ELECTROCHEMICAL CELLS AND METHODS FOR ELECTROCHEMICAL CONVERSION OF CARBON DIOXIDE

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 63/683,500, filed Aug. 15, 2024 entitled “DEVICES AND METHODS FOR ELECTROCHEMICAL CONVERSION OF CARBON DIOXIDE” which is herein incorporated by reference in its entirety.

GOVERNMENT RIGHTS

This invention was made with government support under DE-FE0031916 awarded by the U.S. Department of Energy, National Energy Technology Laboratory.

The government has certain rights in the invention.

BACKGROUND

Electrochemical carbon dioxide reduction is a promising a technology for the production of clean fuels and decarbonization of the chemical industry. However, there remains several issues with current technologies, including, for example, low operating current density, high cell resistance, low faradaic efficiency of the product, and cathode flooding.

Certain embodiments of the invention address one or more of the deficiencies described above. Some embodiments of the invention include electrochemical cells for converting carbon dioxide. Other embodiments of the invention include methods for converting carbon dioxide comprising using an embodiment of the electrochemical cell. In some embodiments, the conversion of carbon dioxide produces one or more —O—(O)CH from one or more —OH on certain compounds (e.g., formula (I)) in the catholyte solution of the electrochemical cell. Additional embodiments of the invention are also disclosed herein.

SUMMARY

Some embodiments of the invention include electrochemical cells for converting carbon dioxide. In certain embodiments, the electrochemical cell comprises a cathode diffusion electrode, a catholyte solution, a cation exchange membrane, an anode gas diffusion electrode, and an anolyte solution. Other embodiments of the invention include methods for converting carbon dioxide comprising applying a voltage across the cathode gas diffusion electrode and the anode gas diffusion electrode of an embodiment of the electrochemical cell. In some embodiments, the conversion of carbon dioxide produces one or more —O—(O)CH from one or more —OH on certain compounds (e.g., formula (I)) in the catholyte solution. Additional embodiments of the invention are also disclosed herein.

Other embodiments of the invention include an electrochemical cell comprising a cathode gas diffusion electrode comprising a cathode catalyst and a cathode substrate; optionally, a cathode mesh spacer; a catholyte solution which is in contact with the cathode gas diffusion electrode; a cation exchange membrane which is in contact with the catholyte solution; an anode gas diffusion electrode which is in contact with the cation exchange membrane; and an anolyte solution which is contact with the anode gas diffusion electrode.

In certain embodiments, the catholyte solution comprises a compound of formula (I) R—OH (I), where R is C₁-C₁₂ alkyl, C₂-C₁₂ alkenyl, C₂-C₁₂ alkynyl, C₂-C₁₂ alkoxy, aryl, cycloalkyl, heteroaryl, or heterocyclyl, which C₁-C₁₂ alkyl, C₂-C₁₂ alkenyl, C₂-C₁₂ alkynyl, C₂-C₁₂ alkoxy, aryl, cycloalkyl, heteroaryl, or heterocyclyl is optionally substituted with one or more of halogen, hydroxy (—OH), methanoyl (—COH), carboxy (—CO₂H), nitro (—NO₂),—NH₂,—N(CH₃)2, cyano (—CN), ethynyl (—CCH), propynyl, sulfo (—SO₃H), morpholinyl,—CO-morpholin-4-yl,—C(O) NH₂, —C(O) N (CH₃)2, C₁-C₃ alkyl, C₁-C₃ perfluoronated alkyl,—CF₃,—OCF₃, C₁-C₃ alkoxy, or C₁-C₈ alkyl substituted with 1, 2, or 3—OH; less than 12 vol % of water; less than 20 mM of a strong acid; and a nonaqueous solvent which is different from the compound of formula I.

In other embodiments, the anolyte solution is an aqueous solution with a pH from 0.1 to 3.5.

In some embodiments, the cathode gas diffusion electrode comprises Pb, SnO, Bi metal, Zn, Pd, or Bi₂O₃, or an alloy thereof, or carbon paper, carbon fibers, glassy carbon, carbon nanofibers, carbon nanotubes, graphene, metallic foam, or a combination thereof. In other embodiments, the cathode catalyst comprises Pb, SnO, Bi metal, Zn, Pd, or Bi₂O₃, or an alloy thereof, or a combination thereof. In still other embodiments, the cathode substrate comprises carbon paper, carbon fibers, glassy carbon, carbon nanofibers, carbon nanotubes, graphene, metallic foam, or a combination thereof.

In certain embodiments, the electrochemical cell comprises the cathode mesh spacer. In some instances, the cathode mesh spacer is in contact with the cathode gas diffusion electrode, the cathode mesh spacer is in contact with the catholyte, and the cathode gas diffusion electrode is in contact with the catholyte.

In some embodiments, R is C₁-C₁₂ alkyl, C₂-C₁₂ alkoxy, cycloalkyl, or heterocyclyl, which C₁-C₁₂ alkyl, C₂-C₁₂ alkoxy, cycloalkyl, or heterocyclyl is optionally substituted with one or more of halogen, hydroxy (—OH), methanoyl (—COH), carboxy (—CO₂H), nitro (—NO₂),—NH₂,—N(CH₃)₂, cyano (—CN), ethynyl (—CCH), propynyl, sulfo (—SO₃H), morpholinyl,—CO-morpholin-4-yl,—C(O) NH₂,—C(O) N (CH₃)₂, C₁-C₃ alkyl, C₁-C₃ perfluoronated alkyl,—CF₃,—OCF₃, C₁-C₃ alkoxy, or C₁-C₈ alkyl substituted with 1, 2, or 3—OH. In other embodiments, R is C₁-C₁₂ alkyl, C₂-C₁₂ alkoxy, cycloalkyl, or heterocyclyl, which C₁-C₁₂ alkyl, C₂-C₁₂ alkoxy, cycloalkyl, or heterocyclyl is optionally substituted with one or more of halogen, hydroxy (—OH), nitro (—NO₂),—NH₂,—N(CH₃)₂, cyano (—CN), ethynyl (—CCH), propynyl, sulfo (—SO₃H), morpholinyl, C₁-C₃ alkyl, C₁-C₃ perfluoronated alkyl,—CF₃,—OCF₃, C₁-C₃ alkoxy, or C₁-C₈ alkyl substituted with 1, 2, or 3—OH. In still other embodiments, R is C₁-C₁₂ alkyl, which C₁-C₁₂ alkyl is optionally substituted with one or more of halogen, hydroxy (—OH), nitro (—NO₂),—NH₂,—N(CH₃)₂, cyano (—CN), ethynyl (—CCH), propynyl, sulfo (—SO₃H), morpholinyl, C₁-C₃ alkyl, C₁-C₃ perfluoronated alkyl,—CF₃,—OCF₃, C₁-C₃ alkoxy, or C₁-C₈ alkyl substituted with 1, 2, or 3—OH. In yet other embodiments, R is C₁-C₆ alkyl, which C₁-C₆ alkyl is optionally substituted with one or more of halogen, hydroxy (—OH),—NH₂,—N(CH₃)₂, ethynyl (—CCH), propynyl, C₁-C₃ alkyl, C₁-C₃ perfluoronated alkyl,—CF₃,—OCF₃, C₁-C₃ alkoxy, or C₁-C₈ alkyl substituted with 1, 2, or 3—OH.

In certain embodiments, formula (I) is methanol, ethanol, propenol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, or decanol.

In other embodiments, the catholyte solution comprises from 5 to 30 vol % of the compound of formula (I). In some embodiments, the catholyte solution comprises less than 5 vol % of water.

In yet other embodiments, the strong acid in the catholyte solution comprises hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid, nitric acid, chloric acid, perchloric acid, or a combination thereof. In other embodiments, the concentration of the strong acid in the catholyte solution is from 2 to 18 mM.

In still other embodiments, the nonaqueous solvent in the catholyte solution comprises an aprotic solvent or propylene carbonate. In yet other embodiments, the catholyte solution comprises from 70 to 95 vol % of the nonaqueous solvent.

In some embodiments, the surface tension of the catholyte solution is from to 45 (mN/m).

In other embodiments, the anode gas diffusion electrode comprises IrO₂, RuO₂, carbon paper, titanium, titanium mesh, or a combination thereof.

In still other embodiments, the anolyte solution has a pH from 0.5 to 3.0. In certain embodiments, the anolyte solution comprises a strong acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid, nitric acid, chloric acid, perchloric acid, or a combination thereof.

In some embodiments, the catholyte further comprises a strong acid cation exchange medium.

In still other embodiments, the electrochemical cell further comprises an anion exchange membrane which is in contact with the cathode gas diffusion electrode and/or the optional cathode mesh spacer, and which is also in contact with the catholyte.

In some embodiments, the electrochemical cell further comprises a catholyte inlet port, a catholyte outlet port, or both. In certain embodiments, the electrochemical cell further comprises an anolyte inlet port, an anolyte outlet port, or both.

In other embodiments, the electrochemical cell further comprises a gas inlet port and a gas outlet port, to permit a flow of a gas to be in contact with the cathode gas diffusion electrode.

In still other embodiments, a gas comprising CO₂ is in contact with the cathode gas diffusion electrode and the gas comprising CO₂ comprises other gases, inert gases, nitrogen, oxygen, argon, methane, water vapor, neon, carbon monoxide, flue gases, gases from the output of power plants, gases from the output of industrial plants, or a combination thereof.

Some embodiments of the invention include methods for converting CO₂. In certain embodiments, the method comprises applying a voltage potential across the cathode gas diffusion electrode and the anode gas diffusion electrode of the electrochemical cell as described herein, wherein the voltage is sufficient to convert CO₂ in a gas comprising CO₂ that is in contact with the cathode gas diffusion electrode to produce one or more

from one or more hydroxyls (—OH) of a compound of formula (I) in the catholyte solution.

In other embodiments, the faradaic efficiency to convert CO₂ to produce one or more

from one or more hydroxyls (—OH) of a compound of formula (I) in the catholyte solution, is more than 30%.

In yet other embodiments, the current density of the electrochemical cell is from −0.1 to −500 mA cm⁻² or from 1 to 40 mA cm⁻².

Other embodiments of the invention are also discussed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

The following drawings form part of the present specification and are included to further demonstrate certain aspects of the present invention. The invention may be better understood by reference to one or more of these drawings in combination with the description of specific embodiments presented herein.

FIG. 1: (A) An illustrative embodiment of an electrochemical cell. (B) Cross-sectional cell schematic of an embodiments of an electrochemical cell, the flow electrolyzer, with aqueous 5 mM H₂SO₄ anolyte and a catholyte mixture of sat. KCl in MeOH and 1 M NBu₄PF₆ in PC. (C-D) Optical images of the (C) assembled and (D) exploded view of the flow electrolyzer.

FIG. 2: Optical images of contact angle measurements for (A) 100% PC, (B) 90% PC/10% MeOH, and (C) 100% MeOH, each on a wet-proofed Toray paper GDE. (D) Measured surface tension (blue, left axis) and contact angle on a wet-proofed Toray paper GDE (red, right axis) as a function of MeOH concentration (vol %) in PC. (E) Viscosities for mixtures of 1 M NBu₄PF₆ in PC and sat. KCl in MeOH measured at 25° C.

FIG. 3: Flow electrolyzer performance with varying MeOH electrolyte concentration (vol %) in PC electrolyte. (A) Current density vs potential behavior, (B) product faradaic efficiency at 20 mA cm⁻², (C) current density at a cell voltage of 4.0 V, and (D) cell resistance (blue, left axis) and cell voltage at 20 mA cm⁻² (red, right axis). In each case, the catholyte contained 10 mM HCl, and CO₂ was supplied to the cell at 20 sccm. (E) The pH measured (left axis) at the start (red square) and at the end (green square) of electrolysis at 20 mA cm⁻² with catholyte at different MeOH concentration (vol %) in PC, and the corresponding equilibrium conversion of formic acid (FA) product to methyl formate (MF) (mol %) after electrolysis (blue, right axis). In each case, the catholyte contained 10 mM HCl, and CO₂ was supplied to the cell at 20 sccm.

