METHODS AND SYSTEM FOR ELECTROCHEMICAL PRODUCTION OF FORMIC ACID FROM CARBON DIOXIDE

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 63/264,572, filed Nov. 24, 2021, which is incorporated by reference herein in its entirety.

BACKGROUND

The efficient electrochemical conversion of CO₂ to produce aqueous solutions of formate (HCOO⁻) salts at high efficiency in an electrochemical system has been the subject of extensive studies. However, there are limited examples of electrochemical conversion of CO₂ to directly produce pure aqueous solutions (e.g., no electrolytes) of formic acid at high efficiency and high concentration. The challenge for direct production of formic acid, rather than formate, is that formate is the product that is produced at the alkaline pHs that are typical near the cathode reaction of CO₂. The formate may then be subjected to a post process to acidify (protonation of formate to formic acid) and purify (concentrate the formic acid and remove the electrolyte salts and excess water by dialysis, distillation or other suitable method) to produce the final concentrated formic acid product. This extra process and its accompanying expense could be avoided if pure, concentrated aqueous solutions of formic acid could be produced at high efficiency.

Some examples of CO₂ electrolysis directly to formic acid utilize a central flow compartment that contains an ionically conductive acidic resin. The formate anion that is produced by the reaction of CO₂ with the catalyst on the cathode side may travel through an anion exchange membrane into the central flow compartment. The acidic resin in the compartment will then allow for the formate to be protonated forming formic acid (HCOOH) which may then be collected once exited from the central flow compartment by a flow of deionized water through the compartment. This device design may operate at good efficiency if the concentration of formic acid is low as dictated by the flow rate of water though the central flow compartment. Faster flow rates keep the concentration in the central flow compartment low by diluting the produced formic acid and clearing it from the device.

If the flow rate of water through the central flow compartment is low the concentration of formic acid in the central flow compartment will be high. The large concentration gradient of formic acid leads to crossover of formic acid across the anion exchange membrane (AEM) toward the cathode which leads to a decrease in the pH and facilitates hydrogen production because of the increased concentration of protons (H+). The electrochemical reduction of protons to hydrogen is a competing reaction to the electrochemical reduction of CO₂ and represents a loss in current efficiency (aka faradaic efficiency).

Thus there is a need for a modified electrochemical system that has increased faradaic efficiency when directly generating formic acid from carbon dioxide.

SUMMARY

This disclosure relates to an electrochemical system for converting carbon dioxide to formic acid by the protonation for formate ions with hydronium ions. In some embodiments, the electrochemical system comprises an electrochemical cell in electrical communication with and electrical energy source. In some embodiments, the electrochemical cell comprises a cathode compartment, a first central flow compartment, a second central flow compartment and an anode compartment. In some examples, the cell may further comprise a first anion exchange membrane interposed between and ionically communicating with the cathode compartment and the first central flow compartment, a second anion exchange membrane interposed between and ionically communicating with the first central flow compartment and the second central flow compartment, and a cation exchange membrane interposed between and ionically communicating with the second central flow compartment and the anode compartment. In some embodiments, the electrical energy source applies a potential difference across the anode and the cathode. In other embodiments, the first central flow compartment has a first central flow compartment inlet and a first central flow compartment outlet, and the second central flow compartment has a second central flow compartment inlet and a second central flow compartment outlet. In some embodiments, the cathode compartment produces formate from carbon dioxide and the anion compartment produces hydronium ions from water. In some embodiments, the configuration of the electrochemical cell defines a fluid flow path, an ionic conduction path, or a combination thereof. Some embodiments include carrier media, which are employed to rinse ions from the first central flow compartment into the second central flow compartment, and also to efflux formic acid from the second central flow compartment.

In some embodiments, the cathode compartment comprises a cathode current collector, a gas flow channel inlet, a gas diffusion electrode (GDE) structure, and a GDE electrocatalyst layer, and the anode compartment comprises an anode base current collector, an anolyte solution inlet, an anode diffusion layer, and an anode catalyst. In other embodiments, the first central flow compartment comprises an anion exchange material, and the second central flow compartment comprises a cation exchange material.

In some embodiments, the electrochemical cell has a faradic efficiency of 60% or more, and the electrochemical cell generates 15% or more formic acid concentration.

In some examples, the fluid flow path in the first central flow compartment is opposite the fluid flow path in the second central flow compartment. In other examples, the fluid flow path in the first central flow compartment is parallel to the fluid flow in the second central flow compartment. In other embodiments, the fluid flow path in the first central flow compartment is independent from the fluid flow path in the second central flow compartment. In some embodiments, the fluid flow path in the first central flow compartment comprises a first flow rate and a second flow rate.

In some embodiments, the carrier media in the first central flow compartment comprises a first carrier medium and second carrier medium and the fluid flow path in the second central flow compartment define a first efflux direction and a second efflux direction. In other examples, the first central flow chamber contains an anion exchange material.

Some examples include a method for making formic acid, comprising:

• • contacting an electrically active cathode to a CO₂ source material to convert CO₂ to HCOO—; separating the formed HCOO— from the cathode; passing the formed HCOO— through a first anion exchange membrane along an ion conduction path; passing the formed HCOO— through a first central flow compartment containing an anion exchange material; passing the formed HCOO— through a second anion exchange membrane from the first flow compartment into a second central flow compartment along an ion conduction path; contacting an electrically active anode to a water source to convert the water source into hydronium ions and hydroxyl ions; separating the formed hydronium ions from the anode; selectively passing the formed hydronium ions into the second central flow compartment through a cation exchange membrane separating the second central flow compartment from the anode compartment along an ion conduction path; forming formic acid in the second central flow compartment with the transported HCOO— from the first central flow compartment and the hydronium ions from the anode compartment, where the HCOO⁻ may be protonated to form formic acid; rinsing formic acid present in the first central flow compartment along an independent flow path with a carrier medium; and removing the formic acid product effluent from the second central flow compartment along the fluid flow path.

In some embodiments, the fluid flow path comprises passing (or rinsing) a carrier medium from the first central flow compartment into the second central flow compartment, at a flow rate between 0.5 mL/hour and 10 mL/hour. In some examples, the carrier medium comprises a liquid or a gas. In some embodiments, the carrier medium comprises distilled water. In other embodiments, the carrier medium comprises nitrogen gas. Some embodiments include a flow path that is oblique to the ionic conduction path. In some embodiments, the method reduces the concentration of formic acid or hydronium ions adjacent the cathode and the concentration of formate ions adjacent to the anode. In some embodiments, the formic acid concentration is lower in the first central flow compartment as compared to the second central flow compartment.

These and other embodiments are described in greater detail below.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is a schematic of the electrochemical system described herein.

FIG. 2 is a schematic of the electrochemical system described herein.

