Porous Separators Coated With Boron-Containing Species For Electrolyzers

CROSS REFERENCE TO RELATED APPLICATIONS

[0001]This application claims the benefit of U.S. Provisional Patent No. 63/701,537 filed Sep. 30, 2024, which is incorporated by reference herein in its entirety for all purposes.

BACKGROUND

[0002]Carbon dioxide (CO₂) accumulation in the atmosphere is a major culprit in global warming. Capturing it using a decarbonized source of electricity at emitting sources or directly from the air (through direct air capture) and converting it into valuable chemicals and fuels is a promising way to both reduce its atmospheric concentration and offer sustainable alternatives to current fossil-fuel-derived feedstocks. Among the envisioned conversion technologies, polymer-electrolyte-membrane-based electroreduction technology stands out by its versatility (possible use at a wide range of temperatures and pressures) and amenability to generate a wide range of products.

[0003]Such electrolyzers have gained significant interest over the last years, as they allow the production of valuable chemicals such as hydrogen, carbon monoxide (CO), ethylene, ethanol, methane, formic acid, oxalic acid, acetic acid, propane, propanol, ammonia, amino acids, urea, carbon- and nitrogen-containing products through the conversion of water, CO₂, CO and/or carbonate ions (CO₃²⁻) or bicarbonate ions (HCO₃⁻), and/or nitrogen-containing compounds such as but not limited to nitrous oxides and/or N₂.

[0004]Common electrolyzer designs include multiple cells that are stacked onto each other. In a stack, each individual cell comprises an anode and a cathode, separated by a membrane to provide selective ion conductivity. Individual cells are physically supported on each side by conductive polar plates. Polar plates are configured to apply electric potential between the cathode and the anode to drive reduction and oxidation reactions of reactants. Such reactants are transported towards the anode and cathode through flow fields/suitable supports next to the polar plates. As the conversion of reactants into valuable molecules is driven by electrical power, it is desirable to increase the energy efficiency of the electrolyzers to reduce the power requirement. There is a need for suitable electrolyzer components, including separator membranes, that support improved efficiency of performance.

SUMMARY

[0005]This disclosure relates to separators, containing boron species, that are used in electrolyzers. In specific embodiments of the invention, the electrolyzers can be oxocarbon electrolyzers. In specific embodiments of the invention, an electrolysis reactor includes an anode area and a cathode area with a separator separating the anode area and the cathode area. The separator contains boron species on and within the separator. The separator can be formed by electrically insulative material while being ionically conductive. As such, the separator can allow for ionic migration between the anode area and cathode area while still separating the anode area and the cathode area. The separator can also serve as a support for one or more electrodes (e.g., an electrode in the anode area or an electrode in the cathode area). The separator can be formed entirely of electrically insulative material. The incorporation of boron containing species onto and within a separator is a simple, inexpensive and versatile method of producing separators for electrolysis. As such, using approaches disclosed herein, a separator containing boron species within an electrolysis reactor can provide for migration of ionic species between the anode and cathode while the overall cost of the electrolyzer is greatly reduced. Furthermore, ion exchange membranes that contain ionic charge bound to the polymeric backbone have to have trade-offs in design as the amount of incorporated ionic charge and mechanical stability are negatively correlated. Approaches disclosed herein exhibit significant benefits in that the separator can be made mechanically sturdy without regard to optimizing for a negatively correlated property.

[0006]The use of a separator containing boron species provides significant benefits as compared to other approaches because the cost of fabrication is lower and because the separator is overall more reliable than alternative approaches. The ion conducting separator membrane in an electrolyzer is one of its major sources of unreliability. The necessity to present both an ion exchange environment and structural stability to the electrode presents a zero-sum game, where increases to the structural stability of the membrane generally comes at the cost of ion exchange capacity and visa-versa. This makes the production of stable electrolyzer stacks particularly difficult and important. The separator is a critical component and membrane ruptures in one cell may lead to deactivation of the entire unit. The use of ion exchange membranes that contain ionic charge bound to the polymeric backbone also prevents the use of high differential pressures across the electrolyzer, due to structural weakness, but these high differential pressures are often desirable to encourage the correct catalytic environment in the system. High differential pressures are also an unavoidable result of the source of the having a variable pressure (e.g., an industrial waste source) and therefore must be tolerated when processing the reactant and product species.

[0007]In specific embodiments of the invention, an electrolysis reactor includes an anode area and a cathode area with a porous separator separating the anode area and the cathode area. The porous separator can have pores with cross sections having an average size less than one millimeter down to nanometers. The porous separator can include a porous network formed by a set of such pores that extend through the separator from one side of the separator to another side of the separator. The porous network extends through the separator in that there are paths from the one side of the separator to the other side of the separator through the porous network. In specific embodiments of the invention, this porous network can be filled with a liquid electrolyte after the separator is installed in the electrolyzer. Using the approaches disclosed herein, an electrolysis reactor can thereby provide for facile migration of ionic species between the anode and cathode to improve the performance of the electrolyzer. In specific embodiments of the invention, an electrolysis reactor can utilize a porous separator containing boron species. The boron species containing separator can be formed by electrically insulative material while being ionically conductive via the migration of ions through the porous network. A conductive electrolyte of the electrolysis reactor can fill the pores of the separator to provide a path for ions to migrate through the separator.

[0008]In specific embodiments of the invention, the separators disclosed herein can be coated to improve the performance of the electrolysis reactor in which the separator is utilized. The coating is comprised of two steps; first an alcohol-containing polymer is applied to the surface of the separator followed by a reaction between said alcohol-containing polymer and a boron containing species. The coating can be selected such that it increases the hydrophilicity of the separator such as by increasing the hydrophilicity of the surfaces of the pores in a porous separator. The coating can be selected such that it can withstand contact with the electrolyte of an electrolysis reactor, can withstand oxidation, and can withstand the general conditions of a separator in an electrolysis reactor such that the coating stays on the separator and the performance of the separator does not degrade during usage of the separator in an electrolysis reactor. The coatings can be selected to be insoluble in the electrolyte on an electrolyzer as well as any chemicals produced by the electrolyzer. The coating can also be selected to have a similar chemical structure as the separator to assure the coating meshes well with the separator, or in some cases, the coating can comprise a copolymer where sections of the copolymer have a similar chemical structure to the separator. In specific embodiments, both the material of which the separator is formed, and the coating, can be selected in combination to assure good adherence of the coating to the separator and improved performance of the electrolysis reactor.

