Free-standing porous solid electrolyte for efficient co2 electrolysis

Abstract

A porous solid electrolyte composition includes ion exchange particles and a polymer binder. The porous solid electrolyte composition has a porosity of 20-60% and an ionic conductivity of 2-12 mS / cm. A method for making the porous solid electrolyte composition includes dissolving a polymer binder in a solvent to form a solution, adding ion exchange particles and salt to the solution, casting the solution onto a substrate at an elevated temperature, maintaining the elevated temperature for at least 10 hours to form a composite, molding the composite to form a solid electrolyte under elevated pressure and temperature, and immersing the solid electrolyte in deionized water for at least 2 hours to remove excess salt. A process for carbon dioxide reduction includes introducing carbon dioxide and water streams to an electrolysis cell including the porous solid electrolyte composition, and applying a voltage to the electrolysis cell to produce carbon dioxide reduction products.

Description

ATTORNEY DOCKET NO.17500-261WO1 FREE-STANDING POROUS SOLID ELECTROLYTE FOR EFFICIENT CO2 ELECTROLYSIS STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

[0001] This invention was made with government support under Grant No. 2029442 awarded by the National Science Foundation and Grant No. DE-EE0010839 awarded by U.S. Department of Energy. The government has certain rights in the invention. BACKGROUND

[0002] The electrochemical CO2reduction reaction (CO2RR) can convert CO2from industrial emissions into valuable products, therefore contributing to a reduction in greenhouse gas emissions. The CO2reduction process can be conducted in an electrochemical flow cell, where CO2and an electrolyte are fed into a reactor where a potential drives the reduction of CO2 over metal electrodes. This electrochemical reaction results in the production of various carbon-based compounds, such as carbon monoxide (CO), formic acid, methane, or ethylene, depending on the catalyst and conditions. Achieving high energy efficiency for CO2 reduction to a desired product is essential for making the process economically viable and environmentally sustainable. Efficient and selective catalysts, refinement in reactor design, and innovative electrode and membrane materials contribute to improving the overall energy efficiency of the CO2 reduction reaction.

[0003] The reduction of CO2represents a promising strategy for addressing carbon emissions while producing valuable fuels and chemicals. However, conventional CO2reduction flow reactors typically employ liquid-based electrolytes, resulting in expensive post-synthesis purification steps to recover the product.

[0004] Solid electrolytes can potentially address these limitations by producing a pure liquid product. However, solid electrolytes presently available in the art, such as particle-based solid electrolytes, generally have either poor ionic conductivity and / or insufficient porosity to enable recovery of the product using a continuous aqueous stream. Such particle-based solid electrolytes may also have poor long-term stability, scalability, reusability, and challenging cell assembly. The particles can be dislodged from the reactor, leading to conductivity loss and clogging of the outlet. The loadingATTORNEY DOCKET NO.17500-261WO1 of the cell with these particles can be inconsistent, resulting in variable performance. Such drawbacks have prevented large-scale deployments of the solid electrolyte layer design. Accordingly, there exists a need for an improved solid electrolytes for the reduction of carbon dioxide. SUMMARY

[0005] This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

[0006] In one aspect, embodiments disclosed herein relate to a porous solid electrolyte composition for carbon dioxide electrolysis. The porous solid electrolyte composition includes ion exchange particles and a polymer binder. The porous solid electrolyte composition has a porosity in a range of from 20% to 60% and an ionic conductivity in a range of from 2 mS / cm to 12 mS / cm.

[0007] In another aspect, embodiments disclosed herein relate to a method for making a porous solid electrolyte composition. The method includes dissolving a polymer binder in a solvent to form a solution, adding ion exchange particles and a salt to the solution, and casting the solution onto a substrate at an elevated temperature. The method further includes maintaining the elevated temperature for at least 10 hours to form a composite, molding the composite to form a solid electrolyte under an elevated pressure and temperature, and immersing the solid electrolyte in deionized water for at least 2 hours to remove excess salt, thereby forming the porous solid electrolyte composition.

[0008] In another aspect, embodiments disclosed herein relate to a process for carbon dioxide reduction. The process includes introducing a carbon dioxide stream to an electrolysis cell, where the electrolysis cell includes an anode compartment comprising an anode, a cathode compartment comprising a cathode, and a porous solid electrolyte composition. The process further includes introducing a water stream to the electrolysis cell, and applying a voltage to the electrolysis cell to produce at least one carbon dioxide reduction product. The porous solid electrolyte compositionATTORNEY DOCKET NO.17500-261WO1 includes ion exchange particles and a polymer binder, where the porous solid electrolyte composition has a porosity in a range of from 20% to 60% and an ionic conductivity in a range of from 2 mS / cm to 12 mS / cm.

[0009] Any combinations of the various embodiments and implementations disclosed herein can be used in a further embodiment, consistent with the disclosure. Other aspects and advantages of the claimed subject matter will be apparent from the following description and the appended claims. BRIEF DESCRIPTION OF DRAWINGS

[0010] FIGs.1A-1B are schematic diagrams of an electrolysis cell according to one or more embodiments.

[0011] FIG. 1C is a schematic diagram of a porous solid electrolyte composition according to one or more embodiments.

[0012] FIG.2 is a plot of degree of sulfonation vs. chlorosulfonic acid to polysulfone molar ratio of a polymer binder according to one or more embodiments.

[0013] FIG. 3 is a general scheme for synthesis of sulfonated polysulfone polymer binder according to one or more embodiments.

[0014] FIG. 4 is NMR spectra of sulfonated polysulfone polymer binder according to one or more embodiments.

[0015] FIG. 5 is a schematic diagram of a porous solid electrolyte composition production process according to one or more embodiments.

[0016] FIG. 6 is a schematic diagram of a flow reactor according to one or more embodiments.

[0017] FIG. 7 is a plot of ionic conductivity and ohmic resistance vs. degrees of sulfonation of porous solid electrolyte compositions according to one or more embodiments.

[0018] FIG. 8 is a plot of hardness vs. binder percentage of porous solid electrolyte compositions according to one or more embodiments.ATTORNEY DOCKET NO.17500-261WO1

[0019] FIG.9 is a plot showing tensile strain vs. tensile stress of porous solid electrolyte compositions according to one or more embodiments.

[0020] FIG.10 is a plot showing % mass loss during salt leaching vs. binder percentage of porous solid electrolyte compositions according to one or more embodiments.

[0021] FIG. 11 is a plot of ionic conductivity and ohmic resistance vs. binder percentage of porous solid electrolyte compositions according to one or more embodiments.

[0022] FIG. 12 is a plot showing porosity, water uptake and swelling ratio vs. binder percentage of porous solid electrolyte compositions according to one or more embodiments.

[0023] FIG.13 is a plot of ionic conductivity vs. test duration of porous solid electrolyte compositions according to one or more embodiments.

[0024] FIG. 14 is a graph illustrating electrochemical performance of porous solid electrolyte compositions according to one or more embodiments.

[0025] FIG. 15 is a plot of ohmic resistance and hardness vs. binder percentage of porous solid electrolyte compositions according to one or more embodiments.

[0026] FIGs.16A-16C are schematic diagrams illustrating the internal effect between the surface of porous solid electrolyte compositions, membranes and catalyst in an electrolysis cell according to one or more embodiments.

[0027] FIG.17 is a graph showing Faradaic efficiency of formate generation in porous solid electrolyte compositions according to one or more embodiments.

[0028] FIG.18 is a graph showing Faradaic efficiency of formate generation, hydrogen evaluation reaction and CO generation in porous solid electrolyte compositions according to one or more embodiments.

[0029] FIG.19 is plot of current vs. potential for an electrolysis cell according to one or more embodiments.

[0030] FIG. 20 is a graph showing Faradaic efficiency of multi-carbon products produced in porous solid electrolyte compositions according to one or more embodiments.ATTORNEY DOCKET NO.17500-261WO1

[0031] FIG. 21 is a plot of current vs. potential for porous solid electrolyte compositions according to one or more embodiments.

[0032] FIG.22 is a graph showing Faradaic efficiency of CO generation in porous solid electrolyte compositions according to one or more embodiments.

[0033] FIG. 23 is a graph showing Faradaic efficiency of C2H4generation in porous solid electrolyte compositions according to one or more embodiments.

[0034] FIG.24 is a graph showing Faradaic efficiency of formate generation in porous solid electrolyte compositions according to one or more embodiments.

[0035] FIG.25 is a graph showing Faradaic efficiency of ethanol generation in porous solid electrolyte compositions according to one or more embodiments.

[0036] FIG.26 is a graph showing Faradaic efficiency of acetate generation in porous solid electrolyte compositions according to one or more embodiments.

[0037] FIG. 27 is a graph showing Faradaic efficiency of n-propanol generation in porous solid electrolyte compositions according to one or more embodiments.

[0038] FIG.28 is a graph showing Faradaic efficiency of H2 generation in porous solid electrolyte compositions according to one or more embodiments. DETAILED DESCRIPTION

[0039] Embodiments disclosed herein generally relate to conductive, porous, free- standing solid electrolytes and methods for the reduction of carbon dioxide. Embodiments of the present disclosure address the aforementioned challenges associated with the reduction process of carbon dioxide (CO2), such as electrolytes having poor ionic conductivity and insufficient porosity, to enable the recovery of valuable products.

[0040] Embodiments of the present disclosure relate to an approach to produce a conductive, free-standing, and porous solid electrolyte for CO2electrolysis by combining ion exchange particles with a polymer binder.

