SYSTEMS AND METHODS OF IMPROVED ELECTROCHEMICAL CARBON DIOXIDE (CO2) REDUCTION

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. provisional application No. 63/738,035, filed Dec. 23, 2024, the contents of which are hereby incorporated herein by reference.

FIELD

The present invention generally relates to the field of electrochemistry, and more particularly, to electrochemical cells, components thereof, and electrochemical reactions for converting carbon dioxide (CO₂) into usable products.

INTRODUCTION

The following is not an admission that anything discussed below is part of the prior art or part of the common general knowledge of a person skilled in the art.

Carbon dioxide (CO₂) is the primary greenhouse gas attributed to global warming. The amount of CO₂ emission from anthropogenic activities, such as manufacturing, and the excess CO₂ currently present in the atmosphere, needs to be reduced or removed to mitigate its impact on global warming.

Formate compounds are valuable industrial chemicals and have wide uses in a number of sectors. For example, potassium formate (KCOOH) has been used as a fertilizer, a drilling fluid in the oil and gas industry, and as a de-icing agent in airport runways. Calcium formate (Ca(COOH)₂) is used as an animal feed preservative and an additive in cement. Ammonium formate (NH₄COOH) is used as a reagent in the reductive amination of aldehydes and ketones and as an additive in chromium electroplating. Alkylammonium formate (RNH₃COOH) has uses as an ionic liquid mobile phase in chromatography. However, conventional means of producing formate compounds involve processes that are toxic, dangerous, and/or carbon intensive.

Synthesis gas (syngas) is useful in industrial applications to produce methanol and liquid hydrocarbons through the Fischer-Tropsch process. Additionally, syngas is a source of H₂ for fuel cells and ammonia production. Ethylene is essential for the production of polymers such as polyethylene, polyvinyl chloride, polystyrene, and chemicals such as ethylene oxide, ethylene glycol, ethanol, acetic acid, acrylonitrile. However, similar to above, conventional means of producing syngas or ethylene involves processes that are toxic, dangerous and/or carbon intensive.

Developing technology that harnesses renewable energy to convert CO₂ into chemicals and materials may reduce reliance on fossil fuels and petrochemicals and mitigate CO₂ emissions.

SUMMARY

The following introduction is provided to introduce the reader to the more detailed discussion to follow. The introduction is not intended to limit or define any claimed or as yet unclaimed invention. One or more inventions may reside in any combination or sub-combination of the elements or process steps disclosed in any part of this document including its claims and figures.

In a broad aspect, in accordance with some embodiments, there is provided a method of preparing a cathode. The method comprises: adding a bismuth source to an acid bath; adding one or more additives to the bath; submerging a counter electrode either into the bath's solution or in a different electrolyte solution separated from the bath via an ion-exchange membrane; submerging a porous metal substrate into the bath's solution; and applying an electrical potential across the porous metal substrate and the counter electrode, thereby electrodepositing a bismuth coating onto the porous metal substrate.

In some embodiments, the electrical potential is applied for a period of time such that the bismuth coating is approximately at least 0.01 millimeter thick.

In some embodiments, the acid bath is filtered to obtain a clear solution subsequent to adding the one or more additives to the acid bath.

In some embodiments, the bismuth source may comprise at least one of bismuth oxide, bismuth chloride, bismuth bromide, bismuth iodide, and bismuth nitrate.

In some embodiments, the one or more additives may comprise one or more polyols.

In some embodiments, the one or more additives may comprise at least one of aminopolycarboxylic acid and hydroxycarboxylic acid

In some embodiments, the one or more additives may comprise an alkali metal halide.

In some embodiments, the acid bath may comprise at least one of inorganic acid and organic acid.

In some embodiments, the porous metal substrate may comprise a metal foam.

In some embodiments, the porous metal substrate may comprise a metal mesh.

In some embodiments, the method may further comprise pre-treating the porous metal substrate to enhance an adherence property of the porous metal substrate prior to the submerging the porous metal substrate into the acid bath.

In some embodiments, the pre-treating the porous metal substrate may comprise submerging the porous metal substrate into a pre-treatment solution comprising Bi³⁺ ions.

In some embodiments, the Bi³⁺ ions may be produced using at least one of bismuth halide or bismuth nitrate salts.

In some embodiments, the porous metal substrate may comprise a porosity of approximately between 75 ppi and 130 ppi for metal foams or mesh number of approximately between 100 and 200 for metal meshes.

In another broad aspect, in accordance with some embodiments, there is provided a membrane for separating anolytes and catholytes in an electrochemical cell. The membrane comprises: a non-ion-selective layer comprising a non-ion-selective material; a first ion-selective layer comprising a first ion-selective material; and a second ion-selective layer comprising a second ion-selective material.

In some embodiments, the first ion-selective layer and the second ion-selective layer are fixed to one another through chemical grafting.

In some embodiments, the non-ion-selective layer is fixed to the first ion-selective layer and the second ion-selective layer through mechanical pressing or hot-pressing.

In some embodiments, the first ion-selective layer may comprise an anion exchange membrane and the second ion-selective layer comprises a cation exchange membrane.

In some embodiments, the non-ion-selective material may comprise a hydrophilic polymer.

In some embodiments, the non-ion-selective layer may be disposed adjacent to an anode, the second ion-selective layer is disposed adjacent to a cathode, and the first ion-selective layer is disposed in between the non-ion selective layer and the second ion-selective layer.

In some embodiments, the non-ion-selective layer may be configured to block a quantity oxygen from contacting the first ion-selective layer and the second ion-selective layer.

In some embodiments, the membrane may further comprise one or more additional ion-selective layers, the one or more additional ion-selective layers comprising the second ion-selective material, and wherein the one or more additional ion-selective layers are fixed to the non-ion-selective layer, the first ion-selective layer, and the second ion-selective layer through mechanical pressing or hot-pressing.

In some embodiments, the one or more additional ion-selective layers may be disposed adjacent to the second ion-selective layer.

In some embodiments, the non-ion-selective layer may be configured to block a quantity of oxygen from contacting the first ion-selective layer, the second ion-selective layer, and the one or more additional ion-selective layers.

In another broad aspect, in accordance with some embodiments, there is provided a method of producing a product using electrochemical reduction. The method comprises: introducing a gas, the gas comprising carbon dioxide, into a base solution, thereby producing a catholyte solution; feeding the catholyte solution into a cathode chamber of an electrolytic cell and feeding the anolyte solution into the anode chamber of an electrolytic cell, the electrolytic cell comprising: the cathode chamber comprising a cathode; and an anode chamber comprising an anode; applying a first electric potential across the anode and the cathode for a first period of time; applying a second electric potential across the anode and the cathode for a second period of time, wherein the second electric potential is substantially reduced in comparison to the first electric potential; and extracting the product from the cathode chamber.

In some embodiments, the method further comprises turning off the electrolytic cell and feeding the cathode chamber with deionized water during off time before conducting a new reaction.

In some embodiments, the first period of time comprises approximately at least 8 hours.

In some embodiments, the first period of time ranges from approximately at least 8 hours to the time needed for the CO₂-captured catholyte solution to be fully converted into formate solution.

In some embodiments, a concentration of the carbon dioxide within the gas may comprise approximately 10% or less.

In some embodiments, a concentration of the carbon dioxide within the gas comprises approximately 50% or less.

In some embodiments, the anode may comprise one or more nickel-based metallic meshes or foams.

In some embodiments, the electrolytic cell may further comprise: a membrane separating the anode chamber and the cathode chamber, the membrane comprising: a non-ion-selective layer comprising a non-ion-selective material; a first ion-selective layer comprising a first ion-selective material; and at least one second ion-selective layers comprising a second ion-selective material.

In some embodiments, the first ion-selective layer and the second ion-selective layer are fixed to one another through chemical grafting.

In some embodiments, the non-ion-selective layer is fixed to the first ion-selective layer and the at least one second ion-selective layers through mechanical pressing or hot-pressing.

In some embodiments, the first ion-selective layer may comprise an anion exchange membrane and the at least one second ion-selective layers comprises a cation exchange membrane.

In some embodiments, the non-ion-selective material may comprise a hydrophilic polymer.

In some embodiments, the non-ion-selective layer may be disposed adjacent to an anode, the at least one second ion-selective layers are disposed adjacent to a cathode, and the first ion-selective layer is disposed in between the non-ion selective layer and the second ion-selective layer.

In some embodiments, the non-ion-selective layer may be configured to block a quantity oxygen from contacting the first ion-selective layer and the at least one second ion-selective layers.

In some embodiments, the base solution may comprise an alkali metal hydroxide and the product comprises a corresponding alkali metal formate.

In some embodiments, the base solution may comprise KOH and the product may comprise potassium formate.

In some embodiments, the base solution may comprise NaOH and the product may comprise sodium formate.

In some embodiments, the base solution may comprise NH₄OH and the product may comprise ammonium formate.

In some embodiments, the base solution may comprise methylamine and the product may comprise methylammonium formate.

In some embodiments, the base solution may comprise KOH and the product may comprise syngas.

In some embodiments, the base solution may comprise KOH and the product may comprise ethylene.

In some embodiments, the method may further comprise treating the ammonium formate with a metal oxide to produce a corresponding alkaline-earth metal formate.

In some embodiments, the metal oxide may further comprise calcium oxide and the alkaline-earth metal formate may comprise calcium formate.

In some embodiments, the metal oxide may comprise magnesium oxide and the alkaline-earth metal formate comprises magnesium formate.

In some embodiments, the metal oxide may comprise barium oxide and the alkaline-earth metal formate comprises barium formate.

In some embodiments, the extracting the product from the cathode chamber may comprise extracting a product solution from the cathode chamber and evaporating the product solution under vacuum.

In some embodiments, the cathode may comprise a porous metal substrate and a bismuth coating.

In some embodiments, the bismuth coating may be at least 0.01 millimeter thick.

In some embodiments, the method may further comprise regenerating the cathode by feeding an ion solution comprising bismuth into the cathode chamber and electrodepositing the bismuth onto the cathode.

In some embodiments, the cathode may comprise a porous metal substrate and a silver coating.

In some embodiments, the cathode may comprise a porous metal substrate and a copper coating.