[0009]In specific embodiments, separators with coatings such as those described in the prior paragraph have been modified by reacting them with a boron-containing species. A boron-containing species (e.g. borax) can react with a coating polymer in the coating to bond with adjacent hydroxyl groups on the coating surface. The surface of the coating extends to the surfaces of pores distributed throughout the separator. The boron-containing species can further increase the hydrophilicity of the pore surfaces, which can improve the surface wettability of the separator to an electrolyzer solvent and increase the ionic transport through the separator membrane between the cathode and anode. Moreover, the boron-containing species physically crosslinks two or more alcohol-containing polymers improving the mechanical stability as well as decreasing the coatings solubility in electrolyte. In specific embodiments the result is higher electrolytic efficiency without negatively affecting structural stability of the underlying separator.

[0010]In specific embodiments, a separator for an electrolyzer cell is provided. The separator for an electrolyzer cell comprises a porous substrate having pores which provide a fluid path through the porous substrate from a first side of the porous substrate to an opposite side of the porous substrate and formed of one or more hydrophobic polymers or copolymers; and a coating that coats the pores of the porous substrate while maintaining the fluid path, wherein the coating is formed of an alcohol-containing polymer and a boron-containing species that is reacted with the alcohol-containing polymer.

[0011]In specific embodiments, a method of forming a separator is provided. The method comprises creating a porous substrate from a hydrophobic homopolymer or copolymer, submerging the porous substrate into a nonaqueous solvent whereby the pores in the porous substrate are filled with the nonaqueous solvent, adsorbing an alcohol-containing polymer onto the porous substrate including inside the pores contained therein, and reacting the alcohol-containing polymer with a boron-containing species.

[0012]In specific embodiments, an electrolysis reactor is provided. The electrolysis reactor comprises an aqueous or gaseous anode area with an aqueous or gaseous oxidation substrate, an aqueous or gaseous cathode area with species as an aqueous or gaseous reduction substrate, and a separator separating the anode area and the cathode area while allowing ionic migration between the anode area and cathode area, wherein: (i) the separator is a polymer having a coating; and (ii) the coating is formed of an alcohol-containing polymer and a boron-containing species that is reacted with the alcohol-containing polymer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]The accompanying drawings illustrate various embodiments of systems, methods, and other aspects of the disclosure. A person with ordinary skills in the art will appreciate that the illustrated element boundaries (e.g., boxes, groups of boxes, or other shapes) in the figures represent one example of the boundaries. It may be that in some examples one element may be designed as multiple elements or that multiple elements may be designed as one element. In some examples, an element shown as an internal component of one element may be implemented as an external component in another and vice versa. Furthermore, elements may not be drawn to scale. Non-limiting and non-exhaustive descriptions are described with reference to the following drawings. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating principles.

[0014]FIG. 1 is a diagram of an example electrolysis reactor in accordance with specific embodiments of the inventions herein.

[0015]FIG. 2 is a process and a diagram illustrating a method of creating a boron-containing separator in accordance with specific embodiments of the inventions herein.

[0016]FIG. 3 is a process and a diagram illustrating a method of creating a boron-containing separator in accordance with specific embodiments of the inventions herein.

[0017]FIG. 4 is a data plot of voltage potential and Faradaic efficiency percentage of various chemicals produced in a carbon monoxide electrolyzer cell with various boron-containing separators produced in accordance with examples 3A and 3B as disclosed herein.

[0018]FIG. 5 is a data plot of voltage potential and Faradaic efficiency percentage of various chemicals produced in a carbon monoxide electrolyzer cell with various boron-containing separators produced in accordance with examples 4A, 4B, and 4C as disclosed herein.

[0019]FIG. 6 is a data plot of voltage potential and Faradaic efficiency percentage of various chemicals produced in a carbon monoxide electrolyzer cell with various boron-containing separators produced in accordance with examples 5A, 5B, and 5C as disclosed herein.

[0020]FIG. 7 is a data plot of voltage potential and Faradaic efficiency percentage of various chemicals produced in a carbon monoxide electrolyzer cell with various boron-containing separators produced in accordance with examples 5A and 6 as disclosed herein.

[0021]FIG. 8 is a data plot of voltage potential and Faradaic efficiency percentage of various chemicals produced in a carbon monoxide electrolyzer cell with different numbers of stacked boron-containing separators produced in accordance with example 7 as disclosed herein.

[0022]FIG. 9 is a data plot of voltage potential and Faradaic efficiency percentage of various chemicals produced in a carbon monoxide electrolyzer cell with a commercially available separator and a boron-containing separators produced in accordance with example 8 as disclosed herein.

[0023]FIG. 10 is a data plot of voltage potential and Faradaic efficiency percentage of various chemicals produced in a carbon monoxide electrolyzer cell with a boron-containing separator produced in accordance with example 9 as disclosed herein.

[0024]FIG. 11 is a data plot of voltage potential a carbon monoxide electrolyzer cell with a separator created using a control method.

DETAILED DESCRIPTION

[0025]Reference will now be made in detail to implementations and embodiments of various aspects and variations of systems and methods described herein. Although several exemplary variations of the systems and methods are described herein, other variations of the systems and methods may include aspects of the systems and methods described herein combined in any suitable manner having combinations of all or some of the aspects described.

[0026]Methods and systems related to novel separators containing boron species and electrolysis reactors utilizing such novel separators in accordance with the summary above are disclosed in detail herein. The methods and systems disclosed in this section are nonlimiting embodiments of the invention, are provided for explanatory purposes only, and should not be used to constrict the full scope of the invention. It is to be understood that the disclosed embodiments may or may not overlap with each other. Thus, part of one embodiment, or specific embodiments thereof, may or may not fall within the ambit of another, or specific embodiments thereof, and vice versa. Different embodiments from different aspects may be combined or practiced separately. Many different combinations and sub-combinations of the representative embodiments shown within the broad framework of this invention, that may be apparent to those skilled in the art but not explicitly shown or described, should not be construed as precluded.

