On Demand Carbon Monoxide Generator For Therapeutic and Other Applications

Abstract

A device that can produce carbon monoxide for therapeutic and laboratory applications is disclosed. The device includes and electrochemical cell that converts carbon dioxide or a carbon dioxide containing molecule such as a carbonate or bicarbonate or bicarbonate into carbon monoxide and oxygen. The cell contains additives so pure carbon monoxide is obtained.

Description

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority to and the benefit under 35 U.S.C. §119(e) to U.S. Provisional Application 61/540,044, entitled “On Demand Carbon Monoxide Generator for Therapeutic and Other Applications,” filed Sep.28, 2011. This application is related to U.S. Non-Provisional Patent Application US 2011/0237830 filed Jul. 4, 2010, entitled “Novel Catalyst Mixtures,” which claims the benefit of U.S. Provisional Patent Application Ser. No. 61/317,955 filed Mar. 26, 2010, entitled “Novel Catalyst Mixtures,” and the application is also related to international application WO 2011/120021, entitled “Novel Catalyst Mixtures,” filed Mar. 25, 2011, which claims the benefit of both of the above applications. This application is also related to international patent application WO201206240, “Novel Catalyst Mixtures,” filed Jul. 1, 2011, which claims the benefit of above applications US 2011/0237830 and WO 2011/120021, and which also claims the benefit of U.S. Provisional Patent Application 61/484,072, “Novel Catalyst Mixtures,” filed May 9, 2011, and U.S. Non-Provisional patent application Ser. No. 13/174,365, “Novel Catalyst Mixtures,” filed Jun. 30, 2011. The present application is also related to U.S. Provisional Application 61/499,225, entitled “Low Cost Carbon Dioxide Sensors,” filed Jun. 29, 2011, and U.S. Provisional Application 61/540,044, entitled “On Demand Carbon Monoxide Generator for Therapeutic and Other Applications,” filed Sep. 28, 2011. The present application is also related to U.S. patent application Ser. No. 13/530,058 entitled “Sensors for Carbon Dioxide and Other End Uses,” filed Jun. 21, 2012, which claims benefit from each of the aforementioned patent applications and provisional patents. The present application is also related to continuation-in-part application U.S. Ser. No. 13/445,887, “Electrocatalysts for Carbon Dioxide Conversion,” filed Apr. 12, 2012, which is based on the above U.S. Non-Provisional Patent Application US 2011-0237830 filed Jul. 4, 2010. In addition, the present application is related to international patent application PCT/US12/43651, “Low Cost Carbon Dioxide Sensors,” filed Jun. 21, 2012, which claims the benefit of the above U.S. Provisional Patent Application 61/499,255, entitled “Low Cost Carbon Dioxide Sensors,” filed Jun. 29, 2011. Each of the above applications is hereby incorporated herein by reference in its entirety.

STATEMENT OF GOVERNMENT INTEREST

This invention was made, at least in part, with U.S. government support under Department of Energy Grant DE-SC0004453. The U.S. government has certain rights in the invention.

FIELD OF THE INVENTION

This patent relates to a system for the production of carbon monoxide on demand. The devices of this invention are applicable, for example, for production of carbon monoxide in chemical laboratories or therapeutic settings.

BACKGROUND

Carbon monoxide (CO) is widely used as an industrial chemical, in chemical laboratories. Clinical applications of CO are just starting to appear. There are many chemical processes to generate carbon monoxide on an industrial scale such as those disclosed in U.S. Pat. Nos. 2,218,262, 2,665,972, 3,046,093, and 4,564,513. However, clinical and laboratory applications still rely on gas cylinders to supply carbon monoxide. Carbon monoxide is poisonous and if a cylinder leaks it could lead to hazardous conditions. Further, cylinders are not a convenient delivery mode in a clinical application.

At present there is a need for a carbon monoxide delivery system that does not rely on gas cylinders, and instead creates carbon monoxide on demand.

A few previous carbon monoxide generators have been disclosed. For example, U.S. Pat. Nos. 6,948,352, 7,951,273, and patent application 2005/0100478 disclose devices that are able to generate nanograms/hr of carbon monoxide for calibration purposes, but the devices cannot produce the mg/min of carbon monoxide needed for some clinical applications. Also, the reactions in the devices produce toxic byproducts when they are run at the mg/min scale.

Patent application US 2011/0217226 provides a method to convert formic acid to carbon monoxide, but formic acid is corrosive to mucus membranes. Traces of formic acid can be released from the device when cartridges are changed or during a device failure, which would not be preferred for inhalation therapy.

There are also a number of electrochemical processes that convert CO₂ or other compounds into a variety of products including carbon monoxide, as outlined in U.S. Pat. Nos. 3,959,094, 4,240,882, 4,523,981, 4,545,872, 4,595,465, 4,608,132, 4,608,133, 4,609,440, 4,609,441, 4,609,451, 4,620,906, 4,668,349, 4,673,473, 4,711,708, 4,756,807, 4,818,353, 5,064,733, 5,284,563, 5,382,332, 5,457,079, 5,709,789, 5,928,806, 5,952,540, 6,024,855, 6,660,680, 6,987,134, 7,157,404, 7,378,561, 7,479,570, and the papers reviewed by Hori (Modern Aspects of Electrochemistry, 42, 89-189, 2008) (“the Hori Review”), Gattrell, et al. (Journal of Electroanalytical Chemistry, 594, 1-19, 2006) (“the Gattrell review”), DuBois (Encyclopedia of Electrochemistry, 7a, 202-225, 2006) (“the DuBois review”). None of the previously disclosed electrochemical methods produce carbon monoxide at purities suitable for clinical applications. In particular, most of the previous processes produce acid or organic byproducts. Further, the Hori review indicates that all of the electrochemical systems developed so far produce streams that are less than 90% CO. For example, the Hori review shows that under the best conditions a gold or silver working electrode produces a CO stream that contains over 10% hydrogen, and about 1% of acetic acid. The acetic acid would preclude the use of the device in inhalation therapy, and the high hydrogen concentration would create an explosion hazard when the stream is mixed with oxygen for inhalation therapy.

SUMMARY OF THE INVENTION

The invention provides a new carbon dioxide generator design that can produce carbon monoxide on demand at the mg/min rate needed for clinical applications, at the purities needed for these applications, and does not use any corrosive or toxic starting materials. The general approach is to start with carbon dioxide or a related carbonate or bicarbonate, and use a device to convert that material into carbon monoxide (CO) on demand. The advantage is that one does not use any toxic or corrosive starting materials, so the process is safe even if there is a small leak.

The device may include an electrochemical cell with a working electrode, a counter electrode, and an electrolyte in between, wherein the electrochemical cell is active for CO₂ reduction to carbon monoxide and oxygen. One supplies either CO₂ or a CO₂ containing compound such as a carbonate or bicarbonate to the working electrode, and applies a voltage between the working electrode and the counter electrode to produce carbon monoxide at a controlled rate.

The system may also include a means to control the rate of production of carbon monoxide. Electrochemical devices are particularly preferred since one can precisely control the rate of carbon monoxide production by controlling either the voltage or current to the electrochemical cell.

Examples of reactions that may occur on the working electrode of an electrochemical device include:

CO₂+2e−→CO+½O₂²⁻

CO₂+2H⁺+2e−→CO+H₂O

CO₂+H₂O+2e−→CO+2OH⁻

HCO₃⁻+H₂O+e−→CO+2OH⁻

HCO₃⁻+3H⁺+2e−→CO+2H₂O

where e− is an electron. The examples given above are merely illustrative and are not meant to be an exhaustive list of all possible reactions on the working electrode.