[0041] By optimizing the binder content, degree of sulfonation, and porosity, ionic conductivities as high as 10.4 mS / cm may be achieved while maintaining excellentATTORNEY DOCKET NO.17500-261WO1 mechanical properties of the porous solid electrolytes. Employing a Bi(NO3)2·5H2O (BOON) catalyst, the porous solid electrolyte of certain embodiments of the present disclosure, may sustain a Faradaic efficiency exceeding 90% for the production of pure formic acid (HCOOH) and may exhibit remarkable stability at 100 mA / cm2, maintaining a cell potential close to 3.5 V over 220 hours. Additionally, using a Cu2O catalyst, the porous solid electrolyte of certain embodiments of the present disclosure may display promising efficacy in generating multi-carbon products including ethylene, ethanol, and n-propanol. Some embodiments of the present disclosure demonstrate a promising porous solid electrolyte that may be used in CO2electrolysis systems, water deionization systems, dialysis systems, water treatment systems, and contribute to the development of zero carbon emission and utilization technologies. POROUS SOLID ELECTROLYTE COMPOSITION

[0042] In one aspect, embodiments disclosed herein relate to a porous solid electrolyte composition (porous solid electrolyte, composite polyelectrolyte, polyelectrolyte) for carbon dioxide electrolysis. The porous solid electrolyte composition includes ion exchange particles and a polymer binder.

[0043] In one or more embodiments, the ion exchange particles include crosslinked polymeric particles that are porous or non-porous and that may include charged ionic groups such as ionized functional groups including, for example, sulfonates, carboxylates, quaternized amines, or combinations thereof. In one or more embodiments, the ion exchange particles are one or more selected from the group consisting of DOWEX®, AmberLite™, Duolite™, poly(styrene-divinylbenzene), polyacrylic resin, and Purolite™ particles.

[0044] In one or more embodiments, the ion exchange particles have an average particle size in a range of from about 5 µm to about 85 µm, such as in a range of from a lower limit selected from any one of 5, 10, 15, 20, 25, 30, 35 and 37 µm, to an upper limit selected from any one of 70, 74, 80 and 85 µm, where any lower limit may be paired with any upper limit.

[0045] In one or more embodiments, the ion exchange particles are present in the porous solid electrolyte composition in an amount of from about 6 wt% to about 20 wt%, such as in an amount of from a lower limit selected from any one of 6 wt%, 8ATTORNEY DOCKET NO.17500-261WO1 wt%, and 10 wt%, to an upper limit selected from any one of 10 wt%, 12 wt%, 15 wt%, 18 wt% and 20 wt%, based on the total weight of the porous solid electrolyte composition, where any lower limit may be paired with any upper limit.

[0046] In one or more embodiments, the polymer binder included in the porous solid electrolyte composition immobilizes ion exchange particles. In one or more embodiments, the polymer binder includes a sulfonated polysulfone binder. The sulfonated polysulfone binder may have a degree of sulfonation in a range of from about 30% to about 100%, such as in a range of from a lower limit selected from any one of 30, 40 and 50%, to an upper limit selected from any one of 50, 60, 70, 80, 90 and 100%, where any lower limit may be paired with any upper limit. The sulfonated polysulfone binder may have a degree of sulfonation of 70%. Without being bound by any particular theory, increasing the degree of sulfonation in the sulfonated polysulfone binder may enhance the ionic conductivity of the resulting porous solid electrolyte. At a substantially high degree of sulfonation, the sulfonated polysulfone binder may swell and can become completely soluble in water. The sulfonation degree of the polymer binder is defined as the number of sulfonate groups per repeat unit of the polymer, determined through analysis ofNMR spectra.

[0047] In one or more embodiments, the polymer binder includes a short side chain perfluorosulfonic acid and / or a polytetrafluoroethylene copolymer. The polymer binder may include, for example, an Aquivion®polymer, and / or a Fumion®polymer. In one or more embodiments, the polymer binder is a sulfonated polyether ether ketone polymer. In one or more embodiments, the polymer binder is Nafion™.

[0048] In one or more embodiments, the polymer binder is present in the porous solid electrolyte composition in an amount of from about 6 wt% to about 20 wt%, such as in a range of from a lower limit selected from any one of 6, 8, and 10 wt%, to an upper limit selected from any one of 12, 14, 16, 18 and 20 wt%, where any lower limit may be paired with any upper limit, based on the total weight of the porous solid electrolyte composition. In one or more embodiments, the amount of ion exchange particles depends on the size of the porous solid electrolyte composition. For example, if a plate including the porous solid electrolyte composition has dimensions of 1 inch x 1 inch and 1.5 to 2 mm thick, the ion exchange particles may be present in an amount of about 1 g.ATTORNEY DOCKET NO.17500-261WO1 PROPERTIES OF POROUS SOLID ELECTROLYTE COMPOSITION

[0049] In one or more embodiments, the porous solid electrolyte composition has a porosity in a range of from about 20% to about 60%. For example, the porosity of the porous solid electrolyte composition may have a lower limit of any one of 20%, 25%, 30% 35%, and 40% and an upper limit of any one of 40%, 45%, 50%, 55% and 60%, where any lower limit may be paired with any mathematically compatible upper limit. As described herein, the porosity of the porous solid electrolyte composition is determined by the method described in the EXAMPLES section.

[0050] The porous solid electrolyte composition may have an ionic conductivity ranging from about 2 mS / cm to about 12 mS / cm. For example, the ionic conductivity may have a lower limit of any one of 2, 3, 4, 5, 6, and 7 mS / cm and an upper limit of any one of 6, 7, 8, 9, 10, 10.4, 11 and 12 mS / cm, where any lower limit may be paired with any mathematically compatible upper limit. As described herein, the conductivity of the porous solid electrolyte composition is determined by the method described in the EXAMPLES section.

[0051] The porous solid electrolyte composition may be conductive and free-standing. A porous solid electrolyte composition that is “free-standing” means that the composition has a solid structure that retains its shape without any support, and can be placed in and removed from an assembly quickly and easily, such as an electrolysis cell. A free-standing porous solid electrolyte composition possesses the above features which cannot be possessed by other forms of electrolytes such as powder, paste or liquid electrolytes. A free-standing porous solid electrolyte composition can be re-used, cleaned or removed from one assembly and placed in another assembly quickly and easily.

[0052] Advantageously porous solid electrolyte composition may be recyclable and / or reusable. For example, once formed, the porous solid electrolyte composition may be used for a period of time, then disassembled from the cell in which it was used, rinsed and re-used in a different cell without significant loss of conductivity. Further details of the reuse and recycling of the material as explained in the EXAMPLES section. ELECTROLYSIS CELLATTORNEY DOCKET NO.17500-261WO1

[0053] In another aspect, embodiments disclosed herein relate to an electrolysis cell. The electrolysis cell includes an anode, a cathode and a porous solid electrolyte composition.

[0054] FIGs.1A-1B are schematic diagrams of an electrolysis cell according to one or more embodiments. The electrolysis cell 100 includes a middle layer 102 which includes a porous solid electrolyte composition 110 (composite polyelectrolyte), an anode compartment 104 including an anode 120, and a cathode compartment 106 including a cathode 130. The middle layer 102 may further include a structure configured to allow a placement of the porous solid electrolyte composition 110, such as a plate structure with an opening, as shown in FIG.1A. The anode compartment 104 may further include a catalyst 140 and a cation (proton) exchange membrane (CEM) 160, and the cathode compartment 106 may further include a catalyst 140 and an anion exchange membrane (AEM) 150.

[0055] In the present disclosure, an electrolysis cell which includes the catalyst 140 in the anode compartment and / or cathode compartment is referred to as a “solid electrolyzer,” “solid-state electrolyzer,” or a “CO2RR electrolyzer.” An electrolysis cell which does not include the catalyst 140 in the anode compartment and cathode compartment is referred to as a “flow reactor.” The electrolysis cell of one or more embodiments includes the solid electrolyzer, the flow reactor, or combinations thereof. In the flow reactor, a carbon paper may be included in place of the catalyst 140 in the solid electrolyzer, as shown in FIG.6.

[0056] During operation, a carbon dioxide stream containing CO2is introduced to the cathode compartment 106 of the electrolysis cell 100. At least a portion of CO2 entering the cathode compartment 106 of the electrolysis cell 100 is reacted to form a carbon-containing anion, such as formate anion (HCOO-) at the cathode 130, and the carbon-containing anion such as HCOO- enters the porous solid electrolyte composition 110 in the middle layer 102 through the anion exchange membrane 150.

[0057] A feed water stream including water is introduced to the anode compartment 104 of the electrolysis cell 100 and at least a portion of the water is reacted to form O2and hydrogen ions (H+) at the anode 120. The produced H+then enters the porousATTORNEY DOCKET NO.17500-261WO1 solid electrolyte composition 110 in the middle layer 102 through the cation exchange membrane 160.

[0058] The carbon-containing anion, such as HCOO-, and H+then react within the porous solid electrolyte composition 110 to form a carbon dioxide reduction product such as formic acid (HCOOH). Water is introduced through the porous solid electrolyte composition 110 to collect the produced carbon dioxide reduction product such as HCOOH, and the mixture of the carbon dioxide reduction product and water is then retrieved from the electrolysis cell 100.

[0059] In the present disclosure, a “carbon dioxide reduction product” refers to a carbon-containing product produced by reacting a carbon-containing anion obtained by reducing carbon dioxide, and H+ion.

