazine-1,4-dione

[0137]

[0138] Dissolve 1.2g of 5-amino-2,3-dihydrophthalazine-1,4-dione (6.9mmol) in 200ml of ACN until the amine derivative is completely dissolved. Add 3eq of tert-butyl nitrite (2.07g, 3ml of a 90% solution). After 5 minutes, add 1eq of activated carbon cloth. Stir the reaction mixture for 24 hours, filter it, and wash it with equal parts of acetonitrile, DMF, acetone, and methanol. Dry the modified carbon at 100°C for 4 hours.

[0139] Example 12

[0140] Surface modification of carbon using 4-aminobenzenesulfonic acid

[0141]

[0142] Dissolve 1 gr of 4-aminobenzenesulfonic acid (6.3 mmol) in 200 ml of ACN until the amine derivative is completely dissolved. Add 3 eq of tert-butyl nitrite (1.95 gr, 2.76 ml of a 90% solution). After 5 minutes, add 2 eq of activated carbon cloth and stir for 24 hours. Filter the reaction mixture and wash with equal parts of acetonitrile, DMF, acetone, and methanol. Dry the modified carbon at 100°C for 4 hours.

[0143] Example 13

[0144] Surface modification of carbon using 2-amino-1,9-dihydro-6H-purin-6-one

[0145]

[0146] Dissolve 1 gram of 2-amino-1,9-dihydro-6H-purin-6-one (8 mmol) in 150 ml of 1 M HCl until the amine derivative is completely dissolved. Add 2 eq of sodium nitrite (0.9 gr) and Fe powder (0.1 gr), followed by 2 eq of activated carbon cloth. Stir the mixture at room temperature for 4 hours. Filter the reaction mixture and wash with equal parts of acetonitrile, DMF, acetone, and methanol. Dry the modified carbon at 100°C for 4 hours.

[0147] Example 14

[0148] Surface modification of carbon using 7H-purine-6-amine

[0149]

[0150]

[0151] Dissolve 1 gr of 7H-purin-6-amine (8 mmol) in 150 ml of 1 M HCl until the amine derivative is completely dissolved. Add 2 eq of sodium nitrite (0.9 gr) and iron powder (0.1 gr), followed by 2 eq of activated carbon. Stir the mixture at room temperature for 4 hours. Filter the reaction mixture and wash with equal parts of acetonitrile, DMF, acetone, and methanol. Dry the modified carbon at 100°C for 4 hours.

[0152] Example 15

[0153] Testing electrodes made of surface-modified carbon

[0154] The performance of the electrodes was evaluated using cyclic voltammetry (CV). CV was performed in a three-electrode setup. The working electrode was a disk made of modified carbon (4 mm diameter) with an average weight of 2 mg (≈15 mg / cm 2 ). The counter electrode (11 mm in diameter) was made of unmodified carbon with an average weight of 11 mg. A saturated calomel electrode (SCE) was used as a reference electrode. The electrodes were immersed in distilled water under vacuum and then immersed in the electrolyte solution. A three-electrode T cell was assembled by introducing the immersed electrodes onto a glassy carbon current collector and separated by a separator. H2SO4 (1 M, 2 M, and 4 M), HCl (1 M, 2 M, and 4 M), and KOH (1 M, 2 M, and 6 M) were used as electrolyte solutions. The scan rate was in the range of 2 mV / s to 20 mV / s.

[0155] Figures 2 to 11 The voltammograms shown in FIG, corresponding to Examples 5 to 14, respectively, show that each grafted molecule changes the normal properties of the native carbon host from EDL capacitor performance to the faradaic contribution of the redox molecule on the surface ( Figure 2 :2MH2SO4 3,4,5-trimethoxyaniline; Figure 3 : 4M KOH 4-aminobenzenethiol; Figure 4 : 4M KOH 4,4'-diaminodiphenyl disulfide; Figure 5 : 6M H2SO4 5-amino-2-hydroxybenzoic acid; Figure 6 : 4M HCl 5-aminoisophthalic acid; Figure 7 : 6M KOH 2,7-diaminophenanthrene-9,10-dione; Figure 8 : 2M HCl 5-amino-2,3-dihydrophthalazine-1,4-dione; Figure 9 : 2M H2SO4 4-aminobenzenesulfonic acid; Figure 10 : 1M HCl 2-amino-1,9-dihydro-6H-purin-6-one; Figure 11 : 1 M HCl-7H-purin-6-amine).

