ELECTRODES FOR ELECTROCHEMICAL CAPACITORS BASED ON SURFACE-MODIFIED CARBON

Abstract

A process for preparing surface-modified carbon, comprising adding carbon material to a solution of a reaction product of primary aromatic amine and excess molar amount of nitrite source, and recovering surface-modified carbon bearing redox-active sites. Surface-modified carbon material, electrodes and capacitors based thereon are also provided.

Claims

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

2. A process according to claim 1, comprising combining in a solution a primary aromatic amine and excess molar amount of nitrite source, wherein said excess is at least 10 molar percent (1.10 molar equivalents of nitrite source), and adding carbon material to said solution.

3. A process according to claim 2, wherein the excess molar amount of nitrite source is from 50 to 200 molar percent (from 1.5 to 3 molar equivalents).

4. A process according to claim 1, wherein the solution is an organic solution.

5. A process according to claim 1, wherein the solution is acidic aqueous solution.

6. A process according to claim 1, wherein the primary aromatic amine is represented by the formula (RED).sub.n-Ar—(NH2).sub.m, in which: Ar represents an aromatic or conjugated system comprising one or more rings; m is 1 or 2; RED represents a functional group capable of undergoing redox reactions, optionally in a protected form, wherein RED is either attached to one or more rings of Ar, or forms part of such rings; n is the number of RED groups in the primary aromatic amine, n=1, 2 or 3, the RED groups being the same or different.

7. A process according to claim 6, wherein Ar is a benzene ring, m=1, the RED group is in a protected form, such that the primary aromatic amine is (OPi).sub.n-substituted wherein Pi is alkyl.

8. A process according to claim 7, wherein Pi is methyl and n equals 3, such that the (OPi).sub.n-substituted aniline used is 3,4,5-trimethoxyaniline: ##STR00027##

9. A process according to claim 9, further comprising the steps of: collecting a carbon material having 3,4,5-methoxybenzene groups attached to its surface: ##STR00028## and chemically or electrochemically cleaving the protecting groups, to recover surface-modified carbon material bearing 3,4,5-trihydroxybenzene groups: ##STR00029##

10. A process according to claim 6, wherein Ar is a benzene ring, m=1, said benzene ring being substituted with two different RED groups, both in a protected form, such that the primary aromatic amine is (OPi).sub.ni—(COOP2){circumflex over ( )}-substituted aniline, where OPi is protected hydroxyl, COOP2 is protected carboxylic acid, and ni and 3,4 are independently 1 or 2.

11. A process according to claim 10, wherein Pi is —Si(CH3)3 and P2 is —CH.sub.3.

12. A process according to claim 10, comprising isolating the carbon material and cleaving the protecting groups Pi and P2 to restore the hydroxyl and carboxylic acid redox active functionalities, thereby recovering surface-modified carbon bearing redox-active sites.

13. A process according to claim 6, wherein Ar consists of conjugated polycycles composed of fused six-membered rings, such that (RED).sub.n-Ar—(NH2).sub.m is an amino-substituted quinone, where RED is provided by the keto functionality incorporated in the quinone system.

14. A process according to claim 13, wherein the quinone is selected from the group consisting of 2-amino-anthraquinone, 2-amino-9,1O-phenanthrenequinone; and 2,7-diamino-9,10-phenanthrenequinone.

15. A process according to claim 14, wherein the quinone is 2,7-diamino-9,1O-phenanthrenequinone: ##STR00030##

16. A process according to claim 6, wherein Ar comprises a biphenyl system with a linker connecting the phenyl rings and m=2, such that the primary aromatic amine is of the formula 2HN—C6H5-Z—C6H5-NH2, where Z indicates the linker incorporating RED groups.

17. A process according to claim 16, wherein 2HN—C6H5-Z—C6H5-NH2 is: ##STR00031##

18. A process according to claim 6, wherein the primary aromatic amine is: ##STR00032##

19. Surface-modified carbon, selected from the group consisting of: trihydroxybenzene-grafted carbon: ##STR00033## 2-hydroxybeznoic acid-grafted carbon electrode material: ##STR00034## 1,9-dyhydro-6H-purine-6-one-grafted carbon: ##STR00035## wherein the comb-like structure indicates the carbon surface.

