PRODUCTION OF HYDROGEN FROM CARBOHYDRATES USING VIOLOGEN CATALYSTS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001]This application claims the benefit of U.S. Provisional Application No. 63/426,082, filed Nov. 17, 2022; the entire contents of this application are hereby incorporated by reference.

BACKGROUND

[0002]This invention relates generally to a process for producing hydrogen gas through the electrolytic oxidation of carbohydrates with the consumption of carbon dioxide and concomitant production of sodium carbonate and sodium bicarbonate.

[0003]Hydrogen is a valuable, high-volume industrial gas used in a number of important processes. It is also being explored as a fuel source for domestic transportation use because of its high-energy content and non-polluting characteristics. Hydrogen, however, is expensive to produce, and conventional production from natural gas concomitantly produces carbon dioxide, an undesirable greenhouse gas.

[0004]Carbohydrates represent an alternate source for hydrogen production as they are energy rich, inexpensive and renewable. Nevertheless, there are no viable processes to utilize carbohydrates for the production of hydrogen.

[0005]Reactions involving the electrolysis of water in the presence of carbon dioxide (or carbonic acid) to produce hydrogen face a number of limitations for practical use including the use of reactive elemental metals like sodium, lithium, and other electropositive metals. Moreover, process that compete with commercially competitive electrical power sources would also be desirable.

[0006]There remains, therefore, a need for alternate ways to produce hydrogen from a renewable carbohydrate fuel without producing undesirable byproducts.

BRIEF SUMMARY

[0007]The present invention relates to an apparatus and method for producing hydrogen from carbohydrates with carbon dioxide and hydroxide source.

[0008]In one aspect, an apparatus for producing hydrogen is disclosed, the apparatus comprising a processing unit including a first chamber and a second chamber isolated from the first chamber, a first solution disposed within the first chamber, a second solution disposed within the second chamber, and an electrode barrier disposed between the first chamber and second chamber, the electrode barrier in contact with the first solution and second solution. In some aspects, the electrode barrier is configured to selectively allow passage of ions from the first chamber to the second chamber. In some embodiments, the first solution comprises a carbohydrate, an electrolyte, and a first catalyst and the second solution comprises carbon dioxide, and a second catalyst.

[0009]In another aspect, the carbohydrate in the first solution can be glucose.

[0010]In another aspect, the electrolyte can be an aqueous solution of sodium hydroxide.

[0011]In another aspect, the electrode barrier comprises a sodium ion permeable membrane disposed between a first layer of electrically conductive material and a second layer of electrically conductive material, the first layer of electrically conductive material in contact with the first solution and the second layer of electrically conductive material in contact with the second solution.

[0012]In another aspect, the first catalyst is attached to the electrode barrier in the first chamber and the second chamber.

[0013]In another aspect, the first catalyst is attached to a polymer, and the polymer is attached to the electrode barrier in the first chamber and the second chamber.

[0014]In another aspect, the electrode barrier comprises a porous material and is configured to transfer electrons from a reduced form of the first catalyst attached to the electrode barrier in the first chamber to the first catalyst attached to the electrode barrier in the second chamber.

[0015]In another aspect, the first catalyst diffuses throughout the first solution.

[0016]In another aspect, the first solution is an aqueous solution with a pH between about 11 and about 13.

[0017]In another aspect, the first solution is at a temperature between about 40° Celsius and 60° Celsius.

[0018]In another aspect, the second solution is an aqueous solution with a pH less than 7.

[0019]In another aspect, a hydrogen permeable membrane is located in a headspace of the second chamber and configured to separate gaseous hydrogen from off gasses in the headspace.

[0020]In one aspect, a method for producing hydrogen is disclosed, the method comprising providing an apparatus, such as the apparatus disclosed above, and providing carbon dioxide to the second solution in the second chamber.

[0021]In another aspect, the method of producing hydrogen further comprises passing ions from the first chamber through the electrode barrier and into the second chamber and collecting hydrogen gas produced from the second chamber.

[0022]In another aspect, the method of producing hydrogen further comprises continuously adding carbon dioxide to the second chamber.

[0023]Other systems, methods, features and advantages of the invention will be, or will become, apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be within the scope of the invention, and be encompassed by the following claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 illustrates an embodiment of the dual chamber apparatus of the present disclosure with a multi-layer electrode barrier.

[0025]FIG. 2 illustrates another embodiment of the dual chamber apparatus of the present disclosure with a single layer electrode barrier.

[0026]FIG. 3 plots hydrogen evolution by various concentrations of platinum nanoparticles vs. commercial platinum black or palladium black with carbohydrates in examples described herein at pH 4, 2.5 mM methyl viologen, and 50 mM of sodium chloride (NaCl).

DETAILED DESCRIPTION OF THE DRAWINGS AND THE PRESENTLY PREFERRED EMBODIMENTS

Definitions

[0027]Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0028]Units, prefixes, and symbols may be denoted in their SI accepted form. Numeric ranges recited herein are inclusive of the numbers defining the range and include and are supportive of each integer within the defined range. Unless otherwise noted, the terms “a” or “an” are to be construed as meaning “at least one of.” The section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described. All documents, or portions of documents, cited in this application, including but not limited to patents, patent applications, articles, books, and treatises, are hereby expressly incorporated by reference in their entirety for any purpose.

[0029]Throughout this application, the term “about” is used to indicate that a value includes the standard deviation of error for the device of method being employed to determine the value.

