Integrated system for electrosynthesis of co and related methods

Abstract

An integrated electrolysis system for electrochemically converting CO2 to CO is provided, the system comprising a pH downshifter comprising: an anode inlet configured to deliver a post-capture liquid comprising carbonate anions and having an alkaline pH to an anode of the pH downshifter; the anode configured to induce a hydrogen oxidation reaction that generates protons and converts the post-capture liquid to an anolyte comprising bicarbonate anions and having a reduced pH as compared to the alkaline pH of the postcapture liquid; a cathode in electrical communication with the anode, the cathode configured to induce a hydrogen evolution reaction that generates hydroxide anions; a cation exchange membrane between the anode and the cathode; and an anode outlet configured to deliver the anolyte to a bicarbonate electrolyzer.

Description

Atty. Dkt. No. 00100-0416-PCTINTEGRATED SYSTEM FOR ELECTROSYNTHESIS OF CO AND RELATED METHODSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to U.S. provisional patent application number 63 / 730,044 that was filed December 10, 2024, and to U.S. provisional patent application 63 / 752,165 that was filed January 31, 2025, the entire contents of both of which are incorporated herein by reference.REFERENCE TO GOVERNMENT RIGHTS

[0002] This invention was made with government support under N00014-22- 1-26-90 awarded by the Department of Defense. The government has certain rights in the invention.BACKGROUND

[0003] Direct air capture (DAC) followed by electrochemical conversion lowers the carbon intensity of fuels and chemicals. Typically, an alkaline solution captures CO2 as K2CO3, and concentrated CO2is released through energy-intensive drying and calcination steps at -900 °C, requiring 8-10 GJ / ton CO2. In carbon capture and upgrade (CCU) processes, producing carbon monoxide (CO) from captured CO2 adds 13-16 GJ / ton CO, considerably higher than the lower heating value (LHV) of -10 GJ / ton for CO.

[0004] Reactive capture integrates CO2 capture and upgrade into a single system. Electrochemically generated CO from captured CO2 (existing as carbonate or bicarbonate solutions), used in syngas processes, is considered the most energy-efficient and economically viable product. Syngas is a common raw material for producing hydrocarbons and oxygenates via processes like CO hydrogenation and Fischer-Tropsch synthesis.SUMMARY

[0005] Provided are integrated electrolysis systems which may be used to electrochemically convert CO2 (e.g.. from air) to CO. Methods of using the integrated electrolysis systems are also provided.

[0006] An embodiment 1 is an integrated electrolysis system for electrochemically converting CO2 to CO, the system comprising a pH downshifter comprising: an anode inlet configured to deliver a post-capture liquid comprising carbonate anions and having anAtty. Dkt. No. 00100-0416-PCT alkaline pH to an anode of the pH downshifter; the anode configured to induce a hydrogen oxidation reaction that generates protons and converts the post-capture liquid to an anolyte comprising bicarbonate anions and having a reduced pH as compared to the alkaline pH of the post-capture liquid; a cathode in electrical communication with the anode, the cathode configured to induce a hydrogen evolution reaction that generates hydroxide anions; a cation exchange membrane between the anode and the cathode; and an anode outlet configured to deliver the anolyte to a bicarbonate electrolyzer. The system further comprises the bicarbonate electrolyzer in fluid communication with the pH downshifter, the bicarbonate electrolyzer configured to generate Z-CO2 and to electrochemically reduce the Z-CO2 to CO.

[0007] An embodiment 2 is the system according to embodiment 1, wherein the alkaline pH is at least 12 and the reduced pH is not more than 10.

[0008] An embodiment 3 is the system according to embodiment 2, wherein the reduced pH is not more than 9.

[0009] An embodiment 4 is the system according to any of embodiments 1-3, wherein the bicarbonate electrolyzer comprises a cathode configured to electrochemically reduce the z- CO2 to CO; an anode in electrical communication with the cathode, the anode configured to induce an oxidation reaction that generates protons to combine with the bicarbonate anions to generate the Z-CO2; and membrane between the cathode and the anode.

[0010] An embodiment 5 is the system according to embodiment 4, wherein the oxidation reaction is another hydrogen oxidation reaction.

[0011] An embodiment 6 is the system according to embodiment 4, wherein the oxidation reaction is an oxygen evolution reaction carried out in an acidic anolyte.

[0012] An embodiment 7 is the system according to any of embodiments 4-6, wherein the cathode comprises a supported catalyst comprising a metal phthalocyanine covalently bound to a conductive support material via amide linkages.

[0013] An embodiment 8 is the system according to embodiment 7, wherein the metal phthalocyanine is functionalized with carboxylate groups and the conductive support matenal is functionalized with amine groups to provide the amide linkages.

[0014] An embodiment 9 is the system according to any of embodiments 7-8, wherein the metal phthalocyanine is cobalt phthalocyanine and the conductive support material is carbon nanotubes.Atty. Dkt. No. 00100-0416-PCT

[0015] An embodiment 10 is the system according to any of embodiments 1-3, wherein the bicarbonate electrolyzer comprises a cathode configured to electrochemically reduce the / -CO2 to CO; an anode in electrical communication with the cathode; and a bipolar membrane between the cathode and the anode, the bipolar membrane configured to induce a water dissociation reaction that generates protons to combine with the bicarbonate anions to generate the 7-CO2.

[0016] An embodiment 11 is the system according to embodiment 10, wherein the cathode comprises a supported catalyst comprising a metal phthalocyanine covalently bound to a conductive support material via amide linkages.

[0017] An embodiment 12 is the system according to embodiment 11, wherein the metal phthalocyanine is functionalized with carboxylate groups and the conductive support material is functionalized with amine groups to provide the amide linkages.

[0018] An embodiment 13 is the system according to any of embodiments 11-12, wherein the metal phthalocyanine is cobalt phthalocyanine and the conductive support material is carbon nanotubes.

[0019] An embodiment 14 is the system according to any of embodiments 1-13, further comprising (c) an air contactor in fluid communication with the pH downshifter, the air contactor configured to capture CO2 and provide the post-capture liquid.

[0020] An embodiment 15 is the system according to embodiment 14, wherein the pH downshifter further comprises a cathode outlet configured to deliver a catholyte from the pH downshi Iter to the air contactor.

[0021] An embodiment 16 is the system according to any of embodiments 14-15, wherein the bicarbonate electrolyzer further comprises a cathode outlet configured to deliver a catholyte from the bicarbonate electrolyzer to the cathode of the pH downshifter or to the air contactor.

[0022] An embodiment 17 is method of using the system according to any of embodiments 1-16 to electrochemically convert CO2 to CO, the method comprising delivering the post-capture liquid to the anode of the pH downshifter; generating a potential difference between the anode and cathode of the pH downshifter to induce the hydrogen oxidation reaction; delivering the anolyte from the pH downshifter to a cathode of the bicarbonate electrolyzer, the anolyte comprising the bicarbonate anions; generating Z-CO2 in aAtty. Dkt. No. 00100-0416-PCT catholyte of the bicarbonate electrolyzer from the bicarbonate anions; and reducing the Z-CO2 to CO at a cathode of the bicarbonate electrolyzer.

[0023] An embodiment 18 is the method according to embodiment 17, further comprising flowing air through an air contactor in fluid communication with the pH downshifter to capture CO2 and provide the post-capture liquid.