20. Trihydroxybenzene-grafted carbon of claim 19: ##STR00036## wherein thermogravimetric analysis conducted under nitrogen atmosphere with a heating rate of 10 or 20° C. per minute, up to temperature of 450°, indicates weight loss of not less than 15%.

21. Surface-modified carbon, wherein 9,10-phenanthrenequinone is grafted to the carbon: ##STR00037## wherein thermogravimetric analysis conducted under nitrogen atmosphere with a heating rate of 10 or 20° C. per minute, up to temperature of 450°, indicates weight loss of not less than 20%.

22. A capacitor comprising a pair of spaced apart electrodes, a separator disposed in the space between said electrodes and an electrolyte solution, wherein at least one of said electrodes is made of the surface-modified carbon defined in claim 19.

23. A capacitor according to claim 22, wherein the electrode is as defined in claim 21, and the electrolyte solution comprises one or more salts dissolved in water.

24. A capacitor according to claim 23, wherein the salt is a halide salt.

25. A capacitor according to claim 24, wherein the salt is sodium bromide or barium chloride.

Description

EXAMPLES

[0082] Thermogravimetric analyses (TGA) were conducted using a TGA-GC-MS (EI/CI) Clarus 680/Clarus SQ 8C instrument by Perkin Elmer under to evaluate the thermal stability of the grafted moieties. 6.5 mg of modified carbon cloth electrode was subjected to a TGA oven, with a heating rate of 10 or 20° C./min from 25 to 900° C. under nitrogen atmosphere (balance purge 80 mL/min; sample purge 20 mL/min) in alumina crucibles.

[0083] Cyclic voltammetry (CV) measurements were carried out in a BioLogic VSP potentiostat and analyzed using ECLAB software.

Examples 1-2 (of the Invention) and 3-4 (Comparative)

[0084] A set of experiments was conducted to investigate the effect nitrite present in excess to 2-aminoanthraquinone in the reaction mixture, before addition of carbon.

[0085] The experiment of Example 1 took place in organic system: Dissolve 0.5 gr of 2-aminoanthraquinone (2.2 mmol) in 350 ml ACN until complete dissolution of the amine derivative. Add 3 eq of tertbutyl nitrite 0.69 gr (1 ml 90% solution). After 5 minutes, add 1 eq of active carbon cloth. Stir the reaction mixture for 24 hours; then filter the reaction mixture and wash with aliquot amounts of acetonitrile, DMF, acetone and methanol. Dry the modified carbon at 100° C. for 4 hours.

[0086] The experiment of Example 2 took place in aqueous system: Dissolve 0.5 gr of 2-aminoanthraquinone (2.2 mmol) in 400 ml 2M HCl until complete dissolution of amine derivative. Add 3 eq of sodium nitrite 0.455 gr. After 5 minutes add 1 eq of active carbon cloth. Stir the mixture for 24 hours; then filter the reaction mixture and wash with aliquot amount of acetonitrile DMF acetone and methanol. Dry the modified carbon at 100° C. for 4 hours.

[0087] The experiment of Example 3 took place in organic system: Dissolve 0.5 gr of 2-aminoanthraquinone (2.2 mmol) in 350 ml ACN until complete dissolution of the amine derivative. Add 1 eq of tertbutyl nitrite 0.23 gr (0.33 ml 90% solution), followed by 1 eq of active carbon. Stir the reaction mixture for 30 min and add another 1 eq of tertbutyl nitrite 0.23 gr (0.33 ml 90% solution), stir for 30 min, then add another 1 eq of tertbutyl nitrite 0.23 gr (0.33 ml 90% solution) and stir for 24 hours. Filter the reaction mixture and wash with aliquot amount of acetonitrile, DMF, acetone and methanol. Dry the modified carbon at 100° C. for 4 hours.

