Small molecule-based electrodes for producing green methane and town gas from carbon dioxide at high rates

Abstract

The invention provides an electrolytic cell based on a small molecule catalyst membrane electrode assembly. The electrolytic cell is used for large-scale production of green methane from carbon dioxide and water. A method of manufacture includes depositing a first layer of small molecules with carbon black and ionomers on a gas diffusion layer to form a molecular electrode for CO2 conversion. The molecular electrode is used to manufacture a membrane electrode assembly (MEA) having an electrolyte membrane and an anode. The MEA is capable of converting CO2 into CH4 as well as urban fuel gas for direct use. The present invention provides a 3, 5-diamino-1, 2, 4-triazole (DAT)-based membrane electrode assembly for CO2 to CH4 with a Faraday efficiency of (52 + / -4)% and a conversion frequency of 11530 h <-1 > at 250 mA * cm <-2 >. Due to the spatially distributed active sites and the appropriate energy level of the molecular orbital, the DAT electrode continues through * COOH-* C (OH) 2-* COH to produce CH4 from CO2.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to U.S. Provisional Application Serial No. 63 / 587,837, filed October 4, 2023, the entire contents of which are incorporated herein by reference. Background Technology

[0003] Electrochemical CO2 reduction reactions (CO2RR) for value-added fuels and feedstocks typically rely on metal-based catalysts. While molecular catalysts are more tunable than metal catalysts, they still cannot catalyze CO2 to hydrocarbons for long-term operation at industrially relevant current densities, and the catalytic mechanism remains unclear.

[0004] Renewable energy-driven electrochemical CO2 reduction reaction (CO2RR) is a promising approach to convert CO2 into value-added fuels and chemicals, particularly hydrocarbons and oxygen-containing compounds with high energy densities, such as CH4, C2H4, and C2H5OH. 1-3 Developing highly selective CO2RR catalysts is crucial for reducing separation costs and improving energy efficiency. 4 Furthermore, for practical applications, CO2RR electrolyzers are required to operate at high current densities (> 200 mA cm⁻¹). -2 It exhibits considerable durability under these conditions. 5,6 .

[0005] Hori and his colleagues’ pioneering work revealed Cu’s ability to convert CO2 into ethylene and methane. 7 Furthermore, subsequent work identified up to sixteen products on Cu foil. 8,9 The fundamental reason for this phenomenon is the abundance of various binding sites with suitable adsorption energies on the Cu surface, leading to the adsorption of multiple intermediates in CO2RR. The overall reaction selectivity is determined by the relative stability of intermediates in different reaction pathways on the Cu surface. 10,11 Selectivity can be partially modulated by tailoring binding sites to specific reaction pathways, such as creating active sites with weak Cu-carbon binding to modulate selectivity for ethanol rather than ethylene. 12 Unfortunately, under electrochemical conditions, the surface of transition metals is highly dynamic, and the precise configuration of active sites is often unknown, thus altering the reaction pathway for the formation of the target product. 13,14 .

[0006] Homogeneous catalysts with well-defined structures and tunable local coordination at the molecular level offer opportunities for tailoring specific reaction pathways. Nevertheless, most reported molecular catalysts, particularly small-molecule catalysts, primarily focus on CO / formate as the final product at low current densities. 15-17 Products involving more than two electron transfers, such as CH4 or C2H4, are rarely observed. The formation of these products on heterogeneous catalysts requires a reaction between two surface-adsorbed intermediates, and such interactions between molecular catalytic intermediates in solution are challenging. 18,19 Immobilizing molecular catalysts on high-surface-area electrodes increases the surface concentration of active sites for further reduction of species. 20 Although the production of methanol, ethanol, and acetate was observed on polyaniline- or polypyrrole-based catalysts, their activity (< 10 mA cm⁻¹) was significantly lower than that of heterogeneous catalysts. -2 The stability (< 3 hours) is not satisfactory. 17,21,22 At high current densities, molecular catalysts are unstable for long-term operation. 20,23 Therefore, understanding and designing molecular electrodes for the stable conversion of CO2 into products other than CO / formate remains a formidable challenge. Summary of the Invention

[0007] Embodiments of the present invention provide an electrolyzer based on a small-molecule catalyst membrane electrode assembly for the scalable production of green methane from carbon dioxide and water. According to one embodiment, a manufacturing method includes depositing a first layer of small molecules, carbon black, and ionomers onto a gas diffusion layer to form a molecular electrode for CO2 conversion. The molecular electrode is used to manufacture a membrane electrode assembly (MEA) having an electrolyte membrane and an anode. The MEA is capable of converting CO2 into CH4 and town fuel gas for direct use.

[0008] Examples provide a triazole molecularly catalyzed CO2RR system based on a membrane electrode assembly (MEA) for selective electro-methanation, e.g., electrolysis for 10 hours at a total current of 10 A. A comprehensive mechanistic study using density functional theory (DFT) calculations revealed that the high CO2RR activity of 3,5-diamino-1,2,4-triazole (DAT) is associated with a good match between the energy levels of the leading-edge orbitals of CO2 and the energy levels of the least occupied molecular orbitals. The key intermediate *COH in CO2 to CH4 conversion is formed via an unconventional pathway of *C(OH)2 for sequential protonation to produce the final product CH4. Examples utilize DAT modified on a gas diffusion electrode to achieve CO2 to CH4 activity, where at 250 mA cm⁻¹…-2 At this point, the Faradaic efficiency (FE) is (52 ± 4)%, and the turn-over frequency (TOF) of the methane conversion is... CH4 ) is 11530 h -1 .

[0009] Examples of electrochemical methods combining renewable energy-derived electricity provide lower carbon emissions than conventional methods for town gas generation, demonstrating their key role in promoting carbon neutrality and mitigating climate issues. In some embodiments, the molecular electrode is metal-free, significantly reducing costs compared to commonly used noble metal-based catalysts. Advantages include the absence of undesirable impurities in the generated town gas compared to gases produced by conventional methods, and its immediate usability. According to embodiments of the invention, a test system operated at a total current of 10 A for 10 hours has demonstrated a CH4 production rate of 23.0 mmol / h. -1 . Attached Figure Description

[0010] Figure 1A-1C Catalyst screening for CO2RR according to embodiments of the present invention is shown. 1A, Molecular structures of 1,2,4-triazole derivatives 1-18. 1B, Calculated energy levels and *H adsorption energies of the highest occupied molecular orbitals (HOMOs) on the molecular catalysts (MC). The *H adsorption energies are averaged considering different -NH groups on the molecule as deprotonation sites. 1C, In-situ Raman spectra of a gas diffusion electrode (GDE) modified with MC-15 (3,5-diamino-1,2,4-triazole, DAT) in 0.1 M KHCO3 solution. All experiments were conducted with CO2 in the feed, except for the gray line (top, air).

[0011] Figures 2A-2D The CO2 reduction reaction (CO2RR) performance on a molecular catalyst according to embodiments of the present invention is demonstrated. 2A, the molecular catalyst is deposited on a gas diffusion electrode for CO2RR. 2B, at 250 mA cm⁻¹ -2 The Faradaic efficiency (FE) of CH4 on a series of triazole molecular catalysts at a current density of 2C. TAZ, ATA, and DAT are abbreviations for 1,2,4-triazole, 3-amino-1,2,4-triazole, and 3,5-diamino-1,2,4-triazole, respectively. The main product from CO2RR is 2C at 50 mA cm⁻¹. -2up to 350 mA cm -2 FE at different current densities. Energy efficiency (EE) on 2D, DAT. CH4 ) and CH4 at 50 mA cm -2 Up to 350 mA cm -2 Partial current densities (j) under different current densities CH4 The values ​​are averages, and the error bars indicate the SD (n = 3 repeated trials).

[0012] Figures 3A-3D This study presents mechanistic insights into the CO2-to-CH4 conversion on a DAT according to embodiments of the present invention. 3A, obtained by in-situ differential electrochemical mass spectrometry at 250 mA cm⁻¹. -2 The generation rates of CH4 and H2 of gases fed in a "CO2-CO-CO2" sequence at a current density. 3B, Since formaldehyde cannot be fed into the MEA electrolyzer, in a flow cell with 0.1 M KHCO3, at 50 mA cm⁻¹ -2 The production rates of CH4 and H2 during CO2RR with and without formaldehyde (HCHO) at current densities. 3C, the free energy distribution of CO2RR with respect to CH4 at the amine site of the DAT molecular catalyst at -1 V relative to the reversible hydrogen electrode (RHE). 3D, the proposed CO2RR pathway on the DAT molecular catalyst.

[0013] Figures 4A-4E A large-scale molecular catalytic platform for electrochemical electro-gas conversion according to an embodiment of the present invention is shown. 4A, from left to right, represents an MEA electrolyzer at 4 cm⁻¹. 2 20 cm 2 and 81 cm 2 The following is a photograph. 4B, at different CO2 flow rates, with a total current of 10 A, at 81 cm⁻¹ 2 The Faraday efficiency (FE) and single-pass carbon efficiency (SPCE) of CO2 to CH4 conversion on the DAT electrode. c, at different CO2 flow rates and a total current of 10 A, 81 cm⁻¹ 2 Concentration of gaseous products on the DAT electrode. 4D, with an effective area of ​​4 cm². 2 20 cm 2 and 81 cm 2 The rate of CO2 to CH4 generation during stability testing on a DAT electrode. 4E, with an effective area of ​​4 cm². 2 20 cm2 and 81 cm 2 The total amount and energy of CH4 produced during the continuous electro-gas conversion process at the DAT electrode. The energy of CO2 to CH4 conversion is obtained by multiplying the amount of CH4 produced (mol) by the lower heating value of CH4 (802.23 kJ mol). -1 ).

[0014] Figure 5 The calculated energy levels of the highest occupied molecular orbital (HOMO) and *H adsorption energy on the studied molecular catalyst (MC) after deprotonation, according to embodiments of the present invention, are presented. Both the HOMO energy level and the *H adsorption energy are averaged considering different -NH atoms on the molecule as deprotonation sites.

[0015] Figure 6 The calculated CO2 adsorption energy and HOMO level on the studied molecular catalyst (MC) according to embodiments of the present invention are shown. The CO2 adsorption energy is an average value considering different -NH groups on the molecule as adsorption sites.

[0016] Figure 7 The calculated Bader charge of a DAT molecule according to an embodiment of the present invention is shown. Based on electron density information calculated using VASP software, the data is obtained using the work of Hekelman et al. 24 The proposed Bader charge method calculates the Bader charge of atoms.