[0027]The electrolyzers used in accordance with the approaches disclosed herein can have various architectures. The electrolyzer can include an anode area and a cathode area. A liquid or gas can be provided to the cathode area of the reactor as a reduction substrate. Useful chemicals can be produced in the cathode area, in the anode area, or in a separating area located between the cathode area and the anode area of the electrolyzer. The rate at which the reaction occurs can be dependent upon the degree of ionic migration across one or more separators between the cathode area and the anode area. The electrolyzer can be a single planar electrolyzer. The electrolyzer can be a stack of cells. The cells in the stack can utilize bipolar plates. The bipolar plates can be charged to initiate reactions within the reactor. The electrolyzer can also be a filter press electrolyzer or a tubular electrolyzer.

[0028]FIG. 1 includes an illustration of an electrolysis reactor cell 100 in the form of a single planar electrolyzer in accordance with specific embodiments of the inventions disclosed herein. In this particular example, the electrolyzer cell shows operation of an oxocarbon electrolysis reactor cell, but most portions of this description would also apply to other electrochemical cells. The oxocarbon electrolysis reactor cell 100 includes a separator and electrode assembly such as electrode assembly 130, a flow field such as flow fields 110 and 120, and polar plates 102 and 104. Additionally, the oxocarbon electrolysis reactor cell 100 includes an inlet 113 and an outlet 114 for an anodic stream, as well as an inlet 123 and an outlet 124 for the cathodic stream. An oxocarbon can be provided at the inlet 123 in the cathodic stream. The oxocarbon can be humidified. A useful chemical can be provided at outlet 114 in the anodic stream. The electrode assembly can comprise an anode 132, a cathode 134, and a porous separator membrane 140. The porous separator membrane can be a single membrane or can comprise several separate layers with similar or different properties. The polar plates can be monopolar plates or bipolar plates (BPP) if part of a stack. The cell can also comprise end plates, gasketing, sealing of any shape, insulating layers and other materials that have not been represented in the FIG. 1 for clarity. In specific embodiments, the electrolytes in the electrolysis reactor cell are at least partially in aqueous solution.

[0029]In embodiments where the electrolyzer contains multiple cells 100, the reactor can have cells implemented as an electrolysis stack, where subsequent cells can be physically separated by bipolar plates that can ensure mechanical support for each of the electrolysis cells on each side of the BPP. BPP can also ensure electrical series connection between subsequent electrolysis cells and introduce/remove the reactants/products respectively. At the end of the stack, only one side of the plate can be in contact with the terminal cell; it is then called a monopolar plate. End plates to provide pressure on the stack and rigid bars to maintain the structure of the stack can also be present. At the extremities of the stack, current collectors can allow connection to an external power supply, which can also be used, among other elements, for electrical monitoring of the stack. The stack can be assembled within a stack casing allowing its mechanical support and compression, as well as provisioning and transporting the reactant and product streams to and from the stack. The stack casing can comprise end plates that ensure electrical isolation of the stack and provide the inlet and outlets for the reactant and product streams. Alternatively, insulator plates can be placed between end plates and the monopolar plate to ensure electrical insulation of the stack versus the stack casing depending on the material of the end plate.

[0030]The following describes a boron-containing separator and methods of creating a boron-containing separator. In specific embodiments, a boron-containing separator comprises a porous substrate and a coating formed of an alcohol-containing polymer that has been reacted with a boron-containing species.

[0031]In specific embodiments, the substrate is a porous material that is chemically inert and ideally prepared of a hydrophobic polymer material. The substrate should be mechanically strong to prevent the formation of defects during handling and within the application. Furthermore, the substrate should be compatible with the alcohol-containing polymer such that the alcohol-containing polymer can change the surface wettability of the substrate to be sufficiently hydrophilic. The substrate can be prepared from poly(ethylene) but may be prepared from other polymer materials, such as but not limited to; poly(propylene), poly(butylene), poly(butadiene), poly(styrene), poly(vinyl fluoride), poly(vinylidene fluoride), poly(tetrafluoroethylene), poly(hexafluoropropylene), poly(vinyl chloride), poly(chlorotrifluoroethylene), or poly(dimethylsiloxane). The substrate may be prepared from a copolymer material by combining monomers used to prepare the above listed homopolymer materials. For example, the substrate may be prepared from a copolymer of poly(ethylene-co-propylene). The substrate may be prepared from a blend of two or more different polymer materials listed above. Polymer materials may be homopolymers or copolymers. The substrate may be uniformly porous throughout the material, or pore sizes may be irregular depending on how they are formed. The pores can be between 1 nm and 100 μm in size, but these can be various sizes as set by the desired mechanical stability and ionic conductivity of the separator. The substrate can be a flat sheet with uniform thickness and can be between 1 and 1000 μm in thickness.

[0032]In specific embodiments, the alcohol-containing polymer can be a homopolymer or a copolymer. The alcohol-containing polymer is a polymer formed from one or more types of monomers such that the resulting polymer contains at least one alcohol functional group. The alcohol-containing polymer is not required to provide mechanical stability to the separator but is expected to modify the surface wettability of the porous substrate. Therefore, the alcohol-containing polymer is expected to remain on the surface of the substrate for the lifetime of the separator. Alcohol-containing polymers can be composed of homopolymers or copolymers prepared by chain-growth polymerization of alcohol-containing unsaturated or cyclic monomers such as acrylates, methacrylates, styrenes, olefins, vinyls, acrylamides, methacrylamides, epoxides, lactams and lactones; one or more variety of monomer may be selected and one or more monomer from the same comonomer classification can be used. Therefore, in specific embodiments, all monomer repeat units in the polymer would contain at least one alcohol functional group. Alcohol-containing polymers can be composed of copolymers prepared by chain-growth polymerization of at least one alcohol-containing unsaturated or cyclic monomer such as acrylates, methacrylates, styrenes, olefins, vinyls, acrylamides, methacrylamides, epoxides, lactams and lactones, and at least one unsaturated monomer that does not contain an alcohol functional group from the following monomer classes; acrylates, methacrylates, styrenes, olefins, vinyls, acrylamides, methacrylamides. Therefore, in specific embodiments, not all monomer repeat units on the copolymer would contain an alcohol functional group but the copolymer would contain at least one alcohol functional group.