[0156] Example 16

[0157] Incorporation of 3,4,5-trihydroxybenzene into carbon cloth using 3,4,5-trimethoxyaniline and characterization of the resulting electrodes

[0158] The study reported in this example consists of two parts. In the first part, 3,4,5-trimethoxyaniline (TMA) was added to carbon cloth via diazo chemistry. This process resulted in the grafting of 3,4,5-trimethoxybenzene (TMB) onto the carbon. The TMB-surface-modified carbon cloth was then analyzed to determine the surface composition by X-ray photoelectron spectroscopy (XPS), the specific surface area by the Brunauer-Emmett-Teller (BET) method, and the weight loss of the sample as the temperature increased by thermogravimetric analysis (TGA).

[0159] Next, in the second part, the electrochemically inert 3,4,5-trimethoxybenzene was deprotected to remove the methoxy group and obtain the corresponding electroactive 3,4,5-trimethoxybenzene (THB). The THB-surface-modified carbon cloth was then tested as an electrode material.

[0160] Part A: Grafting and Characterization by XPS, BET, and TGA

[0161]

[0162] Dissolve 100 mg of 3,4,5-trimethoxyaniline (TMA, 0.546 mmol) in 100 ml of acetonitrile until the amine derivative is completely dissolved. Add three equivalents of tert-butyl nitrite (0.240 ml of a 90% solution) and then add 100 mg of Kynol TMThe mixture was stirred for 30 minutes. The modified cloth was filtered and washed with equal parts of dimethylformamide, acetonitrile, acetone, and methanol, and dried under vacuum at 60°C to yield 125 mg of modified carbon (with 25 wt% of the grafting molecule, i.e., 3,4,5-trimethoxybenzene, added).

[0163] Surface elemental and chemical state analysis was performed by X-ray photoelectron spectroscopy (XPS). XPS studies were performed using a Thermo Scientific NEXSA spectrometer with a monochromatic Al Kα source. The measured spectra were taken at a PE of 200 eV and at 50 eV for high-resolution spectroscopy. In situ charge neutralization was used, and each set of measurements was recalibrated relative to C1s at 284.8 eV. Due to the conductive nature of the sample, only slight charging was observed in the range of tens of meV. Quantification was performed using the RSF of the NEXSA after "smart" baseline correction. Peak fitting was performed using the gaussian-lorentian 70:30 peak and reasonable FWHM values.

[0164] Spectrum Figure 12a -f, arranged as follows: Figure 12a and 12d C1s spectra of unmodified and surface-modified carbon cloth, respectively; Figure 12b and 12e O1s spectra of unmodified and surface-modified carbon cloth, respectively; Figure 12c and 12f N1s spectra of unmodified and surface-modified carbon cloth, respectively.

[0165] XPS spectroscopy confirmed the addition of 3,4,5-trimethoxyaniline to the carbon cloth via diazo chemistry:

[0166] exist Figure 12d The C1s spectrum of the modified carbon shown in Figure 3 shows a well resolved and strong peak at a binding energy of 286.5 eV, which is assigned to the additional methoxy groups (carbon oxides) that are part of the grafted molecules added to the carbon. Figure 12a This peak was not seen in .

[0167] Comparatively modified ( Figure 12e ) and unmodified carbon cloth ( Figure 12b ), the grafted carbon cloth exhibits a much stronger peak in the O1s spectrum than the unmodified one. This is due to the addition of three oxygen atoms per grafted molecule. The enhanced higher binding energy peak at 533.5 eV reflects the enrichment of higher electron density oxygen sites. This suggests that oxygen is in a higher oxidation state in the grafted electrode. This result indicates that oxygen originating from the carbon surface has a lower binding energy than oxygen from the methoxy / hydroxyl groups of the grafted molecules.