FIG. 3 is a schematic of the electrochemical system cell described herein.

DETAILED DESCRIPTION

This disclosure relates to an electrochemical system for converting carbon dioxide to formic acid. The electrochemical systems described herein may also be referred to as electrolyzers or electrochemical devices.

As used herein, the term “fluidly communicating” refers to the fluid contact between described components or elements herein. This may include actual fluid flow or merely fluid contact between elements.

As used herein, the term “ionically communicating” refers to the ionic passage between described components or elements herein. This may include actual flow of aforedescribed ions or merely ionic contact effecting the passage of charge or creating the aforementioned ionic member, e.g., formate, hydroxide and or hydronium ions.

As used herein, the term “countercurrent communication” refers to the crossover of some chemical element between two flowing bodies flowing in opposite directions.

As used herein, the term “fluid flow path” refers to the path of the carrier medium flow through the inlet and outlets defined herein, generally under the influence of an external pump or input volume.

As used herein, the term “ionic conduction path” refers to the ionic communication, that allows charged particles to flow from the anode to the cathode upon the application of voltage supplied by the power supply, e.g., formate and or hydroxyl ions moving from the cathode to the anode; and hydronium ions moving from the anode to the cathode.

As used herein, “concentration gradient flow path” refers to the free diffusion of chemical species generated by differences in concentration gradient, e.g., differential concentrations of HCOOH.

Use of the term “may” or “may be” should be construed as shorthand for “is” or “is not” or, alternatively, “does” or “does not” or “will” or “will not,” etc. For example, the statement “the carrier medium may be liquid” should be interpreted as, for example, “In some embodiments, the carrier medium is a liquid,” or “In some embodiments, the carrier medium is not a liquid.”

FIG. 1 is a schematic illustrating a system, such as system 10, for the electrochemical reduction of a selected reactant, e.g., carbon dioxide, to a selected product, e.g., formic acid. In some embodiments, the system may control pH. The system may be configured for the direct production of formic acid in accordance with an embodiment of the present disclosure. It is believed these embodiments further separate, isolate, and/or distance the anodic formic acid production from the cathodic generation of formate to provide increased faradaic efficiency.

It is contemplated that system operates according to the overall chemical equations:

Anode Reaction:2H₂O→4H⁺+4e⁻+O₂  (1)

Cathode Reaction: CO₂+H⁺+2e⁻→HCOO⁻  (2)

Overall Reaction: 2 CO₂+2H₂O→2HCOOH+O₂  (3)

The potential competing side reactions that may occur at the cathode are as follows:

CO₂+2H⁺+2e⁻→CO+H₂O  (4)

2H₂O+2e⁻→2OH⁻+H₂  (5)

Another reaction is the combination of generated H⁺ ions or protons with formed hydroxide ions and forming water as the product as follows:

Water Forming Reaction: H⁺+OH⁻→H₂O  (6)

Second central flow compartment (vide infra) Reaction: H⁺+HCOO⁻→HCOOH  (7)

In FIG. 1, the system may include an electrochemical cell, such as cell 12, and an electrical system, such as electrical system 14, that are in electrical communication. As shown in FIG. 2 and FIG. 3, the electrochemical cell may be implemented as a divided electrochemical cell having at least four electrochemical compartments, elements or regions, e.g., cathode compartment 22, first central flow compartment 24, second central flow compartment 26 and anode compartment 28, wherein a first anion exchange membrane 32, a second anion exchange membrane 34, and a cation exchange membrane 36 form, define, or may separate the cell compartments 22, 24, 26, and 28. In some embodiments, the electrochemical cell may define a fluid flow path of a carrier medium. In some embodiments the electrochemical cell may define a separate ionic conduction path. In some embodiments, the electrochemical cell utilizes an energy source, within the electric system (not shown), which may generate an electrical potential between the positive, connected anode, such as anode 42, and the negative, connected to gas diffusion electrode (GDE) cathode structure, such as cathode structure 52. The electrical energy source may provide a DC voltage with the positive terminal on the anode and the negative on the cathode. The energy source may be configured to supply a constant voltage or constant current to the electrochemical cell or other electrochemical system described herein.

In some embodiments, the electrochemical cell may have a cathode compartment comprising a cathode assembly, such as assembly 50. The cathode assembly, such as assembly 50, may comprise a gas diffusion electrode (GDE) structure and the cathode current collector, such as cathode current collector 52. For the purposes of the present disclosure, the terms “structure” and “layer” are deemed to be equivalent. The cathode current collector may utilize various designs to flow and distribute a gas, such as carbon dioxide gas, into and out of the GDE reaction zone. One such “flow field” is a serpentine design, in which the reactant gas travels into and past the GDE electrode reaction zone following a gas flow plenum pattern etched into the current collector. In some embodiments, the cathode assembly may have a cathode interface surface. In some embodiments, the cathode interface surface may have a surface area. The cathode compartment may have a reactant, e.g. carbon dioxide (CO₂) gas, passed through cathode flow channel inlet, such as inlet 58, which may be suitably humidified with water or remain dry, and depleted reactant (CO₂ gas) outlet stream passed out through cathode flow channel or outlet, such as outlet 57, through which the depleted gas, fluid, or liquid in the GDE may be collected.

In some embodiments, the gas diffusion electrode may include the GDE gas diffusion layer, such as gas diffusion layer 54, and the GDE electrocatalyst layer, such as layer 56. The gas diffusion layer may provide the distribution of the CO₂ reactant into GDE electrocatalyst layer. In some embodiments, the GDE electrocatalyst layer may consist of a deposit of high surface area fine particles or nanoparticles of metals and/or metal oxides as well as various non-metals and non-metal compounds deposited on the GDE gas diffusion layer, providing the region where CO₂ may be electrochemically reduced to formate ions (HCOO⁻). In some embodiments, the electrocatalyst material(s) may be admixed with or already bonded onto high surface area conductive substrate materials such as carbon paper, powdered carbon and the like. In some embodiments, various bonding agents in certain weight percentages may also be applied to help the GDE electrocatalyst layer, such as electrocatalyst layer 56, adhere to the GDE gas diffusion layer (e.g., layer 54), such as polytetrafluoroethylene (PTFE) or polymeric functionalized ion exchange monomers of the same composition as the anion exchange membrane, such as imidazoliums. In some embodiments, the GDE electrocatalyst layer may be modified to provide a balance of hydrophobic and hydrophilic properties to obtain the desired CO₂ reduction reaction chemistry and mass transfer. It may be that the GDE electrocatalysts are chemically stable to the potential acidic, neutral, or basic conditions that may be present in the reduction of CO₂ to a formate ion or formic acid in the cathode.