[0033]Alcohol-containing polymers may also be composed of polymers prepared by step-growth polymerization of amines, alcohols, thiols, carboxylic acids, esters, acid halides, isocyanates, alkenes such that an unreacted alcohol functional group remains on each monomer repeat unit. One or more variety of step-growth monomer may be selected and one or more monomer from the same comonomer classification can be used. Alcohol-containing copolymers may also be composed of polymers prepared by step-growth polymerization of amines, alcohols, thiols, carboxylic acids, esters, acid halides, isocyanates, alkenes such that an unreacted alcohol functional group is not present on every monomer repeat unit but there is at least one alcohol functional group on the copolymer. One or more variety of step-growth monomer may be selected and one or more monomer from the same comonomer classification can be used. Alcohol-containing copolymer may also be crosslinked to limit solubility of the polymer in electrolyte as well as controlling the total swelling in the electrolyte solution. Crosslinking may be covalent or non-covalent in nature. Crosslinking may be achieved during or after polymerization of the copolymer.

[0034]Alcohol-containing polymers can be prepared by post-polymerization modification of polymers containing functional groups that are capable of being transformed into alcohols. For example, polymers containing alkenes can undergo hydration reactions to prepare alcohols. Polymers containing aldehydes, ketones, carboxylic acids, esters, and epoxides, can similarly undergo reactions into polymers containing an alcohol group using various methods known to those with skill in the art. Alcohol-containing polymers prepared via post-polymerization modification may be homopolymers or copolymers depending on the initial copolymer transformed. Moreover, not every monomer repeat unit may contain an alcohol depending on the initial copolymer transformed.

[0035]In specific embodiments, the boron-containing species may be added to the separator following the treatment of the substrate with the alcohol-containing (co) polymer. The boron containing species is expected to react with the alcohol functional groups present on the alcohol-containing polymer to further modify the surface properties of the treated separator. In specific embodiments, suitable boron containing species include but are not limited to disodium;3,7-dioxido-2,4,6,8,9-pentaoxa-1,3,5,7-tetraborabicyclo [3.3.1] nonane; decahydrate (i.e. borax), sodium tetrahydroxyborate, boric acid, sodium tetraborate, sodium tetrahydridoborate, potassium tetrahydroxyborate, potassium tetraborate, potassium tetrahydridoborate, lithium tetraborate, lithium tetrahydroxyborate, lithium tetrahydridoborate, boron trifluoride, boron trichloride, boron tribromide, diboron trioxide, and triiodoborane. Alcohol-containing polymer can be treated with boron-containing species by dissolving the boron-containing species in a suitable solvent prior to treatment. In specific embodiments, a catalyst for the modification of alcohol-containing polymer with the boron-containing species is not required, but in other embodiments, a suitable catalyst may be added to increase the rate of reaction or decrease the reaction temperature required to complete the modification. In specific embodiments, reaction of the boron-containing species can create crosslinks between alcohol-containing polymer chains, whether different portions of the same chain or links among different chains. The degree of crosslinking depends upon particular polymers chosen as well as other reaction conditions.

[0036]Preparation of the separator membrane can be achieved using a variety of methods or ordering of steps. In specific embodiments of the invention, the porous substrate is treated with an alcohol-containing polymer before modification of the alcohol-containing polymer with a boron-containing species. In specific embodiments, it is also possible to chemically modify the alcohol-containing polymer with the boron-containing species prior to treatment of the substrate with the now modified alcohol-containing polymer. In some cases, this may be easier to accomplish when the degree of crosslinking in the modified alcohol-containing polymer is relatively low. In specific embodiments, the substrate may be filled with a boron-containing species before addition of alcohol-containing polymer to the substrate to complete the chemical modification of the alcohol-containing polymer with the boron-containing species within the substrate.

[0037]In specific embodiments, the alcohol-containing polymer can be applied to the surface of the substrate by submerging the substrate in a solution of the alcohol-containing polymer. Any suitable solvent may be used such that the structure of the substrate is not negatively affected, and the alcohol-containing polymer is sufficiently soluble. Any suitable solvent may be used such that the structure of the substrate is not negatively affected, and the alcohol-containing polymer is dispersed; however, the solvent must be able to fully penetrate the porous structure at the time of coating the substrate with the alcohol-containing polymer so that the pore surfaces can be covered to the desired degree. The alcohol-containing polymer can be any concentration in the solution as well as saturating the solution. In specific embodiments, the alcohol-containing polymer may be applied to the surface of the substrate by submerging the substrate in molten alcohol-containing polymer. Any temperature may be used as long as the substrate is not negatively affected, and the alcohol-containing polymer is suitably molten. In specific embodiments, the alcohol-containing polymer may be applied to the surface of the substrate by any suitable coating technique including doctor blade, slot-dic, screen printing, roller coating, painting, spraying, dip coating, spin coating, inkjet printing, and metering rod. The alcohol-containing polymer may be applied in the molten state or as plasticizer softened solid. The substrate treated with alcohol-containing polymer can be subsequently dried or stored in a wet state before chemical modification with the boron-containing species. In specific embodiments, an alcohol-containing polymer can be reacted with a boron containing species and then applied to the porous substrate in any of the coating techniques previously presented.

[0038]In specific embodiments, the alcohol-containing polymer on the surface of the substrate is chemically modified by the boron-containing species by submerging the alcohol-containing polymer treated substrate in a solution of the boron-containing species. Any suitable solvent may be used such that the structure of the substrate is not negatively affected, the alcohol-containing polymer is not removed from the surface of the substrate, and the boron-containing species is suitably soluble or dispersed. Boron-containing species can be any concentration in the solution as well as fully saturating the solution. In specific embodiments, alcohol-containing polymer on the surface of the substrate is chemically modified by the boron-containing species by submerging the alcohol-containing polymer treated substrate in a molten boron-containing species. Any molten boron-containing species and temperature may be used such that the structure of the substrate is not negatively affected, the alcohol-containing polymer is not removed from the surface of the substrate, and the boron-containing species can react with the alcohol-containing polymer. In specific embodiments, the boron-containing species may be applied to the surface of the substrate treated with alcohol-containing polymer by any suitable coating technique including doctor blade, slot-die, screen printing, roller coating, painting, spraying, dip coating, spin coating, inkjet printing, and metering rod. In specific embodiments, the boron-containing species can be combined with a suitable catalyst to increase the efficiency of the alcohol-containing polymer modification. A catalyst and the boron-containing species can be dissolved together in solution or the catalyst can be dissolved in a molten boron-containing species. This combination can be reacted or applied in any of the techniques previously presented.