[0024] An embodiment 19 is the method according to any of embodiments 17-18, further comprising delivering the catholyte from the bicarbonate electrolyzer to the cathode of the pH downshifter or to the air contactor.

[0025] An embodiment 20 is the method according to any of embodiments 17-19, further comprising generating a potential difference between an anode and cathode of the bicarbonate electrolyzer to induce another hydrogen oxidation reaction at the anode of the bicarbonate electrolyzer that generates protons to combine with the bicarbonate anions to generate the Z-CO2.

[0026] 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

[0027] Illustrative embodiments of the disclosure will hereafter be described with reference to the accompanying drawings.

[0028] FIGS. 1A-1D. Schematic illustration of an integrated system according to an illustrative embodiment. FIG. 1 A shows a schematic illustration of an integrated system according to an illustrative embodiment that combines direct air capture in an air contactor, a pH adjustment loop in a pH downshifter, and a reactive capture loop in a bicarbonate electrolyzer for CO / syngas generation. The pH adjustment loop includes the hydrogen evolution (HER) and hydrogen oxidation (HOR) coupled reactions. The reactive capture loop includes a bicarbonate electrolysis reaction coupled with a hydrogen oxidation reaction. FIG. IB shows a cation exchange membrane (CEM)-based electrolyzer for bicarbonate electrolysis with an acidic oxygen evolution reaction (OER) at the anode. FIG. 1C shows a bipolar membrane (BPM)-based electrolyzer for bicarbonate electrolysis with alkaline OER at the anode. FIG. ID shows an alternative CEM-based electrolyzer for bicarbonate electrolysis with HOR at the anode, as is further described in Example 1.Atty. Dkt. No. 00100-0416-PCT

[0029] FIGS. 2A-2C. Electrochemical performance using an illustrative HER-HOR pH downshifter. FIG. 2A shows a schematic illustration of the illustrative integrated system including a pH downshifter configured to induce HER-HOR to reduce pH. FIG. 2B shows a schematic illustration of an illustrative slim flow cell set-up for the pH downshifter. The slim flow7channel at the anode side circulates the solution to downshift pH. FIG. 2C shows cell voltage (left y-axis) and anolyte pH (right y-axis) in the pH downshifter using post-capture liquid from the direct air capture (DAC) unit (which may be referred to as an air contactor) that contains 0.32 M KOH + 1.34 M K2CO3. The electrolysis was performed at 30 mA cm'2.

[0030] FIGS. 3A-3C. Electrochemical performance for bicarbonate reduction in various electrolyzers. FIG. 3A shows a comparison of Faradaic efficiency to CO in a BPM- OER electrolyzer and the illustrative CEM-HOR electrolyzer from 50-300 mA / cm2. FIG. 3B shows cell voltage (left y-axis) and energy efficiency to CO and syngas (right y-axis) from 50-300 mA / cm2for the illustrative CEM-HOR electrolyzer. FIG. 3C shows cell voltage (left y-axis) and Faradaic efficiency to CO (right y-axis) for 180 hours of electrolysis at 100 mA / cm2using a Phen@Ni-SAC catalyst with a commercial BPM.

[0031] FIGS. 4A-4B. Electronic structure of CoPc modulated via the addition of different functional groups. FIG. 4A shows another integrated system according to an illustrative embodiment comprising an air contactor, a pH downshifter based on internal hydrogen looping, and a bicarbonate electrolyzer. FIG. 4B shows calculated Bader charges of the Co sites in the CoPc catalysts, including unfunctionalized CoPc on unfunctionalized CNT (denoted Control), amino-CoPc on unfunctionalized CNT (denoted Amino-CoPc / CNT), unfunctionalized CoPc on CNT-NH2 (denoted Amine), carboxylate-CoPc on unfunctionalized CNT (denoted Carboxylate). CoPc-COOH on CNT-NH2 without amide linkages (denoted No-linkage) and CoPc-COOH on CNT-NH2 with amide linkages (denoted Amide). A higher value represents a greater degree of electron deficiency.

[0032] FIGS. 5A-5D. Bicarbonate electrolysis performance as a function of functional group selection on CoPc and CNTs. FIG. 5A shows cell voltage comparison of the different CoPc catalysts; a commercial BPM + Ni foam anode was employed. FIG. 5B shows CO FE performance comparison for the different CoPc catalysts. FIG. 5C shows CO / H2 FE of the Amide catalyst at different current densities. FIG. 5D shows CO FE and cell voltage for the Amide catalyst using a custom BPM and NiFeOx anode. FIG. 5E show s a stability7test during bicarbonate electrolysis over the course of continuous operation at 100Atty. Dkt. No. 00100-0416-PCT mA cm'2using the Amide catalyst. Experiments were conducted in N2-saturated 3 M KHCOs. An 85-pm-thick PTFE porous interposer layer was sandwiched between BPM and cathode.

[0033] FIGS. 6A-6G. Electronic tuning of functionalized CoPc / CNT samples. FIGS.6A-6B show cyclic voltammograms (CV) of the different CoPc catalysts, all in a 3 M KHCO3 solution saturated with Ar. The dotted lines indicate the CQH / CO1redox reaction in CoPc. FIG. 6C shows the potentials (at 10 mA cm'2) obtained from LSV of the different CoPc catalysts in a 3 M KHCO3 solution saturated with CO2 and N2. FIGS. 6D-6G show in- situ Raman spectra of Amide, Carboxylate, Amine, and Control catalysts in 3 M KHCO3. In- situ analysis was performed in a flow cell having three compartments. Materials were coated on hydrophobic carbon paper as the cathode, with a Pt wire serving as anode. All potentials are referenced to RHE.

[0034] FIGS. 7A-7D. System demonstration and energy assessment. FIG. 7A shows the change of cell voltage, pH. and carbonate / bicarbonate species ratio as a function of the duration of continuous operation of the pH downshifter operating at a current density of 25 mA cm'2. FIG. 7B shows the change of pH and carbonate / bicarbonate concentration as a function of the duration of continuous operation of the bicarbonate electrolyzer. FIG. 7C shows the dependence of FEco on the input solution composition, where each solution is saturated using N2. FIG. 7D shows a comparison among approaches to CO2 to CO upgrade from dilute sources.DETAILED DESCRIPTION

[0035] Integrated electrolysis systems are provided which may be used to electrochemically convert CO2 (e.g., from air) to CO. In an embodiment, such a system comprises a pH downshifter and a bicarbonate electrolyzer in fluid communication with one another. The system may further comprise an air contactor in fluid communication with one. or both, of the pH downshifter and the bicarbonate electrolyzer.