In some embodiments, the method may further comprise treating the potassium formate with a plant-based polymer to produce a desiccant.

In another broad aspect, in accordance with some embodiments, there is provided an electrochemical cell. The electrochemical cell comprises: a cathode chamber comprising a cathode; an anode chamber comprising an anode; and a membrane separating the cathode chamber and the anode chamber. The membrane comprises: a non-ion-selective layer comprising a non-ion-selective material; a first ion-selective layer comprising a first ion-selective material; and a second ion-selective layer comprising a second ion-selective material.

In some embodiments, the cathode may comprise: a porous metal substrate; and a bismuth coating, wherein the bismuth coating is approximately at least 0.01 millimeter thick.

In some embodiments, the porous metal substrate may comprise a porosity of approximately between 75 ppi and 130 ppi for metal foams or a mesh number of approximately between 100 and 200 for metal meshes.

In some embodiments, the first ion-selective layer and the second ion-selective layer are fixed to one another through chemical grafting.

In some embodiments, the non-ion-selective layer is fixed to the first ion-selective layer and the second ion-selective layer through mechanical pressing or hot-pressing.

In some embodiments, the first ion-selective layer may comprise an anion exchange membrane and the second ion-selective layer may comprise a cation exchange membrane.

In some embodiments, the non-ion-selective material may comprise a hydrophilic polymer.

In some embodiments, the non-ion-selective layer may be disposed adjacent to an anode, the second ion-selective layer may be disposed adjacent to a cathode, and the first ion-selective layer may be disposed in between the non-ion selective layer and the second ion-selective layer.

In some embodiments, the non-ion-selective layer may be configured to block a quantity oxygen from contacting the first ion-selective layer and the second ion-selective layer.

In some embodiments, the electrochemical cell may further comprise one or more additional ion-selective layers, the one or more additional ion-selective layers comprising the second ion-selective material, and wherein the one or more additional ion-selective layers are fixed to the non-ion-selective layer, the first ion-selective layer, and the second ion-selective layer through mechanical pressing or hot-pressing.

In some embodiments, the one or more additional ion-selective layers may be disposed adjacent to the second ion-selective layer.

In some embodiments, the non-ion-selective layer may be configured to block a quantity of oxygen from contacting the first ion-selective layer, the second ion-selective layer, and the one or more additional ion-selective layers.

In some embodiments, the anode may comprise one or more nickel-based meshes or foams.

In some embodiments, the electrochemical cell may further comprise: a first and second plate comprising a corrosion-resistant metal; and a first and second gasket comprising a heat-resistant silicone rubber.

DRAWINGS

For a better understanding of the embodiments described herein and to show more clearly how they may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings which show at least one exemplary embodiment, and in which:

FIG. 1 shows a method of producing various chemicals in accordance with known methods.

FIGS. 2A and 2B show example systems for electrochemical CO₂ reduction in accordance with previously known embodiments.

FIG. 3 show example reactions for producing formates in accordance with presently described embodiments

FIG. 4 shows the operational life of an example cathode prepared in accordance with previously known embodiments.

FIG. 5 shows a diagram of the operation of a bipolar membrane in accordance with previously known embodiments.

FIG. 6 shows an example process for the production of alkali metal formates in accordance with presently disclosed embodiments.

FIG. 7 shows an example process for the production of ammonium formate in accordance with presently disclosed embodiments.

FIG. 8 shows an example process for the production of alkylammonium formates in accordance with presently disclosed embodiments.

FIG. 9 shows an example process for the production of alkaline earth metal formates in accordance with presently disclosed embodiments.

FIG. 10 shows an example process for the production of desiccants in accordance with presently disclosed embodiments.

FIG. 11 shows an example process for the production of syngas/ethylene in accordance with presently disclosed embodiments.

FIG. 12 shows an exploded view of an example electrochemical cell in accordance with presently disclosed embodiments.

FIG. 13 shows an example cathode in various stages of preparation in accordance with presently disclosed embodiments.

FIG. 14 shows an example membrane in accordance with presently disclosed embodiments.

FIG. 15 shows a graph of the faradaic efficiency of an electrochemical cell in accordance with presently disclosed embodiments.

FIGS. 16A and 16B show example graphs of the performance of desiccants created in accordance with presently disclosed embodiments.

FIG. 17 shows a flowchart of a method of preparing a cathode in accordance with presently disclosed embodiments in accordance with an example.

FIG. 18 shows a flowchart of a method of preparing a cathode in accordance with presently disclosed embodiments in accordance with another example.

FIG. 19 shows a flowchart of a method of producing various products by electrochemical reduction.

DESCRIPTION OF VARIOUS EMBODIMENTS

Numerous embodiments are described in this application and are presented for illustrative purposes only. The described embodiments are not intended to be limiting in any sense. The invention is widely applicable to numerous embodiments, as is readily apparent from the disclosure herein. Those skilled in the art will recognize that the present invention may be practiced with modification and alteration without departing from the teachings disclosed herein. Although particular features of the present invention may be described with reference to one or more particular embodiments or figures, it should be understood that such features are not limited to usage in the one or more particular embodiments or figures with reference to which they are described.

The terms “an embodiment,” “embodiment,” “embodiments,” “the embodiment,” “the embodiments,” “one or more embodiments,” “some embodiments,” and “one embodiment” mean “one or more (but not all) embodiments of the present invention(s),” unless expressly specified otherwise.

The terms “including,” “comprising” and variations thereof mean “including but not limited to,” unless expressly specified otherwise. A listing of items does not imply that any or all of the items are mutually exclusive, unless expressly specified otherwise. The terms “a,” “an” and “the” mean “one or more,” unless expressly specified otherwise.

As used herein and in the claims, two or more parts are said to be “coupled”, “connected”, “attached”, “joined”, “affixed”, or “fastened” where the parts are joined or operate together either directly or indirectly (i.e., through one or more intermediate parts), so long as a link occurs. As used herein and in the claims, two or more parts are said to be “directly coupled”, “directly connected”, “directly attached”, “directly joined”, “directly affixed”, or “directly fastened” where the parts are connected in physical contact with each other. As used herein, two or more parts are said to be “rigidly coupled”, “rigidly connected”, “rigidly attached”, “rigidly joined”, “rigidly affixed”, or “rigidly fastened” where the parts are coupled so as to move as one while maintaining a constant orientation relative to each other. None of the terms “coupled”, “connected”, “attached”, “joined”, “affixed”, and “fastened” distinguish the manner in which two or more parts are joined together.

Further, although method steps may be described (in the disclosure and/or in the claims) in a sequential order, such methods may be configured to work in alternate orders. In other words, any sequence or order of steps that may be described does not necessarily indicate a requirement that the steps be performed in that order. The steps of methods described herein may be performed in any order that is practical. Further, some steps may be performed simultaneously.

As used herein and in the claims, a group of elements are said to ‘collectively’ perform an act where that act is performed by any one of the elements in the group, or performed cooperatively by two or more (or all) elements in the group.

As used herein and in the claims, a first element is said to be “received” in a second element where at least a portion of the first element is received in the second element unless specifically stated otherwise.

Some elements herein may be identified by a part number, which is composed of a base number followed by an alphabetical or subscript-numerical suffix (e.g., 112a, or 112₁). Multiple elements herein may be identified by part numbers that share a base number in common and that differ by their suffixes (e.g., 112₁, 112₂, and 112₃). All elements with a common base number may be referred to collectively or generically using the base number without a suffix (e.g., 112).

Presently disclosed are electrolytic systems for electrochemical CO₂ reduction (ECR) using gas mixtures containing low concentrations of carbon dioxide to produce products such as formate, syngas, and ethylene. Additionally, desiccant materials may be produced by combining a product of the ECR with plant-based polymers.

Formate compounds may be conventionally produced through a direct reaction between formic acid (HCOOH) and a corresponding base. FIG. 1 shows a conventional method 100 for producing formic acid as well as metal and (alkyl)ammonium formate compounds. For example, ammonium formate can be produced by reacting formic acid with ammonia, as shown in step 106. However, formic acid is often produced industrially via a two-step process involving a reaction between Carbon monoxide (CO) and methanol to make methyl formate (HCOOCH₃), as shown in step 102, followed by a hydrolysis reaction, as shown in step 104. CO and methanol are fossil-based compounds and highly toxic chemicals. Additionally, the formation of methyl formate occurs at high temperature and pressure, which may be energy intensive. As such, extreme care is needed for the production of methyl formate from CO and methanol. Steps 106 and 108 also show various other products that can be produced from formic acid.

Syngas (synthetic gas) contains primarily hydrogen (H₂) and CO and is conventionally produced through steam methane reforming, partial oxidation of hydrocarbons (e.g., methane) or coal gasification. Ethylene (C₂H₄) is conventionally produced through cracking processes in oil refinery settings, in which hydrocarbons are broken down into lighter molecules at high temperatures.

Electrochemical reduction of CO₂ may be used to produce formate, syngas, and ethylene. Electrocatalysts such as bismuth, tin, and indium may be used in the production of formates. Electrocatalysts such as silver and zinc may be used in the production of syngas. Electrocatalysts such as copper may be used in the production of ethylene. Reactor designs for these reactions have previously primarily focused on designing catalyst structures to achieve high-selectivity for the conversion of CO₂ towards products. Small catalyst sizes (e.g., 1-5 cm²) and low current densities are typically used in such designs. There is still a need for designs capable of bridging the gap between lab-scale research and practical applications of such reactions.

The present disclosures describe systems and methods of producing formate compounds, syngas, and ethylene from CO₂ waste at room temperature and ambient pressure. The presently described systems and methods may have a lower carbon footprint than conventional methods of producing formic acid and formate compounds, which generally require using toxic gases, such as CO and methanol, at high temperature and pressure. Additionally, systems and methods are described for upcycling waste like CO₂ emissions and agricultural residues to produce valuable products, such as reusable desiccants, which may offer a greener alternative to silica gel-based desiccants.

There are two primary types of ECR systems, primarily varying based on the nature of the inlet: gas-fed and liquid-fed. FIG. 2A shows an example gas-fed ECR system 200 and FIG. 2B shows an example liquid-fed ECR system 210. The gas-fed system 200 and liquid-fed system 210 uses CO₂ gas and CO₂-captured liquid, respectively, as inputs 222A and 222B into the cathodes of the systems.