[0039]In specific embodiments, the coating does not substantially add to the overall extent of porous substrate as measured from the first side to the opposite side. Similarity in structure and composition of the polymers chosen for both the substrate and the alcohol-containing polymer influences how well the alcohol-containing polymer coats the surface. In specific embodiments, the alcohol-containing polymer may form a very thin coating that adsorbs to the substrate polymer surfaces including the pore surfaces. The coating thickness may be as thin as a single monolayer or few layers. Thicker layers may wash away as part of the coating process. The boron-containing species does not add appreciably to the thickness of the coating on its own as it only stays on the surface where it has reacted with the hydroxyl groups of the alcohol-containing polymer. Care must be taken in selection of both materials as well as reaction conditions. It has been previously mentioned that the boron-containing species can form crosslinks between the same or different alcohol-containing polymer chains. While it may be possible for these crosslinks to stabilize a thicker coating than mentioned in this embodiment, it would be counterproductive for many applications for the coating to be too thick. Also as previously mentioned, the alcohol-containing polymer reacted with a boron-containing species can increase the hydrophilicity of the porous surfaces of the separator and thus increase the ion transport through the separator. If the coating thickness is too high, it may overly restrict or block fluid flow through the pores, which would lead to a net decrease in ion transport.

[0040]FIG. 2 describes a process 200 of creating a boron-containing separator according to specific embodiments of the invention. The figure shows the process 200 in an inset with steps 202-210; the illustrations to the right illustrate various states of the substrate during the process, labeled 220-225. In step 202, a porous substrate 240 is created using the materials previously presented. The porous substrate 240 is shown in state 220 with a number of pores. The illustration is a cross section of the porous substrate where the pore sizes are exaggerated for clarity. Though the pores are shown as separate, in the porous substrate overall they are connected in such a way as to allow fluid connection between the top and bottom of the substrate. In step 204, a selected alcohol-containing polymer is dissolved in a nonaqueous solvent. The nonaqueous solvent, for example dimethyl sulfoxide (DMSO), is selected to be partially nonpolar such that it can wet the pore surfaces of the hydrophobic substrate but also dissolve the alcohol-containing polymer to draw it into the pores.

[0041]In step 206, the porous substrate 240 is immersed in the nonaqueous solvent that has the alcohol-containing polymer. State 221 shows the non-aqueous solvent 241 surrounding the substrate where most of the pores still contain air, though pore 242 shows some solvent infiltration. State 222 shows all the pores filled with the solvent 241. In step 208, the alcohol-containing polymer is adsorbed onto the porous substrate. This is illustrated in state 223 where after some time, the thicker lines around the pores represent a thin coating of alcohol-containing polymer on the pore surfaces. In this embodiment, step 208 begins soon after step 206 as the alcohol-containing polymer is delivered to the interior pore surfaces as the solvent displaces the air in the pores. Note that the alcohol-containing polymer is not chemically bonded to the surface of the pores here; rather, they are held on by van der Waals or other hydrophobic forces. The strength of these forces is related to the materials of both the substrate and the polymer chain backbone. Furthermore, when a copolymer was selected for the alcohol-containing polymer where portions of the copolymer contain alcohol groups, and other portions do not, the portions without alcohol groups may be more chemically similar to the porous substrate material and thus exhibit a stronger bonding force. Regardless of type of polymer, the alcohol-containing polymer should be chosen so that it maintains a durable bond when coating the substrate polymer.

[0042]In step 210, a boron-containing species reacts with the alcohol-containing polymer. In an example, state 224 shows the substrate submerged in an aqueous solution 243 of boric acid and potassium hydroxide. State 224 also shows the beginning of the aqueous solution filling pore 244 and displacing the nonaqueous solvent. The alcohol-containing polymer coating has increased the hydrophilicity of the porous surfaces; because the surfaces is now more wettable by the aqueous solvent, it is now more easily permeated by the solvent so that the nonaqueous solvent can be displaced. By state 225, all the pores have been filled with the aqueous solution, and after sitting for a specified amount of time, the alcohol-containing polymer coating has been reacted with the boric acid to form a complex with the boron, shown in dotted lines. The finished separator can be removed from solution and used for its intended purpose.

[0043]Certain steps can be modified yet still create a similar separator to the one described in process 200. FIG. 3 describes a process 300 of creating a boron-containing separator according to specific embodiments of the invention. Process 300 is similar to process 200 but certain steps are switched. The figure shows the process 300 in an inset with steps 302-310; the illustrations to the right illustrate various states of the substrate during the process, labeled 320-326. In step 302, a porous substrate 340 is created using the materials previously presented in a similar manner as in step 202. Porous substrate 340 shown in state 320 is equivalent to porous substrate 240. In step 304, the porous substrate 340 is immersed in a nonaqueous solvent, for example isopropyl alcohol (IPA). State 321 shows the nonaqueous solvent 341 starting to permeate into pore 342, and by state 322, the nonaqueous solvent has displaced all the air. A different solvent may be used in this step compared to process 200 as it achieves a slightly different purpose than step 204 shown previously, although a solvent such as DMSO could still be used for this process. In this example, IPA is more nonpolar than water and DMSO; here the somewhat nonpolar IPA can easily wet all the interior surfaces. In step 306, a selected alcohol-containing polymer is dissolved in water. In step 308, the alcohol-containing polymer is adsorbed onto the porous surfaces. This is achieved by submerging the substrate in the aqueous alcohol-containing polymer solution 344 as shown in state 323. Over time, pores such as pore 344 become filled with solution 343. Finally state 324 shows a substrate where the pores are filled with the aqueous solution and alcohol-containing polymer has coated the pore walls. Note that this may not have occurred in a reasonable timeframe without the earlier step of submerging the substrate in a nonaqueous solvent. In our example, the IPA is sufficiently nonpolar to be able to permeate and completely wet the surfaces of even a highly nonpolar substrate as, for example, poly(ethylene). IPA is also highly soluble in water; it is thought that the presence of IPA in the pores allows water along with any dissolved solutes to readily permeate through the separator and displace the IPA. In the process, hydrophobic interactions allow the alcohol-containing polymer to bond with the pore surfaces.