Key to the invention is the discovery of a catalyst mixture for the working electrode that produces at least 20 times more CO than hydrogen, and does not produce significant quantities of other impurities. The catalyst mixture may include components that enhance the rate of CO formation and/or decrease the rate of hydrogen formation. The catalyst mixture may include at least one Catalytically Active Element, and at least one Helper Catalyst and/or Hydrogen Suppressor. The Helper Catalyst can include, for example salts of choline, or choline derivatives or EMIM and its derivatives. When the Catalytically Active Element and the Helper Catalyst are combined, the rate and/or selectivity of a chemical reaction to produce CO can be enhanced over the rate seen in the absence of the Helper Catalyst. For example, the overpotential for electrochemical conversion of carbon dioxide to CO can be substantially reduced, and the current efficiency (namely, selectivity) for CO₂ conversion can be substantially increased.

In one aspect, the present invention includes an electrochemical cell with a fluid phase, the cell including a hydrogen evolution suppressor material. It is preferred that the hydrogen suppressor has a vapor pressure of less than 10⁻² ton so as to not substantially contaminate the product stream. The hydrogen evolution suppressor may include at least one positively charged nitrogen or phosphorus atom in its structure. The nitrogen could be, for example, part of a quaternary amine group or an imidizolium. The hydrogen suppressor molecules can also have at least one polar group selected from the group consisting of —OR, —COR, —COOR, —NR₂, —PR₂, —SR and X, where each R independently can be H or a linear, branched, or cyclic C₁-C₄ aliphatic group, and X is a halide, such as chlorine or fluorine. In particular, the polar group or groups can include at least one hydroxyl group and/or at least one halide atoms, but these molecules would preferably not contain a carboxylic acid group or be ionic salts of a carboxylic acid, since these can lead to acid byproducts. An example of such a hydrogen evolution suppressor molecule would be a salt including the choline cation, or a choline derivative of the form R₁R₂R₃N⁺(CH₂)_nOH or R₁R₂R₃N⁺(CH₂)_nCl, wherein n=1-4, and R₁, R₂, and R₃ are independently selected from the group consisting of aliphatic C₁-C₄ groups, —CH₂OH, —CH₂CH₂OH, —CH₂CH₂CH₂OH, —CH₂CHOHCH₃, —CH₂COH, —CH₂CH₂COH, and —CH₂COCH₃ and molecules where one or more chlorine or fluorine is substituted for hydrogen in aliphatic C₁-C₄ groups, —CH₂OH, —CH₂CH₂OH, —CH₂CH₂CH₂OH, —CH₂CHOHCH₃, —CH₂COH, —CH₂CH₂COH, or —CH₂COCH₃. The electrochemical cell can also include a Catalytically Active Element, which could be at least one of the following chemical elements: V, Cr, Mn, Fe, Co, Ni, Cu, Sn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Ir, Pt, Au, Hg, Al, Si, C, In, Sn, Tl, Pb, Bi, Sb, Te, U, Sm, Tb, La, Ce, Nd.

In another aspect, the present invention includes a method of suppressing hydrogen gas evolution from water that might be present in a system to create carbon monoxide on demand, the method including the steps of: (i) providing an electrochemical cell having a fluid phase and a negative electrode, (ii) providing in the fluid phase a hydrogen evolution suppressor as described above that includes a cation containing at least one positively charged nitrogen or phosphorus group and at least one polar group selected from the group consisting of —OR, —COR, —COOR, —NR₂, —PR₂, —SR and X, where each R independently can be H or a linear, branched, or cyclic C₁-C₄ aliphatic group, and X is a halide, and (iii) operating the electrochemical cell with the negative electrode at a potential that would cause hydrogen gas evolution from water that might be present in an electrochemical cell if the hydrogen evolution suppressor were not present. The electrochemical cell could be as described in the previous paragraph.

In yet another aspect, the present invention includes a carbon monoxide generator that includes an Active Element, Helper Catalyst Mixture, in which the addition of the Helper Catalyst improves the rate or yield of CO production, while simultaneously decreasing the rate or yield of the undesired side reactions. The undesired reaction may be the evolution of hydrogen gas or the creation of some poisonous impurity. The Helper Catalyst can include a cation containing at least one positively charged nitrogen or phosphorus group and at least one polar group selected from the group consisting of —OR, —COR, —COOR, —NR₂, —PR₂, —SR and X, where each R independently can be H or a linear, branched, or cyclic C₁-C₄ aliphatic group, —COOR is not a carboxylic acid, and X is a halide. For example, the cation could contain at least one quaternary amine group and at least one halide or hydroxyl group, but no carboxylic acid group or carboxylic acid salt. The quaternary amine cation can be, for example, choline cations, or choline cation derivatives of the form R₁R₂R₃N⁺(CH₂)_nOH or R₁R₂R₃N⁺(CH₂)_nCl, where n=1-4, and R₁, R₂, and R₃ are independently selected from the group that includes aliphatic C₁-C₄ groups, —CH₂OH, —CH₂CH₂OH, —CH₂CH₂CH₂OH —CH₂CHOHCH₃ , —CH₂COH, —CH₂CH₂COH, and —CH₂COCH₃ and molecules where one or more chlorine or fluorine is substituted for hydrogen in aliphatic C₁-C₄ groups, —CH₂OH, —CH₂CH₂OH, —CH₂CH₂CH₂OH, —CH₂CHOHCH₃, —CH₂COH, —CH₂CH₂COH, and —CH₂COCH₃

In still another aspect of the present invention, this application discloses a catalyst mixture having a Catalytically Active Element and a Helper Catalyst in which the Helper Catalyst also functions as a director molecule. The Helper Catalyst/director molecule would be a molecule containing at least one positively charged group and at least one group for surface attachment. The positively charged group can be, for example, a phosphonium group, or an amine group, such as a quaternary amine. The group for surface attachment can be, for example, a polar group selected from the group consisting of —OR, —COR, —COOR, —NR₂, —PR₂, —SR and X, where each R independently can be H or a linear, branched, or cyclic C₁-C₄ aliphatic group, —COOR is not a carboxylic acid, and X is a halide.

In still another aspect of the invention, this application discloses a carbon monoxide generator that includes a removable cartridge containing CO₂ or a chemical compound containing CO₂ such as a carbonate or bicarbonate, and a means to convert CO₂ to CO with hydrogen concentrations below 5% of the CO concentration, and less than 5 ppm of acetic acid or other impurities.

Finally the invention is not limited to the production of CO. A similar design with other reactants may be used as a generator for other therapeutic gases such as nitric oxide.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a typical electrochemical cell.

FIG. 2 is a schematic diagram of how the potential of the system changes as it proceeds along the reaction coordinate in the absence of the ionic liquid if the system goes through a (CO₂)⁻ intermediate. The reaction coordinate indicates the fraction of the reaction that has been completed. A high potential for (CO₂)⁻ formation can create a high overpotential for the reaction, which leads to enhanced hydrogen production.

FIG. 3 illustrates how the potential could change when a Helper Catalyst is used. In this case the reaction could go through a CO₂ complex rather than a (CO₂)⁻ intermediate, substantially lowering the overpotential for the reaction.

FIGS. 4a, 4b and 4c illustrate some of the cations that can be used to form a complex with (CO₂)⁻.

FIGS. 5a and 5b illustrate some of the anions that can help to stabilize the (CO₂)⁻ anion.

FIG. 6 illustrates some of the neutral molecules that can be used to form a complex with (CO₂)⁻.

FIG. 7 shows a schematic diagram of a cell used for the experiments in testing Catalytically Active Element, Helper Catalyst Mixtures, and in Specific Examples 1 and 4 to 7.

FIG. 8 represents a comparison of the cyclic voltammetry for (i) a blank scan where the catalyst was synthesized as in the described testing procedure for Catalytically Active Element, Helper Catalyst Mixtures, where the EMIM-BF4 was sparged with argon, and (ii) a scan where the EMIM-BF4 was sparged with CO₂. Notice the large negative peak associated with CO₂ complex formation.

FIG. 9 represents a series of Broad Band Sum Frequency Generation (BB-SFG) spectra taken sequentially as the potential in the cell was scanned from +0.0 V to −1.2 V with respect to the standard hydrogen electrode (SHE).

FIG. 10 shows a CO stripping experiment done by holding the potential at −0.6 V for 10 or 30 minutes and then measuring the size of the CO stripping peak between 1.2 and 1.5 V with respect to the reversible hydrogen electrode (RHE).