Gas-fed system 200 contains a cathode 202 where the CO₂ reduction reaction occurs. In such systems, cathode 202 may be specifically designed in the form of a gas diffusion electrode (GDE). In a gas-fed system 200, CO₂ gas is used as input 222A into cathode 202. The ECR reaction is performed by providing electrical energy to system 200. For example, an electric potential difference derived from a power source may be applied across cathode 202 and anode 206. Desired output products such as formate, syngas, and ethylene may be produced at cathode 202 as outputs 224A. A GDE may contain two layers: a gas-diffusion layer and a catalyst layer. The gas-diffusion layer is hydrophobic and porous, allowing for the pass-through of CO₂ gas while preventing the penetration of the catholyte solution. The catalyst layer receives electrons provided from the power source and catalyzes the CO₂ reduction reaction. Gas-fed system 200 may also contain an anion exchange membrane 204 and an iridium-based anode 206.

A number of difficulties may be associated with the use of gas-fed system. For one, gas-fed systems may often suffer from degraded catalytic activity within a short operational time. These operating lifetimes are typically observed at within 100 hours of operation. Such lifetimes are typically insufficient for industrial applications, which may require thousands of hours of continuous operation. This problem is especially compounded when the system is operated at industry-relevant current densities (e.g., ≥100 mA/cm²).

The degradation occurs in part due to the reconstruction of the catalyst over time, wherein the surface of the catalyst layer changes under the applied electric field, thereby promoting a competing reaction of H₂O reduction and quenching the CO₂ reduction reaction. Additionally, the catalyst layer may become detached from its substrate over time. Further, the catalyst may be poisoned by deposition of species during operation. Lastly, the catalyst layer may become covered by salt, a problem that is especially common in gas-fed systems. Salt (e.g., bicarbonate) forms due to the reaction of CO₂ gas and the hydroxide that is generated as a byproduct by the catalyst during the ECR reaction.

Additionally, gas-fed systems additionally require high-purity CO₂ gas as input. However, flue gases from industrial plants typically contain high concentrations of contaminants (e.g., O₂, NO_x, SO_x). These gaseous impurities are stronger oxidants than CO₂ and thus will be more readily reduced before the ECR reaction occurs. As such, the presence of these impurities significantly quenches the desired ECR reaction. Similarly, atmospheric air typically contains 21% O₂ and only 0.04% CO₂. Therefore, when feeding air into an electrolyzer, the oxygen reduction reaction dominates and no significant ECR reaction occurs. As they are often unable to work with impure CO₂ sources, gas-fed systems may often be considered too inefficient for real-world applications.

Further, gas-fed systems may have low conversion rates. Gas-fed systems typically have a <5% single pass conversation rate of CO₂. In other words, less than 5% of the pure CO₂ fed into the reactor is reduced to product. Additionally, some bicarbonate produced at the cathode side may migrate to the anode of the system, which can be difficult to recover, resulting in the loss of some CO₂ in the system.

In addition, gas-fed systems may be difficult to scale up with respect to electrode surface area. For example, electrodes with areas ranging from 1-5 cm² are commonly disclosed in academia. However, in practice, electrodes may require surface areas in the order of square meters or at least a few hundreds of square centimeters per electrolytic unit cell to be useful in industrial applications, as given the same current density (measured in mA/cm²), an increase in the size of the electrode would result in an increase in total current, which may lead to an increase in total products produced, while reducing the cost for multiple-cell assembly and maintenance. The gas-diffusion layer of the cathode 202 may be comprised of carbon paper, which generally has suitable inherent hydrophobicity and electron conductivity properties for such applications. However, the hydrophobicity of carbon may rapidly decrease during the course of the ECR reaction. As a result of this, the catholyte solution may be able to pass through the gas diffusion layer, resulting in flooding of the cathode. In turn, this may lead to a blocking of the CO₂ gas in the reaction, quenching the ECR reaction. Additionally, carbon paper can be fragile, making it a difficult material to work with during assembly of the gas-diffusion electrode into the ECR system.

Recently system designs have focused on using polytetrafluoroethylene (PTFE) membranes for the gas-diffusion layer of a GDE. These cathodes are typically prepared by depositing a thin layer (e.g. a few hundred nanometers thick) of metal catalyst on PTFE membranes. The resulting electrodes may show high selectivity and stability for formate, syngas, and ethylene. However, due to the non-conductive nature of PTFE, such electrodes may be limited in size (e.g., having an area of around 1-5 cm²). As the conductivity of the catalyst layer may significantly decrease when scaled up, it can be a challenge to scale up PTFE-based cathodes without sacrificing performance.

Further, gas-fed systems may exhibit problems with product isolation and purification. As gas-fed systems typically have a low single pass conversion ratio of CO₂ (e.g., about 5% of CO₂ may be converted in a single pass), desired gas products such as syngas and ethylene may be mixed with excess, unconverted CO₂. These desired products may need to be separated after ECR through a separation process. Similarly, formate is typically produced at low concentrations (e.g., ≤1 mol/L), as using highly concentrated catholyte solution accelerates the flooding of the cathode and salt formation, quickly quenching catalytic activity therewithin. As such, separating the formate from the solution may present significant costs.

In addition, existing gas-fed ECR systems commonly utilize iridium-based anodes as they exhibit high stability for the water-oxidation reaction. However, these anodes can be costly, which can inhibit feasibility for industrial applications.

Referring back to FIG. 2B, example liquid-fed system 210 may contain a cathode 212, a bipolar membrane 214, and a nickel anode 216. In such systems, CO₂-captured liquid, such as CO₂ dissolved in an alkaline solution, is fed as input 222B into cathode 212 for the ECR reaction. The ECR reaction is performed by providing electrical energy to system 210. For example, an electric potential difference derived from a power source may be applied across cathode 212 and anode 216. Desired output products such as formate, syngas, and ethylene are produced at cathode 202 as outputs 224B.

Liquid-fed system 210 may operate with CO₂-captured liquid as input 222B instead of direct CO₂ gas. Thus, liquid system 210 may have higher tolerance for impurity in input 222B and can work with diluted sources of CO₂. Additionally, as the method of reaction in liquid-fed system 200 differs from gas-fed systems, salt formation on the cathode may be avoided. Further, when used with bipolar membranes and alkaline anolytes, nickel anodes can be used, thus resulting in cost savings over gas-fed systems.

However, liquid-fed system 210 may still present a number of difficulties that need to be resolved. For one, the selectivity of liquid-fed systems is typically much lower than that of gas-fed systems when run at high current densities (e.g., at ≥100 mA cm⁻²) due to the low solubility of CO₂ in aqueous solutions (around 34 mM), which results in a mass transfer issue as fewer molecules of CO₂ may be able to reach the reaction site. Additionally, highly stable catalysts are still required, as there may still be issues with catalyst reconstruction and detachment of the catalyst from the substrate over the course of operation in liquid-fed systems. Further, scaling up liquid-fed systems for industrial applications is also challenging.

Lastly, anolyte neutralization is an issue with liquid-fed systems. For example, in system 210, nickel anode 216 may turn into black nickel oxide powder, thereby losing its structure and electron conductivity, as anolyte pH decreases. Thus, an alkali metal hydroxide solution with pH≥14, such as a KOH solution, may be used to protect nickel anode 216. However, during the ECR reaction, dissolved CO₂ in the catholyte may pass through bipolar membrane 214 and migrate to the anolyte, gradually neutralizing the KOH to form KHCO₃. To resolve these problems, Iridium-based anodes may be used instead of nickel. Alternatively, the KOH anolyte solution may need to be changed frequently. Both solutions introduce added costs, making ECR impractical.

The presently described inventions may address one or more of the above noted challenges for liquid-fed ECR systems. The present disclosures describe cathodes, anodes, membranes, and electrolysis methods to address the above-mentioned challenges in existing ECR challenges. Further, the described inventions may be useful for producing a range of formate salts. Additionally, these inventions can also be applied to catalysts for producing syngas and ethylene. Additionally, the present disclosure describes ways of taking CO₂ from emission sources with low CO₂ concentrations and directly converting them into value-added products.

As will be described further, the present disclosure addresses production of formic acid and formate salts using alternative methods that may be less toxic and less carbon-intensive than conventional means. For example, the conventional process described in FIG. 1 involves the use of CO and methanol, which can be deadly even at very low concentrations. Additionally, high temperatures and pressures are required to perform the reaction.

In contrast, the presently described techniques allow the preparation of alkali metal (e.g. potassium, sodium), ammonium, and alkylammonium formate compounds using CO₂ as a precursor for formate through electrochemical CO₂ reduction conducted at room temperature and ambient pressure. Reference is made to FIG. 3, which shows example chemical reactions 300 using electrochemical CO₂ reduction in accordance with presently disclosed embodiments. Reaction 302 shows the use of CO₂, which is generally considered minimally toxic by inhalation, and H₂O, as reactants for the production of various formate compounds. Reaction 304 shows the production of metal formate compounds, including those that cannot be produced directly via ECR (e.g., calcium formate). Such compounds can be prepared by treating ammonium formate, which may be produced in reaction 302, with a corresponding metal oxide (e.g., quicklime CaO). The ammonia formed may then be recovered for further ECR reactions. In addition to formates, other useful products, such as syngas and ethylene, may be produced by using an appropriate catalyst and modifying the reaction conditions.

In order to contextualize the advantages of the presently disclosed methods, reference is first made to FIG. 4, which illustrates an operating timeline 400 of an example cathode 420 for ECR systems prepared in accordance with a conventional method of cathode preparation. A substrate 402 for the cathode 420 is shown, which may be comprised of a material that can conduct electricity and upon which the catalyst material may adhere to for the purposes of the reaction. For example, the substrate 402 may be comprised of carbon or metal. Catalyst 410 for cathode 420 is also shown at various stages of presence upon the surface of substrate 402 in the operating cycle of the cathode 420. At 404, substrate 402 is shown prior to catalyst deposition, with no catalyst present on its surface. At 406, catalyst 410 is deposited upon substrate 402 by some means of deposition. For example, catalyst 410 may be deposited by means of spraying the catalyst, electrodepositing the catalyst, or by using galvanic exchange. Catalyst 410 may be selected to be suitable for a CO₂ reduction reaction and may be selected with high selectivity and stability in mind. Achieving high levels with respect to both may be difficult, as some catalysts may exhibit good selectivity towards products at the beginning of the reaction but may not be stable over extended periods of operation, and thus, may degrade over time. This instability may be due to, for example, the detachment of the catalyst layer from the substrate and/or the reconstruction of the catalyst surface. At 408, the cathode 420 is shown after some period of use in one or more ECR reactions. Portions or all of catalyst 410 may have detached from the substrate or have gone under structural reconstruction.