[0030]The term “alkyl” as used herein, means a straight or branched hydrocarbon radical or group having at least one carbon atom including but not limited to saturated C₁-C₆ such as: methyl, ethyl, 1-propyl and 2-propyl, 1-butyl, 2-butyl, 2-methyl-1-propyl, 1,1-dimethylethyl, 1-pentyl, 2-pentyl, 3-pentyl, 2-methyl-1-butyl, 3-methyl-1-butyl, 2,2-dimethylpropyl, 1-hexyl, 2-hexyl, 3-hexyl, 2-methyl-1-pentyl, 3-methyl-1-pentyl, 4-methyl-1-pentyl, 3,3-dimethyl-1-butyl, 3,3-dimethyl-2-butyl, 2-ethyl-1-butyl and the like; C₇-C₁₂ such as: 1-heptyl, 2-heptyl, 3-heptyl, 4-heptyl, 2-methyl-1-hexyl, 4-methyl-1-hexyl, 5-methyl-1-hexyl, 1-octyl, 2-octyl, 3-octyl, 4-octyl, 6-methyl-1-heptyl, 5,5-dimethyl-1-hexyl, 2-ethyl-1-hexyl, 2-methyl1-1-heptyl, 2-propyl-1-pentyl, 1-nonyl, 2-nonyl, 2-ethyl-2-methyl-1-hexyl, 4-methyl-1-octyl, 3,5,5-trimethyl-1-hexyl, 1-decyl, 2-decyl, 4-ethyl-1-octanyl, 2-methyl-1-nonyl, 4-methyl-1-nonyl, 8-methyl-1-nonyl, 1-undecyl (1-hendecyl), 2-undecyl, 7-methyl-1-decyl, 1-dodecyl, 5-dodecyl, 2-butyl-1-octyl, 10-methyl-1-undecyl and the like; C₁₃-C₁₈ such as: 1-tridecyl, 4-methyl-1-dodecyl, 11-methyl-1-dodecyl, 1-butyldecyl, 11-methyl-1-tridecyl, 1-pentadecyl, 1-hexadecyl, 2-hexyl-1-decyl, 1-heptadecyl, 14-methyl-1-hexadecyl, 15-methyl-1-hexadecyl, 1-octadecyl, 16-methyl 1-heptadecyl and the like; C₁₉-C₃₂ such as 1-nonadecyl, 2-methyl-1-octadecyl, 10-methyl-1-octadecyl, 17-methyl-1-octadecyl, 2,6,10,14-tetramethylpentadecyl, 1-eicosyl (1-arachidinyl, 1-leicosanyl), 18-methyl-1-nonadecyl, 1-heneicosyl, 19-methyl-1-eicosyl and 1-docosyl (1-behenyl), 1-tricosyl, 1-tetracosyl, 1-pentacosyl, 1-hexacosyl, 1-heptacosyl, 1-octacosyl, 1-nonacosyl, 1-triaconstyl, 2,6,10,15,19,23-hexamethyl-1-tetracosyl, 1-hentriaconsyl, 1-dotriacontyl and the like. Alkyl groups may be unsubstituted or substituted. Alkyl also includes groups having three or more carbons that contain 1 or more sites of unsaturation, that group being known as cycloalkyl groups or radicals.

[0031]The term “cycloalkyl” as used herein means a monocyclic or polycyclic hydrocarbyl group. Illustrative examples of a cycloalkyl group or radical include cyclopropyl, cycloheptyl, cyclooctyl, cyclodecyl, cyclobutyl, adamantyl, norpinanyl, decalinyl, norbornyl, cyclohexyl, and cyclopentyl. Cycloalkyl groups may be unsubstituted or substituted.

[0032]The term “aryl” means an aromatic carbocyclic ring having from 6 to 14 carbon atoms. Illustrative examples of an aryl group or radical include, but are not limited to, phenyl, 1-naphthyl, 2-naphthyl, 1-anthryl, 2-antrhyl, 9-anthryl, 1-phenanthryl, 2-phenanthryl, 3-phenanthryl, 4-phenanthryl, 5-phenanthryl, and the like; including fused ring systems with rings that have less than 6 carbons such as 1-acenaphthyl, 3-acenaphthyl, 4-acenaphthyl, 5-acenaphthyl, 1-azulyl, 2-azulyl, 4-azulyl, 5-azulyl, 6-azulyl and the like. Aryl groups may be unsubstituted or substituted with one or more electron donating groups and electron withdrawing groups. The term “aryl” also includes heteroaryls unless otherwise designated.