[0017] Figure 8 In-situ Raman spectra of a DAT-coated gas diffusion electrode (GDE) according to an embodiment of the present invention during cathodic polarization in a 0.1 M KHCO3 solution are shown. Except for the gray lines, all experiments were conducted with CO2 in the feed. 669 cm⁻¹ -1 1035 cm -1 and 1136 cm -1 The nearby peaks are related to the "breathing" and vibration of the DAT ring skeleton. 25,26 858cm -1 The peaks nearby are due to symmetrical CNC stretching on the DAT ring. 25,26 .

[0018] Figures 9A-9B XRF spectra of commercially available DAT powder (9A) and a DAT-coated electrode (9B) according to embodiments of the present invention are shown. The peaks at energies from 18 keV to 22 keV are due to the Rh target. This was achieved by spraying an ink containing the following onto an area of ​​4 cm². 2The following were used to prepare DAT-coated electrodes on carbon paper (Toray TGP-H-060, Fuel Cell Store): 0.1 mmol DAT molecules (≥ 98%, Aladdin), 0.8 mL 2-propanol (HPLC, RCI Labscan), 0.4 mL deionized water (18.25 MΩ cm), and 0.3 µL perfluorosulfonic acid ionomer (PFSA, Aquivion). ® D79-25BS) and 4.7 mg of commercial carbon nanoparticles (Vulcan XC 72R, Fuel Cell Store).

[0019] Figure 10 This demonstrates an embodiment of the invention at 250 mA cm⁻¹ -2 The gaseous product distribution of CO2RR at different electrodes in the MEA at the given current density is shown in Table 5. The composition of the cathode catalysts for experiments A, B, C, and D is shown in Table 5. The values ​​are averages, and the error bars indicate the SD (n = at least 2 replicates).

[0020] Figure 11A-11C The calibration curves of CH4 (11A), CO (11B), and H2 (11C) obtained by DEMS from signals with m / z = 15, 28, and 2, respectively, according to embodiments of the present invention are shown.

[0021] Figure 12 This demonstrates the results obtained according to differential electrochemical mass spectrometry (DEMS) at 250 mA cm⁻¹ according to embodiments of the present invention. -2 At current density 13 FE of gaseous products on DAT molecular catalyst during CO2 electrolysis.

[0022] Figure 13 This demonstrates an embodiment of the invention at 50 mA cm⁻¹ -2 Up to 350 mA cm -2 The full cell voltage of a MEA containing a DAT electrode under varying total current density.

[0023] Figure 14 This demonstrates an embodiment of the invention at 50 mV s -1 Cyclic voltammetry (CV) was performed at scan rates with and without 10 mM MDAT in 0.1 M KHCO3 aqueous solution.

[0024] Figure 15 Differential pulse voltammetry (DPV) was demonstrated for standard DAT aqueous solutions at concentrations of 8.3 µM, 16.4 µM, 24.4 µM, 40.0 µM, 69.8 µM, 97.7 µM, and 148.9 µM. According to an embodiment of the invention, 0.1 M KHCO3 was used as the supporting electrolyte.

[0025] Figure 16 A calibration curve of DAT concentration obtained by DPV according to an embodiment of the present invention is shown.

[0026] Figure 17 The DPV of a DAT sample collected from both the electrode and the anion exchange membrane after 1 hour of CO2 electrolysis in an MEA is shown. According to an embodiment of the invention, 0.1 M KHCO3 is used as the supporting electrolyte.

[0027] Figure 18 This demonstrates an embodiment of the invention at 50 mA cm⁻¹ -2 The production rates of CH4 and H2 during CO2RR on a DAT molecular catalyst in a flow cell at a current density (without the addition of HCHO). The timescale is the same as that of CO2RR experiments with HCHO.

[0028] Figure 19 The UV-vis spectra of DAT aqueous solutions according to embodiments of the present invention are shown in the cases of addition of HCHO, CO2 purging, and no treatment.

[0029] Figure 20Nuclear magnetic resonance (NMR) spectra of samples according to embodiments of the present invention are shown (performed using a Bruker AVANCE III HD 500): DAT+HCHO: 0.5 mL of aqueous formaldehyde solution added to 9 mL of DMSO containing 10 mM DAT; HCHO: 0.5 mL of aqueous formaldehyde solution added to 9 mL of DMSO; and DAT: 0.45 mL of H2O and 0.05 mL of methanol (to simulate the solvent of commercially available formaldehyde solution) added to 9 mL of DMSO containing 10 mM DAT. Each sample was packed in an NMR tube at a 9:1 ratio with DMSO-D6 (99.9%, Cambridge Isotope Laboratories, Inc.) as the deuterated solvent. The peaks at chemical shifts of 5 (doublet) and 10.5 (singlet) ppm in the DAT sample correspond to the hydrogen atoms of -NH2 and -NH- on the DAT molecule, respectively. The absence of DAT characteristic peaks in the DAT+HCHO sample indicates that HCHO alters the molecular structure of DAT.

[0030] Figures 21A-21C This demonstrates an embodiment of the invention at 4 cm. 2 (21A), 20 cm 2 (21B) and 81 cm 2 (21C) Cell voltage and total current during continuous CO2 electrolysis on DAT electrode under the condition of effective area.

[0031] Figures 22A-22C This demonstrates an embodiment of the invention at 4 cm. 2 (22A), 20 cm 2 (22B) and 81 cm 2 Faraday efficiency of gaseous products during continuous CO2 electrolysis on a DAT electrode under the condition of effective area (22C). Detailed Implementation

[0032] The examples considered screening molecular catalysts for efficient CO2 RR. CO2 to curved *CO2 δ- The first activation step of the structure is crucial for subsequent catalytic processes. Considering the electrophilic nature of carbon in the CO2 molecule, although not bound by theory, the inventors hypothesized that 1,2,4-triazole derivatives with abundant N sites could effectively facilitate activation. The inventors first screened 1,2,4-triazole derivatives ( Figure 1A The ability of 1-18 in the text to activate CO2. These derivatives are triazoles with different functional groups to modulate the leading energy levels of molecular orbitals. 27CO2 is activated by electron transfer from the highest occupied molecular orbital (HOMO) of the molecular catalyst (MC) to the lowest unoccupied molecular orbital (LUMO) of CO2. When the MC is deprotonated, the HOMO energy tends to increase in order to better align with the LUMO energy of the CO2 molecule for activation. Figure 5 Of all the molecules studied, entry-15 (DAT) with an appropriate HOMO energy level favored CO2 activation. Figure 1B and Figure 6 Because the amine group (-NH2) of the DAT molecule has a high electron density, it is conducive to nucleophilic attack on CO2. Therefore, CO2 activation is most likely to occur on the amine group (-NH2) of the DAT molecule. Figure 7 Experimentally, the inventors have observed the activation of CO2 through the -NH2 site using in-situ Raman spectroscopy. Figure 1C Under CO2 saturated conditions, CO2 only appeared on the DAT electrode. δ- (approximately 1410 cm) -1 ) and -NH-CO- (approximately 1304 cm -1 (Related peaks) 25 These peaks are due to the strong interaction between CO2 and the amine groups on DAT, which are at 600 cm⁻¹ -1 Up to 1200 cm -1 It has characteristic peaks ( Figure 8 ).

[0033] The examples demonstrated beneficial electrochemical CO2 reduction performance. Encouraged by these observations, the inventors fabricated molecular electrodes with highly active sites by spraying a mixture of small molecules and carbon nanoparticles onto carbon paper. Figure 2A (See Methods for details), the small molecules include 1,2,4-triazole (TAZ), 3-amino-1,2,4-triazole (ATA), and 3,5-diamino-1,2,4-triazole (DAT). At 250 mA cm⁻¹ -2 At a constant current density, CH4 is the main CO2RR product for both ATA and DAT (Table 1). From TAZ to DAT, FE was observed. CH4 The increase is consistent with the increase in the number of amine groups, and is consistent with previous calculations for active sites. Figure 2B DAT showed the highest FE. CH4 (52 ± 4)%, this is a record for molecular catalysts for electro-methanation, and it is comparable to the highest FE of state-of-the-art heterogeneous catalysts. CH4 Comparable (Tables 2 and 3). Only a small amount of CH4 (FE) is generated on the bare electrode.CH4 = (1 ± 0.4)%. Trace amounts of metallic impurities (3.5 nmol / cm³) were detected on the DAT electrode. -2 Copper, 5.0 nmolcm -2 Iron and 7.0 nmol cm -2 Zinc), these metallic impurities are introduced from spray gun corrosion during electrode manufacturing. Comparative experiments with varying amounts of metallic impurities show that FE CH4 The low percentage (below 10%) demonstrates that DAT molecules are responsible for the high selectivity and activity of CO2RR (Method 1 and Method 2). Figure 9A-10 The inventor also conducted... 13 CO2 isotope labeling experiments to confirm 13 The generation of CH4 eliminates potential contamination from the substrate (Method 2 and Figure 11A-12 ).

[0034] Focusing on DAT, the inventors studied the product distribution of CO2RR at different current densities. FE was observed on DAT. CH4 The volcanic shape distribution is at 250 mA cm⁻¹. -2 The peak value was reached at (52 ± 4)%. Figure 2C ), corresponding partial current density (j CH4 The value was (129 ± 11) mA cm. -2 And an energy efficiency of (13.0 ± 1.6)% ( Figure 2D and Figure 13 To investigate the intrinsic activity of DAT during CO2RR, differential pulse voltammetry (DPV) was used at 250 mA cm⁻¹, treating the two amine groups as active sites. -2 The density of DAT active sites was measured to be 0.046 µmol / cm² after CO2 electrolysis. -2 (Method 3 and) Figure 14-17 Based on the active site density, the CO2 to CH4 conversion frequency (TOF) on the DAT molecular catalyst is 11530 h⁻¹. -1 This is nearly two orders of magnitude higher than the conversion frequency reported on Cu NP (Table 7), indicating that the intrinsic activity of CO2 to CH4 conversion on DAT is high.

[0035] The focus now shifts to exploring the mechanistic implications of the CO2 to CH4 conversion pathway. It has been reported that the CO2 to CH4 conversion pathway on heterogeneous catalysts proceeds via key intermediates *CHO or *COH generated from the protonation of *CO. 3,29To explore whether intermediates *CHO or *COH are suitable for DAT electrodes, the inventors used gases introduced in a "CO2-CO-CO2" sequence to study the formation of CH4 by in-situ differential electrochemical mass spectrometry (DEMS). Figure 3A After switching the feed gas from CO2 to CO, the CH4 production rate decreased by 40% (from 0.12 µmol / s in CO2RR). -1 cm -2 Decreased to 0.071 µmol s in CORR -1 cm -2 Upon switching back to CO2, the decrease in activity was irreversible, indicating that the *CO pathway may be detrimental on the DAT electrode. The inventors then increased the *CHO content by introducing HCHO into the electrolyte. 1,30 A nearly 50% decrease in CH4 production rate was observed; upon addition of HCHO, the CH4 production rate decreased from 14 nmol / s. -1 cm -2 Reduced to 6.5 nmol s -1 cm -2 ( Figure 3B and Figure 18 This observation is not surprising, because DAT can react with HCHO to form a stable conjugated structure and prevent further reactions, which is consistent with... 1 H NMR spectroscopy, UV-Vis spectroscopy (method 4 and Figures 19-20 ) and related technical documents 31-33 Consistent.