[0044]Finally, in step 310, a boron-containing species reacts with the alcohol-containing polymer. In an example, state 325 shows the substrate submerged in a second aqueous solution 345 of boric acid and potassium hydroxide. State 325 also shows the beginning of the aqueous solution filling pore 346 and displacing the aqueous solution of the alcohol-containing polymer. Similarly to before, the alcohol-containing polymer coating has further increased the hydrophilicity of the porous surfaces; because the surfaces is now more wettable by the aqueous solvent 345, and in this case as the pores already contain water, the substrate is easily permeated by the new aqueous solvent 345. By state 326, all the pores have been filled with the second aqueous solution, and after sitting for a specified amount of time, the alcohol-containing polymer coating has been reacted with the boric acid to form a complex with the boron, shown in dotted lines. The finished separator can be removed from solution and used for its intended purpose.

[0045]Which process to use can depend on several factors including substrate material, boron-containing species, and particularly the alcohol-containing polymer. For example, if polyvinyl alcohol is chosen as the alcohol-containing polymer, then, since it is fully soluble in water, process 300 can be used where both the alcohol-containing polymer as well as the boron-containing species are added in aqueous solution. However, if a copolymer such as poly(ethylene-co-vinyl alcohol) is the alcohol-containing polymer, then depending on the ratio between ethylene and vinyl alcohol monomers, the solubility in water may be insufficient; in this case, process 200 may be more appropriate.

[0046]The following are various examples showing preparation of boron-containing separators in accordance with this disclosure as well as supporting data illustrating their capabilities in an electrolyzer. Charts associated with the various examples are shown with curves relative to one another using relative units.

Example 1—Preparation of Boron-Containing Separator in Aqueous Solution of Borax

[0047]Poly(ethylene-co-vinyl alcohol) (0.14 g) was dissolved in dimethyl sulfoxide (13.86 g). Porous poly(ethylene) substrate (16 cm²) was submerged entirely in the poly(ethylene-co-vinyl alcohol) solution at room temperature. After 24 hours the porous poly(ethylene) substrate was removed and placed into a solution of anhydrous borax (0.28 g) in distilled water (13.72 g) and heated overnight at 90° C. Porous poly(ethylene) substrate was then placed into distilled water ready for testing.

[0048]The reaction of poly(ethylene-co-vinyl alcohol) with borax is shown in the following equation:

Example 2—Preparation of Boron-Containing Separator in Aqueous Solution of Boric Acid and Potassium Hydroxide

[0049]Poly(vinyl alcohol) (0.14 g) was dissolved in dimethyl sulfoxide (13.86 g). Porous poly(ethylene) substrate (16 cm²) was submerged entirely in the poly(ethylene-co-vinyl alcohol) solution at room temperature. After 24 hours the porous poly(ethylene) substrate was removed and placed into a solution of boric acid (0.28 g) and potassium hydroxide (0.28 g) in distilled water (13.44 g) at room temperature. After 24 hours the porous poly(ethylene) substrate was removed from the boric acid and potassium hydroxide solution and placed into distilled water until required for testing.

[0050]The reaction of poly(ethylene-co-vinyl alcohol) with boric acid and potassium hydroxide is shown in the following equation:

Example 3-Comparison of Separators with Multiple Substrate Thicknesses Created at Higher Temperature

[0051]Example 3A. Porous poly(ethylene) substrate (25 μm thick, 16 cm² surface area) was submerged entirely within a 0.1 wt % solution of poly(ethylene-co-vinyl alcohol) in dimethyl sulfoxide (14 g) at room temperature. After 24 hours the treated porous poly(ethylene) substrate was removed and submerged entirely within a 0.1 wt % solution of anhydrous borax in distilled water (14 g) and heated at 90° C. for 24 hours. Treated porous poly(ethylene) substrate was removed and placed into distilled water prior to testing.

[0052]Example 3B. Porous poly(ethylene) substrate (220 μm thick, 16 cm² surface area) was submerged entirely within a 0.5 wt % solution of poly(ethylene-co-vinyl alcohol) in dimethyl sulfoxide (14 g) at room temperature. After 24 hours the treated porous poly(ethylene) substrate was removed and submerged entirely within a 2 wt % solution of anhydrous borax in distilled water (14 g) and heated at 90° C. for 24 hours. Treated porous poly(ethylene) substrate was removed and placed into distilled water prior to testing.

[0053]FIG. 4 shows the voltage potential and Faradaic efficiency percentage (FE %) over time for a CO electrolyzer cell at 5 cm², 200 mA/cm² with the separators created in Examples 3A-B. The charts show the conversion efficiency as to dihydrogen (open markers) and ethylene (filled markers) for the two different separators. Curves for Example 3A-B are shown as squares and circles respectively. Both examples were created with PEVA in DMSO followed by an aqueous borax solution heated to 90° C. The thicker sample exhibits a higher selectivity toward desired ethylene production than the thinner sample.

Example 4—Comparison of Separators Created at Room Temperature with Varying Concentrations of PEVA in DMSO and Borax with Hydrochloric Acid

[0054]Example 4A. Porous poly(ethylene) substrate (25 μm thick, 16 cm² surface area) was submerged entirely within a 0.01 wt % solution of poly(ethylene-co-vinyl alcohol) in dimethyl sulfoxide (14 g) at room temperature. After 24 hours the treated porous poly(ethylene) substrate was removed and submerged entirely within a 2 wt % solution of anhydrous borax in 2.3% hydrochloric acid (14 g) at room temperature. Treated porous poly(ethylene) substrate was removed and placed into distilled water prior to testing.

[0055]Example 4B. Porous poly(ethylene) substrate (25 μm thick, 16 cm² surface area) was submerged entirely within a 0.1 wt % solution of poly(ethylene-co-vinyl alcohol) in dimethyl sulfoxide (14 g) at room temperature. After 24 hours the treated porous poly(ethylene) substrate was removed and submerged entirely within a 2 wt % solution of anhydrous borax in 2.3% hydrochloric acid (14 g) at room temperature. Treated porous poly(ethylene) substrate was removed and placed into distilled water prior to testing.

[0056]Example 4C. Porous poly(ethylene) substrate (25 μm thick, 16 cm² surface area) was submerged entirely within a 0.5 wt % solution of poly(ethylene-co-vinyl alcohol) in dimethyl sulfoxide (14 g) at room temperature. After 24 hours the treated porous poly(ethylene) substrate was removed and submerged entirely within a 2 wt % solution of anhydrous borax in 2.3% hydrochloric acid (14 g) at room temperature. The treated porous poly(ethylene) substrate was removed and placed into distilled water prior to testing.