[0033]The term “heteroaryl” means an unsaturated monocyclic group or radical of 5 or 6 atoms, an unsaturated fused bicyclic group or radical of from 8 to 10 atoms, or an unsaturated fused tricyclic group or radical of from 11 to 14 atoms, the cyclic groups having 1 or 2 heteroatoms independently selected from O, N, or S. Illustrative examples of monocyclic heteroaryl include 2- or 3-thienyl, 2- or 3-furanyl, 1-, 2-, or 3-pyrrolyl, 1-, 2-, or 4-imidazolyl, 1-, 3-, or 4-pyrazolyl, 2-, 4-, or 5-oxazolyl, 2-, 4-, or 5-thiazolyl, 3-, 4-, or 5-isoxazolyl, 3-, 4-, or 5-isothiazolyl, 2-, 3-, or 4-pyridinyl, 3- or 4-pyridazinyl, 2- or 3-pyrazinyl, and 2-, 4-, or 5-pyrimidinyl. Illustrative examples of bicyclic heteroaryl include 2-, 3-, 4-, 5-, 6-, 7-, or 8-quinolinyl, 1-, 3-, 4-, 5-, 6-, 7-, or 8-isoquinolinyl, 1-, 2-, 3-, 4-, 5-, 6-, or 7-indolyl, 2-, 3-, 4-, 5-, 6-, or 7-benzo[b]thienyl, 2-, 4-, 5-, 6-, or 7-benzofuran, 2-, 4-, 5-, 6-, or 7-benzoxazolyl, 2-, 4-, 5-, 6-, or 7-benzothiazolyl, and 1-, 2-, 3-, 4-, 5-, 6-, or 7-benzimidazolyl. Illustrative examples of tricyclic heteroaryl include 1-, 2-, 3-, or 4-dibenzofuranyl, 1-, 2-, 3-, or 4-dibenzothienyl, and 1-, 2-, 3-, 4-, 5-, 6-, 7-, 8-, or 9-(1,2,3,4-tetrahydroacridinyl). Heteroaryl groups may be unsubstituted or substituted.

[0034]As used above, a fused bicyclic group or radical is a group wherein two ring systems share two and only two atoms. As used above, a fused tricyclic group or radical is a group wherein three ring systems share four and only four atoms.

[0035]The terms “alkylaryl” and “arylalkyl” as used herein, means an alkyl portion where alkyl is defined above and to include an aryl portion where aryl is defined above. Illustrative examples of alkylaryl include, but are not limited to, toluene, ethylbenzene, propylbenzene, and xylene. Examples of arylalkyl include, but are not limited to benzyl, 2-phenylethyl, 3-phenylpropyl, 4-phenylethyl, phenylpropyl, 3-methyl-3-phenylpropyl, 1-naphthylmethyl, 1-naphthylethyl, 3-(1-naphthyl)-propyl, 4-(1-naphthyl)-butyl, 4-(2-naphthyl)-butyl, and 4-phenylheptyl.

[0036]The term “alkylthio” as used herein, means straight or branched chain alkylsulfides of from 1 to 18 (C₁-C₁₈) carbons with a sulfide group. Illustrative examples include, but are not limited to, methylthio, ethylthio, isopropylthio.

[0037]The term “alkylammonium” as used herein, means radical or group containing a cationic nitrogen (also called a quaternary nitrogen, or tetravalent nitrogen) with one or more alkyl groups as defined above. Examples include, but are not limited to monoalkylammonium, dialkylammonium, trialkylammonium, and tetraalkylammounium. In compounds with an alkylammonium group, a counterion, i.e., an anion, is usually present to offset the positive charge.

[0038]The term “carbohydrate” as used herein, refers to a carbohydrate with a reducing end. “Carbohydrate” means aldoses and ketoses having the general stoichiometric formula C_n(H₂O)_n, and includes monosaccharides, oligosaccharides and polysaccharides as well as substances derived from monosaccharides by reduction of the carbonyl group (alditols) such as glycerol (glycerin), maltitol, sorbitol, and isomalt, by oxidation of one or more terminal groups to carboxylic acids, or by replacement of one or more hydroxy group(s) by a hydrogen atom, an amino group (amino sugar), thiol group or similar groups. It also includes derivatives of these compounds. By way of example, carbohydrates include sugars such as such as glucose, mannose, galactose, fructose, glyceraldehyde, dihydroxyacetone, erythrose, ribulose, xylulose, sedoheptulose, ribose, deoxyribose, sorbose, glucosamine, and galactosamine; disaccharides such as isomaltose, maltose, cellobiose, lactose, and raffinose; ketoses including trioses such as dihydroxyacetone, tetroses such as erythrulose, pentoses such as ribulose and xylulose, and hexoses such as fructose, psicose, sorbose, tagatose; aldoses including trioses such as glyceraldehyde, tetroses such as erythrose and threose, pentoses such as ribose, arabinose, xylose, and lyxose, and hexoses such as allose, atlrose, glucose, mannose, gulose, idose, galactose, talose; oligosaccharides; polysaccharides such as starch, glycogen, cellulose, glycoprotein, glycosaminoglycan, and glycolipid. For clarity, in some embodiments, carbohydrates lacking a reducing end are excluded.

[0039]The term “amino sugar” as used herein means monosaccharides having one hydroxyl group, i.e., alcohol, (commonly but not necessarily in position 2) replaced by an amino group, systematically known as x-deoxy-x-monosaccharides. By way of example, D-glucosamine or 2-amino-2-deoxy-D-glucopyranose is an amino sugar. Other illustrative amino sugars include but are not limited to erythrosamine, threosamine, ribosamine, arabinosamine, xylosamine, lyxosamine, allosamine, altrosamine, glucosamine, mannosamine, idosamine, galactosamine, talosamine, and their derivatives. The amino sugars include both aldose and ketose sugars. Additionally, the amino sugars may be of a straight-chain structure; however, the aldehyde or ketone group of the amino sugar may react with a hydroxyl group on a different carbon atom to form a hemiacetal or hemiketal, in which case there is an oxygen bridge between the two carbon atoms, forming a heterocyclic ring. Amino sugar rings with five and six atoms are called furanose and pyranose forms, respectively and exist in equilibrium with their corresponding straight-chain form. It should be noted that the ring form has one more optically active carbon than the straight-chain form, and so has both an a and a β form, which interconvert in equilibrium. The term “amino sugar” also means glycosylamines, amino sugars where the nitrogen is substituted with a functional group other than H. Illustrative examples of glycosylamines include N-acetylglucosamine, N-methylglucosamine.