FIG. 4: Flow electrolyzer performance with varying catholyte HCl concentration (mM) in 90/10 vol % PC/MeOH. (A) Current density vs potential behavior, (B) product faradaic efficiency at 20 mA cm⁻², and (C) cell resistance (blue, left axis) and cell voltage at 20 mA cm⁻² (red, right axis). In each case, CO₂ was supplied to the cell at 20 sccm. (D) The pH measured (left axis) at the start (red square) and at the end (green square) of electrolysis at 20 mA cm⁻² with catholyte at different HCl concentrations (mM) in 90/10 vol % PC/MeOH, and the corresponding equilibrium conversion of formic acid (FA) product to methyl formate (MF) (mol %) after electrolysis (blue, right axis). In each case, CO₂ was supplied to the cell at 20 sccm.

FIG. 5: Flow electrolyzer performance with varying CO₂ flow rate (sccm) using 90/10 vol % PC/MeOH. (A) Current density vs potential behavior, (B) product faradaic efficiency at 20 mA cm⁻², and (C) cell resistance (blue, left axis) and cell voltage at 20 mA cm⁻² (red, right axis). In each case, the catholyte contained 10 mM HCl. (D) The pH measured (left axis) at the start (red square) and at the end (green square) of electrolysis at 20 mA cm⁻² with different CO₂ flow rates (sccm) using 90/10 vol % PC/MeOH, and the corresponding equilibrium conversion of formic acid (FA) product to methyl formate (MF) (mol %) after electrolysis (blue, right axis). In each case, the catholyte contained 10 mM HCl.

FIG. 6: Flow electrolyzer performance with varying applied potential in 90/10 vol % PC/MeOH. (A) Current density vs time chronoamperometric behavior, (B) product faradaic efficiency, and (C) cell resistance (blue, left axis) and the absolute value of methyl formate partial current density, IJMFl (orange, right axis). In each case, the catholyte contained 10 mM HCl, and CO₂ was supplied to the cell at 20 sccm. (D) The pH measured (left axis) at the start (red square) and at the end (green square) of electrolysis under different applied potentials using 90/10 vol % PC/MeOH, and the corresponding equilibrium conversion of formic acid (FA) product to methyl formate (MF) (mol %) after electrolysis (blue, right axis). In each case, the catholyte contained 10 mM HCl, and CO₂ was supplied to the cell at 20 sccm.

FIG. 7: Flow electrolyzer performance with and without dilute water in the catholyte, using either 10/0 vol % MeOH/H₂O or 9/1 vol % MeOH/H₂O, both with a balance of 90 vol % PC. (A) Current density vs potential behavior, and (B) faradaic efficiency (left axis) and the absolute value of methyl formate partial current density, IJMFl (orange, right axis), at cell voltages of 4.5 and 7.0 V.

FIG. 8: Flow electrolyzer performance during extended electrolysis at −20 mA cm⁻² in 90/10 vol % PC/MeOH catholyte with 10 mM HCl and a CO₂ flow rate of 20 sccm. (A) Cell voltage vs time chronopotentiometric behavior, (B) product faradaic efficiency (left axis) and the absolute value of methyl formate partial current density, IJMEl (orange, right axis), and (C) the catholyte pH measured (left axis) during electrolysis and the corresponding conversion of formic acid (FA) product to methyl formate (MF) (mol %) (blue, right axis).

FIG. 9: (A) An illustrative embodiment of an electrochemical cell. (B) Cross-sectional cell schematic for an embodiment of an electrochemical cell.

DETAILED DESCRIPTION

While embodiments encompassing the general inventive concepts may take diverse forms, various embodiments will be described herein, with the understanding that the present disclosure is to be considered merely exemplary, and the general inventive concepts are not intended to be limited to the disclosed embodiments.

Some embodiments of the invention include electrochemical cells for converting carbon dioxide. In certain embodiments, the electrochemical cell comprises a cathode diffusion electrode, a catholyte solution, a cation exchange membrane, an anode gas diffusion electrode, and an anolyte solution. Other embodiments of the invention include methods for converting carbon dioxide comprising applying a voltage across the cathode gas diffusion electrode and the anode gas diffusion electrode of an embodiment of the electrochemical cell. In some embodiments, the conversion of carbon dioxide produces one or more —O—(O)CH from one or more —OH on certain compounds (e.g., formula (I)) in the catholyte solution. Additional embodiments of the invention are also disclosed herein.

As used herein (unless otherwise specified), the term “alkyl” means a monovalent, straight or branched hydrocarbon chain. For example, the terms “C₁-C₇ alkyl” or “C₁-C₄ alkyl” refer to straight- or branched-chain saturated hydrocarbon groups having from 1 to 7 (e.g., 1, 2, 3, 4, 5, 6, or 7), or 1 to 4 (e.g., 1, 2, 3, or 4), carbon atoms, respectively. Examples of C₁-C₇ alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, i-propyl, n-butyl, s-butyl, t-butyl, n-pentyl, s-pentyl, n-hexyl, and n-septyl. Examples of C₁-C₄ alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, i-propyl, n-butyl, s-butyl, and t-butyl.

As used herein (unless otherwise specified), the term “alkenyl” means a monovalent, straight or branched hydrocarbon chain that includes one or more (e.g., 1, 2, 3, or 4) double bonds. Examples of alkenyl groups include, but are not limited to, vinyl, allyl, 1-propenyl, 2-propenyl, 1-butenyl, 2-butenyl, 3-butenyl, 1-pentenyl, 2-pentenyl, 3-pentenyl, 4-pentenyl, 1-hexenyl, 2-hexenyl, 3-hexenyl, 4-hexenyl, and 5-hexenyl.

As used herein (unless otherwise specified), the term “alkoxy” means any of the above alkyl groups which is attached to the remainder of the molecule by an oxygen atom (alkyl —O—). Examples of alkoxy groups include, but are not limited to, methoxy (sometimes shown as MeO—), ethoxy, isopropoxy, propoxy, and butyloxy.

As used herein (unless otherwise specified), the term “alkynyl” means a monovalent, straight or branched hydrocarbon chain that includes one or more (e.g., 1, 2, 3, or 4) triple bonds and that also may optionally include one or more (e.g. 1, 2, 3, or 4) double bonds in the chain. Examples of alkynyl groups include, but are not limited to, ethynyl, 1-propynyl, 2-propynyl, 1-butynyl, 2-butynyl, 3-butynyl, 1-pentynyl, 2-pentynyl, 3-pentynyl, 4-pentynyl, 1-hexynyl, 2-hexynyl, 3-hexynyl, 4-hexynyl, and 5-hexynyl.

As used herein (unless otherwise specified), the term “aryl” means a monovalent, monocyclic or bicyclic, 5, 6, 7, 8, 9, 10, 11, or 12 membered aromatic hydrocarbon group. Examples of aryl groups include, but are not limited to, phenyl, naphthyl, tolyl, and xylyl. For a bicyclic aryl that is designated as substituted, one or both rings can be substituted.

As used herein (unless otherwise specified), the term “cycloalkyl” means a monovalent, monocyclic or bicyclic, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 membered hydrocarbon group. The rings can be saturated or partially unsaturated. Examples of cycloalkyl groups include, but are not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, and bicycloalkyls (e.g., bicyclooctanes such as [2.2.2] bicyclooctane or [3.3.0] bicyclooctane, bicyclononanes such as [4.3.0] bicyclononane, and bicyclodecanes such as [4.4.0] bicyclodecane (decalin), or spiro compounds). For a monocyclic cycloalkyl, the ring is not aromatic. For a bicyclic cycloalkyl, if one ring is aromatic, then the other is not aromatic. For a bicyclic cycloalkyl that is designated as substituted, one or both rings can be substituted.

As used herein (unless otherwise specified), the term “halogen” means monovalent Cl, F, Br, or I.

As used herein (unless otherwise specified), the term “heteroaryl” means a monovalent, monocyclic or bicyclic, 5, 6, 7, 8, 9, 10, 11, or 12 membered, hydrocarbon group, where 1, 2, 3, 4, 5, or 6 carbon atoms are replaced by a hetero atom independently selected from nitrogen, oxygen, or sulfur atom, and the monocyclic or bicyclic ring system is aromatic. Examples of heteroaryl groups include, but are not limited to, thienyl (or thiophenyl), furyl, indolyl, pyrrolyl, pyridinyl, pyrazinyl, oxazolyl, thiaxolyl, quinolinyl, pyrimidinyl, imidazolyl, triazolyl, tetrazolyl, 1H-pyrazol-4-yl, 1-Me-pyrazol-4-yl, pyridin-3-yl, pyridin-4-yl, 3,5-dimethylisoxazolyl, 1H-pyrrol-3-yl, 3,5-di-Me-pyrazolyl, and 1H-pyrazol-4-yl. For a bicyclic heteroaryl, if one ring is aryl, then the other is heteroaryl. For a bicyclic heteroaryl, one or both rings can have one or more hetero atoms. For a bicyclic heteroaryl that is designated as substituted, one or both rings can be substituted.

As used herein (unless otherwise specified), the term “heterocyclyl” means a monovalent, monocyclic or bicyclic, 5, 6, 7, 8, 9, 10, 11, or 12 membered, hydrocarbon, where 1, 2, 3, 4, 5, or 6 carbon atoms are replaced by a hetero atom independently selected from nitrogen atom, oxygen atom, or sulfur atom, and the monocyclic or bicyclic ring system is not aromatic. Examples of heterocyclyl groups include, but are not limited to, tetrahydropyran, pyrolidinyl (e.g., pyrrolidin-1-yl, pyrrolidin-2-yl, pyrrolidin-3-yl, or pyrrolidin-4-yl), piperazinyl (e.g., piperazin-1-yl, piperazin-2-yl, piperazin-3-yl, or piperazin-4-yl), piperidinyl (e.g., piperadin-1-yl, piperadin-2-yl, piperadin-3-yl, or piperadin-4-yl), and morpholinyl (e.g., morpholin-1-yl, morpholin-2-yl, morpholin-3-yl, or morpholin-4-yl,). For a bicyclic heterocyclyl, if one ring is aromatic (e.g., monocyclic aryl or heteroaryl), then the other ring is not aromatic.

For a bicyclic heterocyclyl, one or both rings can have one or more hetero atoms. For a bicyclic heterocyclyl that is designated as substituted, one or both rings can be substituted.

As used herein (unless otherwise specified), the term “hetero atom” means an atom selected from nitrogen atom, oxygen atom, or sulfur atom.

As used herein (unless otherwise specified), the terms “hydroxy” or “hydroxyl” indicates the presence of a monovalent-OH group.

As used herein (unless otherwise specified), the term “substituted” (e.g., as in substituted alkyl) means that one or more hydrogen atoms of a chemical group (with one or more hydrogen atoms) can be replaced by one or more non-hydrogen substituents selected from the specified options. The replacement can occur at one or more positions. The term “optionally substituted” means that one or more hydrogen atoms of a chemical group (with one or more hydrogen atoms) can be, but is not required to be, substituted.

Electrochemical Cells

Some embodiments of the invention include an electrochemical cell, as disclosed herein. Some embodiments of the electrochemical cell are referred to as flow electrolyzers. In certain embodiments, the electrochemical cell comprises (1) a cathode gas diffusion electrode (e.g., having a first surface and a second surface), (2) optionally, a cathode mesh spacer (e.g., having a first surface and a second surface), (3) a catholyte solution which is in contact with the cathode gas diffusion electrode, (4) a cation exchange membrane (e.g., having a first surface and a second surface) which is in contact with the catholyte solution, (5) an anode gas diffusion electrode (e.g., having a first surface and a second surface) which is in contact with the cation exchange membrane, and (6) an anolyte solution which is contact with the anode gas diffusion electrode.