[0168] As expected, almost no nitrogen atoms were detected in the unmodified carbon cloth ( Figure 12c ). In contrast, TMA-grafted carbon cloth ( Figure 12f ) exhibits a strong nitrogen peak around 400 eV. A smaller, but still discernible, peak occurs at a slightly lower binding energy, approximately 402.2 eV. These peaks are likely due to alternate grafting pathways / side reactions associated with diazo chemistry, leaving nitrogen-containing moieties on the carbon surface. For example, diazonium salts couple directly to the carbon substrate, rather than "normal" diazo chemistry, which results in spontaneous degradation to N2 and aryl radicals, with N2 leaving the carbon surface. However, the detection of nitrogen on the carbon surface indirectly confirms the grafting process.

[0169] BET measurements were performed in a Quantachrome NOVA 3200e surface area and pore size analyzer using nitrogen as the adsorbent. TM The surface area of the carbon cloth is about 1500m 2 The results listed in Table 1 show a significant decrease in surface area, demonstrating extensive grafting of 3,4,5-trimethoxybenzene (TMB).

[0170] Table 1

[0171]

[0172] For the unmodified (commercial carbon cloth material) and surface-modified carbon cloth material, TGA was performed using the above instrument under nitrogen at a heating rate of 10 K / min. Figure 13 The attached thermogram shows that the TMA surface-modified carbon cloth sample loses about 25% of its weight at a temperature of 450° C. That is, TGA shows that the mass loading of THB on the activated carbon exceeds 25%.

[0173] Part B: Electrochemical deprotection and characterization

[0174] The grafted TMB molecules were electrochemically deprotected to yield electroactive THA molecules. The deprotection reaction occurred in a three-electrode T-cell using sulfuric acid as the electrolyte and TMA-modified carbon cloth as the working electrode. Electrochemical measurements were then performed to evaluate the performance of the THA-grafted electrodes.

[0175] A Swagelok three-electrode T cell was used for the electrochemical deprotection reaction and subsequent measurements. The electrodes were made of PTFE cylinders assembled with 2 and 4 mm glassy carbon rods, which served as current collectors and terminals. The working electrode consisted of a 6 mm diameter, 7 mg average weight (≈25 mg / cm 2) is punched out of modified carbon cloth, which is similar to the real electrode in commercial devices. The counter electrode with a diameter of 2 × 12 mm is punched out of unmodified carbon cloth with an average weight of 46 mg (12 mm double disk), resulting in an electrode mass loading of about 40 mg / cm 2 NKK cellulose paper was used as a separator. The electrode was immersed in distilled water and gently swirled under vacuum to achieve good wetting, then immersed in a 2M H2SO4 solution to allow osmotic pressure to draw the solution into the pores throughout the electrode block. A saturated calomel electrode (SCE) was used as the reference electrode.

[0176] Without wishing to be bound by theory, electrochemical irreversible cleavage of the methoxy groups (in 2 M sulfuric acid electrolyte solution at 0.7 V vs. SCE) converts the inactive grafted TMA molecules into electroactive THA as shown in the following scheme:

[0177]

[0178] Polarization shows activation at potentials up to 0.6 V vs. SCE. Early protonation of oxygen leads to an E1 reaction of the lean sulfate ion nucleophile on the positively charged methyl group. This process is Figure 14A Grafted in This is well demonstrated in the cyclic voltammetry of THB on carbon cloth. The first cyclic voltammetry cycle of TMA grafted carbon cloth shows that the methoxy group breaks off to form trihydroxybenzene at a scan rate of 2mV / s until the third cycle. The voltammograms recorded at different scan rates in 2M H2SO4 electrolyte solution are shown in Figure 14B The peak current associated with methoxyl group cleavage occurred at 0.6–0.7 V, and the compound became redox active at 0.1–0.5 V.