In some examples, the GDE cathode electrocatalyst layer, e.g., electrocatalyst layer 56, in the electrochemical cell may comprise compositions containing Au, Ag, Bi, Cu, Ga, Pb, Pd, In, Sb, Sn, Zn, W, as well as transition metals, their oxides, and their metal alloys including binary, ternary, and quaternary alloys and higher and the like. In some embodiments, the electrocatalysts may comprise a mixture of metals, and/or a combination of metals and oxides deposited on a conductive substrate carrier such as carbon or graphite. In some embodiments, the deposited electrocatalysts may be sized in the nanoparticle size range or larger, in a range of about 0.5 nm to about 1000 nm, about 0.5-1 nm, about 1-5 nm, about 5-10 nm, about 10-25 nm, about 25-50 nm, about 50-100 nm, about 100-250 nm, about 250-500 nm, about 500-1000 nm, or about 0.5-100 nm, about 100-1000 nm, about 1000 nm or greater, or any size in a range bounded by any of these values. In some examples, the deposited electrocatalysts may also be applied in multiple coatings or layers of these metals, metal oxides, and metal alloys onto the selected conductive carrier. In some embodiments, the deposited electrocatalysts may then be further heat treated using various atmospheric gases such as oxygen, nitrogen, hydrogen, and the like or under a vacuum to convert the electrocatalysts into intermetallic compounds and/or oxides. The preferred electrocatalysts may have a high hydrogen overvoltage in order to reduce the potential side reactions that may occur at the cathode that may form hydrogen from the reduction of water. If the cathode product is formic acid, the electrocatalysts may be resistant to alkaline or acidic conditions at the cathode reaction conditions. In other embodiments, the selected catalysts may be selective in producing selected CO₂ reduction products other than formate, such as acetate, acetic acid, carbon monoxide, ethylene, ethanol, ethylene glycol, acrylic acid, and the like.

In some embodiments, conductive electrocatalyst support materials may include carbon, graphite, titanium suboxides such as Ti₄O₇ and Ti₅O₉, metal and metal oxide particles, conductive nitride compounds, doped semiconductors made from silicon and germanium, and others that are commercially used in fuel cells in the form of high surface area powders, fibers, and other physically obtainable forms. In some examples, the electrocatalyst on the support material may then be applied to a GDE gas diffusive layer conductive cathode substrate in order to form the electrocatalyst layer on the GDE structure. The electrocatalyst on the GDE conductive support may be applied by any suitable methods including spray deposition when the catalyst mix is placed into a solvent or liquid carrier, by deposition by ink jet and air-brush methods and the like. Other methods include the preparation and application of wet pastes that may then be dried, condensed, and bonded under heat and pressure onto the GDL substrate. The GDL substrate, which allows the CO₂ gas to pass to the electrocatalyst layer, may be constructed of various materials such as conductive carbon or graphite in the form of planar fibers and papers, felts and the like. In other embodiments, the GDL may also incorporate additional materials such as a layer of metal screen or metal particles to provide good electrical conductivity within the GDE structure and to the cathode current collector.

In some embodiments, the electrochemical cells described herein may have a first central flow compartment or flow channel, bounded, defined and/or enclosed by a first anion exchange membrane, second anion exchange membrane and/or rigid plates positioning the anion exchange membranes. In some embodiments, the second anion exchange membrane may be disposed between the first central flow compartment and the second central flow compartment. In some embodiments, the architecture of the cathode compartment, the first central flow compartment, the second central flow compartment and the anode compartment may define an electrolyzer longitudinal axis, e.g., a line passing through a central point of such respective compartments and/or extending from the cathode compartment to the anode compartment.

In some embodiments, the first anion exchange membrane and second anion exchange membrane may selectively block or reduce the ionic flow of cations, e.g., hydronium ions into the cathode compartment and/or the first central flow compartment. In some embodiments, the first anion exchange membrane and second anion exchange membrane may selectively provide an ionic conduction path for the generated formate from the cathode compartment to the first central flow compartment and/or the second central flow compartment. In some embodiments, the first anion exchange membrane and second anion exchange membrane may selectively block or reduce the free diffusion of formic acid under the influence of a concentration gradient from the first central flow compartment (higher concentration of formic acid) to the cathode compartment (lower concentration of formic acid). In some embodiments, the first anion exchange membrane and second anion exchange membrane may selectively block or reduce the free diffusion of formic acid under the influence of a concentration gradient from the second central flow compartment (higher concentration of formic acid) to the first central flow compartment. It is believed that the absence of or low concentration of counter ions (sodium or potassium), may minimize the solubility of formate. As a result, the transport of the formate to the first and second central flow compartments may be confined by interaction with the cationic functional groups within the basic or anionic resin and the passage of such formate from cationic functional group to cationic functional group within the resin or respective membrane. In some embodiments, the first anion exchange membrane and the second anion exchange membrane may allow formate (HCOO—) ions generated within the cathode compartment to pass into the first and second central flow compartment to interact with hydronium ions transported into the second central flow compartment.

In some embodiments, the first central flow compartment may contain a porous media, such as anion exchange (basic) resins and the like. In some embodiments, the anion exchange resin may comprise a cation functional group, e.g., ammonium. It is believed the positively charged functional group, e.g., ammonium, may support or interact with formate or hydroxyl anions to aid in the passage of the formate therethrough. It is believed this may confine the transport or movement of the formate from within the cathode compartment to the first and second central flow compartments. It is believed that since there is an absence or low concentration of counter ions (sodium or potassium) which would enable aqueous solubility, the transport of formate through the anion exchange membranes may be confined through the anion exchange membrane through the interaction of the formate with the cation functional groups on the membrane. In some embodiments, the presence of a cationic functional group may provide a basis for interacting with the formate which may be conveyed or transported to the second central flow compartment. In some embodiments, the application of current to the anode and cathode through a connecting circuit may provide additional charge influence to the generated formate, hydroxide, and hydronium, e.g., the negative polarity of the cathode, will attract the hydronium ions and the positive polarity of the anode will attract the generated formate.

In some embodiments, having at least a first central flow compartment and a second central flow compartment may additionally physically, ionically and/or chemically separate, distance and or isolate the cathode compartment from generated formic acid and/or hydronium ions. In some embodiments, having at least a first and second central flow compartment may additionally physically, ionically and or chemically separate, distance and or isolate the anode compartment from generated formate and/or hydroxyl ions. In some embodiments, having at least a first central flow compartment and a second central flow compartments may additionally physically, ionically and or chemically isolate the cathode compartment from generated formic acid and/or hydronium ions.

In some embodiments, the electrochemical cell comprising the elements described herein, e.g., passageways defined within the walls or elements defining the cathode compartment, anode compartment, first central flow compartment and a second central flow compartment, may define a fluid flow path. It is believed that some formic acid may be present in the first central flow compartment and or the cathode compartment as a result of diffusion of formic acid formed in the second central flow compartment and crossing over through the second anion exchange membrane into the first central flow compartment and/or the diffusion of hydronium ion into the first central flow compartment and interaction with formate present there. It is believed that the fluid flow path contributes to the increased faradic efficiency and improved formic acid production of the currently described embodiments. In some embodiments, the fluid flow path may rinse or return formic acid and or hydronium ions from the first central flow compartment to the second central flow compartment.

In some embodiments, the defined first central flow compartment inlet, such as inlet 60, may receive the carrier medium into the first central flow compartment. In an embodiments, a defined first central flow compartment outlet, such as outlet 62, may efflux the carrier medium from the first central flow compartment. In another embodiment, a defined second central flow compartment inlet, such as inlet 64 may receive a carrier medium into the second central flow compartment. In some embodiments, a defined second central flow compartment outlet, such as outlet 66, may efflux the carrier medium from the second central flow compartment. In some embodiments, pathways or fluid communications may provide a fluid flow path to pass a carrier medium, e.g., a solution or a gas, into the first central flow compartment at various flow rates and or pass from the first central flow compartment outlet to the second central flow compartment inlet. It is believed that providing a rinsing and/or blocking of the hydronium ions and generated formic acid from reaching the cathode compartment and/or remaining in the first central flow compartment. In some embodiments, the fluid flow rate may be about 0.5 mL/hour to about 10 mL/hour, about 0.5-1 mL/hour, about 1-1.5 mL/hour, about 1.5-2 mL/hour, about 2-2.5 mL/hour, 2.5-3 mL/hour, about 3-3.5 mL/hour, about 3.5-4 mL/hour, about 4-4.5 mL/hour, 4.5-5 mL/hour, about 5-5.5 mL/hour, about 5.5-6 mL/hour, about 6-6.5 mL/hour, about 6.5-7 mL/hour, about 7-7.5 mL/hour, about 7.5-8 mL/hour, about 8-8.5 mL/hour, about 8.5-9 mL/hour, about 9-9.5 mL/hour, about 9.5-10 mL/hour, or about 0.5 ml/hour, about 1 mL/hour, about 6 mL/hour, about 10 mL/hour, or about 1-6 ml/hour, about 1-10 mL/hour, about 6-10 ml/hour, or any flow rate in a range bounded by any of these values. In some embodiments, the passage of the carrier medium may rinse or flush formic acid and or hydronium ions present in the first central flow compartment back into the second central flow compartment. In some embodiments, the fluid flow path may reduce the concentration of formic acid in the first central flow compartment and or the cathode compartment.

In some embodiments, the carrier medium flows in a first direction within the first central flow chamber. In some embodiments, the carrier medium may flow in a second direction in the second central flow chamber. In some embodiments, the first fluid flow direction and the second fluid flow direction may be in opposite directions. In some embodiments, the first fluid flow direction and the second fluid flow direction may be in the same or parallel directions. In some embodiments, the first fluid flow path direction and the second fluid flow path direction may be oblique and/or perpendicular to the cathode-anode axis, and/or the ionic conduction flow between the first central flow chamber and the second central flow chamber, e.g., through the anion exchange membrane. In some embodiments, the fluid flow path and or the carrier medium flow may be independent of each other, e.g., the carrier medium flow in the first central flow compartment and the second central flow compartment may be at different flow rates from one another. In some embodiments, the fluid flow rate in the first central flow compartment and second central flow compartments may be at different flow rates from one another, e.g., at a first efflux flow rate and a second efflux flow rate. In some embodiments, the carrier flow may be independently about 1 mL per 1 hour, per 6 hours, per 12 hours, per 24 hours, or per 72 hours (e.g. substantially zero). In some embodiments, the efflux from the first central flow compartment and/or second central flow compartment may be vented to the external atmosphere. In some embodiments, the first fluid flow path and the second fluid flow path may define a first efflux direction and a second efflux direction and/or efflux sides of the electrochemical cell. In some embodiments, the efflux and/or efflux sides may be on the same and/or different sides, e.g., effluxing on the top and/or the bottom. In some embodiments, the carrier flow media may be different from one another, e.g., water in one central flow compartment and nitrogen gas in the other central flow compartment. In some embodiments, the carrier media may be independent of each other, e.g., the carrier medium may be a first carrier medium and a second carrier medium. In some embodiments, the flow rate in the first central flow compartment may be the same or different in the second central flow compartment.

In some embodiments the fluid flow paths may be defined within the electrochemical elements, e.g., the rigid plates and/or the gaskets between elements and/or defining respective elements. In some embodiments, the fluid flow paths may comprise external fluid communicating elements for fluid communication of the first central flow compartment and the second central flow compartment, e.g., tubing and or piping connecting various positional permutations of efflux and influx (on the same side, both on the top or bottom, on different sides) to the respective central flow compartments. In some embodiments, hydroxide ions may react with CO₂ generating carbonate and bicarbonate which may transport into the first and/or second central flow compartments and upon reacting with a proton may generate CO₂ gas. It is believed that having the efflux compartment in the upright position may better facilitate the removal of the generated CO₂ gas therefrom. In some embodiments, the efflux of the first central flow compartment and/or second central flow compartment may be input into a gas/liquid separator to separate the CO₂ gas from the liquid portion.

In some embodiments, the architecture of the cathode compartment, the first central flow compartment, the second central flow compartment, the anode compartment, the first and second anion exchange membranes and the cation exchange membrane may define an ionic conduction path for selectively conveying and or transporting the generated formate and or the generated hydronium ions to the second central flow compartment to generate formic acid. In some embodiments, the ionic conductive path comprises a path through the first anion exchange membrane into the first central flow compartment. In some embodiments, the ionic conductive path comprises a path through the second anion exchange membrane into the second central flow compartment from the first central flow compartment. In some embodiments, the ionic conductive path comprises a path through the cation exchange membrane into the second central flow compartment from the anode compartment. In some embodiments, there may be two ionic conducting paths: a first through the first anion exchange membrane and/or substantially parallel to the longitudinal electrochemical cell axis from the cathode compartment to the first central flow compartment, and a second ionic conducting path from the first central flow compartment to the second central flow compartment, e.g., one through the second anion exchange membrane into the second central flow compartment.

In some embodiments, the ionic conduction path and the fluid flow paths may be substantially perpendicular to one another as shown in FIGS. 2 and 3. The carrier fluid passed into the first central flow compartment inlet may be deionized water or a properly selected gas. In some embodiments, the flow of the solution input may at least pass through the first central flow compartment from the first central flow compartment inlet to the first central flow compartment outlet, and further into the inlet of the first central flow compartment, as indicated in FIG. 2 by arrows 70A, 70B, and 70C. In some embodiments, the general flow direction of the solution input may be at least oblique or perpendicular, when passing from the inlets to the outlets, to the general flow direction of the formate ions passing through the first anion exchange membrane and/or the second anion exchange membrane.

In some embodiments, the electrochemical cells described herein may comprise a second central flow compartment, bounded, defined and/or enclosed by a cation exchange membrane, a second anion exchange membrane, and/or rigid plates holding the respective membranes therein. In some embodiments, the cation exchange membrane may be disposed between the second central flow compartment and the anode compartment. In some embodiments, the cation exchange membrane may block or reduce the ionic flow of anionic and neutral materials, e.g., formate and formic acid, respectively, into the anode compartment. In some embodiments, the cation exchange membrane may allow generated hydronium (H⁺ or H₃O⁺) ions generated within the anode compartment to pass into the second central flow compartment to interact with formate transported thereto. In some embodiments, the second central flow compartment may contain a porous media, such as cation (acidic) exchange resins and the like to enhance the conductivity in the second central flow compartment where formic acid solution product may be formed from the formate transported from the cathode compartment and the hydronium ions generated and transported from the anode compartment. In the second central flow compartment, hydronium ions may enter the compartment through the cation exchange membrane and formate may at least enter the compartment through the second anion exchange membrane. The ionic combination of the hydronium ions and formate may form formic acid in the second central flow compartment. In some embodiments, the second central flow compartment input may pass an aqueous carrier medium or gas into second central flow compartment at various flow rates to return generated formic acid product into the second central flow compartment, which may then leave the second central flow compartment as formic acid product through second central flow compartment outlet.

In some embodiments, the first central flow chamber and the second central flow chamber may be juxtaposed to one another. In some embodiments, an anion exchange membrane, separates and/or divides the first central flow chamber and second central flow chamber. In some embodiments, the first anion exchange membrane and/or the ionic conducting path therethrough may have an interface surface area of 33% or more, 50% or more, or 75% or more relative to the cathode interface surface area, such as interface surface area 59 (see FIG. 3), and/or 33% or more, 50% or more, or 75% or more relative to the anode interface surface area, such as interface surface area 49, the exposed surface area of the cathode and or the surface area through which the generated formate may pass from the cathode compartment to the first or second central flow compartment, respectively. In some embodiments, an ionic conduction path, e.g., the path of generated formate, may be defined or created between the first and second central flow compartments through the anion exchange membrane. In some embodiments, the formate may be influenced towards the anode under the influence of a positive potential on the anode and/or a negative potential on the cathode. In some embodiments, the ionic conduction path may be substantially parallel to the longitudinal electrochemical cell (cathode-anode) axis. In some embodiments, the first anion exchange membrane provides for the crossover of formate between the first central flow compartment and second central flow compartment concurrently while the fluid flow path from the first central flow compartment to the second central flow compartment may provide two flowing bodies, the carrier medium, the same or different carrier media, flowing, in opposite directions, same directions, effluxing out on the same side, different sides or opposite sides of the respective central flow compartments, and/or at the same or different flow rates.

Some embodiments of the electrochemical cell include an anode compartment comprising an anode collector, an anode catalytic layer and/or an anode assembly, such as assembly 40. The anode assembly may be positioned immediately adjacent to the cation exchange membrane 36, and may additionally comprise an anode base current collector 42 used for conducting the current to the anode assembly, anode base current collector, which are used to conduct the current directly from the anode base current collector to an anode diffusion layer, such as layer 44, and the anode catalyst, such as anode catalyst 46. The cation exchange membrane, e.g., cation exchange membrane 36, may selectively control a flow of cations (such as hydronium ions) between anode compartment 28 and the second central flow compartment, e.g., central flow compartment 26. In some embodiments, the cation exchange, e.g., cation exchange membrane 36, membrane may include a polymer type cation exchange membrane. In some embodiments, the cation exchange membrane may comprise an anion functional group, e.g., a sulfonate anion group, supported on a support or bead element. Suitable, but non-limiting examples include Nafion cationic membrane. In some embodiments, the cation exchange membrane preferably may be a perfluorinated sulfonic acid-based cation exchange membrane, which may be resistant to the oxidation reactions at the anode. In addition, the cation exchange membrane blocks the passage of anions, such as the formate ion, from passing into the anode compartment, where it could be oxidized to CO₂ or CO. It is believed the cationic exchange resin may allow the ionic conduction of positive, e.g., hydronium ions therethrough, and/or restrict or minimize the passage of negative ions, e.g., formate ions therethrough.

In some embodiments, the anode compartment may have an anolyte solution inlet or input, such as inlet or input 48, and an anolyte solution outlet or output, such as outlet or output 47. The anolyte solution may be deionized water, or an aqueous solution containing a conductive non-oxidizable acid such as sulfuric or phosphoric acid. Generated gases, such as oxygen, may exit through the anolyte solution outlet.

The selection of the anode materials and anode electrocatalysts for the electrochemical cell depends on the selected anode reaction for the electrochemical cell and process. For oxygen evolution, titanium may be the preferred current collector due to its resistance to anodic corrosion. In some embodiments, the electrocatalyst material may comprise or consist of precious metals such as Au, Ir, Ru, Rh, Ni and Pt as metals, as well as a combination of these metals as alloys, or as a combination of their oxides and oxide mixtures with each other and with other metal and metal oxides or any suitable compound as dimensionally stable anodes or mixed metal oxides (MMO's). Other metal oxides in the mixtures may include the oxides of titanium, tantalum, tin and the like. The electrocatalyst may be applied by various deposition methods such as spray deposition (e.g., when the catalyst mix is placed into a solvent or liquid carrier), ink jet, air-brush methods, CVD (chemical vapor deposition), electroplating, the application of wet pastes (e.g., those that may then be dried, condensed, and bonded under heat and pressure onto the anodic or cathodic substrate), and the application of dissolved metal salts in a solvent on the substrate followed by thermal conversion to the corresponding oxides, in order to form MMO coatings. Additionally, nanoparticles of the metals and oxides of these materials may also be applied to the anode surface to form high surface area electrode coatings, and may incorporate a small amount of a binder material (e.g., Nafion branded membrane material), to bind the catalysts to the surface. The selected binder material may preferably be oxidation resistant. Alternatively, the nanoparticles may also be applied to the cation exchange membrane surface by any suitable method, for the fabrication of fuel cells in utilizing an MEA (membrane electrode assembly) type material. Other binders may include polymers and plastics, such as PVDF (polyvinylidene difluoride), PVC (polyvinyl chloride), PTFE (polytetrafluoroethylene) and the like.

In some embodiments, high surface area anode structures may be used, which may help promote the reactions at the anode surfaces. In another embodiment, the high surface area anode base material may be in a reticulated form composed of fibers, sintered metal powder, sintered screens, and the like, and may be sintered, welded, or mechanically connected to a current distributor back plate that is commonly used in bipolar electrochemical cell assemblies. In addition, the high surface area reticulated anode structure may also contain areas having additional applied catalysts on and/or near the electrocatalytic active surfaces of the anode surface structure that may enhance and/or promote reactions that may occur in the bulk solution away from the anode surface. The anode structure may be gradated, such that the density of the anode varies in the vertical or horizontal direction to allow the easier escape of gases from the anode structure. In this gradation, there may be a distribution of particles of materials mixed in the anode structure that may comprise catalysts, for example, precious metals such as platinum and precious metal oxides such as ruthenium oxide, in addition to other catalysts such as transition metal oxide catalysts.

The electrochemical cell anode may also comprise flat carbon/graphite plates, RVC (reticulated vitreous carbon) foams, carbon cloth, or carbon felts/tissue. Carbon cloth may be used as an electrically conductive material to provide good electrical contact with the anode back plate current collector.

Suitable anode structures may include: plates made from carbon or graphite, RVC, carbon cloth woven with or without an activated carbon layer, various loadings of PTFE, carbon paper and tissue, carbon felts, woven and non-woven carbon fibers, conductive diamond films, iridium, platinum, and ruthenium oxide coatings on titanium materials such as expanded metal or screens, ruthenium and iridium oxide plated or deposited onto a carbon felt or carbon cloth as an electrocatalyst, electrocatalyst coated graphene, and other suitable commercial anode materials used in electrochemical processes and fuel cells.

In some embodiments, the electrochemical system may comprise a power source, electrically connected to the anode and cathode. The operating cell voltages for electrochemical cell disclosed in the embodiments in this disclosure have any suitable voltage, such as about 0.5 to about 20 volts depending on the anode and cathode chemistry employed in addition to the cell operating current density. In some embodiments, the operating cell voltage may range from about 0.5-1 volt, about 1-5 volts, about 5-10 volts, about 10-20 volts, about 1-10 volts, about 2-8 volts, about 2-4 volts, or about any voltage in a range bounded by any of these values. The operating current density of the electrochemical cells may range from about 5 mA/cm² to as high as 1,500 mA/cm² or more.

In some embodiments, the electrochemical cell may comprise a plurality of rigid flow field plates for peripherally mounting and positioning the respective elements described above, e.g., the first and/or second anion exchange membrane, the cation exchange membrane, the cathode and/or the anode assembly, and defining the respective first and second central flow chambers. In some embodiments, the plurality of rigid field plates may be separated by a plurality of gasket members. In some embodiments, the plurality of rigid field plates and/or the gaskets may have a plurality of communicating passageways therethrough, e.g., aligned apertures allowing communication of the carrier media from outside the electrochemical cell to the interior of the defined first and second central flow chambers. In some embodiments, external fluid communicating tubes may allow the insertion of the carrier medium into the first central flow compartment, moving the carrier from the first central flow compartment into the second flow compartment, and/or removing the generated formic acid (HCOOH) from the second central flow compartment.

In some embodiments, a method for making formic acid may comprise contacting an electrically active cathode to a CO₂ source material to convert CO₂ to HCOO⁻; separating the formed HCOO⁻ from the cathode; passing the formed HCOO⁻ through an anion exchange membrane; passing the formed HCOO⁻ through a first central flow compartment containing an anion exchange material; isolating and ionically communicating the formed HCOO⁻ from the cathode by passing the formed HCOO⁻ from the first central flow compartment to a second central flow compartment containing acidic ion exchange resin and in electrical contact with the anode; forming formic acid in the second central flow compartment and/or removing the product effluent from the second central flow compartment. Some formic acid may pass from the second central flow compartment into the first central flow compartment. It is believed that the flow of the carrier medium from the first central flow compartment to the second central flow compartment can aid in the return of the formic acid into the second central flow compartment, away from the cathode compartment. In some embodiments, passing the formed formic acid from the first central flow compartment to the second central flow compartment may be at a slow flow rate, for example, about 0.5 mL/hour to about 10 mL/hour, about 0.5-1 mL/hour, about 1-1.5 mL/hour, about 1.5-2 mL/hour, about 2-2.5 mL/hour, 2.5-3 mL/hour, about 3-3.5 mL/hour, about 3.5-4 mL/hour, about 4-4.5 mL/hour, 4.5-5 mL/hour, about 5-5.5 mL/hour, about 5.5-6 mL/hour, about 6-6.5 mL/hour, about 6.5-7 mL/hour, about 7-7.5 mL/hour, about 7.5-8 mL/hour, about 8-8.5 mL/hour, about 8.5-9 mL/hour, about 9-9.5 mL/hour, about 9.5-10 mL/hour, or about 0.5 ml/hour, about 1 mL/hour, about 6 mL/hour, about 10 mL/hour, or about 1-6 ml/hour, about 1-10 mL/hour, about 6-10 ml/hour, or any flow rate for liquid carrier medium in a range bounded by any of these values. In some embodiments, the passing the formed formic acid from the first central flow compartment to the second central flow compartment may be at a flow rate about 0.5-50 mL/min, about 0.5-1 mL/min, about 1-5 mL/min, about 5-10 mL/min, about 10-25 mL/min, about 25-50 mL/min, about 1-10 mL/min, or about 0.5 mL/min, 1.0 mL/min to 10.0 mL/min and 50 mL/min or any flow rate for a gas carrier medium in a range bounded by any of these values. In some embodiments, passing the formed formic acid includes providing a fluid medium, wherein the fluid medium may comprise a liquid or a gas. In some embodiments, the carrier medium may be the same in the first and second central flow compartments. In some embodiments, the carrier medium may be different in the first and second central flow compartments. In some embodiments, the carrier medium may be liquid. In some embodiments, the liquid may be distilled and or deionized water. In some embodiments, the carrier medium may be a gas. In some embodiments, the carrier medium may be nitrogen gas (N₂). In some embodiments, some of the formic acid generated in the second central flow compartment may crossover the second anion exchange membrane and into the first central flow compartment. This unwanted crossover may be mitigated by flowing a solution or gas from the first central flow compartment and passing the formic acid into the input of the second central flow compartment. In some embodiments, the construction, positioning and material selected herein may mitigate the formic acid crossover problems of previous electrolyzer embodiments. In examples wherein the formic acid diffuses from the second central flow compartment into the first central flow compartment, the carrier medium fluid flowing into first central flow compartment may rinse this formic acid back into the second central flow compartment, away from the cathode. In some embodiments, the hydroxide or other anions contained in the basic anion exchange resin within the first central flow compartment may serve to deprotonate the formic acid that has passed therein from the second central flow compartment into the first central flow compartment before it may reach the cathode and/or cathode compartment.