The term contact refers to full physical contact (e.g., 100% contact of a material's surface with some or all of another material's surface; a material can be, for example, a gas diffusion electrode, a membrane, a mesh spacer, a catholyte, an anolyte, or a gas) or to partial physical contact (e.g., less than 100% contact of a material's surface with some or all of another material's surface, where less than 100% can be 99%, 98%, 95%, 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10%, 5%, or 1%). The term electrical contact means, for instance, that electrons (e.g., via electrical current) have the ability to flow between the two materials which may or may not be in physical contact (e.g., full physical contact or partial physical contact). Of course, two materials in electrical contact may not be in physical contact (e.g., full physical contact or partial physical contact). If two electrically conductive materials are in physical contact (e.g., full physical contact or partial physical contact), then they will typically be in electrical contact.

FIG. 1A illustrates certain embodiments of the electrochemical cell, comprising a gas comprising CO₂ (101) in contact with a cathode gas diffusion electrode (102) (e.g., having a first surface and a second surface), a catholyte solution (103) which is in contact with the cathode gas diffusion electrode (102), a cation exchange membrane (104) (e.g., having a first surface and a second surface) which is in contact with the catholyte solution (103), an anode gas diffusion electrode (105) (e.g., having a first surface and a second surface) which is in contact with the cation exchange membrane (104), and an anolyte solution (106) which is contact with the anode gas diffusion electrode (105).

In other embodiments, the cathode gas diffusion electrode (e.g., having a first surface and a second surface) comprises a cathode catalyst and a cathode substrate.

In certain embodiments, the catholyte solution comprises

• • (a) a compound of formula (I), which is R—OH (I), where R is an C₁-C₁₂ alkyl, C₂-C₁₂ alkenyl, C₂-C₁₂ alkynyl, C₂-C₁₂ alkoxy, aryl, cycloalkyl, heteroaryl, or heterocyclyl, which C₁-C₁₂ alkyl, C₂-C₁₂ alkenyl, C₂-C₁₂ alkynyl, C₂-C₁₂ alkoxy, aryl, cycloalkyl, heteroaryl, or heterocyclyl can optionally be substituted with one or more of halogen (e.g., F, Cl, Br, or I), hydroxy (—OH), methanoyl (—COH), carboxy (—CO₂H), nitro (—NO₂),—NH₂,—N(CH₃)₂, cyano (—CN), ethynyl (—CCH), propynyl, sulfo (—SO₃H), morpholinyl,—CO-morpholin-4-yl,—C(O) NH₂,—C(O) N (CH₃)₂, C₁-C₃ alkyl, C₁-C₃ perfluoronated alkyl,—CF₃,—OCF₃, C₁-C₃ alkoxy, or C₁-C₈ alkyl substituted with 1, 2, or 3—OH,
  • (b) less than 12 vol % of water,
  • (c) less than 20 mM of an acid (e.g., a strong acid), and
  • (d) a nonaqueous solvent, where the nonaqueous solvent is not the same as the compound of formula I (such as methanol).

In some embodiments, the anolyte solution is an aqueous solution with a pH from 0.1 to 3.5.

The cathode gas diffusion electrode can comprise any catalyst suitable to convert (e.g., selectively convert) CO₂ to formate or formic acid. Examples of the cathode gas diffusion electrode include, but are not limited to, Pb, SnO, Bi metal, Zn, Pd, Bi₂O₃, metallic foam, or an alloy thereof, or a combination thereof. In some embodiments, the cathode substrate comprises carbon paper, carbon fibers, glassy carbon, carbon nanofibers, carbon nanotubes, graphene, metallic foam, or a combination thereof. In other aspects, the cathode gas diffusion electrode is (a) stable or partially stable when in contact with acid, (b) stable or partially stable against reduction, (c) microporous or partially microporous (e.g., to gases), (d) conductive or partially conductive, or (e) a combination thereof.

Partially stable, as used herein, means that the cathode gas diffusion electrode does not degrade such that one or more properties of the cathode gas diffusion electrode (e.g., one or more of electrical conductivity, surface area for catalysis, surface area for catalyst attachment, mechanical stability, porosity, pore-size distribution, tortuosity, or formation factor) are not affected (e.g., increased or decreased, as appropriate) by more than 50%, more than 40%, more than 30%, more than 20%, more than 10%, or more than 5%.

In some embodiments, the catalyst of the cathode gas diffusion electrode is suitable for catalyzing CO₂ to

(also referred to as HC (O) OH).

In yet other embodiments, the electrochemical cell comprises a cathode mesh spacer (e.g., having a first surface and a second surface), the cathode mesh spacer is in contact with the cathode gas diffusion electrode, the cathode mesh spacer is in contact with the catholyte, the cathode gas diffusion electrode is in contact with the catholyte, or a combination thereof. In some embodiments, the electrochemical cell comprises a cathode mesh spacer and the cathode gas diffusion electrode is not in physical contact (but is in electrical contact) with the catholyte.

The cathode mesh spacer can be made of any suitable material, such as but not limited to polytetrafluoroethylene or polypropylene.

With regard to formula (I), in certain embodiments, R can be C₁-C₁₂ alkyl, C₂-C₁₂ alkoxy, cycloalkyl, or heterocyclyl, which C₁-C₁₂ alkyl, C₂-C₁₂ alkoxy, cycloalkyl, or heterocyclyl can optionally be substituted with one or more of halogen (e.g., F, Cl, Br, or I), hydroxy (—OH), methanoyl (—COH), carboxy (—CO₂H), nitro (—NO₂),—NH₂,—N (CH₃)₂, cyano (—CN), ethynyl (—CCH), propynyl, sulfo (—SO₃H), morpholinyl,—CO-morpholin-4-yl,—C(O) NH₂,—C(O) N (CH₃)₂, C₁-C₃ alkyl, C₁-C₃ perfluoronated alkyl,—CF₃,—OCF₃, C₁-C₃ alkoxy, or C₁-C₈ alkyl substituted with 1, 2, or 3—OH. In other embodiments, R can be C₁-C₁₂ alkyl, C₂-C₁₂ alkoxy, cycloalkyl, or heterocyclyl, which C₁-C₁₂ alkyl, C₂-C₁₂ alkoxy, cycloalkyl, or heterocyclyl can optionally be substituted with one or more of halogen (e.g., F, Cl, Br, or I), hydroxy (—OH), nitro (—NO₂),—NH₂,—N (CH₃)₂, cyano (—CN), ethynyl (—CCH), propynyl, sulfo (—SO₃H), morpholinyl, C₁-C₃ alkyl, C₁-C₃ perfluoronated alkyl,—CF₃,—OCF₃, C₁-C₃ alkoxy, or C₁-C₈ alkyl substituted with 1, 2, or 3—OH. In still other embodiments, R can be C₁-C₁₂ alkyl, which C₁-C₁₂ alkyl can optionally be substituted with one or more of halogen (e.g., F, Cl, Br, or I), hydroxy (—OH), nitro (—NO₂),—NH₂,—N(CH₃)₂, cyano (—CN), ethynyl (—CCH), propynyl, sulfo (—SO₃H), morpholinyl, C₁-C₃ alkyl, C₁-C₃ perfluoronated alkyl,—CF₃,—OCF₃, C₁-C₃ alkoxy, or C₁-C₈ alkyl substituted with 1, 2, or 3—OH. And in yet other embodiments, R can be C₁-C₆ alkyl, which C₁-C₆ alkyl can optionally be substituted with one or more of halogen (e.g., F, Cl, Br, or I), hydroxy (—OH),—NH₂,—N(CH₃)₂, ethynyl (—CCH), propynyl, C₁-C₃ alkyl, C₁-C₃ perfluoronated alkyl,—CF₃,—OCF₃, C₁-C₃ alkoxy, or C₁-C₈ alkyl substituted with 1, 2, or 3—OH.

In some aspects, formula (I) can be methanol, ethanol, propenol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, or decanol. In other aspects, formula (I) is methanol, ethanol, propenol, or butanol.

In some embodiments, the composition comprising the compound of formula (I) can comprise any suitable first supporting electrolyte at any suitable concentration. Supporting electrolytes can sometimes be part of the catholyte solution. Suitable supporting electrolytes can include but are not limited to KCl, NaCl, Ha2SO₄, and NaHCO₃). Suitable concentrations of supporting electrolytes can include but are not limited to saturated concentrations of the supporting electrolyte.

In certain embodiments, the catholyte solution can comprise 0.1, 0.5, 1.0, 1.5, 2.0, 2.5, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 95, 99, or 100 vol % of the compound of formula (I); or from 0.1 to 100, from 0.1 to 99, from 0.1 to 75, from 0.1 to 50, from 1 to 50, from 5 to 50, from 5 to 40, from 5 to 30, from 5 to 25, or from 5 to 20 vol % of the compound of formula (I).

In other embodiments, the catholyte solution can comprises 0, 0.01, 0.05, 0.1, 0.5, 1.0, 1.5, 2.0, 2.5, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 vol % of water; or from 0.01 to 12, from 0.1 to 12, from 0.1 to 10, from 0.1 to 5, from 0.1 to 2.0, from 0.1 to 1.5 vol % of water, or less than 10 vol % of water, less than 5 vol % of water, less than 2.5 vol % of water, less than 2.0 vol % of water, less than 1.5 vol % of water, less than 1.0 vol % of water, less than 0.5 vol % of water, less than 0.1, less than 0.05, or less than 0.01 vol % of water.

In still other embodiments, the catholyte solution can comprise any suitable acid (e.g., strong acid). Examples of suitable acids include, but are not limited to hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid, nitric acid, chloric acid, perchloric acid, or a combination thereof. The concentration of the acid (e.g., strong acid) can be any suitable concentration such as but not limited to 0, 0.1, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 mM; or from 0.1 to 20, from 0.1 to 15, from 0.1 to 12, from 0.1 to 10, from 0.1 to 8, from 0.1 to 5, from 0.1 to 2, from 2 to 18, from 5 to 15, from 7 to 13, or from 8 to 12 mM.

In certain embodiments, the nonaqueous solvent in the catholyte solution can comprise any suitable solvent at any suitable concentration (e.g., 1, 2, 5, 10, 20, 30, 40, 50 60, 70, 80, 85, 90, 95, or 99 vol %). For example, the nonaqueous solvent can comprise an aprotic solvent, such as but not limited to propylene carbonate (e.g., at 90% vol %). In other embodiments, the nonaqueous solvent can comprise any suitable second supporting electrolyte at any suitable concentration (0.01, 0.05, 0.1, 0.2, 0.5, 1, 2, 3, 4, 5, 7, or 10 M). For example, the nonaqueous solvent can comprise a second supporting electrolyte, such as but not limited to NBu₄PF₆ (e.g., 1M NBu₄PF₆). In some embodiments, the catholyte solution can comprise 0.1, 0.5, 1.0, 1.5, 2.0, 2.5, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 95, 99, or 100 vol % of the nonaqueous solvent; or from 50 to 99, from 50 to 95, from 60 to 95, from 70 to 95, from 75 to 95, or from 80 to 95 vol % of the nonaqueous solvent. In other embodiments, the catholyte solution can have a surface tension of 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45 or 50 (mN/m), or from 30 to 50, from 30 to 45, from 31 to 44, from 34 to 40, from 35 to 39, or from 36 to 38 (mN/m), for example, at 20, 25, or 30° C.

Sometimes the catholyte can comprise any suitable strong acid cation exchange medium in any suitable amount for the desired process. In some instances, examples of suitable strong acid cation exchange medium for the desired process can include but are not limited to Amberlite IRC-120H or Supelco. In other instances, examples of suitable amounts of suitable strong acid cation exchange medium for the desired process can be, but is not limited to packed at 99.9, 99.8, 99.5, 99, 98, 97, 96, 95%, 90%, 80%, 75%, 50%, 25% or 10% or less than 100%, of the catholyte space.

In some embodiments, the cation exchange membrane (a) is stable or partially stable when in contact with acid, (b) blocks or partially blocks gas permeation, (c) blocks or partially blocks permeation of catholyte or permeation of chemical compounds in the catholyte (e.g., blocks or partially blocks permeation of the compound of formula (I) and/or permeation of the nonaqueous solvent), or (d) is a combination thereof.

