Methods, catalysts and systems for performing electrochemical carbon dioxide reduction reactions in strong acidic medium

Abstract

The invention provides a method for electrochemically converting carbon dioxide into methanol in an acidic electrolyte environment (pH < 6). The method includes using an electrochemical cell provided with a cathode provided with a modified catalyst comprising a metal phthalocyanine functionalized by covalently attached cationic imine groups, the introduced functional groups creating a hydrophobic, gas-philic interface, increasing localized carbon monoxide availability of the catalyst surface while inhibiting competitive hydrogen evolution reaction production. By applying a suitable potential, the electrochemical cell effectively selectively and efficiently converts carbon dioxide to methanol under strongly acidic conditions.

Description

(19) State Intellectual Property Office (12) Invention Patent Application (10) Application Publication Number (43) Application Publication Date (21) Application Number 202511045739.9 (22) Application Date 2025.07.29 (30) Priority Data 63 / 676,895 2024.07.29 US (71) Applicant City University of Hong Kong Address Tat Chee Road, Kowloon, Hong Kong, China (72) Inventors Ye Ruquan Song Yun (74) Patent Agency Shenzhen Yibao Intellectual Property Agency (General Partnership) 44588 Patent Attorney Wang Qin Cao Yucun (51) Int.Cl. C25B 3 / 07 (2021.01) C25B 3 / 26 (2021.01) C25B 11 / 085 (2021.01) C25B 9 / 00 (2021.01) B82Y 40 / 00 (2011.01) (54) Title of Invention: Method, Catalyst, and System for Electrochemical Carbon Dioxide Reduction in Strongly Acidic Media (57) Abstract: This invention provides a method for electrochemically converting carbon dioxide into methanol in an acidic electrolyte environment (pH < 6). The method includes an electrochemical cell using a cathode equipped with a modified catalyst comprising a metal phthalocyanine covalently linked to a cationic imine group. The introduced functional group generates a hydrophobic-hydrophilic interface, improving the local availability of carbon monoxide on the catalyst surface while suppressing the competitive hydrogen evolution reaction. By applying an appropriate potential, the electrochemical cell effectively and selectively converts carbon dioxide into methanol under strongly acidic conditions. Claims 1 page, Description 18 pages, Drawings 80 pages, CN 121428575 A 2026.01.30 CN 1 21 42 85 75 A 1. A method for carrying out an electrochemical reduction reaction of carbon dioxide to produce methanol in an acidic electrolyte, characterized in that it comprises: providing an electrochemical cell including a cathode, an anode, and an acidic electrolyte with a pH value lower than 6; disposing a modified molecular catalyst on the cathode, wherein the modified molecular catalyst comprises a metal phthalocyanine functionalized with a covalently linked cationic imine group; and applying a potential to the electrochemical cell to drive a conversion reaction of carbon dioxide to methanol at the cathode; wherein the surface of the modified molecular catalyst has a hydrophobic-aerophilic interface to improve the availability of local carbon monoxide and inhibit hydrogen evolution reaction. 2. The method according to claim 1, wherein the conversion reaction of carbon dioxide to methanol achieves a methanol Faradaic efficiency of at least 60% and a methanol partial current density of at least 130 mA / cm⁻². 3. The method according to claim 1, wherein the metal phthalocyanine comprises one or more of cobalt phthalocyanine, nickel phthalocyanine, iron phthalocyanine, and their derivatives.4. The method of claim 1, wherein the cationic imine group comprises an alkyl chain having at least 6 carbon atoms. 5. The method of claim 4, wherein the alkyl chain comprises 6 or 10 carbon atoms. 6. The method of claim 1, wherein the hydrophobic-aerophilic interface enhances the surface coverage of carbon monoxide through van der Waals interactions and inhibits the reduction reaction of hydrated hydrogen ions through electrostatic repulsion. 7. The method of claim 1, wherein the potential ranges from -1.2 V to -1.5 V relative to the reversible hydrogen electrode potential. 8. A catalyst for electrochemical carbon dioxide reduction reaction, characterized in that it comprises: a layered nanosheet structure of a metal phthalocyanine, the metal phthalocyanine comprising one or more of cobalt phthalocyanine, nickel phthalocyanine, iron phthalocyanine, and their derivatives; wherein the layered nanosheet structure of the metal phthalocyanine is post-modified by covalent grafting of a cationic imine group having an alkyl chain having at least 6 carbon atoms; wherein the cationic imine group forms a hydrophobic-aerophilic interface on the catalyst surface; and wherein the catalyst inhibits hydrogen evolution reaction and enhances methanol selectivity under acidic conditions. 9. The catalyst of claim 8, wherein the alkyl chain comprises 6 or 10 carbon atoms. 10. The catalyst of claim 8, wherein the thickness of the layered nanosheet structure of the metal phthalocyanine is 1 nm to 2 nm. 11. A system for electrochemically converting carbon dioxide into methanol, characterized in that it comprises: an electrochemical cell including a cathode, an anode, and a liquid electrolyte with a pH value below 6, wherein the catalyst of claim 8 is disposed on the cathode; a gas supply device that continuously supplies carbon dioxide to the cathode; and a power source that applies a potential between the cathode and the anode; wherein the system achieves a methanol partial current density of at least 130 mA / cm⁻². 12. The system of claim 11, wherein the system is continuously operable and the Faraday efficiency of methanol exceeds 60%. Claims 1 / 1 Page 2 CN 121428575 A Method, Catalyst, and System for Electrochemical Carbon Dioxide Reduction in Strongly Acidic Media Cross-Reference to Related Applications

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 676,895, filed July 29, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0002] The present invention relates to the field of electrochemical reaction technology, and more particularly, to a method, catalyst, and system for reducing carbon dioxide to methanol by electrocatalysis in strongly acidic media. Background Art

[0003] The electrocatalytic reduction of carbon dioxide driven by renewable energy is a promising approach because it can synthesize high-value-added fuels and help alleviate environmental problems. Currently, there are various methods for converting carbon dioxide into chemical products.Electrocatalysts for carbon dioxide are widely used, but most catalysts are suitable for producing two-electron reduction products, such as carbon monoxide and formic acid. Therefore, how to selectively produce products with higher reduction degrees (such as methanol, methane, and ethylene) remains a major challenge. In particular, methanol has attracted special attention due to its high volumetric energy density, liquid-phase stability, and potential as a hydrogen carrier; however, the preparation of methanol by the electroreduction of carbon dioxide involves a six-electron transfer process, which is kinetically slow, leading to poor selectivity, high overpotential, and low current density.

[0004] To overcome the above limitations, researchers have developed a variety of catalytic materials for methanol synthesis, including metal complexes, single-atom catalysts, metal oxides, and metal alloys. Among them, cobalt phthalocyanine (CoPc) molecular catalysts have shown excellent performance in the selective reduction of one-carbon (C1) due to their tunable coordination environment and well-defined structure. A related study in 2019 showed that uniformly dispersing cobalt phthalocyanine on multi-walled carbon nanotubes (MWCNTs) can promote the multi-electron transfer process and effectively convert carbon dioxide into methanol. Subsequent studies have also confirmed that cobalt phthalocyanine-based catalysts can be used for the electroreduction of carbon dioxide or carbon monoxide to produce methanol. It is generally believed that the reaction pathway involves intermediates such as carbon monoxide and aldehydes. The rate-limiting step is the hydrogenation of carbon monoxide (*CO) adsorbed on the catalyst surface to form formyl groups (*CHO) adsorbed on the catalyst surface. However, this pathway is easily affected by side reactions such as carbon monoxide re-adsorption, carbon monoxide desorption, and hydrogen evolution reaction. Although neutral or alkaline electrolytes can partially inhibit the hydrogen evolution reaction, they can lead to carbonate formation, resulting in carbon loss, and the cost of electrolyte regeneration can reach 55% of the overall cost. To improve the selectivity of methanol as the final product, some studies have proposed cascade catalytic strategies, which involve converting carbon dioxide to carbon monoxide and carbon monoxide to methanol in series or in stages (see Figure 1A). However, such methods require additional intermediate product separation and system integration steps, increasing the capital investment and operating costs of the reaction equipment. Overall, whether through direct conversion or cascade catalysis, the current selective methanol electrosynthesis is still limited by a low partial current density, typically below 50 mA·cm⁻².

[0005] In contrast, strongly acidic electrolytes have the potential advantage of avoiding carbonate formation and improving carbon dioxide utilization. However, high proton concentrations in acidic environments can enhance the hydrogen evolution reaction, thereby inhibiting the selective formation of methanol. To address this issue, there are currently two main strategies to limit the concentration of hydrated hydrogen ions at the catalytic interface: one is to introduce high concentrations of alkali metal ions into the acidic electrolyte. For example, Hu et al. reported that hydrated potassium ions (K⁺) can modulate the local electric field and suppress the concentration of hydrated hydrogen ions. (See page 1 / 18 of the specification, CN 121428575 A)Hydrogen ions migrate towards the cathode and suppress the hydrogen evolution reaction, but at high overpotentials, this shielding effect is weakened by the rupture of the hydrated shell; the second is to modify the electrode surface hydrophobically to prevent hydrated hydrogen ions and water from diffusing to the catalyst. Although this method can effectively suppress the hydrogen evolution reaction, its practical application is often limited by the decrease in electrode conductivity and mass transport performance.

[0006] In view of this, the present invention provides a method, catalyst and system for carrying out efficient electrochemical reactions in a strongly acidic medium to achieve highly selective reduction of carbon dioxide to methanol, while effectively suppressing the hydrogen evolution reaction, overcoming the limitations of the prior art. Summary of the Invention

[0007] The object of the present invention is to provide a method, compound and system to solve the above-mentioned technical problems.

[0008] According to a first aspect of the present invention, a method is provided for carrying out an electrochemical reduction reaction of carbon dioxide in an acidic electrolyte to generate methanol. More specifically, the method includes the following steps: providing an electrochemical cell comprising a cathode, an anode, and an acidic electrolyte with a pH value below 6; disposing a modified molecular catalyst on the cathode, wherein the modified molecular catalyst comprises a metal phthalocyanine functionalized with a covalently linked cationic imine group; and applying a potential to the electrochemical cell to drive a conversion reaction of carbon dioxide to methanol at the cathode.

[0009] In one embodiment, the surface of the modified molecular catalyst has a hydrophobic-aerophilic interface to improve the availability of local carbon monoxide and suppress the hydrogen evolution reaction.

[0010] In another embodiment, the conversion reaction of carbon dioxide to methanol can achieve a methanol Faradaic efficiency of at least 60% and a methanol partial current density of at least 130 mA / cm2.

[0011] In another embodiment, the metal phthalocyanine comprises one or more of cobalt phthalocyanine (CoPc), nickel phthalocyanine (NiPc), iron phthalocyanine (FePc), and their derivatives.

[0012] In another embodiment, the cationic imine group comprises an alkyl chain having at least 6 carbon atoms.

[0013] In another embodiment, the alkyl chain comprises 6 or 10 carbon atoms.