[0060] FIG.1C is a schematic diagram showing details of the porous solid electrolyte composition 110. The porous solid electrolyte composition 110 includes a polymer binder 170 and ion exchange particles 180.

[0061] In one or more embodiments, the porous solid electrolyte composition 110 included in the electrolysis cell 100 is any of the porous solid electrolyte compositions as previously described.

[0062] In one or more embodiments, the anode compartment 104 includes a cation (proton) exchange membrane (e.g., Nafion™) and a catalyst (e.g., IrO2) for the oxygen evolution reaction. In one or more embodiments, the cathode compartment 106 includes an anion exchange membrane (e.g., PiperION®) and a catalyst (e.g., Bi(NO3)2·5H2O, Cu2O) for carbon dioxide electrochemical reduction. METHOD OF MAKING A POROUS SOLID ELECTROLYTE COMPOSITION

[0063] In yet another aspect, embodiments disclosed herein relate to a method for making a porous solid electrolyte composition. The method includes dissolving a polymer binder in a solvent to form a solution, adding ion exchange particles and a salt to the solution, casting the solution onto a substrate at an elevated temperature, maintaining the elevated temperature for at least 16 hours to form a composite, molding the composite to form a solid electrolyte under an elevated pressure andATTORNEY DOCKET NO.17500-261WO1 temperature, and immersing the solid electrolyte in deionized water for at least 24 hours to remove excess salt, thereby forming the porous solid electrolyte composition.

[0064] In the dissolving step, the polymer binder may be dissolved in a suitable solvent to form a solution. The solvent may include, but is not limited to, N-methyl-2- pyrrolidine, ethanol, and dimethyl sulfoxide. The polymer binder may be any of the polymer binder previously described, and may be, for example, sulfonated polysulfone.

[0065] The ion exchange particles in the adding step may be any of the ion exchange particles as previously described. The ion exchange particles may include, but are not limited to, poly(styrene-divinylbenzene). The salt may include, but is not limited to, sodium chloride (NaCl).

[0066] In the adding step, the ion exchange particles may be added to the polymer binder solution produced in the dissolving step such that the weight ratio of the ion exchange particles to the polymer binder solution (“binder solution ratio”) is in a range of from about 0.9:1.3 to about 1:1.2, for example, at a ratio of 0.9:1.3, 1:1.2, or 1.1:1.1.

[0067] In the adding step, the amount of salt may be adjusted based on the particle size of the ion exchange particles. The amount of added salt with respect to the amount of the added ion exchange particles by weight (“salt ratio”) may be in a range of from about 0.4 to about 0.85, such as in a range of from a lower limit selected from an one of 0.4, 0.5, 0.6, 0.7 and 0.8, to an upper limit selected from any one of 0.6, 0.7, 0.8 and 0.85, where any lower limit may be paired with any mathematically compatible upper limit.

[0068] For smaller ion exchange particles, such as particles having a dimeter in a range of from about 1 to 10^μm, a higher salt ratio of from about 0.8 to about 0.85 by weight with respect to the amount of ion exchange particles may be required to maintain sufficient porosity, likely due to the denser packing and reduced void space between particles. Larger ion exchange particles, such as particles having a diameter in a range of from 30 to 100^μm, the salt ratio in a range of from about 0.4 to about 0.6 may be sufficient to produce a porous structure, as the larger particle size naturally introduces more interstitial space.ATTORNEY DOCKET NO.17500-261WO1

[0069] In the adding step, the overall mass mas ratio of the ion exchange particles, polymer binder solution and salt may be adjusted based on any of the combinations of the above binder solution ratio ranges and the salt ratio ranges. The adding may be conducted such that the overall mass ratio of the ion exchange particles, polymer binder solution, and salt is, for example, about 1:1.2:0.5.

[0070] The substrate in the casting step may be a suitable substrate available in the art, and may be, for example, polytetrafluoroethylene (PTFE) including Teflon. The casting may be conducted at an elevated temperature, which is at a temperature above room temperature, such as at a temperature of 30 °C or higher, 40 °C or higher, 50 °C or higher, or 60 °C or higher. The casting may be conducted at an elevated temperature in a range of from about 30 °C to about 300 °C, for example, in a range of from a lower limit selected from any one of 30, 40, 50, 60 and 70 °C to an upper limit selected from any one of 80, 90, 100, 150, 200, and 300 °C, where any lower limit may be paired with any upper limit. The casting may be conducted at an elevated temperature of about 75 °C.

[0071] In the maintaining step, the elevated temperature applied to the cast solution is maintained for at least 10 hours, such as for a duration in a range of from about 10 hours to 100 hours, such as in a range of from a lower limit selected from any one of 10, 16, 20, and 30 hours, to an upper limit selected from any one of 50, 75 and 100 hours, where any lower limit may be paired with any upper limit. The maintaining step is conducted to remove the solvent from the cast solution and to form a composite.

[0072] After the composite is formed, the molding step may be conducted to form the solid electrolyte. The molding step may include compressing the composite under an elevated pressure and temperature (hot-pressing). The molding step may be conducted, for example, by using a hot press.

[0073] The elevated temperature for the molding may be a temperature above room temperature, such as a temperature of 30 °C or higher, 40 °C or higher, 50 °C or higher, 60 °C or higher, 70 °C or higher, 80 °C or higher, 90 °C or higher, 100 °C or higher, or 110 °C or higher, such as a temperature in a range of from about 30 °C to about 300 °C, for example, in a range of from a lower limit selected from any one of 30, 40, 50, 60, 70, 80, 90, 100 and 110 °C, to an upper limit selected from any one ofATTORNEY DOCKET NO.17500-261WO1 120, 140, 150, 200, and 300 °C, where any lower limit may be paired with any upper limit. The elevated temperature may be 115 °C.

[0074] The elevated pressure for the molding may be a pressure in a range of from about 1 MPa to about 50 MPa, such as in a range of from a lower limit selected from any one of 1, 5, 10, 15, 20 and 25 MPa, to an upper limit selected from any one of 35, 40, 45, and 50 MPa, where any lower limit may be paired with any upper limit. The elevated pressure for the molding may be about 31 MPa. The above elevated pressure range may provide an appropriate pressure for molding of the solid electrolyte having width and length (width x length) in a range of from about 2 cm x 2 cm to about 10 cm x 10 cm.

[0075] The molding may be conducted for at least 1 hour, such as for a duration in a range of from about 1 hour to about 100 hours, such as in a range of from a lower limit selected from any one of 1, 2, and 5 hours, to an upper limit selected from any one of 10, 50, 75 and 100 hours, where any lower limit may be paired with any upper limit. The molding may be conducted for about 2 hours.

[0076] The immersing of the solid electrolyte may be conducted once or may be conducted more than once, such as 3 times (3 rinsing cycles), in order to provide sufficient salt removal. The deionized water may be changed between each rinsing cycles to provide deionized water substantially free of salt in each rinsing cycles.

[0077] The duration of the immersing may be influenced by the number of rinsing cycles. The immersing of the solid electrolyte in deionized water may be conducted for a duration of at least 2 hours to remove excess salt, such as NaCl, by leaching.

[0078] The duration of the immersing may be in a range of from about 2 hours to about 120 hours, such as in a range of from a lower limit selected from any one of 2, 5, 10 and 24 hours, to an upper limit selected from any one of 50, 100 and 120 hours, where any lower limit may be paired with any upper limits. The duration of the immersing may be about 24 hours. The above duration of the immersing represents a total amount of immersion time, in case there is more than one rinsing cycle. In one or more embodiments, when the number of the rinsing cycle in the immersing is 3, the total duration of the immersing may be 2 hours.ATTORNEY DOCKET NO.17500-261WO1

[0079] The method may further include mixing the solution including the polymer binder, ion exchange particles and salt after the adding step and before the casting step. The mixing may be conducted, for example, at least 10 minutes, such as for a duration in a range of about 10 minutes to about 30 minutes.

[0080] The method may further include cooling the formed solid electrolyte in the molding step before the immersing step. METHOD OF PRODUCING A SULFONATED POLYSULFONE BINDER

[0081] In another aspect, embodiments disclosed herein relate to a method for producing sulfonated polysulfone as a polymer binder.

[0082] The method includes dissolving a polysulfone resin in a solvent to produce a polysulfone solution, adding a sulfur-containing compound capable of introducing sulfonic acid groups to polysulfone, such as sulfonic acid or sulfuric acid, to the polysulfone solution to form a sulfonated polysulfone precipitate, washing the sulfonated polysulfone precipitate, and drying the washed sulfonated polysulfone precipitate to obtain the sulfonated polysulfone polymer binder.

[0083] The solvent in the dissolving step of the polysulfone resin may include an organic solvent such as chloroform.

[0084] The sulfur-containing compound in the adding step may be any compound capable of introducing sulfonic acid groups to polysulfone. The sulfur-containing compound may include, for example, sulfonic acid and sulfuric acid. The sulfonic acid in the adding step may include chlorosulfonic acid.

[0085] The adding of the sulfonic acid may be conducted such that the degree of sulfonation in the produced sulfonated polysulfone polymer binder is in a range of from about 30% to about 100%. The degree of sulfonation may be determined using, for example,1H NMR spectroscopy. The degree of sulfonation may be controlled by varying the molar ratio of the sulfonic acid to the polysulfone resin in the polysulfone solution. The molar ratio of the sulfonic acid to the polysulfone resin may be in a range of from about 0.3 to about 1.3, which corresponds to the above mentioned degree of sulfonation range, as shown in FIG.2, which is a degree of sulfonation vs. sulfonic acid / polysulfone resin molar ratio graph.ATTORNEY DOCKET NO.17500-261WO1

[0086] The washing of the sulfonated polysulfone precipitate may be conducted with a suitable medium, such as deionized water.