Partially stable, as used herein, means that the cation exchange membrane does not degrade such that one or more properties of the cation exchange membrane (e.g., one or more of conductivity, ability to transport numbers of ions and water, diffusion permeability, electroosmotic permeability, value of limiting current in the current-voltage curve, ion selectivity, electrical resistance, mechanical strength, or chemical stability) are not affected (e.g., increased or decreased, as appropriate) by more than 50%, more than 40%, more than 30%, more than 20%, more than 10%, or more than 5%.

In some embodiments, the cation exchange membrane (e.g., having a first surface and a second surface) (a) comprises a polymer comprising negatively charged functional groups (e.g., SO₃, PO3, COO, and C₆H₄₀), (b) is a copolymer of poly (tetrafluoroethylene) and polysulfonyl fluoride vinyl ether (e.g., Nafion), (c) is a Fumasep cation exchange membrane, (d) comprises a polymer comprising perfluorosulfonic acid side changes (e.g., Aquivion), (e) comprise poly (norbornene) based resin (e.g., Xergy), or (f) is a combination thereof.

In some embodiments, the electrochemical cell does not comprise the cation exchange membrane.

In other embodiments, the electrochemical cell comprises an anion exchange membrane (e.g., having a first surface and a second surface). In certain embodiments, the anion exchange membrane is stable or partially stable when in contact with the catholyte and/or cathode gas diffusion elecrode. In other embodiments, the anion exchange membrane is suitable for the desired process. Examples of the anion exchange membrane include but are not limited to Selemion AMV (100 microns thick, Bellex International corporation) or Sustainion (e.g., those found at Dioxide Materials)).

Partially stable, as used herein, means that the anion exchange membrane does not degrade such that one or more properties of the anion exchange membrane (e.g., one or more of conductivity, ability to transport numbers of ions and water, diffusion permeability, electroosmotic permeability, value of limiting current in the current-voltage curve, ion selectivity, electrical resistance, mechanical strength, or chemical stability) are not affected (e.g., increased or decreased, as appropriate) by more than 50%, more than 40%, more than 30%, more than 20%, more than 10%, or more than 5%.

When used, sometimes the anion exchange membrane can be in contact with the cathode gas diffusion electrode, in contact with the catholyte, or in contact with both. When used, sometimes the anion exchange membrane is in contact with the cathode gas diffusion electrode and/or the optional cathode mesh spacer; sometimes the anion exchange membrane is also in contact with the catholyte. See, for example, Gautam et al. (2023) “Two-Membrane Dual Non-Aqueous/Aqueous Electrolyte Flow Cell Operation for Electrochemical Conversion of CO₂ to Methyl Formate” ChemSusChem, Article e202301337, 9 pages (which is incorporated by reference herein in its entirety) (see FIG. 2B in Gautam et al. 2023). See also FIG. 9 as disclosed herein.

FIG. 9A illustrates certain embodiments of the electrochemical cell, comprising a gas comprising CO₂ (901) in contact with a cathode gas diffusion electrode (902) (e.g., having a first surface and a second surface), an anion exchange membrane (907) (e.g., having a first surface and a second surface) which is in contact with the cathode gas diffusion electrode (902), a catholyte solution (903) which is in contact with the anion exchange membrane (907), a cation exchange membrane (904) (e.g., having a first surface and a second surface) which is in contact with the catholyte solution (903), an anode gas diffusion electrode (905) (e.g., having a first surface and a second surface) which is in contact with the cation exchange membrane (904), and an anolyte solution (906) which is contact with the anode gas diffusion electrode (905).

In certain aspects, the anode gas diffusion electrode (e.g., having a first surface and a second surface) can comprise any catalyst suitable to convert (e.g., selectively convert) H₂O to hydrogen ions and O₂. Suitable examples of the anode gas diffusion electrode include but are not limited to IrO₂, RuO₂, carbon paper, titanium (e.g., titanium mesh), or a combination thereof. In other embodiments, the anode gas diffusion electrode (a) is stable or partially stable against oxidation, (b) is stable or partially stable against acid (e.g., strong acid), (c) is conductive or partially conductive, or (d) is a combination thereof.

Partially stable, as used herein, means that the anode gas diffusion electrode does not degrade such that one or more properties of the anode gas diffusion electrode (e.g., one or more of electrical conductivity, surface area for catalyst attachment, mechanical stability, porosity, pore-size distribution, tortuosity, or formation factor) are not affected (e.g., increased or decreased, as appropriate) by more than 50%, more than 40%, more than 30%, more than 20%, more than 10%, or more than 5%.

In still other embodiments, the anode gas diffusion electrode is suitable for catalyzing H₂O to O₂ and hydrogen ions.

In some embodiments, the anolyte solution has a pH of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, or 3.5, or from 0.1 to 3.5, from 0.5 to 3.0, from 1.0 to 2.5, or from 1.5 to 2.0. In certain embodiments, the anolyte solution can comprise an acid such as a strong acid, including but not limited to hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid, nitric acid, chloric acid, perchloric acid, or a combination thereof. In other embodiments, the anolyte solution comprises an acid (e.g., a strong acid) at a concentration of 0.1, 0.3, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 150, or 200 mM, or from 0.1 to 200, from 0.5 to 50, from 1 to 10, from 2 to 8, or from 4 to 6 mM.

In certain embodiments, the electrochemical cell comprises a catholyte inlet port, a catholyte outlet port, or both. In some embodiments, the catholyte flow rate is 0.001, 0.01. 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.45, 0.6, 065, 0.7, 0.75, 0.8, 0.85, 0.90, 0.95, 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, or 3 mL min⁻¹, or from 0.001 to 3, from 0.25 to 2.5, or from 0.5 to 2 mL min⁻¹.

In other embodiments, the electrochemical cell comprises an anolyte inlet port, an anolyte outlet port, or both. In still other embodiments, the anolyte flow rate is 0.001, 0.01. 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.45, 0.6, 065, 0.7, 0.75, 0.8, 0.85, 0.90, 0.95, 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6, 1.7, 1.8, 1.9, 2, 2. 1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, or 3 mL min⁻¹, or from 0.001 to 3, from 0.25 to 2.5, or from 0.5 to 2 mL min⁻¹.

In yet other embodiments, electrochemical cell comprises a gas inlet port and a gas outlet port (e.g., to permit gas to be exposed to and/or to flow over the cathode gas diffusion electrode). In still other embodiments, the electrochemical cell comprises a gas inlet port and a gas outlet port, to permit a flow of a gas to be in contact with the cathode gas diffusion electrode. In some embodiments, a gas comprising CO₂ enters by the gas inlet port, the gas is in contact with the cathode gas diffusion electrode, and the processed gas exits by the gas outlet port. In certain embodiments, a gas comprising CO₂ is in contact with the cathode gas diffusion electrode. The gas comprising CO₂ can flow at any suitable rate (e.g., for a desired electrochemical reaction), including but not limited to flowing at a rate of 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, or 80 sccm (standard cubic centimeter per minute), or from 1 to 80, from 5 to 50, or from 10 to 40 sccm. The gas comprising CO₂ can comprises CO₂ at any suitable concentration (e.g., for a desired electrochemical reaction), including but not limited to a concentration of 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 98, 99, 99.9, or 100 vol %, or from 1 to 100, from 10 to 100, from 50 to 100, from 75 to 100, or from 90 to 100 vol %. The gas comprising CO₂ can comprise other gases which may or may not be suitable for the desired use (e.g., for a desired electrochemical reaction); these other gases include but are not limited to inert gases, nitrogen, oxygen, argon, methane, water vapor, neon, carbon monoxide, flue gases, gases from the output of power plants, gases from the output of industrial plants, or combinations thereof.

In certain embodiments, the electrochemical cell is suitable to convert CO₂ (e.g., the CO₂ in a gas as described herein that is in contact with the cathode gas diffusion electrode) to produce

(also referred to as —O—(O)CH) from an OH on a compound from formula (I) in the catholyte solution.

In other embodiments, the electrochemical cell is (a) suitable to convert CO₂ (e.g., the CO₂ in a gas as described herein that is in contact with the cathode gas diffusion electrode) to produce

from the OH on R—OH, (b) suitable to convert CO₂ (e.g., the CO₂ in a gas as described herein that is in contact with the cathode gas diffusion electrode) to produce one or more

from one or more hydroxyls that are a substituent of R (e.g., hydroxy (—OH) or C₁-C₈alkyl substituted with 1, 2, or 3—OH), or (c) a combination thereof.

Methods of Using Electrochemical Cells

Some embodiments of the invention include methods for converting carbon dioxide, the method comprising applying a voltage potential across the cathode gas diffusion electrode and the anode gas diffusion electrode of the electrochemical cell described herein. In certain embodiments, the voltage is sufficient to convert CO₂ (e.g., the CO₂ in a gas as described herein that is in contact with the cathode gas diffusion electrode) to produce one or more

from one or more hydroxyls of a compound of formula (I) in the catholyte solution. The method, in other embodiments, is a conversion of CO₂ (e.g., the CO₂ in a gas as described herein that is in contact with the cathode gas diffusion electrode) to produce one or more

from one or more hydroxyls of a compound of formula (I) and is (a) a conversion of CO₂ (e.g., the CO₂ in a gas as described herein that is in contact with the cathode gas diffusion electrode) to produce

from the OH on R—OH, (b) a conversion of CO₂ (e.g., the CO₂ in a gas as described herein that is in contact with the cathode gas diffusion electrode) to produce one or more

from one or more hydroxyls that are a substituent on R (e.g., hydroxy (—OH) or C₁-C₈ alkyl substituted with 1, 2, or 3—OH), or (c) a combination thereof.

In some embodiments, the method comprises applying a voltage potential across the cathode gas diffusion electrode and the anode gas diffusion electrode of the electrochemical cell as described herein, wherein the voltage is sufficient to convert CO₂ in a gas that is in contact with the cathode gas diffusion electrode to produce one or more

from one or more hydroxyls (—OH) of a compound of formula (I) in the catholyte solution.

In certain instances, the faradaic efficiency to convert CO₂ (e.g., the CO₂ in a gas as described herein that is in contact with the cathode gas diffusion electrode) to produce one or more

from one or more hydroxyls of a compound of formula (I) in the catholyte solution, is 0.1, 1, 5, 10, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 99%, or more than 10, more than 20, more than 30, more than 40, more than 45, more than 50, more than 55, more than 60, more than 65, more than 70, more than 75, more than 80, or more than 90%.

In other embodiments, the applied voltage is-1.0, −2.0, −2.5, −3.0, −3.5, −4.0, −4.5, −5.0, −5.5, −6.0, −6.5, −7.0, −7.5, −8.0, −8.5, −9.0, −9.5, −10.0, −10.5, −11.0, −11.5, −12.0, −12.5, −13.0, −13.5, or 14.0 volts (vs. anode gas diffusion electrode), or from 1.0 to 14.0, from 3.0 to 10.0, from 3.5 to 8.0, from 4.0 to 7.5 or from 4.5 to 7.0 volts (vs. anode gas diffusion electrode).

In some embodiments, the voltage is applied for 0.1, 0.5, 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 250, 300, 400, 450, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, or 1800 minutes, or from 0.1 to 1800, from 1 to 1500, from 5 to 1000, from 10 to 500, from 15 to 250, or from 15 to 180 minutes, or more than 0.1, more than 1, more than 5, more than 10, or more than 15 minutes.

In other embodiments, the current density of the cell is-0.1, −0.5, −1, −2, −3, −4, −5, −6, −7, −8, −9, −10, −11, −12, −13, −14, −15, −16, −17, −18, −19, −20, −21, −22, −23, −24, −25, −26, −27, −28, −29, −30, −32, −34, −36, −38, −40, −45, −50, −55, −60, −65, −70, −75, −80, −85, −90, −95, −100, −125, −150, −175, −200, −300, −400, or 500 mA cm⁻², or from 0.1 to 500, from 0.1 to 200, from 0.5 to 100, from 1 to 40, from 5 to 25, or from 10 to 20 mA cm⁻².

In yet other embodiments, the cell resistance is 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 32, 34, 36, 38, 40, 45, 50, 55, 60, 65, 70, 75, 80, or 90 ohms (52), or from 0.1 to 90, from 0.5 to 50, from 1 to 30, from 2 to 25, from 5 to 15, or from 6 to 9 ohms (52).