[0014] In another embodiment, the hydrophobic-aerophilic interface enhances the surface coverage of carbon monoxide through van der Waals interactions and inhibits the reduction of hydrated hydrogen ions through electrostatic repulsion.

[0015] In another embodiment, the potential ranges from -1.2 V to -1.5 V relative to the reversible hydrogen electrode potential.

[0016] According to a second aspect of the invention, a catalyst for an electrochemical carbon dioxide reduction reaction is provided. More specifically, the catalyst comprises a layered nanosheet structure of a metal phthalocyanine, the metal phthalocyanine comprising one or more of cobalt phthalocyanine (CoPc), nickel phthalocyanine (NiPc), iron phthalocyanine (FePc), and their derivatives; a cationic imine group is introduced into the layered nanosheet structure of the metal phthalocyanine by covalent grafting for post-synthetic modification, and the cationic imine group has at leastAn alkyl chain with 6 carbon atoms.

[0017] In one embodiment, the cationic imine group forms a hydrophobic-hydrophilic interface on the catalyst surface.

[0018] In another embodiment, the catalyst inhibits hydrogen evolution reaction and enhances methanol selectivity under acidic conditions.

[0019] In another embodiment, the alkyl chain comprises 6 or 10 carbon atoms.

[0020] In another embodiment, the thickness of the layered nanosheet structure of the metal phthalocyanine is 1 nanometer to 2 nanometers.

[0021] According to a third aspect of the invention, a system for electrochemically converting carbon dioxide into methanol is provided. More specifically, the system comprises the following components: an electrochemical cell including a cathode and an anode disposed with the above-described catalyst and a liquid electrolyte with a pH value below 6; a gas supply device for continuously supplying carbon dioxide to the cathode; and a power source for applying a potential between the cathode and the anode. Specification 2 / 18 pages 4 CN 121428575 A

[0022] In one embodiment, the system achieves a methanol partial current density of at least 130 mA / cm2.

[0023] In another embodiment, the electrochemical system can operate continuously and the Faraday efficiency of methanol exceeds 60%.

[0024] Referring to the accompanying drawings, embodiments of the present invention will be described in more detail below, wherein:

[0025] Figures 1A-1C show a system for molecular multi-electron carbon dioxide reduction, wherein Figure 1A shows a tandem electrolyzer structure for solving the problem of poor selectivity in multi-electron reduction of molecular catalysts; Figure 1B shows the method of the present invention for directly reducing carbon dioxide to methanol by controlling the electric field; and Figure 1C shows a comparison of the effects of using an imine-C6 catalyst and existing catalysts to electrosynthesize methanol via a direct or tandem path under different pH conditions;

[0026] Figure 2 shows the synthesis route of a catalyst according to an embodiment of the present invention;

[0027] Figures 3A-3F show the structural features and surface properties of the catalyst, wherein Figure 3A is a transmission electron microscope image and structural diagram of imine-C6; Figure 3B is an atomic force microscope image of imine-C6; Figure 3C is an atomic force microscope image of imine; and Figures 3D to 3F are N1s of different catalysts, respectively. X-ray photoelectron spectroscopy (XPS) (Figure 3D), zeta potential diagram (Figure 3E), and contact angle test results (Figure 3F);

[0028] Figures 4A-4C show transmission electron microscope images of imine (Figure 4A), imine-C1 (Figure 4B), and imine-C10 (Figure 4C), respectively;

[0029] Figures 5A-5B show atomic force microscope images of imine-C1 and imine-C10, respectively;

[0030] Figure 6 shows the X-ray diffraction patterns of 1,8,15,22-tetraaminophthalocyanine cobalt (CoTAPc), imine, imine-C1, imine-C6, and imine-C10;

[0031] Figures 7A-7D show the energy dispersive X-ray spectral analysis of imine-C6, including the corresponding transmission electron microscope images (Figure 7A), carbon elemental distribution map (Figure 7B), nitrogen elemental distribution map (Figure 7C), and cobalt elemental distribution map (Figure 7D);

[0032] Figures 8A-8D show the Fourier transform infrared reflectance spectra (FTIR, Figure 8A), 13C nuclear magnetic resonance (NMR) maps (Figure 8B), Co 2p X-ray photoelectron energy spectrum (Figure 8C), and ultraviolet-visible absorption spectra (UV-vis, Figure 8D) of 1,8,15,22-tetraaminophthalocyanine cobalt, imine, imine-C1, imine-C6, and imine-C10, respectively;

[0033] Figure 9 shows the Zeta potential distribution maps of 1,8,15,22-tetraaminophthalocyanine cobalt, imine, imine-C1, imine-C6, and imine-C10;

[0034] Figures 10A-10E show the cyclic voltammetry (CV) curves of 1,8,15,22-tetraaminophthalocyanine cobalt (Figure 10A), imine (Figure 10B), imine-C1 (Figure 10C), imine-C6 (Figure 10D), and imine-C10 (Figure 10E) in an argon-saturated 0.5M potassium bicarbonate electrolyte;

[0035] Figures 11A-11F show the electrocatalytic carbon dioxide reduction reaction performance of various catalyst samples in an H-type battery using carbon dioxide-saturated 0.5M potassium bicarbonate as the electrolyte, wherein Figure 11A shows the linear sweep voltammetry (LSV) curves of 1,8,15,22-tetraaminophthalocyanine cobalt, imine, imine-C1, imine-C6, and imine-C10; and Figures 11B to 11F show the cyclic voltammetry (CV) curves of 1,8,15,22-tetraaminophthalocyanine cobalt (Figure 10A), imine (Figure 10B), imine-C1 (Figure 10C), imine-C6, and imine-C10, respectively. 1,8,15,22-Tetraaminophthalocyanine cobalt (Fig. 11B), imine (Fig. 11C), imine-C1 (Fig. 11D), imine-C6 (Fig. 11E), and imine-C10 (Fig. 11F) chronoamperometric (CA) test curves;

[0036] Figs. 12A-12E show the product distribution of the catalytic carbon dioxide reduction reaction in the H-type battery, respectively using 1,8,15,22-tetraaminophthalocyanine cobalt (Fig. 12A), imine (Fig. 12B), imine-C1 (Fig. 12C), imine-C6 (Fig. 12D), and imine-C10 (Fig. 12E) as catalysts;

[0037] Figs. 13A-13H show the electrocatalytic carbon dioxide reduction reaction performance, wherein Figs. 13A-13C show the methanol Faradaic efficiency (FECH3OH, Fig. 13A) and methanol partial current density of the H-type battery in a carbon dioxide-saturated 0.5M potassium bicarbonate solution, respectively. Page 5 CN 121428575 A (jCH3oH, Figure 13B) and Tafel slope (Figure 13C); Figure 13D is a schematic diagram of a flow battery using an acidic electrolyte; Figures 13E and 13F show the methanol method in an acidic flow battery using a mixed solution of 3.0M potassium chloride and 0.05M sulfuric acid as the electrolyte.Faraday efficiency (Figure 13E) and methanol partial current density (Figure 13F); Figure 13G shows the proton nuclear magnetic resonance (1H NMR) spectra of the products obtained using 12CO2 and 13CO2 as carbon sources in a 3.0M potassium chloride and 0.05M sulfuric acid electrolyte system; and Figure 13H compares the maximum methanol Faraday efficiency and methanol partial current density in the carbon dioxide reduction and carbon monoxide reduction reactions using imine-C6 catalysts under different pH conditions;

[0038] Figure 14 shows the electrochemical impedance spectroscopy (EIS Nyquist plot) of 1,8,15,22-tetraaminophthalocyanine cobalt, imine, imine-C1, imine-C6 and imine-C10 measured at -0.2V;

[0039] Figures 15A-15F illustrate the performance of catalytic carbon dioxide reduction in an acidic flow battery, where Figure 15A shows the linear sweep voltammetric curves of 1,8,15,22-tetraaminophthalocyanine cobalt, imine, imine-C1, imine-C6, and imine-C10; and Figures 15B-15F show the chronoamperometric detection curves of 1,8,15,22-tetraaminophthalocyanine cobalt (Figure 15B), imine (Figure 15C), imine-C1 (Figure 15D), imine-C6 (Figure 15E), and imine-C10 (Figure 15F), respectively;

[0040] Figures 16A-16E show the performance of 1,8,15,22-tetraaminophthalocyanine cobalt (Figure 16A) in an acidic flow battery. Distribution of carbon dioxide reduction reaction products when imine (Fig. 16B), imine-C1 (Fig. 16C), imine-C6 (Fig. 16D), and imine-C10 (Fig. 16E) are used as catalysts;

[0041] Fig. 17 shows the stability test results of the imine-C6 catalyst in the carbon dioxide reduction reaction in an acidic flow battery;

[0042] Figs. 18A-18B show the changes in the imine-C6 catalyst before and after CO2 electrolysis, where Fig. 18A is the UV-Vis absorption spectrum; and Fig. 18B is the Co 2p X-ray photoelectron spectrum;

[0043] Figures 19A-19B show the catalytic performance of carbon dioxide reduction in an alkaline flow battery using different catalysts, including 1,8,15,22-tetraaminophthalocyanine cobalt, imine, imine-C1, imine-C6, and imine-C10. Figure 19A shows the methanol current density obtained by different catalysts; and Figure 19B shows the corresponding methanol Faradaic efficiency.

[0044] Figures 20A-20F show the electrocatalytic performance of different catalysts in the flow battery. Figure 20A shows the linear sweep voltammetry curve; and Figures 20B-20F show the chronoamperometric test curves for 1,8,15,22-tetraaminophthalocyanine cobalt (Figure 20B), imine (Figure 20C), imine-C1 (Figure 20D), imine-C6 (Figure 20E), and imine-C10 (Figure 20F), respectively.