FIG. 11 Is a plot of the Faradaic efficiency of the process of forming the desired CO and the undesired hydrogen, and the turnover rate as a function of the applied cell potential for the cell in Specific Example 3.

FIG. 12 shows a comparison of the cyclic voltammetry for (i) a blank scan where the catalyst was synthesized as in Specific Example 4 where the water-choline chloride mixture was sparged with argon and (ii) a scan where the water-choline chloride mixture was sparged with CO₂.

FIG. 13 represents a comparison of the cyclic voltammetry for (i) a blank scan where the catalyst was synthesized as in Example 5 where the water-choline iodide mixture was sparged with argon and (ii) a scan where the water-choline iodide mixture was sparged with CO₂.

FIG. 14 shows a comparison of the cyclic voltammetry for (i) a blank scan where the catalyst was synthesized as in Example 6 where the water-choline chloride mixture was sparged with argon and (ii) a scan where the water-choline chloride mixture was sparged with CO₂.

FIGS. 15a and 15b each show a plot of cyclic voltammetry of palladium in the presence of different hydrogen suppressors. In each case the potential is reported versus the measured value of RHE.

FIGS. 16a and 16b each show a plot of cyclic voltammetry of platinum in the presence of different hydrogen suppressors. In each case the potential is reported versus the measured value of RHE.

FIGS. 17a and 17b each show a plot of cyclic voltammetry of platinum/ruthenium in the presence of different hydrogen suppressors. In each case the potential is reported versus the measured value of RHE.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT(S)

It is understood that the invention is not limited to the particular methodology, protocols, and reagents, etc., described herein, as these can vary as the skilled artisan will recognize It is also to be understood that the terminology used herein is used for the purpose of describing particular embodiments only, and is not intended to limit the scope of the invention. It also is to be noted that as used herein and in the appended claims, the singular forms “a”, “an”, and “the” include the plural reference unless the context clearly dictates otherwise. Thus, for example, a reference to “a linker” is a reference to one or more linkers and equivalents thereof known to those familiar with the technology involved here. Also, the term “and/or” is used to indicate one or both stated cases may occur, for example A and/or B includes (A and B) and (A or B).

Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art to which the invention pertains. The embodiments of the present invention and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments and/or illustrated in the accompanying drawings and detailed in the following description. It should be noted that the features illustrated in the drawings are not necessarily drawn to scale, and features of one embodiment can be employed with other embodiments as the skilled artisan would recognize, even if not explicitly stated herein.

Any numerical value ranges recited herein include all values from the lower value to the upper value in increments of one unit provided that there is a separation of at least two units between a lower value and a higher value. As an example, if it is stated that the concentration of a component or value of a process variable such as, for example, size, angle size, pressure, time and the like, is, for example, from 1 to 90, specifically from 20 to 80, more specifically from 30 to 70, it is intended that values such as 15 to 85, 22 to 68, 43 to 51, 30 to 32 etc., are expressly enumerated in this specification. For values which are less than one, one unit is considered to be 0.0001, 0.001, 0.01 or 0.1 as appropriate. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value are to be treated in a similar manner.

Moreover, provided immediately below is a “Definitions” section, where certain terms related to the present invention are defined specifically. Particular methods, devices, and materials are described, although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention. All references referred to herein are incorporated by reference herein in their entirety.

Definitions

The term “electrochemical conversion of CO₂” as used here refers to an electrochemical process where carbon dioxide, carbonate, or bicarbonate is converted into another chemical substance in a step of the process.

The term “CV” as used here refers to a cyclic voltammogram or cyclic voltammetry.

The term “Overpotential” as used here refers to the potential (voltage) difference between a reaction's thermodynamically determined reduction or oxidation potential and the potential at which the event is experimentally observed.

The term “Cathode Overpotential” as used here refers to the overpotential on the cathode of an electrochemical cell.

The term “Anode Overpotential” as used here refers to the overpotential on the anode of an electrochemical cell.

The term “Electron Conversion Efficiency” refers to selectivity of an electrochemical reaction. More precisely, it is defined as the fraction of the current that is supplied to the cell that goes to the production of a desired product.

The term “Catalytically Active Element” as used here refers to a chemical element that can serve as a catalyst for the electrochemical conversion of CO₂ or another species of interest in a desired reaction.

The term “Helper Catalyst” refers to an organic molecule or mixture of organic molecules that does at least one of the following: (a) speeds up a chemical reaction, or (b) lowers the overpotential of the reaction, without being substantially consumed in the process.

The term “Active Element, Helper Catalyst Mixture” refers to a mixture that includes one or more Catalytically Active Element(s) and at least one Helper Catalyst.

The term “Ionic Liquid” refers to salts or ionic compounds that form stable liquids at temperatures below 200 ° C.

The term “Deep Eutectic Solvent” refers to an ionic solvent that includes a mixture which forms a eutectic with a melting point lower than that of the individual components.

The term “Director Molecule” (or “Director Ion”) refers to a molecule or ion that increases the selectivity of a reaction. If a director molecule (or ion) is added to a reaction mixture, the selectivity for a desired reaction goes up. This effect may be the result of suppressing undesired side reactions, even if the desired reaction is also slowed, as long as the selectivity toward the desired reaction is increased.

The term “Hydrogen Suppressor” refers to a molecule that either: (a) decreases the rate of hydrogen formation, or (b) increases the overpotential for hydrogen formation, when the molecule is added to a reaction mixture.

The term “EMIM” refers to 1-ethyl-3-methylimidazolium.

The term “Carbon Dioxide Source” refers to a device or molecule that can provide carbon dioxide to a system. The source may be in the form of a bottle, packet, cartridge or other form. The Carbon Dioxide Source may include gaseous, liquid, solid or supercritical carbon dioxide, and chemical compounds that can be easily converted to carbon dioxide such as carbonates and bicarbonates.

The term “Pure Enough To Be Used In A Clinical Application” refers to a gas mixture that a) includes carbon monoxide, b) has at least 10 times as much carbon monoxide as hydrogen on a molar basis and c) has less than 1 ppm of any corrosive or toxic material other than carbon monoxide.

Specific Description

The earlier related applications U.S. Ser. No. 12/830,338, U.S. Ser. No. 13/174365, PCT/US11/42809, PCT/US11/30098 and provisional patent application U.S. 61/499,225 by Masel et al. described Active Element, Helper Catalyst Mixtures where the mixture does at least one of the following: (1) speeds up a chemical reaction; or (2) lowers the overpotential of the reaction, without being substantially consumed in the process.

For example, such mixtures can lower the overpotential for CO₂ conversion to a value less than the overpotential seen when the same Catalytically Active Element is used without the Helper Catalyst.

In the course of exploring these Active Element, Helper Catalyst Mixtures, it was found that certain materials that were being tested as Helper Catalysts, such as salts of the choline cation (N,N,N-trimethylethanolammonium cation) and/or 1-ethyl-3-methylimidazolium tetrafluoroborate could also raise the overpotential for certain undesirable side reactions, including the evolution of hydrogen gas from electrolysis of water and the formation of side products such as acetic acid. As part of this effort, we found that it was possible to produce carbon monoxide electrochemically with purity to meet the needs for a therapeutic carbon monoxide generator i.e. 20 times as much carbon monoxide as hydrogen, and less than 1 ppm of other byproducts. Further, one could precisely control the CO delivery rate by controlling the current or voltage applied to the electrochemical cell.