[0087] The drying step of the washed sulfonated polysulfone precipitate may be conducted at a temperature in a range of from about 50 °C to about 115 °C, such as in a range of from a lower limit selected from any one of 50 and 60 °C to an upper limit selected from any one of 110 and 115 °C, where any lower limit may be paired with any upper limit. The drying step may be conducted at a temperature of about 60 °C, 75 °C, 80 °C, 90 °C, or 110 °C. The drying step may be conducted under atmospheric pressure, or under vacuum. The drying may be conducted using suitable equipment in the art, such as a hot plate and / or a vacuum oven.

[0088] The drying may be conducted for a duration of at least 30 minutes, such as in a range of from about 30 minutes to about 36 hours, such as drying for 30 minutes, 6 hours 10 hours, 24 hours or 36 hours. The drying may include multiple drying steps which may have the same drying conditions or different conditions. Each of the multiple drying steps may have a drying temperature and duration in the aforementioned ranges. PROCESS FOR CARBON DIOXIDE REDUCTION

[0089] In one aspect, embodiments disclosed herein relate to a process for carbon dioxide reduction. The process includes introducing a feed stream including carbon dioxide (carbon dioxide stream) to an electrolysis cell, introducing a feed stream including water (feed water stream) to the electrolysis cell, and applying a voltage to the electrolysis cell to produce at least one carbon dioxide reduction product. According to one or more embodiments, the process for carbon dioxide reduction further includes collecting at least one carbon dioxide reduction product.

[0090] The electrolysis cell may be any of the electrolysis cell as previously described. The electrolysis cell may be a flow reactor, a solid-state electrolyzer, or combinations thereof.

[0091] The introduction step of the carbon dioxide stream may include introducing the carbon dioxide stream into the cathode compartment of the electrolysis cell.ATTORNEY DOCKET NO.17500-261WO1

[0092] The introduction step of the feed water stream may include introducing the feed water stream into the anode compartment of the electrolysis cell.

[0093] The application of a voltage to the electrolysis cell causes the carbon dioxide included in the carbon dioxide stream to react at the cathode to form carbon- containing anions, such as formate ions, and water included in the feed water stream to react at the anode to form oxygen and H+ions. The formed carbon-containing anions and H+ions then flow into the porous solid electrolyte composition, where the carbon-containing anions and H+ions react to produce at least one carbon dioxide reduction product.

[0094] In one or more embodiments, the carbon dioxide reduction product is selected from the group consisting of formic acid, carbon monoxide, methane, ethylene, ethanol, n-propanol, and combinations thereof.

[0095] According to one or more embodiments, the electrolysis cell including the porous solid electrolyte composition sustains a Faradaic efficiency of at least 90% over at least 220 hours when the at least one carbon dioxide reduction product is formic acid (formate selectivity of at least 90%). In one or more embodiments, the electrolysis cell including the porous solid electrolyte composition maintains a cell potential of about 3.5 V for at least 220 hours at a current density of at least 100 mA / cm2. EXAMPLES

[0096] The following examples are provided to illustrate embodiments of the present disclosure. The examples are not intended to limit the scope of the present invention, and they should not be so interpreted. EXAMPLE 1 SYNTHESIS OF SULFONATED POLYSULFONE (sPSF) BINDER

[0097] An exemplary polymer binder of one or more embodiments was produced as follows. The general reaction scheme for sulfonating polysulofone is shown in FIG. 3:ATTORNEY DOCKET NO.17500-261WO1

[0098] 6.0 g of polysulfone beads (Acros Organics, MW = 60,000) were completely dried in a vacuum oven at 120 °C for 24 hours. In a 250-mL round-bottom flask, the dried polysulfone resin was dissolved in 80 mL (approx. 120 g) of CHCl3 (99%, Sigma-Aldrich). The mixture, sealed with a rubber septum, was purged with N2 for 20 min while stirring. Next, while vigorously stirring at room temperature, chlorosulfonic acid (99%, Sigma-Aldrich) was added dropwise using a glass syringe, resulting in the formation of sulfonated polysulfone precipitate having a deep pink color. To achieve the desired degree of sulfonation (DS), the quantity of chlorosulfonic acid was varied over the range of 600 µL to 1 mL and aliquots were periodically extracted to monitor the progress of sulfonation. The degree of sulfonation was systematically varied from 30 to 100%.

[0099] The reaction was then quenched by adding the reaction solution to a 600 mL ice bath. After washing the precipitate polymer several times with deionized (DI) water, the sPSF was dried on a hot plate for 30 min at each of the following temperatures in succession: 60, 75, 90, and 110 °C. Finally, the sPSF was dried overnight in a vacuum oven at 80 °C, resulting in approximately 6.6 grams of faint pink solids.

[0100] 1H NMR spectroscopy was used to quantify the degree of sulfonation in the final product. The calculated degree of sulfonation, representing sulfonate groups per PSF repeat unit, was determined to be 70%. To assess the reproducibility and control of the sulfonation degree, variations in molar ratios of chlorosulfonic acid and dried PSF were employed in accordance with the described protocol.

[0101] Material characterizations of sPSF binder

[0102] The sulfonation degree of the sPSF is defined as the number of sulfonate groups per polysulfone (PSF) repeat unit, determined through analysis ofNMR spectra. ExemplaryNMR spectra of sulfonated polysulfone (sPSF) having various sulfonation degree, captured on a 600 MHz Bruker Avance spectrometer, are illustrated in FIG.4.

[0103] To prepare the samples, PSF or sPSF was completely dissolved in CDCl3 or DMSO-d6 (Cambridge Isotope Laboratories), respectively. Calculation of the degree of sulfonation (DS) involved applying Kopf's formula, with 'r' representing the ratio of combined integrations of1H NMR peaks in the spectra of FIG.4, related to protonsATTORNEY DOCKET NO.17500-261WO1 a, b, and c, divided by the combined integration peaks for protons d and e. The composite polyelectrolytes were fabricated with sPSF binder with 70% degree of sulfonation maintaining high ionic conductivity with high mechanical integrity. FIG. 2 displays the measured degrees of sulfonation for various sPSF samples synthesized using different ratios of chlorosulfonic acid to PSF. EXAMPLE 2 PRODUCTION OF POROUS SOLID ELECTROLYTE COMPOSITION

[0104] An exemplary porous solid electrolyte composition (a composite polyelectrolyte) was produced as follows. The composite polyelectrolytes were fabricated by drop casting and melt pressing a blend of polymer (sPSF), ion exchange particles (Dowex® 50W X8, H+form strongly acidic, 200-400 mesh, Sigma-Aldrich) and NaCl salt (Laboratory grade, Sigma-Aldrich), as illustrated in FIG.5.

[0105] Specifically, the sPSF was first dissolved in N-methyl-2-pyrrolidone (NMP, Sigma-Aldrich) to produce a 14 wt % solution of sPSF in NMP (binder solution). Next, 1 g of the Dowex® ion exchange particles and 0.5 g of NaCl were added to the binder solution at an overall mass ratio of 1.2:1:0.5. The mixture was stirred for 10 min and then cast onto a square Teflon mold (2.54 cm × 2.54 cm and depth of 2.0 mm) and heated on a hot plate at 75 °C for 16 h to remove the NMP solvent. Next, the composite polyelectrolyte was covered with a sheet of Teflon and hot-pressed at 115 °C with a load of two metric tons for 2 hours.

[0106] The samples were then allowed sufficient time to cool down before being carefully removed from the hot press. Afterward, the composite polyelectrolyte was extracted from the mold and immersed in deionized water for a 24-hour period to facilitate the leaching of NaCl, resulting in the formation of a porous composite polyelectrolyte. The deionized water was replaced three times throughout the salt leaching process, and particles that were removed from the composite polyelectrolyte during leaching were collected, vacuum-filtered, and rinsed with methanol to remove water. Subsequently, the porous composite polyelectrolyte samples were dried within a vacuum oven for 24 hours and weighed to determine the mass loss of the ion exchange particles from the composite polyelectrolyte. In order to enhance the ionic conductivity of composite polyelectrolytes with optimum binder (70% degree ofATTORNEY DOCKET NO.17500-261WO1 sulfonation), the concentration of the sPSF binder was varied from 6 to 20 wt % in the final composite polyelectrolytes. PREPARATION OF BI(NO3)2.5H2O (BOON) CATALYST

[0107] 970 mg of Bi(NO3)2.5H2O and 500 mg of cetyltrimethylammonium bromide (CTAB) were dissolved in 60 mL of deionized water. 3.0 g of urea was mixed with 40 mL of ethanol to form a homogeneous solution. The urea-ethanol solution was added to the Bi solution and then stirred for 30 minutes. After making a homogenous solution, the solution was kept in a 90 °C water bath for 4 hours. The white BOON catalysts were collected by centrifuge at 8,000 rpm for 10 min with deionized water and alcohol washing at least three times. PREPARATION OF CU2O CATALYST

[0108] 66.0 mg of trisodium citrate, 0.25 mL of 1.2 M CuSO4, 0.25 mL of 4.8 M NaOH, and 0.25 mL of 1.2 M ascorbic acid were added to 100 mL of deionized water sequentially under continuous stirring and with five-minute intervals between each reagent added. After adding all reagents, the solution was stirred for an extra 30 minutes, and Cu2O particles were collected by centrifuge at 8,000 rpm for 10 min with deionized water washing at least three times. CHARACTERIZATION OF POROUS SOLID ELECTROLYTE COMPOSITION

[0109] Water uptake, swelling ratio, and porosity measurements:

[0110] To evaluate the water uptake and swelling ratio, produced porous solid electrolyte composition examples (composite polyelectrolytes) were carefully blotted with a tissue to remove excess water after salt leaching process. The wet mass (mwet) and wet length (lwet) of each composite polyelectrolyte were measured. Next, the composite polyelectrolytes were dried in a vacuum oven for 3 days before measuring the dry mass (mdry) and dry length (ldry) of each composite polyelectrolyte. The water uptake was defined as (mwet – mdry) / mdry and the swelling ratio was (lwet – ldry) / ldry.