[0045] Figures 21A-21E show the product distribution of carbon dioxide reduction reaction in a flow battery using 1,8,15,22-tetraaminophthalocyanine cobalt (Figure 21A), imine (Figure 21B), imine-C1 (Figure 21C), imine-C6 (Figure 21D), and imine-C10 (Figure 21E) as catalysts, respectively;

[0046] Figures 22A-22B show the electrocatalytic performance of carbon monoxide reduction reaction in an H-type battery in 0.5M potassium bicarbonate solution using 1,8,15,22-tetraaminophthalocyanine cobalt, imine, imine-C1, imine-C6, and imine-C10 as catalysts, respectively, wherein Figure 22A shows the methanol partial current density; and Figure 22B shows the methanol Faradaic efficiency;

[0047] Figures 23A-23F show the performance of catalytic carbon monoxide reduction reaction in an H-type battery, wherein Figure 23A shows the 1,8,15,22-tetraaminophthalocyanine cobalt (Figure 21A), imine (Figure 21B), imine-C1 (Figure 21C), imine-C6 (Figure 21D), and imine-C10 as catalysts, respectively. Linear sweep voltammetric curves of 22-tetraaminophthalocyanine cobalt, imine, imine-C1, imine-C6, and imine-C10; and chronoamperometric curves of 1,8,15,22-tetraaminophthalocyanine cobalt (Figure 23B), imine (Figure 23C), imine-C1 (Figure 23D), imine-C6 (Figure 23E), and imine-C10 (Figure 23F), respectively;

[0048] Figures 24A-24E show the product distribution of carbon monoxide produced by catalysis using 1,8,15,22-tetraaminophthalocyanine cobalt (Figure 24A), imine (Figure 24B), imine-C1 (Figure 24C), imine-C6 (Figure 24D), and imine-C10 (Figure 24E) as catalysts in an H-type electrolytic cell;

[0049] Figures 25A-25B show the performance of 1,8,15,22-tetraaminophthalocyanine cobalt, imine, imine-C1, imine-C6, and imine-C10 in catalyzing the carbon monoxide reduction reaction in an acidic flow battery, where Figure 25A shows the methanol partial current density; and Figure 25B shows the methanol Faradaic efficiency;

[0050] Figures 26A-26F show the performance of catalyzing the carbon monoxide reduction reaction in an acidic flow battery, where Figure 26A is the linear sweep voltammetric curve of each catalyst (1,8,15,22-tetraaminophthalocyanine cobalt, imine, imine-C1, imine-C6, and imine-C10); Figures 26B-26F show 1,8,15,22-tetraaminophthalocyanine cobalt (Figure 26B), imine (Figure 26C), and imine-C1 (Figure 26D), respectively. Chronoamperometric curves of imine-C6 (Fig. 26E) and imine-C10 (Fig. 26F);

[0051] Figs. 27A-27E show the chromoamperometric curves of imine-C6 (Fig. 26E), imine (Fig. 27B), imine-C1 (Fig. 27C), imine-C6 (Fig. 27D), and imine-C10 (Fig. 27E) as catalysts in an acidic flow battery.Distribution of carbon reduction reaction products;

[0052] Figures 28A-28B show the performance of carbon monoxide reduction reaction catalyzed by 1,8,15,22-tetraaminophthalocyanine cobalt, imine, imine-C1, imine-C6 and imine-C10 catalysts in an alkaline flow battery, wherein Figure 28A shows the methanol Faraday efficiency; and Figure 28B shows the methanol partial current density;

[0053] Figures 29A-29F show the performance of the catalysts in the alkaline flow battery for catalytic carbon monoxide reduction. Figure 29A shows the linear sweep voltammetry curves of each catalyst (1,8,15,22-tetraaminophthalocyanine cobalt, imine, imine-C1, imine-C6, and imine-C10); and Figures 29B-29F show the chronoamperometric curves of 1,8,15,22-tetraaminophthalocyanine cobalt (Figure 29B), imine (Figure 29C), imine-C1 (Figure 29D), imine-C6 (Figure 29E), and imine-C10 (Figure 29F), respectively.

[0054] Figures 30A-30E show the product distribution of 1,8,15,22-tetraaminophthalocyanine cobalt (Figure 30A), imine (Figure 30B), imine-C1 (Figure 30C), imine-C6 (Figure 30D), and imine-C10 (Figure 30E) in an alkaline flow battery catalyzing the reduction of carbon monoxide;

[0055] Figure 31 shows a comparison of the performance of different catalysts in converting carbon dioxide to methanol under different pH conditions;

[0056] Figures 32A-32J show the detection results of catalyst surface properties, where Figures 32A-32B show the in-situ attenuated total reflectance surface-enhanced infrared absorption spectra (ATR-) of water on the surfaces of 1,8,15,22-tetraaminophthalocyanine cobalt (Figure 32A) and imine-C6 (Figure 32B) at different potentials in a carbon dioxide-saturated 0.5M potassium sulfate + 0.05M sulfuric acid electrolyte. Figure 32C shows the ratio of strong to weak hydrogen-bonded water (SEIRAS); Figure 32D shows the rotating disk electrode voltammetry curves at 600 rpm in an argon-saturated 0.5 M potassium sulfate + 0.05 M sulfuric acid electrolyte; Figures 32E-32F show the in-situ attenuated total reflectance surface-enhanced infrared absorption spectra of 1,8,15,22-tetraaminophthalocyanine cobalt (Figure 32E) and imine-C6 (Figure 32F) in a carbon dioxide-saturated 0.5 M potassium sulfate + 0.05 M sulfuric acid electrolyte catalyzing the carbon dioxide reduction reaction; Figure 32G shows the performance of imine cation-C6 in a carbon dioxide-saturated 0.5 M potassium sulfate + 0.05 M deuterated sulfuric acid / heavy water solution; Figure 32H shows the area ratio of formyl group to carbonyl group characteristic peaks at different potentials (AreaCHO / AreaCO); Figure 32I shows cyclic voltammetry of a platinum disk electrode at 300 rpm in various 5 mM pyridyl electrolytes saturated with carbon monoxide; and Figure 32J shows the anodic charge of the aggregate region in Figure 32I;

[0057] Figures 33A-33B show the in-situ attenuated total reflectance surface-enhanced infrared absorption spectra of imine cation-Cl (Figure 33A) and imine cation-ClO (Figure 33B) in a carbon dioxide-saturated 0.5M potassium sulfate + 0.05M sulfuric acid electrolyte;

[0058] Figure 34 shows the proportion of moderately hydrogen-bonded water calculated based on the in-situ attenuated total reflectance surface-enhanced infrared absorption spectra;

[0059] Figures 35A-35C show the O-H vibrations of 1,8,15,22-tetraaminophthalocyanine cobalt, imine cation-Cl, imine cation-C6, and imine cation-ClO in a carbon dioxide-saturated 0.5M potassium sulfate + 0.05M sulfuric acid electrolyte, respectively, representing weakly hydrogen-bonded (Figure 35A), moderately hydrogen-bonded (Figure 35B), and strongly hydrogen-bonded (Figure 35C) water molecules;

[0060] Figures 36A-36B show the linear sweep voltammetric curves of 1,8,15,22-tetraaminophthalocyanine cobalt, imine cation-C1, imine cation-C6 and imine cation-C10, respectively, measured at 600 rpm in argon-saturated 0.5M potassium sulfate (Figure 36A) and 0.1M potassium hydroxide + 0.45M potassium sulfate (Figure 36B);

[0061] Figures 37A-37B show the in-situ attenuated total reflectance surface-enhanced infrared absorption spectra of imine cation-C1 (Figure 37A) and imine cation-C10 (Figure 37B) during carbon dioxide reduction reaction in carbon dioxide-saturated 0.5M potassium sulfate + 0.05M sulfuric acid;

[0062] Figure 38 shows the in-situ attenuated total reflectance surface-enhanced infrared absorption spectrum of imine cation-C6 during carbon dioxide reduction reaction in carbon dioxide-saturated 0.5M potassium bicarbonate;

[0063] Figures 39A-39B show the peak area integral values ​​of CO (*CO, Figure 39A) and CHO (*CHO, Figure 39B) adsorbed on the catalyst surface, respectively;

[0064] Figures 40A-40F show the results of the interface molecular dynamics simulation, where Figure 40A shows the simulation model, which includes 1 molecule, 500 water molecules, 5 hydrated hydrogen ions, and 9 chloride ions for balancing electroneutrality; Figures 40B-40C show the radial distribution functions of water molecules (Figure 40B) and hydrated hydrogen ions (Figure 40C), respectively; Figure 40D is the diffusion coefficient of hydrated hydrogen ions calculated according to the two-phase thermodynamics (2PT) method; Figure 40E is the radial distribution function of carbon monoxide; Figure 40F is the entropy and free energy of carbon monoxide calculated according to the two-phase thermodynamics method;

[0065] Figures 41A-41E illustrate the electrocatalytic performance of 4-β-aminometal phthalocyanine nickel (NiTAPc) and its derived imine cation-C6 (nickel), where Figure 41A shows the linear sweep voltammetry curves; Figure 41B shows the carbon monoxide Faradaic efficiency; and Figure 41C shows...The carbon monoxide partial current density of 4-β-aminometal phthalocyanine nickel and imine cation-C6 (nickel) during carbon dioxide reduction reaction in an acidic flow cell; and Figures 41D-41E show the chronoamperometric curves of 4-β-aminometal phthalocyanine nickel (Figure 41D) and imine cation-C6 (nickel) (Figure 41E), respectively;

[0066] Figure 42 shows the linear sweep voltammetry curves of 4-β-aminometal phthalocyanine nickel and imine cation-C6 (nickel) in an argon-saturated 0.5M potassium sulfate + 0.005M sulfuric acid electrolyte at a rotation rate of 600 rpm; and

[0067] Figure 43 shows the cyclic voltammetry curves of a platinum disk electrode in an argon-saturated 5mM pyridyl electrolyte at a rotation rate of 300 rpm. Detailed Description

[0068] In the following description, systems, compounds, and methods for performing electrochemical reactions such as the electrosynthesis of methanol by carbon dioxide reduction reaction via multi-electron molecules in a strongly acidic medium are listed as preferred embodiments. It will be apparent to those skilled in the art that modifications, including additions and / or substitutions, can be made without departing from the scope and spirit of the invention. Specific details may be omitted below to avoid obscuring the invention; however, this document is prepared to enable those skilled in the art to practice the techniques disclosed herein without excessive experimentation.

[0069] Selective multi-electron molecular carbon dioxide reduction under strongly acidic conditions faces numerous challenges, including a lack of suitable catalysts, competition from hydrogen evolution reactions, and slow product formation rates. Therefore, conventional molecular carbon dioxide reduction reactions are typically carried out in neutral or alkaline environments to improve reaction performance, but this approach also results in significant carbon loss and increased operating costs.

[0070] As used herein, the term “local carbon monoxide availability” refers to the concentration and retention capacity of carbon monoxide molecules near the active site of an electrocatalyst during an electrochemical carbon dioxide reduction reaction. It reflects the effective retention efficiency of carbon monoxide (whether as an intermediate or a feedstock) near the catalyst surface, which is beneficial for the efficient conduction of subsequent reactions (such as the conversion of carbon monoxide to methanol).

[0071] According to a first aspect of the invention, a method is provided for the electrochemical reduction of carbon dioxide to methanol in an acidic electrolyte (see page 6 / 18 of CN 121428575 A). More specifically, the method includes the use of a modified molecular catalyst to overcome the limitations of carbon dioxide reduction in an acidic environment. The method of the invention includes the use of an electrochemical cell having a cathode, an electrolyte, and an anode, wherein the electrolyte has a pH less than 6, presenting an acidic environment. Although it is generally believed that hydrogen evolution reaction dominates under acidic conditions, which is unfavorable for carbon dioxide reduction, the present invention transforms this environment into a reaction medium favorable for the selective conversion of carbon dioxide to methanol by introducing a unique catalyst.