[0036] Therefore, the above results encourage the inventors to reconsider reaction processes beyond the commonly accepted *CO pathway on conventional catalysts. The inventors used DFT calculations to obtain the energy distributions of different reaction pathways for CO2 electrolysis on DAT (…). Figure 3C Unlike heterogeneous catalysts, the formation of *COH, in addition to *CHO, is advantageous on molecular catalysts. Following the first proton-coupled electron transfer process of CO2 to *COOH, the unexpected intermediate *C(OH)2 is formed. The energy change for *COOH to *C(OH)2 (0.54 eV) is lower than that for *COOH to *CO (0.62 eV). Figure 3C This may be because carbon in the *C(OH)2 pathway tends to maintain its covalently saturated state rather than dehydrate on the molecular catalyst to form unsaturated *CO. Therefore, the *COOH-*C(OH)2-*COH pathway is energy-favorable, thus skipping the *CO intermediate. The resulting *COH with unsaturated carbon bonds becomes the active species for subsequent steps. The spatially dispersed active sites of the molecular catalyst inhibit C…2+ The reaction pathway, because surface CC coupling typically requires a distance of less than 2.1 Å. 34 On the other hand, the interaction with the molecular catalyst enables the intermediate to undergo subsequent protonation, thus exhibiting high selectivity for CH4. Figure 3D ).

[0037] Some embodiments provide for the scaling up of molecular electrodes for electrochemical fuel conversion. The advantages of DAT electrodes, including high conversion frequencies and low capital costs, warrant exploring scaling opportunities. Molecular electrodes for MEAs range from 4 cm⁻¹ 2 Gradually increased to 81cm 2 The CO2 flow rate ranged from 45 sccm to 218 sccm. Figure 4A At a total current of 10 A, the DAT electrode (81 cm) 2 ) obtained 54% FE CH4 Furthermore, the single-pass carbon efficiency (SPCE) for CH4 is close to 10%. Figure 4B It is worth mentioning that by adjusting the CO2 flow rate to 108 sccm, the molecular membrane electrode assembly can produce gaseous products of CH4, CO, and H2 at concentrations of 27%, 15%, and 53%, respectively, which is precisely the composition of commercial town gas. Figure 4C The generated town gas can be used directly without further processing, thereby reducing the capital costs of removing sulfur or nitrogen-containing components in traditional industrial processes. 35-37 The large-scale CO2RR system using molecular catalysts can operate stably for more than 10 hours, with an average CH4 production rate of 23.0 mmol / h. -1 ( Figure 4D and Figures 21A-22C The production rate is approximately ten times that of previously reported CO2RR electrolyzers (Table 8). At a total energy of 184 kJ, approximately 5.6 L of methane was produced. Figure 4E These results demonstrate the enormous potential of combining molecular catalysts with electrochemical electro-gas conversion devices for commercial applications.

[0038] The inventors have investigated molecular catalysts according to embodiments of the present invention for selective and scalable electro-methanation from CO2. At a total current of 10 A, the 3,5-diamino-1,2,4-triazole (DAT) molecular catalyst exhibits a high Faradaic efficiency exceeding 50% for CH4. The conversion frequency reaches up to 11530 h⁻¹. -1This implies that its inherent high activity and the leading molecular orbitals of DAT are related to the correct alignment with CO2. The amine groups in DAT may be the active sites for nucleophilic attack to activate CO2. Unlike heterogeneous catalysts, CO2 reduction on DAT was found to occur via the "*COOH-*COH-*C(OH)2" pathway. The spatially dispersed active sites and flexible structure of the molecular electrode enable rapid and stable CO2 to CH4 conversion. These findings broaden our understanding of the mechanism and provide valuable directions for the design of catalysts for CO2 hydrogenation.

[0039] Materials and Methods

[0040] Materials including 1,2,4-triazole (99%), 3-amino-1,2,4-triazole (96%), 3,5-diamino-1,2,4-triazole (≥98%), and potassium bicarbonate (KHCO3, ACS, 99.7-100.5%) were purchased from Aladdin Company (Shanghai Aladdin Biochemical Technology Co., Ltd., Shanghai, China) and used as is. Carbon nanoparticles (Vulcan XC 72R) and perfluorosulfonic acid ionomers (PFSA, Aquivion) ​​were also used. ® D79-25BS and carbon paper (Toray TGP-H-060) were purchased from Fuel Cell Store (Bryan, Texas, USA). 2-Propanol (HPLC) was purchased from RCI Labscan (Bangkok, Thailand). Anion exchange membrane (Sustainion X37-50 RT) was purchased from Dioxide Materials (Boca Raton, Florida, USA). Iridium chloride (IrCl3·xH2O, 99.8%) was purchased from Alfa Aesar (Ward Hill, Massachusetts, USA). Titanium mesh (100 mesh, 99.96%) was purchased from Hebei Yichang Metal Wire Mesh Co., Ltd. (Shijiazhuang, Hebei Province, China). Aqueous solutions were prepared using deionized water with a resistivity of 18.25 MΩ cm.

[0041] Regarding electrode fabrication, unless otherwise specified, all molecularly coated electrodes comprised a carbon paper-based GDL substrate onto which an ink solution containing triazole molecules was sprayed. A solution containing 0.1 mmol triazole molecules, 0.8 mL 2-propanol, 0.4 mL deionized water, 0.3 µL perfluorosulfonic acid ionomer, and 4.7 mg commercially available carbon nanoparticles was used in an effective area of ​​4 cm². 2The coating was applied to carbon paper. Large-scale DAT-coated electrodes were prepared using the same method and ink formulation, but with proportionally increased ink volume and carbon paper substrate area. Bare electrodes without coating were prepared using the same spraying method, except that the ink solution did not contain triazole molecules. IrO2-coated Ti-based (e.g., mesh) anodes for catalyzing the oxygen evolution reaction in MEA electrolyzers were prepared using a previously reported dip-coating method. 38 .

[0042] For characterization, in-situ Raman spectroscopy was performed using a 785 nm diode laser and a Renishaw inVia Raman microscope (Renishaw PLC, Wotton-under-Edge, Gloucestershire, UK) in a modified flow cell with a water immersion objective. CO2 flowed through the gas chamber at a rate of 50 sccm. An Ag / AgCl (3 M KCl) electrode and nickel foam were used as the reference and counter electrodes, respectively. The working and counter electrodes were separated by an anion exchange membrane with an effective area of ​​1 cm². 2 The working electrode was a DAT-coated Ag-PTFE electrode, which was prepared by spraying 0.06 mmol DAT and 0.2 µL perfluorosulfonic acid ionomer onto 100 nm Ag-PTFE GDE (Beijing Zhongxingweiye Instrument Co., Ltd., Beijing) evaporated by an electron beam (EB-600, Innovative Vacuum Solution Co., Ltd., Hsinchu, Taiwan, China).

[0043] Regarding electrochemical measurements, to investigate the electrochemical CO2RR performance, a chronopotentiometric method powered by an electrochemical workstation (ZENNIUMpro, Zahner-Elektrik GmbH & Co. KG, Kronach - Gundelsdorf, Bavaria, Germany) was used in a membrane electrode assembly (MEA) electrolyzer (5 cm⁻¹). 2Electrolysis was performed at Dioxide Materials, Boca Raton, Florida, USA. The MEA comprised a cathode electrode (molecularly coated carbon fiber paper), an anode electrode (IrO2-coated Ti substrate (e.g., mesh)), and an anion exchange membrane (Sustainion X37-50 RT, Dioxide Materials, Boca Raton, Florida, USA), which was pre-activated in 1 M KOH for at least 48 hours. Pure CO2 gas (99.99%, Air Products (Hong Kong) Co. Limited, Hong Kong SAR, China) was humidified in deionized water at 40°C and discharged at a rate of 45 mL / min, controlled by a mass flow controller (Beijing Sevenstar Flow Co., LTD., Beijing, China). -1 The deionized water anolyte containing 0.1 M KHCO3 is continuously supplied to the cathode flow field at a flow rate of 8 mL / min. -1 The flow rate circulates through the anode flow field. For large-scale CO2RR on the DAT electrode, electrolysis is performed at 25 cm⁻¹. 2 (Dioxide Materials, Boca Raton, Florida, USA), 20 cm 2 Effective area of ​​the electrode) and 100 cm 2 Suzhou Sinero Technology Co., Ltd. (Suzhou, Jiangsu, China), 81 cm 2 The effective area of ​​the electrode) was measured in a MEA electrolytic cell and powered by a potentiostat (PP222, Zahner Elektrik GmbH, Kronach-Gundelsdorf, Bavaria, Germany). For a 25 cm⁻¹ electrode… 2 The MEA electrolyzer has flow rates of 68 mL / min for both the anolyte (0.1 M KHCO3) inlet and the CO2 inlet. -1 And 127 sccm. For 100 cm 2 The MEA electrolyzer has an anolyte inlet flow rate of 130 mL / min. -1 The CO2 flow rate varied from 52 sccm to 218 sccm.

[0044] Unless otherwise specified, gaseous products were analyzed using a gas chromatograph (Ramin GC 2060, Shanghai, China) equipped with a flame ionization and thermal conductivity detector. Calibration curves for CO, CH4, C2H4, and H2 were obtained by injecting standard gas samples with different concentrations equilibrated through CO2 (Scientific Gas Engineering Co., Ltd., Hong Kong SAR, China). Liquid products were quantified by nuclear magnetic resonance spectroscopy (Bruker AVANCE III HD 500, Billerica, Massachusetts, USA) using dimethyl sulfoxide (DMSO, 99.97%, Fisher Chemical, Waltham, Massachusetts, USA) as an internal standard. The Faraday efficiency (FE) for each product was calculated based on the following equation:

[0045]

[0046] in It is the amount of products of electron transfer. is the number of moles of the product, F is the Faraday constant, and Q is the total charge passing through during electrolysis.

[0047] The energy efficiency of the full-cell CO2-to-CH4 conversion in an MEA is calculated based on the following equation:

[0048]

[0049] in The voltage applied between the cathode and anode in the MEA without IR correction, for CO2RR 3 , The measured Faraday efficiency of the product (CH4) is expressed as a percentage, and .

[0050] For CO2RR, assuming each DAT molecule provides 2 active sites (-NH2), the CO2 to CH4 conversion frequency (TOF) on DAT can be calculated using the following equation.