[0036] The pH downshifter comprises an anode, a cathode in electrical communication with the anode, and a cation exchange membrane between the anode and the cathode. The pH downshi Iter comprises an anode inlet which may be used to deliver a post-capture liquid comprising carbonate anions (CO?2') and having an alkaline pH to the anode. The alkaline pH of the post-capture liquid may be at least 12, at least 12.5. at least 13. at least 13.5, at least 14,Atty. Dkt. No. 00100-0416-PCT or a range between any of these values. The anode is configured to induce a hydrogen (H2) oxidation reaction (HOR) that generates protons and effectively converts the post-capture liquid to an anolyte comprising bicarbonate anions (HCO3 ) and having a reduced pH as compared to the alkaline pH of the post-capture liquid. That is, the anode serves to downshift (i.e., lower) the pH of the post-capture liquid. The reduced pH of the anolyte may be no more than 10, no more than 9.5, no more than 9, no more than 8.5, no more than 8, or a range between any of these values. The anode may comprise a catalyst capable of inducing the HOR, e.g., a supported transition metal catalyst such as PtRu / KB600. The cathode is configured to induce a hydrogen evolution reaction (HER) and may comprise a catalyst capable of inducing the HER, e.g., a supported transition metal catalyst such as Pt / C. Hydroxide anions produced from the HER increase the catholyte’s pH. including to any of the values described above for the post-capture liquid. The cation exchange membrane allows the passage of cations (e.g., alkali metal cations) originally present in the post-capture liquid and thus, the anolyte, into the catholyte. As further described below, the catholyte may be delivered to an air contactor via a cathode outlet also included in the pH downshifter.

[0037] The bicarbonate electrolyzer is configured to generate CO2 in situ (i.e., / -CO2) and to electrochemically reduce the 7-CO2 to products, e.g., CO. (See FIGS. 1 A-1C.) The bicarbonate electrolyzer comprises a cathode, an anode in electrical communication with the cathode, and a membrane between the anode and the cathode. The bicarbonate electrolyzer further comprises a cathode inlet which may be used to deliver the anolyte comprising the bicarbonate anions from the pH downshifter to the cathode side of the bicarbonate electrolyzer. There, the bicarbonate anions combine with protons to generate the / -CO2. The protons may be generated from a water dissociation reaction induced within the membrane of the bicarbonate electrolyzer (e.g., a bipolar membrane which may comprise a catalyst (e.g., TiCh) to induce water dissociation). (See FIG. 1C.) Alternatively, the protons may be passed through the membrane (e.g.. a cation exchange membrane) from an oxidation reaction occurring at the anode of the bicarbonate electrolyzer. (See FIGS. IB and I D.) With further reference to the cathode of the bicarbonate electrolyzer, it is configured to induce the electrochemical reduction of the Z-CO2, which may be facilitated by using an appropriate catalyst. Illustrative such catalysts will be further described below.

[0038] With further reference to the anode of the bicarbonate electrolyzer, various configurations may be used. In embodiments, the anode is configured similarly to the anode of the pH downshifter, i.e., configured to induce a HOR via an appropriate catalyst, e.g.,Atty. Dkt. No. 00100-0416-PCTPtRu / KB600. (See FIG. ID.) In such an embodiment, and as noted above, protons generated from the HOR may pass through a cation exchange membrane and combine with the bicarbonate anions to generate the / -CO2 on the cathode side of the bicarbonate electrolyzer. In other embodiments, the anode is configured to induce an oxygen evolution reaction (OER) which may be carried out under acidic conditions (i.e., using an acidic anolyte) (see FIG. IB) or under alkaline conditions (i.e., using an alkaline anolyte) (see FIG. 1C). Appropriate catalysts for inducing the OER under these conditions may be used, e.g., IrO2 for OER under acidic conditions; NiFeOx loaded Ni foam for OER under alkaline conditions.

[0039] Regarding catalysts which may be used in the cathode of the bicarbonate electrolyzer, in embodiments, a metal phthalocyanine catalyst is used, which may be denoted as MPc, wherein M is a transition metal. An illustrative metal phthalocyanine catalyst is cobalt phthalocyanine (CoPc). The catalyst may be a supported catalyst comprising a conductive support matenal such as nanostructured carbon and the catalytic species (e.g., CoPc) distributed on surfaces of the conductive material. Carbon nanotubes are a suitable type of nanostructured carbon. One, or both, of the catalytic species and the conductive support material may be functionalized to modify the electronic structure of the catalytic species and facilitate charge transfer. This can increase the number of catalytically active sites within the supported catalyst. For example, with reference to MPc (e.g., CoPc), such functionalization may be used to increase the relative number of catalytically active M(n'1)+Pc sites (e.g., Co^c sites) versus M(n)+Pc sites (e.g., ConPc sites) in the supported catalyst. Raman spectroscopy may be used to quantify the relative number of catalytically active sites. In embodiments, the functionalization may provide a ratio of M(n'1)+Pc:M(n)+Pc (e.g., CO^ CQHPC) that is at least 15, at least 20, at least 25, at least 30, or a range between any of these values. This ratio may be determined using Raman spectroscopy and may refer to a particular potential difference, e.g., -0.04 V vs. RHE, as described in Example 2, below. (See FIGS. 6D-6G.)

[0040] In embodiments, the functionalization provides a covalent linkage between the catalytic species and the conductive support material. In embodiments, the covalent linkage is an amide linkage (i.e., — NRC(O) — ), wherein one “ — ” denotes the covalent bond to the catalytic species and the other denotes the covalent bond to the conductive support material. The R group depends upon the functionalization as explained below. Amide linkages may be achieved by functionalizing one of the catalytic species with carboxylate groups and the other with amine groups. The term “carboxylate” encompasses both protonated / unprotonated formsAtty. Dkt. No. 00100-0416-PCT thereof, i.e., both — COOH and — COO". The term “amine’' refers to — NR2, wherein R is independently selected from hydrogen, alkyl, and aryl. In embodiments, both R groups are hydrogen. Thus, the R group in the amide linkage may be hydrogen, alkyl, aryl, but in embodiments, is hydrogen. After functionalization, formation of the amide linkages may be achieved via heating as described in Example 2, below. This Example also provides additional details regarding synthesis of supported CoPc catalysts that may be used in the cathode of the bicarbonate electrolyzer.

[0041] In embodiments, other catalysts may be used in the cathode of the bicarbonate electrolyzer such as metal atom catalysts (e.g., Ag) and single metal atom catalysts (e.g., Ni single atom catalysts). In these embodiments, the catalysts may further comprise a layer of nitrogen-doped carbon, e.g., 1,10-phenanthroline, thereon.

[0042] Bicarbonate reduction at the cathode of the bicarbonate electrolyzer produces products, e g., CO, which may be collected at a product outlet included in the bicarbonate electrolyzer. The CO may be combined with H2 (e.g., from a water electrolyzer also included in the integrated electrolysis system) to provide syngas. The catholyte of the bicarbonate electrolyzer may be delivered to the pH downshifter via a cathode outlet included in the bicarbonate electrolyte and a cathode inlet included in the pH downshifter.