[0111] The porosity of the composite polyelectrolytes was determined by immersing the composite polyelectrolytes in water and determining the mass of excess water in the composite samples beyond the mass of water sorbed by the Dowex® particles. To do this, 1 gram of dry ion exchange particles were immersed in water, the surface wasATTORNEY DOCKET NO.17500-261WO1 blotted, and the weight of water-swollen particles was measured, which 1.79 grams. This indicated that the swollen particles contain 0.79 g of water per 1 g dry particles.

[0112] Next, the wet mass (mwet) of the composite polyelectrolytes following water immersion was measured. Then, the dry mass (mdry) of the composite polyelectrolytes was determined after drying for three days in a vacuum oven, and used this to determine the total mass of dry particles and binder in the composite. Based on these measurements, the mass of water sorbed by the particles after immersion in water was estimated to be: mwater in particles= mdry particles× 0.8 The sample porosity was then calculated as:where A and t represent the area and thickness of the composite polyelectrolyte, respectively, and ρwateris the density of water.

[0113] Mechanical tensile and surface hardness measurements:

[0114] The surface hardness was measured using a nanoindenter (Hysitron TI 980 TriboIndenter) in displacement control mode, set to 1000 nm with a loading rate of 25 nm / s at ambient temperature. Additionally, the tensile mechanical properties were evaluated utilizing an ARES G2 Rheometer. For the tensile test, rectangular specimens of the composite polyelectrolytes (2.0 cm by 0.8 cm) were subjected to a 0.005 N load. The specimens were clamped at both ends and slowly pulled lengthwise until fractured. The tensile test was performed at a rate of 0.1 mm s-1at ambient temperature.

[0115] Ionic conductivity in a symmetric flow reactor:

[0116] To investigate composite polyelectrolyte water flow and dynamic conductivity, a custom-designed symmetric three-compartment flow reactor was employed. This flow reactor closely mimics the structure of an actual solid-state CO2RR reactor, excluding the cathodic and anodic catalysts. This flow reactor includes two stainless steel plates serving as the anode and cathode and a polytetrafluoroethylene (PTFE) spacer featuring a window in the center measuring 2.54 cm by 2.54 cm with aATTORNEY DOCKET NO.17500-261WO1 thickness of 1.5 mm. The tailor-made 2.54 cm by 2.54 cm square composite polyelectrolyte with a thickness of 1.5 mm, was developed to precisely fit this spacer. To assemble the flow cell, two NafionTMmembranes were utilized as cation exchange membranes (CEM) (Fuel Cell Store) on both sides of the composite polyelectrolyte. The setup allowed quick assessment of ionic conductivity and water permeability of the porous solid electrolytes. A BioLogic VMP3 workstation was employed to record the electrochemical response. The ohmic resistance was determined by potentiostatic electrochemical impedance spectroscopy at frequencies ranging from 0.1 Hz to 100 kHz.

[0117] Carbon Dioxide Electroreduction:

[0118] Electrochemical CO2gas reduction measurements were conducted in two- electrode cell systems. For the two-electrode cell containing a polyelectrolyte layer, PiperION® AEM and a NafionTM117 CEM (Fuel Cell Store) were used for anions and cations exchange, respectively. The cathode was prepared by depositing 40 mg of catalyst onto 6 × 6 cm2of Sigracet® 28 BC gas diffusion electrode (GDE; Fuel Cell Store) with 80 μL of NafionTM117 solution (5%; Sigma-Aldrich). The as-prepared cathode was used as a working electrode, and an IrO2 / C electrode (Fuel Cell Store) was used as an anode. The composite polyelectrolyte was used between the cathode and anode. During the electrocatalytic reaction, 20 sccm of humidified CO2 gas flowed through the cathode gas channels, and pure deionized water flowed in both the middle and anode chamber at 1 and 3 mL min-1, respectively. To make a comparison, the reactor was configured identically, including commercial particles in the middle layer as solid electrolyte. All the electrochemical measurements were run at 25 °C. A BioLogic VSP-300 workstation was employed to record the electrochemical response. The ohmic resistance was determined by potentiostatic electrochemical impedance spectroscopy at frequencies ranging from 0.1 Hz to 200 kHz.

[0119] Analysis of CO2 reduction products:

[0120] During the electrocatalytic reaction, the electrochemical reactor was continuously fed with CO2, and gas products from the reactor were analyzed by gas chromatography (GC; Shimadzu GC-2014). The H2 was measured by a thermal conductivity detector (TCD), and the quantities of any alkane species were analyzedATTORNEY DOCKET NO.17500-261WO1 by a flame ionization detector (FID) with a methanizer. The partial current density for each gas product was calculated as: ^ ^^^^^^ = ^^ ^(Electrode Area)^^^^ where xi is the volume fraction of a certain product by online GC referenced to calibration curves from the standard gas samples (Airgas), v is the flow rate of gas, ni is the number of electrons consumed, F is Faraday’s constant, p0= 101.3 kPa, and R is the gas constant. The Faradaic efficiency (FE) at each potential was calculated by: FE = (ji / jtotal) × 100%

[0121] To quantify the liquid products from the electrochemical reduction reaction,1H Nuclear Magnetic Resonance (NMR) spectroscopy was conducted using a Bruker AVANCE III HD 600-MHz NMR spectrometer. For1H NMR measurements, 500 μL of liquid was directly collected from the middle chamber outlet at each current density and mixed with 100 μL of D2O (Sigma-Aldrich) containing 0.05 μL of dimethyl sulfoxide (DMSO; Sigma-Aldrich) as internal standard. The concentration of each liquid product was calculated using calibration curves made by mixing DMSO with exact concentrations of various products. The energy efficiency of chemical products such as formic acid was calculated using the following equation. !−Energy Efficiency = "# %!&'( )%!!)*× ^ )%!!)+,--where EOER (1.23 V vs. NHE at 298 °K) and ECO2 to HCOOH (-0.199 V vs. NHE at 298 K) are the standard electrode potentials for OER and CO2 reduction to HCOOH, respectively. The potential VCellis the practical solid-state reactor voltage. The pure formic acid production rate was calculated based on the formic acid production rate and formic acid product concentration. Energy consumption was calculated based on the solid-state reactor voltage, current, and pure formic acid production rate.

[0122] Fabrication and characterization of porous composite polyelectrolytes:

[0123] Characteristics of the composite polyelectrolytes of EXAMPLE 2 were investigated. As previously described, the composite polyelectrolytes were fabricated by blending sulfonated polysulfone (sPSF) prepared in EXAMPLE 1 (reactionATTORNEY DOCKET NO.17500-261WO1 scheme shown in FIG. 3) with sulfonated poly(styrene-divinyl benzene) ((poly(St- DVB)) ion exchange particles and NaCl. Specifically, the fabrication procedure involved blending the ion exchange particles, NaCl, and sPSF with NMP, casting in a Teflon mold, hot pressing, and immersing in deionized water to remove NaCl. A representative composite polyelectrolyte production process is illustrated in FIG.5.

[0124] Optical and scanning electron microscopy (SEM) were used to analyze the microstructure of the composite polyelectrolytes, which showed macroscopic voids within the composite polyelectrolytes created by salt leaching.

[0125] To evaluate the performance of composite polyelectrolytes, the ionic conductivity was measured in a custom flow reactor cell designed to mimic the dimensions and environment of the CO2RR electrolyzer, as shown in FIG. 6. The custom flow cell enables measuring ionic conductivity under continuous aqueous flow (2.0 mL min-1) through the composite polyelectrolyte using electrochemical impedance spectroscopy (EIS), facilitating rapid conductivity screening. The ionic conductivities of the samples were also measured in the full CO2RR electrochemical reactor.

[0126] To optimize the properties of the binder, the degree of sulfonation in the polysulfone binder was varied from 30 to 100%, as previously described. The degree of sulfonation was controlled by varying the molar ratio of chlorosulfonic acid used to sulfonate the polysulfone and analyzing the final degree of sulfonation usingNMR, as previously described and shown in FIGs.2 and 4. The results provided in FIG. 7, which is an ionic conductivity vs. ohmic resistance graph of the composite polyelectrolytes with different degrees of sulfonation measured using electrical impedance spectroscopy (EIS), show that increasing the degree of sulfonation in polysulfone enhanced the ionic conductivity of composite polyelectrolytes.