[0040]The term “electrolyte” as used herein, means any substance that dissociates into ions when dissolved in a suitable medium or melted and thus forms a conductor of electricity. The term “electrolyte” includes alkaline hydroxides or alkaline earth hydroxides. Examples include lithium hydroxide, potassium hydroxide, sodium hydroxide, beryllium hydroxide, magnesium hydroxide, calcium hydroxide, strontium hydroxide and mixtures of the same. In some examples, the electrolyte is a hydroxide source like sodium hydroxide (NaOH).

[0041]The terms “violene” and “violene compound” as used herein means a compound of the general formula X—(CR—CR′)_n—X′, where X and X′ are independently a heteroatom such as oxygen, sulfur, or nitrogen independently substituted with H, alkyl, alkylaryl, alkylthio, and alkylammonium; (CR—CR′) is an aromatic group or apart of an aromatic group; n is an integer so long as aromaticity of (CR—CR′) is maintained; and R and R′ are each independently H or a bond. Violene compounds may be characterized by the stability of their radical cations through delocalization throughout a π-framework together with a heteroatom.

[0042]Violene compounds include compounds that can become Weitz-type radicals and Würster-type radicals. The substituted heteroatom (N—R for example) or heteroatoms in Weitz-type radicals are directly incorporated within the aromatic system, for example viologen compounds including pyridiniums, conjugated pyridiniums, and bipyridiniums that are defined below. The substituted heteroatom or heteroatoms in Würster-type radicals are not directly incorporated within the aromatic system, for example N¹,N¹,N⁴,N⁴-tetramethylbenzene-1,4-diamine and N⁴,N⁴,N⁴′,N⁴′-tetramethylbiphenyl-4,4′-diamine. Additional examples of violene compounds may be found in Hunig, Pure Appl. Chem. 1967, 15, 109-122 and Hunig et al., Top. Curr. Chem. 1980, 92, 1-44, which are hereby incorporated by reference. A violene compound can be viologen or a salt there of. An example of a viologen is 1,1′-di(hydrocarbyl)-4,4′-bipyridinium salt.

[0043]The term “pyridinium compound” as used herein means a cationic form of pyridine by the addition of a substituent to the ring nitrogen, i.e., by alkylation.

[0044]The term “conjugated pyridinium compound” as used herein means a compound including at least one pyridinium substructure conjugated to an aryl substructure.

[0045]The terms “bipyridinium compound” as used herein means two pydrinium compounds sharing a common carbon-carbon bond.

[0046]The term “electrode” as used herein, means an electric conductor through which an electric current enters or leaves an electrolytic cell.

[0047]The processes and apparatus described herein are directed to methods of making hydrogen utilizing a renewable energy source and one or more catalysts in a dual chamber apparatus. A reaction in one chamber of the apparatus produces electrons that move through a barrier where they reduce hydrogen ions for the production of hydrogen gas (H₂).

[0048]As shown in FIG. 1, an apparatus or processing unit 100 of the present disclosure can include a first chamber 110 and a second chamber 120 separated by an electrode barrier 130. A first electrochemical reaction occurring in the first chamber generates an electrical potential used to power a second electrochemical reaction in the second chamber.

[0049]A catalyst can be used to facilitate the electro chemical reaction in the first chamber 110 resulting in electrical current. The catalyst can be a violene, such as a viologen compound, a pyridinium compound, a conjugated pyridinium compound, or a bipyridinium compound. Example chemical reactions of the disclosed process using glucose as the carbohydrate and sodium hydroxide as the electrolyte are shown below. Reaction (1) occurs in the first chamber, and reaction (2) occurs in the second chamber with the net effect shown in reaction (3).

$\begin{array}{cc}36\mathrm{NaOH}+C_6{H}_{12}{O}_6=6{\mathrm{Na}}_2{\mathrm{CO}}_3+24H_{2}O+24e+24\mathrm{Na}+& \left(1\right)\end{array}$$\begin{array}{cc}24\mathrm{Na}++24C{O}_2+24H_{2}O+24H^{+}+24e=12H_2+24NaHC{O}_3& \left(2\right)\end{array}$$\begin{array}{cc}{C}_6{H}_{12}{O}_6+36\mathrm{NaOH}+24C{O}_2=12H_2+6{\mathrm{Na}}_2{\mathrm{CO}}_3+24NaHC{O}_3& \left(3\right)\end{array}$

[0050]Thus, the exemplary process described in the equations above is the consumption of glucose, sodium hydroxide, and carbon dioxide to produce hydrogen gas, sodium carbonate, and sodium bicarbonate.

[0051]Referring to FIG. 1, a two-part electrochemical cell 100 for producing hydrogen gas is shown. The electrochemical cell 100 includes two chambers 110 and 120. A headspace 150 associated with chamber 2 captures hydrogen gas produce by the electrochemical reactions described herein.