For example, catalyst 410 may be bismuth, which may be suitable for ECR applications. Substrate 402 may be carbon paper. At 406, catalyst 410 may be deposited upon substrate 402 by spraying bismuth ink upon the substrate or by electrodeposition, thus coating the substrate with a thin layer (e.g., a few hundred nanometers thick) of bismuth nanoparticles. However, the resulting cathode may not be stable because bismuth nanoparticles do not adhere well to carbon surfaces, and therefore may not adhere well to substrate 402, which is comprised of carbon. Accordingly, the bismuth nanoparticles may be leached out into the catholyte solution. The nanoparticles may also aggregate into larger nanoparticles during the ECR reaction, resulting in rapidly decreasing selectivity.

Alternatively, substrate 402 may be made of metal. Galvanic exchange techniques may be used to deposit a thin layer (e.g., a few hundred nanometers thick) of bismuth catalyst 410 on the metallic catalyst 402. However, the thinness of the catalyst layer, in addition to weak adherence of bismuth atoms to the metal substrate, may once again result in low stability of the cathode and reduced selectivity after some time of operation.

In contrast, the presently disclosed methods for cathode preparation result in cathodes that achieve both high selectivity and stability in ECR reactions. The cathodes used in the presently described embodiments, such as cathode 1210 of cell 1200 in FIG. 12, may contain a thick and homogenous layer of catalyst material strongly adhered on the substrate. The presently disclosed methods allow for depositing a thick and well-bonded layer of bismuth on the metal substrate of the cathode. The thickness of the catalyst layer may help ensure that the reaction can be operated for a longer period of time even if parts of the catalyst layer begin leaching out during the ECR reaction.

Anodes in typical ECR systems may be iridium-based. This may provide the advantage of high stability regardless of the pH of the anolyte. However, iridium can be rare and expensive, reducing economic viability of using such anodes. Nickel based anodes, such as nickel foam or mesh, can be used, but they may only have effectiveness in highly alkaline conditions. When the pH of the anolyte decreases below 14, Ni metal turns into black Ni oxide powder, losing its structure and electrical conductivity.

In some embodiments, the presently disclosed systems use anodes based on nickel foams or meshes. One or more sheets of nickel foams or meshes may facilitate prolonged functioning of the anode.

In some embodiments, the presently disclosed systems utilize partially neutralized anolyte solution as a base solution to capture CO₂, of which the solution is then reused as a catholyte.

Reference is next made to FIG. 5, which shows a diagram 500 of the operation of a typical bipolar membrane 504 as known in the art. Bipolar membrane 504 typically contains a cation exchange membrane (CEM) and an anion exchange membrane (AEM) pressed together. In liquid-fed electrolyzers, the bipolar membrane is typically used in a reverse-bias mode, in which the CEM side of membrane 504 faces cathode 502 and the AEM side of the membrane 504 faces an anode 506. Anode 506 may be nickel-based. During an ECR reaction, H⁺ ions may be generated at the CEM side of membrane 504. The H⁺ ions may then acidize bicarbonate/carbamate to form CO₂ in situ, which may then be reduced on the cathode surface to form certain products.

However, bipolar membrane 504 may allow CO₂ crossover from the cathode side to the anode size, which may neutralize an alkali hydroxide anolyte solution at the anode side. The pH of the solution may then be decreased, and the performance of the Ni anode for water oxidation may be reduced. Additionally, the AEM side of membrane 504 may degrade over time when exposed to oxygen (O₂) gas in alkaline conditions as a result of the generation of highly reactive superoxide anion radical and hydroxyl free radicals.

ECR reactions to produce formate in accordance with known methods typically involve running the reaction continuously. Additionally, a fixed current or voltage may be applied to the cell. In some cases, stopping the reaction, i.e., leaving the cell at an open circuit potential, can lead to catalyst degradation. Additionally, such reactions are typically run using gas-diffusion electrodes and using pure CO₂ gas. When an oxidizing gas is present together with CO₂, the ECR reaction may be quenched.

The presently disclosed systems and methods also describe innovative and novel uses of formates in combination with plant-based agricultural waste to make desiccants. Formate salts produced with ECR reactions may be combined with plant-based polymers to produce desiccants that have higher adsorption capacity and lower regeneration temperatures than those of silica gel.

Reference is next made to FIG. 12, which shows an exploded view of an example electrochemical cell 1200 for performing an electrochemical carbon dioxide reduction reaction in accordance with embodiments described herein. Cell 1200 may be an electrolytic cell configured to perform an electrochemical reduction reaction. Various components of cell 1200 are shown in an exploded view. Cell 1200 may contain a cathode chamber containing a cathode 1210, an anode chamber containing an anode 1204, and a membrane 1208 separating the cathode chamber and the anode chamber. The body of cell 1200 may be comprised of two body plates 1202A and 1202B, which enclose and secure anode 1204, membrane 1208, cathode 1210, and gaskets 1206A, 1206B from opposite sides.

Gasket 1206A is disposed in between and creates an air-tight seal between body plate 1202A and membrane 1208. Gasket 1206A contains an aperture 1212, adequately sized to allow the anode 1204 to pass entirely through. Similarly, gasket 1206B is disposed in between and creates an air-tight seal between body plate 1202B and membrane 1208. Gasket 1206B also contains an aperture 1212, sized suitably to allow the cathode 1210 to pass entirely through. Gaskets 1206A, B may be made of heat-resistant silicone rubber.

Body plates 1202A and 1202B may be constructed of corrosion-resistant metals such as titanium or stainless steel. Body plates 1202A, 1202B may contain inlets/outlets 1220A, 1220B, respectively, to facilitate the delivery and removal of chemicals from the anode and cathode chambers. For example, anolyte solution containing potassium hydroxide (KOH) may be pumped through inlet/outlet 1220A to the anode chamber for improving the conductivity of the anode. Similarly, catholyte solution may be circulated through inlet/outlet 1220B for the ECR reaction to remove depleted catholyte solution that contains products of ECR and deliver fresh catholyte solution that contains fresh reactants. For example, an external reservoir containing potassium bicarbonate (KHCO₃) solution may be connected to inlet/outlet 1220B through a pump to deliver fresh catholyte solution to the cathode.

Cell 1200 contains anode 1204 and cathode 1210 for facilitating oxidation and reduction reactions in the cell. Cathode 1210 may be immersed in catholyte solution in a cathode chamber. The cathode chamber can be any chamber in the cell adequately sized to hold some volume of catholyte solution and the cathode. In the illustrated embodiment, the cathode chamber is formed by the cavity formed in the aperture 1212 of the gasket 1206B, with the body plate 1202B and membrane 1208 forming opposite end-walls of the chamber. Fresh catholyte solution may be pumped into the formed cathode chamber and catholyte solution containing products of the reaction can be removed through inlet/outlet 1220B.

Similarly, anode 1204 may be immersed in anolyte solution in an anode chamber. Similarly to the cathode 1210, the anode chamber can be any chamber configured to hold some volume of anolyte solution. In the illustrated embodiment, the anode is formed by the cavity formed in the aperture 1212 of the gasket 1206A, with the body plate 1202A and membrane 1208 forming opposite end-walls of the chamber. Anolyte solution may be delivered through inlet/outlet 1220A in body plate 1202A. As the volume of the anolyte solution may decrease during operation due to water oxidation, water may be provided over time, for example, through an external reservoir connected by pump.

A power source may be configured to apply an electrical potential difference across cathode 1210 and anode 1204 for the purposes of driving the reduction and oxidation reaction at the cathode and anode, respectively. A negative terminal of the power source may be connected to cathode 1210, allowing the cathode to supply electrons for reduction, and a positive terminal may be connected to anode 1204, allowing the anode to strip electrons for oxidation.

The anode may be nickel-based. Specifically, one or more sheets of Ni foams or meshes may be pressed together to produce the anode. The porosity of the foam may be 75 ppi or greater and the mesh number may be 100 or greater.

The cathode may be made of a metal catalyst coated onto a metal mesh or foam substrate. For example, the cathode may be comprised of a bismuth layer coated onto a porous metal foam made of, for example, nickel, aluminum, copper, titanium or steel. The catalyst layer may have thickness in the range of tens of micrometers, enhancing stability of the cathode. Cathode 1210 may be prepared in accordance with the following methods, which may offer advantages in stability and selectivity compared to previous methods. Reference is next made to FIG. 17, which shows a flowchart of a method 1700 of preparing a cathode in accordance with the presently disclosed embodiments. Reference is also made to FIG. 13, which depicts an example cathode 1210 of FIG. 12 in various stages of preparation in accordance with presently disclosed embodiments.

In the embodiment of FIG. 17, the method begins at 1702, with preparing an acid bath. The acid bath may be an electrodeposition bath. Electrodeposition may be used to deposit a catalyst layer on the metal foam/mesh. The electrodeposition bath used should allow for deposition of the catalyst layer with high thickness and strong adherence to the substrate. In addition, the bath should preferably be stable for multiple uses.

The method proceeds to 1704 with adding a catalyst source to the acid bath. For example, bismuth may be desired as the catalyst, which may be suitable for, for example, the production of formate products. Examples of the bismuth source include bismuth oxide (Bi₂O₃), bismuth nitrate (Bi(NO₃)₃), or other suitable bismuth compounds.