[0051]

[0052] Where j CH4 The partial current density of CH4 (A cm⁻¹) -2 F is the Faraday constant, ne CH4 n is the number of electrons required for each type of CO2 to be reduced to CH4. DATIt is the number of moles of DAT remaining on the cathode side calculated based on DPV (mol / cm). -2 ).

[0053] To evaluate the electro-fuel performance of the unit, the energy (kJ) of the generated CH4 was calculated based on the following equation:

[0054]

[0055] in It represents the amount of CH4 produced (mol), and LHV indicates the lower heating value of CH4 (802.23 kJ mol). -1 ).

[0056] Regarding DFT calculations, unless otherwise stated, all first-principles density functional calculations in this work were performed using the Vienna Ab initio Simulation software package (VASP, VASP Software GmbH, Vienna, Austria). 39-41 The Perdew-Burke-Ernzerhof method within the generalized gradient approximation functional (GGA-PBE) is used to describe electron-related interactions. 42 The projector-enhanced wave method at a cutoff energy of 500 eV is used to describe electro-ion interactions. 43 In the Grimme scheme, long-range dispersive vdW interactions between atoms were investigated using the DFT-D3 method. 44 The Brillouin zone integral is performed using a 1 × 1 × 1 Monkhorst–Pack k-point network. 45 Geometric optimization was performed using a force-based conjugate gradient algorithm.

[0057] Regarding the CO reduction reaction (CORR) and HCHO reduction reaction, for CORR in MEA, CO gas (99.99%, from Asia Pacific Gas Enterprise Co., Ltd., Hong Kong SAR, China) was humidified in deionized water at 40°C and discharged at a flow rate of 45 mL / min controlled by a mass flow controller (Beijing Qixing Huachuang Flowmeter Co., Ltd., Beijing, China). -1 The flow rate is continuously supplied to the cathode flow field. A deionized water anolyte containing 0.1 M KHCO3 is pumped through a peristaltic pump at a rate of 8 mL / min. -1The flow rate circulates through the anode flow field. As mentioned in Method 2, gaseous products are detected and quantified using DEMS. Electrolysis of CO2 containing HCHO was performed in an electrochemical flow cell electrolyzer with a three-electrode configuration. An Ag / AgCl electrode (saturated with KCl, IDA) and a Pt mesh (30 mm × 15 mm, 99.99%, Gaoss Union, Wuhan, Hubei, China) were used as the reference and counter electrodes, respectively. The cathode gas diffusion electrode was formed by spraying a solution containing the following onto an area of ​​2.25 cm². 2 The following mixture was prepared on carbon paper (Sigracet 39 BB, Fuel Cell Store, Blaine, Texas, USA): 4.4 mg DAT molecules, 0.33 mL 2-propanol, 0.17 mL deionized water, 0.46 µL perfluorosulfonic acid ionomer (PFSA, Aquivion® D79-25BS, Fuel Cell Store, Blaine, Texas, USA), and 2.0 mg commercial carbon nanoparticles (Vulcan XC 72R, Fuel Cell Store, Blaine, Texas, USA). Pure CO2 was purged into a 37% aqueous formaldehyde solution (stabilized with 10% methanol, VWR) heated to 40°C, and the mixture containing CO2 and HCHO was introduced at a rate of 45 mL / min. -1 The flow rate was purged into the cathode chamber. For comparison, a control experiment was conducted in which pure CO2 was purged into an aqueous solution containing 10% methanol heated to 40°C (to simulate the solvent of commercially available formaldehyde solution), and a mixture of CO2, water vapor, and methanol was purged into the cathode chamber at the same flow rate. Figure 18 ).

[0058] Method 1. Eliminate the influence of metal elements in the catalyst.

[0059] To demonstrate the intrinsic activity of DAT in catalyzing the conversion of CO2 to CH4, the inventors conducted a series of experiments to eliminate the influence of metal elements that might be introduced onto the electrode through contamination. The experiments compared commercially available DAT powder (≥ 98%, Aladdin) and DAT-coated electrodes (…). Figures 9A-9B Energy dispersive X-ray fluorescence (XRF) spectroscopy (Shimadzu EDX-LE) was used to qualitatively screen for metal elements that may be introduced onto the electrodes.

[0060] Peaks of Cu and Br can be identified in DAT powder, which may contain trace amounts of cuprous bromide (CuBr) as a catalyst for the synthesis of organic compounds. S1Peaks for Cu, Ti, Fe, and Zn were observed on the DAT-coated electrode, indicating that these metallic elements may have been introduced during electrode fabrication. To quantify the amount of metallic elements that might contribute to CO2RR performance, boiling concentrated nitric acid (HNO3, 65%, EMSURE) was used. ® After nitration in Reag. Ph Eur (ISO), the bare electrode and the DAT-coated electrode were analyzed by inductively coupled plasma atomic emission spectrometry (ICP-OES, Shimadzu ICPE-9820), and the results are shown in Table 3.

[0061] Compared to the bare electrode, an increase in Cu can be observed on the DAT-coated electrode. Control experiments are needed to rule out the effect of Cu on the DAT-coated electrode. Assuming a 3.5 nmol / cm² concentration exists on the DAT-coated electrode... -2 The inventors prepared electrodes with different Cu forms (Table 4) and compared their CO2RR performance with that of bare electrodes and electrodes coated with ordinary DAT. Figure 10 ).like Figures 9A-9B As mentioned in the description, the DAT-coated electrode is prepared by spraying an ink containing DAT. Bare electrode A is prepared using the same method, but the ink does not contain DAT molecules. Electrode B is prepared using the same method, but without added DAT, and is instead coated at a 4 cm depth. 2 3.5 nmol cm⁻¹ was added to the carbon paper. -2 Cuprous bromide (CuBr). Electrode C was prepared using the same method as electrode B, but with the addition of 35 nmol DAT as a ligand to coordinate with Cu. To further investigate the role of the Cu-DAT complex, the inventors prepared electrode D using ink containing a pre-prepared Cu-DAT complex. The Cu-DAT complex was obtained by mixing CuSO4 (ultrapure, Phampur®, Ph Eur, BP, USP) with DAT in a 1:1 molar ratio in deionized water, followed by filtration of the green suspension to ensure complete coordination of copper with DAT molecules. S2,S3 .

[0062] Although the CH4 selectivity observed on electrodes B, C, and D was slightly improved compared to the bare electrode (A), none of them produced CH4 when FE was above 10%, with the hydrogen evolution reaction dominating (FEH2 > 60%). This indicates that trace amounts of Cu are not a major factor in CO2-to-CH4 conversion performance, whether in the form of Cu or Cu-DAT complexes. It can be concluded that the high activity and selectivity of CO2-to-CH4 conversion observed on DAT-coated electrodes (FE) CH4 >50% mainly comes from DAT molecular catalysts, rather than the introduction of metal elements.

[0063] Method 2. 13 CO2 reduction reaction to identify carbon source.

[0064] To confirm the carbon source provided to CO2RR, at 4 cm 2 MEA uses 12 CO2RR was performed under the same conditions using a DAT catalyst. 13 CO2 reduction reaction. 13 CO2 gas (99%, Scientific Gas Engineering Co., Ltd.) was humidified in deionized water at 40°C and then discharged at a flow rate of 45 mL / min, controlled by a mass flow controller (Beijing Qixing Huachuang Flowmeter Co., Ltd.). -1 The flow rate is continuously supplied to the cathode flow field. A deionized water anolyte containing 0.1 M KHCO3 is pumped through a peristaltic pump at a rate of 8 mL / min. -1 The flow rate circulates through the anolyte. Gas products are sampled by differential electrochemical mass spectrometry (DEMS, Pfeiffer PrismaPro QMG250) using a previously reported sampler. S4 This is used for detection, enabling online collection of gas at the outlet of the cathode flow field in the electrolytic cell. The MS signals at m / z = 15, 17, and 2 are respectively... 12 CH4 13 The characteristics of CH4 and H2 allow for direct quantification. Note that, due to... 12 CO2 or 13 CO2 will be broken down into... 12 CO or 13 CO fragments, therefore the previously reported method was used. S5 Deconvolve the signals at m / z = 28 or 29. A linear relationship exists between the MS signal intensity and the concentration of the corresponding species in the gas. Figure 11A-11C This allows for online detection of the Faraday efficiency during electrolysis via equations M2.1-M2.2.

[0065]

[0066]

[0067] in It is the amount of products of electron transfer. It is the number of moles of product, F is the Faraday constant, Q is the total charge passing through per minute during electrolysis, and c i (ppm) is the concentration of each product obtained from the DEMS calibration curve, and v (sccm) is the measured flow rate of the gas at the electrolyzer outlet. Figure 12 It shows 13The distribution of gaseous products during CO2RR and the data obtained from MS signals at m / z = 17, 29, and 2, respectively. 13 CH4 13 The FE of CO and H2 is carried out on a DAT catalyst. 12 During CO2RR, 13 CH4's FE (45%) and 12 The FE of CH4 is similar, thus confirming that the carbon source is CO2.

[0068] Method 3. Electrochemical measurement and quantification of DAT.

[0069] Electrochemical measurements of DAT were performed using an electrochemical workstation (CH instrument, 660E) with a single-chamber electrochemical cell unit and a Pt mesh electrode (1 cm²). 2 99.99% (Gaoshi Ruilian Company), graphite rods, and Ag / AgCl (KCl saturated, IDA) were used as the working electrode, counter electrode, and reference electrode. Unless otherwise specified, 10 mM DAT molecules in a 0.1 M KHCO3 aqueous solution were used as the electrolyte. Equation - The potential relationship relative to the Ag / AgCl reference electrode was converted to the RHE reference scale. The inventors performed cyclic voltammetry (CV) to characterize the electrochemical behavior of DAT on the working electrode. Figure 14 The study showed a distinct oxidation peak in the DAT solution compared to the blank solution (only 0.1 M KHCO3), indicating that DAT molecules can be oxidized at an oxidation potential lower than that of the oxygen evolution reaction.

[0070] Based on the oxidation of DAT molecules, differential pulse voltammetry (DPV) was used to quantify the amount of DAT on the electrode. DPV tests were performed on DAT dissolved in 0.1 M KHCO3 at different concentrations to obtain the peak current density at an electrode potential of +1.05 V vs RHE (relative to the reversible hydrogen electrode), which is lower than the thermodynamic potential of the oxygen evolution reaction (OER). Figure 15 By plotting the relationship between peak current density and corresponding DAT concentration, R was obtained. 2 The calibration curve with a value of 0.999, such as Figure 16 As shown. The DAT sample after CO2 RR was prepared by immersing both the cathode electrode and the anion exchange membrane in 1 mL of 0.1 M KHCO3 solution, followed by ultrasonic treatment for 30 minutes and filtration. Then, 700 µL of this solution was added to the electrolyte (6 mL of 0.1 M KHCO3) for DPV testing. The peak current density at +1.05 V vs RHE was used to calculate the DAT concentration and the total amount of DAT remaining on the cathode side after CO2 electrolysis. Figure 17 (and Table 5).