Chamber A

[0052]In one embodiment, the process described herein includes the electrochemical reaction embodied in reaction (1) carried out in a first chamber 110 (e.g. Chamber A). As carbohydrate oxidizes in the first chamber, the reaction generates an electrical current. In some embodiments, an electrolyte is included in the first chamber solution. The electrolyte can be a hydroxide, alkaline hydroxide such as lithium hydroxide, potassium hydroxide, and sodium hydroxide, or an alkaline earth hydroxide such as beryllium hydroxide, magnesium hydroxide, calcium hydroxide, and strontium hydroxide. The first solution can be an aqueous solution with a pH between about 11 and about 13. A pH below 11 typically results in a slower and slower rate of reaction typically undesirable. A pH above 13 can degrade the catalyst and thereby reduce the functionality of the apparatus 100. The first solution can be a temperature between about 40° Celsius or above. In some embodiments, the temperature of the solution can be between about 40° and about 60° Celsius. Higher temperature solutions are advantageous for oxidizing carbohydrates with larger or more complex compound structures such as polysaccharides. Lower temperatures can be used for shorter carbohydrates. In some embodiments, the first chamber is anaerobically separated from oxygen sources, i.e. that solution is isolated from atmospheric or other oxygen.

[0053]For example, a solution containing glucose and sodium hydroxide at a 1/36 molar ratio can be supplied to the first chamber 110. As shown in the ionic reaction (4) below, the oxidation of glucose produces 24 electrons along with water and carbonate (CO₃²—). In some embodiments, formate (HCO₂—) can be produced from the reaction in the first chamber 110.

[0054]The electrons produced in the first chamber 110 transfer to the second chamber 120 to supply a second reaction producing hydrogen as shown in reaction (7). Normally, the oxidation of glucose (4) is not spontaneous, i.e., it does not readily occur at an electrode. Accordingly, a first catalyst added to the solution in the first chamber 110 that enables the reaction to occur spontaneously. The first catalyst used in the system can be any catalyst capable of oxidizing carbohydrates to produce electrons. In some embodiments, the first catalyst can be a violene compound, such as a viologen compound, a pyridinium compound, a conjugated pyridinium compound, or a bipyridinium compound.

[0055]In one embodiment, the catalyst can be a violene compound having the general formula X—(CR═CR′)_n—X′, where X and X′ are independently a heteroatom such as oxygen, sulfur, or nitrogen (independently substituted with H, alkyl, alkylaryl, alkylthio, and alkylammonium); (CR═CR′) is an aromatic group or apart of an aromatic group; n is an integer so long as aromaticity of (CR═CR′) is maintained; and R and R′ are each independently H or a bond.

[0056]In some embodiments, the violene compound is a pyridinium compound. Thus, in these embodiments, the catalyst is a pyridinum compound represented by the formula:

[0058]In some embodiments, the violene compound is a conjugated pyridinium compound. Thus, in these embodiments, the catalyst is a conjugated pyridinium compound represented by the formula:

[0060]In some embodiments, the violene compound is a bipyridinium compound. Thus, in these embodiments, the catalyst is a bipyridinium compound represented by the formula:

[0062]In some embodiments, the bipyridinium compound may be a 4,4′-bipyridinium compound represented by the formula:

[0064]In some embodiments, the 4,4′-bipyridinium compound may be a viologen. By way of examples, a viologen can be 1,1′-dibenzyl-4,4′-bipyridinium dichloride (benzyl viologen dichloride), 1,1′-dioctadecyl-4,4′-bipyridinium dibromide (octadecyl viologen dibromide), 1,1′-diethyl-4,4′-bipyridinium dibromide (ethyl viologen dibromide), 1,1′-diethyl-4,4′-bipyridinium diiodide (ethyl viologen diiodide), 1,1′-diethyl-4,4′-bipyridinium diperchlorate (ethyl viologen diperchlorate), 1,1′-dimethyl-4,4′-bipyridinium dichloride (methyl viologen dichloride), and 1,1′-diisopropyl-4,4′-bipyridinium dichloride (isopropyl viologen dichloride). Other examples of viologens are described in The Viologens: Physicochemical Properties, Synthesis and Applications of the Salts of 4,4′-Bipyridine; Monk, Paul S.; Wiley, (2001), which is incorporated herein by reference in its entirety.

[0065]In still another embodiment, the bipyridinium compound may be a 2,2′-bipyridium compound represented by the formula:

[0067]In yet another embodiment, the bipyridinium compound may be represented by the formula:

[0069]In some embodiments, a viologen catalyst can be included in the first solution 112 as the first catalyst where it acts as an electron acceptor and thereby facilitates the oxidation of glucose. In some embodiments, the first solution 112 can include 5-10 mM of methyl viologen (MV) as the catalyst. MV is reduced in the first chamber when it accepts electrons produced from the oxidation of glucose. The reduced catalyst (MVr) contacts the electrode barrier 130 and transfer electrons into the second chamber 120 where they reduce hydrogen ions to form hydrogen gas.

Chamber B

[0070]The electrons from the first chamber 110 are used to reduce hydronium (H⁺) to produce hydrogen gas (H₂) in the second chamber 120 (also referred to as Chamber B) can be visualized in the example ionic chemical reactions (4)-(8) below. Reaction (4) shows the oxidation of glucose occurring in the first chamber. Reactions (5)-(7) occur in the second chamber 120 with the net effect shown in reaction (8).