[0072] The key to this method lies in setting a modified molecular catalyst on the cathode surface. This catalyst comprises metal phthalocyanines, such as cobalt phthalocyanine (CoPc), nickel phthalocyanine (NiPc), iron phthalocyanine (FePc), or derivatives thereof, and further incorporates a cationic imine group via covalent bonds. This imine group has a long-chain alkyl side chain, preferably containing six or ten carbon atoms. Introducing this type of cationic group onto the catalyst via covalent bonding can bring about a dual effect: on the one hand, it can generate electrostatic repulsion, inhibiting the reduction of hydrated hydrogen ions; on the other hand, it can enhance van der Waals interactions to promote the retention of carbon monoxide near the catalytic site.

[0073] By applying an appropriate potential (e.g., relative to a reference electrode, such as a reversible hydrogen electrode, the appropriate potential ranges from -1.2V to -1.5V), this modified molecular catalyst can efficiently drive the electrochemical reduction of carbon dioxide. The hydrophobic and gas-philic interface constructed from long-chain imine groups helps to locally enrich the key intermediate—carbon monoxide, thereby improving the surface coverage of carbon monoxide and the availability of further reactions; at the same time, the interface can effectively repel hydrated hydrogen ions, thereby inhibiting the competitive hydrogen evolution reaction, improving the selectivity of the reaction, and being more conducive to the formation of methanol.

[0074] It is worth noting that this method has significant performance indicators. For example, the conversion process of carbon dioxide to methanol can achieve a methanol Faradaic efficiency of at least 60% and a methanol partial current density of not less than 130 mA·cm⁻², showing that the method has high yield and high energy efficiency. Thus, in a strongly acidic medium environment, its performance is significantly better than the traditional neutral or alkaline carbon dioxide electroreduction method.

[0075] As shown in Figure 1B, the present invention provides a method for electrochemical reactions in a strongly acidic medium to achieve efficient and selective conversion of carbon dioxide to methanol. The key feature of this method is to regulate the interfacial environment around the molecular electrocatalyst, thereby improving its catalytic activity and selectivity under acidic conditions. More specifically, immobilizing cobalt phthalocyanine in the form of an atomically thin layer effectively suppresses the aggregation phenomenon commonly seen under high catalyst loading, while improving electronic conductivity and charge transfer efficiency.

[0076] To further improve catalytic performance, the cobalt phthalocyanine thin layer is post-synthesized and modified by covalently grafting cationic imine functional groups near the cobalt active site. These cationic moieties enhance the local electric field at the catalyst-electrolyte interface, significantly suppressing the hydrogen evolution reaction and expanding the electrochemical reaction window. In addition, by controlling the alkyl chain length of the cationic substituents, the hydrophobicity and gas-lovingness of the interface can be precisely adjusted. The dual regulation strategy of electrostatics and interface properties provides a gas-loving microenvironment, which helps to adsorb and retain carbon monoxide on the catalyst surface, which is quite important for driving the subsequent multi-step cascade reduction of carbon dioxide to methanol.

[0077] Unlike hydrophobic coatings commonly used to hinder mass transfer, the method provided by the present invention retains the diffusion layer.During mass transfer, it also functions as a gas-loving carbon monoxide storage device. This integrated design significantly improves the efficiency of methanol electrosynthesis. Under optimized conditions, in a strongly acidic electrolyte (pH≈1), at a potential of -1.37V (relative to the reversible hydrogen electrode), the partial current density for methanol generation can reach 131.6 mA·cm⁻², and the methanol Faradaic efficiency is 61.5%. At the same time, the Faradaic efficiency of the hydrogen evolution reaction is significantly suppressed to 15.7%, compared to 39.1% for the hydrogen evolution reaction of unmodified cobalt phthalocyanine catalysts.

[0078] This performance is superior to most known systems operating under neutral or alkaline conditions (as shown in Figure 1C). Mechanistic studies, including in-situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy, rotating disk electrode voltammetry, and molecular dynamics simulations, have confirmed that the activity of hydrated hydrogen ions at the interface near the catalyst active site decreases, while the surface coverage of carbon monoxide increases. It is worth noting that this method has good versatility and can be successfully applied to other molecular catalyst systems, such as nickel phthalocyanine (NiPc) catalysts that still produce carbon monoxide as the main product under similar acidic conditions.

[0079] According to a second aspect of the invention, a catalyst for the electroreduction of carbon dioxide is provided, characterized by comprising a layered nanosheet structure constructed from metal phthalocyanines, which may include one or more of cobalt phthalocyanine, nickel phthalocyanine, iron phthalocyanine, or derivatives thereof. These phthalocyanine compounds form a two-dimensional nanosheet structure, which highly exposes the catalytic sites to achieve efficient mass transfer and charge transfer during the electrochemical reaction.

[0080] More importantly, a cationic imine group is introduced into the layered nanosheet structure of the metal phthalocyanine by covalent grafting for post-synthetic modification, wherein the imine group has an alkyl chain with at least six carbon atoms, such as a hexyl (C6) or decyl (C10) chain. Since the modification is covalently bonded, structural stability and interfacial functional stability can be maintained during long-term electrolysis. Introducing these long-chain cationic imine groups has multiple functions: First, the positive charge of the imine cation can regulate the local electric field near the catalyst surface, thereby affecting interfacial ion transport; second, the long alkyl chain endows the catalyst surface with a hydrophobic and gas-loving interface, which can repel water molecules and hydrated hydrogen ions, while effectively enriching carbon monoxide gas near the metal active center.

[0081] This specially designed interfacial microenvironment brings two key functional advantages. First, it effectively suppresses the main side reaction under acidic carbon dioxide electroreduction conditions—hydrogen evolution reaction. This suppression can be attributed to the electrostatic repulsion between the positively charged hydrophobic surface of the catalyst and the hydrophilic hydrated hydrogen ions, as well as the reduction in water splitting activity; second, the gas-loving properties of this interface can promote the retention and enrichment of carbon monoxide on the catalyst surface, thereby facilitating subsequent hydrogenation.The process promotes methanol production. These synergistic effects collectively enhance methanol selectivity and overall catalytic efficiency, enabling the catalytic system to exhibit excellent performance under acidic conditions traditionally considered unfavorable for the reduction of multi-electron carbon dioxide.

[0082] In a particular embodiment, the alkyl chain on the cationic imine group is a hexyl or decyl group having six or ten carbon atoms. These specific chain lengths have been shown in subsequent embodiments to achieve an optimized balance between hydrophobicity and structural integrity, thereby maximizing the desired interfacial effect. Furthermore, the layered nanosheet structure of the metal phthalocyanine catalyst has a thickness ranging from 1 to 2 nanometers, which provides a high specific surface area and minimizes electron and mass transfer resistance during electrocatalysis. Through the synergistic effect of the above structural features, the catalyst system achieves high activity and high selectivity for the electrochemical conversion of carbon dioxide to methanol in acidic media.

[0083] According to a third aspect of the invention, a system for efficiently operating the electrochemical conversion of carbon dioxide to methanol in an acidic environment is also provided. The system includes an electrochemical cell comprising a cathode, an electrolyte, and an anode, wherein the pH of the electrolyte is below 6, i.e., strongly acidic conditions, and the cathode surface is provided with the catalyst as described above.

[0084] The system also includes a gas supply module to directly deliver carbon dioxide gas to the cathode, ensuring a continuous and sufficient supply of reactive gas to the catalyst surface, thereby maintaining a consistent gas concentration at the catalytic interface throughout the electrolysis process and ensuring efficient system operation. In addition, the system is equipped with a power supply for applying a sufficient potential between the cathode and the anode to drive the electrochemical reduction of carbon dioxide to methanol. In a preferred embodiment, the applied potential is typically in the range of -1.2V to -1.5V (relative to the reversible hydrogen electrode) to effectively achieve the reduction and conversion of carbon dioxide in an acidic medium.

[0085] With this system design, a methanol partial current density of at least 130 mA cm⁻² can be achieved, highlighting an important advancement in achieving carbon dioxide electroreduction in an acidic environment; furthermore, the system can maintain a Faraday efficiency of over 60% for methanol generation during continuous operation. The above performance indicators not only reflect the high activity and high selectivity of the catalyst itself, but also demonstrate the good stability and operability of the overall electrochemical system, thus making it particularly suitable for scalable electrochemical conversion applications of converting carbon dioxide to methanol under industrial-related conditions. Specification 8 / 18 pages 10 CN 121428575 A

[0086] Examples

[0087] In the following examples, transmission electron microscopy images were obtained using a Philips™ Technai 12 (accelerating voltage 120 kV) and a JEOL™ JEM-2100F equipped with an energy dispersive spectrometer (EDS) (accelerating voltage 200 kV). Bruker™ was used...Atomic force microscopy images were acquired using the Icon instrument in tap mode. Fourier transform infrared (FTIR) spectra were measured in the 500–4000 cm⁻¹ wavenumber range using a Perkin Elmer™ Spectrum 100 spectrometer with KBr pellets. Solid-state 13C NMR spectra were measured using a Bruker™ Avance III500. The elemental composition of the catalyst was analyzed using X-ray photoelectron spectroscopy (XPS) with an Al X-ray excitation source (1486.6 eV), with all binding energies referenced to the C1 s peak (284.8 eV). UV-Vis spectra were measured using a Shimadzu™ UV1700 instrument. Zeta potentials were recorded using a Malvern Panalytical™ Zetasizer Nano-ZS dynamic light scattering particle size analyzer.

[0088] Faraday efficiency: The Faraday efficiency of methanol production is calculated according to the following formula:

[0089] jCH3OH represents the partial current density of methanol production, jtotal represents the total current, N represents the number of electrons required to produce methanol (N=6 when carbon dioxide is used as raw material; N=4 when carbon monoxide is used as raw material), F represents the Faraday constant (F=96485Cmol-1), nCH3OH is the number of moles of methanol produced, and t is the time (seconds).

[0090] All molecular dynamics simulations were performed using LAMMPS software. A universal force field (UFF) was used to describe all covalent interaction terms (such as bond length, bond angle, and dihedral angle), and also to represent van der Waals interactions. Atomic charges were calculated using the charge balance equation (QEq) proposed by Rappe and Goddard. In addition, the relevant parameters of the charge balance equation can be modified to represent charged N+ species and hydrogen and oxygen atoms in hydrated hydrogen ions. More specifically, the charge balance electronegativity of N+ and hydrated hydrogen ion atoms was adjusted so that the charge that can accumulate on the ions reaches +0.6, in accordance with the charge distribution predicted by Mulliken analysis. All catalysts were surrounded by 500 water molecules, followed by the dissolution of 5 hydrated hydrogen ions and the addition of 9 chloride ions to maintain the electroneutrality of the system. The initial positions of all molecules were randomly generated using Packmol software to avoid spatial distribution bias. The system energy was first minimized, and then heated from 0.1 K to 298.15 K under a canonical ensemble (CNVT) and held at 298.15 K for 2 nanoseconds. The overall density of the system was chosen to be consistent with that of liquid water.