[0057]FIG. 5 shows the voltage potential and Faradaic efficiency percentage (FE %) over time for a CO electrolyzer cell at 5 cm², 200 mA/cm² with the separators created in Examples 4A-C. The charts show the conversion efficiency as to dihydrogen (open markers) and ethylene (closed markers) for the three different separators. Curves for Example 4A-C are shown as squares, circles, and triangles respectively. All three examples were created with PEVA in DMSO followed by an aqueous solution of boric acid and potassium hydroxide at room temperature. All three samples exhibit similar selectivity toward desired ethylene production and voltage potential, though the separator of Example 4C did not last as long as the other two separators. This demonstrates that it is possible to prepare boron containing separators using a different method that operates at room temperature instead of 90° C. HCl is added to the borax to allow that step to progress at room temperature. This figure also shows a wider treat rate range of concentrations of the PEVA molecule in the first step can still lead to similar results in an electrolyzer cell.

Example 5—Comparison of Separators Created at Room Temperature with Varying Thicknesses, Varying Alcohol-Containing Polymers in DMSO, and Boric Acid with Potassium Hydroxide

[0058]Example 5A. Porous poly(ethylene) substrate (120 μm thick, 16 cm² surface area) was submerged entirely within a 0.5 wt % solution of poly(ethylene-co-vinyl alcohol) in dimethyl sulfoxide (14 g) at room temperature. After 24 hours the treated porous poly(ethylene) substrate was removed and submerged entirely within a solution of 1 wt % boric acid and 1 wt % potassium hydroxide in distilled water (14 g) at room temperature. Treated porous poly(ethylene) substrate was removed and placed into distilled water prior to testing.

[0059]Example 5B. Porous poly(ethylene) substrate (25 μm thick, 16 cm² surface area) was submerged entirely within a 0.1 wt % solution of poly(ethylene-co-vinyl alcohol) in dimethyl sulfoxide (14 g) at room temperature. After 24 hours the treated porous poly(ethylene) substrate was removed and submerged entirely within a solution of 1 wt % boric acid and 1 wt % potassium hydroxide in distilled water (14 g) at room temperature. Treated porous poly(ethylene) substrate was removed and placed into distilled water prior to testing.

[0060]Example 5C. Porous poly(ethylene) substrate (25 μm thick, 16 cm² surface area) was submerged entirely within a 1 wt % solution of poly(vinyl alcohol) in dimethyl sulfoxide (14 g) at room temperature. After 24 hours the treated porous poly(ethylene) substrate was removed and submerged entirely within a solution of 2 wt % boric acid and 2 wt % potassium hydroxide in distilled water (14 g) at room temperature. Treated porous poly(ethylene) substrate was removed and placed into distilled water prior to testing.

[0061]FIG. 6 shows the voltage potential and Faradaic efficiency percentage (FE %) over time for a CO electrolyzer cell at 5 cm², 200 mA/cm² with the separators created in Examples 5A-C. The charts show the conversion efficiency as to dihydrogen (open markers) and ethylene (filled markers) for the three different separators. Curves for Example 5A-C are shown as squares, circles, and triangles respectively. This demonstrates that it is possible to prepare boron containing separators using a different method that operates at room temperature instead of 90° C. Potassium hydroxide is added to boric acid to allow that step to progress at room temperature. Demonstrating another species of boric acid that can be used. Also, two kinds of poly(ethylene) substrate are used. Also, two kinds of alcohol-containing polymer, PEVA and PVA are used. This figure shows that the general method can be adapted for different substrates, alcohol-containing polymers and boron-containing species.

Example 6—Preparation and Comparison of a Boron-Containing Separator at Room Temperature Using PVA in Aqueous Solution, and Boric Acid with Potassium Hydroxide

[0062]Porous poly(ethylene) substrate (25 μm thick, 16 cm² surface area) was submerged entirely within 2-propanol (i.e. isopropyl alcohol) (10 mL). After 5 minutes the porous poly(ethylene) substrate was removed from the 2-propanol and submerged entirely within a 0.5 wt % solution of poly(vinyl alcohol) in distilled water (14 g) at room temperature. After 24 hours the treated porous poly(ethylene) substrate was removed and submerged entirely within a solution of 2 wt % boric acid and 2 wt % potassium hydroxide in distilled water at room temperature. Treated porous poly(ethylene) substrate was removed and placed into distilled water prior to testing.

[0063]FIG. 7 shows the voltage potential and Faradaic efficiency percentage (FE %) over time for a CO electrolyzer cell at 5 cm², 200 mA/cm² with the separators created in Examples 5A and 6. The charts show the conversion efficiency as to dihydrogen (open markers) and ethylene (closed markers) for the two different separators. Curves for Example 5A and Example 6 are shown as squares and circles respectively. This demonstrates that it is possible to prepare boron containing separators using a different solvent to dissolve the alcohol containing polymer in. Normally water-based solutions are not suitable because the hydrophobic poly(ethylene) substrate is not wetted by aqueous solvents and the alcohol containing polymer does not treat the surface correctly. However, by wetting the PE first with 2-propanol first this allows the aqueous solvent to interact more with the PE surface. This represents a large cost reduction in solvent use and prevents the use of harmful solvents in favor of water. Potential voltages and FE % are comparable between the two separators.

Example 7—Preparation and Comparison of a Boron-Containing Separator at Room Temperature Using PVA in DMSO, and Boric Acid with Potassium Hydroxide

[0064]20 porous poly(ethylene) substrates (25 μm thick, 16 cm² surface area) were submerged entirely within a 0.5 wt % solution of poly(vinyl alcohol) in dimethyl sulfoxide (70 g) at room temperature. After 24 hours the treated porous poly(ethylene) substrates were removed and submerged entirely within a solution of 2 wt % boric acid and 2 wt % potassium hydroxide in distilled water (70 g) at room temperature. Treated porous poly(ethylene) substrates were removed and placed into distilled water prior to testing.