In some embodiments, a metal foam or mesh with high porosity and electrical conductivity (made of a foam or mesh of a conductor like nickel, copper, aluminum, titanium, stainless steel, etc.) may be used as substrate. The use of a porous metal substrate may improve the operation of the catalyst, as it may allow redepositing the catalyst of both sides of the substrate when needed, such as, for example, when the catalyst layer is depleted. The porosity of the substrate can range from 75-130 ppi for metal foams and the mesh number can range from 100-200 for metal meshes. In some embodiments, an inorganic acid such as nitric or hydrochloric acid or an organic acid such as acetic acid may be used in the acid bath to make the bath solution clear and homogenous, as it may help dissolve other chemicals in the bath. In some embodiments, the acid bath can be filtered to obtain a clear filtrate solution before use.

In some embodiments, in order to enhance the adherence of bismuth on the substrate, pre-treatment of the metal substrate may be performed prior to submerging the porous metal substrate into the acid bath. If the metal foam or mesh is not pre-treated, the catalytic activity of the electrode may quickly decrease due to aggregation and leaching of the catalytic material, such as shown in stage 408 of the conventional cathode of FIG. 4. Metal substrate 1302 may be treated with a solution containing catalyst ions. For example, the substrate 1302 may be treated with a solution containing Bi³⁺ ions by submerging it in an acidic solution containing bismuth salts, such as bismuth halide or bismuth nitrate. A thin layer of bismuth (Bi) will then be deposited on the substrate, which may act as an anchor for further depositing the Bi catalytic material by electrodeposition. In the example embodiment shown in FIG. 13, metal substrate 1302 is first pre-treated, and pre-treated substrate 1304 is used in the subsequent electrodeposition step.

The method proceeds to 1706 with adding one or more additives to the bath. The additives may improve the quality of the deposited catalyst layer. Several additives may be used, in appropriate ratios to one another. For example, aminopolycarboxylic acids, such as nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), and/or dodecane tetraacetic acid (DOTA) may be used as an additive. Hydroxycarboxylic acids, such as glycolic acid, citric acid, and/or tartaric acid may be used as an additive. Another type of additive may include polyols such as glycerol, glucose, and/or polyethylene glycol. Another type of additive may include alkali metal halide such as chloride, bromide, or iodide of sodium or potassium. In some embodiments, the acid bath can be filtered to obtain a clear filtrate solution before use.

The method proceeds to 1708, which includes submerging a counter electrode as well as a porous metal substrate into the bath solution. Subsequently, at 1710, the method includes applying an electrical potential across the porous metal substrate and the counter electrode, thereby electrodepositing a catalyst coating onto the porous metal substrate. The catalyst may be, for example, bismuth. In some embodiments, the electric potential is applied for a period of time such that the resulting coating of catalyst particles is at least 0.01 millimeter thick. In such embodiments, the current density of the electrodeposition process can be selected between 2-200 mA/cm². The deposition time may range between 0.1-10 hours, depending on the current density selected. In some other embodiments, the resulting coating of catalyst particles is approximately 10 micrometer thick. In some further embodiments, the resulting coating of catalyst particles is approximately at least 10 micrometer thick.

Reference is briefly made to FIG. 18, which shows a flowchart of a method 1800 of preparing a cathode in accordance with another example embodiment. Steps 1802, 1804 and 1806 are analogous to steps 1702, 1704 and 1706 of FIG. 17. At 1808, instead of submerging a counter electrode into the bath's solution, the method requires submerging a counter electrode into a different electrolyte solution separated from the bath via an ion-exchange membrane. Step 1808 further includes, submerging a porous metal substrate into the bath's solution. Step 1810 is analogous to step 1710.

Referring to FIG. 13, metal substrate 1304 is shown after electrodeposition with a thick coating of bismuth deposited upon it at 1306. The produced cathode 1306 is a foam or mesh completely covered in Bismuth, with a total thickness of about 10-20 micrometers, that may be able to retain the porosity of the foam/mesh. Cathode 1306 is shown after several successive ECR reactions at 1308, still retaining an adequate bismuth catalyst coating deposited thereupon, in contrast with cathode 420 of FIG. 4, which exhibits degradation of the catalyst over time.

The electrodeposition can be performed inside or outside of cell 1200. For example, in some embodiments, electrodeposition may be performed within the cell 1200, with the cathode already assembled inside the cell. For instance, the electrodeposition bath may be pumped in through inlet/outlet 1220B, and electrical energy may be applied through the cathode and anodes to perform electrodeposition on the cathode. In such instances, cell 1200 may be ready to be used immediately after the deposition process. In some embodiments, the metal substrate 1302 may be electrodeposited outside cell 1200. In such cases, the deposited electrode 1306 may then be assembled, along with other constituent components of the cell, after externally performed deposition.

Referring back to FIG. 12, cell 1200 contains a membrane 1208, which may operate to separate the anolyte and catholyte while allowing ion exchange therebetween. Membrane 1208 is positioned directly adjacent to and in between anode 1204 and cathode 1210. Membrane 1208 may contain multiple layers, including a combination of non-ion-selective and ion-selective membrane layers, pressed together. Membrane 1208 may additionally operate to reduce CO₂ crossover from the cathode side to the anode side, thus improving the operating life of the anode. Referring to FIG. 14, an expanded view of an example membrane 1208 is shown in accordance with the presently described embodiments.

As described previously, previously known bipolar membranes, often prepared by hot pressing a CEM and an AEM, such as membrane 504 of FIG. 5, suffer from delamination over time and significant CO₂ crossover from the cathode side to the anode side, which may negatively affect the pH of the anolyte solution, thus resulting in degradation in anode performance. Additionally, the AEM side of the membrane may be exposed to O₂ gas, and may therefore degrade over time due to its low oxidative stability in alkaline solutions.

Membrane 1208 of FIG. 14 contains a non-ion-selective layer 1402 made of a non-ion-selective material, a first ion-selective layer 1404 made of a first ion-selective material, and a second ion-selective layer 1406 comprising a second ion-selective material. The first ion-selective layer 1404 and the second ion-selective layer 1406 may be fixed to one another through chemical grafting, improving their stability by reducing delamination. The non-ion-selective layer 1402 is fixed to the first ion-selective layer 1404 and the second ion-selective layer 1406 through mechanical pressing or hot-pressing. As shown in the embodiment depicted in FIG. 14, the first ion-selective material for the first ion-selective layer 1404 can be an anion exchange membrane. The second ion-selective material for the second ion-selective layer 1406 can be a cation exchange membrane. In some embodiments, the non-ion-selective material for the non-ion-selective layer 1402 may be a hydrophilic polymer, such as nylon, cellulose, or hydrophilic polytetrafluoroethylene (PTFE) or polyvinylidene difluoride (PVDF). Additionally, depending on the level of chemical and CO₂ crossing blocking required, the membrane may contain more ion-selective layers, such as additional cation exchange membrane layers.

In some embodiments, the non-ion-selective layer is disposed adjacent to an anode, the second ion-selective layer is disposed adjacent to a cathode, and the first ion-selective layer is disposed in between the non-ion selective layer and the second ion-selective layer. For example, as shown in FIG. 14, cation exchange membrane 1406 faces the cathode while non-ion-selective layer 1402 faces the anode. The anion exchange membrane 1404 is sandwiched in between layers 1402 and 1406.

In some embodiments, the non-ion-selective layer may be configured to block a quantity oxygen from contacting the first ion-selective layer and the second ion-selective layer. For example, non-ion selective layer 1402 may operate to block O₂ generated on the anode from contacting anion exchange membrane 1404. This may mitigate the problem of AEM degradation due to exposure of the AEM to O₂ gas. The presence of non-ion selective layer 1402 may additionally prevent the O₂ from crossing over to the cathode, quenching the ECR reaction. The combination of the anion exchange membrane 1404 and the cation exchange membrane 1406 through chemical grafting may operate to prevent CO₂ and chemical crossover across membrane 1208 from the cathode side to the anode side, thus mitigating degradation of the anolyte and the anode. This may be effected, for example, by arranging the layers in the order described above.

In some embodiments, membrane 1208 may contain one or more additional ion-selective layers, the one or more additional ion-selective layers comprising the second ion-selective material, and wherein the one or more additional ion-selective layers are fixed to the non-ion-selective layer, the first ion-selective layer, and the second ion-selective layer through mechanical pressing or hot-pressing. As described above, depending on the level of chemical and CO₂ crossing blocking required, additional ion-selective layers may be added. For example, one or more cation exchange membranes may be added to membrane 1208, which would provide added CO₂ blocking capability, preventing the degradation of anode oxidation ability. In some embodiments, the one or more additional ion-selective layers may be disposed adjacent to the second ion-selective layer. For example, additional cation-exchange membranes can be positioned directly adjacent to ion-selective layer 1406.

Reference is next made to FIG. 19, which is a flowchart of a method 1900 of producing various products by electrochemical reduction reaction. The method may be performed using cell 1200 of FIG. 12.

The method begins at 1902 with introducing a gas containing a concentration of carbon dioxide into a base solution, thereby producing a catholyte solution. The gas may be any source of carbon dioxide, including flue gas from an industrial process. In some embodiments, a concentration of the carbon dioxide within the gas dissolved in the catholyte solution may be as low as 5%. For example, the concentration may be 5-10%. For example, impure flue gas, containing low concentrations of CO₂, may be used. The catholyte solution will then be used as an input into an electrolytic cell for electrochemical CO₂ reduction, such as cell 1200 of FIG. 12. As the electrolytic cell may be a liquid-fed cell, as in cell 1200 of FIG. 12, inlet gas containing a low concentration of CO₂ and other gases can be used for the electrochemical reduction reaction. In contrast, conventionally used gas-fed cells generally require high CO₂ concentrations to operate effectively.

The method proceeds to 1904 with providing the catholyte and anolyte solutions into the cathode and anode chambers of an electrolytic cell, respectively. The electrolytic cell may have a cathode chamber comprising a cathode and an anode chamber comprising an anode. The electrolytic cell may further contain a membrane separating the anode chamber and cathode chamber. The electrolytic cell can be, for example, cell 1200 of FIG. 12, containing anode 1204, cathode 1210, and membrane 1208.