[0071] Method 4. UV-vis spectroscopy of DAT.

[0072] UV-vis spectra were obtained using a Shimadzu UV3600 Plus. The UV absorption peak observed at 210 nm in the DAT standard solution can be attributed to the aromatic N-heterocyclic structure in the DAT molecule. S6 This absorption peak showed no shift after CO2 purging, but a significant redshift to 225 nm was observed with the addition of HCHO, indicating that DAT and HCHO formed an extended conjugated structure. S6,S7 .

[0073] Example 1: Renewable energy-driven electrochemical CO2 reduction on a molecular catalyst according to an embodiment of the present invention The reaction (CO2RR).

[0074] Electrochemical CO2 reduction reactions (CO2RR) are used to produce value-added fuels and feedstocks and typically rely on metal-based catalysts. While molecular catalysts are more tunable than metal catalysts, they still cannot catalyze CO2 to hydrocarbons for long-term operation at industrially relevant current densities, and the catalytic mechanism remains unclear. This example provides a 3,5-diamino-1,2,4-triazole (DAT)-based membrane electrode assembly for CO2 to CH4 conversion, wherein at 250 mA cm⁻¹… -2 The Faraday efficiency is (52 ± 4)%, and the switching frequency is 11530 h. -1 Due to the spatially distributed active sites and appropriate energy levels of molecular orbitals, the DAT electrode continues to generate CH4 from CO2 via *COOH-*C(OH)2-*COH. The experimental system, running for 10 hours at a total current of 10 A, achieved a yield of 23.0 mmol / h. -1 CH4 is produced at a rate that allows it to reach its maximum.

[0075] Renewable energy-driven electrochemical CO2 reduction reaction (CO2RR) is a promising approach to convert CO2 into value-added fuels and chemicals, particularly hydrocarbons and oxygen-containing compounds with high energy densities, such as CH4, C2H4, and C2H5OH. 1-3 Developing highly selective CO2RR catalysts is crucial for reducing separation costs and improving energy efficiency. 4 Furthermore, for practical applications, CO2RR electrolyzers are required to operate at high current densities (> 200 mA cm⁻¹). -2 It exhibits considerable durability under these conditions. 5,6 .

[0076] Hori and his colleagues’ pioneering work revealed Cu’s ability to convert CO2 into ethylene and methane. 7Furthermore, subsequent work identified up to sixteen products on Cu foil. 8,9 The fundamental reason for this phenomenon is the abundance of various binding sites with suitable adsorption energies on the Cu surface, leading to the adsorption of multiple intermediates in CO2RR. The overall reaction selectivity is determined by the relative stability of intermediates in different reaction pathways on the Cu surface. 10,11 Selectivity can be partially modulated by tailoring binding sites to specific reaction pathways, such as creating active sites with weak Cu-carbon binding to modulate selectivity for ethanol rather than ethylene. 12 Unfortunately, under electrochemical conditions, the surface of transition metals is highly dynamic, and the precise configuration of active sites is often unknown, thus altering the reaction pathway for the formation of the target product. 13,14 .

[0077] Homogeneous catalysts with well-defined structures and tunable local coordination at the molecular level offer opportunities for tailoring specific reaction pathways. Nevertheless, most reported molecular catalysts, particularly small-molecule catalysts, primarily focus on CO / formate as the final product at low current densities. 15-17 Products involving more than two electron transfers, such as CH4 or C2H4, are rarely observed. The formation of these products on heterogeneous catalysts requires a reaction between two surface-adsorbed intermediates, and such interactions between molecular catalytic intermediates in solution are challenging. 18,19 Immobilizing molecular catalysts on high-surface-area electrodes increases the surface concentration of active sites for further reduction of species. 20 Although the production of methanol, ethanol, and acetate was observed on polyaniline- or polypyrrole-based catalysts, their activity (< 10 mA cm⁻¹) was significantly lower than that of heterogeneous catalysts. -2 The stability (< 3 h) is not satisfactory. 17,21,22 At high current densities, molecular catalysts are unstable for long-term operation. 20,23 Therefore, understanding and designing molecular electrodes for the stable conversion of CO2 into products other than CO / formate remains a formidable challenge.

[0078] In this example, a triazole-catalyzed CO2RR system based on a membrane electrode assembly (MEA) achieved selective electro-methanation by electrolysis at a total current of 10 A for 10 hours. A comprehensive mechanistic study using DFT calculations revealed that the significantly high CO2RR activity of 3,5-diamino-1,2,4-triazole (DAT) is associated with a good match between the energy levels of the leading-edge orbital of CO2 and the lowest occupied molecular orbital. The key intermediate *COH in CO2 to CH4 conversion is believed to be formed via an unconventional pathway of *C(OH)2 for sequential protonation to produce the final product CH4. Using DAT modified on a gas diffusion electrode, CO2 to CH4 activity was achieved, with a maximum efficiency of 250 mA cm⁻¹. -2 The Faraday efficiency (FE) is (52 ± 4)%, and the conversion frequency (TOF) of methane conversion is [missing value]. CH4 ) is 11530 h -1 .

[0079] The results of Example 1 include the following.

[0080] The screening of molecular catalysts for efficient CO2RR was conducted as follows. (CO2 to curved *CO2) δ- The first activation step of the structure is crucial for subsequent catalytic processes. Considering the electrophilic nature of carbon in the CO2 molecule and not being bound by theory, the inventors hypothesized that 1,2,4-triazole derivatives with abundant N sites could be effectively activated. The inventors first screened 1,2,4-triazole derivatives ( Figure 1A The ability of 1-18 in the text to activate CO2. These derivatives are triazoles with different functional groups to modulate the leading energy levels of molecular orbitals. 27 CO2 is activated by electron transfer from the highest occupied molecular orbital (HOMO) of the molecular catalyst (MC) to the lowest unoccupied molecular orbital (LUMO) of CO2. When the MC is deprotonated, the HOMO energy tends to increase in order to better align with the LUMO energy of the CO2 molecule for activation. Figure 5 Of all the molecules studied, entry-15 (DAT) with an appropriate HOMO energy level favored CO2 activation. Figure 1B and Figure 6 Because the amine group (-NH2) of the DAT molecule has a high electron density, it is conducive to nucleophilic attack on CO2. Therefore, CO2 activation is most likely to occur on the amine group (-NH2) of the DAT molecule. Figure 7 In the experiment, the inventors observed the activation of CO2 through the -NH2 site using in-situ Raman spectroscopy. Figure 1C Under CO2 saturated conditions, CO2 only appeared on the DAT electrode. δ- (approximately 1410 cm)-1 ) and -NH-CO- (approximately 1304 cm -1 (Related peaks) 25 These peaks are due to the strong interaction between CO2 and the amine groups on DAT, which are at 600 cm⁻¹ -1 Up to 1200 cm -1 It has characteristic peaks ( Figure 8 ).

[0081] The electrochemical CO2 reduction performance was studied as follows. A molecular electrode with highly active sites was fabricated by spraying a mixture of small molecules and carbon nanoparticles onto carbon paper. Figure 2A (See Methods for details), the small molecules are 1,2,4-triazole (TAZ), 3-amino-1,2,4-triazole (ATA), and 3,5-diamino-1,2,4-triazole (DAT). At 250 mA cm⁻¹ -2 At a constant current density, CH4 is the main CO2RR product for both ATA and DAT (Table 1). From TAZ to DAT, FE was observed. CH4 The increase is consistent with the increase in the number of amine groups, and is consistent with previous calculations for active sites. Figure 2B DAT showed the highest FE. CH4 (52±4)%, this is a record for molecular catalysts for electro-methanation, and it is comparable to the highest FE of state-of-the-art heterogeneous catalysts. CH4 Comparable (Tables 2 and 3). Only a small amount of CH4 (FE) is generated on the bare electrode. CH4 = (1 ± 0.4)%. Trace amounts of metallic impurities (3.5 nmol / cm³) were detected on the DAT electrode. -2 Copper, 5.0 nmol cm -2 Iron and 7.0 nmol cm -2 Zinc), these metallic impurities are introduced from spray gun corrosion during electrode manufacturing. Comparative experiments with varying amounts of metallic impurities show that FE CH4 The low percentage (below 10%) demonstrates that DAT molecules are responsible for the high selectivity and activity of CO2RR (Method 1 and Method 2). Figure 9A-10 It was carried out. 13 CO2 isotope labeling experiments to confirm 13 The generation of CH4 eliminates potential contamination from the substrate (Method 2 and Figure 11A-12 ).

[0082] Focusing on DAT, the product distribution of CO2RR under different current densities was investigated. FE was observed on DAT. CH4 The volcanic shape distribution is at 250 mA cm⁻¹. -2 The peak value was reached at (52 ± 4)%. Figure 2C ), corresponding partial current density (j CH4 The value was (129 ± 11) mA cm. -2 The energy efficiency is (13.0 ± 1.6)% ( Figure 2D and Figure 13 To investigate the intrinsic activity of DAT during CO2RR, differential pulse voltammetry (DPV) was used at 250 mA cm⁻¹, treating the two amine groups as active centers. -2 The density of DAT active sites was measured to be 0.046 µmol / cm² after CO2 electrolysis. -2 (Method 3 and) Figure 14-17 Based on the active site density, the CO2 to CH4 conversion frequency (TOF) on the DAT molecular catalyst is 11530 h⁻¹. -1 This is nearly two orders of magnitude higher than the conversion frequency reported on Cu NP (Table 7), indicating that the intrinsic activity of CO2 to CH4 conversion on DAT is high.

[0083] The mechanism of CO2 to CH4 conversion was investigated as follows. It has been reported that the CO2 to CH4 conversion pathway on heterogeneous catalysts involves the key intermediate *CHO or *COH generated from the protonation of *CO. 3,29 To explore whether intermediates *CHO or *COH are suitable for DAT electrodes, the formation of CH4 was studied by in-situ differential electrochemical mass spectrometry (DEMS) using gases introduced in the order of "CO2-CO-CO2". Figure 3A After switching the feed gas from CO2 to CO, the CH4 production rate decreased by 40% (from 0.12 µmol / s in CO2RR). -1 cm -2 Decreased to 0.071 µmol s in CORR -1 cm -2 Upon switching back to CO2, the decrease in activity was irreversible, indicating that the *CO pathway may be detrimental on the DAT electrode. An attempt was then made to increase the *CHO content by introducing HCHO into the electrolyte. 1,30 A nearly 50% decrease in CH4 production rate was observed; upon addition of HCHO, the CH4 production rate decreased from 14 nmol / s. -1 cm -2 Reduced to 6.5 nmol s -1 cm -2 ( Figure 3B and Figure 18 This observation can be explained because DAT can react with HCHO to form a stable conjugated structure and prevent further reactions, which is consistent with... 1H NMR spectroscopy, UV-Vis spectroscopy (method 4 and Figure 16-19 ) and previous literature 31-33 Consistent.