Without wishing to be bound by theory, the present disclosure provides data supporting the hypothesis that when a monolayer of an organic compound is adsorbed on a metal surface, the presence of the organic compound can change the binding energy of key intermediates of reactions occurring on (or near) the metal surface. This can lead to changes in reaction rates. For example, data herein suggests that the adsorption of a cationic species such as a quaternary amine on an electrode (typically the negative electrode) of an electrochemical cell tends to stabilize anionic intermediates and destabilize cationic intermediates in electrochemical reactions. If the amine binds too strongly, it will simply poison the surface, but if the binding strength is modest, rate enhancement is possible. Aliphatic quaternary amines would tend to be merely electrostatically attracted to a metal electrode surface, since the positively charged nitrogen is sterically shielded by the aliphatic groups and cannot interact directly with the metal surface. For the same reason, quaternary ammonium cations tend to be electrochemically stable across a wide window of electrode potentials. Choline salts in particular are commercially attractive quaternary amines, because choline chloride is a common food additive for livestock, and it is also sold as a dietary supplement for humans. It is inexpensive, is readily available, and presents minimal hazard. One could reasonably expect that quaternary amine cations with structures similar to choline (for example, structures in which one or more of the methyl groups on the nitrogen is replaced with other small aliphatic groups such as ethyl or propyl groups) would behave in a fashion similar to the choline data disclosed in the present application.

Ionic liquids such as 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM-BF4) could also be used. Imidazoliums would tend to be merely electrostatically attracted to a metal electrode surface, since the positively charged nitrogen is sterically shielded by the aliphatic groups and cannot interact directly with the metal surface. They have very low vapor pressures due to their ionic nature, so they could be used in systems for inhalation therapy.

According to the Hori review, Gattrell, et al. (Journal of Electroanalytical Chemistry, 594, 1-19, 2006), DuBois (Encyclopedia of Electrochemistry, 7a, 202-225, 2006) and references therein, catalysts including one or more of In, Sn, Cd, Zn, Au, Ag, Cu V, Cr, Mn, Fe, Co, Ni, Cu, Sn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Ir, Pt, Au, Hg, Al, Si, In, Sn, Tl, Pb, Bi, Sb, Te, U, Sm, Tb, La, Ce, and Nd all show activity for CO₂ conversion. Hori reports that only Au, Ag, Cu, Zn, Pd, In, Sn and Ga produce significant amounts of CO, but the data disclosed in the specific examples in this patent shows that in the presence of an appropriate helper catalyst, CO is produced on additional metals. Therefore, V, Cr, Mn, Fe, Co, Ni, Cu, Sn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Ir, Pt, Au, Hg, Al, Si, In, Sn, Tl, Pb, Bi, Sb, Te, U, Sm, Tb, La, Ce, and Nd are each examples of Catalytically Active Elements, but the present invention is not limited to this list of chemical elements.

FIGS. 2 and 3 illustrate one possible mechanism by which a Helper Catalyst can enhance the rate of CO₂ conversion to CO. According to Chandrasekaran, et al. (Surface Science, 185, 495-514, 1987) the high overpotentials for CO₂ conversion occur because the first step in the electroreduction of CO₂ is the formation of a (CO₂)⁻ intermediate. It takes energy to form the intermediate as illustrated in FIG. 2. This results in a high overpotential for the reaction.

FIG. 3 illustrates what might happen if a solution containing 1-ethyl-3-methylimidazolium cations (EMIM⁺) is added to the mixture. EMIM⁺ might be able to form a complex with the (CO₂)⁻ intermediate. In that case, the reaction could proceed via the EMIM⁺-(CO₂)⁻ complex instead of going through a bare (CO₂)⁻ intermediate as illustrated in FIG. 3. If the energy to form the EMIM⁺-(CO₂)⁻ complex is less than the energy to form the (CO₂)⁻ intermediate, the overpotential for CO₂ conversion could be substantially reduced. Therefore a substance that includes EMIM⁺ cations could act as a Helper Catalyst for CO₂ conversion.

In most cases, solvents only have small effects on the progress of catalytic reactions. The interaction between a solvent and an adsorbate is usually much weaker than the interaction with a Catalytically Active Element, so the solvent only makes a small perturbation to the chemistry occurring on metal surfaces. However, the diagram in FIG. 3 shows that such an effect could be large.

Of course a Helper catalyst, alone, will be insufficient to convert CO₂ to CO. Instead, one still needs a Catalytically Active Element that can catalyze reactions of (CO₂)⁻ in order to get high rates of CO₂ conversion. Catalysts including at least one of the following Catalytically Active Elements have been previously reported to be active for electrochemical conversion of CO₂: V, Cr, Mn, Fe, Co, Ni, Cu, Sn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Ir, Pt, Au, Hg, Al, Si, In, Sn, Tl, Pb, Bi, Sb, Te, U, Sm, Tb, La, Ce, and Nd.

Many of these catalysts also show activity for a number of other reactions. All of the above elements are specifically included as Catalytically Active Elements for the purposes of the present invention. This list of elements is meant for illustrative purposes only, and is not meant to limit the scope of the present invention.

Further, those skilled in the technology involved here should realize that the diagram in FIG. 3 could be drawn for any molecule that could form a complex with (CO₂)⁻. Previous literature indicates that solutions including one or more of: ionic liquids; deep eutectic solvents; and amines and phosphines, including specifically imidazoliums (also called imidazoniums), pyridiniums, pyrrolidiniums, phosphoniums, ammoniums, prolinates, and methioninates, as well as sulfoniums, can form complexes with CO₂. Consequently, they can serve as Helper Catalysts. Also Davis Jr., et al. (in ACS Symposium Series 856: Ionic Liquids as Green Solvents: Progress and Prospects, 100-107, 2003) list a number of other salts that show ionic properties. Specific examples include compounds including one or more of acetylcholines, alanines, aminoacetonitriles, methylammoniums, arginines, aspartic acids, threonines, chloroformamidiniums, thiouroniums, quinoliniums, pyrrolidinols, serinols, benzamidines, sulfamates, acetates, carbamates, triflates, alkali cations and cyanides. These salts can act as Helper Catalysts. These examples are meant for illustrative purposes only, and are not meant to limit the scope of the present invention.

Of course, not every substance that forms a complex with (CO₂)⁻ will act as a Helper Catalyst. Masel (Chemical Kinetics and Catalysis, Wiley, pages 717-720, 2001,) notes that when an intermediate binds to a catalyst, the reactivity of the intermediate decreases. If the intermediate bonds too strongly to the catalyst, the intermediate will become unreactive, so the substance will not be effective. This provides a key limitation on substances that act as Helper Catalysts. The Helper Catalyst cannot form so strong a bond with the (CO₂)⁻ that the (CO₂)⁻ is unreactive toward the Catalytically Active Element or forms an undesired stable reaction product with the material that was intended to be a Helper Catalyst.

More specifically, one wishes the substance to form a complex with the (CO₂)⁻ so that the complex is stable (that is, has a negative free energy of formation) at potentials less negative than −1 V with respect to the standard hydrogen electrode (SHE). However, the complex should not be so stable that the free energy of the reaction between the complex and the Catalytically Active Element is more positive than about 3 kcal/mol.

Those familiar with the technology involved here should realize that the ability of the Helper Catalyst to stabilize the (CO₂)⁻ also varies with the anion. For example Zhao, et al. (The Journal of Supercritical Fluids, 32, 287-291, 2004) examined CO₂ conversion in 1-n-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF6), but FIG. 3 in Zhao, et al., shows that the BMIM-PF6 did NOT lower the overpotential for the reaction (that is, the BMIM-PF6 did not act as a Helper Catalyst). This may be because the BMIM-PF6 formed such a strong bond to the (CO₂)⁻ that the CO₂ was unreactive with the copper. Similarly Yuan, et al., Electrochimica Acta 54, pages 2912-2915(2009), examined the reaction between methanol and CO₂ in 1-butyl-3-methylimidazolium bromide (BMIM-Br). The BMIM-Br did not act as a Helper Catalyst. This may be because the complex was too weak or that the bromine poisoned the reaction.

Solutions that include one or more of the cations in FIGS. 4a, 4b and 4c, the anions in FIGS. 5a and 5b, and/or the neutral species in FIG. 6, where R₁, R₂ and R₃ (and R₄-R₁₇) include H, OH or a ligand containing at least one carbon atom, are believed to form complexes with CO₂ or (CO₂)⁻. Specific examples include: imidazoliums (also called imidazoniums), pyridiniums, pyrrolidiniums, phosphoniums, ammoniums, sulfoniums, prolinates, and methioninates. All of these examples might be able to be used as Helper Catalysts for CO₂ conversion, and are specifically included in the present invention. These examples are meant for illustrative purposes only, and are not meant to limit the scope of the present invention.