$\begin{array}{cc}{C}_6{H}_{12}{O}_6+36O{H}^{-}=6{\mathrm{CO}}_3^{2-}+24H_{2}O+24e^{-}& \left(4\right)\end{array}$$\begin{array}{cc}24C{O}_2+24H_{2}O=24H_2{\mathrm{CO}}_3& \left(5\right)\end{array}$$\begin{array}{cc}24H_{2}C{O}_3=24H^{+}+24{\mathrm{HCO}}_3^{-}& \left(6\right)\end{array}$$\begin{array}{cc}24H^{+}+24e^{-}=12H_2& \left(7\right)\end{array}$$\begin{array}{cc}{C}_6{H}_{12}{O}_6+36O{H}^{-}+24C{O}_2=6C{O}_3^{2-}+12H_2+24{\mathrm{HCO}}_3^{-}& \left(8\right)\end{array}$

[0071]In some embodiments, a second solution 122 partially fills the second chamber 120 of the apparatus 100. The second solution 122 can be an aqueous solution including carbon dioxide. In some embodiments, the second chamber 120 and second solution 122 are pressurized (preloaded with) carbon dioxide can be pressurized into the solution prior to introducing it to the apparatus. As shown in reaction (5) above, carbon dioxide dissolves in water to produce carbonic acid (H₂CO₃). As shown in reaction (6), the carbonic acid further dissociates producing bicarbonate (HCO₃) and hydrogen ions (H⁺). Hence, the solvation of carbon dioxide in water results in an acidic aqueous solution.

[0072]In some embodiments, the pH of the second solution can be between about 4 and about 12. In some embodiments, the pH of the second solution is less than about 7. In some embodiments, the pH of the second solution is less than about 6.

[0073]The second solution 122 can further include a second catalyst. The second catalyst can be any catalyst compatible with hydrogen ions. In some embodiments, the second catalyst is a metallic catalyst. In some embodiments, the second catalyst is selected from one or more of platinum, palladium, and pentacyanocobaltate ([Co(CN)₅]³⁻). In some embodiments, the second catalyst is platinum. In some embodiments, the second catalyst is palladium. In some embodiments, the second catalyst is pentacyanocobaltate ([Co(CN)₅]³⁻).

[0074]The second catalyst binds hydrogen ions that prevents the hydrogen ions from recombining with aqueous carbon dioxide or any of the intermediaries shown in reactions (5) and (6). The hydrogen ions are made available by the second catalyst until the first catalyst from the first chamber 110 transfers electrons into the second chamber 120 where the electrons bind with the hydrogen ions to form hydrogen gas as shown in reaction (7).

[0075]In some embodiments, carbon dioxide is continuously infused (bubbled or otherwise added) to the second chamber 120 thereby maintaining electrochemical reaction conditions in the second chamber 120. In some embodiments, low-cost waste streams containing hydrogen ions can be used to replace or supplement the hydrogen ions produced from carbon dioxide in the second chamber solution 122. In some embodiments, the cell is run in batch mode in which carbon dioxide and/or waste streams containing hydrogen ions are loaded into the cell without subsequent replacement of the consumed hydrogen ions.

Electrode Barrier

[0076]In one embodiment, an electrode barrier 130 is disposed within the processing unit 100 such that it separates and isolates the first chamber 110 from the second chamber 120. One surface of the barrier 131 is in contact with the first chamber solution 112, and a second surface 132 of the barrier is in contact the second chamber solution 122.

[0077]In some embodiments, the electrode barrier 130 can be a single layer of an electrically conductive material. Such materials include nickel (Ni), cobalt (Co), silver (Ag), gold (Au), platinum (Pt), ruthenium (Ru), graphite, and combinations of the same. The electrically conductive material can be a non-metallic material including particles of metal, metal oxide, or metal alloy. In some embodiments, the material can include other electrode materials such as carbon. The electrically conductive material can be a solid material or in some embodiments, a porous material. For example, a metal foam, such as nickel foam, or a foam material containing metal particles can be used. The porous structure increases the surface area of contact between the electrode barrier and the first and second solutions that can thereby increase the rate and efficiency of electron transfer across the barrier.

[0078]In some embodiments, the electrode barrier 130 can be solid material with a porous surface on one or both sides of the electrode barrier 130. Examples of suitable solid, porous materials for the electrode barrier include metal and carbon foams such as nickel foam. A metal foam is a material or structure consisting of a solid metal with gas-filled pores comprising a large portion of the volume. The pores can be sealed (closed-cell foam) or interconnected (open-cell foam). The defining characteristic of metal foams is a high porosity, typically only 5-25% of the volume is the base metal. In some embodiments, the metal foam is electrically conducting.

[0079]In some embodiments, the electrode barrier 130 includes a ion permeable membrane 140 in between two layers of electrically conductive material 141 and 142. In this configuration, one layer of electrically conductive material 141 contacts the first chamber solution 112 in the first chamber 110, and the other layer 142 contacts the second chamber solution 122 in the second chamber 120. The contact made between the barrier 130 and each solution 112 and 122 facilitates electron transfer from the first chamber 110 to the second chamber 120.

[0080]In some embodiments, the ion permeable membrane is a proton exchange membrane. In some embodiments, the ion permeable membrane is a sodium exchange membrane.