[0084] Therefore, the above results encourage inventors to reconsider reaction processes beyond the commonly accepted *CO pathway on conventional catalysts. Energy distributions for different reaction pathways of CO2 electrolysis on DAT were calculated using density functional theory (DFT). Figure 3C Unlike heterogeneous catalysts, the formation of *COH, in addition to *CHO, is advantageous on molecular catalysts. Following the first proton-coupled electron transfer process of CO2 to *COOH, the unexpected intermediate *C(OH)2 is formed. The energy change for *COOH to *C(OH)2 (0.54 eV) is lower than that for *COOH to *CO (0.62 eV). Figure 3C This may be because carbon in the *C(OH)2 pathway tends to maintain its covalently saturated state rather than dehydrate on the molecular catalyst to form unsaturated *CO. Therefore, the *COOH-*C(OH)2-*COH pathway is energy-favorable, thus skipping the *CO intermediate. The resulting *COH with unsaturated carbon bonds becomes the active species for subsequent steps. The spatially dispersed active sites on the molecular catalyst inhibit C… 2+ The reaction pathway, because surface CC coupling typically requires a distance of less than 2.1 Å. 34 On the other hand, the interaction with the molecular catalyst enables the intermediate to undergo protonation, thereby achieving high selectivity for CH4. Figure 3D ).

[0085] The scaling up of molecular electrodes for electrochemical fuel conversion is proceeding as follows. The high conversion frequency and low capital cost of the DAT electrode justify the pursuit of scaling opportunities. The molecular electrode for MEA starts from 4 cm⁻¹. 2 Gradually increased to 81 cm 2 The CO2 flow rate ranged from 45 sccm to 218 sccm. Figure 4A At a total current of 10 A, the DAT electrode (81 cm) 2 ) obtained 54% FE CH4 Furthermore, the single-pass carbon efficiency (SPCE) for CH4 is close to 10%. Figure 4B By adjusting the CO2 flow rate to 108 sccm, the molecular membrane electrode assembly can produce gaseous products of CH4, CO, and H2 at concentrations of 27%, 15%, and 53%, respectively, which is precisely the composition of commercial town gas. Figure 4C The generated town gas can be used directly without further processing, thus reducing the capital costs of removing sulfur or nitrogen in traditional industrial processes. 35-37The large-scale CO2RR system using molecular catalysts can operate stably for more than 10 hours, with an average CH4 production rate of 23.0 mmol / h. -1 ( Figure 4D and Figures 21A-22C The production rate is approximately ten times that of previously reported CO2RR electrolyzers (Table 8). At a total energy of 184 kJ, approximately 5.6 L of methane was produced. Figure 4E These results demonstrate certain benefits of combining molecular catalysts with electrochemical electro-gas conversion devices for commercial applications.

[0086] This example studies a molecular catalyst for the selective and scalable electro-methanation of CO2. At a total current of 10 A, the 3,5-diamino-1,2,4-triazole (DAT) molecular catalyst exhibits a high Faradaic efficiency exceeding 50% for CH4. The conversion frequency reaches a high of 11530 h⁻¹. -1 This implies that its inherent high activity and the leading molecular orbitals of DAT are related to the correct alignment with CO2. The amine groups in DAT may be the active sites for nucleophilic attack to activate CO2. Unlike heterogeneous catalysts, CO2 reduction on DAT was found to occur via the "*COOH-*COH-*C(OH)2" pathway. The spatially dispersed active sites and flexible structure of the molecular electrode enable rapid and stable CO2 to CH4 conversion. These findings broaden our understanding of the mechanism and suggest future directions for the design of catalysts for CO2 hydrogenation.

[0087] The materials considered in this example include the following: 1,2,4-triazole (99%), 3-amino-1,2,4-triazole (96%), 3,5-diamino-1,2,4-triazole (≥ 98%), and potassium bicarbonate (KHCO3, ACS, 99.7-100.5%) were purchased from Aladdin and used as is. Carbon nanoparticles (Vulcan XC 72R), perfluorosulfonic acid ionomer (PFSA, Aquivion® D79-25BS), and carbon paper (Toray TGP-H-060) were purchased from a fuel cell store. 2-Propanol (HPLC) was purchased from RCI Labscan. The anion exchange membrane (Sustainion X37-50 RT) was purchased from Dioxide Materials. Iridium chloride (IrCl3·xH2O, 99.8%) was purchased from Alfaesa. Titanium mesh (100 mesh, 99.96%) was purchased from Hebei Yichang Metal Wire Mesh Co., Ltd. Electrode preparation was carried out using deionized water with a resistivity of 18.25 MΩ cm. Unless otherwise specified, all molecularly coated electrodes comprised a carbon paper-based GDL substrate coated with an ink solution containing triazole molecules. A solution of 0.1 mmol triazole molecules, 0.8 mL 2-propanol, 0.4 mL deionized water, 0.3 µL perfluorosulfonic acid ionomer, and 4.7 mg commercial carbon nanoparticles was used in an effective area of ​​4 cm². 2 The coating was applied to carbon paper. Large-scale DAT-coated electrodes were prepared using the same method and ink formulation, but with proportionally increased ink volume and carbon paper substrate area. Bare electrodes without coating were prepared using the same spraying method, except that the ink solution did not contain triazole molecules. IrO2-coated Ti-based (e.g., mesh) anodes for catalyzing the oxygen evolution reaction in MEA electrolyzers were prepared using a previously reported dip-coating method. 38 .

[0088] Characterization was performed as follows. In-situ Raman spectroscopy analysis was conducted using a 785 nm diode laser and a Renishaw inVia Raman microscope in a modified flow cell with a water immersion objective. CO2 flowed through the gas chamber at a rate of 50 sccm. An Ag / AgCl (3 M KCl) electrode and nickel foam were used as the reference and counter electrodes, respectively. The working and counter electrodes were separated by an anion exchange membrane. The effective area was 1 cm². 2The working electrode was a DAT-coated Ag-PTFE electrode, which was prepared by spraying 0.06 mmol DAT and 0.2 µL perfluorosulfonic acid ionomer onto 100 nm Ag-PTFE GDE (Beijing Zhongxing Weiye Instrument Co., Ltd.) evaporated by electron beam (EB-600, Innovative Vacuum Solution Ltd.).

[0089] Electrochemical measurements were performed as follows. To investigate the electrochemical CO2RR performance, chronopotentiometry powered by an electrochemical workstation (ZAHNERZENNIUM pro) was used in the membrane electrode assembly (MEA) electrolyzer (5 cm⁻¹). 2 Electrolysis was performed at Dioxide Materials, Inc. The MEA comprised a cathode electrode (molecularly coated carbon fiber paper), an anode electrode (IrO2-coated Ti substrate (e.g., mesh)), and an anion exchange membrane (Sustainion X37-50 RT), which was pre-activated in 1 M KOH for at least 48 hours. Pure CO2 gas (99.99%, Air Products, Inc.) was humidified in deionized water at 40°C and discharged at a rate of 45 mL / min, controlled by a mass flow controller (Beijing Qixing Huachuang Flowmeter Co., Ltd.). -1 The deionized water anolyte containing 0.1 M KHCO3 is continuously supplied to the cathode flow field at a flow rate of 8 mL min⁻¹ using a peristaltic pump. For large-scale CO₂RR on the DAT electrode, electrolysis is carried out at 25 cm⁻¹. 2 (Dioxide Materials, 20 cm) 2 (Electrode with effective area) and 100 cm 2 (Suzhou Shengernuo Technology Co., Ltd., 81 cm) 2 The electrolysis was carried out in a MEA cell (with electrodes of effective area) and powered by a potentiostat (ZAHNER PP222). For a 25 cm⁻¹ electrode... 2 The MEA electrolyzer has flow rates of 68 mL / min for both the anolyte (0.1 M KHCO3) inlet and the CO2 inlet. -1 And 127 sccm. For 100 cm 2 The MEA electrolyzer has an anolyte inlet flow rate of 130 mL / min. -1 The CO2 flow rate varied from 52 sccm to 218 sccm.

[0090] Unless otherwise specified, gaseous products were analyzed using a gas chromatograph (Ramin GC 2060) equipped with a flame ionization and thermal conductivity detector. Calibration curves for CO, CH4, C2H4, and H2 were obtained by injecting standard gas samples (Scientific Gases Engineering Ltd.) at different concentrations equilibrated with CO2. Liquid products were quantified using a nuclear magnetic resonance spectrometer (Bruker AVANCE III HD 500) with dimethyl sulfoxide (DMSO, 99.97%, Feischel Chemicals) as an internal standard. The Faraday efficiency (FE) for each product was calculated based on the following equation:

[0091]

[0092] in It is the amount of products of electron transfer. is the number of moles of the product, F is the Faraday constant, and Q is the total charge passing through during electrolysis.

[0093] The energy efficiency of the full-cell CO2-to-CH4 conversion in an MEA is calculated based on the following equation:

[0094]

[0095] in The voltage applied between the cathode and anode in the MEA without IR correction, for CO2RR 3 , The measured Faraday efficiency of the product (CH4) is expressed as a percentage, and .

[0096] For CO2RR, assuming each DAT molecule provides 2 active sites (-NH2), the CO2 to CH4 conversion frequency (TOF) on DAT can be calculated using the following equation.

[0097]

[0098] Where j CH4 The partial current density of CH4 (A cm⁻¹) -2 F is the Faraday constant, ne CH4 n is the number of electrons required for each type of CO2 to be reduced to CH4. DAT It is the number of moles of DAT remaining on the cathode side calculated based on DPV (mol / cm). -2 ).

[0099] To evaluate the electro-fuel performance of the unit, the energy (kJ) of the generated CH4 was calculated based on the following equation:

[0100]

[0101] in It represents the amount of CH4 produced (mol), and LHV indicates the lower heating value of CH4 (802.23 kJ mol). -1 ).

[0102] The DFT calculations are performed as follows. Unless otherwise stated, all first-principles density functional calculations in this work were performed using the Vienna Ab initio Simulation Software Package (VASP). 39-41 The Perdew-Burke-Ernzerhof method within the generalized gradient approximation functional (GGA-PBE) is used to describe electron-related interactions. 42 The projector-enhanced wave method at a cutoff energy of 500 eV is used to describe electro-ion interactions. 43 In the Grimme scheme, long-range dispersive vdW interactions between atoms were investigated using the DFT-D3 method. 44 The Brillouin zone integral is performed using a 1 × 1 × 1 Monkhorst–Pack k-point network. 45 Geometric optimization was performed using a force-based conjugate gradient algorithm.