The method proceeds to 1906, with applying a first electric potential across the anode and the cathode for a first period of time. The method then continues to 1908, with applying a second electric potential across the anode and the cathode for a second period of time, wherein the second electric potential is substantially reduced in comparison to the first electric potential. For example, the reaction may be run dynamically though repeated on and off sequences. During the ‘on’ sequence, an ‘on’ voltage, such as 3.6V, may be applied for a first time period. The ‘on’ voltage may be configured to produce a fixed current flow through the cell. During the ‘off’ sequences, an open circuit voltage (i.e., zero voltage) may be applied for a second time period, resulting in zero current flow through the cell.

In various embodiments, during the ‘off’ sequences, deionized water is fed into the cathode chamber to replace the catholyte and there is no negative effect on the catalyst. Additionally, the system is reset to a prior state during the ‘off’ sequences, which may help with prolonging the operating life of the cell.

The first period of time may be, for example, 8 hours or more. The second period of time may be, for example, 15 minutes. For example, the ‘on’ voltage may be applied for 8 hours or as long as the time needed for the CO₂-captured catholyte solution to be fully converted into formate solution, and then the system may be allowed to rest and reset for 15 minutes, during which time deionized water is fed into the cathode chamber to replace the catholyte. This may be repeated for as long as the reaction needs to be run. In this way, the reaction may be run dynamically and periodically through ‘on’ and ‘off’ sequences.

The electric potential may be derived from a power source, such as a battery, power supply, utility power, or any other suitable source capable of providing a stable power flow. By applying the potential across the anode and cathode, current may flow through the cell, allowing electron movement for driving the reduction and oxidation reactions.

The method proceeds to 1910, with extracting the product from the cathode chamber. After reaction, the product may be contained in the cathode chamber and can be extracted using any automatic or manual means. For example, the product may be dissolved in the catholyte solution. The solution may be pumped out, and additional fresh catholyte solution may be pumped in to replace the removed solution. The product can be any desired product of electrochemical CO₂ reduction, including, but not limited to, formate products, syngas, and ethylene.

In some embodiments, extracting the product from the cathode chamber may entail extracting a product solution from the cathode chamber and evaporating the product solution under vacuum. For example, potassium bicarbonate in a catholyte solution may be reduced to potassium formate using electrochemical carbon dioxide reduction. The potassium formate that is formed may be dissolved in solution. This solution may be extracted from the cathode chamber. In order to extract the potassium formate solid from the solution, the water in the solution can be evaporated, leaving solid potassium formate behind. The rate of evaporation may be enhanced by use of a vacuum, which lowers the atmospheric pressure around the solution, thereby lowering the boiling point of the solution.

When the cell is not in use, the cathode chamber can be washed with water in order to keep the cell in normal maintained condition. Production can be subsequently resumed by performing the methods of production described herein.

In some embodiments, the electrodes can be regenerated after catalytic activity has declined. While the electrodes specified may exhibit high stability and may be capable of operating for up to thousands of hours, the catalytic activity of the electrodes may nevertheless decline over time. The cathode may be regenerated by redepositing catalyst material in the cell without needing to disassemble the system. For example, for generating the bismuth-based electrodes, bismuth stock solution containing Bi³⁺ ions and additives may be added to the cathode chamber. Electrodeposition may then be performed right within the ECR cell. For electrodeposition, the deposition current density may be set at 10-100 mA/cm², and the period of deposition may range between 5 -15 minutes.

The following examples are provided to illustrate the use of certain embodiments of the presently described methods, such as method 1900 of FIG. 19, in the production of various useful output products, including formates, syngas, ethylene, desiccants, and more.

Example Formate Production

Method 1900 can be performed using an electrolytic cell to produce formate products, such as potassium formate, sodium formate, ammonium formate, methylammonium formate. Calcium formate and other metal formate salts, which are not directly produced through the electrochemical CO₂ reduction reactions, are produced through the chemical reactions between ammonium formate and the corresponding metal oxide/hydroxide. Cell 1200 of FIG. 12 may be used, containing cathode 1210, anode 1204, and membrane 1208, which offer numerous advantages for stability, efficiency, scalability, etc. For such reactions, an active catalyst size of 100 cm² may be used, but the catalyst size may be enlarged depending on the quantity of products needed. The chemicals used in the reaction, such as KOH, NaOH, NH₃, or CaO, are used as received without further purification. Simulated flue gas to be used as input into the electrolytic cell is prepared by mixing CO₂ with other gases, such as O₂, NOx, and/or SOx, with a 10% concentration of CO₂. The flow of input gas is controlled by a flowmeter device.

The reaction may be controlled by a power supply, such as a potentiostat, allowing a fixed current or voltage to be provided to the cell for the reaction. A timer may be used to control the on and off time of the cell. For example, for every 24 hours of operation, the cell may be turned off for 3-15 minutes. Two pumps are used to circulate the catholyte and anolyte solutions. A stirrer is additionally used to stir the catholyte solution.

The produced formate products may be characterized by nuclear magnetic resonance spectroscopy. The faradaic efficiency (FE) of formate is determined using the following formula: FE=(n×F×η)/(J×t), where n is the number of electrons (n=2 for formate), F is the Faradaic constant (96485 C/mol), η is the number of moles of formate formed, J is the total current (Ampere) and t is the electrolysis time (in seconds).

Reference is made to FIG. 6, which shows a flow diagram of an example process 600 for the production of alkali metal formates using presently disclosed methods, which includes such products as potassium formate, sodium formate, and cesium formate. FIG. 6 shows a base solution 602, a catholyte solution 614, a pump 604, an electrolytic cell 612 containing cathode 610 and anode 606, and output product 616. Base solution 602 may be combined with flue gas containing CO₂ to be converted into catholyte solution 614, which may be fed and recirculated to cathode 610 using pump 604 to perform the ECR reaction to produce output formate product 616.

For the production of potassium formate, base solution 602 may contain KOH. For example, 4 liters of 4 M KOH solution can be prepared by dissolving 1054 g KOH solid (industrial grade, 85%) in water. The obtained solution can then be bubbled with a simulated flue gas containing 10% CO₂ by concentration, under stirring, for 24 hours. The flow of gas can be set at 3 liter/min. The following reaction takes place: KOH+CO₂→KHCO₃. After 1 day, the KOH is substantially converted into potassium bicarbonate (KHCO₃) due to the CO₂ capture, producing an oversaturated solution 614 that contains excess KHCO₃ solids, which may be used as the catholyte for the ECR reaction. The anolyte used for anode 606 may be 1 liter of 4 M KOH. There is no need to add more KOH or change the anolyte solution during ECR. The KOH may be used to improve the conductivity of the anolyte. The catholyte and anolyte solutions are circulated through the cathode chamber and anode chamber, respectively. The catholyte is continuously bubbled with a dilute CO₂ stream at a flowrate of 100 ml/min under vigorous stirring. The power source is configured to produce a voltage of around 3.6 V to the electrodes by applying a fixed current of 10 A flowing through the cell.

The water at the anolyte decreases in volume as it is oxidized to O₂ at the anode 606 at a rate of around ˜81 g/day. 81 g of fresh water is also added daily into the anolyte, maintaining the volume of the anolyte solution at 1 liter. The water may be added automatically by using a pump. At the cathode 610, potassium bicarbonate may be reduced to potassium formate after 120 hours, with an average faradaic efficiency of about 70%. The product solution 616 can then be evaporated under vacuum, which leaves a mass of pure potassium formate solid (˜1.3 kg).

For the production of sodium formate, base solution 602 may contain NaOH. For example, 4 liters of 4 M NaOH can be prepared by dissolving 640 g of NaOH solid in water. The obtained solution can then be bubbled with a simulated flue gas containing 10% CO₂ by concentration, under stirring, for 24 hours. The gas may be flowed at 3 liter/min. The following reaction takes place: NaOH +CO₂→NaHCO₃. After 1 day, the NaOH is substantially converted into sodium bicarbonate, giving an oversaturated solution 614 that contains excess NaHCO₃ solids. This solution may then be used as the catholyte for the ECR reaction. 1 liter of 4 M KOH is prepared and used as the anolyte for the reaction. The KOH may improve the conductivity of the anolyte. It is generally not necessary to add more KOH or change the anolyte solution during the reaction. The catholyte and anolyte solutions are circulated through the cathode chamber and anode chamber, respectively. The catholyte is continuously bubbled with a dilute CO₂ stream at a flowrate of 100 mL/min, under stirring. The power source is configured to produce a voltage of around 3.6 V by applying a fixed current of 10 A to the cell.

The water at the anolyte decreases in volume as it is oxidized to O₂ at the anode 606 at a rate of around ˜81 g/day. 81 g of fresh water is also added daily into the anolyte, maintaining the volume of the anolyte solution at 1 liter. The water may be added automatically by using a pump. At the cathode 610, sodium bicarbonate may be reduced to sodium formate after 132 hours, with an average faradaic efficiency of about 65%. The product solution 616 can then be evaporated under vacuum, which leaves a mass of pure sodium formate solid (˜1 kg).

Reference is next made to FIG. 7, which shows a flow diagram of an example process 700 for the production of ammonium formate using presently disclosed methods. FIG. 7 shows a base solution 702, a catholyte solution 714, a pump 704, an electrolytic cell 712 containing cathode 710 and anode 706, and output product 716. Base solution 702 may be combined with flue gas containing CO₂ to be converted into catholyte solution 714, which may be fed to cathode 710 using pump 704 to perform the ECR reaction to produce output formate product 716.

Base solution 702 may contain NH₄OH. For example, 4 liters of 4 M NH₄OH can be prepared by diluting a 30% industrial NH₄OH solution. The obtained solution can then be bubbled with a simulated flue gas containing 10% CO₂ by concentration, under stirring, for 24 hours. The gas may be flowed at 3 liter/min. The following reaction takes place: NH₄OH+CO₂→NH₄HCO₃. After 1 day, the ammonia is substantially converted into ammonium bicarbonate, giving an oversaturated solution 714 that contains excess NH₄HCO₃ solids. This solution may then be used as the catholyte for the ECR reaction. Pump 704 may deliver the solution 714 into cathode 710. 1 liter of 4 M KOH is prepared and used as the anolyte for anode 706. The KOH may improve the conductivity of the anolyte. It is generally not necessary to add more KOH or change the anolyte solution during the reaction. The catholyte and anolyte solutions are circulated through the cathode and anode chambers, respectively. The catholyte is continuously bubbled with a dilute CO₂ stream at a flowrate of 100 mL/min, under stirring. The power source is configured to produce a voltage of around 3.6 V by applying a fixed current of 10 A to the cell.