[0043] The configurations of the pH downshifter and the bicarbonate electrolyzer described above enable further integration with an air contactor configured to capture CO2 as well as continuous operation in which various chemicals are recycled between system components. The air contactor may comprise an alkali hydroxide (e.g., KOH) solution through which a source of CO2 (e.g., air) flows under conditions to capture the CO2 as a carbonate (e.g., K2CO3) and provide the post-capture liquid described above. As also noted above, the air contactor and the pH downshifter may be in fluid communication with one another, e.g., via the anode inlet of the pH downshifter (for delivery of post-capture liquid to the pH downshifter), via the cathode outlet of the pH downshifter (for delivery of catholyte to the air contactor), or both. Similarly, the pH downshifter and the bicarbonate electrolyzer are in fluid communication with one another, e.g., via the anode outlet of the pH downshifter and the cathode inlet of the bicarbonate electrolyzer (for delivery of anolyte to the bicarbonate electrolyzer), via the cathode outlet of the bicarbonate electrolyzer and the cathode inlet of the pH downshifter (for delivery’ of catholyte to the pH downshifter), or both.Atty. Dkt. No. 00100-0416-PCT

[0044] Illustrative integrated electrolysis systems are shown in FIGS. 1A and 4A and are described in detail in the Examples, below. The integrated electrolysis system 100 of FIG. 1A comprises an air contactor, a pH downshifter, and a bicarbonate electrolyzer, each of which are labeled in the figure. In this embodiment, the membrane of the bicarbonate electrolyzer is a cation exchange membrane and its anode is configured to induce the HOR. The integrated electrolysis system 400 of FIG. 4A also comprises an air contactor, a pH downshifter, and a bicarbonate electrolyzer, each of which is labeled in the figure. In this embodiment, the membrane of the bicarbonate electrolyzer is a bipolar exchange membrane and its cathode comprises a supported catalyst comprising CoPc covalently bound to carbon nanotubes via amide linkages. Its anode is configured to induce OER under alkaline conditions. The integrated electrolysis system 400 also uses a different fluid communication scheme as compared to integrated electrolysis system 100 in that the catholyte of the bicarbonate electrolyzer is delivered to the air contactor versus the pH downshifter. An alternative fluid communication scheme between system components is shown in FIG. 2A showing another schematic of the integrated electrolysis system 100 (here, DAC refers to the air contactor and RC refers to the bicarbonate electrolyzer). FIG. 2B shows a schematic of the pH downshifter used in both the integrated electrolysis systems 100 and 400. Each of these figures demonstrate that the disclosed electrolyzers and systems may comprise additional components as desired, e.g., flow field plates, gas diffusion layers, flow channels, current collectors, other inlets / outlets, etc.

[0045] Methods for producing CO (with or without H2) are also provided. Such a method comprises delivering a post-capture liquid comprising carbonate anions and having an alkaline pH to an anode of a pH downshifter (any of the disclosed pH downshifters may be used); delivering an anolyte from the pH downshifter to a cathode of a bicarbonate electrolyzer (any of the disclosed bicarbonate electrolyzers may be used) in fluid communication with the pH downshifter, the anolyte comprising bicarbonate anions and having a reduced pH as compared to the alkaline pH of the post-capture liquid; generating i- CO2 in a catholyte of the bicarbonate electrolyzer from the bicarbonate anions; and reducing the Z-CO2 to CO at the cathode of the bicarbonate electrolyzer. The methods may further comprise generating the post-capture liquid in an air contactor in fluid communication with the pH downshifter. The methods may further comprise delivering a catholyte from the pH downshifter to the air contactor. In each of the embodiments in these methods, a potential difference is generated between respective cathodes and anodes in order to induce theAtty. Dkt. No. 00100-0416-PCT relevant reduction and oxidation reactions. The methods may be carried out using any of the disclosed pH downshifters, bicarbonate electrolyzers, and air contactors.

[0046] The present methods and sy stems may be characterized by various properties including Faradic efficiency (e.g., at least 65%, at least 68%, at least 70%, at least 72%, at least 75%, or a range of between any of these values) towards CO. These values may refer to specific operating conditions described in the Examples below.EXAMPLES

[0047] Example 1

[0048] Introduction

[0049] Both bipolar membrane (BPM) and cation exchange membrane (CEM)-based electrolyzers have been used for bicarbonate electrolysis. In a CEM-based electrolyzer, the anodic reaction is the oxygen evolution reaction (OER) in an acidic anolyte (FIG. IB). Protons, generated from the concentration gradient between the acidic anode and the alkaline cathode, along with migration driven by the electric field, combine with bicarbonate to produce i-COi. This i-COi is then reduced to CO on the cathode catalysts. The CEM-based electrolyzer cannot maintain steady-state operation without continuously adding acid and salt to the anolyte, as the initial pH gradient will be lost due to co-ion transport and neutralization. Additionally, the anode requires a noble metal catalyst, such as IrO2.

[0050] In a BPM-based bicarbonate electrolyzer, H+ions are produced from water dissociation (WD) within the BPM. The inclusion of both a cation exchange layer (CEL) and an anion exchange layer (AEL) in the BPM significantly reduces ion crossover, allowing for asymmetric electrolyte pH (FIG. 1C). The BPM-based bicarbonate system faces challenges such as high cell voltages, which can exceed 3.7 V at 100 mA / cm2due to the slow kinetics of WD in the BPM. Although WD catalysts have been introduced to enhance the rate of water dissociation, they have faced stability issues. Furthermore, using BPMs is more costly compared to using CEMs.

[0051] This Example describes an illustrative integrated system for DAC to syngas / CO (see FIG. 1A). To address the pH mismatch between DAC and bicarbonate electrolysis, a hydrogen evolution reaction (HER) / hydrogen oxidation reaction (HOR) loop was engineered that lowered the pH from approximately 13.5 to 8.9, achieving an average cell voltage of 0.57 V and a charge efficiency of 72%. The resulting bicarbonate-rich solution, now at theAtty. Dkt. No. 00100-0416-PCT appropriate pH, was then used to generate CO in a reactive capture loop. Further, a CEM- based electrolyzer was designed with HOR at the anode, which reliably and continuously supplied protons from the anode to the cathode for Z-CO2 generation. By further incorporating a Ni single-atom catalyst (Ni-S AC) with a thin layer of nitrogen-doped carbon, a high faradaic efficiency (FE) of 73% for CO was achieved and maintained for 180 hours. The integrated DAC-to-CO system, which included both the pH adjustment and reactive bicarbonate electrolysis, resulted in a lower energy consumption of 27.7 GJ / tonCO.

[0052] Results and Discussion

[0053] pH downshifter to convert a post-capture liquid to a bicarbonate-rich liquid

[0054] As illustrated in FIG. 1 A, the pH of a KOH-based air contactor may exceed 13.7, while a KHCOs-fed electrolyzer operates at a pH of 9-10. It is crucial that the pH of the KHCOs-fed electrolyzer not become too high, as this can lead to a significant drop in CO FE. For example, using Ag catalysts, the CO FE in a 3 M KHCOs-fed electrolyzer (pH —8.5) was > 60%, but dropped sharply to < 20% in a 1.5 M K2COs-fed electrolyzer (pH -12.5).Therefore, to maintain high CO FE during electrolysis, the inlet and outlet pH of the KHCOs- fed electrolyzer must be carefully controlled to prevent it from rising too high.

[0055] To address the compatibility issue between a DAC unit and a reactive capture electrolyzer, a pH downshifter was developed to balance the pH levels between the capture and conversion stages (FIGS. 2A-2B). As show n in FIG. 2B, the HER and HOR coupled reactions were performed in a slim flow cell in which Pt / C on hydrophilic carbon paper was utilized for the cathode and PtRu / KB600 on hydrophobic carbon paper was utilized for the anode. A CEM (Nafion 212 membrane) was used for K+transport across the membrane to carry the charge.