[0091] Example 1: Synthesis and Characterization of Catalysts

[0092] The cationized nanosheets were synthesized by a two-step method. The first step was to react 1,8,15,22-tetraaminophthalocyanine cobalt with 2,5-The di-tert-butyl-1,4-benzoquinone (DTBBQ) condensation is followed by alkylation of the product using alkyl iodides (n-CxH2x+1I, x = 1, 6, 10). This yields the corresponding imine-functionalized materials, named imine cations-Cx. As shown in Figure 2, in imine cation-C1, R1 and R2 are both methyl groups; in imine cation-C6, R1 is n-C6H11 and R2 is methyl; in imine cation-C10, R1 is methyl and R2 is n-C10H21.

[0093] Synthesis of imine: 4 mg of 1,8,15,22-tetraaminophthalocyanine cobalt and 20 mg of 2,5-di-tert-butyl-1,4-benzoquinone were dissolved in a mixed solvent consisting of 5 mL of dimethylacetamide (DMAc), 2 mL of ethanol, and 0.2 mL of 6M acetic acid (Hac). The mixture was transferred to a 20 mL high-pressure Schlenk reaction tube, sonicated for 10 minutes, and subjected to three rounds of freeze-vacuum-thaw degassing. The reaction tube was then sealed and reacted at 120 °C for 72 hours. After cooling to room temperature, diethyl ether was added to precipitate the reactants, and large precipitates were removed by centrifugation at 3,000 rpm for 10 minutes. The imine-linked nanosheets were then recovered by centrifugation at 10,000 rpm for 30 minutes. The nanosheets were then washed three times with N,N-dimethylformamide (DMF) and ethanol to remove residual impurities. The resulting product was vacuum-dried overnight at 60 °C to obtain an imine precursor powder.

[0094] Preparation of imine cation-C1: 30 mg of imine precursor powder was dispersed in 10 mL of N,N-dimethylformamide, and sonicated in a 25 mL round-bottom flask for 10 minutes. Then, 200 μL of iodomethane was added, and the mixture was stirred at 50 °C for 12 hours. After the reaction was complete, diethyl ether was added to precipitate the product. The product was then centrifuged at 12,000 rpm for 30 minutes and washed with ethanol. The final product was freeze-dried to obtain a loose powder, which is the imine cation-C1.

[0095] Synthesis of imine cation-C6: 30 mg of imine precursor powder and 0.2 mL of 1-iodohexane were added to 10 mL of N-methyl-2-pyrrolidone (NMP) and placed in a 50 mL high-pressure Schlenk reaction tube. After sonication for 10 minutes, the tube was subjected to three rounds of freezing-vacuuming-thawing degassing treatment. The reaction tube was sealed and reacted at 120 °C for three days. After the reaction was completed, the product was thoroughly washed with ethyl acetate and dried under vacuum at 60 °C. To achieve complete quaternization, the obtained solid was treated with methyl iodine under the same conditions as imine cation-C1 to obtain imine cation-C6.

[0096] The synthesis method of imine cation-C10 is the same as that of imine cation-C6, except that the alkylating agent used is 1-iododecane instead of 1-iodohexane.

[0097] Transmission electron microscopy (TEM) images (Figs. 3A and 4) show that the imine-modified functionalized material forms a two-dimensional nanosheet structure. Atomic force microscopy (AFM) analysis (Figs. 3B-3C and 5) shows that the alkylated imine nanosheets are approximately 1.3 nm thick, significantly thinner than the unmodified imine material (approximately 6 nm). This decrease in thickness can be attributed to the introduction of in-plane cationic charges, which facilitate the exfoliation and dispersion of the material. Powder X-ray diffraction (PXRD) patterns (Fig. 6) reveal that these covalent organic nanosheets have an amorphous structure. The original imine sample exhibits a broad diffraction peak at 26.4°, while the modified imine cationic sample shows a shifted peak at 21°, indicating an increased interlayer spacing. Elemental mapping by energy-dispersive X-ray spectroscopy (EDS) (Fig. 7) further confirms the uniform distribution of cobalt atoms on the surface of the imine cationic-C6 material.

[0098] In the synthesis of imine cations-C6 and imine cations-C10, an additional methylation step is required to completely convert the imine into an imine cation. This is because alkylation using bulky hexyl or decyl iodoalkanes results in incomplete quaternization due to steric hindrance. For example, as shown in the X-ray photoelectron energy N1s spectrum, only about 30% of the imine is converted into an imine cation when treated with only decyl iodoalkane; however, complete quaternization can be achieved with subsequent methylation. Furthermore, this methylation step can increase the zeta potential of the material from 11.4 mV to 35.5 mV, close to the observed value of imine cation-C1.

[0099] Complete conversion of the imine into an imine cation is crucial for improving the electroreduction performance of carbon dioxide in acidic media. The introduction of the cation charge can effectively reduce the enrichment of hydrated hydrogen ions at the interface, thereby inhibiting the hydrogen evolution reaction. Complete alkylation treatment increased the Faraday efficiency of methanol from 32% to 54%, and the partial current density of methanol also increased from 54 mA·cm⁻² to 115 mA·cm⁻².

[0100] The chemical structure characteristics of the synthesized catalyst were detected by Fourier transform infrared spectroscopy, solid-state 13C nuclear magnetic resonance spectroscopy, and X-ray photoelectron spectroscopy. As shown in Figure 8A, the Fourier transform infrared spectrum of 1,8,15,22-tetraaminophthalocyanine cobalt showed characteristic vibrational absorption peaks of the phthalocyanine ring at 1709, 1608, 1490, 1341, 1261, 825, and 750 cm⁻¹, and N-H stretching vibration peaks appeared at 3324 and 3206 cm⁻¹. In the imine material, the N-H absorption signal disappeared, and an imine (C=N) stretching vibration peak appeared at 1655 cm⁻¹, indicating that the imine bond was indeed formed. In the imine cation sample, new absorption peaks were observed at 945 cm⁻¹ and 1479 cm⁻¹, which were attributed to the C-N⁺ stretching vibration and the bending vibration mode of the alkyl group, respectively. Furthermore, the imine cation-C6 and imine cation-C10 samples showed stronger C-H stretching vibrations at 2922 and 2869 cm⁻¹, respectively.The signal further confirms the successful introduction of the alkyl chain.

[0101] As shown in Figure 8B, the solid-state 13C NMR spectrum shows a broad resonance due to the paramagnetism of the cobalt center, as well as characteristic peaks related to the alkyl chain: imine cation-C1 appears at 59 ppm, imine cation-C6 at 56.1 ppm, and imine cation-C10 at 53.4 ppm. The N1s spectrum in the X-ray photoelectron spectroscopy (Figure 3D) shows that the binding energy peak of the nitrogen atom in the imine cation is located at 401.8 eV. Deconvolution analysis shows that the ratio of imine cation, pyrrole nitrogen, and pyridine nitrogen is approximately 1:1:1, indicating that the imine has been almost completely converted into imine cation. The Co 2p spectrum (Figure 8C) shows that, compared with the unmodified 1,8,15,22-tetraaminophthalocyanine cobalt (Co 2p3 / 2 at 780.4 eV, Co 2p1 / 2 at 795.9 eV), the Co 2p binding energy in the imine cation sample shifts to a lower value, reflecting the strong electron-withdrawing effect of the imine cation group.

[0102] The UV-Vis absorption spectrum (Figure 8D) shows that, compared with 1,8,15,22-tetraaminophthalocyanine cobalt and imine, the Q band of the imine cation sample undergoes a blue shift, further supporting that the functionalization of the imine cation leads to an electron-deficient environment.

[0103] First, the ionic properties of the material surface were evaluated by zeta potential testing (Figures 3E and 9). The measured zeta potential values ​​were -37.7 mV for 1,8,15,22-tetraaminophthalocyanine cobalt, -16.8 mV for imine, 38.4 mV for imine cation-C1, 36.4 mV for imine cation-C6, and 35.5 mV for imine cation-C10, indicating that the material had been successfully converted into an imine cation structure with a positively charged surface. To further evaluate the hydrophobicity and aerophilicity of the material, static water contact angles were tested (Figure 3F). 1,8,15,22-tetraaminophthalocyanine cobalt exhibited hydrophilicity with imine, with contact angles of 31° and 45°, respectively; in contrast, the contact angles of imine cation-C6 and imine cation-C10 reached 112° and 105°, respectively, showing significantly enhanced hydrophobicity.

[0104] To further evaluate the affinity of the material for gaseous carbon dioxide, the catalyst film was immersed in water and its interaction with carbon dioxide bubbles was observed to measure the carbon dioxide contact angle. The results showed that 1,8,15,22-tetraaminophthalocyanine cobalt and imine exhibited anaerobic properties, with carbon dioxide contact angles of 140° and 133°, respectively, indicating weak interaction with the gas. In contrast, the carbon dioxide contact angles of imine cation-C6 and imine cation-C10 were significantly reduced, at 46° and 65°, respectively, indicating stronger aerophilicity and gas wetting ability.

[0105] The above results show that by changing the structure of the imine cation, especially by adjusting the length of its alkyl chain, the surface charge, hydrophobicity, and gas affinity around the active site of the catalyst can be systematically controlled. This structural tunability provides a strategic means for controlling interfacial mass transfer characteristics, which is particularly suitable for carbon dioxide reduction reactions. The relevant performance will be further detailed in subsequent examples.

[0106] Example 2: Electrochemical carbon dioxide reduction performance

[0107] First, the electrocatalytic carbon dioxide reduction performance of the catalyst was evaluated in an H-type battery, using 0.5M potassium bicarbonate as the electrolyte.

[0108] H-type battery configuration: Carbon dioxide reduction reaction test was carried out in a glass H-type battery (model: Gaoss UnionTM C007-10), with 0.5M potassium bicarbonate as the electrolyte and 10 mL of electrolyte for both the anode and cathode. The working electrode was prepared as follows: 10 mg of imine cation-C6 catalyst and 10 mg of multi-walled carbon nanotubes (MWCNTs) were dispersed in 10 mL of anhydrous ethanol, respectively, and labeled as dispersion A and dispersion B. After mixing 0.2 mL of dispersion A with 1.0 mL of dispersion B, 2 μL of 5% (w / v) Nafion solution was added, and the mixture was ultrasonically mixed for 30 minutes to obtain a uniform catalyst ink. Subsequently, 100 μL of the catalyst ink was drop-coated onto the surface of a glassy carbon electrode (geometric area of ​​0.5 cm²) and dried at room temperature. Platinum sheet and silver / silver chloride electrode were used as counter electrode and reference electrode, respectively.

[0109] Before electrochemical testing, the electrolyte at the cathode was bubbled with 99.99% pure carbon dioxide (Linde) for 20 minutes to achieve carbon dioxide saturation. During the test, carbon dioxide was continuously introduced into the cathode chamber at a flow rate of 5 standard cubic centimeters per minute (sccm), and linear scanning voltammetry was used for testing (scan rate of 50 mV / s). The gaseous products were detected by an online gas chromatograph (Shanghai Ruimin Instruments GC 2060), and the liquid products were quantitatively analyzed by a 1H nuclear magnetic resonance spectrometer (Bruker™ AVANCE AVIII 300), with dimethyl sulfoxide (DMSO) as an internal standard. In the NMR test, 450 μL of the electrolyte after the reaction was mixed with 50 μL of a 10 mM DMSO solution prepared in heavy water for analysis.