In still other embodiments, the absolute value of the current density of a compound produced from the conversion to one or more

from one or more hydroxyls of a compound of formula (I) in the catholyte solution is 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 32, 34, 36, 38, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 125, 150, 175, 200, 300, 400, or 500 mA cm⁻², or from 0.1 to 500, from 0.1 to 200, from 0.1 to 100, from 0.1 to 80, from 0.5 to 40, from 5 to 35, from 8 to 25, from 9 to 20, or from 10 to 15 mA cm⁻².

Some embodiments of the invention encompass methods for making an electrochemical cell, as described herein.

The presently disclosed subject matter is further illustrated by the following specific but non-limiting examples. The following examples may include compilations of data that are representative of data gathered at various times during the course of development and experimentation related to the present invention.

Examples

Example Set A-Electrochemical Conversion of CO₂ to Methyl Formate in an Electrochemical Cell with Mixed Propylene Carbonate (PC)/Methanol (MeOH) Catholyte

In this example, CO₂R flow electrolysis has been investigated using catholyte mixtures of Propylene Carbonate (PC)/Methanol (MeOH) with variable concentration, acidity, and CO₂ flow rate to find optimal conditions for methyl formate selectivity without flooding the GDE cathode. Further information can be found in Uttarwar et al. (2024) “Electrochemical Conversion of CO₂ to Methyl Formate in a Flow Electrolyzer with Mixed Propylene Carbonate/Methanol Catholyte” ACS Sustainable Chem. Eng., Vol. 12, pp. 13263-13273 (“Uttarwar”), which is herein incorporated by reference in its entirety. Additional information can be found in Gautam et al. (2023) “Two-Membrane Dual Non-Aqueous/Aqueous Electrolyte Flow Cell Operation for Electrochemical Conversion of CO₂ to Methyl Formate” ChemSusChem, Vol. 17, Article No. e202301337 (9 pages) (“Gautam”), which is herein incorporated by reference in its entirety.

As described in this example, methanol was mixed with propylene carbonate as a catholyte for a gas-fed CO₂ flow electrolyzer that avoided cathode flooding. Simultaneously, a dual aqueous anolyte was used for water oxidation as a scalable and sustainable anodic half-reaction. The performance effect of methanol concentration, catholyte acidity, CO₂ flow rate, and dilute water in the catholyte were investigated. In some instances, with 10 vol % methanol in 90 vol % propylene carbonate, 63% faradaic efficiency for methyl formate ester product was sustained without cathode flooding.

Experimental

Chemicals and Materials

Tetrabutylammonium hexafluorophosphate, (NBu₄PF_{6, 98}%, Thermo Scientific Chemicals), potassium chloride (KCl, ACS grade, VWR Life Science), propylene carbonate (C₄H₆₀₃, J. T. Baker), methanol (CH₃OH, ≥99.8%, VWR Chemicals BDH®), hydrochloric acid (HCl, ACS grade, Pharmco), and sulfuric acid (H₂SO₄, ACS grade, Pharmco) were used as received. The flow cell used a 5 cm² T4 titanium flowfield with a serpentine channel (Dioxide Materials) as the anode endplate, a 5 cm² 904 L stainless steel flowfield with a serpentine channel (Dioxide Materials) as the cathode endplate, and a custom-machined central compartment flow channel made of PEEK (thickness=1.5 mm). An IrO₂-coated GDE (Dioxide Materials) served as the anode, a Bi₂O₃-coated GDE (Dioxide Materials) served as the cathode, and a sheet of Nafion 117 (Ion Power) was used as a cation-exchange membrane. The projected active area of each electrode was 5 cm².

Electrochemical Measurements

In all experiments, the anolyte consisted of aqueous 5 mM H₂SO₄, which was determined to be an effective composition for stabilizing the catholyte pH at an appropriate value to maximize methyl formate selectivity. The catholyte was a mixture of 1 M NBu₄PF₆ in PC with saturated KCl (˜56 mM) in MeOH, with different supporting electrolyte salts for each solvent based on solubility and sufficient solution conductivity. The concentration of either MeOH or PC in the catholyte is hereafter referred to by the corresponding volumetric percentage (vol %) of the corresponding solvent, which in each case includes the associated ratio of the supporting electrolyte salt. The total catholyte mixture included 10 mM HCl to keep the pH low to promote methyl formate production, except where a different concentration of HCl was specified. The pH measurements were conducted using a Laqua glass body pH probe filled with saturated KCl in methanol and calibrated using aqueous buffers.

The flow electrolyzer (an embodiment of an electrochemical cell) was constructed and operated as shown in FIG. 1B-D, with pure CO₂ introduced behind the cathode GDE, anolyte introduced behind the anode GDE, and catholyte introduced into the central compartment between the cathode GDE and the membrane. A polypropylene mesh (10×10 mesh size, McMaster-Carr) was inserted between the cathode GDE and the membrane to maintain a consistent catholyte flow spacing and prevent the Nafion from touching the GDE during swelling and deformation when exposed to flowing PC/MeOH. A mass flow controller (Teledyne Hastings Instruments) provided CO₂ at a flow rate of 20 sccm (unless stated otherwise), a peristaltic pump (Masterflex L/S) provided an anolyte flow rate of 1.0 mL min⁻¹, and a syringe pump (NE-300 Just Infusion) provided a catholyte flow rate of 0.8 mL min⁻¹, with both catholyte and anolyte flowing in a single-pass configuration. The Nafion membrane was presoaked overnight in the experimental catholyte mixture and subsequently rinsed with DI water on the anode-facing side prior to measurements. Electrochemical measurements were performed using a Gamry 1000E potentiostat. Current density vs potential behavior was measured at a scan rate of 25 mV s⁻¹. The uncompensated cell resistance, R_s, was measured using electrochemical impedance spectroscopy (EIS). Product FEs were determined from chronopotentiometric bulk electrolyses at a constant current density of 20 mA cm⁻², except when determining potential-dependent behavior, in which case electrolyses were conducted at a corresponding constant potential. In each case, FEs were determined after 15 min of electrolysis. Product molar formation rate and the product output concentration can be determined from the experimental data as described in the SI.

Product Quantification

Gaseous products were analyzed by gas chromatography (GC, SRI 8610) with in-line GC measurements with a thermal conductivity detector (TCD) and flame ionization detector (FID) and quantified using corresponding calibration gases. Liquid products were analyzed by proton nuclear magnetic resonance (1H-NMR) spectroscopy (Agilent V NMRS 700 MHz). For NMR product analysis, 600 μL of the catholyte was mixed with 200 μL d6-DMSO (Cambridge Isotopes, 99.9%) and a DMF internal standard at a final concentration of 3 mM. Samples were then analyzed in an NMR equipped with an HCN cryoprobe using two-signal solvent suppression pulse sequence. The integration of formic acid and methyl formate peaks were measured against the DMF internal standard using a calibration curve. FEs were calculated by determining the charge required to produce the measured species concentration and dividing by the total charge passed during that period of electrolysis as measured by the potentiostat. FE error bars represent the standard deviation in three separate experiments.

Solvent Fluid Property Measurements

The surface tension of catholyte mixtures were measured with an automatic surface tensiometer (Kyowa DY-300). The contact angle for catholyte mixtures was measured on 50% wet-proofed Toray paper GDEs using an optical imaging goniometer (Biolin Scientific, Attension Theta Lite) in the static contact angle mode. Viscosity of catholyte mixtures was measured at 25° C. with a viscometer (RheoSense micro VISC).

Results and Discussion

Effect of Methanol Concentration

The use of pure MeOH solvent in the catholyte in a single-membrane flow reactor design leads to catholyte wetting and crossover of the porous GDE. This is due to the low surface tension of MeOH and corresponding low contact angle on the PTFE wet-proofed Toray paper GDE surface. As seen in the goniometer optical images, the contact angle for 100 vol % MeOH on the GDE was only 65.9° (FIG. 2). PC, with a notably higher surface tension, resulted in a 151.7° contact angle. Surfaces are considered to be superhydrophobic or superoleophobic when the contact angle of water droplets or oil droplets, respectively, is >150°. Thus, the wet-proofed GDE was effectively super-repellent to PC, indicating that it should be resistant to flooding under typical operating conditions in pure PC. However, MeOH is required in the catholyte for electrochemical CO₂R with in-situ esterification to methyl formate, so the solvent fluid properties were evaluated with variable concentrations of MeOH in PC. While the surface tension decreased steadily with increasing MeOH vol %, the corresponding contact angle dropped rapidly with the addition of small amounts of MeOH. At only 10 vol % MeOH in PC, the contact angle dropped to 115.8°, lower than a pure PC droplet, but much higher than a pure MeOH droplet and still effectively non-wetting on the GDE. Between 20-80 vol % MeOH, the contact angle decreased slowly with increasing MeOH before dropping sharply again at higher MeOH concentrations (FIG. 2D). The criteria for avoiding GDE flooding thus favors low MeOH content in the catholyte. The viscosity for PC/MeOH mixtures at room temperature was measured as well, with 7.1 cP for 1 M NBu₄PF₆ in 100 vol % PC rapidly dropping upon the addition of MeOH and approaching 0.6 cP for sat. KCl in 100 vol % MeOH (FIG. 2E).

The electrochemical CO₂R performance of the flow electrolyzer with catholyte mixtures of saturated KCl in MeOH and 1 M NBu₄PF₆ in PC was evaluated as a function of the MeOH concentration as shown in FIG. 3. The current density vs potential (J-E) behavior was a strong function of the catholyte composition (FIG. 3A), as was the corresponding product distribution (FIG. 3B). For pure PC (0 vol % MeOH), the current density started out very low, then increased rapidly with MeOH, peaking at 10 vol % MeOH before declining again to a local minimum at 50 vol % MeOH, and then peaking again at 90 vol % MeOH (FIG. 3C). With 100 vol % MeOH, the current density dropped sharply again, correlated with the observation of GDE flooding and catholyte crossover into the gas-fed CO₂ chamber. Flooding, as determined by liquid catholyte exiting in the gaseous CO₂ outlet stream, was only observed for the case of pure MeOH. The MeOH-concentration-dependent current density was consistent with a similar trend measured by EIS for the cell resistance (FIG. 3D), indicating that solution and membrane conductivity played a significant role in affecting the flow electrolyzer current density.

With pure PC (0 vol % MeOH), the cell displayed no methyl formate production, as expected in the absence of MeOH as a reactant (FIG. 1A), but also yielded no formic acid. The lack of formic acid may be related to the limited proton availability in the aprotic PC, with the low H+ concentration from the dilute acid preferentially directed toward HER to yield 14.8% H₂ FE (FIG. 3B). While there was some CO detected (10.6% FE), more than 74% of the charge passed in pure PC catholyte did not result in a product observed with either GC or 1H-NMR. Most of this charge was assumed to go to the production of oxalate anions, which are the majority CO₂R product in aprotic PC. With the addition of only 1 vol % MeOH, methyl formate was detected at 8.8% FE along with 6.7% FE for unconverted formic acid. The methyl formate selectivity reached a maximum at 62.5% FE with 10 vol % MeOH, with only 0.9% FE for formic acid. Indeed, while the equilibrium conversion of formic acid to methyl formate was incomplete at low MeOH concentrations, at 10 vol % MeOH and above the conversion was generally high (≥95 mol %) (FIG. 3E). A minimal concentration of MeOH appeared to be needed to promote the acid-catalyzed Fischer esterification reaction (FIG. 1B).

Interestingly, there was an increase in the cell resistance and decrease in the current density measured at intermediate MeOH concentrations which coincided with a decrease in CO₂R FE in this range (˜ 30-70 vol % MeOH). Without wishing to be bound by theory, this may have to do with non-ideal interactions in the binary mixture between aprotic PC and protic MeOH. The viscosity of PC/MeOH mixtures decreases with increasing MeOH content without any maxima at intermediate composition (FIG. 2E), so the decreased electrolyzer performance in this range is not likely attributable to viscosity effects. However, there is an appreciable negative excess molar volume for binary mixtures of PC+MeOH that peaks at intermediate compositions, indicating that the components can fit into each other's structure to an extent, causing a decrease in the volume of the mixture. Moreover, the supporting electrolyte ion mobilities and associated solution conductivity are complex, with the cation and anion solvation depending on the ion species and the solvent mixture composition.