[0056] The post-capture liquid from the air contactor, composed of 0.32 M KOH and 1 .34 M K2CO3, was introduced into the anode compartment of the pH downshifter. The anolyte pH was monitored at various time intervals. After the optimization of flow rates and flow channel thicknesses, an average cell voltage of 0.67 V was achieved over 20 hours of electrolysis at 30 mA / cm2(FIG. 2C). The average charge efficiency — representing the charge used for pH downshifting rather than CO2 release — w as 72%. After 20 hours, the final measured pH was 8.8, corresponding to a carbonate:bicarbonate ratio of 0.04:2.91.

[0057] The pH downshifter was compared with a bipolar membrane electrodialysis (BPMED) system. In the BPMED system, Fe(CN)e3' and Fe(CN)e4' redox couples wereAtty. Dkt. No. 00100-0416-PCT employed for the anode and cathode reactions to minimize overpotentials. The BPMED system featured two flow chambers for pH modulation. It included three membranes: two CEM for K+transport and one BPM positioned in between. The BPM facilitated water dissociation into H+and OH , resulting in a pH reduction in the anode chamber and a pH increase in the cathode chamber.

[0058] The BPMED system gave a cell voltage of 1.2 V at a current density of 25 mA / cm2, which was significantly higher than that of the pH downshifter based on the coupled HER-HOR reactions. The higher voltage of the BPMED system was primarily attributed to the slower water dissociation process, which typically requires around 0.8 V, and the increased resistance of the cell was due to the two flow chambers. By contrast, the pH dow shifter makes use of a single How chamber.

[0059] CEM-HOR based bicarbonate electrolyzer for CO generation

[0060] As illustrated in FIGS. 1 A and ID, a bicarbonate reactive capture loop using a CEM for CO generation was then developed. Electrolysis was conducted in a zero-gap membrane electrode assembly (MEA) configuration. The cathode of the bicarbonate electrolyzer employed a Ni-SAC catalyst, synthesized according to Kim. J. H. et al. Energy & Environmental Science 15, 4301-4312 (2022). For the HOR at the anode, PtRu / KB600 was utilized as the catalyst. With a continuous supply of H2, a minimized cell voltage of 1.0 V was achieved at a current density of 100 mA / cm2(FIG. 3B). The CO FE was maintained above 65% across current densities of 100-300 mA / cm2, with a peak CO FE of 70% at 300 mA / cm2(FIG. 3A). An energy efficiency (EE) of 30% and 51% was achieved for CO and syngas production, respectively (FIG. 3B). This projected syngas EE was an estimate based on using an efficient water electrolyzer (EE = 65%) to provide the “missing” H2 to form 2:1 H2:CO syngas. The H2 in the CEM-HOR bicarbonate electrolyzer was also supplied from the efficient water electrolyzer.

[0061] For comparison, the same Ni-SAC catalyst was also tested in a BPM-based electrolyzer for bicarbonate electrolysis. Similar CO FE values were observed in both systems, with a slight increase in CO FE at 100-300 mA / cm2in the present CEM-based electrolyzer as compared to the BPM-based electrolyzer. This could be because the H+transport through the HOR and CEM was more efficient than water dissociation in the BPM system. As such, more H+could couple with bicarbonate to release a higher amount of / -CO2 in the CEM-based electrolyzer. More importantly, the cell voltage of 1.0 V in the presentAtty. Dkt. No. 00100-0416-PCTCEM-based electrolyzer was much lower than that of 4.0 V in the BPM-based electrolyzer at 100 mA / cm2

[0062] Largely enhanced stability in the present CEM-HOR based bicarbonate electrolyzer for CO generation

[0063] Existing reactive bicarbonate and carbonate capture systems have demonstrated limited stability, generally under 25 hours. The instability anses from two main factors: the inherent instability of the systems themselves and the instability of the catalysts used. For instance, in systems using commercial BPMs, the primary issue is the instability of the cathode catalysts. In CEM systems with acidic anolytes at the anode, stability is compromised by both the system and the cathode catalysts.

[0064] By contrast, the CEM-HOR-based electrolyzer was more stable due to real-time H+generation from the HOR, driven solely by the electric field through H+crossover across the CEM. Since the Ni-SAC catalyst exhibited a notable drop in CO FE after a certain period, use of a thin layer of nitrogen-doped carbon on the catalyst was evaluated. Specifically, the Ni-SAC catalyst was coated with 1,10-phenanthroline (Phen) as the nitrogen source. As shown in FIG. 3C, this modification significantly improved the stability of the Ni-SAC catalyst, extending its operational time to over 180 hours while maintaining a CO FE of > 60%.

[0065] Energy consumption calculations

[0066] Energy consumption calculations were performed for a sequential capture-and- release process followed by gas-fed electrochemical CO2 upgrade and the integrated process described in this Example, with any H2 supplemented from a water electrolyzer. The present integrated system including the air contactor, the pH downshifter, and the bicarbonate electrolyzer gave a projected energy expense of 27.7 GJ / ton of CO. This included 0.48, 5.1, and 22.1 GJ / ton for the air contactor, pH downshifter, and the bicarbonate electrolyzer, respectively (Table 1, last column). The major advantage was the elimination of the CO2 regeneration and circulation steps in sequential DAC-plus-electrolysis. In terms of syngas production, the present integrated system had an energy expense of 46 GJ / ton of syngas (Table 2), which was also much higher than the sequential processes of DAC-to-syngas.

[0067] Table 1. Comparison of energy and carbon intensity for sequential vs. integrated processes for CO production.Atty. Dkt. No. 00100-0416-PCTa CCh-to-CO conversions were 80% in gas CO2 reduction electrolyzers. 99% of CO2 from the air was converted into CO in the carbonate electrolyzers. b In the home-made BPM system, the bicarbonate reduction cell voltage was 2.7 V at 100 mA / cm2. In the commercial BPM system, the cell voltage was 3.8 V at 100 mA / cm2. c H2 was supplied from a water electrolyzer with energy' efficiency of 65%.

[0068] Table 2. Comparison of energy' and carbon intensity for sequential vs. integrated processes for syngas production.Atty. Dkt. No. 00100-0416-PCTa CCh-to-CO conversions were 80% in gas CO2 reduction electrolyzers. 99% of CO2 from the air was converted into CO in the carbonate electrolyzers. h In the home-made BPM system, the bicarbonate reduction cell voltage was 2.7 V at 100 mA / cm2. In the commercial BPM system, the cell voltage was 3.8 V at 100 mA / cm2.CH2: CO = 2: 1If FEco < 33%, additional CO was supplied from DAC-SOEC process. When the SOEC was assumed, the EE to CO was set to 60%. The analysis assumed (as in column 1. DAC+SOEC), the need for CO2 regeneration, circulation, and an air contactor. The resultant effective EE for CO was 25% in this case of “CO-infill,” the same as for the CO contributed in column 1.If FEco > 33%, additional H2 was supplied from water electrolyzer having EE for H2 of 65%. d H2was supplied from a water electrolyzer with energy efficiency of 65%.