[0110] Under argon saturation conditions (Figures 10A-10E), the half-wave potential (E1 / 2) corresponding to the Co2+ / Co3+ redox pair of the imine cation-functionalized catalyst was positively shifted compared to that of imine and 1,8,15,22-tetraaminophthalocyanine cobalt, possibly due to the electron-withdrawing effect of the grafted cation groups. The electron potential corresponding to the Co2+ / Co3+ oxidation peak was calculated by integration.The charges were 1,8,15,22-tetraaminophthalocyanine cobalt (0.18 mC), imine (0.23 mC), imine cation-C1 (0.29 mC), imine cation-C6 (0.35 mC), and imine cation-C10 (0.30 mC), respectively, indicating that the density of electrocatalytic active sites in the imine cation functionalized system was significantly improved.

[0111] Further linear sweep voltammetry was performed in carbon dioxide saturated electrolyte (Figures 11 and 12) to compare the carbon dioxide reduction reaction activity of each catalyst. Among them, imine cation-C6 showed the highest onset potential (-0.35 V, relative to the reversible hydrogen electrode) closest to the positive value and the highest current density in the potential range of -0.4 V to -1.2 V. Subsequently, chronoamperometric tests were performed, and the gas phase and liquid phase products were analyzed by online gas chromatography and proton nuclear magnetic resonance. The results showed that only three products—hydrogen, carbon monoxide, and methanol—were detected in all samples. At a potential of -1.0 V, the imine cation-C6 catalyst achieved the highest methanol split current density (11.62 mA·cm⁻²) and methanol Faradaic efficiency (62.3%), and the lowest hydrogen Faradaic efficiency (13.5%). In contrast, the uncationized imine catalyst exhibited a methanol Faradaic efficiency of 20.4% and a hydrogen Faradaic efficiency of 29.4% under the same conditions.

[0112] Analysis of the Tafel slope obtained by fitting the methanol split current density (Figure 13) shows that imine cation-C6 has the most favorable reaction kinetics, with a Tafel slope of 105 mV·dec⁻¹, significantly lower than that of 1,8,15,22-tetraaminophthalocyanine cobalt (276 mV·dec⁻¹), imine (249 mV·dec⁻¹), imine cation-C1 (143 mV·dec⁻¹), and imine cation-C10 (140 mV·dec⁻¹). The lower Tafel slope indicates that the material has better electron transfer capability and more favorable interfacial mass transfer performance, which can be attributed to the ultrathin structure of imine cation-C6 and its gas-loving interface. Electrochemical impedance spectroscopy further verified this conclusion, and the results showed that imine cation-C6 had the lowest charge transfer resistance, only 0.9 Ω, indicating a significant improvement in its electron transport efficiency (Figure 14). The slightly higher Tafel slopes of imine cation-C1 and imine cation-C10 may originate from lower surface carbon monoxide coverage and poorer ionic conductivity, respectively.

[0113] In addition, the carbon dioxide electrolysis performance of each catalyst was evaluated using a flow cell under acidic conditions (pH≈1) (Figures 13D-13F, 15, and 16). In short, the working electrode of the flow cell was prepared as follows: 2.5 mg of catalyst, 2.5 mg of...Carbon black and 25 μL of a 5% (w / w) Nafion solution were added to 1 mL of anhydrous ethanol and ultrasonically dispersed for 30 minutes to obtain catalyst ink. This ink was then coated onto a 1 x 2.5 cm² gas diffusion layer to form a working electrode with an active area of ​​0.5 x 2 cm². The cathode and anode chambers were separated by a proton exchange membrane. The electrolyte used was a 3M potassium chloride + 0.05M sulfuric acid solution. 50 mL of the cathode electrolyte was circulated at a flow rate of 5 mL / min, while the anode electrolyte was maintained at 10 mL / min using a peristaltic pump. Carbon dioxide and carbon monoxide gases were introduced into the liquid electrolyte from the back of the gas diffusion layer at flow rates of 3 standard centimeters per minute and 5 standard centimeters per minute, respectively. The product detection method was the same as for the H-type battery. In addition, electrolysis experiments were conducted under alkaline conditions using a mixed solution of 0.2M potassium hydroxide + 1.5M potassium chloride, with an anion exchange membrane as the separator.

[0114] The test results show that the imine cation-C6 exhibits high methanol selectivity under acidic conditions, and its methanol Faradaic efficiency increases with increasing negative potential, reaching a peak of 61.5% at -1.37V (Figure 13E). In contrast, the 1,8,15,22-tetraaminophthalocyanine cobalt and imine catalysts are less tolerant to acidic conditions, with hydrogen Faradaic efficiencies exceeding 35% at -1.38V; at -1.37V, the methanol fraction current density of the imine cation-C6 reaches 131.6 mA·cm⁻², which is 538% and 961% higher than that of imine (20.7 mA·cm⁻²) and 1,8,15,22-tetraaminophthalocyanine cobalt (12.4 mA·cm⁻²), respectively (Figure 13F).

[0115] To verify the source of methanol, isotope labeling experiments were conducted. The presence of a characteristic double peak at 3.54 ppm and 3.06 ppm in 13CH3OH (Figure 13G) confirmed that the generated methanol originated from carbon dioxide rather than impurity contamination. Long-term stability testing (Figure 17) showed that the imine cation-C6 maintained a stable current density (203.86 mA·cm⁻²) for 8 hours at -1.35 V, with an average methanol Faraday efficiency of 57.3%. Further analysis of the catalyst's structural stability after electrolysis using X-ray photoelectron spectroscopy and UV-Vis absorption spectroscopy (Figure 18) revealed almost no change in the Co 2p X-ray photoelectron spectroscopy peak position, indicating no significant change in the cobalt(II) center. The UV-Vis absorption spectra before and after electrolysis were also largely consistent with those in the specification (pages 12 / 18, CN 121428575 A), indicating good structural stability of the imine cation-C6 under electrochemical operating conditions.

[0116] Example 3: Methanol electrosynthesis under different pH conditions

[0117] Further carbon dioxide reduction and carbon monoxide reduction reactions were carried out under acidic (pH≈1) and alkaline (pH≈13) conditions, and the electrocatalytic methanol production performance of the catalyst was evaluated.

[0118] Carbon monoxide reduction reaction was tested in a self-made H-type battery, where the volumes of the cathode and anolyte were both 1.75 mL. 10 mg of carbon black and 50 μL of Nafion solution were dispersed in 10 mL of anhydrous ethanol and ultrasonically mixed to form a dispersion; then 2 mL of the dispersion was mixed with 0.2 mL of imine cation-C6 catalyst dispersion A and ultrasonically treated for 15 minutes to form a uniform ink. 400 μL of catalyst ink was drop-coated onto a gas diffusion electrode with an area of ​​2 × 2 cm2 as the working electrode.

[0119] The summary results of the comparison between the maximum methanol Faraday efficiency and the methanol partial current density are shown in Figure 13H, and Figures 19 to 30 provide complete electrochemical test data. It is worth noting that all imine cation-functionalized catalysts exhibited higher methanol Faraday efficiency under acidic carbon dioxide reduction reaction conditions, while the unmodified 1,8,15,22-tetraaminophthalocyanine cobalt and imine catalysts performed better under alkaline conditions. This result further verifies that the cationic imine functional group plays a key role in improving the conversion of carbon dioxide to methanol in acidic media. More importantly, the carbon dioxide reduction reaction performance of imine cation-C6 under acidic and alkaline conditions is basically the same, which is attributed to their similar interfacial environment, both having high surface carbon monoxide coverage and low hydride ion concentration. This also shows that imine cation-C6 can achieve efficient multi-electron transfer process to synthesize methanol under strongly acidic conditions, breaking the traditional dependence on alkaline environment for carbon dioxide to methanol conversion.

[0120] To further elucidate the methanol formation mechanism, carbon monoxide reduction reaction tests were also conducted using a flow battery with carbon monoxide gas supply. Under these conditions, the imine cation-C6 achieved the highest methanol Faradaic efficiency (67.3%), the lowest hydrogen Faradaic efficiency (32.7%) representing competitive hydrogen evolution efficiency, and the lowest methanol partial current density (104.9 mA·cm⁻²) at -1.52 V (relative to the reversible hydrogen electrode). Consistent with the results of the carbon dioxide reduction reaction, the imine cation-C6 also exhibited the lowest hydrogen Faradaic efficiency and hydrogen current density in the carbon monoxide reduction reaction (see Figures 24, 27, and 30). Although the methanol partial current density in the carbon monoxide reduction reaction was slightly lower than that in the carbon dioxide reduction reaction, the difference was not significant after normalizing the number of electron transfer steps, indicating that the carbon monoxide to methanol conversion step is likely the rate-limiting step in the entire carbon dioxide to methanol conversion reaction pathway. Furthermore, the results also show that the gas-philic interface introduced by the hydrophobic alkyl chain can effectively enrich the local carbon monoxide concentration, making the surface carbon monoxide coverage in the carbon dioxide reduction reaction close to that of direct carbon monoxide donation.The carbon monoxide reduction reaction under carbon dioxide conditions is used to improve the methanol yield.

[0121] Next, the performance of the methanol electrocatalysts of the present invention and the prior art is compared, and the results are shown in Figure 31 (and the representative catalysts summarized in Figure 1C). Under acidic conditions, the imine cation-C6 catalyst exhibits excellent performance in converting carbon dioxide into methanol, and its methanol Faradaic efficiency and methanol partial current density are the highest among the molecular catalyst systems known to date. It is worth noting that the electrocatalytic activity of the present invention in acidic electrolytes is not only comparable to that in neutral or alkaline systems, but in most cases it can even exceed the latter, highlighting the technical advantages of the strategy of the present invention in realizing the electrosynthesis of methanol by molecular catalysts in strong acid media.

[0122] Example 4: Mechanism Discussion

[0123] Although the imine cation-Cx series catalysts are similar in structure, their performance in the electrocatalytic carbon dioxide reduction reaction is significantly different. Assuming that the difference in methanol generation efficiency is mainly due to external interface factors rather than the difference in cobalt activity itself, in-situ attenuated total reflectance-surface enhanced infrared absorption spectroscopy was performed in an acidic electrolyte (0.5M potassium sulfate + 0.05M sulfuric acid) to study the structure of water molecules at the catalyst interface (see Figures 32A-32B, Figure 33).