The water at the anolyte decreases in volume as it is oxidized to O₂ at the anode at a rate of around ˜81 g/day. 81 g of fresh water is also added daily into the anolyte, maintaining the volume of the anolyte solution at 1 liter. The water may be added automatically by using a pump. At the cathode, ammonium bicarbonate may be reduced to ammonium formate after 144 hours, with an average faradaic efficiency of about 60%. The product solution 716 can then be evaporated under vacuum, which leaves a mass of pure ammonium formate solid (˜1 kg).

Reference is next made to FIG. 8, which shows a flow diagram for an example process 800 for the production of alkylammonium formates using presently disclosed methods, which includes such products as methylammonium formate and ethylammonium formate. FIG. 8 shows a base solution 802, a catholyte solution 814, a pump 804, an electrolytic cell 812 containing cathode 810 and anode 806, and output product 816. Base solution 802 may be combined with flue gas containing CO₂ to be converted into catholyte solution 814, which may be fed to cathode 810 using pump 804 to perform the ECR reaction to produce output formate product 816.

For the production of methylammonium formate, base solution 802 may contain methylamine. For example, 4 liters of 4 M methylamine solution can be prepared. The solution can then be bubbled with a simulated flue gas containing 10% CO₂ by concentration, under stirring, for 24 hours. The gas may be flowed at 3 liter/min. The following reaction takes place: 2CH₃NH₂+CO₂→CH₃NH₃⁺CH₃NHCO₂⁻. After 1 day, the methylamine is substantially converted into methylammonium carbamate, giving a clear solution 814 that may then be used as the catholyte for the ECR reaction. 1 liter of 4 M KOH is prepared and used as the anolyte for anode 806. The KOH may improve the conductivity of the anolyte. It is generally not necessary to add more KOH or change the anolyte solution during the reaction. The catholyte and anolyte solutions are circulated through the cathode and anode chambers, respectively. The catholyte is continuously bubbled with a dilute CO₂ stream at a flowrate of 100 mL/min, under stirring. The power source is configured to produce a voltage of around 3.6 V by applying a fixed current of 10 A to the cell.

The water at the anolyte decreases in volume as it is oxidized to O₂ at the anode at a rate of around ˜81 g/day. 81 g of fresh water is also added daily into the anolyte, maintaining the volume of the anolyte solution at 1 liter. The water may be added automatically by using a pump. At the cathode 810, methylammonium carbamate may be reduced to methylammonium formate after 168 hours, with an average faradaic efficiency of about 50%. The product solution 816 is then evaporated under vacuum, which leaves a mass of pure methylammonium formate liquid (˜1.2 kg).

The advantage of this technology compared to conventional ECR technologies is the ability to use any gas inlet that has a concentration of CO₂ from 5% to 100%, even with a high concentration of oxidizing gases such as Oxygen. In contrast, conventional gas-fed ECR technologies do not work with gas inlets that has >5% O₂. The following example shows the production of potassium formate using a gas inlet that has 50% CO₂, 10% O₂ and 40% N₂ by concentration. For the production of potassium formate, base solution 602 may contain KOH. For example, 2 liters of 2 M KOH solution can be prepared by dissolving 250 g KOH solid (industrial grade, 90%) in water. The obtained solution can then be bubbled with a simulated flue gas containing 50% CO₂, 10% O₂, 40% N₂ by concentration, under stirring, for 12 hours. The flow of gas can be set at 0.4 liter/min. The following reaction takes place: KOH+CO₂→KHCO₃. After 6 hours, the KOH is substantially converted into potassium bicarbonate (KHCO₃) due to the CO₂ capture, producing a solution 614 that contains KHCO₃, which may be used as the catholyte for the ECR reaction. The anolyte used for anode 606 may be 2 liters of 2 M KOH. There is no need to add more KOH or change the anolyte solution during ECR. The KOH may be used to improve the conductivity of the anolyte. The catholyte and anolyte solutions are circulated through the cathode chamber and anode chamber, respectively. The catholyte is continuously bubbled with a dilute CO₂ stream containing 50% CO₂, 10% O₂ and 40% N₂ at a flowrate of 100 ml/min under vigorous stirring. The power source is configured to produce a voltage of around 3.6 V to the electrodes by applying a fixed current of 10 A flowing through the cell.

The water at the anolyte decreases in volume as it is oxidized to O₂ at the anode 606 at a rate of around ˜81 g/day. 81 g of fresh water is also added daily into the anolyte, maintaining the volume of the anolyte solution at 1 liter. The water may be added automatically by using a pump. At the cathode 610, potassium bicarbonate may be reduced to potassium formate after 31 hours, with an average faradaic efficiency of about 70%. The product solution 616 can then be evaporated under vacuum, which leaves a mass of pure potassium formate solid (˜336 g).

For increasing the rate of production of potassium formate, a larger electrolytic cell, with 500 cm² electrodes, can be used. A base solution 602 may contain KOH. For example, 6 liters of 2 M KOH solution can be prepared by dissolving 750 g KOH solid (industrial grade, 90%) in water. The obtained solution can then be bubbled with a simulated flue gas containing 10% CO₂ by concentration, under stirring, for 24 hours. The flow of gas can be set at 3 liter/min. The following reaction takes place: KOH+CO₂→KHCO₃. After 1 day, the KOH is substantially converted into potassium bicarbonate (KHCO₃) due to the CO₂ capture, producing a solution 614, which may be used as the catholyte for the ECR reaction. The anolyte used for anode 606 may be 6 liters of 2 M KOH. There is no need to add more KOH or change the anolyte solution during ECR. The KOH may be used to improve the conductivity of the anolyte. The catholyte and anolyte solutions are circulated through the cathode chamber and anode chamber, respectively. The catholyte is continuously bubbled with a dilute CO₂ stream at a flowrate of 1000 ml/min under vigorous stirring. The power source is configured to produce a voltage of around 3.6 V to the electrodes by applying a fixed current of 50 A flowing through the cell.

The water at the anolyte decreases in volume as it is oxidized to O₂ at the anode 606 at a rate of around ˜403 g/day. 403 g of fresh water is also added daily into the anolyte, maintaining the volume of the anolyte solution at 1 liter. The water may be added automatically by using a pump. At the cathode 610, potassium bicarbonate may be reduced to potassium formate after 19 hours, with an average faradaic efficiency of about 70%. The product solution 616 can then be evaporated under vacuum, which leaves a mass of pure potassium formate solid (˜1 kg).

For further increasing the rate of production of formate salts, multiple electrolytic cells, each with 500 cm² electrodes, can be run in parallel.

The anolyte solution after one or several batches of ECR reaction can be partially neutralized due to the CO₂ crossover from the cathode side to the anode side. It can be treated, for example by filtration, if needed and utilized as a base solution to capture CO₂, of which the solution is then reused as a catholyte.

Reference is next made to FIG. 9, which shows a flow diagram for an example process 900 for the production of alkaline-earth metal formates using presently disclosed methods, including such products as calcium formate, barium formate, and magnesium formate. FIG. 9 shows a base solution 902, a catholyte solution 910, a pump 906, an electrolytic cell 916 containing cathode 912 and anode 908, intermediate product 914, and output product 918. Base solution 902 may be combined with flue gas containing CO₂ to be converted into catholyte solution 910, which may be fed to cathode 912 using pump 906 to perform the ECR reaction to produce intermediate product 914, which contains ammonium formate. A reagent may be added to the ammonium formate to produce the output alkaline earth metal formate 918. Ammonia 904 may also be produced in the process, and may be reused at the start of the process for the production of ammonium formate.

Taking the example of the production of calcium formate, ammonium formate may be the intermediate product 914, and may be produced in accordance with presently described methods, such as the methods depicted in FIG. 7. Four liters of 4 M ammonium formate solution 914 may be treated with 450 g of quicklime CaO to produce an output product 918 containing calcium formate. The following reaction takes place: 2NH₄COOH+CaO->2NH₃+Ca(COOH)₂+H₂O. In addition to formate, a quantity of ammonia 904 is also produced. Output product 918 may be in solution, which may be evaporated at 100 degrees Celsius until dry to give 1 kg of solid calcium formate. The ammonia 904 can be condensed with a cold-water condenser. The ammonia solution 904 can then be reused for capturing CO₂ and generating more ammonium formate, thereby repeating the cycle. In some embodiments, ammonium formate solution 914 can be treated with barium oxide to produce output product 918 containing barium formate. In some embodiments, ammonium formate solution 914 can be treated with magnesium oxide to produce output product 918 containing magnesium formate.

The stability of the ECR system may be monitored by quantifying the product produced over time. Any product of the reaction can be monitored, including those described herein. For example, FIG. 15 shows a graph 1500 of the faradaic efficiency of sodium formate production over time at a cathodic current density of 200 mA/cm². Over time, faradaic efficiencies drop as bicarbonate concentration in the catholyte decreases. At times 1502, the bicarbonate-to-formate conversion was completed and the depleted catholyte solution was changed with a fresh bicarbonate solution, resulting in the faradaic efficiency of the conversion returning to its original value.

Example Syngas Production

Syngas can be produced using method 1900 in a similar manner to formates, with modifications to certain aspects, such as the catalyst used. The catalyst for syngas production may be based on silver (Ag). A commercial copper mesh with high porosity (mesh number 100-200) and high electrical conductivity can be used as substrate. In some other examples, a silver mesh may be used. The cathode can be prepared using pre-treatment and electrodeposition. The anode can be substantially similar to that used for the production of formates.