[0069] Example 2

[0070] Introduction

[0071] This Example describes the development of a fully electrified, integrated system comprising an air contactor, a pH downshifter that downshifts the pH of the post-capture liquid from the air contractor to that of bicarbonate, and a bicarbonate electrolyzer that generates z-CO2and electrochemically reduces the Z-CO2 to CO. The illustrative integrated system is schematically shown in FIG. 4A. In this system, the cathode of the bicarbonateAtty. Dkt. No. 00100-0416-PCT electrolyzer employs a cobalt phthalocyanine (CoPc) catalyst comprising an electrondeficient cobalt (Co) center capable of activating CO2 at a lower applied reducing voltage. The catalyst was grafted to a conductive support by reacting carboxylate groups on functionalized cobalt phthalocyanine (CoPc) with amine groups on functionalized carbon nanotubes to form amide linkages, which facilitate efficient charge transfer through the Co center. As noted above, an electrified pH downshifter was added to promote CO2 availability in the processed post-capture liquid, leading to higher CO selectivity in the ensuing reactive capture phase. Bicarbonate electrolysis at 2.7 V at 100 mA cm'2with CO selectivity of 70% was achieved. The illustrative integrated system provided an atmospheric-CCh-to- concentrated-CO-stream energy intensity' of 35 GJ / tonCO, a figure inclusive of the pH- downshifter electricity and of the projected downstream CO / H2 gas separation.

[0072] Experimental methods

[0073] Electrode preparation

[0074] All reagents used in this Example were purchased from suppliers without further purification. Cobalt(II) 2, 3 -naphthal ocyanine was purchased from Millipore sigma and Cobalt(II) 2,9,16,23-tetra(carboxy)phthalocyanine was purchased from April Scientific. The functionalized carbon nanotubes (CNTs), including carboxylate-CNT and amino-CNT were purchased from XFNANO. Nafion D520CS was ordered from Ion Power.

[0075] To form the catalysts, 200 mg of the CNTs were dispersed in 100 mL of dimethylformamide (DMF) using sonication. Then, an appropriate amount of cobalt(II) phthalocyanine (CoPc) dissolved in 20 mL of DMF was added into the solution drop by drop, and the solution was stirred under 110 °C for 12 h under a reflux condenser. Afterwards, the sample was filtered and washed with DMF several times to remove unreacted precursors. Then the samples were freeze-dried and used for further experiments. This preparation procedure was applied to form 6 catalyst samples: Amide, Carboxylate, Control, Amine, and Amino-CoPc / CNT. A 7thno-linkage sample was prepared using the same methods as the Amide catalyst, but no heat was used. The composition of these catalyst samples are described in detail below.

[0076] Catalyst inks were prepared by dispersing each catalyst sample in methanol with added Nafion ionomer by ultrasonication. The ink was well-sonicated for a good dispersion of catalyst. The mass ratio of the catalyst and ionomer was 1: 1. The ink was then airbrushedAtty. Dkt. No. 00100-0416-PCT onto a hydrophilic carbon substrate (Freudenberg H23, Fuel cell store) to a final loading of ~1.5 mg cm2.

[0077] NiFeOx electrodes were prepared as follows. First, Ni foam was washed with 6 M HC1 and Dl-water for 15 min under sonication. Then, a 40 mL solution with 4 mmol NFUF, 10 mmol urea, 2 mmol Ni(NO3)2-6H2O, and 2 mmol Fe(NO3)3 9H2O was prepared and transferred to a 50 mL Teflon-lined stainless steel autoclave. The hydrothermal growth of the hydroxides on Ni foam was performed at 120 °C for 6 hours with a heating rate of 3 °C min followed by sonication in Dl-water and drying in the oven at 80 °C.

[0078] Electrochemical measurements

[0079] A cathode was cut into a 1.5 cm x 1.5 cm piece and placed onto the MEA cathode plate with a flow window with a dimension of 1 cm * 1 cm. A porous interposer layer (2 cm x 2 cm 85 pm-thick PTFE) was carefully placed onto the cathode. When using a custom BPM, a Ti Ch-coaled Nafion membrane was placed onto the porous interposer layer with the TiCh layer facing up, then covered by a Piperion (2 cm x 2 cm) membrane. A NiFeOx loaded Ni foam was placed onto the Piperion membrane as the anode. Two stainless steel flow-field plates with serpentine channels were used to sandwich the electrodes. The catholyte and anolyte were circulated by peristaltic pumps (INTLLAB) at 15 ml min '. The applied current was controlled by an Autolab potentiostat / galvanostat. The membrane used to separate catholyte and anolyte was either a commercial (Fumasep FBM, Fuel Cell Store) or the custom-designed BPM. The pore size of the hydrophilic interposer layer was controlled at 0.1, 1, 5 and 10 pm for PTFE membrane, 10, 20 and 41 pm for Nylon membrane, and 10 pm for PPE membrane. The catholyte was 3 M KHCOs, and the anolyte was 1 M KOH. All experiments were performed at room temperature.

[0080] CV was conducted by a general three electrode configuration from -0.2 to 1.0 V (vs. RHE) at a scan rate of 500 mV s1in N2-saturated 3.0 M KHCO3 electrolyte to observe the redox behavior of cobalt sites. The catalyst loading amount was 0. 1 mg cm'2

[0081] Materials characterization

[0082] X-ray photoelectron spectroscopy (XPS) w as carried out on a Thermo Scientific NEXSA G2 XPS spectrometer, equipped with an Al K alpha radiation source and electron flood-gun, at a pressure of 8 x 10smbar 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 conducted by JEOL JSM-7900FLV SEM at anAtty. Dkt. No. 00100-0416-PCT 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. Aberration corrected scanning transmission electron microscopy (STEM) images and energy-dispersive X-ray spectroscopy (EDS) mappings were taken from aken using JEOL ARM200CF TEM equipped with a dual SDD EDS detector. For transmission electron microscopy (TEM), the sample was dispersed in ethanol followed by drop-casting on the grid. Founer-transform infrared (FTIR) measurements were carried out using a Nicolet iS50 FTIR spectrometer equipped with a Harrick Scientific Praying Mantis DRIFTS accessory.

[0083] In-situ Raman analysis was conducted with a Renishaw inVia Raman spectrometer using an in-house in situ cell and a *50 water immersion lens. Materials were coated on hydrophobic carbon paper as the cathode in electrolytes of 3 M KHCO3 and purged with CO2 from the backside. In-situ analysis was performed in a flow cell having three compartments, with a Pt wire serving as the anode. All potentials were referenced to Ag / AgCl.

[0084] Results and Discussion

[0085] Functionalized molecular catalysts

[0086] The functionalization of CoPc with electron-donating groups (amine groups) on unfunctionalized CNTs (denoted Amino-CoPc / CNT) and electron-withdrawing groups (carboxylate groups) on unfunctionalized CNTs (denoted Carboxylate) was studied in order to evaluate the modulation of the electronic state of the cobalt center.

[0087] DFT was used to provide an initial assessment of the impact of functional groups on the Co center of CoPc. As shown in FIG. 4B, the Bader charge on the Co sites showed that carboxylate groups induced electron depletion on the Co center, whereas amine groups induced electron-rich conditions.

[0088] Bicarbonate electrolysis performance was screened in a two-electrode membrane electrode assembly (MEA) electrolyzer using a commercial BPM with an 85-pm-thick PTFE porous interposer layer sandwiched between BPM and the cathode. As show n in FIG. 5A, it was observed that the Carboxylate catalyst (2) lowered overpotential while the Amino- CoPc / CNT catalyst (4) had little effect on overpotential. As shown in FIG. 5B, neither functionalization enhanced CO selectivity compared to the Control catalyst (3) composed of unfunctionalized CoPc and unfunctionalized CNT. That is, catalysts (2), (3), and (4) showed similar FEco 46-51 % at 100 mA cm'2.Atty. Dkt. No. 00100-0416-PCT

[0089] It was hypothesized that CO selectivity might be improved by facilitating charge transfer between the CNT support and the Co center of CoPc. Specifically, inclusion of a covalent bond, such as an amide linkage, between functional groups on the CNT support and functional groups on CoPc was examined.