[0124] More specifically, attenuated total reflectance surface enhanced infrared absorption spectroscopy was performed using a Nicolet™ iS50 Fourier transform infrared spectrometer equipped with a liquid nitrogen-cooled HgCdTe (MCT) detector. The catalyst ink was prepared as follows: 5 mg of catalyst, 5 mg of carbon black, 50 μL of 5% Nafion solution (by weight) and 10 mL of anhydrous ethanol were mixed evenly; 1 mL of the dispersion was drop-coated onto the surface of a gold-plated thin-film silicon prism (60°, 20 x 0.95 mm) and allowed to air dry naturally. A total of 32 scans were performed to obtain attenuated total reflectance-surface-enhanced infrared absorption spectra with a spectral resolution of 4 cm⁻¹, using the spectra obtained at open circuit potential (OCP) as background.

[0125] It is known that the water structure at the catalyst interface is closely related to the hydrogen evolution reaction activity. Through the stretching vibration signal of water observed in the attenuated total reflectance-surface-enhanced infrared absorption spectra, these vibrations can be decomposed into three peaks centered at 3600, 3450, and 3250 cm⁻¹, corresponding to water molecules in weak, moderate, and strong hydrogen bond states, respectively. The relative proportions of the three water states on different catalyst surfaces are summarized in Figures 32C and 34. Among them, in the potential range of -0.5V to -1.3V (relative to the reversible hydrogen electrode), the imine cation -C6 shows the highest proportion of strong hydrogen bond water molecules, which is unfavorable to the hydrogen evolution reaction due to its high water dissociation energy; in contrast, the proportion of weak hydrogen bond water in 1,8,15,22-tetraaminophthalocyanine cobalt increases significantly from 10.98%.The increase was as high as 22.27%, while the increase of imine cation-C6 was only 4.5% to 8.33%, indicating that the hydrophobic microenvironment provided by imine cation-C6 effectively inhibited the conversion of interfacial water into the "two-H-down" configuration that promotes the hydrogen evolution reaction. In addition, imine cation-C6 also exhibited a lower water molecule Stark tuning rate (see Figure 35), indicating that the interaction between interfacial water molecules and the catalyst surface was weaker.

[0126] To further detect the correlation between the hydrogen evolution reaction activity and the interfacial water structure, a rotating disk electrode test was performed in an argon-saturated 0.5M potassium sulfate + 0.05M sulfuric acid electrolyte (see Figure 32D). The electrode used in the rotating disk electrode test was prepared as follows: 2 mg of catalyst and 2 mg of carbon black were added to 1 mL of anhydrous ethanol and 20 μL of 5% by weight Nafion solution, and ultrasonically dispersed for 20 minutes to obtain a uniform ink; then, 10 μL of ink was drop-coated onto a rotating disk electrode (Pine Research) with a diameter of 5 mm and dried at room temperature. The electrolyte was saturated with argon gas and subjected to linear scan voltammetry at a scan rate of 10 mV / s. The acidic, neutral, and alkaline electrolytes used were 0.5 M potassium sulfate + 0.05 M sulfuric acid, 0.5 M potassium sulfate, and 0.1 M potassium hydroxide + 0.45 M potassium sulfate, respectively.

[0127] Due to the reduction of hydrated hydrogen ions, the hydrogen evolution reaction initiation potential was approximately -0.3 V. Among the tested samples, the imine cation -C6 showed the closest positive initiation potential (-0.38 V) and exhibited the lowest current density in the range of -0.4 V to -1.35 V, indicating that its hydrated hydrogen ion reduction kinetics were the slowest. Furthermore, the hydrogen evolution reaction activity of the imine cation -C1 was lower than that of imine and 1,8,15,22-tetraaminophthalocyanine cobalt, further confirming that the cationic imine group can inhibit hydrated hydrogen ions through electrostatic repulsion. At more negative potentials, hydrated hydrogen ions are depleted, causing the hydrogen evolution reaction to become a diffusion-limited stage, with the current density approaching a plateau (approximately -200 mA·cm⁻²). Under higher overpotentials, water reduction becomes the dominant reaction. In contrast, the rotating disk electrode curves under neutral and alkaline conditions (Figure 36) did not show a current plateau, indicating that water reduction is the dominant reaction pathway. Notably, imine cation-C6 exhibited the lowest current density under all pH conditions, indicating that it is the most effective at inhibiting the water reduction process. In summary, imine cation-C6 effectively inhibits the hydrogen evolution reaction by repelling hydrated hydrogen ions through its cation structure and regulating the configuration of interfacial water molecules.

[0128] In addition to the interfacial water effect, the hydrophobic alkyl chain on the imine cation group can also enhance local gas solubility and promote the enrichment of intermediates. The enhancement of intermediate signals in the in-situ attenuated total reflectance surface-enhanced infrared absorption spectrum further enhances the signal of intermediates.Further evidence supports the above conclusions (see Figures 32E, 32F, and 37). Characteristic peaks at approximately 1,960 and 1,640 cm⁻¹ were observed in all imine-cation-modified catalysts, corresponding to adsorbed carbon monoxide and water molecules, respectively. Furthermore, a significant signal for the formyl intermediate adsorbed on the catalyst surface was observed at approximately 1,760 cm⁻¹, an intermediate that was often difficult to detect in previous studies of molecular carbon dioxide reduction reactions, mainly due to low catalyst loading and limited gas solubility. Isotope substitution experiments using heavy water (Figure 32G) on pages 14 / 18 of the specification (CN 121428575 A) further validated the above indications. The O-H stretching vibration peak at approximately 3,500 cm⁻¹ shifted to approximately 2,600 cm⁻¹ (O-D), and the C=O stretching vibration of the formyl group adsorbed on the catalyst surface shifted from 1,760 cm⁻¹ to 1,737 cm⁻¹ (CDO). The imine cation -C6 in a neutral electrolyte (0.5M potassium bicarbonate) was analyzed by attenuated total reflectance surface-enhanced infrared absorption spectroscopy, as shown in Figure 38. Similar peak positions and evolution trends were observed, consistent with its electrochemical performance in achieving efficient methanol synthesis in both acidic and neutral electrolytes (see Figures 13A and 13E).

[0129] Further analysis of the integral area of ​​the characteristic peaks of carbon monoxide and formyl intermediates adsorbed on the catalyst surface by in-situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy was performed to evaluate the coverage concentration of intermediates on the catalyst surface (see Figures 32H and 39). Among the tested catalysts, 1,8,15,22-tetraaminophthalocyanine cobalt showed weak carbon monoxide adsorption only at potentials of -1.2V and -1.3V, and no signal of adsorbed formyl groups was observed within the measured potential window. For the imine cation-C1 catalyst, the adsorbed carbon monoxide reached stability at -1.0V, but the adsorbed formyl group signal was significantly lower than that of imine cation-C6 and imine cation-C10, indicating that the hydrogenation step of converting adsorbed carbon monoxide to adsorbed formyl groups was inhibited on imine cation-C1. Possible reasons include competitive adsorption of adsorbed carbon dioxide, desorption of adsorbed carbon monoxide, or surface coverage by hydrogen. In contrast, imine cation-C6 exhibited higher formyl group coverage, and the formyl group / carbon monoxide coverage ratio was also better than other samples (see Figure 32H). The above results show that the longer alkyl chain on imine cation-C6 helps to increase the local carbon monoxide surface concentration, thereby promoting the multi-electron reduction pathway and achieving efficient methanol production.

[0130] To further clarify the role of alkyl chain length in increasing the local carbon monoxide concentration, a series of pyridinium salt electrolytes were used on a platinum electrode for carbon monoxide oxidation experiments (see Figure 32I). In short, the carbon monoxide oxidation test used a directA 5 mm diameter platinum rotating disk electrode was used as the working electrode, and the electrolyte was a 5 mM pyridinium salt solution. Specifically, the pyridine system used a mixed solution of 5 mM pyridine and 5 mM sodium fluoroborate.

[0131] As shown in Figure 43, after switching the supply gas from argon to carbon monoxide, a carbon monoxide oxidation peak appeared. Integrated charge densities of 1.37, 2.06, 3.13, and 4.46 mC·cm⁻² were observed in pyridine, pyridinium cation-C1, pyridinium cation-C6, and pyridinium cation-C10 solutions, respectively. These results show that the surface coverage of carbon monoxide increases with the increase of the alkyl chain length of the pyridinium cation. Furthermore, the cyclic voltammetric curves of pyridinium cation-C6 and pyridinium cation-C10 exhibit a significant hysteresis phenomenon between the pre-scan and reverse scans, typically reflecting the "poisoning" effect caused by surface carbon monoxide enrichment. In contrast, the cyclic voltammetry curves of pyridine cation-C1 and pyridine showed a strong PtOx reduction cathode peak near approximately 0.76 V, reflecting lower carbon monoxide coverage and higher water adsorption capacity. These results indicate that the imine cation-C6, with its higher proportion of long-chain alkyl modification, effectively enhances the carbon monoxide dissolution and retention capacity at the catalyst interface. This conclusion is consistent with the phenomenon revealed by in-situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy and further explains the excellent performance of imine cation-C6 in the methanol generation reaction.

[0132] Example 5: Mechanism Exploration

[0133] Molecular dynamics simulations were used to further evaluate the local microenvironment around the catalytic site. Specifically, under conditions of 298.15 K and simulated liquid water density, the effects of imine cation catalysts with different alkyl chain lengths on the spatial distribution of water and hydrated hydrogen ions were analyzed (see Figures 40A-40C). The radial distribution function (RDFs, g(r)) of water shows that the imine cation-C1 exhibits a major solvation shell peak at approximately , while the imine cation-C6 and imine cation-C10 also exhibit additional peaks at approximately , showing strong hydrophobicity to disrupt the structure of water molecules near the catalyst surface.

[0134] The distribution of hydrated hydrogen ions near the positively charged quaternary ammonium imine cation sites was analyzed by radial distribution function, and the results showed significant differences between different catalysts. For the imine cation-C1, the first peak at approximately corresponds to the second solvation shell of hydrated hydrogen ions located at the N+ center (see Figure 40C); after this peak, the radial distribution function value first drops to zero, and then gradually increases between approximately , indicating that the hydrated hydrogen ions move away from the vicinity of the N+ center to avoid electrostatic repulsion.

[0135] The radial distribution function curve of the imine cation-C6 shows a double peak at approximately and , indicating that the hydrated hydrogen ions are located at approximately and .The ions are still mainly distributed in the second solvation shell, but their positions fluctuate more than those of the imine cation-C1. The peak values ​​of the two peaks are 2.74 and 1.29, respectively, which are significantly lower than the single peak value of 4.12 for the imine cation-C1, indicating that the residence frequency of hydrated hydrogen ions in this region is reduced, which is consistent with the phenomenon of the longer alkyl chain inhibiting the hydrogen evolution reaction observed in the experiment. In addition, a secondary compensation peak appears at about , which may be due to the redistribution caused by the further migration of hydrated hydrogen ions from the N+ region. Thereafter, the radial distribution function curve gradually rises again at .

[0136] For the imine cation-C10, the peak value at about completely disappears, indicating that the solvation shell of N+ is completely destroyed and hydrated hydrogen ions cannot approach this region. On the contrary, it shows a stronger compensation peak at about (radial distribution function value of 0.53), which is higher than that of the imine cation-C6 (0.37), indicating that hydrated hydrogen ions are further repelled and moved away. Subsequently, the radial distribution function value continues to rise at a greater distance.