In general one can determine whether a given substance S is a Helper Catalyst for a reaction R catalyzed by an active metal M as follows:

(a) Fill a standard 3-electrode electrochemical cell with the electrolyte commonly used for reaction R. Common electrolytes such as 0.1 M sulfuric acid or 0.1 M KOH in water can also be used.

(b) Mount the active metal into the 3 electrode electrochemical cell and provide an appropriate counter electrode.

(c) Run several CV cycles to clean the active metal.

(d) Measure the reversible hydrogen electrode (RHE) potential in the electrolyte.

(e) Load the reactants for the reaction R into the cell, and measure a CV of the reaction R, noting the potential of the peak associated with the reaction R.

(f) Calculate V1=the difference between the onset potential of the peak associated with reaction and RHE.

(g) Calculate V1A=the difference between the maximum potential of the peak associated with reaction and RHE.

(h) Add 0.0001 to 99.9999% of the substance S to the electrolyte.

(i) Measure RHE in the reaction solution with Helper Catalyst.

(j) Measure the CV of reaction R again, noting the potential of the peak associated with the reaction R.

(k) Calculate V2=the difference between the onset potential of the peak associated with reaction and RHE.

(1) Calculate V2A=the difference between the maximum potential of the peak associated with reaction and RHE.

If V2<V1 or V2A<V1A at any concentration of the substance S between 0.0001 and 99.9999%, the substance S is a Helper Catalyst for the reaction.

Further, the Helper Catalyst could be in any one of the following forms: (i) a solvent for the reaction; (ii) an electrolyte; (iii) an additive to a component of the system; or (iv) something that is bound to at least one of the catalysts in a system. These examples are meant for illustrative purposes only, and are not meant to limit the scope of the present invention.

Those familiar with the technology involved here should recognize that one might only need a tiny amount of the Helper Catalyst to have a significant effect. Catalytic reactions often occur on distinct active sites. The active site concentration can be very low, so in principle a small amount of Helper Catalyst can have a significant effect on the rate. One can obtain an estimate of how little of the helper catalyst would be needed to change the reaction from the Pease, et al., JACS 47, 1235 (1925) study of the effect of carbon monoxide (CO) on the rate of ethylene hydrogenation on copper. This paper is incorporated into this disclosure by reference. Pease, et al., found that 0.05 cc (62 micrograms) of carbon monoxide (CO) was sufficient to almost completely poison a 100 gram catalyst towards ethylene hydrogenation. This corresponds to a poison concentration of 0.0000062% by weight of CO in the catalyst. Those familiar with the technology involved here know that if 0.0000062% by weight of the poison in a Catalytically Active Element-poison mixture could effectively suppress a reaction, then as little as 0.0000062% by weight of Helper Catalyst in an Active Element, Helper Catalyst Mixture could enhance a reaction. This provides an estimate of a lower limit to the Helper Catalyst concentration in an Active Element, Helper Catalyst Mixture.

The upper limit is illustrated in Example 1 below, where the Active Element, Helper Catalyst Mixture could have approximately 99.999% by weight of Helper Catalyst, and the Helper Catalyst could be at least an order of magnitude more concentrated. Thus, the range of Helper Catalyst concentrations for the present invention can be 0.0000062% to 99.9999% by weight.

Further, the Helper Catalyst could enhance the rate of a reaction even if it does not form a complex with a key intermediate. Examples of possible mechanisms of action include the Helper Catalyst (i) lowering the energy to form a key intermediate by any means, (ii) donating or accepting electrons or atoms or ligands, (iii) weakening bonds or otherwise making them easier to break, (iv) stabilizing excited states, (v) stabilizing transition states, (vi) holding the reactants in close proximity or in the right configuration to react, or (vii) blocking side reactions. Each of these mechanisms is described on pages 707-742 of Masel, Chemical Kinetics and Catalysis, Wiley, NY (2001). All of these modes of action are within the scope of the present invention.

Also, the invention is not limited to just the catalyst. Instead it includes a process or device that uses an Active Element, Helper Catalyst Mixture as a catalyst. Electrolytic cells and other devices to produce CO that include Helper Catalysts or Hydrogen Suppressors are specifically included in the present invention.

In particular it includes a device that includes an electrochemical device for the production of CO that includes an Active Element and either a Helper Catalyst and/or a Hydrogen Suppressor and a means to deliver the CO to a patient. The device may include a means to supply CO₂ to the device. It may also include a CO sensor that allows the CO concentration to be accurately controlled.

A specific design is an inline cartridge that would be mounted between the oxygen source and the patient. The cartridge would contain a source of CO₂ such as a carbonate or bicarbonate, an electrochemical cell including an Active Element and either a Helper Catalyst and/or a Hydrogen Suppressor, and a CO sensor. It might include a battery and control system.

Without further elaboration, it is believed that one skilled in the art using the preceding description can utilize the present invention to the fullest extent. The following examples are illustrative only, and not limiting of the disclosure in any way whatsoever. These are merely illustrative and are not meant to be an exhaustive list of all possible embodiments, applications or modifications of the present invention.

SPECIFIC EXAMPLE 1

The following section describes the testing procedure used for an Active Element, Helper Catalyst Mixture as previously disclosed in the related applications cited above. These particular experiments measured the ability of an Active Element, Helper Catalyst Mixture consisting of platinum and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM-BF4) to lower the overpotential for electrochemical conversion of CO₂ to CO and raise the selectivity (current efficiency) of the reaction. Therefore, the test can determine whether EMIM-BF4 and the EMIM⁺ ion can serve as director molecules and director ions, respectively, for the desired reaction. The desired reaction in this test will be the electrochemical reduction of carbon dioxide (typically to primary products such as CO).

The experiments used the glass three electrode cell shown in FIG. 7. The cell consisted of a three neck flask 101, to hold the anode 108, and the cathode 109. Seal 107 forms a seal around anode wire 108. Fitting 106 compresses seal 107 around anode wire 108. Rotary seal 110 facilitates rotation of shaft 111, which in turn causes gold plug 115 to spin. Seal 119 closes the unused third neck of flask 101.

A silver/0.01 molar silver ion reference electrode 103 in acetonitrile was connected to the cell through a Luggin Capillary 102, which includes a seal 117. The reference electrode 103 was fitted with a porous Vycor glass frit (available from Corning, Inc., Corning, N.Y., USA) to prevent the reference electrode solution from contaminating the ionic liquid in the capillary. The reference electrode was calibrated against the ferrocene Fc/Fc+ redox couple. A conversion factor of +535 was used to convert our potential axis to reference the Standard Hydrogen Electrode (SHE). A 25×25 mm platinum gauze 113 (size 52) was connected to the anode while a 0.33 cm² polycrystalline gold plug 115 was connected to the cathode.

Prior to the experiments all glass parts were put through a 1% Nochromix bath (2hrs) (available from Godax Laboratories, Inc., Cabin John, Md., USA), followed by a 50/50 v/v nitric acid/water bath (12 hrs), followed by rinsing with Millipore filtered water (Millipore Corporation, Billerica, Mass., USA). In addition, the gold plug 115 and platinum gauze 113 were mechanically polished using procedures known to workers trained in the technology involved here. The glass parts were then cleaned in a sulfuric acid bath for 12 hours.