[0088] The experiment of Example 4 took place in aqueous system: Dissolve 0.5 gr of 2-aminoanthraquinone (2.2 mmol) in 400 ml 2M HCl until complete dissolution of the amine derivative. Add 1 eq Sodium nitrite 0.15 gr followed by 1 eq of active carbon. Stir the mixture for 30 min, add another 1 eq Sodium nitrite 0.15 gr, stir the mixture for 30 min and add another 1 eq Sodium nitrite 0.15 gr and stir for 24 hours. Filter the reaction mixture and wash with aliquot amount of acetonitrile, DMF, acetone and methanol. Dry the modified carbon at 100° C. for 4 hours.

[0089] Next, each sample was placed in the thermogravimetric analyzer and the thermogravimetric curves showing change in mass with respect to temperature are presented in FIG. 1 (under nitrogen at a temperature rate of 20° C./min). Mass loss is due to elimination and/or decomposition of the grafted quinone derivative from the surface of the carbon and hence indicates the level of grafting achieved for each sample (i.e., the larger the weight loss percentage, the better the grafting method). The thermogravimetric curves attest for the favorable role of excess nitrite present in the reaction mixture before carbon addition to increase 2-aminoanthraquinone grafting onto the carbon, achieving>14 wt % increase.

Examples 5A and 5B

Carbon Surface Modification Using 3,4,5-Trimethoxyanyline

[0090] ##STR00014##

[0091] A: Dissolve 0.8 gr of 3,4,5-Trimethoxyaniline (4.4 mmol) in 300 ml ACN until complete dissolution of the amine derivative. Add 3 eq of tertbutyl nitrite 1.35 gr (1.05 ml 90% solution). After 5 minutes, add 1 eq of active carbon. Stir the mixture for 24 hours. Split the active carbon cloth to two portions and dry. Suspend 1 part of the modified active carbon with 150 ml DCM. Add 40 ml of 1M BBr.sub.3 solution in DCM (3×3 eq) and stir for 48 hr at room temperature. Add 80 ml methanol portionwise, filter and wash with water three times and aliquot amount of acetonitrile, DMF, acetone and methanol. Dry the modified carbon at 100° C. for 4 hours.

[0092] B: Dissolve 3 gr of 3,4,5-Trimethoxyaniline (16 mmol) in 600 ml ACN until complete dissolution of the amine derivative. Add 3 eq of tertbutyl nitrite 5 gr (7.1 ml 90% solution). After 10 minutes, add 1.3 g of active carbon. Stir the mixture for 24 hours at room temperature, filter the reaction mixture and wash with aliquot amount of acetonitrile, DMF, acetone and methanol. Dry the modified carbon at 100° C. for 4 hours to yield 1.93 gr of modified carbon (48% enrichment). Split the active carbon cloth to two portions and dry. Suspend 1 part of the modified active carbon with 150 ml DCM. Add 40 ml of 1M BBr.sub.3 solution in DCM (3×3 eq) and stir for 48 hr at room temperature. Add 80 ml methanol portionwise, filter and wash with water three times and aliquot amount of acetonitrile DMF acetone and methanol. Dry the modified carbon at 100° C. for 4 hours.

Example 6

Carbon Surface Modification Using 4-Aminobenzenethiol

[0093] ##STR00015##

[0094] Dissolve 1 gr of 4-aminobenzenethiol (8 mmol) in 200 ml ACN until complete dissolution of the amine derivative. Add 3 eq of tertbutyl nitrite 2.46 gr (3.48 ml 90% solution). After 5 minutes add 2 eq of activated carbon cloth. Stir the mixture for 24 hours at room temperature, filter the reaction mixture and wash with aliquot amount of acetonitrile, DMF, acetone and methanol. Dry the modified carbon at 100° C. for 4 hours.