[0081]During electron transfer from the first chamber 110 to the second chamber 120, an ionic charge imbalance occurs between the chambers. This imbalance if not addressed would eventually stop the reactions from continuing. When sodium hydroxide is used as an electrolyte, an excess of sodium ions produced from the reaction in the first chamber 110 can accumulate in the first chamber 110 and prevent the reaction from continuing. The reaction in the second chamber 120 requires sodium ions for the formation of hydrogen gas and sodium bicarbonate. To correct this imbalance, an electrode barrier specific to the cation migrating between the two chambers e.g. a sodium permeable membrane when sodium electrolytes are used enables sodium ions from the first chamber 110 to travel into the second chamber 120.

[0082]The electrode barrier 130 can include any proton exchange membrane to correct proton imbalances that may occur in the apparatus. Other selectively permeable membranes such as a hydroxide permeable membrane can be included to facilitate exchange of other ions present in the first and second chambers.

Immobilized Form of First Catalyst

[0083]Without a catalyst, the reactions described above would not occur spontaneously making the process inefficient. The use of an appropriate catalyst can facilitate the reactions and the energy transfer required to produce hydrogen. The first catalyst can be a violoene as generally described above. For example, methyl viologen (MV) acting as a first catalyst is able to extract energy via the 24 electrons removed from glucose in reaction (1) and retain this energy at +460 mV. Formation of hydrogen occurs in CO₂-saturated water with a pH near 5.0 and requires −320 mV of energy to complete. The oxidation of MVr and formation hydrogen has an overall potential of +140 mV indicating that H₂ spontaneously forms under these conditions. Monomethyl viologen (MMV) could also be used as the catalyst.

[0084]Monomethyl viologen (MMV) is MV with one of the two methyl groups removed. MMV has a more positive reduction potential of +880 mV, giving a more favorable overall potential of +550 mV when used to produce hydrogen. This more favorable potential for MMV could benefit the hydrogen formation reaction if resistance to hydrogen formation is encountered at the electrode where hydrogen is formed.

[0085]In some embodiments, the first catalyst can be immobilized or attached to the electrode barrier 130. The catalyst can be attached by directly binding the catalyst to the electrode barrier surface and/or incorporating the catalyst with a polymer side chain which itself is attached to the electrode barrier surface. In some embodiments, the polymer can be electrically conductive and act as an extension of the electrode barrier. Immobilizing the catalyst in proximity to the electrode barrier 130 promotes contact between electrode and electrolyte solution as well as increases electron transfer efficiency across the electrode barrier.

[0086]In the catalysts described above, one or more of the ring structures or individual R-labeled groups may be substituted with an alkylthio group. In some embodiments, the alkylthio group has from 2 to 3 carbons. The thio group can be bound to a metallic structure such as the electrode barrier 130. In some embodiments, the electrode barrier can be a solid structure including particles of metal, metal oxide, or metal alloy. The materials on which the catalyst is attached may have additional or complementary catalytic functionality. Such materials could include nickel (Ni), cobalt (Co), silver (Ag), gold (Au), platinum (Pt), and ruthenium (Ru) and corresponding metal oxides and mixtures comprised of the same. Binding of the catalyst to an electrode surface serves to promote efficiency in the transport of electrons between the electrode and the catalyst. Such binding also serves to retain catalyst inside the apparatus, thus decreasing catalyst replacement requirements and potential for catalyst release to the environment.

[0087]In the catalysts described above, one or more of the ring structures may be substituted with one or more electron withdrawing groups and or electron donating groups. These ring substituents allow tuning of the electrode potential and can improve reactivity.

[0088]In the catalysts described above, one or more of the ring structures may be substituted with one or more positively charged alkyl ammonium groups.

[0089]In still another embodiment, the catalyst functionality can be attached to or incorporated into a polymer. Such a polymer can act to bring the catalyst functionality in proximity to the electrode barrier 130 and to restrict mobility of the catalyst. Thin films of polymer can enhance the efficiency of a fuel cell by promoting intimate contact between the first solution containing the carbohydrate, the electrode barrier 130 acting as a source or sink of electrons, and the catalyst. In addition, the polymer can be of an electronically conductive type so as to act better as an extension of the electrode barrier 130 and to minimize internal electronic resistance in the apparatus.

[0090]For example, a viologen catalyst can be immobilized on the both surfaces 131 and 132 of the electrode barrier. Electrons produced in the first chamber 110 reaction can accumulate as reduced immobilized viologens on the electrode barrier 130 in the first chamber 110. The electrons are then transferred to immobilized viologens immobilized on the electrode barrier surface 132 in the second chamber 120.

[0091]An advantage to immobilizing the first catalyst within the processing unit 100 during use decreases catalyst replacement requirements. In some embodiments, the catalyst can be immobilized on both surfaces 131 and 132 of the electrode barrier 130 within the first and second chambers 110 and 120. In some embodiments, the first catalyst is immobilized to surface 131 only. In some embodiments, the first catalyst is immobilized to surface 132 only.

Homogenous First Catalyst

[0092]In some embodiments, the first catalyst can be added to the solutions in the first and second chambers 110 and 120 and allowed to move freely within the solutions, referred to here as a “homogenous catalyst.” When a reduced first catalyst moving through the first solution 112 contacts the electrode barrier 130, electrons are transferred to the second chamber 120 across the barrier to reduce free moving first catalyst present in the second chamber 120.