[0103] The CO reduction reaction (CORR) and HCHO reduction reaction are carried out as follows. For CORR in MEA, CO gas (99.99%, Asia Pacific Gases Co., Ltd.) is humidified in deionized water at 40°C and then discharged at a flow rate of 45 mL / min controlled by a mass flow controller (Beijing Qixing Huachuang Flowmeter Co., Ltd.). -1 A continuous flow rate of 0.1 MKHCO3 was supplied to the cathode flow field. A deionized water anolyte containing 0.1 MKHCO3 was circulated through the anolyte by a peristaltic pump at a flow rate of 8 mL min⁻¹. Gas products were detected and quantified by DEMS as described in Method 2. CO₂ electrolysis containing HCHO was performed in an electrochemical flow cell electrolyzer with a three-electrode configuration. An Ag / AgCl electrode (saturated with KCl, IDA) and a Pt mesh (30 mm × 15 mm, 99.99%, GCL) were used as the reference and counter electrodes, respectively. The cathode gas diffusion electrode was prepared by spraying a solution containing the following onto a 2.25 cm² area... 2The following mixture was prepared on carbon paper (Sigracet 39 BB, Fuel Cell Store): 4.4 mg DAT molecules, 0.33 mL 2-propanol, 0.17 mL deionized water, 0.46 µL perfluorosulfonic acid ionomer (PFSA, Aquivion® D79-25BS), and 2.0 mg commercial carbon nanoparticles (Vulcan XC 72R, Fuel Cell Store). Pure CO2 was purged into a 37% aqueous formaldehyde solution (stabilized with 10% methanol, VWR) heated to 40°C, and the mixture containing CO2 and HCHO was introduced at a rate of 45 mL / min. -1 The flow rate was purged into the cathode chamber. For comparison, a control experiment was conducted in which pure CO2 was purged into an aqueous solution containing 10% methanol heated to 40°C (to simulate the solvent of commercially available formaldehyde solution), and a mixture of CO2, water vapor, and methanol was purged into the cathode chamber at the same flow rate. Figure 18 ).

[0104] Example 2: According to an embodiment of the present invention, a direct current supply is generated by adjusting (i) the cathode material and (ii) the operating conditions. The town gas used.

[0105] The detailed standard operating procedure for this example includes the following: To generate town gas for direct use, electrolysis is performed in a membrane electrode assembly (MEA) electrolyzer using chronopotentiology powered by an electrochemical workstation at a total current of 10 A. The MEA comprises a cathode electrode (molecularly coated carbon fiber paper), an anode electrode (1.7 mg cm⁻¹), and an anolyte electrode (1.7 mg cm⁻¹). -2 The cathode electrode comprises an IrO2-coated Ti substrate (e.g., a mesh) and an anion exchange membrane. The cathode electrode consists of a carbon paper-based GDL substrate coated with an ink solution containing 3,5-diamino-1,2,4-triazole (DAT) as the cathode material. The ink used for coating contains DAT and commercially available carbon nanoparticles in a 2:1 mass ratio, with the solvent containing 2-propanol, deionized water, and perfluorosulfonic acid ionomer in a 2:1:0.001 volume ratio. The coated area of ​​the cathode is controlled to be 81 cm². 2 An anion exchange membrane is sandwiched between prepared cathode and anode electrodes to construct an MEA electrolyzer. Pure CO2 gas, humidified in deionized water at 40°C, is continuously supplied to the cathode flow field controlled by a mass flow controller. A deionized water anolyte containing 0.1 M KHCO3 is circulated through the anode flow field by a peristaltic pump at a flow rate of 130 mL / min. Figure 4C As shown, the composition of the generated gas can be adjusted by changing the flow rate at the CO2 inlet. When the CO2 inlet flow rate is 53 mL / min... -1 At that time, the concentrations of CO, CH4, H2, and CO2 were approximately 88%, 11%, 4%, and 0%, respectively. The inlet flow rate of CO2 was 81 mL / min.-1 At that time, the concentrations of CO, CH4, H2, and CO2 were approximately 75%, 19%, 10%, and 0%, respectively. The inlet flow rate of CO2 was 218 mL / min. -1 At that time, the concentrations of CO, CH4, H2, and CO2 were approximately 12%, 7%, 6%, and 75%, respectively. The inlet flow rate of CO2 was 108 mL / min. -1 At that time, the concentrations of CO, CH4, H2, and CO2 were approximately 53%, 27%, 15%, and 5%, respectively, which is similar to the composition of directly usable town gas.

[0106] Example 3: Composition and process parameters for manufacturing MEA according to an embodiment of the present invention.

[0107] The MEA for CO2 electrolysis comprises an anode, an ion-exchange membrane, and a cathode, as follows: The anode, ion-exchange membrane, and cathode are sandwiched between two conductive plates as a current collector. The cathode comprises a porous gas diffusion layer permeable to CO2 and electrically connected to one of the current collectors, and a catalyst layer adjacent to the gas diffusion layer. The catalyst layer comprises a conductive substrate, an ionomer binder, and a molecular catalyst. The conductive substrate is a carbon-based material. The ionomer binder comprises a fluorocarbon polymer. The molecular catalyst comprises a nitrogen heterocyclic molecule, said nitrogen heterocyclic molecule comprising at least one of the following: 1,2,4-triazole (TAZ), 3-amino-1,2,4-triazole (ATA), 3,5-diamino-1,2,4-triazole (DAT), imidazole, 2-aminoimidazole, benzimidazole, 1-methylimidazole, or biimidazole.

[0108] Example 4: Process parameters for generating gas from MEA according to an embodiment of the present invention.

[0109] Generating gas from an MEA involves the following steps: applying a voltage between the anode and cathode of the MEA. An MEA for CO2 electrolysis comprises an anode, an ion-exchange membrane, and a cathode. The anode, ion-exchange membrane, and cathode are sandwiched between two conductive plates as a current collector. The cathode comprises a porous gas diffusion layer permeable to CO2 and electrically connected to one of the current collectors, and a catalyst layer adjacent to the gas diffusion layer. The catalyst layer comprises a conductive substrate, an ionomer binder, and a molecular catalyst. The conductive substrate is a carbon-based material. The ionomer binder comprises a fluorocarbon polymer. The molecular catalyst comprises a nitrogen heterocyclic molecule, said nitrogen heterocyclic molecule comprising at least one of the following: 1,2,4-triazole (TAZ), 3-amino-1,2,4-triazole (ATA), 3,5-diamino-1,2,4-triazole (DAT), imidazole, 2-aminoimidazole, benzimidazole, 1-methylimidazole, or biimidazole. CO2 gas is supplied to the cathode side. CO2 diffuses and penetrates the gas diffusion layer and is reduced within the catalyst layer on the cathode. At least one of the gaseous products (CO, CH4, H2) diffuses and penetrates the gas diffusion layer for collection from the cathode outlet. The concentration of CH4 in the gaseous products is at least 7%. The current density is at least 120 mA cm⁻¹. -2 .

[0110] Example 5: Process parameters for generating gas according to an embodiment of the present invention.

[0111] The detailed standard operating procedure includes the following: To generate a gas containing methane, carbon monoxide, hydrogen, and carbon dioxide, electrolysis is performed in a membrane electrode assembly (MEA) electrolyzer using a chronopotentiometric method powered by an electrochemical workstation. The MEA comprises a cathode electrode (molecularly coated carbon fiber paper), an anode electrode (1.7 mg cm⁻¹), and a diaphragm electrode (1.7 mg cm⁻¹). -2 The cathode electrode consists of an IrO2-coated Ti substrate (e.g., a mesh) and an anion exchange membrane. The cathode electrode comprises a carbon paper-based GDL substrate coated with an ink solution containing small molecules. The coating area of ​​the cathode is controlled to be 4 cm². 2 The ink used for spraying contains small molecules and carbon nanoparticles in a mass ratio of 2:1, while the solvent contains 2-propanol, deionized water, and perfluorosulfonic acid ionomer in a volume ratio of 2:1:0.001. An anion exchange membrane is sandwiched between prepared cathode and anode electrodes to fabricate the MEA electrolyzer. Pure CO2 gas, humidified in deionized water at 40°C, is continuously supplied to a flow rate controlled by a mass flow controller at 45 mL / min. -1In the cathode flow field, a deionized water anolyte containing 0.1 M KHCO3 is circulated through the anolyte by a peristaltic pump at a flow rate of 8 mL min⁻¹. Gaseous products, including methane, carbon monoxide, hydrogen, and carbon dioxide, are generated at the outlet of the cathode flow field with a total current of 1 A. For TAZ as the cathode material, the Faraday efficiencies for CO, CH₄, and H₂ are 3%, 9%, and 65%, respectively. For ATA as the cathode material, the Faraday efficiencies for CO, CH₄, and H₂ are 5%, 19%, and 56%, respectively. For DAT as the cathode material, the Faraday efficiencies for CO, CH₄, and H₂ are 8%, 52%, and 27%, respectively.

[0112] All patents, patent applications, provisional applications and publications mentioned or cited herein are incorporated herein by full reference to the extent that they are not inconsistent with the express teachings in this specification, including all figures and tables.

[0113] The following are examples demonstrating the procedures for practicing the present invention. These examples should not be construed as limiting. Unless otherwise stated, all percentages are by weight and all solvent mixture proportions are by volume.

[0114] It should be understood that the examples and embodiments described herein are for illustrative purposes only, and various modifications or variations will be suggested to those skilled in the art in view of them, and such modifications or variations will be included within the spirit and scope of this application and the scope of the appended claims. Furthermore, any element or limitation of any invention or embodiment thereof disclosed herein may be combined with any and / or all other elements or limitations disclosed herein (alone or in any combination) or any other invention or embodiment thereof, and all such combinations are contemplated to be within the scope of the invention, but not limited thereto.

[0115] Table 1. Faradaic efficiency (FE) of products in the electrochemical CO2 reduction reaction (CO2RR) on three triazole molecular catalysts and on a bare electrode without molecular coating. All products are measured at 250 mA cm⁻¹. -2 At the current density, the sample was collected after 1 hour of electrolysis in the membrane electrode assembly.

[0116]

[0117] Table 2. Comparison of molecular catalytic systems used for electrochemical CO2RR.

[0118]

[0119] Table 3. At concentrations above 100 mA cm⁻¹ -2 Current progress in the electrochemical reduction of CO2 to CH4 at current densities.