During the experiment a catalyst ink comprising a Catalytically Active Element, platinum, was first prepared as follows: First 0.056 grams of Johnson-Matthey Hispec 1000 platinum black purchased from Alfa-Aesar was mixed with 1 gram of Millipore water and sonicated for 10 minutes to produce a solution containing a 5.6 mg/ml suspension of platinum black in Millipore water. A 25 μl drop of the ink was placed on the gold plug 115 and allowed to dry under a heat lamp for 20 min, and subsequently allowed to dry in air for an additional hour. This yielded a catalyst with 0.00014 grams of Catalytically Active Element, platinum, on a gold plug. The gold plug was mounted into the three neck flask 101. Next a Helper Catalyst, EMIM-BF4 (EMD Chemicals, Inc., San Diego, Calif., USA) was heated to 120° C. under a −23 in. Hg vacuum for 12 hours to remove residual water and oxygen. The concentration of water in the ionic liquid after this procedure was found to be approximately 90 mM by conducting a Karl-Fischer titration. (That is, the ionic liquid contained 99.9999% of Helper Catalyst.) 13 grams of the EMIM-BF4 was added to the vessel, creating an Active Element, Helper Catalyst Mixture that contained about 99.999% of the Helper Catalyst. The geometry was such that the gold plug formed a meniscus with the EMIM-BF4. Next, ultra-high-purity (UHP) argon was fed through the sparging tube 104 and glass frit 112 for 2 hours at 200 sccm to further remove any moisture picked up by contact with the air. Connector 105 was used to attach the cell to a tube leading to the gas source.

Next, the cathode was connected to the working electrode connection in an SI 1287 Solartron electrical interface (Solartron Analytical, Schaumburg, Ill., USA), the anode was connected to the counter electrode connection and the reference electrode was connected to the reference electrode connection on the Solartron. Then the potential on the cathode was swept from −1.5 V versus a standard hydrogen electrode (SHE) to 1 V vs. SHE, and then back to −1.5 volts versus SHE thirty times at a scan rate of 50 mV/s. The current produced during the last scan is labeled as the “argon” scan in FIG. 8.

Next carbon dioxide was bubbled through the sparging tube at 200 sccm for 30 minutes, and the same scanning technique was used. That produced the CO₂ scan in FIG. 8. Notice the peak starting at −0.2 volts with respect to SHE, and reaching a maximum at −0.4 V with respect to SHE. That peak is associated with CO₂ conversion.

The applicants have also used broad-band sum frequency generation (BB-SFG) spectroscopy to look for products of the reaction, as shown in FIG. 9. Only the desired product carbon monoxide was detected in the voltage range shown (namely, the selectivity is about 100%). Oxalic acid was detected at higher potentials.

Table 1 compares these results to results from the previous literature. The table shows the actual cathode potential. More negative cathode potentials correspond to higher overpotentials. More precisely, the overpotential is the difference between the thermodynamic potential for the reaction (about −0.2 V with respect to SHE) and the actual cathode potential. The values of the cathode overpotential are also given in the table. Notice that the addition of the Helper Catalyst has reduced the cathode overpotential (namely, lost work) on platinum by a factor of 4.5 and improved the selectivity from near zero to nearly 100%.

TABLE 1
(Comparison of data in this test to results
reported in previous literature)
		Cathode		Selectivity to
	Catalytically	potential	Cathode	Carbon
Reference	Active Element	versus SHE	overpotential	Monoxide
Data from	Platinum	−0.4 V	0.2 V	~100%
this test	(+EMIM-BF4)
Hori review	Platinum	−1.07 V	0.87 V	0.1%
Table 3	(+water)

TABLE 2
(Cathode potentials where CO2 conversion starts on a number of
Catalytically Active Elements as reported in the Hori review).
	Cathode		Cathode		Cathode
	potential		potential		potential
Metal	(SHE)	Metal	(SHE)	Metal	(SHE)
Pb	−1.63	Hg	−1.51	Tl	−1.60
In	−1.55	Sn	−1.48	Cd	−1.63
Bi	−1.56	Au	−1.14	Ag	−1.37
Zn	−1.54	Pd	−1.20	Ga	−1.24
Cu	−1.44	Ni	−1.48	Fe	−0.91
Pt	−1.07	Ti	−1.60

Table 2 indicates the cathode potential needed to convert CO₂. Notice that all of the values are more negative than −0.9 V. By comparison, FIG. 8 shows that CO₂ conversion starts at −0.2 V with respect to the reversible hydrogen electrode (RHE), when the Active Element, Helper Catalyst Mixture is used as a catalyst. More negative cathode potentials correspond to higher overpotentials. This is further confirmation that Active Element, Helper Catalyst Mixtures are advantageous for CO₂ conversion.

FIG. 9 shows a series of broad band sum-frequency generation (BB-SFG) spectra taken during the reaction. Notice the peak at 2350 cm⁻¹. This peak corresponded to the formation of a stable complex between the Helper Catalyst and (CO₂)⁻. It is significant that the peak starts at −0.1 V with respect to SHE. According to the Hori review, (CO₂)⁻ is thermodynamically unstable unless the potential is more negative than −1.2 V with respect to SHE on platinum. Yet FIG. 9 shows that the complex between EMIM-BF4 and (CO₂)⁻ is stable at −0.1 V with respect to SHE.

Those familiar with the technology involved here should recognize that this result is very significant. According to the Hori review, the Dubois review and references therein, the formation of (CO₂)⁻ is the rate determining step in CO₂ conversion to products on V, Cr, Mn, Fe, Co, Ni, Cu, Sn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Ir, Pt, Au, Hg, Al, Si, In, Sn, Tl, Pb, Bi, Sb, Te, U, Sm, Tb, La, Ce, and Nd. The (CO₂)⁻ is thermodynamically unstable at low potentials, which leads to a high overpotential for the reaction as indicated in FIG. 2. The data in FIG. 9 shows that one can form the EMIM-BF4-(CO₂)⁻ complex at low potentials. Thus, the reaction can follow a low energy pathway for CO₂ conversion to CO as indicated in FIG. 3.

The Effect of Dilution on the Electrochemical Conversion of CO₂

This experiment shows that water additions speed the formation of CO in the previous reaction. The experiment used the cell and procedures described above, with the following exception: a solution containing 98.55% EMIM-BF4 and 0.45% water was substituted for the 99.9999% EMIM-BF4 used in the experiment above, the potential was held for 10 or 30 minutes at −0.6 V with respect to RHE, and then the potential was ramped positively at 50 mV/sec. FIG. 10 shows the result. Notice the peak between 1.2 and 1.5 V. This is the peak associated with CO formation and is much larger than in the first experiment above. Thus the addition of water has accelerated the formation of CO. Notice also that there is no hydrogen peak in the spectrum. This result shows that EMIM-BF4 can be used as a Hydrogen Suppressor.

SPECIFIC EXAMPLE 2

Steady State Production of Carbon Monoxide

This experiment used the flow cell described in Devin T. Whipple, E. C. Finke, and P. J. A. Kenis, Electrochem. & Solid-State Lett., 2010, 13 (9), B109-B111 (“the Whipple paper”). First, catalyst inks were prepared as follows:

For the cathode: 10 mg of silver nanoparticles (Sigma Aldrich) was sonicated into a solution containing 100 μL of water, 100 μL of isopropyl alcohol and 5.6 μL of 5% perfluorosulfonic acid solution (available under the trade designation Nafion, from Ion Power, Inc., New Castle, Del., USA). The resultant catalyst ink was painted on a 1×1.5 cm section of a 2×3 cm piece of carbon paper (Ion Power, Inc.) and dried with a heat lamp.

The preparation was identical for anode except 4 mg of HiSpec 1000 platinum black (Sigma Adrich) was substituted for the silver.

Both catalysts were mounted in the flow cell described in the Whipple Paper. Five sccm of CO₂ was fed to the anode, and a solution containing 18 mole percent of EMIM-BF4 in water was fed into the gap between the anode and the cathode. At any one time the cell contained approximately 10 mg of silver nanoparticles and approximately 40 mg of EMIM-BF4 Helper Catalyst. A potential was applied to the cell, and the data in Table 3 were measured with a gas chromatograph. Notice that at higher potentials one is able to produce about 0.5 mg/min of CO, without significant hydrogen or other by products. Further, notice that one can precisely control the CO production rate by carefully adjusting the voltage (or applied current). This has the key advantage.