Example 7

Carbon Surface Modification Using 4,4′-Disulfanediyldianiline

[0095] ##STR00016##

[0096] Dissolve 1 gr of 4,4′-disulfanediyldianiline (4 mmol) in 200 ml ACN until complete dissolution of the amine derivative. Add 3 eq of tertbutyl nitrite 1.23 gr (1.74 ml 90% solution). After 5 minutes add 2 eq of activated carbon. Stir the mixture for 24 hours at room temperature, filter the reaction mixture and wash with aliquot amount of acetonitrile, DMF, acetone and methanol. Dry the modified carbon at 100° C. for 4 hours.

Example 8

Carbon Surface Modification Using 5-Amino-2-Hydroxybenzoic Acid

[0097] ##STR00017##

[0098] In 250 ml, round bottom flask dissolve 3 gr of Aminosalicylic acid (19.5 mmol) in 100 ml dry THF. Add slowly 2.34 gr 2.75 ml 1.1 eq of TMSiCl (21.45 mmol) and stir for 1 hour. Add 60 ml methanol and 2 eq of TMSiCl 4.95 ml 4.2 gr (39 mmol) and stir for 24 hours. Concentrate reaction mixture and dissolve in DCM/EtOAc/hexane. Wash with water and recrystallize the product from EtOAc/hexane.

[0099] Dissolve 3.1 gr of protected ASA amino salicylic acid (13 mmol) in 250 ml ACN until complete dissolution of ASA, add 3 eq of tertbutyl nitrite 4.5 gr (5.4 ml 90% solution) after 5 minutes add 1 eq of active carbon. Stir the mixture for 24 hr. Evaporate the reaction mixture and dissolve it in 50 ml of DCM and add 1 eq of BBr3 and stir in ice bath for 3 hours and in room temperature for 24 hr. Quench BBr3 with 3 eq of water/methanol. Add 1 eq of TBAF and stir for 24 hr. Wash with water and filter the reaction mixture, wash with aliquot amount of acetonitrile, DMF, acetone and methanol. Dry the ASA-modified at 100° C. for 4 hours.

Example 9

Carbon Surface Modification Using 5-Aminoisophthalic Acid

[0100] ##STR00018##

[0101] Dissolve 1.6 gr of 5-aminoisophthalic acid (8.8 mmol) in 200 ml ACN until complete dissolution of the amine derivative. Add 3 eq of tertbutyl nitrite 2.73 gr (3.48 ml 90% solution). After 5 minutes, add 2 eq of active carbon cloth. Stir the mixture for 24 hours, filter the reaction mixture and wash with aliquot amount of acetonitrile, DMF, acetone and methanol. Dry the modified carbon at 100 for 4 hours.

Example 10

Carbon Surface Modification Using 2,7-Diaminophenanthrene-9,10-Dione

[0102] ##STR00019##

[0103] Dissolve 3 gr of 2,7-diaminophenanthrene-9,10-dione (13.5 mmol) in 350 ml ACN until complete dissolution of the amine derivative. Add 3 eq of tertbutyl nitrite 4.2 gr (6 ml 90% solution). After 10 minutes add 1.8 g of active carbon cloth. Stir the reaction mixture for 24 hours, filter the reaction mixture and wash with aliquot amount of acetonitrile, DMF, acetone and methanol. Dry the modified carbon at 100° C. for 4 hours to yield 2.6 gr of modified carbon (40% enrichment).

Example 11

Carbon Surface Modification Using 5-Amino-2,3-Dihydrophthalazine-1,4-Dione

[0104] ##STR00020##

[0105] Dissolve 1.2 gr of 5-amino-2,3-dihydrophthalazine-1,4-dione (6.9 mmol) in 200 ml ACN until complete dissolution of the amine derivative. Add 3 eq of tertbutyl nitrite 2.07 gr (3 ml 90% solution). After 5 minutes add 1 eq activated carbon cloth. Stir the reaction mixture for 24 hours, filter the reaction mixture and wash with aliquot amount of acetonitrile, DMF, acetone and methanol. Dry the modified carbon at 100° C. for 4 hours.