At higher MeOH concentration beyond the intermediate composition range (60-90 vol % MeOH), the cell resistance decreased and the methyl formate and overall CO₂R FE increased with increasing MeOH content (FIGS. 3B and 3D). With pure 100 vol % MeOH, the methyl formate selectivity at the galvanostatic condition of −20 mA cm⁻² remained relatively high at 39% FE, but the corresponding cell potential required to reach this current density jumped from 4.2 V at 90 vol % MeOH to 7.0 V at 100 vol % MeOH (FIG. 3D). The sharp increase in cell potential was attributed to increased CO₂R overpotential due to flooding of the cathode GDE which occurred with pure MeOH.

The maximum methyl formate FE (62.5%) occurred with 10 vol % MeOH, which also corresponded to a minimal cell resistance (8.9 (2). Moreover, this catholyte composition was deemed more ideal than the low resistance condition at 90 vol % MeOH because the low MeOH content at 10 vol % had a much higher contact angle to the Toray paper GDE (FIG. 2), thus promoting stability against flooding under extended operation. A catholyte composition of 90/10 vol % PC/MeOH was thus selected as the default for further investigating system parameter effects on the flow electrolyzer performance.

Effect of Catholyte Acidity

The in-situ Fischer esterification of formic acid product to methyl formate sometimes uses low pH conditions. The aqueous anolyte contained 5 mM H₂SO₄ without a supporting electrolyte salt to ensure that charge balance was promoted by the migration of protons across the membrane, thus helping to stabilize the low pH in the catholyte during operation. However, a dilute acid was also added to the catholyte to give it a starting pH in the ideal range to promote methyl formate production. The catholyte acid concentration was varied from 0-15 mM HCl to investigate its effect on the flow electrolyzer behavior (FIG. 4).

As seen in the J-E curves, the current density increased with increasing catholyte HCl concentration (FIG. 4A). This behavior corresponded to a near-linear decrease in the cell resistance with added HCl in this range, from 13.5 $2 without HCl to 7.0 52 with 15 mM HCl. The total cell potential required to pass-20 mA cm⁻² likewise decreased significantly with added catholyte acid concentration (FIG. 4C). The acid ions help to improve both the non-aqueous catholyte solution conductivity and the Nafion permselective cation-exchange membrane ion conductivity.

However, analysis of the product distribution indicated that there was an optimal catholyte acid concentration for methyl formate selectivity (FIG. 4B). Even without added HCl, the initial catholyte pH was high but finished electrolysis at a low value due to proton migration from the anolyte (FIG. 4D), which explains how 26.9% FE for methyl formate was produced at this condition. However, formic acid at 6.4% FE was detected as well, indicating low overall selectivity and poor conversion by esterification in the absence of catholyte HCl. The methyl formate plus formic acid FE increased with the addition of 5 mM HCl but still with incomplete conversion to methyl formate. At 10 mM HCl in the catholyte, the methyl formate FE increased further to 62.5% with almost complete conversion of formic acid. Upon a further increase to 15 mM HCl, however, the methyl formate FE dropped to 42.7% despite complete formic acid conversion and a higher total current density (FIG. 4B and FIG. 4D). The additional current at 15 mM HCl can be attributed primarily to an increase in HER from the increased proton availability, as reflected by the increase in H₂ FE. Thus, while higher catholyte acid concentration lowers the cell resistance and improves both current density and formic acid conversion to methyl formate, beyond 10 mM HCl the high H+ concentration begins to degrade the methyl formate selectivity.

Effect of CO₂ Flow Rate

Achieving the highest CO₂R activity and selectivity for methyl formate in this single-membrane GDE-based flow electrolyzer also required a careful balance of the gaseous CO₂ flow rate. FIG. 5 shows the flow cell performance variation for 90/10 vol % PC/MeOH catholyte using CO₂ flow rates of 10, 20, and 40 sccm. There was a strong current density and methyl formate FE dependence on the CO₂ flow rate, with the peak performance achieved at 20 sccm with 62.5% methyl formate FE. At 10 sccm, the J-E curve displayed the lowest current density and only 31.6% FE for methyl formate. Then at the higher 40 sccm flow rate, the J-E curve again dropped to lower current density values and the methyl formate FE was only 37.6%. These results are consistent with pressure effects in the gaseous CO₂ chamber leading to consequences at the GDE/CO₂/catholyte interface. At the low flow 10 sccm condition, the CO₂ was supplied at a lower total mass flux and the resulting lower pressure behind the GDE may have further slowed the transfer of CO₂ to the catalyst sites, thus leading to lower current density. At the high flow 40 sccm condition, the buildup of pressure behind the GDE is likely to have forced gas bubbles of CO₂ through the porous carbon layer and into the liquid PC/MeOH layer (FIG. 1). This explanation was supported by the observation of a notably greater quantity of gas bubbles exiting the flow cell in the liquid catholyte outlet stream. With gas bubbles crossing the GDE/catholyte interface, a portion of the cathode catalyst would be expected to be blocked from the electrolyte, effectively decreasing the active area and lowering the current density, which was consistent with the measured flow cell behavior. In this flow cell arrangement, a flow rate of 20 sccm CO₂ seems to have appropriately balanced the pressure to optimize the CO₂ mass flux to the catalyst, resulting in the maximum corresponding current density and methyl formate FE (FIG. 5 and FIG. 5D).

Effect of Applied Potential

The flow cell performance for most of the previous conditions was measured galvanostatically at 20 mA cm⁻². To gauge the effect of applied potential, the cell was also investigated potentiostatically with 90/10 vol % PC/MeOH with 10 mM HCl and 20 sccm CO₂ at a range of potentials from 4.5 to 7.0 V total cell voltage (FIG. 6). Despite the high applied bias, the average current density during chronoamperometric electrolysis increased only modestly in a relatively linear fashion (FIG. 6A). A more linear J-E behavior, rather than the exponential current density increase expected of Butler-Volmer kinetics, is indicative of a large ohmic overpotential. The high cell resistance, measured at 7.1-8.0 52 in this range (FIG. 6C), thus highlights the challenge of achieving high-current-density performance in organic solvent-based electrolysis.

The product distribution vs applied potential showed an interesting trend, with the H₂ FE and total CO₂R FE remaining consistent at 7.3-11.0% and 84.1-90.9%, respectively (FIG. 6B). The steady overall CO₂R FE indicates that the reaction was not limited by the mass-transfer of CO₂ even at the higher current density conditions. Furthermore, the molar conversion of formic acid to methyl formate remained nearly complete at all the measured potentials (FIG. 6D), indicating the stabilization of a sufficiently low pH to promote esterification. Notably, however, the methyl formate FE steadily decreased, offset by an increasing CO FE, as the applied bias to the flow cell was increased. Because of the declining methyl formate selectivity, the partial current density for methyl formate only increased modestly with higher cell voltages (FIG. 6C). The decrease in the selectivity for methyl formate despite a steady total CO₂R FE suggests that the proton source may be limiting the production of the formic acid intermediate at higher current densities. In this case the catholyte was 90 vol % aprotic PC, which is highly immiscible with water and thus strongly limits H₂O crossover from the anolyte.⁴⁸ Thus, the concentration of protons was low and only available from the dilute acid or the MeOH solvent, which limits HER and favors CO over HCOOH formation at higher current densities.

Effect of Water in the Catholyte

The hypothesis of a lack of available protons due to low catholyte water content affecting the product distribution was tested by the deliberate introduction of dilute (1 vol %) H₂O into the catholyte. Although H₂O is largely immiscible with PC, it is miscible with MeOH. Therefore, the flow electrolyzer was investigated with a catholyte composition of 90/9/1 vol % PC/MeOH/H₂O to determine what effect the added protic aqueous solvent would have on the performance. Even this dilute 1 vol % water made a significant difference, leading to an enhancement in the current density of the flow cell J-E curves (FIG. 7A). In this case, the cell resistance was 6.8 52, compared to ˜ 8 52 without water, highlighting that even a small amount of water improved the solution and membrane conductivity. The added catholyte H₂O served as an extra source of readily available protons, which led to a significant increase in the H₂ FE at both-4.5 and 7.0 V (FIG. 7B). Because of the increase in H₂ FE, the methyl formate FE did not actually increase in the presence of dilute water. However, with a more available proton source, methyl formate did represent a larger portion of the CO₂R products than CO compared to the case without water. With the increase in current density with dilute water, the partial current density for methyl formate was appreciably higher at 7.0 V relative to the condition without water. Besides the higher FE for H₂ byproduct, the other disadvantage of including water is that it drives the equilibrium for the in-situ esterification reaction back toward formic acid (FIG. 1A). The molar conversion of formic acid to methyl formate declined from 99.5% without H₂O to 81.5% with only 1 vol % H₂O. Thus, the conditions for high methyl formate selectivity without water led to much higher energetic efficiency for CO₂ conversion to methyl formate.

Extended Electrolysis

The durability of the flow electrolyzer performance was tested in 90/10 vol % PC/MeOH catholyte with 10 mM HCl and a flow of 20 sccm CO₂ under galvanostatic conditions at 20 mA cm⁻² for 180 min (FIG. 8). While the molar conversion of formic acid and the methyl formate selectivity remained steady during extended electrolysis, the required cell voltage did not. The applied bias increased significantly over the three-hour electrolysis (FIG. 8A). Notably however, this decline was reversible, and the potential was observed to spike back toward the initial value at times (e.g., ˜ 45 and 120 min) corresponding to a replenishment of catholyte in the syringe pump feeding the central compartment. The flow electrolyzer was operated in a single-pass configuration, meaning that the composition of the catholyte entering the cell did not change throughout the electrolysis. Without wishing to be bound by theory, it is possible that the observed potential drop with the changing of the syringe pump instead reflects a rapid change in the pressure within the cathode chamber. The increase in cell voltage during extended electrolysis may thus correlate to rising backpressure within the cell or trapped bubbles at the GDE or in the PTFE mesh spacer (FIG. 1).

The methyl formate selectivity during extended electrolysis remained fairly steady, holding between 56-67% FE, corresponding to a partial current density of 11.2-13.4 mA cm⁻² (FIG. 8B). Only small quantities of unconverted formic acid were detected, as the measured catholyte pH in this non-aqueous binary solvent mixture remained steady at a sufficiently low value to promote near complete esterification to methyl formate (FIG. 8C). However, one notable change occurred in the gas product evolution over the course of the extended electrolysis. The CO FE decreased from an initial value of 17.6% to 11.0% after 180 min, accompanied by a concomitant increase in CH₄ FE from an initial value of 0.0% (undetected) to 9.3% after 180 min.

CONCLUSIONS

A single-membrane GDE-based flow electrolyzer was modified to perform electrochemical CO₂R in a non-aqueous catholyte coupled with aqueous anolyte for scalability and sustainability. To prevent wetting and flooding of the cathode GDE, higher surface tension aprotic PC solvent was combined with lower surface tension MeOH solvent as a reactant to form a binary solvent mixture catholyte of useful properties for gas-fed CO₂ flow electrolysis to produce methyl formate. Good methyl formate selectivity was achieved with 90 vol % PC and 10 vol % MeOH, reaching an average FE of 62.5% at a current density of 20 mA cm⁻². High concentrations of MeOH trended toward high methyl formate FE as well, but the low surface tension of the dominant MeOH component made these compositions more prone to GDE flooding which would impede CO₂ mass transfer. Also, an additional 10 mM HCl in the catholyte was included, with less acid leading to less esterification to methyl formate, and more acid leading to an increase in byproduct H₂ formation. The CO₂ gas flow rate was also varied, with 20 sccm found to be a good balance for high CO₂ mass flux without causing excess backpressure and CO₂ bubbling across the GDE/catholyte interface. Although the inclusion of dilute water in the catholyte helped to lower the cell resistance and increase the current density, even a small quantity of water decreased the conversion of formic acid to methyl formate via Fischer esterification. A three-hour chronopotentiometric electrolysis demonstrated durable high methyl formate selectivity in this reactor, but the cell performance demonstrated a reversible increase in overpotential that was attributed to pressure effects at the cathode.