Pre-treatment of the cathode may help to improve the adherence of Ag layer on the substrate. If the copper mesh is not pre-treated, the catalytic activity of the electrode may decrease quickly due to aggregation and leaching of the catalytic material. The copper mesh is treated with a saturated solution of silver nitrate in glacial acetic acid for 10 minutes. A thin layer of Ag will then be deposited on the substrate due to the galvanic exchange, which plays the role of anchor for the deposition of Ag catalytic materials on the substrate. A Ag catalytic layer can then be deposited on the pretreated copper mesh via electrodeposition. The electrodeposition bath composition may contain a source of silver and additives to improve the quality of the electrodeposited Ag layer. For example, silver nitrate (AgNO₃) can be used as the source of Ag, and additives may include aminopolycarboxylic acids such as NTA, EDTA, DTPA, and/or DOTA, hydroxycarboxylic acids such as glycolic acid, citric acid, and/or tartaric acid, as well as polyols such as glycerol, glucose, and/or polyethylene glycol. Current density for the electrodeposition process can be selected between 2-200 mA/cm². The deposition time may range between 0.1-10 hours, depending on the current density selected. The electrodeposition can be performed on the metal substrate inside the ECR cell, or the process can be performed externally. The final product of this process is a copper mesh with a silver catalytic layer completely covering its surface.

For the production of syngas, an electrolytic cell such as cell 1200 of FIG. 12 can be used. The reaction can be controlled by a power supply, such as a potentiostat, allowing a fixed current to be produced by applying a fixed voltage to the ECR cell. Two water pumps may be used to circulate the catholyte and anolyte solutions. A stirrer can be used to stir the catholyte solution as well. An active catalyst size of 2 cm² can be used but can be enlarged depending on the quantity of products needed. Simulated flue gas inlet can be prepared by mixing CO₂ with other gases (e.g. N₂, O₂, NO_x, SO_x) with a CO₂ concentration of 10%. The gas products from the ECR reaction, such as carbon monoxide (CO), can be analyzed using a gas chromatograph, for example, PerkinElmer Clarus 50, coupled with a thermal conductivity detector (TCD). Argon can be used as a carrier gas, for example, 99.99% Argon gas from Praxair. The faradaic efficiencies of the gaseous products are determined as a function of operating current, gas chromatography and flow rate at the outlet of the gas chamber using the following relationship: FE=n×F×θ×f_m/J, where n is the number of electrons for a given product (for e.g., n=2 for CO and H₂), F is the faradaic constant, θ is volume fraction of the gases, f_m is the molar reacting gas flow rate, and J is current.

For the production of syngas, the base solution may contain KOH. For example, 1 liter of 0.3 M KOH solution can be prepared by dissolving 19.5 g KOH solid (industrial grade, 85%) in water. The obtained solution can then be bubbled with a simulated flue gas containing 10% CO₂ by concentration, under stirring, for 5 hours. The flow of the gas can be set at 300 mL/min. The following reaction takes place: KOH+CO₂→KHCO₃. The KOH is then substantially converted into potassium bicarbonate (KHCO₃), which may be used as the catholyte for the ECR reaction. The anolyte used may be 1 liter of 1 M KOH. There is no need to add more KOH or change the anolyte solution during ECR. The KOH may be used to improve the conductivity of the anolyte. The catholyte and anolyte solutions are circulated through the cathode and anode chambers, respectively. The catholyte is continuously bubbled with a dilute CO₂ stream at a flowrate of 10 mL/min under vigorous stirring. The power source is configured to produce a voltage of around 3.6 V to the electrodes by applying a fixed current of 200 mA flowing through the cell.

The water at the anolyte decreases in volume as it is oxidized to O₂ at the anode at a rate of around ˜1.7 g/day. Accordingly, 1.7 g of fresh water is added daily into the anolyte, maintaining the volume of the anolyte solution at 1 liter constantly. The water may be added automatically by using a pump. At the cathode, bicarbonate is continuously reduced to syngas, with an average faradaic efficiency of about 60-80%.

Example Ethylene Production

Ethylene can be produced using method 1800 in a similar manner to that of the production of formates, with modifications to certain aspects, such as the catalyst used. Reference is next made to FIG. 11, which shows a flow diagram of an example process 1100 for the production of carbon monoxide and ethylene in accordance with presently disclosed methods. Cell 1112 containing anode 1106 and cathode 1110 is used to perform the ECR reaction. Base solution 1102 is combined with flue gas to form the catholyte solution, which may be fed into cathode 1110 via pump 1104 to be reduced into ethylene and CO.

The catalyst for ethylene production may be based on copper (Cu). A commercial copper mesh with high porosity (mesh number 100-200) and high electrical conductivity can be used as substrate. The cathode can be prepared using pre-treatment and electrodeposition.

Pre-treatment of the cathode may help to improve the adherence of Cu catalytic layer on the substrate. If the Cu cathode is not pre-treated, the catalytic activity of the electrode may decrease quickly due to aggregation and leaching of the catalytic material. The Cu mesh is treated with acetic acid for 30 minute to clean and remove any copper oxide on the surface. A Cu layer can then be deposited on the pretreated Cu mesh via electrodeposition. The electrodeposition bath composition may contain a source of copper, and additives to improve the quality of the electrodeposited Cu layer. For example, copper sulfate (CuSO₄) or copper nitrate (Cu(NO₃)₂) can be used as the source of Cu, and additives may include aminopolycarboxylic acids such as NTA, EDTA, DTPA and/or DOTA, hydroxycarboxylic acids such as glycolic acid, citric acid, and/or tartaric acid, as well as polyols such as glycerol, glucose, and/or polyethylene glycol. Current density for the electrodeposition process can be selected between 2-200 mA/cm². The deposition time may range between 0.1-10 hours, depending on the current density selected. The electrodeposition can be performed on the metal substrate inside the ECR cell, or the process can be performed externally. The final product of this process is a copper mesh with a copper catalytic layer completely covering its surface.

For the production of ethylene, an electrolytic cell such as cell 1200 of FIG. 12 can be used. The reaction can be controlled by a power supply, such as a potentiostat, allowing a fixed current to be produced by applying a fixed voltage to the ECR cell. Two water pumps may be used to circulate the catholyte and anolyte solutions. An active catalyst size of 2 cm² can be used but can be enlarged depending on the quantity of products needed. Simulated flue gas inlet can be prepared by mixing CO₂ with other gases (e.g. N₂, O₂, NOx, SOx) with a CO₂ concentration of 10%. The gas products from the ECR reaction, such as C₂H₄, can be analyzed using a gas chromatograph, for example, the PerkinElmer Clarus 50, coupled with a flame ionization detector (FID) operated at 250° C. Argon can be used as a carrier gas, for example, 99.99% Argon gas from Praxair. The faradaic efficiencies of the gaseous products are determined as a function of operating current, gas chromatography and flow rate at the outlet of the gas chamber using the following relationship: FE=n×F×θ×f_m/J, where n is the number of electrons for a given product (for e.g., n=2 for CO and H₂), F is the faradaic constant, θ is volume fraction of the gases, f_m is the molar reacting gas flow rate, and J is current.

For the production of ethylene using ECR, the base solution 1102 may contain KOH. For example, 1 liters of 0.3 M KOH solution can be prepared by dissolving 19.5 g KOH solid (industrial grade, 85%) in water. The obtained solution can then be bubbled with a simulated flue gas containing 10% CO₂ by concentration, under stirring, for 5 hours. The flow of the gas can be set at 300 mL/min. The following reaction takes place: KOH+CO₂→KHCO₃. The KOH is then substantially converted into potassium bicarbonate (KHCO₃), which may be used as the catholyte for the ECR reaction. The anolyte used may be 1 liter of 1 M KOH. There is no need to add more KOH or change the anolyte solution during ECR. The KOH may be used to improve the conductivity of the anolyte. The catholyte and anolyte solutions are circulated through the cathode and anode chambers, respectively. The catholyte is continuously bubbled with a dilute CO₂ stream at a flowrate of 10 mL/min under vigorous stirring. The power source is configured to produce a voltage of around 3.6 V to the electrodes by applying a fixed current of 200 mA flowing through the cell.

The water at the anolyte decreases in volume as it is oxidized to O₂ at the anode at a rate of around ˜1.7 g/day. Accordingly, 1.7 g of fresh water is added daily into the anolyte, maintaining the volume of the anolyte solution at 1 liter constantly. The water may be added automatically by using a pump. At the cathode 1110, bicarbonate is continuously reduced to the desired output product, ethylene, with an average faradaic efficiency of about 40-50%.

Example Desiccant Production

Desiccants may be produced by combining a formate salt and plant-based polymers in an appropriate ratio. The polymer may be derived from any plant with a sufficient cellulose content, but may specifically be one or more of the following plants: jute, corn, cassava, pal, coconut, bamboo, cotton. To produce the desiccants, a concentrated solution of formate (e.g., potassium formate) can be treated with a proprietary plant-based powder. The resulting mixture may be solidified at 90 degree Celsius. The potassium formate may be produced from an ECR process such as, for example, the methods presently described herein.

Reference is next made to FIG. 10, which shows an example flow diagram 1000 for the production of desiccants in accordance with presently disclosed methods. Process 1002 may be any process for producing formates, including processes 600, 700, 800, 900 of FIGS. 6, 7, 8, 9, respectively. Process 600 for the production of potassium formate is shown as an example. Once potassium formate has been produced, a concentrated solution 1004 containing the potassium formate can be treated with a plant-based powder to produce the output desiccant 1006.

FIGS. 16A and 16B show the performance of the desiccants. FIG. 16A shows a graph 1600 of the water vapor adsorption capacity of a potassium formate-based desiccant (1604) in comparison with the performance of commercial silica gel (1602), which is one of the most popular types of desiccant on the market. The measurements were conducted at 25 degrees Celsius and at various relative humidity values (60%, 70%, and 80%). FIG. 16B shows a graph 1610 of the reusability performance 1612 of the desiccant at a relative humidity of 60%. The desiccant was used and then regenerated at a temperature of 100 degrees Celsius. As shown, the moisture adsorption capacity remains unchanged after 20 cycles of regeneration.

While the above description provides examples of the embodiments, it will be appreciated that some features and/or functions of the described embodiments are susceptible to modification without departing from the spirit and principles of operation of the described embodiments. Accordingly, what has been described above has been intended to be illustrative of the invention and non-limiting and it will be understood by persons skilled in the art that other variants and modifications may be made without departing from the scope of the invention as defined in the claims appended hereto. The scope of the claims should not be limited by the preferred embodiments and examples, but should be given the broadest interpretation consistent with the description as a whole.