[0127] However, there was a trade-off between the degree of sulfonation and the mechanical integrity and stability of the polyelectrolyte. At a substantially high degree of sulfonation, the polysulfone swelled and became completely soluble in water. For instance, a polyelectrolyte with a 100% degree of sulfonation polysulfone binder dissolved during measurement and resulted in loss or release of particles during operation. On the other hand, composite polyelectrolytes with a substantially lowATTORNEY DOCKET NO.17500-261WO1 degree of sulfonation, such as 30% and 40%, maintained mechanical integrity but exhibited poor ionic conductivity. The highest degree of sulfonation obtained without dissolution of the binder was 70%, and this binder produced a composite polyelectrolyte with higher ionic conductivities than those with a lower degree of sulfonation. The binding having a sulfonation degree of 70% yielded a composite polyelectrolyte of optimum properties with a balanced combination of high ionic conductivity and mechanical integrity, making it well-suited for application in a CO2RR electrolyzer. Polysulfone with 70% degree of sulfonation was used as a polymer binder for the examples in the subsequent sections.

[0128] The mechanical properties of the composite polyelectrolytes were accessed through both surface indentation and mechanical tensile tests. Composite polyelectrolytes were produced with varying in binder content from 6 to 20 wt % with respect to the overall mass of binder and ion exchange particles.

[0129] The indentation tests were conducted to measure the surface hardness of the composite polyelectrolytes. FIG.8, which is a hardness vs. binder percentage graph of the composite polyelectrolytes, indicates that an increase in binder percentage led to a corresponding increase in surface hardness.

[0130] Mechanical tensile tests conducted on the composite polyelectrolytes further demonstrated that increasing the binder content increased the composite polyelectrolyte’s tensile strength from approximately 1.25 MPa to approximately 5 MPa with increasing binder content, as shown in FIG. 9. FIG.9 further shows that the modulus, determined from the slope of the stress-strain curve, increased from 0.41 MPa to 1.51 MPa with increasing binder content.

[0131] The particle mass loss of the composite polyelectrolytes was also measured during the salt-leaching process. FIG.10, which is a % mass loss vs. binder % graph of the composite polyelectrolytes, shows that the composite polyelectrolytes with a binder content below 8 wt % exhibited a mass loss of approximately 4%, attributed to mass loss of ion exchange particles from the composite.

[0132] The ionic conductivity and water flow in composite polyelectrolytes with varying binder contents from 6 to 20 wt % were quantified in the custom flow reactor cell. The results are shown in FIG.11. As shown in FIG.11, a direct correlation wasATTORNEY DOCKET NO.17500-261WO1 observed between increased binder percentage and increased ionic conductivity up to a binder content of 16 wt %. The highest conductivity was observed in composite polyelectrolytes with a 16 wt % binder. As the binder percentage exceeded 18 wt % in composite polyelectrolytes, there was a decrease in ionic conductivity. This may be attributed to poor contact between the polyelectrolyte surface and electrode components. The increased surface hardness for polyelectrolytes with higher binder contents can adversely impact the effective contact between the solid electrolyte and electrodes, resulting in high interfacial resistance.

[0133] The water uptake, swelling ratio, and porosity of the composite polyelectrolytes were evaluated at various binder contents. The results are shown in FIG.12. FIG.12 shows that as the binder percentage was increased from 6 to 20 wt %, water absorption decreased from 65.2% to 50% and the swelling ratio decreased from 12.4% to 8.0%. Furthermore, the porosity of composite polyelectrolytes decreased from 51.4% to 26.0% as the binder content increased from 6 to 20 wt %. The decreased porosity may be attributed to increased coverage of pores and voids by the binder. The observed reduction in porosity, especially beyond 16 wt % binder concentrations, impacted water flow. Maintaining a continuous water flow through polyelectrolytes is necessary for operation of CO2electrolysis.

[0134] Additionally, the stability and longevity of composite polyelectrolytes were evaluated by measuring the ionic conductivity of composites with 6, 10, and 16 wt % binder content over an extended period. Using electrochemical impedance spectroscopy (EIS), the ionic conductivity in the flow cell was monitored for 30 day. The results are shown in FIG.13. After each measurement, the cell was disassembled, and the composite polyelectrolytes were removed before conducting the subsequent test.

[0135] As shown in FIG.13, for composite polyelectrolytes with binder contents less than 10 wt %, a substantial decrease in the ionic conductivity was observed over the 30-day testing period. This may be attributed to loss of the ion exchange particles from the polyelectrolytes during operation. Conversely, it was observed that composite polyelectrolytes with binder content exceeding 10 wt % maintained at least 97% of the initial ionic conductivity throughout the entire 30-day duration. This differs significantly from commercial particles, which cannot be easily recycled andATTORNEY DOCKET NO.17500-261WO1 reused over multiple tests. The mechanical and electrochemical properties of the composite polyelectrolytes are summarized in Table 1. Table 1 Summary of mechanical and electrochemical properties of composite polyelectrolytes Binder Content Water Uptake Swelling Ratio Porosity σ (mS E cm-1) (wt %) (%) (%) (%) (MPa) 6 187.67 12.4 51 2.4 1.51 8 146.63 11.5 42 2.6 1.42 10 140.31 10.94 40 3.3 1.3 12 145.88 9.8 39 3.2 0.99 14 105.54 8.62 31 3.5 0.77 16 107.77 8.6 32 5.2 0.63 18 92.70 8.06 27 3.8 0.55 20 96.43 8.48 26 4.1 0.41 EXAMPLE 3

[0136] Performance in the solid-state CO2reduction reaction:

[0137] The performance of composite polyelectrolytes was evaluated for CO2RR in an electrochemical electrolyzer. The exemplary CO2RR electrolyzer of EXAMPLE 3 included three compartments: an anode, a cathode, and a middle layer housing the composite polyelectrolyte, as shown in FIG.1A. In contrast to the simpler symmetric flow reactor, the CO2RR system involves more complex components, including an anion exchange membrane, catalysts, and products and byproducts from the CO2reduction reaction. These additional components contribute to the unique interfacial challenges in the CO2RR system, making the precise balance of binder content crucial for maintaining effective performance and mechanical stability.

[0138] For the CO2RR anode, IrO2 was employed as the catalyst for the oxygen evolution reaction (OER), while the cathode side utilized a gas diffusion electrode (GDE) coated with Bi(NO3)2∙5H2O (BOON) catalyst for CO2reduction. Details regarding the preparation of BOON catalyst are described in the previous section.ATTORNEY DOCKET NO.17500-261WO1

[0139] The anode side of the electrochemical electrolyzer featured NafionTMas the proton exchange membrane, while the cathode side employed PiperION® as the anion exchange membrane.

[0140] Composite polyelectrolytes, with varying binder percentages, were positioned in the middle layer window, as shown in FIG.1A. Th composite polyelectrolytes had a length / width of 2.54 cm on each side and a thickness of 2.0 mm. Assembling the cell with composite polyelectrolytes was easier than with commercial particles since the composite polyelectrolytes could simply be placed in the middle layer chamber and could easily be removed and recycled. By contrast, commercial particles are manually packed, leading to inconsistencies across different tests, and they cannot be easily recycled.

[0141] A series of composite polyelectrolytes were tested in the CO2RR electrolyzer with binder contents varying from 6 to 20 wt %. It was found that the performance of the polyelectrolytes exceeded that of commercial particles. When comparing the CO2RR electrolyzer performance at a fixed current density, a lower potential corresponds to a higher energy efficiency. The potential profile shown in FIG. 14 indicates that up to a total current of 450 mA, the cell potential remained below 4.5 V for composite polyelectrolytes with 8 – 12 wt % binder. As shown in FIG. 14, the best performance was observed in polyelectrolytes with 10 and 12 wt % binder. This demonstrates that composite polyelectrolytes have sufficient conductivity and stability for use in CO2electrolyzers.

[0142] The ionic conductivity and resistance of the composite polyelectrolytes in the CO2RR electrolyzer were measured using the same methodology used for the custom flow reactor experiments, as previously described. The resistance measured in CO2RR was lower than that in the custom flow reactor, which may be attributed to a reactivation process with KHCO3 solution before testing. This reactivation process is necessary to reduce the acidity of the polyelectrolytes and protect the anion exchange membrane during operation.

[0143] In the CO2RR electrolyzer, it was observed that cell resistance decreased as binder content increased up to 12 wt %, after which it increased. This decrease in resistance may be due to the enhanced ionic conductivity of the polyelectrolyte withATTORNEY DOCKET NO.17500-261WO1 higher sulfonated polysulfone content. However, As shown in FIG. 15, when the binder content exceeded 12 wt %, the increased surface hardness of the polyelectrolyte reduced interfacial contact with the electrodes, leading to higher interfacial resistance. Consequently, it may be concluded that the optimal binder content for CO2RR is 10 – 12 wt %.

[0144] SEM images in FIG. 15 illustrate changes in polyelectrolyte surface morphology with binder content ranging from 6 to 20 wt %. As illustrated in the schematic in FIGs 16A-C, at binder contents below 8 wt %, cracking and breakage of polyelectrolytes were observed due to poor mechanical integrity, causing difficulty in the maintenance of the structure and assembly of the electrolyzer. Conversely, a binder content exceeding 14 wt % resulted in the composite polyelectrolytes to be more rigid, necessitating significant pressure for effective electrode contact, higher surface hardness, and reduction in the porosity of the composite polyelectrolytes. The reduction in the porosity affects the interfacial contact between the polyelectrolyte and other components in the electrolyzer. Notably, composite polyelectrolytes with a binder content between 8 – 12 wt % appeared optimal for contact and mechanical stability in the CO2RR electrolyzer.