These results demonstrate that steady state production of useful products can be obtained with Catalytically Active Element-Helper Catalyst Mixtures. It is believed that choline salts or other Helper Catalysts that suppress hydrogen evolution could be readily substituted for the Helper Catalyst EMIM-BF4.

TABLE 3
(Products produced at various conditions)
	Hydrogen	Carbon monoxide
Cathode potential	production rate,	production rate,
Volts vs. RHE	μg/min	μg/min	CO/H2 ratio
−0.358	0	0
−0.862	1.1	2.6	2.4
−1.098	1.4	50	35
−1.434	1.1	250	230
−1.788	0	560	>1000

SPECIFIC EXAMPLE 3

High Quality Carbon Monoxide Production Over a Wide Range of Rates

Example 2 showed that CO could be produced at high rates and selectivities, but when the voltage was decreased, so the rate decreased, the CO₂ to hydrogen ratio was less than 20. This could create a problem in clinical systems where there is a need to produce carbon monoxide over a wide range of rates. This example describes a modified design that allows one to produce pure carbon monoxide over a wider range of conditions.

The apparatus and procedures were the same as in Specific Example 2, except that a Nafion 117 membrane (available from Ion Power, Inc.) was inserted between the cathode and the anode to create separate anode and cathode compartments. The anode compartment contained 100 mM aqueous sulfuric acid flowing at 0.5 ml/min. The cathode compartment contained 18 mol % EMIM-BF₄ in water at 0.5 ml/min. A potential was applied to the cell, and the data in FIG. 11 were measured with a gas chromatograph. Experimentally, only hydrogen, CO and CO₂ were detected at the cathode and only O₂ was detected at the anode. In all cases there was more than 20 times as much CO as H₂ and no other reaction products were detected with the gas chromatograph. This result shows that it is possible to create carbon monoxide electrochemically with enough purity to be used in clinical applications.

SPECIFIC EXAMPLE 4

Use of an Active Element, Helper Catalyst Mixture That Includes Nickel and Choline Chloride to Lower the Overpotential for Electrochemical Conversion of CO₂ to CO and Suppress Hydrogen Formation

This example is to demonstrate that the present invention can be practiced using a second metal, namely, nickel and a second helper catalyst, choline chloride.

The experiment used the cell and procedures described in Specific Example 1 above, with the following exceptions: i) a 10.3% by weight of a Helper Catalyst, choline iodide, in water solution was substituted for the 1-ethyl-3-methylimidazolium tetrafluoroborate and ii) a 0.25 cm² Ni foil purchased from Alfa Aesar of Ward Hill, Mass., USA, was substituted for the gold plug and platinum black on the cathode, and a silver/silver chloride reference was used.

The cell contained 52 mg of nickel and 103 mg of helper catalyst, so the overall catalyst mixture contained 66% of helper catalyst.

FIG. 12 shows a comparison of the cyclic voltammetry for i) a blank scan where the water-choline chloride mixture was sparged with argon and ii) a scan where the water-choline chloride mixture was sparged with CO₂. Notice the negative going peaks starting at about −0.6. This shows that CO₂ is being reduced at −0.6 V. By comparison, the data in Table 2 indicates that a voltage more negative than −1.48 V is needed to convert CO₂ on nickel in the absence of the Helper Catalyst. Thus, the Helper Catalyst has lowered the overpotential for CO₂ conversion.

Another important point is that there is no strong peak for hydrogen formation. A bare nickel catalyst would produce a large hydrogen peak at about −-0.4 V at a pH of 7, while the hydrogen peak moves to −1.2 V in the presence of the Helper Catalyst. The Hori review reports that nickel is not an effective catalyst for CO₂ reduction because the side reaction producing hydrogen is too large. The data in FIG. 12 show that the Helper Catalysts are effective in suppressing hydrogen formation.

Also the Helper Catalyst is very effective in improving the selectivity of the reaction. The Hori review reports that hydrogen is the major product during carbon dioxide reduction on nickel in aqueous solutions. The reported hydrolysis data shows 1.4% selectivity to formic acid, and no selectivity to carbon monoxide. By comparison, analysis of the reaction products in this example by CV indicated that carbon monoxide was the major product during CO₂ conversion on nickel in the presence of the Helper Catalyst. There may have been some formate formation. However, no hydrogen was detected. This example shows that the Helper Catalyst had tremendously enhanced the selectivity of the reaction toward CO.

This example also demonstrates that the present invention can be practiced with a second metal, nickel, and a second helper catalyst, choline chloride. Further, those familiar with the technology involved here will note that there is nothing special about the Active Element, Helper Catalyst pair of nickel and choline chloride.

Those familiar with the technology involved here should realize that since choline chloride and choline iodide (in Specific Example 5 below) are active, other choline salts such as choline bromide, choline fluoride and choline acetate should be active as well.

PREDICTIVE EXAMPLES OF DIRECTOR MOLECULES AND DIRECTOR IONS

The applicants believe that to serve as a director molecule (or ion) for purposes such as suppressing hydrogen evolution in an electrochemical cell, the chemical species should have at least one positively charged group and at least one group for surface attachment (for example, for attachment to the negative electrode). In other words, what is needed is a positively charged species with something to hold the positive charge near the surface, but not to bind so strongly that the surface is poisoned. A number of alcohols, aldehydes, ketones, and carboxylic acids should work, although some carboxylic acids might bind too tightly to the electrode surface, and may thus poison the desired reaction. Similarly, other polar groups in addition to —OR, —COR, and —COOR, such as —NR₂, —PR₂, —SR and halides, where the R groups can independently be hydrogen or ligands containing carbon, (with the possible exception of carboxylic acid groups and their salts,) could serve as satisfactory surface attachment groups. For the positively charged group, a variety of amines and phosphoniums should be satisfactory. The key is to add an attached group to bind them to the surface, and the positive group(s) should not be so large as to be hydrophobic. Methyl, ethyl and propyl quaternary amines should perform well. Imidazoliums (sometimes also called imidazoniums) should also be satisfactory, provided they contain an attachment group. Potassium and cesium cations could also work, since potassium and cesium can attach to the surface under certain conditions. A significant aspect of the present invention is the identification of molecules or ions that can serve as both Helper Catalysts (accelerating or lowering the overpotential for desired reactions) and director molecules (increasing the selectivity toward the desired reaction, for example, by poisoning undesired reactions more than the desired reaction).

COMPARATIVE EXAMPLE 1

Use of an Active Element, Helper Catalyst Mixture Including Palladium and Choline Iodide to Lower the Overpotential for Electrochemical Conversion of CO₂ in Water and Suppress Hydrogen Formation

This example is to demonstrate that hydrogen can be suppressed using palladium as an active element and choline iodide as a Helper Catalyst, but formic acid formation occurs.

The experiment used the cell and procedures described in Specific Example 1, with the following exceptions: i) a 10.3% by weight of a Helper Catalyst, choline iodide, in water solution was substituted for the 1-ethyl-3-methylimidazolium tetrafluoroborate and ii) a 0.25 cm² Pd foil purchased from Alfa Aesar of Ward Hill, Mass., USA, was substituted for the gold plug and platinum black on the cathode, and a silver/silver chloride reference was used.

The cell contained 52 mg of palladium and 103 mg of helper catalyst, so the overall catalyst mixture contained 66% of helper catalyst.

FIG. 13 shows a CV taken under these conditions. There is a large negative peak near zero volts with respect to SHE associated with iodine transformations and a negative going peak at about −0.8 V associated with conversion of CO₂. By comparison the data in Table 2 indicates that one needs to use a voltage more negative than −1.2 V to convert CO₂ on palladium in the absence of the Helper Catalyst. Thus, the Helper Catalyst has lowered the overpotential for CO₂ formation by about 0.5 V.

Unfortunately, analysis of the products of the reaction showed that a significant amount of formic acid was formed. Therefore, this catalyst system would not be preferred for generation of carbon monoxide.