Example 12

Carbon Surface Modification Using 4-Aminobenzenesulfonic Acid

[0106] ##STR00021##

[0107] Dissolve 1 gr of 4-aminobenzenesulfonic acid (6.3 mmol) in 200 ml ACN until complete dissolution of the amine derivative. Add 3 eq of tertbutyl nitrite 1.95 gr (2.76 ml 90% solution). After 5 minutes add 2 eq of activated carbon cloth and stir for 24 hours. Filter the reaction mixture and wash with aliquot amount of acetonitrile, DMF, acetone and methanol. Dry the modified carbon at 100° C. for 4 hours.

Example 13

Carbon Surface Modification Using 2-Amino-1,9-Dihydro-6H-Purin-6-One

[0108] ##STR00022##

[0109] Dissolve 1 gr of 2-amino-1,9-dihydro-6H-purin-6-one (8 mmol) in 150 ml 1M HCl until complete dissolution of the amine derivative. 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 for 4 hours at room temperature, filter the reaction mixture and wash with aliquot amount of acetonitrile, DMF, acetone and methanol. Dry the modified carbon at 100° C. for 4 hours.

Example 14

Carbon Surface Modification Using 7H-Purin-6-Amine on Carbon

[0110] ##STR00023##

[0111] Dissolve 1 gr of 7H-purin-6-amine (8 mmol) in 150 ml 1M HCl until complete dissolution of the amine derivative. Add 2 eq of sodium nitrite (0.9 gr) and Fe powder (0.1 gr) followed by 2 eq of activated carbon. Stir the mixture for 4 hours at room temperature, filter the reaction mixture and wash with aliquot amount of acetonitrile, DMF, acetone and methanol. Dry the modified carbon at 100° C. for 4 hours.

Example 15

Testing Electrodes Made of the Surface-Modified Carbon

[0112] Cyclic voltammetry (CV) was used to assess the performance of the electrodes. CV was carried out in three-electrode set-up. The working electrode was a disc shaped from the modified carbon (4 mm in diameter) with an average weight of 2 mg (≈15 mg/cm.sup.2). Counter electrode (11 mm in diameter) was made from an unmodified carbon with an average weight of 11 mg. A saturated calomel electrode (SCE) was used as reference electrode. Electrodes were immersed in distilled water under vacuum, followed by electrolyte solution. Three electrode T cells were assembled by introducing the soaked electrodes on glassy carbon current collector, separated with a separator. H.sub.2SO.sub.4 (1M, 2M and 4M), HCl (1M, 2M and 4M) and KOH (1M, 2 m and 6M) were used as electrolyte solution. Scan rate was in the range from 2 mV/s to 20 mV/s.

[0113] Voltammograms shown in FIGS. 2 to 11, which correspond to Examples 5 to 14, respectively, indicate that each grafted molecule changes the normal nature of the native carbon host from EDL capacitor behavior to faradaic contribution of the redox molecule on the surface (FIG. 2 2M H2SO4 3,4,5-Trimethoxyaniline, FIG. 3 4M KOH 4-aminobenzenethiol, FIG. 4 4M KOH 4,4′-disulfanediyldianiline, FIG. 5 6M H2SO4 5-amino-2-hydroxybenzoic acid, FIG. 6 4M HCl 5-aminoisophthalic acid, FIG. 7 6M KOH 2,7-diaminophenanthrene-9,10-dione, FIG. 8 2M HCl 5-amino-2,3-dihydrophthalazine-1,4-dione, FIG. 9 2M H2SO4 4-aminobenzenesulfonic acid, FIG. 10 1M HCl 2-amino-1,9-dihydro-6H-purin-6-one, FIG. 11 1M HCl-7H-purin-6-amine.

Example 16

Addition of 3,4,5-Trihydroxybenzene to Carbon Cloth Using 3,4,5-Trimethoxyanyline and Characterization of the so-Formed Electrode

[0114] The study reported in this Example consists of two parts. In the first part, 3,4,5-trimethoxyaniline (TMA) is added to carbon cloth via diazonium-based chemistry. The procedure results in the grafting of 3,4,5-trimethoxybenzene (TMB) to 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 sample weight loss as temperature rises by thermogravimetric analysis (TGA).

[0115] Next, in the second part, 3,4,5-trimethoxybenzene—which is an electrochemically inactive—is deprotected to remove the methoxy groups and give the corresponding electroactive 3,4,5-trimethoxybenzene (THB). The THB-surface modified carbon cloth was then tested as an electrode material.

Part A: Grafting and Characterization by XPS, BET and TGA

[0116] ##STR00024##

[0117] 100 mg of 3,4,5-trimethoxyaniline (TMA, 0.546 mmol) were dissolved in 100 ml of acetonitrile until complete dissolution of the amine derivative. Three equivalents of tert-butyl nitrite was added (0.240 ml of a 90% solution), followed by a 100 mg piece of Kynol™ carbon cloth. The mixture was stirred for 30 min. The modified piece of cloth was filtered and washed with aliquots of dimethylformamide, acetonitrile, acetone, and methanol and dried at 60° C. under vacuum, yielding 125 mg of modified carbon (25 wt % addition of grafted molecule, which is 3,4,5-trimethoxybenzene).

[0118] The surface elemental and chemical state analysis was performed by X-ray photoelectron spectroscopy (XPS). The XPS study was carried with Thermo Scientific Nexsa spectrometer, with monochromated Al Kα source. Survey spectra were carried our at PE of 200 ev and high resolution spectra at 50 eV. In-situ charge neutralization was used, and each set of measurement was recalibrated versus C is at 284.8 eV. Due to the conducting nature of the samples only slight charging was observed, in the ballpark of few 10's of meV. Quantification was done after “smart” baseline correction, using NEXSA's RSFs. Peak fiittings were carried out with gaussian-lorentian 70:30 peaks and reasoneable FWHM values.

[0119] Spectra are presented in FIGS. 12 a-f, and are arranged as follows: FIGS. 12a and 12d are the C is spectra of non-modified and surface-modified carbon cloth, respectively; FIGS. 12b and 12e are the O 1s spectra of non-modified and surface-modified carbon cloth, respectively; and FIGS. 12c and 12f are the N 1s spectra of non-modified and surface-modified carbon cloth, respectively.

[0120] The XPS spectra confirm the addition of 3,4,5-trimethoxyaniline to the carbon cloth through the diazonium chemistry:

[0121] The C is spectra of the modified carbon seen in FIG. 12d exhibits a well resolved and strong peak at a binding energy of 286.5 eV, assigned to the additional methoxy groups (oxidized carbon), which are part of the grafted molecule added to the carbon. This peak is not seen in FIG. 12a, of the non-modified cloth.

[0122] Comparing the O 1s spectra of modified (FIG. 12e) and unmodified carbon cloth (FIG. 12b), it is seen that the grafted carbon cloth in the O 1s spectra shows considerably stronger peak than the unmodified. This is due to the addition of three oxygen atoms per grafted molecule. The intensification of the higher binding energy peak, at 533.5 eV reflects enrichment in higher electron density oxygen sites. Meaning the oxygen is in higher oxidation state in the grafted electrodes. This result indicates that the oxygen originates from the carbons surface has lower levels of binding energy compare to the oxygen at the methoxy/hydroxy from the grafted molecule.

[0123] As expected, nitrogen atoms are barely detected in the unmodified carbon cloth (FIG. 12c). In contrast, the TMA-grafted carbon cloth (FIG. 12f) exhibits a strong peak of nitrogen at around 400 eV. A smaller, but still discernible peak, appears at slightly lower binding energy, at ca. 402.2 eV. These peaks are presumably due to alternate grafting pathways/side reactions associated with diazonium chemistry, leaving N-containing moieties on the carbon surface, e.g., where the diazonium salt is directly coupled to the carbon substrate, instead of the “normal” diazonium chemistry which leads to spontaneous degradation to N.sub.2 and aryl radical, with N.sub.2 departure. Nevertheless, the detection of nitrogen on the carbon surface indirectly attests to the grafting process.

[0124] BET measurements were carried out in a Quantachrome NOVA 3200e surface area and pore size analyzer with nitrogen as an adsorbent. The surface area of the commercial activated carbon (Kynol™ carbon cloth) is ˜1500 m.sup.2/g. The results tabulated in Table 1 indicate a significant drop in surface area, attesting to an extensive grafting of 3,4,5-trimethoxybenzene (TMB).

TABLE-US-00001 TABLE 1 Surface area Surface area Carbon cloth [m.sup.2/g] [%] Plain 1495 100 TMB modified 139 9

[0125] TGA was performed under nitrogen at a temperature increase rate of 10K/min using the instrument mentioned above, for unmodified (commercial carbon cloth material) and the surface-modified carbon cloth material. The thermogram appended as FIG. 13 indicates a weight loss of about 25% up to temperature of 450° C. for the TMA-surface modified carbon cloth sample. That is, TGA indicates 25% mass loading of THB over activated carbon.

Part B: Electrochemical Deprotection and Characterization

[0126] The grafted molecule TMB underwent electrochemical deprotection to give the electroactive THA molecule. The deprotection reaction took place in a three-electrode T cell, with sulfuric acid as electrolyte solution, where the TMA-surface modified carbon cloth served as the working electrode and was followed by electrochemical measurements to evaluate the performance of the THA-grafted electrode.

[0127] Swagelok three electrode T cell was used for the electrochemical deprotection reaction and subsequent measurements. Electrodes were made of PTFE cylinder assembled with 2, 4 mm glassy carbon rods, serving as both current collectors and terminals. Working electrodes were punched from the modified carbon cloth 6 mm in diameter with an average weight of 7 mg (≈25 mg/cm.sup.2) which resembles real life electrodes as found in commercial devices, and counter electrodes of 2×12 mm in diameter were punched from an unmodified carbon cloth with an average weight of 46 mg (double disks of 12 mm), resulting in an electrode mass loading of about 40 mg/cm.sup.2. NKK cellulose paper was used as a separator. Electrodes were immersed in distilled water and slightly swirled under vacuum to allow good wetting, followed by soaking in H.sub.2SO.sub.4 (2M) solution to allow the osmotic pressure to bring in the solution to the pores within the entire electrode mass. A saturated calomel electrode (SCE) was used as the reference electrode.

[0128] Without wishing to be bound by theory, the electrochemical irreversible cleavage of the methoxy group (at 0.7 V vs. SCE in 2M sulfuric acid electrolyte solution), transforming the inactive grafted TMA molecule into the electroactive THA, is illustrated by the scheme depicted below:

##STR00025##

[0129] Polarization is shown to be activation at potentials up to a 0.6 V vs. SCE. Early protonation of the oxygen directs an E1 reaction of the poor sulfate ion nucleophile on the positively charged methyl. This process is demonstrated well in the cyclic voltammetry of THB grafted on Kynol® carbon cloth in FIG. 14A. The first cyclic voltammetry cycles for the TMA-grafted carbon cloth indicate cleavage of the methoxy groups to form trihydroxybenzene up to the third cycle at a scan rate of 2 mV/s. Voltammograms recorded at different scan rates in the 2M H.sub.2SO.sub.4 electrolyte solution are seen in FIG. 14B. The peak currents related to the methoxy cleavage take place at 0.6-0.7 V and compound is transformed to the THB redox active at 0.1-0.5 V.

[0130] The THB-modified electrode was then studied by galvanostatic measurement in the three-electrode set up with 2M H.sub.2SO.sub.4 electrolyte solution. The charge/discharge voltage profile obtained by cycling across a voltage window of −0.4V to 0.8V with a current density of 3 A/g is shown in FIG. 15A. Discharge capacity of 65 mAh/g was measured over 2000 cycles; it then dropped to 55 mAh/g and maintained at this value for additional 2500 cycles. Thus, overall, galvanostatic measurements and prolonged cycling, over 4500 cycles, of THB grafted on Kynol™ cloth, indicate the good performance of the electrode material in acidic electrolyte. The plateau at around 0.1-0.5 V vs. SCE, indicates a faradaic redox reaction.

[0131] The major results of the galvanostatic measurements are tabulated in Table 2, alongside those reported for anthraquinone(AQ)-grafted Kynol™ cloth in Electrochemical Society 165 (14) A3342-A3349 (2018) and for dihydroxybenzne(DHB)-grafted Kynol™ cloth in Electrochemical Society 166 (6) A1147-A1153 (2019). The results indicate that AQ-grafted carbon cloth, DHB-grafted carbon cloth and THB-grafted carbon cloth exhibit comparable capacitance increase.

TABLE-US-00002 TABLE 2 Mass Potential Current Grafted Electrolyte loading [V] vs. Capacity density molecule solution [%] SCE [mAh/g] [A/g] Plain 1M H.sub.2SO.sub.4 0 0.4-−0.6 20 10 AQ 1M H.sub.2SO.sub.4 25 0.4-−0.6 65 10 DHB 1M H.sub.2SO.sub.4 41 0.8-−0.2 75 1 THB 2M H.sub.2SO.sub.4 25 0.8-−0.4 65 3

Example 17

Addition of 2,7-Diamino-9,10-Phenanthrenequinone to Carbon Cloth and Characterization of the so-Formed Electrode

[0132] 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 diazonium-based chemistry. The PQ-surface modified carbon cloth was then analyzed to determine sample weight loss as temperature rises by thermogravimetric analysis (TGA).

[0133] Next, in the second part, The PQ-surface modified carbon cloth was tested as an electrode material.

Part A: Grafting and Characterization by TGA

[0134] ##STR00026##

[0135] The procedure described in Example 10 was repeated. A sample (3-5 mg) was subjected to TGA under the conditions mentioned above. The thermogram is appended in FIG. 16. A reference sample consisting of the commercial Kynol™ cloth was also tested. The results indicate a weight loss of ˜40-50% in the surface-modified carbon up to ˜500° C., owing to the weight gained as a result of the molecules added to the carbon.

Part B: Electrochemical Characterization

[0136] The PQ-grafted carbon cloth was tested in two/three-electrode cell described in the previous Example in neutral electrolyte solutions (sodium bromide and barium chloride), by cyclic voltammetry and galvanostatic measurements.

[0137] FIGS. 17A-C describe the testes performed in a two electrodes configuration cell with saturated sodium bromide electrolyte solution. The working electrode was the commercial, unmodified Kynol® cloth (6 mm in diameter; weight of 5 mg). The counter electrode was the PQ-grafted carbon cloth (12 mm in diameter; weight of 35 mg). Voltammograms produced at scan rates of 1 mV and 5 mV are given in FIG. 17A (red and blue lines, respectively). For the galvanostatic measurement, a current density of 1 A/g was applied. The results shown in FIG. 17B indicate galvanostatic charge-discharge voltage profile of a full cell. Performance over prolonged cycling (1000 cycles) is illustrated in FIG. 17C, indicating an initial discharge capacity of 35 mAh/g and energy density of 35 Wh/Kg.

[0138] FIGS. 18A-C describe the testes performed in the three-electrode cell with saturated barium chloride electrolyte solution. The working electrode was the PQ-grafted Kynol® carbon cloth (6 mm in diameter; weight of 7 mg). The counter electrode was the commercial Kynol® carbon cloth (12 mm in diameter; weight of 27 mg). Voltammogram produced at scan rate of 5 mV is shown in FIG. 18A, indicating the contribution of the redox reactions. From FIG. 18B (obtained with current density of 1 A/g), 60 mAh/g discharge capacity is obtained. Discharge capacity and efficiency versus cycle number up to 500 cycles are plotted in FIG. 18C, indicating a stable performance over prolonged cycling.