The prevention of cathode GDE flooding and the minimization of anolyte water crossover enabled by the use of PC in the catholyte made it possible to achieve high methyl formate FE in a single-membrane gas-fed flow electrolyzer.

Example Set B-A two membrane example of the electrochemical cell

An illustrative embodiment to decrease flooding of the cathode GDE with methanol is demonstrated with FIG. 9. FIG. 9A shows an illustrative embodiment of a two membrane electrochemical cell which comprises an anion exchange membrane (907) between the cathode GDE (902) and the catholyte (903). FIG. 9A illustrates certain embodiments of the electrochemical cell, comprising a gas comprising CO₂ (901) in contact with a cathode gas diffusion electrode (902), an anion exchange membrane (907) which is in contact with the cathode gas diffusion electrode (902), a catholyte solution (903) which is in contact with the anion exchange membrane (907), a cation exchange membrane (904) which is in contact with the catholyte solution (903), an anode gas diffusion electrode (905) which is in contact with the cation exchange membrane (904), and an anolyte solution (906) which is contact with the anode gas diffusion electrode (905).

FIG. 9B shows a schematic representation of an embodiments of the electrochemical cell. In this design, an anion exchange membrane (AEM) is on the cathode side. This can sometimes lead to alkaline conditions for CO₂R and encourages crossover of the formate anion, HCOO″, to the central compartment where it can recombine with protons from the anode crossing the CEM. In addition, unconverted CO₂ at the AEM interface can react with the produced OH to form bicarbonate, which also migrates across the AEM. FIG. 9B shows amberlite strong acid cation exchange media in the central compartment, which leads to acidic conditions in the catholyte that promote the formation of protonated formic acid.

Example Set C-Certain Embodiments

1. An electrochemical cell comprising

• • a cathode gas diffusion electrode comprising a cathode catalyst and a cathode substrate,
  • optionally, a cathode mesh spacer,
  • a catholyte solution which is in contact with the cathode gas diffusion electrode,
  • a cation exchange membrane which is in contact with the catholyte solution,
  • an anode gas diffusion electrode which is in contact with the cation exchange membrane, and
  • an anolyte solution which is contact with the anode gas diffusion electrode;
    wherein
  • (i) the catholyte solution comprises
    • (a) a compound of formula (I)

• • where R is an C₁-C₁₂ alkyl, C₂-C₁₂ alkenyl, C₂-C₁₂ alkynyl, C₂-C₁₂ alkoxy, aryl, cycloalkyl, heteroaryl, or heterocyclyl, which C₁-C₁₂ alkyl, C₂-C₁₂ alkenyl, C₂-C₁₂ alkynyl, C₂-C₁₂ alkoxy, aryl, cycloalkyl, heteroaryl, or heterocyclyl can optionally be substituted with one or more of halogen (e.g., F, Cl, Br, or I), hydroxy (—OH), methanoyl (—COH), carboxy (—CO₂H), nitro (—NO₂),—NH₂,—N(CH₃)₂, cyano (—CN), ethynyl (—CCH), propynyl, sulfo (—SO₃H), morpholinyl,—CO-morpholin-4-yl,—C(O) NH₂, —C(O) N (CH₃)₂, C₁-C₃ alkyl, C₁-C₃ perfluoronated alkyl,—CF₃,—OCF₃, C₁-C₃ alkoxy, or C₁-C₈ alkyl substituted with 1, 2, or 3—OH.
    • (b) less than 12 vol % of water,
    • (c) less than 20 mM of a strong acid, and
    • (d) a nonaqueous solvent (e.g., the nonaqueous solvent is not a compound of formula I, such as methanol), and
  • (ii) the anolyte solution is an aqueous solution with a pH from 0.1 to 3.5.

2. The electrochemical cell of embodiment 1, wherein the cathode gas diffusion electrode comprises any catalyst suitable to convert (e.g., selectively convert) CO₂ to formate or formic acid, Pb, SnO, Bi metal, Zn, Pd, or Bi₂O₃, or an alloy thereof, or carbon paper, carbon fibers, glassy carbon, carbon nanofibers, carbon nanotubes, graphene, metallic foam, or a combination thereof.

3. The electrochemical cell of any of the previous embodiments, wherein

• • the cathode catalyst comprises any catalyst suitable to convert (e.g., selectively convert) CO₂ to formate or formic acid, Pb, SnO, Bi metal, Zn, Pd, or Bi₂O₃, or an alloy thereof, or a combination thereof.

4. The electrochemical cell of any of the previous embodiments, wherein the cathode substrate comprises carbon paper, carbon fibers, glassy carbon, carbon nanofibers, carbon nanotubes, graphene, metallic foam, or a combination thereof.

5. The electrochemical cell of any of the previous embodiments, wherein the cathode gas diffusion electrode is (a) stable or partially stable when in contact with acid, (b) stable or partially stable against reduction, (c) microporous or partially microporous (e.g., to gases), (d) conductive or partially conductive, or (e) a combination thereof.

6. The electrochemical cell of any of the previous embodiments, wherein the catalyst of the cathode gas diffusion electrode is suitable for catalyzing CO₂ to HC (O) OH.

7. The electrochemical cell of any of the previous embodiments, wherein the electrochemical cell comprises the cathode mesh spacer, the cathode mesh spacer is in contact with the cathode gas diffusion electrode, the cathode mesh spacer is in contact with the catholyte, and the cathode gas diffusion electrode is in contact with the catholyte.

8. The electrochemical cell of any of the previous embodiments, wherein the electrochemical cell comprises the cathode mesh spacer and the cathode mesh spacer comprises polytetrafluoroethylene or polypropylene.

9. The electrochemical cell of any of the previous embodiments, wherein R is an C₁-C₁₂ alkyl, C₂-C₁₂ alkoxy, cycloalkyl, or heterocyclyl, which C₁-C₁₂ alkyl, C₂-C₁₂ alkoxy, cycloalkyl, or heterocyclyl can optionally be substituted with one or more of halogen (e.g., F, Cl, Br, or I), hydroxy (—OH), methanoyl (—COH), carboxy (—CO₂H), nitro (—NO₂),—NH₂,—N(CH₃)₂, cyano (—CN), ethynyl (—CCH), propynyl, sulfo (—SO₃H), morpholinyl,—CO-morpholin-4-yl,—C(O) NH₂,—C(O) N (CH₃)₂, C₁-C₃ alkyl, C₁-C₃ perfluoronated alkyl,—CF₃,—OCF₃, C₁-C₃ alkoxy, or C₁-C₈ alkyl substituted with 1, 2, or 3—OH.

10. The electrochemical cell of any of the previous embodiments, wherein R is an C₁-C₁₂ alkyl, C₂-C₁₂ alkoxy, cycloalkyl, or heterocyclyl, which C₁-C₁₂ alkyl, C₂-C₁₂ alkoxy, cycloalkyl, or heterocyclyl can optionally be substituted with one or more of halogen (e.g., F, Cl, Br, or I), hydroxy (—OH), nitro (—NO₂),—NH₂,—N(CH₃)₂, cyano (—CN), ethynyl (—CCH), propynyl, sulfo (—SO₃H), morpholinyl, C₁-C₃ alkyl, C₁-C₃ perfluoronated alkyl,—CF₃,—OCF₃, C₁-C₃ alkoxy, or C₁-C₈alkyl substituted with 1, 2, or 3—OH.

11. The electrochemical cell of any of the previous embodiments, wherein R is an C₁-C₁₂ alkyl, which C₁-C₁₂ alkyl can optionally be substituted with one or more of halogen (e.g., F, Cl, Br, or I), hydroxy (—OH), nitro (—NO₂),—NH₂,—N(CH₃)₂, cyano (—CN), ethynyl (—CCH), propynyl, sulfo (—SO₃H), morpholinyl, C₁-C₃ alkyl, C₁-C₃ perfluoronated alkyl,—CF₃,—OCF₃, C₁-C₃ alkoxy, or C₁-C₈ alkyl substituted with 1, 2, or 3—OH.

12. The electrochemical cell of any of the previous embodiments, wherein R is an C₁-C₆ alkyl, which C₁-C₆ alkyl can optionally be substituted with one or more of halogen (e.g., F, Cl, Br, or I), hydroxy (—OH),—NH₂,—N(CH₃)₂, ethynyl (—CCH), propynyl, C₁-C₃ alkyl, C₁-C₃ perfluoronated alkyl,—CF₃,—OCF₃, C₁-C₃ alkoxy, or C₁-C₈ alkyl substituted with 1, 2, or 3—OH.

13. The electrochemical cell of any of the previous embodiments, wherein formula (I) is methanol, ethanol, propenol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, or decanol.

14. The electrochemical cell of any of the previous embodiments, wherein formula (I) is methanol, ethanol, propenol, or butanol.

15. The electrochemical cell of any of the previous embodiments, wherein a composition comprising the compound of formula (I) (e.g., as added to the catholyte solution) further comprises a first supporting electrolyte (e.g., KCl) at any suitable concentration (e.g., saturated KCl).

16. The electrochemical cell of any of the previous embodiments, wherein the catholyte solution comprises 0.1, 0.5, 1.0, 1.5, 2.0, 2.5, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 95, 99, or 100 vol % of the compound of formula (I); or 0.1 to 100, from 0.1 to 99, from 0.1 to 75, from 0.1 to 50, from 1 to 50, from 5 to 50, from 5 to 40, from 5 to 30, from 5 to 25, or from 5 to 20 vol % of the compound of formula (I).

17. The electrochemical cell of any of the previous embodiments, wherein the catholyte solution comprises 0, 0.01, 0.05, 0.1, 0.5, 1.0, 1.5, 2.0, 2.5, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 vol % of water; or from 0.01 to 12, from 0.1 to 12, from 0.1 to 10, from 0.1 to 5, from 0.1 to 2.0, from 0.1 to 1.5 vol % of water, or less than 10 vol % of water, less than 5 vol % of water, less than 2.5 vol % of water, less than 2.0 vol % of water, less than 1.5 vol % of water, less than 1.0 vol % of water, less than 0.5 vol % of water, less than 0.1, less than 0.05, or less than 0.01 vol % of water.

18. The electrochemical cell of any of the previous embodiments, wherein the strong acid in the catholyte solution comprises hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid, nitric acid, chloric acid, perchloric acid, or a combination thereof.

19. The electrochemical cell of any of the previous embodiments, wherein the concentration of the strong acid in the catholyte solution is 0, 0.1, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 mM; or from 0.1 to 20, from 0.1 to 15, from 0.1 to 12, from 0.1 to 10, from 0.1 to 8, from 0.1 to 5, from 0.1 to 2, from 2 to 18, from 5 to 15, from 7 to 13, or from 8 to 12 mM.

20. The electrochemical cell of any of the previous embodiments, wherein the nonaqueous solvent in the catholyte solution comprises an aprotic solvent (e.g., propylene carbonate).

21. The electrochemical cell of any of the previous embodiments, wherein the nonaqueous solvent further comprises a second supporting electrolyte (e.g., NBu₄PF₆) at any suitable concentration (e.g., 1M NBu₄PF₆).

22. The electrochemical cell of any of the previous embodiments, wherein the catholyte solution comprises 0.1, 0.5, 1.0, 1.5, 2.0, 2.5, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 95, 99, or 100 vol % of the nonaqueous solvent; or from 50 to 99, from 50 to 95, from 60 to 95, from 70 to 95, from 75 to 95, or from 80 to 95 vol % of the nonaqueous solvent.

23. The electrochemical cell of any of the previous embodiments, wherein the cation exchange membrane (a) is stable or partially stable when in contact with acid, (b) blocks or partially blocks gas permeation, (c) blocks or partially blocks chemical compounds (e.g., permeation of the compound of formula (I) and/or permeation of the nonaqueous solvent), or (d) a combination thereof.