COMPARATIVE EXAMPLE 2

Use of an Active Element, Helper Catalyst Mixture That Includes Palladium and Choline Chloride to Suppress Hydrogen Formation

This example is to demonstrate that hydrogen can be suppressed using palladium as an active element and choline chloride as a Helper Catalyst, but formic acid formation occurs.

The experiment used the cell and procedures in Counter Example 1, with the following exception: a 6.5% by weight choline chloride in water solution was substituted for the choline iodide solution.

The cell contained 52 mg of palladium and 65 mg of Helper Catalyst, so the overall catalyst mixture contained 56% of Helper Catalyst. FIG. 14 shows a comparison of the cyclic voltammetry for (i) a blank scan where the water-choline chloride mixture was sparged with argon and (ii) a scan where the water-choline chloride mixture was sparged with CO₂. Notice the negative going peaks starting at about -0.6. This shows that CO₂ is being reduced at −0.6 V. By comparison the data in Table 2 indicates that a voltage more negative than −1.2 V is needed to convert CO₂ on palladium in the absence of the Helper Catalyst. Thus, the overpotential for CO₂ conversion has been lowered by 0.6 V by the Helper Catalyst.

Another important point is that there is no strong peak for hydrogen formation. A bare palladium catalyst would produce a large hydrogen peak at about −0.4 V at a pH of 7, while the hydrogen peak moves to −1.2 V in the presence of the Helper Catalyst. The Hori review reports that palladium is not an effective catalyst for CO₂ reduction because the side reaction producing hydrogen is too large. The data in FIG. 12 show that the Helper Catalysts are effective in suppressing hydrogen formation. The same effect can be observed in FIG. 13 for the choline iodide solution on palladium in Comparative Example 1

Cyclic voltammetry was also used to analyze the reaction products. Formic acid was the only product detected. By comparison, the Hori review reports that the reaction is only 2.8% selective to formic acid in water. Thus the Helper Catalyst has substantially improved the selectivity of the reaction to formic acid. Unfortunately, formic acid is not preferred for therapeutic applications.

SPECIFIC EXAMPLE 5

(Demonstration of Hydrogen Suppression With Other Choline Derivatives)

The experiments were the same as in Specific Example 4, except that one of (a) choline acetate, (b) choline BF4, (c) (3-chloro-2-hydroxypropyl)trimethyl ammonium chloride, (d) butyrylcholine chloride, and (e) (2-chloroethyl)trimethylammonium chloride were used instead of choline chloride (which is also shown here for comparison.) FIGS. 15a, 15b, 16a, 16b, 17a and 17b show CVs taken as described in Specific Example 1 on platinum, palladium and platinum/ruthenium catalysts. Note that these CVs are plotted vs. RHE, rather than vs. SHE as in FIGS. 8, 10, and 12-14. In all cases hydrogen evolution is expected at 0V with respect to RHE, but negligible hydrogens observed. This result shows that (a) choline acetate, (b) choline BF4, (c) (3-chloro-2-hydroxypropyl)trimethyl ammonium chloride, (d) butyrylcholine chloride, and (e) (2-chloroethyl)trimethylammonium chloride are all hydrogen suppressors.

The examples given above are merely illustrative and are not meant to be an exhaustive list of all possible embodiments, applications or modifications of the invention. Thus, various modifications and variations of the described methods and systems of the invention will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Although the invention has been described in connection with specific embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described modes for carrying out the invention which are obvious to those skilled in the chemical arts or in the relevant fields are intended to be within the scope of the appended claims.

The disclosures of all references and publications cited above are expressly incorporated by reference in their entireties to the same extent as if each were incorporated by reference individually.

While particular elements, embodiments and applications of the present invention have been shown and described, it will be understood that the invention is not limited thereto, since modifications can be made by those skilled in the art without departing from the scope of the present disclosure, particularly in light of the foregoing teachings.

Claims

1. An carbon monoxide generator for chemical laboratory or therapeutic uses, comprising wherein the output of the carbon monoxide generator contains at least 20 times as much CO as H2 on a molar basis.

a. A Carbon Dioxide Source, and

b. A means to convert carbon dioxide to carbon monoxide,

2. The carbon monoxide generator in claim 1 with a Carbon Dioxide Source comprising at least one of solid CO2, liquid CO2, gaseous CO2, a carbonate or a bicarbonate.

3. The carbon monoxide generator in claim 1 comprising an electrochemical cell

4. The carbon monoxide generator in any of the preceding claims, comprising at least one of a) a Helper Catalyst b) A Directing Molecule or c) a Hydrogen Suppressor.

5. The Carbon Dioxide Source in claim 1 comprising at least one of a) a Helper Catalyst b) A Directing Molecule or c) a Hydrogen Suppressor.

6. The device in claim 4 or 5, with at least one of

a) the Helper Catalyst,

b) The Directing Molecule or

c) the Hydrogen Supressor

comprising at least one cation and/or at least one anion.

7. The device in any of claim 4, 5, or 6 wherein at least one of

a) the Helper Catalyst,

b) The Directing Molecule or

c) the Hydrogen Supressor

has a concentration of between about 0.000006 2% and 99.999% by weight.

8. The device of any of claims 4-7, wherein at least one of

a) the Helper Catalyst,

b) The Directing Molecule or

c) the Hydrogen Supressor

comprises at least one of the following: phosphines, imidazoliums, pyridiniums, pyrrolidiniums, phosphoniums, sulfoniums, prolinates, methioninates, or alkali ions.

9. The device of any of claims 4-8, wherein at least one of

a) the Helper Catalyst,

b) The Directing Molecule or

c) the Hydrogen Supressor

comprises cholines or a choline salt.

10. The device of any one of claims 4 through 9 wherein at least one of

a) the Helper Catalyst,

b) The Directing Molecule or

c) the Hydrogen Supressor

comprises 1-ethyl-3-methylimidazolium cations.

11. The device of any of claims 4 through 10 wherein at least one of

a) the Helper Catalyst,

b) The Directing Molecule or

c) the Hydrogen Supressor

comprises tetrafluoroborate anions.

12. The device of any of claims 4 through 11, wherein at least one of

a) the Helper Catalyst,

b) The Directing Molecule or

c) the Hydrogen Supressor

comprises potassium or cesium cations.

13. The device of any of claims 4 through 12, wherein at least one of

a) the Helper Catalyst,

b) The Directing Molecule or

c) the Hydrogen Supressor

comprises tetrafluoroborate anions, and

is a solvent, electrolyte or additive.

14. The device of any of claims 4 through 13 above, wherein the Director Molecule comprises:a positively charges species further comprising at least one polar group selected from —OR, —COR, —COOR, —NR2, —PR2, —SR, or halides, where the R groups can independently be hydrogen or ligands containing carbon.

15. The device of any of claims 4 through 14 above, wherein the Hydrogen Suppressor comprises: a choline derivative of the form R1R2R3N+ (CH2)nOH or R1R2R3N+ (CH2)nCl, wherein n=1-4, and R1, R2, and R3 are independently selected from the group consisting of aliphatic C1-C4 groups, —CH2OH, —CH2CH2OH, —CH2CH2CH2OH, —CH2CHOHCH3, —CH2COH, —CH2CH2COH, and —CH2COCH3 and molecules where one or more chlorine or fluorine is substituted for hydrogen in aliphatic C1-C4 groups, —CH2OH, —CH2CH2OH, —CH2CH2CH2OH, —CH2CHOHCH3, —CH2COH, —CH2CH2COH, or —CH2COCH3. 16 A portable carbon monoxide generator for chemical laboratory or therapeutic use, comprising the device of any of the above claims.

16. The device of any of claims 2 through 14 above wherein the device comprises a cartridge that fits in the line between an oxygen source and a patient.

17. A method of producing carbon monoxide for chemical laboratory or therapeutic uses, comprising the steps of:

providing the device of any of the above claims;

providing carbon dioxide, a carbonate, or a bicarbonate from the Carbon Dioxide Source to the device;

providing any additional water, solvent, or electrolyte as may be needed;

applying a source of energy, such as an electric current, to the device; and

directing the carbon monoxide thus produced to the intended point of use.