[0145] Formic acid production using composite polyelectrolytes

[0146] One benefit of the solid-state electrolyzer with a composite polyelectrolyte is its ability to collect pure liquid products directly during the CO2RR process. This feature enhances the economic feasibility of the process by reducing the need for costly downstream separation and purification steps. Techno-economic analyses (TEA) demonstrates that producing high-purity products directly within the electrolyzer can lead to substantial cost savings.

[0147] To further evaluate the economic viability of the composite polyelectrolyte, a recent TEA was conducted and compared to liquid-based and particle-based electrolytes through a breakeven analysis, assessing the operational hours required for the composite polyelectrolyte to offset separation costs.

[0148] In addition to eliminating post-processing costs, the composite polyelectrolyte also offers enhanced stability and reusability, further improving the overall efficiency and economic viability of the system. To demonstrate this, A solid-state electrolyzerATTORNEY DOCKET NO.17500-261WO1 was implemented to produce formic acid (HCOOH) using the formate-selective Bi(NO3)2∙5H2O (BOON) catalyst and composite polyelectrolytes with various binder contents.

[0149] The experiment was conducted by varying a range of current densities from 50 to 200 mA cm-2. In an industry-favorable scenario where current density exceeds 150 mA cm-2, competitive reactions like the hydrogen evolution reaction (HER) and carbon monoxide (CO) generation can become more prevalent, leading to decreased energy efficiency. Using the composite polyelectrolytes, formate Faradaic efficiency consistently exceeded 90% across the entire tested current density range, as shown in FIG. 17. In contrast, the same cell configuration with the BOON catalyst using particulate solid-state electrolytes was unable to surpass 30 mA cm-2, and at 200 mA cm-2, the cell achieved only 72% Faradaic efficiency.

[0150] Composite polyelectrolytes with binder contents of 8, 10, and 12 wt % exhibited outstanding performance across all applied current densities. Utilizing the polyelectrolyte with 12 wt % binder facilitated the operation of CO2RR at a substantial current density of 200 mA cm-2, ensuring consistent high selectivity for formate production with Faradaic efficiency above 90% and effectively suppressing competitive HER and CO reactions, as shown in FIG.18. The partial current density of 179.63 mA cm-2for formate generation at 200 mA cm-2of total current density suggests that optimized composite polyelectrolytes could efficiently promote formic acid generation by enhancing ion transport due to reduced interfacial resistance between electrodes and porous polyelectrolyte surface. This underscores the potential of the composite polyelectrolyte for industrial applications, addressing a crucial challenge associated with particle usage and increasing current density, where HER and CO generation typically escalate.

[0151] Stability and durability of composite polyelectrolyte

[0152] The stability of the composite polyelectrolyte was tested by monitoring the cell voltage and Faradaic efficiency of the CO2RR of EXAMPLE 3 (EX 3) under continuous operation at 100 mA cm-2. The optimized polyelectrolyte was utilized with 12 wt % binder for the CO2RR test with the BOON electrocatalyst.ATTORNEY DOCKET NO.17500-261WO1

[0153] The device displayed outstanding stability, maintaining a high formate selectivity of 80 to 90% for 220 hours of continuous operation with a cell potential of 3.5 V. In this configuration, it was possible to continuously produce 50 mM of pure formic acid with a production rate of 0.376 µmol s cm-2and an energy efficiency of 33.55%.

[0154] The results were compared to various publicly available reference examples, as shown in Tables 2-3. In a comparable cell setup employing commercial particles and the BOON catalyst, the solid-state electrolyzer was stable for only up to 100 hours even at a relatively low current density (30 mA cm-2). By comparison, the solid-state reactor with the composite polyelectrolyte was more stable for longer times and at higher current densities (100 mA cm-2). Table 2Table 3ATTORNEY DOCKET NO.17500-261WO1

[0155] Moreover, the energy efficiency of the CO2 electrolyzer for formic acid production increased from 7.45% with commercial particles to 31% with the composite polyelectrolyte during the first 100 hours. This stability was superior to other electrolyzers for formic acid production reported in the published literature, with the best longevity in prior studies only up to 180 hours. This emphasizes how composite polyelectrolytes enable continuous and efficient long-term operation of the CO2RR electrolyzer.

[0156] To demonstrate scalability, large-scale polyelectrolytes were fabricated with areas of 10, 25, and 100 cm2. A large-scale polyelectrolyte reactor with a 25 cm2reactive area was tested. The large-scale cell showed stable operation voltage while maintaining uniform contact and high Faradaic efficiency of formic acid during the operation. This scaled-up system generated an average of 32.74 mmol of formic acid per hour.

[0157] Multi-carbon chemical production with composite polyelectrolytes:

[0158] To demonstrate the wide applicability of composite polyelectrolytes, production of chemicals beyond formic acid HCOOH was investigated using the Cu2O nanocube electrocatalyst, which can generate multiple C2+products. In this setup, optimal composite polyelectrolytes with a binder content of 12 wt % was employed in the CO2RR of EXAMPLE 3.

[0159] FIG. 19 is a current vs. potential for electrochemical cell with composite polyelectrolytes (12 wt % binder) middle layer for multicarbon production. FIG.19 shows that the selectivity of ethylene, the main C2+ product of the Cu2O electrocatalyst from the CO2RR, was around 40% at a current density of 300 mA cm-2, while the CO and HER reactions were less than 20%.

[0160] FIG. 20 is a graph showing Faradaic efficiency of multi-carbon products (formate, ethylene, ethanol, and n-propanol) with optimized composite polyelectrolyte middle layer (12 wt % binder). FIG. 20 indicates that formate and ethanol selectivity during the electrocatalytic process were as high as 20% and 15% for current densities 50 and 200 mA cm-2, respectively.ATTORNEY DOCKET NO.17500-261WO1

[0161] Specifically, the composite polyelectrolytes exhibited superior ethylene selectivity compared to commercial particles, effectively suppressing other competing reactions like the formation of other C2+ products (e.g. ethanol and acetate) and the hydrogen evolution reaction (HER). This enhanced selectivity may be attributed to the more uniform and stable morphology compared with particulate resins. Composite polyelectrolytes with binder contents of 8 to 12 wt % in the Cu2O-containing CO2RR electrolyzer were also compared, as shown in FIGs.21-28.

[0162] The above porous solid electrolyte composition of one or more embodiments, which includes a polymer binder such as sulfonated polysulfone as a binder and ion exchange particles such as poly(styrene-divinyl benzene) may be implemented in solid-state CO2RR electrolyzers to produce formate and other multi-carbon products. the properties of the binder and the composition of the composite polyelectrolytes may be optimized.

[0163] The above results show that the porous solid electrolyte composition of one or more embodiments outperformed commercial ion exchange particles in terms of mechanical stability and ionic conductivity. The porous solid electrolyte composition enabled long-term efficient operation of the CO2RR which can be easily recovered and re-used. Accordingly, the porous solid electrolyte composition is shown to addresses the above-noted drawbacks for CO2 electrolysis, and may provide advancement in large-scale, energy-efficient solid-state CO2 electrolyzers for CO2 capture and reduction.

[0164] Technoeconomic (TEA) and Life Cycle Assessment (LCA):

[0165] A key challenge in CO2 electrolysis is the high cost associated with product separation, with industrial reports estimating separation costs at $2,533,834 per 1000 m3 / h for conventional gas-phase CO2electrolysis systems. Solid-state electrolytes, including the composite polyelectrolyte, offer a promising alternative to reduce these separation costs. Prior studies suggest that replacing aqueous electrolytes with solid- state electrolytes can significantly lower separation costs by eliminating the need for complex electrolyte separation processes. Unlike particle-based electrolytes, which are disposed of after each use, the composite polyelectrolyte is reusable for at leastATTORNEY DOCKET NO.17500-261WO1 one month. However, there are additional costs associated with the binder and other chemical and energy inputs required to produce the composite polyelectrolyte.

[0166] To evaluate this impact, a technoeconomic analysis (TEA) was conducted to assess the additional cost of the binder, accounting for material and energy inputs during synthesis. The analysis includes a cost breakdown of 10 wt % and 12 wt % composite polyelectrolytes, as well as the sulfonated polysulfone binder. Additionally, a break-even analysis is conducted to compare the cost of composite polyelectrolytes with the separation processes required for liquid electrolytes. Industrial separation costs are evaluated against small-scale composite polyelectrolyte production hours per 1000 m³.

[0167] According to the General Techno-Economic Analysis of CO₂ Electrolysis Systems, “[i]ndustrial reports have assessed the costs of biogas upgrading using PSA, providing an estimate for the separation costs associated with CO₂ electrolysis gas product purification in commercial systems. Based on these studies, a reference cost of $1,990,000 per 1000 m³ / h capacity was used, with a capacity scaling factor of 0.7 and operating costs limited to electricity at 0.25 kWh / m³. Notably, this estimate does not include additional costs related to gas utilization, transportation, compression, or storage.”