24. The electrochemical cell of any of the previous embodiments, wherein the cation exchange membrane (a) comprises a polymer comprising negatively charged functional groups (e.g., SO₃″, PO3, COO, and C₆H₄₀), (b) is a copolymer of poly (tetrafluoroethylene) and polysulfonyl fluoride vinyl ether (e.g., Nafion), (c) is a.

Fumasep cation exchange membrane, (d) comprises a polymer comprising perfluorosulfonic acid side changes (e.g., Aquivion), (e) comprise poly (norbornene) based resin (e.g., Xergy), or a combination thereof.

25. The electrochemical cell of any of the previous embodiments, wherein

• • the anode gas diffusion electrode comprises any catalyst suitable to convert (e.g., selectively convert) H₂O to hydrogen ions and O₂, IrO₂, RuO₂, carbon paper, titanium (e.g., titanium mesh), or a combination thereof

26. The electrochemical cell of any of the previous embodiments, wherein the anode gas diffusion electrode (a) is stable or partially stable against oxidation, (b) is stable or partially stable against acid (e.g., strong acid), (c) is conductive or partially conductive, or (d) a combination thereof.

27. The electrochemical cell of any of the previous embodiments, wherein the anode gas diffusion electrode is suitable for catalyzing H₂O to O₂ and hydrogen ions.

28. The electrochemical cell of any of the previous embodiments, wherein the anolyte solution has a pH of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, or 3.5, or from 0.1 to 3.5, from 0.5 to 3.0, from 1.0 to 2.5, or from 1.5 to 2.0.

29. The electrochemical cell of any of the previous embodiments, wherein the anolyte solution comprises a strong acid (e.g., comprises hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid, nitric acid, chloric acid, perchloric acid, or a combination thereof).

30. The electrochemical cell of any of the previous embodiments, wherein the catholyte further comprises a strong acid cation exchange medium (e.g., Amberlite IRC-120H, Supelco) in an amount suitable for the desired process (e.g., packed at 100%, 95%, 90%, 80% 75%, 50%, 25% or 10% of the catholyte space).

31. The electrochemical cell of any of the previous embodiments, wherein

• • (a) the electrochemical cell optionally does not comprise the cation.

exchange membrane and

• • (b) the electrochemical cell further comprises an anion exchange membrane which is stable or partially stable when in contact with the catholyte, which is suitable for the desired process (e.g., Selemion AMV (100 microns thick, Bellex International corporation) or Sustainion (e.g., those found at Dioxide Materials)) and which is in contact with the cathode gas diffusion electrode and also in contact with the catholyte. See, for example, Gautam et al. (2023) “Two-Membrane Dual Non-Aqueous/Aqueous Electrolyte Flow Cell Operation for Electrochemical Conversion of CO₂ to Methyl Formate” ChemSusChem, Article e202301337, 9 pages (incorporated herein by reference in its entirety).

32. The electrochemical cell of any of the previous embodiments, wherein the electrochemical cell further comprises a catholyte inlet port, a catholyte outlet port, or both.

33. The electrochemical cell of any of the previous embodiments, wherein (a) the electrochemical cell further comprises a catholyte inlet port and a catholyte outlet port and (b) the catholyte flow rate is 0.001, 0.01. 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.45, 0.6, 065, 0.7, 0.75, 0.8, 0.85, 0.90, 0.95, 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, or 3 mL min⁻¹, or from 0.001 to 3, from 0.25 to 2.5, or from 0.5 to 2 mL min⁻¹.

34. The electrochemical cell of any of the previous embodiments, wherein the electrochemical cell further comprises an anolyte inlet port, an anolyte outlet port, or both.

35. The electrochemical cell of any of the previous embodiments, wherein (a) the electrochemical cell further comprises an anolyte inlet port and an anolyte outlet port and (b) the anolyte flow rate is 0.001, 0.01. 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.45, 0.6, 065, 0.7, 0.75, 0.8, 0.85, 0.90, 0.95, 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, or 3 mL min⁻¹, or from 0.001 to 3, from 0.25 to 2.5, or from 0.5 to 2 mL min⁻¹.

36. The electrochemical cell of any of the previous embodiments, wherein the electrochemical cell further comprises a gas inlet port and a gas outlet port, to permit gas to be exposed to the cathode gas diffusion electrode.

37. The electrochemical cell of any of the previous embodiments, wherein a gas comprising CO₂ enters by the gas inlet port, the gas is exposed to the cathode gas diffusion electrode, and the processed gas exits by the gas outlet port.

38. The electrochemical cell of any of the previous embodiments, wherein a gas comprising CO₂ is exposed to the cathode gas diffusion electrode, and the gas comprising CO₂ flows at a rate of 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, or 80 sccm (standard cubic centimeter per minute), or from 1 to 80, from 5 to 50, or from 10 to sccm.

39. The electrochemical cell of any of the previous embodiments, wherein a gas comprising CO₂ comprises CO₂ at a concentration of 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 98, 99, 99.9, or 100 vol %, or from 1 to 100, from 10 to 100, from 50 to 100, from 75 to 100, or from 90 to 100 vol %.

40. The electrochemical cell of any of the previous embodiments, wherein a gas comprising CO₂ comprises other gases (e.g., inert gases, nitrogen, oxygen, argon, methane, water vapor, neon, carbon monoxide, flue gases, gases from the output of power plants, or gases from the output of industrial plants).

41. The electrochemical cell of any of the previous embodiments, wherein the electrochemical cell is suitable to convert CO₂ to produce —O—(O)CH from an OH on a compound from formula (I) in the catholyte solution.

42. The electrochemical cell of any of the previous embodiments, wherein the electrochemical cell is (a) suitable to convert CO₂ to produce —O—(O)CH from the OH on R—OH, (b) suitable to convert CO₂ to produce —O—(O)CH from one or more hydroxide moieties that are a substituent of R (e.g., hydroxy (—OH) or C₁-C₈alkyl substituted with 1, 2, or 3—OH), or (c) a combination thereof.

43. A method for converting carbon dioxide, the method comprising

• • applying a voltage potential across the cathode gas diffusion electrode and the anode gas diffusion electrode of the electrochemical cell according to any of the previous embodiments;
  • wherein the voltage is sufficient to convert CO₂ to produce-O—(O)CH from one or more hydroxyls of a compound of formula (I) in the catholyte solution.

44. The method of embodiment 43 or the electrochemical cell of embodiments 1 to 42, wherein the conversion of CO₂ to produce —O—(O)CH from one or more hydroxyls of a compound of formula (I) is (a) a conversion of CO₂ to produce-O—(O)CH from the OH on R—OH, (b) a conversion of CO₂ to produce —O—(O)CH from one or more hydroxide moieties that are a substituent on R (e.g., hydroxy (—OH) or C₁-C₈ alkyl substituted with 1, 2, or 3—OH), or (c) a combination thereof.

45. The method of any of embodiments 43 to 44 or the electrochemical cell of embodiments 1 to 42, wherein the faradaic efficiency to convert CO₂ to produce-O—(O)CH from one or more hydroxyls of a compound of formula (I) in the catholyte solution, is 0.1, 1, 5, 10, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 99%, or more than 10, more than 20, more than 30, more than 40, more than 45, more than 50, more than 55, more than 60, more than 65, more than 70, more than 75, more than 80, or more than 90%.

46. The method of any of embodiments 43 to 45 or the electrochemical cell of embodiments 1 to 42, wherein the applied voltage is-1.0, −2.0, −2.5, −3.0, −3.5, −4.0, −4.5, −5.0, −5.5, −6.0, −6.5, −7.0, −7.5, −8.0, −8.5, −9.0, −9.5, −10.0, −10.5, −11.0, −11.5, −12.0, −12.5, −13.0, −13.5, or 14.0 volts (vs. anode gas diffusion electrode), or from 1.0 to −14.0, from 3.0 to 10.0, from 3.5 to 8.0, from 4.0 to 7.5 or from 4.5 to 7.0 volts (vs. anode gas diffusion electrode).

47. The method of any of embodiments 43 to 46 or the electrochemical cell of embodiments 1 to 42, wherein the voltage is applied for 0.1, 0.5, 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 250, 300, 400, 450, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, or 1800 minutes, or from 0.1 to 1800, from 1 to 1500, from 5 to 1000, from 10 to 500, from 15 to 250, or from 15 to 180 minutes, or more than 0.1, more than 1, more than 5, more than 10, or more than 15 minutes.

48. The method of any of embodiments 43 to 47 or the electrochemical cell of embodiments 1 to 42, wherein the current density of the cell is-0.1, −0.5, −1, −2, −3, −4, −5, −6, −7, −8, −9, −10, −11, −12, −13, −14, −15, −16, −17, −18, −19, −20, −21, −22, −23, −24, −25, −26, −27, −28, −29, −30, −32, −34, −36, −38, −40, −45, −50, −55, −60, −65, −70, −75, −80, −85, −90, −95, −100, −125, −150, −175, or 200 mA cm⁻², or from 0.1 to 200, from 0.5 to 100, from 1 to 40, from 5 to 25, or from 10 to 20 mA cm⁻².

49. The method of any of embodiments 43 to 48 or the electrochemical cell of embodiments 1 to 42, wherein the cell resistance is 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 32, 34, 36, 38, 40, 45, 50, 55, 60, 65, 70, 75, 80, or 90 ohms ((2), or from 0.1 to 90, from 0.5 to 50, from 1 to 30, from 2 to 25, from 5 to 15, or from 6 to 9 ohms (52).

50. The method of any of embodiments 43 to 49 or the electrochemical cell of embodiments 1 to 42, wherein the absolute value of the current density of a compound produced from the conversion to —O—(O)CH from one or more hydroxyls of a compound of formula (I) in the catholyte solution is 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 32, 34, 36, 38, 40, 45, 50, 55, 60, 65, 70, 75, or 80 mA cm⁻², or from 0.1 to 80, from 0.5 to 40, from 5 to 35, from 8 to 25, from 9 to 20, or from 10 to 15 mA cm⁻².

The headings used in the disclosure are not meant to suggest that all disclosure relating to the heading is found within the section that starts with that heading. Disclosure for any subject may be found throughout the specification.

It is noted that terms like “preferably,” “commonly,” and “typically” are not used herein to limit the scope of the claimed invention or to imply that certain features are critical, essential, or even important to the structure or function of the claimed invention. Rather, these terms are merely intended to highlight alternative or additional features that may or may not be utilized in a particular embodiment of the present invention.

As used in the disclosure, “a” or “an” means one or more than one, unless otherwise specified. As used in the claims, when used in conjunction with the word “comprising” the words “a” or “an” means one or more than one, unless otherwise specified. As used in the disclosure or claims, “another” means at least a second or more, unless otherwise specified. As used in the disclosure, the phrases “such as”, “for example”, and “e.g.” mean “for example, but not limited to” in that the list following the term (“such as”, “for example”, or “e.g.”) provides some examples but the list is not necessarily a fully inclusive list. The word “comprising” means that the items following the word “comprising” may include additional unrecited elements or steps; that is, “comprising” does not exclude additional unrecited steps or elements.

Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as reaction conditions, and so forth used in the specification and claims 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 this specification and claims are approximations that can vary depending upon the desired properties sought to be obtained by the presently-disclosed subject matter.

As used herein, the term “about,” when referring to a value or to an amount of mass, weight, time, volume, concentration or percentage is meant to encompass variations of in some embodiments ±20%, in some embodiments ±10%, in some embodiments ±5%, in some embodiments ±1%, in some embodiments ±0.5%, and in some embodiments ±0.1% from the specified amount, as such variations are appropriate to perform the disclosed method.

Detailed descriptions of one or more embodiments are provided herein. It is to be understood, however, that the present invention may be embodied in various forms. Therefore, specific details disclosed herein (even if designated as preferred or advantageous) are not to be interpreted as limiting, but rather are to be used as an illustrative basis for the claims and as a representative basis for teaching one skilled in the art to employ the present invention in any appropriate manner. Indeed, various modifications of the invention in addition to those described herein will become apparent to those skilled in the art from the foregoing description and the accompanying figures. Such modifications are intended to fall within the scope of the appended claims.

What is claimed is: