Systems and methods for energy-efficient electrified ethylene production from carbonate capture liquid

Abstract

Electrolyzers are provided that comprise a cathode comprising a dilute metal alloy catalyst comprising single atoms of a first metal M1 distributed within a metallic matrix composed of a second metal M2, the cathode in contact with a catholyte comprising carbonate ions; an anode in electrical communication with the cathode; and a membrane configured to generate in situ CO2 in the catholyte. Methods of producing ethylene using the electrolyzers are also provided.

Description

SYSTEMS AND METHODS FOR ENERGY-EFFICIENT ELECTRIFIED ETHYLENE PRODUCTION FROM CARBONATE CAPTURE LIQUIDCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to U.S. provisional patent application number 63 / 639,088 that was filed April 26, 2024, the entire contents of which are incorporated herein by reference, and to U.S. provisional patent application number 63 / 707,389, that was filed October 15. 2024, the entire contents of which are incorporated herein by reference.BACKGROUND

[0002] Direct air capture (DAC) of CO2 is typically implemented by utilizing alkali hydroxides as capture solutions to form carbonate. The release of CO2 and the regeneration of alkali hydroxide require an energy -intensity thermal cycle up to 900 °C. In addition, the subsequent valorization of gaseous CO2 into products leads to additional energy demands and system complexities.SUMMARY

[0003] Provided are electrochemical reactive capture systems (i.e., electrolyzers) configured to generate CO2 in situ (i.e., Z-CO2), to reduce the Z-CO2 to products (e.g.. CO), and to synthesize a hydrocarbon (e.g., ethylene) from the CO. The electrolyzers comprise certain dilute metal alloy catalysts for inducing carbon-carbon coupling reactions to produce the hydrocarbon and may further comprise an additional catalyst for facilitating the reduction of CO2 to CO. The catalysts and related methods are also provided.

[0004] The present disclosure includes an Example (Example 1) below demonstrating a reactive capture system that integrates CO2 capture with the electrochemical upgrade of CO2 into ethylene. First, the origins of limitations of ethylene production in prior electrochemical reactive capture systems were studied using in situ Raman spectroscopy. It was found that the CO2-starved local reaction environment on catalyst surfaces leads to a dominant hydrogen evolution reaction, outcompeting CO2 electroreduction and suppressing C-C coupling. Next, catalyst strategies were developed to facilitate CO2 activation and promote the cooperative adsorption of key Ci intermediates for enhanced spatial availability of C1-C1 coupling. This was achieved by a porous dilute alloy catalyst design and tandem catalysis systemoptimization. As a result, a 41% ethylene Faradaic efficiency (FE) with nearly 100% CO2 utilization at 200 mA cm2was achieved in the electrochemical reactive capture system, resulting in a 65 weight% ethylene concentration in the product stream. The carbonate-to- ethylene system had an overall ethylene energy efficiency of 15.6% at 200 mA / cm2, which is 1.5-fold higher than the most efficient existing reactive capture systems.

[0005] A second Example (Example 2) is also included that demonstrates another reactive capture system that integrates CO2 capture with its electrochemical conversion into ethylene. To enhance ethylene production and mitigate the impact of liquid products, particularly organic acids (OA), on the pH of the capture solution and its subsequent regeneration, a series of d-block metal (M = Ru, Rh, Pd, Au, Ag, Hl) doped Cu-based dilute alloy cataly sts were screened. A high-performing Hf-Cu catalyst was characterized, including via in situ Raman spectroscopy. It was found that the synergistic effects of the bimetallic sites promoted carbon-carbon coupling while increasing the conversion of in situ generated CO2 to CO intermediates, thereby suppressing the formation of formic acid. A Faradaic efficiency for ethylene (FE) of 37.5% was found along with an FEc2H4 / FEtotaioA ratio of 44.6, which is 12-fold higher than existing Cu catalysts.

[0006] In one aspect, an electrolyzer is provided that comprises a cathode comprising a dilute metal alloy catalyst comprising single atoms of a first metal Mi distributed within a metallic matrix composed of a second metal M2, the cathode in contact with a catholyte comprising carbonate ions; an anode in electrical communication with the cathode; and a membrane configured to generate in situ CO2 in the catholyte.

[0007] Other principal features and advantages of the disclosure will become apparent to those skilled in the art upon review of the following drawings, the detailed description, and the appended claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Illustrative embodiments of the disclosure will hereafter be described with reference to the accompanying drawings.

[0009] FIG. 1 shows a schematic illustration of the integrated route of reactive CO2 capture.

[0010] FIGS. 2A-2C show in situ Raman spectra of a Cu catalyst during electrolysis with(FTG. 2A) 50% CO2 + 50% Ar (FIG. 2B) 33% CO2 + 67% Ar (FIG. 2C) 20% CO2 + 80% Ar.FIG. 2D shows a comparison of the relative amount of certain Raman bands corresponding to the different types of absorbed CO on the Cu catalyst (bridged CO, low-frequency band (LFB) linear CO, and high-frequency band (HFB) linear CO) as determined from the in situ Raman spectra. FIGS. 2E-2F show FEs of H2, CO (FIG. 2E) and C2H4 (FIG. 2F) on the Cu catalyst measured at 50% CO2 + 50% Ar, 33% CO2 + 67% Ar, 20% CO2 + 80% Ar in 1.5 M K2CO3.

[0011] FIG. 3A shows a schematic illustration of the Bi-Cu porous dilute alloy catalyst. FIG. 3B shows a HAADF-STEM image of the Bi-Cu dilute alloy catalyst. FIGS. 3C-3D show aberration-corrected HAADF-STEM images of the Bi-Cu dilute alloy catalyst, confirming the uniform distribution of individual Bi atoms in the Cu matrix.

[0012] FIG. 4A shows in situ Raman spectra of the Bi-Cu dilute alloy catalyst during electrolysis with 20% CO2 + 80% Ar. FIG. 4B shows a comparison of the relative amounts of Raman bands corresponding to the different types of absorbed CO (bridged CO, low- frequency band (LFB) linear CO, and high-frequency band (HFB) linear CO) as determined from the in situ Raman spectra. FIG. 4C shows LFB CO adsorption ratios on the Bi-Cu dilute alloy catalyst and the comparative Cu catalyst. FIG. 4D shows FEs of C2H4 on the Bi-Cu dilute alloy catalyst and the comparative Cu catalyst in 1.5 M K2CO3. FIG. 4E shows FEs of C2H4 of a series of p-block metal (M = Al, Ga, Sn, In. Bi) doped Cu dilute alloy catalysts in carbonate electrolysis system. FIG. 4F shows a comparison of C2H4 FE of the Bi-Cu dilute alloy catalyst and the comparative Cu catalyst in the carbonate electrolysis system.

[0013] FIG. 5A shows products distribution in the carbonate electrolysis system using the CoPc HC / Bi-Cu tandem catalyst (left bars) and the comparative Cu catalyst (right bars) under different current densities. FIG. 5B shows ethylene energy efficiency of the CoPc HC / Bi-Cu tandem catalyst and the comparative Cu catalyst. FIG. 5C shows CO2 utilization of the CoPc HC / Bi-Cu tandem catalyst in the current density range of 100-400 mA cm’2. FIG. 5D shows ethylene concentration at the outlet and CO2 utilization in the illustrative system used in the Example, below, and literature benchmark CO2R systems, including alkaline CO2R, neutral CO2R, and acidic CO2R.

[0014] FIG. 6 shows the Cu K-edge extended X-ray absorption fine structure (EXAFS) spectra of the Bi-Cu dilute alloy catalyst under the in situ electrochemical reduction condition of 50 mA cm’2, Bi-CuO (Bi-Cu under open circuit potential), Cu foil and CuO reference samples.

[0015] FIG. 7A shows ethylene FE and H2 FE for a series of d-block metals (M = Ru, Rh, Pd. Au, Ag, HI) doped Cu dilute alloy catalysts. FIG. 7B shows the liquid products FE comparison of the dilute alloy catalysts. FIG. 7C shows ethylene FE as a function of Hf amount (mol%). FIG. 7D shows formate concentration and ethylene FE of Hf-Cu (2 mol%) and a comparative Cu nanoparticle (NP) catalyst after 300 min reduction in 200 mL 1.5 M K2CO3.

[0016] FIG. 8A shows a comparison of the relative amounts of Raman bands corresponding to the different types of absorbed CO (bridged CO, low-frequency band (LFB) linear CO, and high-frequency band (HFB) linear CO) as determined from in situ Raman spectra for the Hf-Cu dilute alloy catalyst. FIG. 8B shows the same comparison but for the comparative Cu catalyst.DETAILED DESCRIPTION

[0017] Electrolyzers are provided which are configured to generate CO2 in situ (i.e., i- CO2) in an electrolyte contained within the electrolyzer, to reduce the / -CO2 to products (e.g., CO), and to synthesize a hydrocarbon (e.g., ethylene) from the CO. Such an electrolyzer comprises a cathode comprising a dilute metal alloy catalyst, an anode in electrical communication with the cathode, and a membrane between the cathode and the anode.

[0018] The dilute metal alloy catalyst, which is further described below, is configured to catalyze carbon-carbon coupling reactions to produce the hydrocarbon. This includes the dilute metal alloy catalyst exhibiting the ability to increase the binding of CO thereto and to enable the cooperative binding of intermediates in the carbon-carbon coupling reactions. thereby providing a lower energy pathway to formation of the desired hydrocarbon. This may further include the dilute metal alloy catalyst exhibiting the abi 1 i ty to suppress the formation of organic acids, e.g., formic acid, acetic acid. The term “organic acids,” encompasses the protonated and unprotonated versions thereof, e.g., both formic acid and formate. The cathode may further comprise an additional catalyst (distinct from the dilute metal alloy catalyst), also further described below, that is capable of catalyzing the electrochemical reduction of CO2 to CO.

[0019] The dilute metal alloy catalyst comprises (or consists ol) a first metal Mi distributed within a metallic matrix composed of a second metal M2. The first metal Mi may be in the form of individual atoms (versus a collection or aggregation of such individualatoms) distributed within the metallic matrix. The first metal Mi may be selected from p- block metals and combinations thereof. In embodiments, the first metal Mi is selected from Al, Ga, Sn, In, Bi, and combinations thereof. In embodiments, the first metal Mi is Bi. The first metal Mi may be selected from d-block metals and combinations thereof In embodiments, the first metal Mi is selected from Ru, Rh, Pd, Au, Ag, Hf, and combinations thereof. In embodiments, the first metal Mi is Hf. A combination of a p-block metal(s) and a d-block metal(s) may also be used as the first metal Mi. The second metal M2 may be Cu. Other metals that may be used for the second metal M2 include Ag, Au, and Zn. The term “alloy” is used in view of the presence of the two different metal elements (Mi and M2). The term “dilute” is used since the amount of the first metal Mi in the dilute metal alloy catalyst is generally much less than that of the second metal M2. This includes the dilute metal alloy catalyst having Mi present at a mol% of no more than 5 mol%, no more than 4 mol%, no more than 3 mol%, no more than 2 mol%, no more than 1 mol%, or a range of between any of these values. Mol% refers to (total moles of Mi) / (total moles of Mi and M2)*100. The term “doped” may also be used, e.g., the metallic matrix composed of the second metal M2 is doped with the first metal Mi. A schematic of an illustrative Bi-Cu dilute metal alloy catalyst is shown schematically in FIG. 3A. Another illustrative catalyst is a Hf-Cu dilute metal alloy catalyst.

[0020] The first metal Mi is generally homogeneously and uniformly distributed within the metallic matrix composed of the second metal M2, w hich may be confirmed using EDS element maps. Similarly, aberration-corrected HAADF-STEM images such as those shown in FIGS. 3C-3D for the illustrative Bi-Cu dilute metal alloy catalyst may be used to confirm that the Mi element (e.g., Bi) is distributed as individual, isolated atoms (i.e., single atoms) within the M2 (e.g., Cu) metallic matrix (versus multiple atoms aggregated together in a cluster or particle). EXAFS spectra such as shown in FIG. 6 may be used to confirm that Mi and M2 are in their metallic states (versus being bound to a non-metal atom such as oxygen). In addition, PXRD and XPS may be used as described in Example 2 to confirm that Mi and M2 are in their metallic states.

[0021] The dilute metal alloy catalyst may be nanostructured, i.e., the solid material of the dilute metal alloy catalyst is in the form of a plurality of nanostructures, e.g., nanoribbons as shown in FIG. 3B, for the illustrative Bi-Cu dilute metal alloy catalyst. The nanoribbons may be entangled to form a nanoribbon network in which surfaces of the nanoribbons definea plurality- of pores distributed throughout the nanoribbon network of the dilute metal alloy catalvst.

[0022] As noted above, the dilute metal alloy catalysts exhibit the ability to increase the binding of CO thereto and to enable the cooperative binding of intermediates in the carboncarbon coupling reactions, thereby providing a lower energy pathway to formation of the desired hydrocarbon. This may be confirmed using in situ Raman spectroscopy as described in the Examples, below. For example, in situ Raman spectra may be used to quantify the amount of low-frequency band (LFB) linear CO bound to surfaces of the dilute metal alloycatalysts. As shown in FIGS. 4B and 4C, the dilute metal alloy catalysts exhibit relatively high amounts (intensities) of LFB linear CO as compared to comparative catalysts composed of only M2, even at low amounts of CO2. This includes at least 50%, at least 55%, at least 60%, at least 65%, at least 70% LFB linear CO, at least 75% LFB linear CO, at least 80% LFB linear CO, at least 85% LFB linear CO, or a range of between any of these values. These percentages refer to the amount of LFB linear CO as compared to the total amount of bridged CO, LFB linear CO, and HFB linear CO. These values may be referenced to electrolysis using a feedstock of 20% CO2 / 80% Ar and an applied electric potential vs. Ag / AgCl in a range of from -1.0 to -2.0 V (or at a specific applied electric potential such as -1.6, -1.8, or - 2.0 V). In situ Raman spectra may also be used to confirm the existence of peaks corresponding to intermediates in the desired carbon-carbon coupling reactions, e.g., for ethylene, one or more of peaks at 1218 cm’1, 1450 cm’1, and 1647 cm’1. As demonstrated in the Examples, below, the ability of the dilute metal alloy catalysts to facilitate CO binding and carbon-carbon coupling reactions in this way translates into very high FE to ethylene and further results in suppression of the formation of organic acids such as formic acid. (See FIGS. 4D-4F and 7C- 7D.)

[0023] Methods for synthesizing the dilute metal alloy catalysts are described in the Examples, below. Briefly, the methods involve a solvothermal-annealing-electrochemical reduction route. Such a method comprises combining a precursor of the first metal Mi (e.g., a metal salt such as a metal halide) with a precursor of the second metal M2 (e.g., a metal salt such as a metal nitrate) in a solvent (e.g., aqueous solution at basic pH) under conditions (e.g., heat, pressure, mixing, period of time) to form a solid product which may be recovered by filtration. Next, annealing the solid product in air provides a dilute metal alloy catalyst precursor comprising oxygen, e.g., the second metal M2 is present as an oxide. (See FIG. 6.) Next, an appropriate electric potential may be applied to the dilute metal alloy catalystprecursor to induce electrochemical reduction to convert the M2 oxide to its metallic state and provide the dilute metal alloy catalyst. (See FIG. 6.)

[0024] The electrochemical reduction may be carried out by providing the dilute metal alloy precursor catalyst as a dilute metal alloy precursor ink (which may further comprise other components, e.g., a solvent (e.g., an alcohol), an ionomer (e.g., Nafion)) and coating the ink onto a substrate (e.g., carbon paper) at a desired surface coverage. Ultimately, this coated substrate may be used as the cathode of the electrolyzer. Applying the appropriate electric potential reduces M2 to its metallic state.

[0025] Conditions being used during the dilute metal alloy catalyst synthesis method described above (including type and relative amounts of precursors; solvothermal temperature, pressure, time; annealing temperature, time; applied potential, etc.) as well as parameters such as relative amounts of the various components in the dilute metal alloy precursor ink may be adjusted to achieve a desired result, e.g., a maximum FE to a desired hydrocarbon (e.g., ethylene), a minimum amount of an organic acid (e.g.. formic acid) in the catholyte, etc.

[0026] As noted above, the cathode may further comprise another catalyst (in addition to the dilute metal alloy catalyst). This additional catalyst may be a supported catalyst comprising (or consisting of) a porous, conductive support and a catalyst distributed thereon. This catalyst is distinct from the dilute metal alloy catalyst as described above and is one capable of catalyzing the electrochemical reduction of CO2 to CO. Illustrative such catalysts include metal phthalocyanines, e.g., cobalt phthalocyanine (CoPc). The porous, conductive support is composed of a solid conductive material (e.g., carbon) having surfaces which define a plurality of pores distributed throughout the solid conductive material. The surface area of the porous, conductive support may be at least 1000 m2 / g. at least 1200 m2 / g, at least 1400 m2 / g. or a range of between any of these values. The solid surfaces of the porous, conductive support may define at least two populations of pores, each having a different size. A first population of pores may have a larger size, which may be in a range of from 2 nm to 50 nm, from 10 nm to 35 nm, or from 10 nm to 20 nm. Such pores may be referred to as mesopores. A second population of pores may have a smaller size, which may be less than 2 nm, less than 1 nm, or in a range of from 1 to 2 nm. Such pores may be referred to as micropores. The porous, conductive support may have a greater number of larger pores (e.g., mesopores) as compared to smaller pores (e.g., micropores). The porous, conductive supportmay have a pore ratio (defined as the number of larger pores to smaller pores) of at least 7, at least 10, at least 13, or at least 15, or a range of between any of these values. Surface area, pore size, pore distribution, and pore ratios may be measured using Brunauer-Emmett-Teller (BET) analysis. The pore sizes above may be diameters and they may be average values as determined by BET analysis. It is noted that the solid conductive material itself may be in the form of a plurality of particles, e.g., as in a powder. However, the pores in this paragraph refer to those defined within such particles and are distinguished from any additional pores formed between neighboring individual particles. Porous, conductive supports having at least two populations of differently sized pores (e.g., both mesopores and micropores) within the ranges of pore ratios described above may be referred to as hierarchically porous (HP) supports and may also be referred to herein by the label “HC.”

[0027] An illustrative method for synthesizing a hierarchically porous carbon support is provided in Example 1, below. The Example 1 also describes an illustrative method for forming the additional catalyst by combining a dispersion of the porous, conductive support with a dispersion of the catalyst under appropriate conditions. Similar to the dilute metal alloy catalyst, the additional cataly st may also be provided as an ink (which may further comprise other components, e.g., a solvent, an ionomer). This additional catalyst ink may be coated onto the same substrate being used for the dilute metal alloy catalyst precursor ink. The electrochemical reduction described above to provide the dilute metal alloy catalyst may be carried out after coating the substrate with the additional catalyst ink. Conditions being used during the processes described in this paragraph as well as parameters such as relative amounts of the various components in the additional catalyst ink and the relative amounts of the additional catalyst ink and the dilute metal alloy catalyst precursor ink may be adjusted to achieve a desired result, e.g., maximum faradic efficiency to CO, maximum faradic efficiency to a desired hydrocarbon (e.g., ethylene), ), a minimum amount of an organic acid (e.g.. formic acid) in the catholyte, maximum % CO2 utilization, maximum amount of the desired hydrocarbon in an output stream from the electrolyzer, or combinations thereof.

[0028] The term '‘tandem” may be used in reference to the combination of any of the disclosed dilute metal alloy catalysts for hydrocarbon synthesis along with any of the disclosed additional catalysts for CCh-to-CO reduction may be referred to using the term “tandem,” e.g.. tandem catalysts, tandem electrode, tandem cathode, etc.

[0029] In the present electrolyzers, the cathode comprising the dilute metal alloy catalyst and the additional catalyst (if present) is in contact with a catholyte comprising carbonate ions (CO32). The catholyte may be an aqueous alkali metal carbonate (e.g., K2CO3) solution.

[0030] The membrane between the anode and the cathode of the electrolyzer is configured to generate the Z-CO2 in the catholyte. This may be accomplished by the membrane being configured to dissociate water contained within the electrolyzer, thereby generating protons and hydroxide ions. The membrane may be a bipolar membrane. On the cathode side of the electrolyzer, the protons may combine with the carbonate ions to generate the / -CO2 in the catholyte. The membrane may comprise a catalyst to facilitate water dissociation.

[0031] The anode of the electrolyzer may be configured to facilitate the formation of oxygen (O2) from hydroxide ions present in the anolyte (including those generated by the bipolar membrane). Various anodes and anolytes (e g., alkali metal hydroxides such as KOH) capable of achieving oxygen evolution may be used.

[0032] The electrolyzer may further comprise other components, e.g., an interposer layer between the cathode and the membrane, flow field plates, etc.

[0033] An illustrative electrolyzer, which may be used as the “liquid-fed carbonate electrolyzer” shown in FIG. 1, comprises a cathode comprising any of the disclosed dilute metal alloy catalysts (e.g., Bi-Cu dilute metal alloy catalyst or a Hf-Cu dilute metal alloy catalyst) and any of the disclosed additional catalysts (e.g., CoPc / HC), the cathode in contact with an aqueous K2CO3 solution as the catholyte (fed to the electrolyzer via a feed inlet). The carbonate ions in the catholyte react with the protons from the bipolar membrane to generate Z-CO2 in the catholyte. Generating a potential difference between the anode and the cathode induces reduction of the Z-CO2 to CO at the cathode as catalyzed by the CoPc catalyst thereon. At the same time, ethylene is generated by the carbon-carbon coupling reactions between CO molecules as catalyzed by the dilute metal alloy catalyst. This can occur with suppressed formation of organic acids, including formic acid. The ethylene may be collected as a product stream via an outlet. The disclosed electrolyzers may be a component of a larger reactive CO2 capture system.

[0034] Methods for producing a hydrocarbon (e.g., ethylene) from CO2 are also provided. Z-CO2 are also provided. Such a method comprises generating Z-CO2 in a catholyte comprising carbonate ions, the catholyte in contact with a cathode of an electrolyzer, thecathode comprising a dilute metal alloy catalyst and optionally, an additional catalyst; reducing the z-CCh to CO at the cathode; and inducing carbon-carbon coupling reactions to produce a hydrocarbon from the CO. Other hydrocarbons that may be produced include ethanol, acetate, and n-propanol. The methods may be carried out using any of the disclosed electrolyzers, any of the disclosed dilute metal alloy catalysts, and any of the disclosed additional catalysts.

[0035] The present methods may be characterized by the high FEhydrocarbon values (e.g., at least 30%, at least 35%, at least 40%, at least 45%, or a range of between any of these values) and high FEhydrocarbon / FEtotai organic acid ratios (e.g., at least 35, at least 40, at least 40, or a range between any of these values) as described herein. These values may refer to carrying out the methods under the specific set of electrolysis conditions used as described in Examples 1 or 2, below. The methods may be characterized by producing a product stream comprising a high amount of the desired hydrocarbon, e.g., greater than 50 weight%. greater than 55 weight%, greater than 60 weight%, or a range between any of these values. (See FIG. 5D.) Weight% refers to (total weight of desired hydrocarbon) / (total weight of products)* 100. These values may refer to carrying out the methods under the specific set of electrolysis conditions used to obtain the results shown in FIG. 5D as described in Example 1, below.

[0036] Also encompassed are the dilute metal alloy catalysts themselves, e g., Bi-Cu dilute metal alloy catalyst. Hf-Cu dilute metal alloy catalyst. The tandem catalysts, e.g., Bi- Cu dilute metal alloy catalyst combined with CoPc / HC, are also encompassed.EXAMPLES

[0037] Example 1

[0038] Additional information, including that referenced as “data not shown’7may be found in U.S. provisional patent application number 63 / 639,088 that was filed April 26, 2024, the entire contents of which are incorporated herein by reference.

[0039] Introduction

[0040] Air-to-ethylene conversion has been accomplished by sequencing direct air capture (DAC) and gas-phase CO2 electrolysis. A typical direct air capture (DAC) process uses alkali hydroxide (e.g., KOH) to turn CO2 into carbonate, followed by a calcium loop to regenerate hydroxide and release concentrated CO2. The calcium loop involves a calcinationprocess operating at -900 °C which consumes >90% of the DAC energy input. Gas-phase CO2 is upgraded to ethylene in an electrolyzer.

[0041] By contrast and to improve the overall energy efficiency of the air-to-ethylene process, reactive capture systems integrate CO2 capture and upgrade (FIG. 1). This route can potentially promote air-to-chemical efficiency by circumventing the need for CO2 regeneration, purification, and compression before feeding to the electrolyzer, and for CO2 recirculation. Ethylene production in a reactive capture electrolyzer relies on in situ CO2 (z- CO2) generated by carbonate acidification. The protons are generated through water dissociation in a bipolar membrane (BPM) junction and migrate through a cation-exchange layer (CEL) under reverse bias. However, the low local CO2 concentration (typically < 5 vol%) near the catalyst surface is a significant challenge to C2+ selectivity. For example, the most efficient existing carbonate-to-ethylene reactive capture systems have exhibited an ethylene Faradaic efficiency of 34% with an air-to-ethylene energy efficiency of 10%.

[0042] Methods

[0043] Chemicals

[0044] Bismuth(III) chloride (BiCis) (>98%), copper(II) nitrate trihydrate(Cu(NOs)23H2O), sodium hydroxide (NaOH), cobalt phthalocyanine (CoPc), zinc nitrate hexahydrate (Zn(NC>3)2-6H2O), 2-methylimidazole, bis(4-hydroxyphenyl) sulfone, phosphonitrilic chloride trimer, N,N-diethylethanamine, and potassium carbonate (K2CO3) were purchased from Sigma- Aldrich. Copper nanoparticles (25 nm) were purchased from US Research Nanomaterials. The commercial BPM membrane (Fumasep FBM) used to separate the catholyte and anolyte and gas diffusion layer (Freudenberg H23) were from Fuel Cell Store. Nafion dispersions (D520CS) were purchased from Ion Power. Distilled water (DI- water) with 18.2 M cm resistivity, was obtained from a Milli-Q reference water purification system.

[0045] Electrode preparation

[0046] 0.5 mmol of BiCh was dispersed in 2 mL ethanol and added dropwise to a 40 mL solution with 5 mmol Cu(NO3)23H2O immersed in an ice water bath (< 4 °C) followed by dropwise addition of 10 mL 1.2 M NaOH aqueous solution. Subsequently, the mixture was subjected to vigorous magnetic stirring for 15 min to form a uniform dispersion. Then the homogeneous mixture was transferred into a 100 mL high-pressure steel reactor, which wasthen sealed and heated at 150 °C for 2 h. The resulting black solid was obtained by filtration and washed repeatedly by water and ethanol, respectively, and then vacuum-dried in an oven at 60 °C. The obtained powder was annealed at 400 °C in air for 3 h to obtain Bi-CuO. The catalyst ink was prepared by dispersing the synthesized Bi-CuO catalyst powder in 2- propanol with added Nafion ionomer and was well-sonicated for a good dispersion of catalyst. The ink was then airbrushed onto the carbon paper, giving the final catalyst loading of ~ 2 mg cm2.

[0047] 4 mg CoPc and 60 mg hierarchically porous carbon (HC) were separately sonicated in 60 ml DMF to disperse. Then, the CoPc dispersion solution was added dropwise to the HC suspension with vigorous magnetic stirring. The mixed dispersion was sonicated for 30 min and stirred for 24 h at RT. Subsequently, the CoPc@HC was obtained by washing with DMF many times until colorless, followed by drying in a vacuum at 80 °C for 12 h.

[0048] HC was synthesized by the following procedures. 6 mmol Zn(NOs)2-6H2O, 24 mmol 2-methylimidazole and 100 ml methanol were mixed with vigorous stirring for 3 min at room temperature (RT). Subsequently, the mixture was kept at 35 °C for 6 h. The precipitate was collected, washed and finally dried in a vacuum oven at 80 °C for 12 h to prepare the ZIF-8. 400 mg as-prepared ZIF-8 powder was dispersed in 40 ml methanol. Then, 100 ml methanol containing 325 mg of bis(4-hydroxyphenyl) sulfone and 152 mg of phosphonitrilic chloride trimer was added and stirred for 15 minutes. 1 ml of N,N- diethylethanamine was slowly added to the dispersion, followed by stirring at 25 °C for 15 hours. The resulting precipitate marked as ZIF-8@PZS was collected, washed, and finally dried in a vacuum at 80 °C overnight. Thereafter, the ZIF-8^PZS powder was placed in a quartz boat in a tube furnace with a heating rate of 5 °C min'1to 950 °C and maintained for 3 h to provide the HC.

[0049] In a typical procedure, the CoPc7 / ,HC / BiC'u electrode was prepared by spraying CoPc@HC uniformly dispersed ink including CoPc@HC, 2-propanol and Nafion ionomer to the as-prepared Bi-CuO electrode with the CoPc@HC loading of 0.5 mg cm2. followed by in situ electrochemical reduction in 50 mA cm-2for 30 min.

[0050] Ni foam was first sonicated by 6 M HC1 and Dl-water for 15 min respectively. Then, the cleaned Ni foam was transferred to a 50 mL Teflon-lined stainless-steel autoclave with uniform mixed 2 mmol Ni(NO3)2 6H2O, 2 mmol Fe(NCh)3-9H2O, 4 mmol NH4F, and 10 mmol urea in 40 mL solution. The hydroxides were synthesized on Ni foam throughhydrothermal growth, conducted at 120 °C for 6 hours with a heating rate of 3 °C min '. Subsequently, the FeNi-precursor / nickel foam (NF) was washed by DI- water and dried in an oven at 80 °C. To prepare (FexNii-x)2P / NF, FeNi-precursor / NF and 1.0 g ofNaFbPCh FbO were positioned in distinct locations within a quartz boat placed inside a tube furnace, with NaFbPCh FbO located upstream in the gas flow. Following purging with argon (Ar), the center of the furnace was raised to 300 °C at a ramping rate of 1 °C min'1and maintained at this temperature for 1 h in a static Ar atmosphere. Subsequently, the system naturally cooled down to ambient temperature.

[0051] Electrochemical measurements

[0052] The flow electrolyzer comprised two stainless steel flow-field plates featuring serpentine channels, along with PTFE and silicone gaskets. The membrane electrode assembly (MEA), consisting of two electrodes and a membrane, was formed after the assembly of the cell hardware. Peristaltic pumps (INTLLAB) circulated the catholyte and anolyte at a rate of 20 ml min - 1. The applied current was regulated by a BioLogic potentiostat / galvanostat.

[0053] A commercial (Fumasep FBM, Fuel Cell Store) or custom-designed BPM membrane separated the catholyte and anolyte. The cathode utilized the as-prepared BiCu catalyst, with a filter membrane inserted as the interposer layer between the cathode and cation exchange layer (CEL) of the bipolar membrane. The catholyte was 1.5 M K2CO3, and the anolyte was 1 M KOH.

[0054] Product analysis

[0055] The gas products (H2, CO, CH4 and C2H4) were monitored by GC (Shimadzu2014, PerkinElmer Clarus 580) equipped with a thermal conductivity detector (TCD) and a flame ionization detector (FID) equipped with a Methanizer. Ar (100 mL min1) was purged as the carrier gas to carry the gas products out of the system for quantification. The calibration curve was established by analyzing the standard calibration gases with different concentrations (10-10,000 ppm).

[0056] The Faradaic efficiency (FE;) can be calculated by equations as follows: n^F FE, = x 100 % Qwhere n< is the moles of product z; z, is the number of electrons transferred for one product molecule; A is the Faraday constant (96.485 C moE1): Q is the total charge passed through the electrolytic cell.

[0057] The carbon utilization can be calculated by the equations as follows:Carbon utlization = X 100 % = (1-2FncO2x100 %where n°02is the moles of theoretical CCh that can be generated from the BPM-based electrolyzer; nC02is the moles of gas CO2 detected at the outlet; F is the Faraday constant (96,485 C mo1); Q is the total charge passed through the electrolytic cell.

[0058] Materials characterization

[0059] Powder X-ray diffraction (PXRD) spectra were collected on a STOE-STADI P powder diffractometer operating at 40 kV voltage and 40 mA current with Cu-K a 1 X-ray radiation ( = 0. 154056 nm) in transmission geometry. Aberration corrected scanning transmission electron microscopy (STEM) images and energy-dispersive X-ray spectroscopy (EDS) mappings were obtained using JEOL ARM200CF TEM equipped with a dual SDD EDS detector. Transmission electron microscopy (TEM) samples were prepared by scratching the nanopowders from the cathode surface. The scratched material was dispersed in 2-propanol follow ed by drop-casting on the grid. X-ray photoelectron spectroscopy (XPS) was conducted on a Thermo Scientific NEXSA G2 XPS spectrometer, equipped with an Al K alpha radiation source and electron flood-gun. at a pressure of 8x108mbar with a pass energy of 50 eV. All spectra were calibrated with the C Is peak at 284.8 eV. Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDS) was carried out by JEOL JSM-7900FLV SEM at an accelerating voltage of 10 kV with backscattered electron detection, which was equipped with a light-element X-ray detector and an Oxford Aztec energy-dispersive X-ray analysis system. N2 and CO2 isotherms were operated by a Micromeritics 3Flex instrument, and samples were dried at 373 K under dynamic vacuum for 12 h until the pressure stabilized below 5*10'6bar. Brunauer-Emmett-Teller (BET) method was utilized to calculate surface area from N2 adsorption isotherm.

[0060] In situ Raman spectra w ere recorded with a Renishaw inVia Raman spectrometer using an in-house in situ cell and a x50 water immersion lens. Cu nanoparticles and BiCu catalyst was used as the cathode in electrolytes of 0.5 M KHCO3. purged with CO2 from the backside. Pt wire and Ag / AgCl were used as the anode and reference electrodes, respectively.

[0061] CO2capture from the atmosphere when combined with electrochemical conversion, provides a potentially carbon-neutral approach to produce chemicals and fuels. Ethylene stands out among all value-added chemicals, with a global market of 150 million metric tons per year, rendering it the foremost hydrocarbon chemical produced globally.

[0062] Results and Discussion

[0063] In initial studies using a Cu nanoparticle (Cu NP) catalyst (a comparative catalyst) in a carbonate electrolysis system, it was confirmed that a high H2 FE > 55% with a low ethylene FE < 18% were obtained (data not shown). CO2 availability was constrained to simulate the low Z-CO2 concentration in the carbonate electrolysis system. In situ Raman spectroscopy showed that, as the local CO2 concentration decreased, three major bands associated with surface-adsorbed *CO at 300-500 cm'1and 1900-2150 cm'1appeared at an elevated applied potential, including bridged CO, low-frequency band (LFB) linear CO, and high-frequency band (HFB) linear CO (FIGS. 2A-2C). Concurrently, the relative amount of the associated low-frequency band (LFB) linear CO, recognized as conducive to C-C coupling, was diminished (FIG. 2D). Furthermore, it was observed that the Cu NP catalyst exhibited a clear increase in H2 FE and a notable decline in CO FE and ethylene FE as the local CO2 concentration decreased (FIG. 2E-2F). These findings indicated that in a carbonate electrolysis system, the CO2-starved local reaction environment favored the kinetically more facile hydrogen evolution reaction (HER), outcompeting CO2 electroreduction and disfavoring C-C coupling.

[0064] Thus, catalyst designs were developed to facilitate CO2 adsorption and activation and favor ethylene production over HER and Ci products in a CCh-starved carbonate electrolysis system. Catalyst designs included the introduction of a guest metal into porous Cu to form dilute alloy catalysts, with adjacent dual active sites. This approach was based on the inventors' insight that a porous structure may promote CO2 adsorption and activation and the adjacent dual active sites may enable the cooperative adsorption of key Ci intermediates to enhance the spatial availability of C1-C1 coupling. Guest metals from the p-block, displaying elevated overpotential for HER and extraordinary p-d orbital hybridization were used.

[0065] A range of p-block metal (M = Al, Ga. Sn. In, Bi) doped Cu porous dilute alloy catalysts were synthesized via a solvothermal-annealing-electrochemical reduction route (FIG. 3 A). Taking the synthesis and structural characterization of Bi-Cu porous dilute alloyas an example, a Bi doped CuO (Bi-CuO) was synthesized through a solvothermal procedure, followed by annealing. Subsequently, the Bi-Cu dilute alloy catalyst was obtained via in situ electrochemical reduction. In situ X-ray absorption spectroscopy (XAS) was carried out to investigate the structure evolution from the Bi-CuO material to Bi-Cu porous dilute alloy catalyst during in situ electrochemical reduction. The binding energies of normalized adsorption peaks in the Cu K-edge X-ray adsorption near-edge spectra (XANES) shifted from 8985 eV for open circuit potential (OCP) to 8980 eV under in situ electrochemical reduction condition of 50 mA cm'2(data not shown). This shift indicated the conversion of Bi-CuO to the metallic Bi-Cu state. This structure evolution was further confirmed by the extended X- ray absorption fine structure (EXAFS) spectra. As shown in FIG. 6, the peak located at approximately 1.5 A associated with Cu-0 coordination vanished, and the peak located at approximately 2.2 A ascribed to Cu-Cu coordination appeared when applying current density of 50 mA cm'2during the in situ electroreduction treatment.

[0066] Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-angle annular dark-field STEM (HAADF-STEM) images of the Bi-Cu dilute alloy catalyst showed an interlaced porous nanoribbon morphology (FIG. 3B). A lattice spacing of 0.21 nm ascribed to the Cu (111) facet was observed in high-resolution TEM images (data not shown). The energy-dispersive X-ray spectroscopy (EDS) elemental maps revealed a uniform distribution of individual Bi atoms in the Cu matrix (data not shown). Aberration- corrected HAADF-STEM images were performed to directly observe the structure of the Bi- Cu dilute alloy catalyst at the atomic level, where bright dots associated with Bi atoms were distinguished in the Cu matrix (FIGS. 3C-3D).

[0067] In situ Raman measurements of the Bi-Cu dilute alloy catalyst were then carried out under constrained CO2 availability. As shown in FIG. 4A, the bands located in the SOO- SOO cm'1region were ascribed to the frustrated rotation of *CO on Cu and with Cu-CO stretching. Another set of bands in the 1900-2150 cm'1region w ere associated with surface- bonded CO stretching. Notably, the peaks in these CO-related regions appeared at lower applied potential on the Bi-Cu dilute alloy catalyst as compared to those on the comparative Cu catalyst. Additionally, it was found that the bands of Cu-CO stretching showed a blueshift on the Bi-Cu dilute alloy catalyst as compared to the comparative Cu catalyst, meaning a stronger binding of CO to the Bi-Cu surface. Moreover, on the Bi-Cu dilute alloy catalyst, new emerging peaks were observed at approximately 1450 cm'1and 1647 cm'1(*CHO) and a peak at approximately 1218 cm'1(*OCCHO). This finding indicates the Bi-Cu dilute alloycatalyst has adjacent dual active sites that enabled the cooperative adsorption of *CO intermediate and *CHO intermediate and consequently asymmetric CO-CHO coupling to obtain *OCCHO: a lower-energy-barrier pathway toward ethylene. As shown in FIG. 4B, the 2000-2150 cm’1bands were deconvolved into three peaks and assigned to bridge CO, the low-frequency band (LFB), and the high-frequency band (HFB) linear CO at approximately 2050 cm’1, 2075 cm’1, and 2095 cm’1, respectively. As shown in FIGS. 4B and 4C, higher LFB CO ratios were observed on the Bi-Cu dilute alloy catalyst as compared to the comparative Cu catalyst, confirming that the Bi-Cu dilute alloy catalyst promotes LFB CO adsorption, thus facilitating C-C coupling. It was further observed that even at low CO2 concentrations, the Bi-Cu dilute alloy catalyst exhibited a higher C2H4 FE and a lower H2 FE compared to those on the comparative Cu catalyst (FIG. 4D). This demonstrates that the incorporation of the p-block metal Bi into Cu, at an amount to form a dilute alloy catalyst, enhances the electrochemical synthesis of ethylene from carbonate capture liquid.

[0068] As shown in FIG. 4E, a series of p-block metal (M = Al, Ga, Sn, In, Bi) doped Cu dilute alloy catalysts were evaluated in a reactive capture system with K2CO3 simulating the post-capture liquid. It was found that the Bi-Cu dilute alloy catalyst stood out from these candidates. It was discovered that the Bi-Cu dilute alloy catalyst had a higher ethylene FE and a higher ethylene partial current density compared with the comparative Cu catalyst across the current density range of 100-400 mA cm’2. Notably, the dilute Bi-Cu catalyst showed a peak ethylene FE of 35% at 300 mA cm’2while the comparative Cu catalyst exhibited a maximum ethylene FE of 18% at 200 mA cm’2. (See FIG. 4F.) These results indicate that the implementation of adjacent-dual-site Bi-Cu dilute alloy catalyst promoted ethylene production, resulting in an increase in ethylene concentration in the outlet stream from 33 wt% to 53 wt%.

[0069] Additional strategies were pursued to further improve ethylene production in this CO2-starved reactive capture system. It was reasoned that a portion of in situ generation of CO2 ( / -CO2) was converted into carbonate at the catalyst surface due to the locally alkaline conditions, which would further limit CO2 availability. It was further reasoned that improving CO coverage would assist in suppressing hydrogen evolution and promoting C-C coupling for enhanced ethylene production. Thus, a tandem catalysis system was developed to achieve highly efficient and selective conversion of CO2 to CO (CO2-to-CO) at the catalyst surface to preserve the reactant and create a greater CO coverage, by deploying a CO2-to-CO catalyst layer on the Bi-Cu dilute alloy catalyst in tandem.

[0070] To implement this strategy, a supported catalyst composed of hierarchical porous carbon (HC as the catalyst support) and a CoPc catalyst was synthesized to facilitate CO2 activation and conversion into CO. Then, a CoPc HC / Bi-Cu tandem catalyst was then fabricated. This CoPc HC / Bi tandem catalyst achieved an increase in the ethylene FE from 32% to 41%, along with a higher selectivity of multicarbon products (C2+) with a peak C2+ FE of 53% (FIG. 5 A).

[0071] A higher energy efficiency of ethylene production was pursued by reducing the voltage loss across the BPM and anodic oxygen evolution reaction (OER). Specifically, an efficient water dissociation (WD) catalyst was employed with the BPM, and aNiFeP foam was utilized as the OER catalyst. This optimization led to an ethylene energy efficiency of 15.6% at 200 mA cm'2(FIG. 5B). This energy efficiency was 1.5-fold higher than that observed in the most efficient existing reactive capture system for ethylene electrosynthesis (data not shown). A carbon utilization exceeding 99% was observed in the current density range of 100-400 mA cm'2(FIG. 5C). This carbon utilization far surpasses those observed in gaseous CO2 reduction systems. These results demonstrate that the present reactive capture system generated a product stream without CO2. The high ethylene FE of 41% and almost 100% CO2 utilization using the CoPc HC / Bi-Cu tandem catalyst contributed to a 65 wt% of ethylene concentration in the outlet stream, which greatly outperformed benchmark alkaline / neutral / acidic CO2 reduction systems and reactive capture systems (FIG. 5D). In contrast, product gas streams from gaseous CO2 reduction systems are typically diluted by unreacted CO2. The subsequent regeneration and separation of unreacted CO2 leads to a considerable energetic penalty on these systems.

[0072] A preliminary technoeconomic analysis to estimate energy cost of ethylene production was conducted, taking into account upstream generation for the gas-phase CO2 and carbonate capture solutions, electrolysis, separation, and carbonate regeneration. The present reactive capture system exhibited an energy intensity of ethylene production of 325 GJ ton1, marking a 35% reduction compared to the most efficient reactive capture system, and also comparing favorably with benchmark alkaline / neutral / acidic CO2 reduction systems (data not shown). This decreased energy cost of the reactive capture system benefited from the elimination of CO2 separation and regeneration. Additionally, the integration of capture and conversion steps in reactive capture system offered the added advantage by significantly reducing capital costs as separate CO2 regeneration and circulation modules typically constitute significant contributions to the overall capital cost of a commercial plant.

[0073] Example 2

[0074] Additional information, including that referenced as “data not shown" may be found in U.S. provisional patent application number 63 / 707,389 that was filed October 15, 2024, the entire contents of which are incorporated herein by reference.

[0075] Introduction

[0076] Reactive capture is a concept that couples direct air capture (DAC) of carbon dioxide (CO2) with the subsequent electrochemical reduction of the captured CO2 in the same solution. This approach involves capturing CO2 from the atmosphere using an alkaline solution, such as potassium hydroxide (KOH), and subsequently reducing the captured carbonate solution electrochemically to chemicals and fuels. The integration of these processes not only addresses the urgent need for reducing atmospheric CO2 concentrations but also provides a scalable and economically viable solution for achieving carbon neutrality and mitigating climate change. The regeneration of the alkaline capturing solution is a critical aspect of this approach, as it ty pically requires significant energy input. The present Example 2 describes experiments using dilute alloy catalysts to minimize the formation of organic acids (e.g. formic acid, acetic acid) during the electrochemical reduction, which is crucial to enhancing the overall energy' efficiency and maintaining the operational sustainability of the DAC system.

[0077] Specifically, the accumulation of organic acids during the electrochemical reduction process can significantly impact the performance and longevity of the CO2 capture system. These acids alter the pH of the capturing solution, reducing its capacity’ to absorb CO2 effectively. Ensuring the production of minimal organic acids during electrochemical reduction is essential to preserve the alkaline nature of the capturing solution, thereby maintaining its CO2 absorption efficiency. By optimizing the electrocatalysts to minimize byproduct formation as described in this Example 2, the overall energy demand for solution regeneration can be reduced, making the DAC approach more sustainable and cost-effective.

[0078] Ethylene is distinguished among value-added chemicals for its critical role in the global chemical industry. With the largest market share, current annual production rate of ethylene is 150 million metric tons, positioning it as the most extensively’ produced hydrocarbon chemical worldwide. It serves as a fundamental precursor for a wide range of chemicals and materials, including polyethylene, ethylene oxide, and ethylene dichloride, which are integral to the manufacture of plastics, solvents, and other industrial products. Thisversatility- and high demand highlight the necessity- for efficient and sustainable production methods. In addition to enhancing the Faradic efficiency (FE) of ethylene, this Example 2 describes experiments using dilute alloy catalysts to minimize the formation of liquid organic acids during the process. Suppressing the production of these acids not only conserves energy but also helps maintain the stability- and effectiveness of the capture solution, further contributing to the overall efficiency and sustainability of ethylene production systems.

[0079] Methods

[0080] Chemicals

[0081] Hafnium (IV) chloride (HfCU) (98%), anhydrous copper (II) chloride (CuCb), sodium hydroxide (NaOH), isopropanol and potassium carbonate (K2CO3) were purchased from Sigma-Aldrich. The gas diffusion layer (Freudenberg H23) and commercial bipolar membrane (BPM) (Fumasep FBM) were from Fuel Cell Store. Copper nanoparticles (25 nm) were purchased from US Research Nanomaterials. Nafion dispersions (D520CS) were purchased from Ion Power. Deionized water (Dl-water) with 18.2 MQ cm resistivity was obtained from a Milli-Q reference water purification system.

[0082] Catalyst synthesis and electrode preparation

[0083] All the chemicals were used without further purification as received from Sigma- Aldrich. 1.5 mmol of anhydrous CuCb was dissolved in 20 mL of DI water and sonicated for 15 min as solution A. 0.03 mmol HfCh was dissolved in 5 mL of DI water and sonicated for 15 min as solution B. Then solution B was added dropwise to solution A under vigorously stirring. After solution A and B were thoroughly- mixed, 5 mL of DI water containing 3.6 g of NaOH was added drop by drop. The mixture solution was vigorously stirred for 15 min, then transferred to a 50 mL Teflon-lined stainless-steel autoclave and maintained at 100 °C for 12 h. The precipitate was washed with DI water and ethanol respectively, and then dried in a vacuum oven. The obtained powder was annealed at 300 °C for 3 h to provide Hf-CuO catalyst. The Hf-Cu catalyst was obtained by in situ electroreduction of the Hf-CuO catalyst under 50 mA / cm2for 10 min. An electrocatalyst ink was formed by dispersing the synthesized Hf-CuO catalyst powder in 2-propanol with added Nafion ionomer and sonicating for 1 h to obtain good dispersion of the catalyst. The ink was then airbrushed onto the hydrophilic carbon paper, giving the final catalyst loading of around 2 mg cm2.

[0084] Electrochemical measurements

[0085] The flow electrolyzer consisted of two stainless steel flow-field plates with serpentine channels and silicone and PTFE gaskets. The membrane electrode assembly (MEA) comprised two electrodes and a membrane. It was formed after the assembly of the cell hardware. Catholyte and anolyte were circulated at a rate of 20 rpm by peristaltic pumps. The applied current was regulated by a BioLogic potentiostat / galvanostat. A commercial BPM or custom-designed BPM was used to separate the catholyte and anolyte. The cathode utilized the as-prepared Hf-Cu catalyst, with a hydrophilic PTFE filter membrane inserted as an interposer layer between the cathode and the cation exchange layer (CEL) of the BPM. A 1.5 M K2CO3 solution was applied as the catholyte, and the anolyte was 1 M KOH solution.

[0086] Product analysis

[0087] The gas products (H2, CO, CH4 and C2H4) were monitored by GC (PerkinElmer Clarus 580) equipped with a thermal conductivity detector (TCD) and a flame ionization detector (FID) equipped with a Methanizer. Ar (100 rnL min ') was purged as the carrier gas to carry the gas products out of the system for quantification. The calibration curve was established by analyzing the standard calibration gases with different concentrations (10- 10,000 ppm).

[0088] The Faradaic efficiency (FE;) can be calculated by equations as follows: n:ZiFFE; = x 100 % Q where is the moles of product z; ztis the number of electrons transferred for one product molecule; / ’ is the Faraday constant (96.485 C moE1): Q is the total charge passed through the electrolytic cell.

[0089] The carbon utilization can be calculated by the equations as follows:Carbon utlization = X 100 % = (1-2FncO2x100 %Q where n°02is the moles of theoretical CO2 can be generated from the BPM-based electrolyzer; nC02is the moles of gas CO2 detected at the outlet; F is the Faraday constant (96,485 C moE1); Q is the total charge passed through the electrolytic cell.

[0090] Materials characterization

[0091] Powder X-ray diffraction (PXRD) spectra was collected on a STOE-STADI P powder diffractometer with Cu-Kal X-ray radiation ( / . = 0.154056 nm) in transmissiongeometry operating at the voltage of 40 kV and the current of 40 mA. X-ray photoelectron spectroscopy (XPS) spectra were obtained on a Thermo Scientific NEXSA G2 XPS spectrometer, equipped with an Al K alpha radiation source and electron flood-gun, at a pressure of 8x1smbar with a pass energy of 50 eV. All spectra were calibrated with the C Is peak at 284.8 eV. Aberration corrected scanning transmission electron microscopy (STEM) images and energy-dispersive X-ray spectroscopy (EDS) mappings were obtained using JEOL ARM200CF TEM equipped with dual SDD EDS detector. The scratched sample was thoroughly dispersed in isopropanol followed by drop-casting on the grid. In situ Raman was conducted with a Renishaw inVia Raman spectrometer employing an in-house in situ cell and a x50 water immersion lens. Cu nanoparticles and Hf-Cu catalyst on hydrophobic carbon paper was used as the cathode in electrolyte of 1.5 M K2CO3 solution, purged with CO2 from the backside. Pt wire and Ag / AgCl were used as the anode and reference electrodes respectively.

[0092] Results and Discussion

[0093] Initial research in the reactive capture system was conducted with Cu nanoparticle (Cu NP) catalysts as comparative catalysts, which produced ethylene with FE around 18.4%. However, the generation of organic acids, primarily formic acid, was also observed. The accumulation of these organic acids is detrimental to the regeneration of the alkaline solution used for CO2 capture and the kinetics of the capture of CO2. Therefore, designing catalysts that can more effectively convert in situ released CO2 in the reactive capture system into *CO intermediates, thereby suppressing formic acid formation and promoting the coupling reactions of Ci intermediates, is a primary focus of this Example 2.

[0094] This Example 2 examines the use of certain dilute alloy catalysts with dual active sites. Particularly, Cu dilute alloy catalysts doped with d-block metals are examined. D-block metals exhibit strong adsorption properties for CO2 and its intermediates, which is crucial for stabilizing these species during the catalytic process. This stabilization helps to lower the activation energy of the reaction and improves the overall reaction kinetics. Moreover, d- block metals possess variable oxidation states, allowing them to facilitate multiple electron transfer processes essential for CO2 reduction, making them ideal for improving the production of ethylene and addressing the challenges associated with formic acid formation in reactive capture systems.

[0095] A solvothermal-electrochemical reduction technique was used to synthesize a variety of d-block metal (M = Ru, Rh. Pd. Au, Ag, Hf) doped Cu dilute alloy catalysts. Using Hf-Cu as an example, Hf-doped CuO (Hf-CuO) was first synthesized via a solvothermal method and then subjected to annealing. Following this, the Hf-Cu dilute alloy catalyst was prepared via in situ electrochemical reduction. Powder X-ray diffraction (PXRD) measurements were carried out to investigate the structure evolution from the Hf-CuO material to Hf-Cu dilute alloy catalyst after the electrochemical reduction. Diffraction peaks at 43.1°, 50.2°, 73.8° corresponding to (111), (200), (220) facets of the crystalline Cu (JCPDS 04-0836) were observed, indicating the thorough reduction of Hf-CuO into metallic Hf-Cu catalyst (data not shown). X-ray photoelectron spectroscopy (XPS) further confirmed the copper states of the Hf-Cu catalysts after the carbonate reduction process. The XPS peak at a binding energy of 952 eV in the Cu 2p spectrum suggested the dominant state of Cu in HF- Cu was metallic state. Aberration-corrected HAADF-STEM images were collected to directly observe the structure of Hf-Cu at the atomic level, where bright dots associated with Hf atoms were distinguished in the Cu matrix (data not shown). No obvious Hf clusters or nanoparticles were observed, indicating uniformly dispersed isolated, single Hf atoms distributed throughout the Cu matrix. The diffraction pattern further indicated that the Hf- CuO was fully reduced to Hf-Cu.

[0096] Next, in situ Raman spectra of the Hf-Cu dilute alloy catalyst and the comparative Cu NP catalyst were obtained under a dilute CO2 concentration (CO2: Ar = 1:4). The bands observed in the 300-500 cm'1range were attributed to the frustrated rotation of *CO on Cu and Cu-CO stretching. Another set of bands in the 1900-2150 cm'1range corresponded to surface-bonded CO stretching. Notably, these CO-related peaks appeared at lower applied potentials on the Hf-Cu dilute alloy catalyst compared to the comparative Cu catalyst, indicating that CO production is more facile on Hf-Cu. This also suppresses formic acid production, as the mechanisms for CO and formic acid formation are competitive. Further analysis revealed that the bands in the 2000-2150 cm'1range could be deconvolved into three peaks, assigned to bridge CO, the low-frequency band (LFB) linear CO, and the high- frequency band (HFB) linear CO at approximately 2030 cm'1, 2060 cm'1and 2090 cm'1, respectively. As shown in FIGS. 8A-8B, notably, the ratios of LFB CO on the Hf-Cu dilute catalyst were higher than those on the comparative Cu catalyst, demonstrating that Hf-Cu promotes the formation of LFB CO adsorption, which is typically favorable for facilitating C- C coupling.

[0097] In a reactive capture system using K2CO3 solution to simulate the post-capture liquid, a series of d-block metal (M = Ru, Rh, Pd, Au. Ag, Hf) doped Cu dilute alloy catalysts were screened. Among these candidates, the Hf-Cu dilute alloy catalyst distinguished itself by exhibiting the lowest total FE for liquid products, with acetic acid production being negligible (FIG. 7B). Additionally, the Hf-Cu dilute alloy catalyst exhibited a better ethylene FE and a higher ethylene partial current density compared with the comparative Cu catalyst across the current density range of 100-500 mA cm’2(FIG. 7D). Notably, after the optimization of the Hf-Cu dilute alloy catalyst, those with 2 mol% Hf showed a peak ethylene FE of 37.5% at 400 mA cm’2and leading to FEC2H4 / FEOA around 44.6 (FIGS. 7C and 7D). In comparison, the comparative Cu catalyst exhibited an ethylene FE of 16.2% at 400 mA cm’2and the FECZH FEOA is about 3.8. In addition, the total amount of formic acid was only 29 ppm in 200 mL catholyte on the Hf-Cu dilute alloy catalyst, compared to 84 ppm in 200 mL catholyte on the comparative Cu catalyst after 5 hours. These results indicate that the implementation of the Hf-Cu dilute alloy catalyst promotes ethylene production and suppresses the production of formic acid, ensuring the longevity’ of the capture solution.

[0098] Conclusions

[0099] In this Example 2, a CO2 reactive capture sy stem was implemented that eliminates the separation and regeneration steps of CO2, integrating capture and reaction to address issues of high energy consumption and cost. The designed dilute alloy catalyst. Hf-Cu. demonstrated an FEC2H4 of 37.5%, while significantly reducing the formation of organic acids: FEC2H4 / FEOA was about 44.6 compared to 3.8 for the comparative Cu NP catalyst, thereby extending the lifespan of the capture solution and lowering costs. Through a series of characterizations and in situ Raman spectroscopy, it was elucidated that the Hf-Cu dilute alloy catalyst enhances carbon-carbon coupling and facilitates the rapid conversion of CO2 to CO over formic acid, thereby suppressing the formation of organic acids.

[0100] The word "illustrative" is used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as "illustrative" is not necessarily to be construed as preferred or advantageous over other aspects or designs. Further, for the purposes of this disclosure and unless otherwise specified, "a" or "an" means "one or more."

[0101] The foregoing description of illustrative embodiments of the invention has been presented for purposes of illustration and of description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations arepossible in light of the above teachings or may be acquired from practice of the invention. The embodiments were chosen and described in order to explain the principles of the invention and as practical applications of the invention to enable one skilled in the art to utilize the invention in various embodiments and with various modifications as suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.

[0102] If not already included, all numeric values of parameters in the present disclosure are proceeded by the term “about” which means approximately. This encompasses those variations inherent to the measurement of the relevant parameter as understood by those of ordinary skill in the art. This also encompasses the exact value of the disclosed numeric value and values that round to the disclosed numeric value.

[0103] If not already included, all numeric values of parameters in the present disclosure are proceeded by the term “about” which means approximately. This encompasses those variations inherent to the measurement of the relevant parameter as understood by those of ordinary skill in the art. This also encompasses the exact value of the disclosed numeric value and values that round to the disclosed numeric value.

[0104] Unless otherwise indicated, and in recognition of the inherent nature of the techniques described herein, throughout the present disclosure, terms and phrases such as “absence,” “free,” “does not comprise,” etc. encompass, but do not require a perfect absence of the referenced entity.

[0105] Unless otherwise indicated, the term “type” as used herein refers to chemical formula such that a single type means the same chemical formula and different t pe means different chemical formula. Similarly, use of “more” as in “one or more” refers to use of different types of the relevant entity.

[0106] Throughout the present disclosure, terms such as “comprising” and the like may be replaced with terms such as “consisting” and the like.

Claims

WHAT IS CLAIMED IS:1 . An electrolyzer comprising: a cathode comprising a dilute metal alloy catalyst comprising single atoms of a first metal Mi distributed within a metallic matrix composed of a second metal M2, the cathode in contact with a catholyte comprising carbonate ions; an anode in electrical communication with the cathode; and a membrane configured to generate in situ CO2 in the catholyte.

2. The electrolyzer of claim 1, wherein Mi is selected from p-block metals.

3. The electrolyzer of claim 2, wherein Mi is selected from Al, Ga, Sn, In, Bi, and combinations thereof.

4. The electrolyzer of claim 1, wherein Mi is selected from d-block metals.

5. The electrolyzer of claim 4, wherein Mi is selected from Ru, Rh, Pd, Au, Ag,Hf, and combinations thereof.

6. The electrolyzer of claim 1 , wherein M2 is selected from Cu, Ag, Au, and Zn.

7. The electrolyzer of claim 1, wherein the dilute metal alloy catalyst is a Bi-Cu dilute metal alloy catalyst or a Hf-Cu dilute metal alloy catalyst.

8. The electrolyzer of claim 1, wherein Mi is present at an amount of no more 5 mol%.

9. The electrolyzer of claim 1, wherein the dilute metal alloy catalyst is in the form of a plurality of nanoribbons which are entangled to form a nanoribbon network wherein nanoribbon surfaces of the nanoribbon network define a plurality of pores distributed throughout.

10. The electrolyzer of claim 1, wherein the dilute metal alloy catalyst is characterized by an amount of low-frequency band linear CO bound to surfaces of the dilute metal alloy catalyst that is at least 65% using a feedstock of 20% CO2 / 80% Ar and an applied potential versus Ag / AgCl of -1.6 V.

11. The electrolyzer of any of the preceding claims, the cathode further comprising an additional catalyst comprising a porous, carbon support composed of solid carbon having surfaces which define a plurality of pores distributed throughout the solid carbon, the porous, carbon support further comprising a metal phthalocyanine catalyst distributed on surfaces of the porous, carbon support.

12. The electrolyzer of claim 1 1, wherein the plurality of pores comprises mesopores and micropores.

13. The electrolyzer of claim 11, wherein the metal phthalocyanine catalyst is cobalt phthalocyanine.

14. The electrolyzer of claim 1, wherein the membrane is a bipolar membrane.

15. The electrolyzer of claim 1, wherein the catholyte comprises an aqueous alkali metal carbonate solution.

16. The electrolyzer of claim 1, wherein Mi is selected from Al. Ga, Sn, In, Bi, Ru. Rh, Pd, Au, Ag, Hf, and combinations thereof; M2 is Cu; and Mi is present at an amount of no more 5 mol%.

17. The electrolyzer of claim 16, wherein the dilute metal alloy catalyst is a Bi-Cu dilute metal alloy catalyst or a Hf-Cu dilute metal alloy catalyst.

18. The electrolyzer of claim 17, the cathode further comprising an additional catalyst comprising a porous, carbon support composed of solid carbon having surfaces which define a plurality of mesopores and micropores distributed throughout the solid carbon, the porous, carbon support further comprising a metal phthalocyanine catalyst distributed on surfaces of the porous, carbon support.

19. The electrolyzer of claim 18. wherein the metal phthalocyanine catalyst is cobalt phthalocyanine.

20. A method for producing ethylene, the method comprising generating the in situ CO2 in the catholyte of the electrolyzer of claim 1, reducing the in situ CO2 to CO at the cathode, and inducing carbon-carbon coupling reactions to produce ethylene from the CO.

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