[0090] Thus, additional catalysts were prepared by grafting carboxylate-modified CoPc onto amino-modified CNT substrates. The carboxylate groups could anchor to amine groups via 7t-7t interactions and a covalent bond could be formed between the groups after heating. High-resolution transmission electron microscopy and associated energy-dispersive X-ray spectroscopy were used to confirm the loading of carboxylate CoPC onto aminofunctionalized CNTs (data not shown). Formation of amide bonds was evidenced using X-ray Photoelectron Spectroscopy (data not shown). The resulting catalysts were denoted Amide while comparative catalysts prepared the same way but without heating were denoted Nolinkage.

[0091] As shown in FIG. 5 A, the Amide catalysts (1) showed a similarly low overpotential as compared to that of the Carboxylate catalysts (2). However, as shown in FIG. 5B, the Amide catalysts (1) simultaneously showed an increased FEco of -70% at 100 mA cm'2. This FE was maintained at 150 mA cm'2and remained above 60% up to 300 mA cm'2. By contrast, FIG. 5B shows that the No-linkage catalyst had an FEco < 40%. Finally, another comparative catalyst composed of unfunctionalized CoPc and amino-functionalized CNT (denoted Amine (5)) was also evaluated. Additional results for the Amide catalyst are shown in FIG. 5C. The results highlight the critical role of amide bonding in improving FEco.

[0092] Mechanistic studies

[0093] Next, cyclic voltammograms (CVs) were obtained. CoPc was compared with / without functional groups, and it was found that in an Ar-saturated electrolyte, all samples showed a reversible redox couple between 0.048 V and 0.266 V, assigned to the CoH / Co1redox. Co11needs to transform to Co1to be active for CO2 reduction. As shown in FIG. 6A, among all the catalysts, the Carboxylate catalyst show ed a positive shift of its CoII / CoIredox peaks compared to the Control catalyst, implying that the -COOH groups on the Pc ligand withdrew' electron density away from the cobalt center. In contrast, the CoII / CoIredox peaks of the Amino-CoPc / CNT catalyst showed a negative shift compared to the Control catalyst as well as compared to the Carboxylate catalyst. This result was consistent with their similar cell voltage trend (see FIG. 5A), and with the hypothesis that the electron-Atty. Dkt. No. 00100-0416-PCT withdrawing functionality is linked to the overpotential reduction in these materials. As shown in FIG. 6C (and other data not shown). CO2RR activities were compared through linear sweep voltammetry (LSV) potentials under CO2 vs. N2 atmosphere. These agreed well with the cell voltage trend shown in FIG. 5A: in CO2, the Amide catalyst displayed a lower potential at 10 mA cm'2. In the N2 atmosphere, the Amide catalyst showed a higher HER potential compared with that in CO2 atmosphere, indicating faster CO2 reduction kinetics compared to those for HER. In contrast, the Carboxylate catalyst showed similar potentials in CO2 and N2 atmospheres. These results were consistent with the observed higher FEco of the Amide catalyst as shown in FIG. 5B.

[0094] Operando Raman spectroscopy was used (FIGS. 6D-6G) to probe the transformation from Co11(Raman shift: 754 cm'1) to Co1(Raman shift: 747 cm'1). For the Amide. Carboxylate, and Amine catalysts, Co11started to transform to Co1at 0. 16 V vs. RHE; but only at -0.04 V vs. RHE for the Control catalyst. At 0. 16 V vs. RHE, a higher Co1:CoI1~3.2 was observed for the Amide catalyst, while the value was 2.2 for the Carboxylate catalyst and 0.5 for the Amine catalyst. At -0.04 V vs. RHE, the transformation of Co11to Co1was more complete in the Amide catalyst than the other catalysts, as evidenced from the higher CoLConratio of 30 compared to the Carboxylate catalyst (3. 1) and the Amine catalyst (11.6). At a more negative potential of -0.24 V vs. RHE, Co1was the dominant species with no observable Co11in all samples. The Raman indicated that the trend in the Co11to Co1transformation w as as follows (in order of increasing difficulty): Amide (most facile) < Carboxylate < Amine < Control (most difficult).

[0095] These results agreed with cyclic voltammogram studies (FIGS 6A and 6B) that also indicated that the Amide catalyst enabled the Co center to be more easily reduced to Co1confirming that an electron-deficient nature contributed to CO2 reduction at a lowered overpotential.

[0096] System demonstration

[0097] To build a full cell, a NiFeOx electrode and a BPM using TiCh as the w ater dissociation catalyst w ere employed to pursue a lower Vceii, and 2.7 V was achieved at 100 mA cm'2(FIG. 5D). The contribution of each electrolyzer component on the cell voltage w as evaluated (data not shown). The interposer layer was also optimized to maximize CO FE (data not shown).Atty. Dkt. No. 00100-0416-PCT

[0098] As shown in FIG. 4A, in the full cell, a pH downshifter (FIG. 4A) was added at the front end to adjust the pH of post-capture liquid (—12) to that of bicarbonate (~9). The lower pH promoted Z-CO2 availability but consumed more electricity. Therefore, the electricity consumption of each step w as evaluated with various pH downshifter effluent pHs.

[0099] As described in Example 1 , an electrochemical hydrogen loop was used in the pH downshifter: the anode oxidized hydrogen and generated protons, partially acidifying the solution flowing in the slim flow' chamber; potassium migrated through the cation exchange membrane to the cathode, combining with the OH’ generated from the hydrogen evolution reaction occurring there. Thus, the pH downshifter outputted KOH solution ready for reuse as the DAC sorbent in the air contactor upstream. Hydrogen produced from the cathode was fed to the anode for continuous operation.

[0100] The pH downshifter was fed using a simulated post-capture liquid consisting of 1.5 M K2CO3 solution, and the anolyte pH (and thus carbonate:bicarbonate relative composition) as well as the cell voltage were monitored (FIG. 7A). The device converted 93% of the carbonate to bicarbonate at the final pH ~9, while consuming 3.8 GJ / tonCCh (hence ~6 GJ / tonCO) of electricity (other data not show n). In parallel, KOH was regenerated in the catholyte, approaching the stoichiometry of generated bicarbonate.

[0101] Continuous bicarbonate electrolysis was performed using the pH ~9 post-pH- downshifted solution as the feedstock. The change of pH and the corresponding bicarbonate concentrations are shown vs. elapsed time in FIG. 7B. From these, it was concluded that dissolved inorganic carbon was converted to CO, while carbonate was delivered at the liquid phase outlet of the system. This post-electrolysis solution w as again input into the pH downshifter to get back to pH ~9, and CO production was again demonstrated (other data not shown).