In some embodiments, the method and or electrochemical cell described herein has an improved faradic efficiency, e.g., greater than 50%, greater than 55%, greater than 60%, greater than 65%, greater than 70%, greater than 75%, or greater than 80%. Any suitable method may be used to determine faradic efficiency. In some embodiments, the method and or electrochemical cell described herein has an improved formic acid product concentration of greater than 15%, greater than 20%, greater than 25%, or greater than 30%. Any suitable method for determining formic acid concentration may be employed, e.g., UV Absorption measurement, acid base titration, liquid chromatography, pH measurement conversion to concentration, etc. It is believed the improved faradic efficiency and/or improved formic acid production (higher produced formic acid concentrations) are a result of the reduced formic acid and or hydronium ion presence in the cathode compartment, and/or in the first central flow compartment, and/or the reduced formate or formic acid presence in the anode compartment. It is believed that this is achieved, at least in part by the fluid flow of the carrier medium, e.g., rinsing, of formic acid from the first central flow compartment back into the second central flow compartment; interposing of the anion exchange membranes to block cationic ions from the cathode compartment, interposing of the cation exchange membranes to block anionic or neutral species from the anode compartment; and or providing separate ionic conduction paths and fluid flow paths.

EMBODIMENTS

Embodiment 1 An electrochemical device for converting CO2 to formic acid by the protonation of formate with hydronium ions, the device comprising:

• • (a) cathode comprising a quantity of cathode catalyst, said cathode having a cathode reactant introduced thereto via at least one cathode reactant flow channel, for generating formate;
  • (b) an anode comprising a quantity of anode catalyst, said anode having an anode reactant introduced thereto via at least one anode reactant flow channel for generating hydronium ion;
  • (c) a first central flow compartment, located between said anode and said cathode, said first central flow compartment having a first central flow compartment inlet and a first central flow compartment outlet, the first central flow compartment containing an anion exchange material, the first central flow compartment for receiving generated formate;
  • (d) a second central flow compartment, located between said anode and said cathode, the second central flow compartment containing a cation exchange material, and having a second central flow compartment inlet and a second central flow compartment outlet, the second central flow compartment for receiving generated formate and generated hydronium ions, the second central flow compartment separated from the first central flow compartment.
  • (e) a cation exchange membrane interposed between said anode and said second central flow compartment, and ionically communicating the anode and the second flow compartment and blocking formate and/or formic acid from the anode;
  • (f) a first anion exchange membrane interposed between and ionically communicating said cathode and said first central flow compartment and blocking formic acid and/or hydronium ions from the cathode;
  • (g) a second anion exchange membrane interposed between and ionically communicating said first and second central flow compartments and blocking formic acid and/or hydronium ions from the cathode;
  • (h) an ionic conductive path defined between the cathode compartment and the second central flow compartments, passing formate therethrough;
  • (i) a fluid flow path defined within the electrochemical cell, the fluid flow extending between the first and second central flow compartments, passing carrier medium therethrough and rinsing formic acid or hydronium ions from the first central flow compartment into the second central flow compartment; and
  • (j) a source of electrical energy that applies a potential difference across the anode and the cathode, wherein said cathode is encased in a cathode chamber and at least a portion of the cathode catalyst is directly exposed to a CO2 source reactant during electrochemical conversion of the CO2 to the reaction product.

Embodiment 2 The electrochemical device of embodiment 1, wherein the second central flow compartment is interposed between the first central flow compartment and the anode.

Embodiment 3 The electrochemical device of embodiment 1, wherein the first central flow compartment is interposed between the second flow compartment and the cathode.

Embodiment 4 The electrochemical cell of embodiment 1, wherein the electrochemical cell has a faradic efficiency of greater than 60%.

Embodiment 5 The electrochemical cell of embodiment 1, wherein the electrochemical cell generates at least 15% formic acid concentration.

Embodiment 6 The electrochemical cell of embodiment 1, wherein the fluid flow in the first central flow compartment is opposite the fluid flow in the second central flow compartment.

Embodiment 7 The electrochemical cell of embodiment 1, wherein the fluid flow in the first central flow compartment is parallel to the fluid flow in the second central flow compartment.

Embodiment 8 The electrochemical cell of embodiment 1, wherein the fluid flow path in the first central flow compartment is independent from the carrier medium flow in the second central flow compartment.

Embodiment 9 The electrochemical cell of embodiment 8, wherein the fluid flow path in the first central flow compartment comprises a first and second flow rates.

Embodiment 10 The electrochemical cell of embodiment 8, wherein the carrier media in the first central flow compartment comprises a first and second carrier media.

Embodiment 11 The electrochemical cell of embodiment 8, wherein the first and second fluid flow paths define a first and second efflux directions.

Embodiment 12 The electrochemical device of embodiment 1, wherein the first central flow chamber contains an anion exchange material.

Embodiment 13 A method for making formic acid, comprising:

• • Contacting an electrically active cathode to a CO2 source material to convert CO2 to HCOO—;
  • Separating the formed HCOO— from the cathode
  • Passing the formed HCOO— through a first anion exchange membrane along an ion conduction path;
  • Passing the formed HCOO— through a first central flow compartment containing an anion exchange material;
  • Passing the formed HCOO— through a second anion exchange membrane from the first flow compartment into a second central flow compartment along an ion conduction path;
  • Contacting an electrically active anode to a water source material to convert the water source into hydronium ions and hydroxyl ions;
  • Separating the formed hydronium ions from the anode;
  • Selectively passing the formed hydronium ions into the second central flow compartment through a cation exchange membrane separating the second central flow compartment from the anode compartment along an ion conduction path;

Forming formic acid in the second central flow compartment with the transported HCOO— from the first central flow compartment and the hydronium ions from the anode compartment, where the HCOO⁻ may be protonated to form formic acid;

• • Rinsing formic acid present in the first central flow compartment along an independent flow path with a carrier medium; and
  • Removing the formic acid product effluent from the second central flow compartment along the fluid flow path.

Embodiment 14 The method of embodiment 13, wherein the fluid flow path comprises passing a carrier medium from the first central flow compartment into the second central flow compartment.

Embodiment 15 The method of embodiments 13, wherein rinsing the formed formic acid from the first central flow compartment to the second flow compartment is at a flow rate between 0.5 ml/hour and 10 ml/hour.

Embodiment 16 The method of embodiment 13, wherein the carrier medium comprises a liquid or a gas.

Embodiment 17 The method of embodiment 13, wherein the carrier medium comprises distilled water.

Embodiment 18 The method of embodiment 13, wherein the carrier medium comprises nitrogen gas.

Embodiment 19 The method of embodiment 13, wherein fluid flow path is at least oblique to the ionic conduction path.

Embodiment 20 The method of embodiment 13, wherein the method reduces the concentration of formic acid or hydronium ions adjacent the cathode.