[0179] The THB-modified electrodes were then investigated by galvanostatic measurements in a three-electrode setup using 2 M H2SO4 electrolyte solution. Figure 15A Shown are the charge / discharge voltage curves obtained by cycling over a voltage window of -0.4 V to 0.8 V at a current density of 3 A / g. Figure 15B The discharge capacity measured at 2000 cycles is shown to be 65 mAh / g; it then drops to 55 mAh / g and remains at this value for an additional 2500 cycles. TM Galvanostatic measurements of THB grafted on cloth and extended cycling over 4500 cycles demonstrate the good performance of the electrode material in acidic electrolytes. The plateau around 0.1–0.5 V vs. SCE indicates a Faradaic redox reaction.

[0180] The main results of the galvanostatic measurements are listed in Table 2, along with the results of the anthraquinone (AQ)-grafted Kynol reported in Electrochemical Society 165(14)A3342-A3349(2018). TM Kynol grafted with dihydroxybenzene (DHB) reported in Electrochemical Society 166(6)A1147-A1153(2019) TM The results show that AQ-grafted carbon cloth, DHB-grafted carbon cloth and THB-grafted carbon cloth show comparable capacitance increase.

[0181] Table 2

[0182]

[0183] Example 17

[0184] Addition of 2,7-diamino-9,10-phenanthrenequinone to carbon cloth and characterization of the resulting electrode

[0185] The study reported in this example consists of two parts. In the first part, 2,7-diamino-9,10-phenanthrenequinone (PQ) was added to carbon cloth via diazo chemistry. The carbon cloth surface modified with PQ was then analyzed by thermogravimetric analysis (TGA) to determine the weight loss of the sample as the temperature increased.

[0186] Next, in the second part, PQ surface-modified carbon cloth was tested as an electrode material.

[0187] Part A: Grafting and characterization by TGA

[0188]

[0189] The procedure described in Example 10 was repeated. Samples (3-5 mg) were subjected to TGA under the above conditions. The thermogram is attached. Figure 16 Commercial Kynol TM The results show that up to ~500°C, the surface modified carbon loses about 40-50% of its weight due to the added weight of the molecules added to the carbon.

[0190] Part B: Electrochemical Characterization

[0191] The PQ-grafted carbon cloth was tested in two- / three-electrode cells as described in the previous examples by cyclic voltammetry and galvanostatic measurements in neutral electrolyte solutions (sodium bromide and barium chloride).

[0192] Figure 17A-C describes the test performed in a two-electrode configuration cell with a saturated sodium bromide electrolyte solution. The working electrode was a commercially available, unmodified The counter electrode was a PQ-grafted carbon cloth (diameter 6 mm; weight 5 mg). Figure 17A The voltammograms generated at scan rates of 1 mV and 5 mV are given in (red and blue lines, respectively). For the galvanostatic measurements, a current density of 1 A / g was applied. Figure 17B The results shown in Figure 2 show the constant current charge-discharge voltage curves of the full cell. The performance of the extended cycle (1000 cycles) is shown in Figure 2. Figure 17C As shown, the initial discharge capacity is 35mAh / g and the energy density is 35Wh / Kg.

[0193] Figure 18A -C describes the tests carried out in a three-electrode cell with a saturated barium chloride electrolyte solution. The working electrode is a PQ-grafted Carbon cloth (diameter 6 mm; weight 7 mg). The counter electrode is commercially available Carbon cloth (diameter 12 mm; weight 27 mg). The voltammogram generated at a scan rate of 5 mV is shown in Figure 2. Figure 18A As shown, the contribution of redox reaction is shown. Figure 18B (obtained at a current density of 1 A / g), a discharge capacity of 60 mAh / g was obtained. Figure 18C The discharge capacity and efficiency are plotted versus the cycle number up to 500 cycles, showing that the performance is stable over extended cycling.

Claims

1. A method for preparing surface-modified carbon, comprising adding a carbon material to a solution of a reaction product of an aromatic primary amine and a molar excess of a nitrite source, and recovering the surface-modified carbon with redox active sites.

2. The method of claim 1 , comprising mixing an aromatic primary amine and a molar excess of a nitrite source in a solution, wherein the excess is at least 10 mole percent (1.10 molar equivalents of nitrite source), and adding a carbon material to the solution.