[0065]FIG. 8 shows the voltage potential and Faradaic efficiency percentage (FE %) over time for a CO electrolyzer cell at 5 cm², 200 mA/cm² with the different numbers of separators created in Example 7 and stacked in a single electrolyzer cell. The charts show the conversion efficiency as to dihydrogen (open markers) and ethylene (closed markers) for the different separators. Curves for a stack of 2 separators, 3 separators, 5 separators, and 9 separators are shown as squares, circles, triangles, and diamonds respectively. The process of creating separators for FIG. 8 shows the ability of the concepts disclosed herein to scale by producing multiple separators at once, as well as using less solvent. Placing multiple separators on top of each other within the cell was also shown to not affect the product selectivity whilst imparting a modest voltage penalty at 9 layers. Stacking multiple layers also decreased the product crossover across the cell. That is, stopping the reaction gas (carbon oxide) or production gases (ethylene and hydrogen) from crossing the separator and coming out of the anode side. Stacking multiple separators within the same cell has been shown to be an effective method as more separator thickness slows down the gas crossover. This method would not be viable with a commercial material as they are very expensive but as the disclosed separators uses a combination of commodity materials with a simple preparation method there is little downside to using multiple separator membranes within the same cell.

Example 8—Preparation and Comparison of a Larger Surface Area Boron-Containing Separator at Room Temperature Using PVA in DMSO, and Boric Acid with Potassium Hydroxide

[0066]Porous poly(ethylene) substrate (25 μm thick, 64 cm² surface area) was submerged entirely within a 1 wt % solution of poly(vinyl alcohol) in dimethyl sulfoxide (56 g) at room temperature. After 24 hours the treated porous poly(ethylene) substrate was removed and submerged entirely within a solution of 2 wt % boric acid and 2 wt % potassium hydroxide in distilled water (56 g) at room temperature. Treated porous poly(ethylene) substrate was removed and placed into distilled water prior to testing.

[0067]FIG. 9 shows the voltage potential and Faradaic efficiency percentage (FE %) over time for a CO electrolyzer cell at 50 cm₂, 200 mA/cm² with the separators created in Example 8 and a commercial separator referred to as Zirfon 220 (Agfa). The charts show the conversion efficiency as to dihydrogen (open markers) and ethylene (closed markers) for the different separators. Curves for Example 8 and Zirfon 220 are shown as squares and circles respectively. This figure shows that the separator procedure can be scaled in surface area as well as total number of separators prepared. The procedure was not optimized for this scale but the cell performance is very similar to that of the commercial standard material, Zirfon 220. Zirfon 220 is a state-of-the-art separator that is widely employed for alkaline electrolysis systems.

Example 9—Preparation and Comparison of a Boron-Containing Separator at Room Temperature Using PVA in DMSO, and Boric Acid with Potassium Hydroxide, Including a Wash Step

[0068]Porous poly(ethylene) substrate (23 μm thick, 16 cm² surface area) was submerged entirely within a 0.5 wt % solution of poly(vinyl alcohol) in dimethyl sulfoxide (14 g) at room temperature. After 24 hours the treated porous poly(ethylene) substrate was submerged entirely within DMSO (14 g). After 24 hours the treated and washed porous poly(ethylene) substrate was removed and submerged entirely within a solution of 2 wt % boric acid and 2 wt % potassium hydroxide in distilled water (14 g) at room temperature. Treated porous poly(ethylene) substrate was removed and placed into distilled water prior to testing.

[0069]FIG. 10 shows the voltage potential and Faradaic efficiency percentage (FE %) over time for a CO electrolyzer cell at 5 cm², 200 mA/cm² with the separator created in Example 9. The charts show the conversion efficiency as to dihydrogen (open markers) and ethylene (closed markers) for the different separators. Curves for Example 9 are shown as squares. This figure shows that the separator can still be prepared when the separator is placed in DMSO after the first PVA in DMSO treatment but before the crosslinking step in the boric acid and KOH. If a layer of excess PVA was simply placed on the poly(ethylene) separator, then it would be expected to be removed by a DMSO wash. However, as adsorption of a thin surface layer of PVA to the poly(ethylene) depends on hydrophobic forces and van der Waals interactions, the DMSO wash is not capable of removing the PVA and therefore the washed separator still performs as expected during carbon monoxide electrolysis.

Example 10—Preparation of boron-containing separator using only aqueous solutions

[0070]Porous poly(ethylene) substrate (23 μm thick, 16 cm² surface area) was submerged entirely within a 0.5 wt % solution of poly(vinyl alcohol) in distilled water (14 g) at room temperature. After 24 hours the treated porous poly(ethylene) substrate was removed and submerged entirely within a solution of 2 wt % boric acid and 2 wt % potassium hydroxide in distilled water (14 g) at room temperature. Treated porous poly(ethylene) substrate was removed and placed into distilled water prior to testing.

[0071]FIG. 11 shows the voltage potential of attempted carbon monoxide electrolysis performance at 5 cm², 200 mA/cm², using the separator prepared in Example 10. The solid line is the applied voltage and the dashed line is the resulting current for the cell. Faradaic efficiency (FE) is not displayed as no current was capable of passing through the separator from Example 10. This figure shows that a desirable boron containing separator cannot be prepared by a method in solely aqueous solutions. As only water was used at each step there was not effective removal of air from the poly(ethylene) pores and therefore PVA could not adsorb to all the pore surfaces prior to the crosslinking step with boric acid and potassium hydroxide. Any surface treatment was, at best, effective only on the top and bottom substrate surfaces. As a result, when the separator was placed in a cell there was insufficient electrolyte filling the separator pores, and because the pores were not wettable by the electrolyte, no ions could cross the separator when a voltage (2.5 V) was applied to the cell. Note that this voltage is much greater than is required for carbon monoxide electrolysis. Therefore, no current was measured across the cell so that FE % was not measured when no products were produced. Despite applying voltage and flowing electrolyte to the anode side for 24 hours, the separator was not able to fill with sufficient electrolyte to work as desired.

[0072]While the separators as described herein were described with reference to use as separators in an oxocarbon electrolyzer, they are not limited to be used in that application. The disclosed separators can be used in other electrochemical cells including those used in the electrolysis of water, the generation of electricity within fuels cells, batteries, chlor-alkali reactors, and electrodialysis reactors. The disclosed separators may also be used in nonelectrochemical separation techniques such as micro- or nanofiltration.

[0073]While the specification has been described in detail with respect to specific embodiments of the invention, it will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing, may readily conceive of alterations to, variations of, and equivalents to these embodiments. These and other modifications and variations to the present invention may be practiced by those skilled in the art, without departing from the scope of the present invention, which is more particularly set forth in the appended claims.