Embodiment 21 The method of embodiment 13, wherein the method reduces the concentration of formate adjacent the anode.

Embodiment 22 The method of embodiment 13, wherein the HCOOH concentration is lower in the first central flow compartment as compared to the second central flow compartment.

EXAMPLES

Example 1—Formic Acid Cell

Example 1

A formic acid cell was assembled similar to but with modifications to that described in U.S. Pat. No. 10,047,446, FIG. 4 (purchased from Dioxide Materials, Inc. (Boca Raton, FL, USA) with details outlined below.

The formic acid cell anode assembly may comprise a stainless steel end plate having a machined gas flow field (5 cm² cell hardware, Dioxide Materials) being used as the cathode current collector. The cathode end plate had an inlet port connection (cathode flow channel inlet) to a humidified carbon dioxide (CO₂) feed gas stream and an outlet gas port connection (cathode flow channel outlet) for the depleted CO₂ gas stream. The cathode current collector had an inlet port connection for the water or gas fluid entering the central flow compartments. A gas diffusion electrode (GDE) cathode with a BiO₂ electrocatalyst (Dioxide Materials) was placed in contact with the stainless steel plate flow field with the BiO₂ catalyst layer facing the anion membrane (AEM) and the uncoated backside of the GDE mounted against the cathode current collector.

The first and second central flow compartments were constructed from a 1/16 inch polycarbonate plastic sheet having a central area of 1 inch width times 1 inch length times 1/16 inch thickness polycarbonate and having an inlet solution port and an outlet solution product port.

The formic acid cell anode assembly may comprise a titanium end plate having a machined flow field (5 cm² cell hardware, Dioxide Materials) being used as the anode current collector. The anode end plate had an inlet port connection (anode flow channel inlet) to a deionized water feed and an outlet port connection (anode flow channel outlet) so that the deionized water could be recirculated within the flow field by a peristaltic pump. The anode current collector had an outlet port connection for the liquid product exiting the central flow compartments. An GDE anode (Dioxide Materials) containing a IrO₂ catalyst layer on a gas diffusion layer positioned with the gas diffusion layer in contact with the anode current collector and the anode electrocatalyst side facing and in contact with the Nation 324 membrane used as the cation exchange membrane.

PTFE gaskets (Dioxide Materials), 0.3 or 0.2 mm thick, were used for sealing the cell compartments and membranes.

The anion exchange membranes (Dioxide Materials) were soaked for 1-3 hours in 1 M KOH solution to help peel it off the liner. After removal from the liner, the membranes were still stored in a 1 M KOH bath for at least 24 hours to allow for the complete anion exchange of the chloride to hydroxide form (Cl⁻->OH⁻) before being used in the formic acid cell for testing.

The final cell assembly order was as follows with an appropriate PTFE gasket between each layer: starting with the titanium anode flow field, then the GDE anode (Dioxide Materials) mounted against the titanium anode flow field with the non-catalyst side of the gas diffusion layer contacting the anode flow field, then the cation Nafion 324 ion exchange membrane in contact with the catalyst coated side of the anode GDE, then the second central flow compartment frame which was filled with Amberlite IR120 resin beads (strong acidic, hydrogen form, Aldrich Fine Chemicals), then the second anion exchange membrane (Sustainion, Dioxide Materials) mounted between the second central flow compartment and the first central flow compartment. A first central flow compartment frame which was filled with strong basic, hydroxyl form, Amberlite IRN-78, Acros was mounted against the second anion exchange membrane. A first anion exchange membrane (Sustainion, Dioxide Materials) mounted between the first central flow compartment and the GDE cathode, then the GDE cathode (Dioxide Materials) with the catalyst face mounted against the first anion exchange membrane, and then the back side of the GDE cathode mounted directly against the stainless steel cathode flow field. PTFE gaskets were utilized to provide a leak-free seal for the cell assembly components. In this particular embodiment, the anode and cathode flow fields acted as rigid mounting plates in which apertures are drilled and held the respective membranes within a centrally defined mounting aperture. A fluid flow path was defined as a plurality of aligned apertures within the circumferentially mounting rigid plates. In some embodiments, connecting external tubing will communicate the first and second central flow compartments in various permutations, e.g., both having an influx at the same side, different sides (top or bottom) or same sides. In some embodiments, different permutations of carrier media will be utilized, e.g., both distilled water and or nitrogen gas. It is anticipated these embodiments will also provide the benefits as the embodiments currently described.

Example 2

The formic acid cell assembly was the same as described in Example 1. DI water was used for the anolyte loop, which used an 80 ml volume in a glass collection bottle. The Anolyte was recycled during cell testing using a peristaltic pump. If the fluid flowed through the central flow compartments was DI water, then a syringe pump was used. If the fluid flowed through the central flow compartments was a gas, then compressed nitrogen gas was used in conjunction with a gas flow meter. The product exiting the second central flow compartment was collected in fractions to be analyzed. The cell was operated at constant current (0.7 amps, current density of 140 mA/cm²) at ambient temperature. After several hours of operation, a 29 wt % formic acid solution concentration was collected and the cell had operated at a calculated 78.7% Faradaic efficiency based on formic acid.

The concentration of formic acid in the experiments were analyzed using a spectrophotometer (UV5Nano, Mettler Toledo) calibrated to the formic acid peak at ˜208 nm.

Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and so forth used in the specification and embodiments are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and attached embodiments are approximations that may vary depending upon the desired properties sought to be obtained. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the embodiments, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

The terms “a,” “an,” “the” and similar referents used in the context of describing the present disclosure (especially in the context of the following embodiments) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. All methods described herein may be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or representative language (e.g., “such as”) provided herein is intended merely to better illuminate the present disclosure and does not pose a limitation on the scope of any embodiment. No language in the specification should be construed as indicating any non-embodied element essential to the practice of the present disclosure.

Groupings of alternative elements or embodiments disclosed herein are not to be construed as limitations. Each group member may be referred to and embodied individually or in any combination with other members of the group or other elements found herein. It is anticipated that one or more members of a group may be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended embodiments.

Certain embodiments are described herein, including the best mode known to the inventors for carrying out the present disclosure. Of course, variations on these described embodiments will become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventor expects skilled artisans to employ such variations as appropriate, and the inventors intend for the present disclosure to be practiced otherwise than specifically described herein. Accordingly, the embodiments include all modifications and equivalents of the subject matter recited in the embodiments as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is contemplated unless otherwise indicated herein or otherwise clearly contradicted by context.

In closing, it is to be understood that the embodiments disclosed herein are illustrative of the principles of the embodiments. Other modifications that may be employed are within the scope of the embodiments. Thus, by way of example, but not of limitation, alternative embodiments may be utilized in accordance with the teachings herein. Accordingly, the embodiments are not limited to embodiments precisely as shown and described.