3. The method of claim 2, wherein the molar excess of the nitrite source is 50 to 200 mole % (1.5 to 3 molar equivalents).

4. The method according to any one of claims 1 to 3, wherein the solution is an organic solution.

5. The method according to any one of claims 1 to 3, wherein the solution is an acidic aqueous solution.

6. The method according to any one of claims 1 to 3, wherein the aromatic primary amine is represented by the formula (RED) n -Ar-(NH2) m Indicates that: Ar represents an aromatic or conjugated system containing one or more rings; m is 1 or 2; RED represents a functional group capable of undergoing redox reactions, which is optionally in protected form, wherein RED is attached to one or more rings of Ar or forms part of these rings; n is the number of RED groups in the aromatic primary amine, n=1, 2 or 3, the RED groups being the same or different.

7. The method according to claim 6, wherein Ar is a benzene ring, m=1, and the RED group is in a protected form such that the aromatic primary amine is (OP1) n -substituted aniline, wherein P1 is an alkyl group.

8. The method according to claim 7, wherein P1 is methyl and n is equal to 3, so that the (OP1) used n -substituted aniline is 3,4,5-trimethoxyaniline:

9. The method according to claim 8, further comprising the steps of: Collect carbon materials with 3,4,5-trimethoxyphenyl groups attached to their surfaces: and chemical or electrochemical cleavage of the protecting groups to recover surface-modified carbon materials bearing 3,4,5-trihydroxyphenyl groups:

10. The method according to claim 6, wherein Ar is a benzene ring, m=1, which is substituted by two different RED groups, both in protected form, such that the aromatic primary amine is (OP1) n1 -(COOP2) n2 -substituted aniline, wherein OP1 is a protected hydroxyl group, COOP2 is a protected carboxylic acid, and n1 and n2 are independently 1 or 2.

11. The method of claim 10, wherein P1 is -Si(CH3)3 and P2 is -CH3.

12. A method according to claim 10 or 11, comprising isolating the carbon material and cleaving the protecting groups P1 and P2 to restore the hydroxyl and carboxylic acid redox-active functional groups, thereby recovering the surface-modified carbon with redox-active sites.

13. The method of claim 6, wherein Ar consists of a conjugated polycyclic ring consisting of fused six-membered rings such that (RED) n -Ar-(NH2) m is an amino-substituted quinone, wherein the RED is provided by the ketone functionality contained in the quinone system.

14. The method of claim 13, wherein the quinone is selected from the group consisting of 2-amino-anthraquinone, 2-amino-9,10-phenanthrenequinone, and 2,7-diamino-9,10-phenanthrenequinone.

15. The method of claim 14, wherein the quinone is 2,7-diamino-9,10-phenanthrenequinone:

16. The method of claim 6, wherein Ar comprises a biphenyl system having a linker connecting a phenyl ring, and m=2, such that the aromatic primary amine has the formula NH2-C6H5-Z-C6H5-NH2, wherein Z represents a linker comprising a RED group.

17. The method according to claim 16, wherein NH2-C6H5-Z-C6H5-NH2 is:

18. The method of claim 6, wherein the aromatic primary amine is:

19. The method of claim 6, wherein the aromatic primary amine is aminoanthraquinone.

20. The method of claim 19, wherein the aromatic primary amine is 2-aminoanthraquinone.

21. A surface-modified carbon material, wherein the carbon is grafted with functional groups capable of undergoing redox reactions using the method of any one of claims 1 to 20.

22. A capacitor comprising a pair of spaced-apart electrodes, a separator disposed in a space between the electrodes and an electrolyte solution, wherein at least one of the electrodes is made of the surface-modified carbon defined in claim 21.

23. The capacitor of claim 22 wherein said electrodes are as defined in claim 22 and said electrolyte solution comprises one or more salts dissolved in water.

24. The capacitor of claim 23 wherein said salt is a halide salt.

25. The capacitor of claim 24 wherein the salt is sodium bromide or barium chloride.

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