[0093]Some embodiments of the present invention can utilize a combination of immobilized and homogenous catalysts. For example, the first catalyst can be immobilized on surface 131 of the electrode barrier 130 in the first chamber 110 and homogenous in the second solution 122 in the second chamber 120. In some embodiments, the first catalyst can be homogenous in the first solution 112 in the first chamber 110 and immobilized on surface 132 of the electrode barrier 130 in the second chamber 120. In some embodiments, the catalyst can be present in only one chamber. For example, the catalyst can homogenous in the first solution 112 in the first chamber 110 only and absent from the second chamber 120, or the catalyst can be homogenous in the second solution 122 of the second chamber only and absent from the first chamber 110. In some embodiments, the catalyst can immobilized on the surface 131 of the electrode barrier 130 in the first chamber 110 and absent from the second chamber 120, or the catalyst can be immobilized on the surface 132 of the electrode barrier 130 in the second chamber 120 and absent from the first chamber 110.

Outputs

[0094]In some embodiments, a hydrogen permeable membrane 160 can be disposed within the headspace 150 of the second chamber 120. As the electrolytic reaction occurs in the second chamber 120, hydrogen gas (H₂) as well as insolubilized carbon dioxide (CO₂) gas collect in the headspace 150. A hydrogen permeable membrane 160 may adjoin the headspace 150 thereby separating the hydrogen gas 170 from any remaining gaseous carbon dioxide.

[0095]In some embodiments, commercially viable byproducts can be produced and collected in addition to hydrogen gas. For example, when glucose and sodium hydroxide are used, byproducts such as sodium carbonate (Na₂CO₃) and sodium bicarbonate (NaHCO₃) can be collected and used as additional byproducts from electrochemical reactions described herein.

[0096]Throughout this specification various indications have been given as to preferred and alternative embodiments of the invention. The foregoing detailed description is, however, to be regarded as illustrative rather than limiting and the invention is not limited to any one of the provided embodiments. It should be understood that it is the appended claims, including all equivalents, are intended to define the spirit and scope of this invention.

EXAMPLES

[0097]Applicant investigated a variety of carbohydrate substrates (listed in the specification) as electron donors to violene electron acceptors. The redox reaction occurred at pH 12 in a phosphate buffer. The carbohydrates converted the violene molecule from the oxidized to the reduced species indicated by the formation of an observed blue color. The solution of the reduced violene molecule was added to a H₂CO₃ solution between pH 4-6. The addition of platinum nanoparticles to this solution lead to the production of hydrogen gas (H₂) that was measured by an increase of pressure in the reaction vessel showing yields of H₂ 50-60% of that expected based on the number of electrons stored in the violene molecule.

[0098]Other experiments with gas chromatography were performed to obtain better quantification of the H₂ produced. Reduced violene reacted with platinum or palladium produced H₂ in buffer solutions between pH 4-6. Violene concentrations ranging from 1-40 mM were investigated. Concentrations of platinum nanoparticles (PtNP) synthesized in the lab ranging from 0.1-40 ppm were investigated. Concentrations of commercially available and known H₂ evolving catalysts Pt-black and Pd-black (Sigma-Aldrich, cat. #205915 and #520810) ranging from 1-10 ppm were also investigated. Results of these experiments are identified in FIG. 3.

Statements

[0104]Statement 2. The apparatus of statement 1, wherein the carbohydrate is glucose.

[0105]Statement 3. The apparatus of statements 1-2, wherein the electrolyte comprises an aqueous solution of sodium hydroxide.

[0106]Statement 4. The apparatus of statements 1-3, wherein the electrode barrier comprises a sodium ion permeable membrane disposed between a first layer of electrically conductive material and a second layer of electrically conductive material, the first layer of electrically conductive material in contact with the first solution and the second layer of electrically conductive material in contact with the second solution.

[0107]Statement 5. The apparatus of statements 1-4, wherein the first catalyst is attached to the electrode barrier in the first chamber and the second chamber.

[0108]Statement 6. The apparatus of statements 1-5, wherein the first catalyst is attached to a polymer, and the polymer is attached to the electrode barrier in the first chamber and the second chamber.

[0109]Statement 7. The apparatus of statements 4-6, wherein the electrode barrier comprises a porous material and configured to transfer electrons from a reduced form of the first catalyst attached to the electrode barrier in the first chamber to the first catalyst attached to the electrode barrier in the second chamber.

[0110]Statement 8. The apparatus of statements 1-4, wherein the first catalyst diffuses throughout the first solution.

[0111]Statement 9. The apparatus of statements 1-8, wherein the first solution is an aqueous solution with a pH between about 11 and about 13.

[0112]Statement 10. The apparatus of statement 9, wherein the first solution is at a temperature between about 40° Celsius and 60° Celsius.

[0113]Statement 11. The apparatus of statements 1-10, wherein the second solution is an aqueous solution with a pH less than 7.

[0114]Statement 12. The apparatus of statements 1-11, further comprising a hydrogen permeable membrane located in a headspace of the second chamber and configured to separate gaseous hydrogen from off gasses in the headspace.

[0115]Statement 13. A method for producing hydrogen comprising providing an apparatus of any one of statements 1-12; and providing carbon dioxide to the second solution.

[0116]Statement 14. The method of statement 13, further comprising passing ions from the first chamber through the electrode barrier and into the second chamber; collecting hydrogen gas produced from the second chamber.

[0117]Statement 15. The method of statements 13-14, further comprising continuously adding carbon dioxide to the second chamber.