[0102] Looking at the full process, it was found that, since bicarbonate electrolysis dominated overall energy consumption, and since bicarbonate electrolysis was much more efficient than carbonate electrolysis, it made sense to shift all the way to bicarbonate pH 8.8. (See FIG. 7C.) In this case, the electrolysis energy was 25 GJ / tonCO, and the total, inclusive of pH downshift, w as 35 GJ / tonCO. As shown in FIG. 7D, when comparing to the alternatives - such as thermal release (calcium looping) - to produce concentrated gas-phase CO2, followed by either gas-phase CO2 coelectrolysis vs. reverse water gas shift (RWGS), theAtty. Dkt. No. 00100-0416-PCT present experimental data closely approaches that of the most-efficient contender, the DAC+RWGS system.

[0103] Conclusions

[0104] In this Example, a pH downshift strategy was applied to enable high CO production performance from atmospheric CO2 via reactive capture. Bicarbonate reduction efficiency was improved at a lowered overpotential by jointly tuning the properties of the CoPc catalyst and support by COOH-functionalizing the CoPc and anchoring it to a -NH2 modified CNT support. A post-capture liquid (pH~12) was converted to KHCO3 (pH~9) in an electrified pH downshifter, and then reactive capture w as performed with -70% FEco at 2.7 full cell voltage at 100 mA cm'2. The bicarbonate electrolysis subsystem showed stability for 30 hours under continuous operation at 100 mA cm'2.The durability of this bicarbonate electrolyzer was studied by observing its continuous operation at a current density of 100 mA cm'2. As shown in FIG. 5E, it was found that 70% CO FE w as maintained over 30 hours.

[0105] Additional information regarding these Examples, including data indicated as not being shown may be found in U.S. provisional patent application number 63 / 730,044 and U.S. provisional patent application 63 / 752,165 that was filed January 31. 2025, the entire contents of both of w hich are incorporated herein by reference.

[0106] 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.”

[0107] The foregoing description of illustrative embodiments of the disclosure has been presented for purposes of illustration and of description. It is not intended to be exhaustive or to limit the disclosure to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the disclosure. The embodiments were chosen and described in order to explain the principles of the disclosure and as practical applications of the disclosure to enable one skilled in the art to utilize the disclosure in various embodiments and with various modifications as suited to the particular use contemplated. It is intended that the scope of the disclosure be defined by the claims appended hereto and their equivalents.

[0108] If not already included, all numeric values of parameters in the present disclosure are proceeded by the term “about” which means approximately. This encompasses thoseAtty. Dkt. No. 00100-0416-PCT 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.

[0109] 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.

[0110] Unless otherw ise indicated, the term “type” as used herein refers to chemical formula such that a single type means the same chemical formula and different type means different chemical formula. Similarly, use of “more” as in “one or more types” refers to use of different types of the relevant entity'.

[0111] Unless otherwise indicated, throughout the present disclosure, terms such as “comprising” and the like may be replaced with terms such as “consisting” and the like.

Claims

Atty. Dkt. No. 00100-0416-PCTWHAT IS CLAIMED IS:1 . An integrated electrolysis system for electrochemically converting CO2 to CO, the system comprising:(a) a pH downshifter comprising: an anode inlet configured to deliver a post-capture liquid comprising carbonate anions and having an alkaline pH to an anode of the pH downshifter, the anode configured to induce a hydrogen oxidation reaction that generates protons and converts the post-capture liquid to an anolyte comprising bicarbonate anions and having a reduced pH as compared to the alkaline pH of the post-capture liquid, a cathode in electrical communication with the anode, the cathode configured to induce a hydrogen evolution reaction that generates hydroxide anions, and a cation exchange membrane between the anode and the cathode, and an anode outlet configured to deliver the anolyte to a bicarbonate electrolyzer; and(b) the bicarbonate electrolyzer in fluid communication with the pH downshifter, the bicarbonate electrolyzer configured to generate Z-CO2 and to electrochemically reduce the / -CO2 to CO.

2. The system of claim 1, wherein the alkaline pH is at least 12 and the reduced pH is not more than 10.

3. The system of claim 2, wherein the reduced pH is not more than 9.

4. The system of claim 1, wherein the bicarbonate electrolyzer comprises a cathode configured to electrochemically reduce the Z-CO2 to CO; an anode in electrical communication with the cathode, the anode configured to induce an oxidation reaction that generates protons to combine with the bicarbonate anions to generate the Z-CO2; and membrane between the cathode and the anode.

5. The system of claim 4, wherein the oxidation reaction is another hydrogen oxidation reaction.

6. The system of claim 4, wherein the oxidation reaction is an oxygen evolution reaction carried out in an acidic anolyte.Atty. Dkt. No. 00100-0416-PCT7. The system of claim 4, wherein the cathode comprises a supported catalyst comprising a metal phthalocyanine covalently bound to a conductive support material via amide linkages.

8. The system of claim 7, wherein the metal phthalocyanine is functionalized with carboxylate groups and the conductive support material is functionalized with amine groups to provide the amide linkages.

9. The system of claim 7, wherein the metal phthalocyanine is cobalt phthalocyanine and the conductive support material is carbon nanotubes.

10. The system of claim 1, wherein the bicarbonate electrolyzer comprises a cathode configured to electrochemically reduce the z-CCh to CO; an anode in electrical communication with the cathode; and a bipolar membrane between the cathode and the anode, the bipolar membrane configured to induce a water dissociation reaction that generates protons to combine with the bicarbonate anions to generate the 1-CO2.

11. The system of claim 10, wherein the cathode comprises a supported catalyst comprising a metal phthalocyanine covalently bound to a conductive support material via amide linkages.

12. The system of claim 11, wherein the metal phthalocyanine is functionalized with carboxylate groups and the conductive support material is functionalized with amine groups to provide the amide linkages.

13. The system of claim 11, wherein the metal phthalocyanine is cobalt phthalocyanine and the conductive support material is carbon nanotubes.

14. The system of claim 1, further comprising (c) an air contactor in fluid communication with the pH downshifter, the air contactor configured to capture CO2 and provide the post-capture liquid.

15. The system of claim 14, wherein the pH dow nshifter further comprises a cathode outlet configured to deliver a catholyte from the pH downshifter to the air contactor.Atty. Dkt. No. 00100-0416-PCT16. The system of claim 15, wherein the bicarbonate electrolyzer further comprises a cathode outlet configured to deliver a catholyte from the bicarbonate electrolyzer to the cathode of the pH downshifter or to the air contactor.

17. A method of using the system of claim 1 to electrochemically convert CO2 to CO, the method comprising delivering the post-capture liquid to the anode of the pH downshifter; generating a potential difference between the anode and cathode of the pH downshifter to induce the hydrogen oxidation reaction; delivering the anolyte from the pH downshifter to a cathode of the bicarbonate electrolyzer, the anolyte comprising the bicarbonate anions; generating Z-CO2 in a catholyte of the bicarbonate electrolyzer from the bicarbonate anions; and reducing the Z-CO2 to CO at a cathode of the bicarbonate electrolyzer.

18. The method of claim 17, further comprising flow ing air through an air contactor in fluid communication with the pH downshifter to capture CO2 and provide the post-capture liquid.

19. The method of claim 18, further comprising delivering the catholyte from the bicarbonate electrolyzer to the cathode of the pH downshifter or to the air contactor.

20. The method of claim 17, further comprising generating a potential difference betw een an anode and cathode of the bicarbonate electrolyzer to induce another hydrogen oxidation reaction at the anode of the bicarbonate electrolyzer that generates protons to combine with the bicarbonate anions to generate the Z-CO2.

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