[0168] Projecting the $1,990,000 per 1000 m3 / h capacity to December 2024 dollar, the separation cost would be approximately $2,533,834 per 1000 m3 / h capacity. For the small-scale composite polyelectrolyte reactor to produce 1000 m3of fuel it would take 809,716,600 hours as shown in the calculations below:

[0169] The results of the analyses are shown in Tables 4 to 6. The analysis indicates that the total cost of the composite polyelectrolyte is approximately 30% higher thanATTORNEY DOCKET NO.17500-261WO1 that of the ion exchange resin (particle-based electrolytes). Most of the additional cost is attributed to the polysulfone binder. However, unlike the particle-based solid electrolytes, the composite polyelectrolytes can be easily washed and reused, and re- using the composite polyelectrolyte just once would result in cost savings relative to employing two particle-based electrolytes, which are not recyclable. The composite polyelectrolytes provide additional benefits such as improved consistency and reliability across different devices. Table 4- Technoeconomic analysis of sulfonated polysulfone Table 5 - Technoeconomic analysis of optimized 10 wt % composite polyelectrolytes.Table 6 - Technoeconomic analysis of optimized 12 wt % composite polyelectrolytesATTORNEY DOCKET NO.17500-261WO1

[0170] A life cycle assessment (LCA) of the composite polyelectrolytes was also conducted to evaluate the environmental impact of polyelectrolytes with 10 and 12 wt% binders, considering the sulfonation of polysulfone as part of the material synthesis process.

[0171] The results of the LCA address the environmental impacts contributed by the synthesis of the composite polyelectrolytes for the 10 and 12 wt % binders since these binder percentages observed the best performance when tested in the CO2RR electrolyzer. The LCA analysis of producing a one-square-inch composite polyelectrolyte unit indicates that the most significant contributors to the assessed impact categories are the sulfonated polysulfone binder, N-methyl-2-pyrrolidone, and electricity consumption. The electricity mix utilized in the LCA was a US mix consisting primarily of coal (32%), natural gas (23%), hydropower (28%), and nuclear (11%). Due to the high dependency on the electricity contribution, impact results would vary depending on the electricity sources utilized to synthesize the composite polyelectrolyte. The LCA data for both polyelectrolytes, as well as the sulfonated polysulfone binder can be found in Tables 7-9. Table 7 - Life cycle assessment (LCA) of one square inch of optimized composite polyelectrolyte with 10 wt % binder contentATTORNEY DOCKET NO.17500-261WO1 Table 8 - Life cycle assessment (LCA) of one square inch of optimized composite polyelectrolyte with 12 wt % binder content Table 9 - Life cycle assessment (LCA) of the sulfonation process for 6 grams of polysulfone beads

[0172] Analysis of the impact category contributions per one functional unit (one- square-inch of polyelectrolyte) reveals that the impact categories most affected by theATTORNEY DOCKET NO.17500-261WO1 synthesis process were fossil fuel depletion, global warming, and smog, which are primarily driven by electricity consumption. The impact contribution magnitudes and uncertainties resulting from the production of the composite polyelectrolyte for each of the considered impact categories were analyzed with the highest impact category being fossil fuel depletion (FFD) and the lowest impact category being Human health carcinogenic (CTUh). The most influenced impact categories in this case are ones that would be responsive to the electricity mix utilized for the synthesis of the polyelectrolytes and could be reduced using less carbon-intensive electricity sources.

[0173] The use of chemicals for the fabrication of the composite polyelectrolyte contributes to environmental and human health impacts. These findings suggest that utilizing low-carbon energy sources for synthesis and optimizing material selection can further improve the sustainability of composite polyelectrolytes. By reducing separation costs, offering long-term reusability, and maintaining competitive material costs, composite polyelectrolytes present a more cost-effective and environmentally sustainable pathway for CO2electrolysis compared to conventional particle-based electrolytes.

[0174] This analysis did not include all the energy and chemical inputs required for the preparation of ion exchange resin, as this information was not readily available. Specifically, due to lack of inventory in the Ecoinvent 3 dataset, the cationic resin created in the lab as the ion exchange particles (commercially similar to Dowex® 50W X8, H+ form strongly acidic, 200-400 mesh, Sigma-Aldrich) utilized in the composite polyelectrolyte was not able to be modeled in SimaPro to analyze the specific environmental impacts individual to that cationic resin. In exchange, the substitute input used from the Ecoinvent 3 dataset was a general cationic resin input.

[0175] The key difference between the cationic resin created and used in the lab and the cationic resin shown in the Ecoinvent 3 dataset is that the resin component in the dataset uses polystyrene whereas the resin component created in the lab utilizes divinylbenzene and styrene along with benzoyl peroxide and polyvinyl alcohol to engineer the copolymer beads. The cationic resin provided by the Ecoinvent 3 dataset also lacks utilizing dichloromethane to sulfonate the beads and only accounts for the sulfuric acid during the sulfonation process. It is to be noted that the electricity mix utilized within the production of the cationic resin in the Ecoinvent 3 dataset is moreATTORNEY DOCKET NO.17500-261WO1 geographically verbose and is not specific to the electricity mix used in the US and the market component accounts for transportation factors not applicable to the cationic resin made domestically within the lab.

[0176] Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from this invention. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims.

Claims

ATTORNEY DOCKET NO.17500-261WO1 CLAIMS What is claimed is:

1. A porous solid electrolyte composition for carbon dioxide electrolysis, comprising: ion exchange particles; and a polymer binder, wherein the porous solid electrolyte composition has a porosity in a range of from 20% to 60% and an ionic conductivity in a range of from 2 mS / cm to 12 mS / cm.

2. The porous solid electrolyte composition of claim 1, wherein the ion exchange particles are selected from the group consisting of DOWEX®, AmberLite™, Duolite™, poly(styrene- divinylbenzene), polyacrylic resin, Purolite™ particles, and combinations thereof.

3. The porous solid electrolyte composition of claim 1 or 2, wherein the ion exchange particles have an average particle size in a range of from 5 µm to 80 µm.

4. The porous solid electrolyte composition of any one of the above claims, wherein the polymer binder comprises a sulfonated polysulfone binder with a degree of sulfonation in a range of from 30% to 100%.

5. The porous solid electrolyte composition of any one of the above claims, wherein the polymer binder comprises a short side chain perfluorosulfonic acid.

6. The porous solid electrolyte composition of any one of the above claims, wherein the porous solid electrolyte composition is free-standing.

7. The porous solid electrolyte composition of any one of the above claims, wherein the polymer binder is present in an amount in a range of from 6 wt% to 20 wt%, based on a total weight of the porous solid electrolyte composition.

8. A method for making a porous solid electrolyte composition, the method comprising: dissolving a polymer binder in a solvent to form a solution; adding ion exchange particles and a salt to the solution, casting the solution onto a substrate at an elevated temperature; maintaining the elevated temperature for at least 10 hours to form a composite;ATTORNEY DOCKET NO.17500-261WO1 molding the composite to form a solid electrolyte under an elevated pressure and temperature; and immersing the solid electrolyte in deionized water for at least 2 hours to remove excess salt, thereby forming the porous solid electrolyte composition.

9. The method of claim 8, wherein the salt is sodium chloride.

10. The method of claim 8 or 9, wherein the polymer binder is a short side chain perfluorosulfonic acid or a sulfonated polysulfone binder with a degree of sulfonation in a range of from 30% to 100%.

11. The method of any of claims 8 to 10, wherein the polymer binder is present in an amount in a range of from 6 wt% to 20 wt%, based on a total weight of the porous solid electrolyte composition.

12. The method of any of claims 8 to 11, wherein the porous solid electrolyte composition has a porosity in a range of from 20% to 60% and an ionic conductivity in a range of from 2 to 10.4 mS / cm.

13. The method of any of claims 8 to 12, wherein the ion exchange particles are selected from the group consisting of DOWEX®, AmberLite™, Duolite™, poly(styrene-divinylbenzene), polyacrylic resin, Purolite™ particles, and combinations thereof.

14. A process for carbon dioxide reduction, comprising: introducing a carbon dioxide stream to an electrolysis cell, wherein the electrolysis cell comprises: an anode compartment comprising an anode; a cathode compartment comprising a cathode; and a porous solid electrolyte composition, wherein the porous solid electrolyte composition comprises ion exchange particles and a polymer binder; and wherein the porous solid electrolyte composition has a porosity in a range of from 20% to 60% and an ionic conductivity in a range of from 2 mS / cm to 12 mS / cm, and introducing a water stream to the electrolysis cell; andATTORNEY DOCKET NO.17500-261WO1 applying a voltage to the electrolysis cell to produce at least one carbon dioxide reduction product.

15. The process of claim 14, further comprising collecting the at least one carbon dioxide reduction product from the electrolysis cell.

16. The process of claim 14 or 15, wherein the at least one carbon dioxide reduction product is selected from the group consisting of formic acid, carbon monoxide, methane, ethylene, ethanol, n-propanol, and combinations thereof.

17. The process of any of claims 14 to 16, wherein the electrolysis cell is selected from the group consisting of a flow reactor, and a solid-state electrolyzer.

18. The process of any of claims 14 to 17, wherein the anode compartment further comprises a proton exchange membrane and a catalyst for an oxygen evolution reaction, and the cathode compartment further comprises an anion exchange membrane and a catalyst for a carbon dioxide electrochemical reduction.

19. The process of any of claims 14 to 18, wherein the at least one carbon dioxide reduction product is formic acid, and the electrolysis cell comprising the porous solid electrolyte composition sustains a Faradaic efficiency of at least 90% over at least 220 hours.

20. The process of any of claims 14 to 19, wherein the electrolysis cell comprising the porous solid electrolyte composition maintains a cell potential of 3.5 V for at least 220 hours at a current density of at least 100 mA / cm2.

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