[0120]

[0121] Table 4. ICP-OES results of bare electrode and DAT-coated electrode digestion in boiling concentrated nitric acid. The bare electrode was prepared by the same spraying method as the DAT-coated electrode, except that the ink did not contain DAT molecules.

[0122]

[0123] Table 5. Electrodes prepared for control experiments by loading different species into the ink. The coating area of ​​each electrode is 4 cm². 2 .

[0124]

[0125] Table 6. Concentration of DAT solution in DPV testing and corresponding peak current density at +1.05 V vs RHE. n on the electrode DAT Used to calculate the time-of-flight (TOF) frequency.

[0126]

[0127] Table 7. Comparison of reported conversion frequencies (TOF) for CO2 to CH4.

[0128]

[0129] Table 8. At levels above 100 mA cm⁻¹ -2 At a current density, the rate of CO2 to CH4 generation was compared with that of a previously reported CO2RR electrolyzer.

[0130]

[0131] Example

[0132] Example 1. A catalyst cathode membrane electrode assembly (MEA) for the electrochemical production of methane and town gas from carbon dioxide, the MEA comprising small molecules, carbon black, and ionomers.

[0133] Example 2. The MEA according to Example 1, wherein the small molecule comprises a nitrogen heterocyclic molecule, wherein the nitrogen heterocyclic molecule comprises 1,2,4-triazole (TAZ), 3-amino-1,2,4-triazole (ATA), 3,5-diamino-1,2,4-triazole (DAT), imidazole, 2-aminoimidazole, benzimidazole, 1-methylimidazole or biimidazole.

[0134] Example 3. The MEA according to any one of the foregoing examples, wherein the nitrogen heterocyclic molecule comprises at least one of TAZ, ATA and DAT.

[0135] Example 4. The MEA according to any one of the foregoing examples, wherein the nitrogen heterocyclic molecule comprises DAT.

[0136] Example 5. The MEA according to any one of the foregoing examples comprises a mixture of small molecules on carbon paper and carbon nanoparticles sprayed on, wherein the small molecules comprise TAZ, ATA and DAT.

[0137] Example 6. The MEA according to any one of the foregoing examples, wherein the weight ratio of carbon particles to small molecules is in the range of 3.5-91.7%.

[0138] Example 7. The MEA according to any one of the foregoing examples, wherein the ionomer and small molecules are in the range of 0.8-3.3%.

[0139] Example 8. An MEA according to any one of the foregoing examples, wherein the MEA comprises a carbon paper-based gas diffusion layer (GDL) substrate.

[0140] Example 9. The MEA according to any one of the foregoing examples, wherein the GDL substrate comprises a spray ink solution containing the small molecules.

[0141] Example 10. The MEA according to any one of the foregoing examples, wherein the ionomer comprises perfluorosulfonic acid ionomer (PFSA).

[0142] Example 11. The MEA according to any one of the foregoing examples, wherein the carbon black comprises carbon nanoparticles.

[0143] Example 12. The MEA according to any one of the foregoing examples is prepared by spraying a solution containing 3,5-diamino-1,2,4-triazole (DAT) molecules, an aqueous carrier, perfluorosulfonic acid ionomer (PFSA) and carbon nanoparticles onto carbon paper.

[0144] Example 13. The MEA according to any one of the preceding examples, wherein the solution contains 3,5-diamino-1,2,4-triazole (DAT) molecules in an aqueous carrier at a ratio of 5 to 20 mg / mL and carbon nanoparticles in an aqueous carrier at a ratio of 2.5 mg / mL to 10 mg / mL.

[0145] Example 14. A method for generating town gas for direct use, the method comprising:

[0146] Provide a membrane electrode assembly (MEA), the MEA comprising:

[0147] A cathode electrode comprising molecularly coated carbon fiber paper;

[0148] An anode electrode comprising an IrO2-coated Ti substrate, and

[0149] Anion exchange membrane;

[0150] Humidified CO2 gas is continuously supplied to the cathode flow field of the MEA at a controlled flow rate;

[0151] The anolyte is circulated through the anolyte flow field of the MEA;

[0152] The controlled flow rate of the CO2 gas is altered to generate town gas for direct use, the town gas containing the following at corresponding concentrations: 0% to 15% CO, 0% to 27% CH4, 0% to 88% H2 and 0% to 90% CO2.

[0153] Example 15. The method according to Example 14, wherein the cathode electrode comprises 3,5-diamino-1,2,4-triazole (DAT) molecules, perfluorosulfonic acid ionomer (PFSA) and carbon nanoparticles on the molecularly coated carbon fiber paper.

[0154] Example 16. The method according to Example 15, wherein the mass ratio of DAT molecules to carbon nanoparticles on the cathode electrode is between 1:1 and 3:1.

[0155] Example 17. The method according to Example 15 or 16, wherein the cathode electrode is prepared with an ink for spraying, the ink containing DAT and commercial carbon nanoparticles in a mass ratio of 2:1, wherein the solvent contains 2-propanol, deionized water and perfluorosulfonic acid ionomer in a volume ratio of 2:1:0.001.

[0156] Example 18. A catalyst cathode membrane electrode assembly (MEA) for the electrochemical generation of methane and town gas from carbon dioxide, the MEA comprising 3,5-diamino-1,2,4-triazole (DAT), carbon black comprising carbon nanoparticles, and an ionomer comprising perfluorosulfonic acid ionomer (PFSA).

[0157] The weight ratio of carbon nanoparticles to DAT ranges from 3.5% to 91.7%.

[0158] The weight ratio of PFSA to DAT is in the range of 0.8-3.3%.

[0159] Example 19. The MEA according to Example 18, wherein the MEA comprises a carbon paper-based gas diffusion layer (GDL) substrate, the GDL substrate being prepared by spraying a solution comprising 3,5-diamino-1,2,4-triazole (DAT) molecules, an aqueous carrier, perfluorosulfonic acid ionomer (PFSA) and carbon nanoparticles onto carbon paper.

[0160] Example 20. The MEA according to Example 18 or 19, wherein the solution contains 5 to 20 mg / mL of DAT molecules and 2.5 to 10 mg / mL of carbon nanoparticles in an aqueous carrier.

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[0207] Supplementary References

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Claims

1. A catalyst cathode membrane electrode assembly (MEA) for electrochemically producing methane and town gas from carbon dioxide, the MEA comprising small molecules, carbon black, and ionomers.

2. The MEA according to claim 1, wherein the small molecule comprises a nitrogen heterocyclic molecule, the nitrogen heterocyclic molecule comprising 1,2,4-triazole (TAZ), 3-amino-1,2,4-triazole (ATA), 3,5-diamino-1,2,4-triazole (DAT), imidazole, 2-aminoimidazole, benzimidazole, 1-methylimidazole or biimidazole.

3. The MEA according to claim 2, wherein the nitrogen heterocyclic molecule comprises at least one of TAZ, ATA, and DAT.

4. The MEA according to claim 3, wherein the nitrogen heterocyclic molecule comprises DAT.

5. The MEA according to claim 3, comprising a mixture of small molecules on carbon paper and carbon nanoparticles sprayed on, wherein the small molecules comprise TAZ, ATA, and DAT.

6. The MEA according to claim 3, wherein the weight ratio of carbon particles to small molecules is in the range of 3.5-91.7%.

7. The MEA according to claim 6, wherein the weight ratio of ionomer to small molecule is in the range of 0.8-3.3%.

8. The MEA of claim 7, wherein the MEA comprises a carbon paper-based gas diffusion layer (GDL) substrate.

9. The MEA of claim 8, wherein the GDL substrate comprises a spray ink solution containing the small molecules.

10. The MEA of claim 9, wherein the ionomer comprises a perfluorosulfonic acid ionomer (PFSA).

11. The MEA of claim 10, wherein the carbon black comprises carbon nanoparticles.

12. The MEA according to any one of the preceding claims is prepared by spraying a solution comprising 3,5-diamino-1,2,4-triazole (DAT) molecules, an aqueous carrier, perfluorosulfonic acid ionomer (PFSA) and carbon nanoparticles onto carbon paper.

13. The MEA according to claim 12, wherein the solution comprises 3,5-diamino-1,2,4-triazole (DAT) molecules in an aqueous carrier at a ratio of 5 to 20 mg / mL and carbon nanoparticles in an aqueous carrier at a ratio of 2.5 mg / mL to 10 mg / mL.

14. A method for generating town gas for direct use, the method comprising: Provide a membrane electrode assembly (MEA), the MEA comprising: A cathode electrode comprising molecularly coated carbon fiber paper; An anode electrode comprising an IrO2-coated Ti substrate, and Anion exchange membrane; Humidified CO2 gas is continuously supplied to the cathode flow field of the MEA at a controlled flow rate; The anolyte is circulated through the anolyte flow field of the MEA; The controlled flow rate of the CO2 gas is altered to generate town gas for direct use, the town gas containing the following at corresponding concentrations: 0% to 15% CO, 0% to 27% CH4, 0% to 88% H2 and 0% to 90% CO2.

15. The method of claim 14, wherein the cathode electrode comprises 3,5-diamino-1,2,4-triazole (DAT) molecules, perfluorosulfonic acid ionomer (PFSA), and carbon nanoparticles on the molecularly coated carbon fiber paper.

16. The method of claim 15, wherein the mass ratio of DAT molecules to carbon nanoparticles on the cathode electrode is between 1:1 and 3:

1.

17. The method of claim 16, wherein the cathode electrode is prepared with an ink for spraying, the ink containing DAT and commercially available carbon nanoparticles in a mass ratio of 2:1, wherein the solvent contains 2-propanol, deionized water and perfluorosulfonic acid ionomer in a volume ratio of 2:1:0.

001.

18. A catalyst cathode membrane electrode assembly (MEA) for electrochemically producing methane and town gas from carbon dioxide, said MEA comprising 3,5-diamino-1,2,4-triazole (DAT), carbon black comprising carbon nanoparticles, and an ionomer comprising perfluorosulfonic acid ionomer (PFSA). The weight ratio of carbon nanoparticles to DAT ranges from 3.5% to 91.7%. The weight ratio of PFSA to DAT is in the range of 0.8-3.3%.

19. The MEA of claim 18, wherein the MEA comprises a carbon paper-based gas diffusion layer (GDL) substrate, the GDL substrate being prepared by spraying a solution comprising 3,5-diamino-1,2,4-triazole (DAT) molecules, an aqueous carrier, perfluorosulfonic acid ionomer (PFSA), and carbon nanoparticles onto carbon paper.

20. The MEA according to claim 19, wherein the solution comprises DAT molecules in an aqueous carrier at a ratio of 5 to 20 mg / mL and carbon nanoparticles in an aqueous carrier at a ratio of 2.5 mg / mL to 10 mg / mL.

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