[0137] The radial distribution function trend described above is consistent with the enhanced inhibition of hydrogen evolution reaction observed in experiments as the alkyl chain length increases. Molecular dynamics simulations also confirm that as the alkyl chain length increases, hydrated hydrogen ions are further repelled to positions away from the catalyst surface due to the disruption of hydrogen bond structure and electrostatic repulsion. Furthermore, the diffusion coefficient of hydrated hydrogen ions was calculated using a two-dimensional thermodynamic method (see Figure 40D), and the results show that the longer the alkyl chain, the worse the diffusivity of hydrated hydrogen ions, further hindering their reduction kinetics at the electrode interface.

[0138] To study the interaction between carbon monoxide and the catalyst, the radial distribution function of carbon monoxide molecules around the imine cation-Cx catalyst was further calculated (see Figure 40E). For the imine cation -C1, a peak appears at approximately 0.5, indicating that the carbon monoxide molecule is located near the molecular plane. In the imine cations -C6 and -C10, a new peak appears at approximately 0.5, due to the interaction between carbon monoxide and the hydrophobic alkyl chain. This indicates that the alkyl chain can act as a gaseous storage, increasing the local concentration of carbon monoxide as a reaction intermediate, thereby promoting the multi-step reduction reaction. Using a two-dimensional thermodynamic method, the entropy and Helmholtz free energy of the carbon monoxide molecule were calculated in the last 100 ps (5 × 20 ps time interval) (see Figure 40F). The results show that as the alkyl chain length increases, the entropy of carbon monoxide gradually decreases, from 15.5 cal·mol⁻¹·K⁻¹ for imine cation -C1 to 15.2 for imine cation -C6, and then to 14.8 for imine cation -C10. This indicates a decrease in the translational degree of freedom of carbon monoxide, reflecting its enhanced binding with the alkyl chain. Consequently, the Helmholtz free energy also gradually increases, consistent with the thermodynamic relationship A = U - TS. These results are consistent with the enhanced carbon monoxide coverage observed in the aforementioned carbon monoxide oxidation test (Figure 32I), explaining at the molecular level the role of imine cations -C6 and -C10 in methanol production.Performance advantages in the reaction.

[0139] To further test the broad applicability of this method, the carbon dioxide electroreduction catalyst known to have carbon monoxide selectivity, nickel phthalocyanine, was further functionalized by introducing an imine cation group. In acidic electrolyte, the imine cation-C6 (nickel) maintained high carbon monoxide selectivity (greater than 90%, see Figure 41) in the potential range of -1.25 to -1.95 V, and reached the highest carbon monoxide current density (380 mA·cm⁻²) at a potential of -1.95 V; in contrast, the unmodified 4-β-aminometal phthalocyanine nickel had poor stability under acidic conditions, with a highest carbon monoxide current density of only 142.6 mA·cm⁻², and was easily affected by the hydrogen evolution reaction at higher overpotentials. As shown in Figure 42, the rotating disk electrode test can further verify that the imine cation-C6 (nickel) exhibits lower hydrogen evolution reaction activity compared to 4-β-aminometal phthalocyanine nickel.

[0140] In summary, this invention proposes a novel interface engineering strategy for constructing an electrocatalytic microenvironment that combines cationicity, hydrophobicity, and gas affinity, thereby achieving efficient electroreduction of carbon dioxide to methanol in acidic media. The introduced positively charged imine cation sites effectively repel hydrated hydrogen ions, thus inhibiting the hydrogen evolution reaction; simultaneously, the hydrophobic long-chain alkyl groups can form a gas-rich layer on the catalyst surface, effectively increasing the local carbon monoxide concentration. The synergistic effect of charge repulsion and van der Waals gas retention enables the system to achieve a methanol Faradaic efficiency of 61.5% and a methanol current density of 131.6 mA·cm⁻² at -1.37V in a strongly acidic electrolyte with pH≈1. Furthermore, this method can be extended to other molecular systems, as shown in the relevant examples of functionalized nickel phthalocyanine, demonstrating the feasibility and versatility of this invention in achieving high-performance carbon dioxide electroreduction by controlling the force field distribution at the solvent-catalyst interface.

[0141] Compared with the prior art, the present invention has the following advantages:

[0142] High efficiency under strong acid conditions

[0143] Traditional carbon dioxide electroreduction technology mostly relies on neutral or alkaline electrolytes, mainly because violent hydrogen evolution reaction and catalyst corrosion are prone to occur under strong acid conditions. The present invention breaks through the problem of high efficiency carbon dioxide electrocatalytic reduction reaction in a strong acid environment (pH≈1). This operation not only simplifies the electrolyte treatment process, but also avoids the problem of carbonate by-product generation common in neutral and alkaline systems, thereby improving the utilization rate of carbon dioxide.

[0144] High selectivity and high methanol yield

[0145] The system achieves a methanol partial current density of 132 mA·cm⁻² and a Faraday efficiency of 62% at a potential of -1.37V (relative to the reversible hydrogen electrode), showing that the present invention has a substantial improvement over the existing methods, while the existing methods are in acidic conditions.It is usually difficult to achieve both high selectivity and productivity in a medium, and improving selectivity and productivity helps to reduce energy consumption and improve the economics of methanol synthesis.

[0146] Effective suppression of hydrogen evolution reaction

[0147] A key innovation of this invention is to significantly suppress the hydrogen evolution reaction by constructing a covalently bonded hydrophobic cation interface. This structure can repel hydrated hydrogen ions and prevent them from approaching the catalyst surface, thereby reducing the generation of side reaction hydrogen and thus improving the selectivity of carbon dioxide reduction to methanol.

[0148] Universal applicability and environmental friendliness

[0149] The molecular catalysts used in this invention (such as cobalt phthalocyanine) can be functionalized through a universal post-synthetic modification strategy without relying on complex nanostructures or precious metal materials, and have good commercial prospects. In addition, this method helps to capture carbon dioxide and utilize resources, supporting the reduction of greenhouse gas emissions and green transformation in the industrial sector.

[0150] Cost-effective and promising for industrial application

[0151] The improvements in selectivity, efficiency and ease of operation of this invention, especially its operation in acidic environments without the need for neutralization treatment or complex electrolyte management, make it a low-cost alternative to existing technologies. This invention has significant practical implications and application value for industries seeking low-carbon methanol production pathways and reducing dependence on fossil resources.

[0152] As used herein, the terms “approximately,” “substantially,” and “about / approximately” are used to describe and explain a small variation, and when used in conjunction with an event or situation, the term can refer to the exact occurrence of the event or situation, or approximately the occurrence of the event or situation. The term “about / approximately” as used herein with respect to a given value or range generally refers to a range of ±10%, ±5%, ±1%, or ±0.5% of the given value or interval, which can be understood herein as from one endpoint to another or between two endpoints. Unless otherwise stated, all ranges disclosed in this disclosure include endpoints. When referring to numerical values ​​or characteristics that are "basically" the same, the term may refer to values ​​within ±10%, ±5%, ±1%, or ±0.5% of the average value. Furthermore, unless otherwise explicitly stated, the term "a" as used herein should be understood to include one or more; additionally, terms such as "first," "second," and "third" are used only as illustrative purposes and are not intended to give numerical meaning or to order them according to their importance. Specification 17 / 18 pages 19 CN 121428575 A

[0153] The above description is provided for illustration and description of the invention and is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations will be apparent to those skilled in the art.

[0154] The above embodiments were chosen and described in order to best explain the principles of the invention and its practical application, thereby enabling the present invention to...Others skilled in the art will be able to understand the various embodiments of the invention and the various modifications suitable for the intended particular purpose. Instruction Manual 18 / 18 Page 20 CN 121428575 A Figure 1A Figure 1B Instruction Manual Drawing 1 / 80 Page 21 CN 121428575 A Figure 1C Figure 2 Instruction Manual Drawing 2 / 80 Page 22 CN 121428575 A Figure 3A Figure 3B Instruction Manual Drawing 3 / 80 Page 23 CN 121428575 A Figure 3C Figure 3D Instruction Manual Drawing 4 / 80 Page 24 CN 121428575 A Figure 3E Instruction Manual Drawing 5 / 80 Page 25 CN 121428575 A Figure 3F Instruction Manual Drawing 6 / 80 Page 26 CN 121428575 A Figure 4A Figure 4B Figure 4C Instruction Manual Drawing 7 / 80 Page 27 CN 121428575 A Figure 5A Figure 5B Instruction Manual Drawing 8 / 80 Page 28 CN 121428575 A Figure 6 Figure 7A Appendix to the Instruction Manual, Page 9 / 80, 29 CN 121428575 A Figure 7B Figure 7C Figure 7D Appendix to the Instruction Manual, Page 10 / 80, 30 CN 121428575 A Figure 8A Figure 8B Appendix to the Instruction Manual, Page 11 / 80, 31 CN 121428575 A Figure 8C Figure 8D Appendix to the Instruction Manual, Page 12 / 80, 32 CN 121428575 A Figure 9 Figure 10A Appendix to the Instruction Manual, Page 13 / 80, 33 CN 121428575 A Figure 10B Figure 10C Appendix to the Instruction Manual, Page 14 / 80, 34 CN 121428575 A Figure 10D Figure 10E Appendix to the Instruction Manual, Page 15 / 80, 35 CN 121428575 A Figure 11A Figure 11B Appendix to the Instruction Manual, Page 16 / 80, 36 CN 121428575 A Figure 11C Figure 11D Instruction manual figures 17 / 80, page 37, CN 121428575 A, Figure 11E, Figure 11F; Instruction manual figures 18 / 80, page 38, CN 121428575 A, Figure 12A, Figure 12B; Instruction manual figures 19 / 80, page 39, CN 121428575 A, Figure 12C, Figure 12D; Instruction manual figures 20 / 80, page 40, CN 121428575 A, Figure 12E, Figure 13A; Instruction manual figures 21 / 80, page 41, CN 121428575 AFigure 13B Figure 13C Appendix to the Instruction Manual, Page 22 / 80, 42 CN 121428575 A Figure 13D Figure 13E Appendix to the Instruction Manual, Page 23 / 80, 43 CN 121428575 A Figure 13F Figure 13G Appendix to the Instruction Manual, Page 24 / 80, 44 CN 121428575 A Figure 13H Figure 14 Appendix to the Instruction Manual, Page 25 / 80, 45 CN 121428575 A Figure 15A Figure 15B Appendix to the Instruction Manual, Page 26 / 80, 46 CN 121428575 A Figure 15C Figure 15D Appendix to the Instruction Manual, Page 27 / 80, 47 CN 121428575 A Figure 15E Figure 15F Appendix to the Instruction Manual, Page 28 / 80, 48 CN 121428575 A Figure 16A Figure 16B Appendix to the Instruction Manual, Page 29 / 80, 49 CN 121428575 Figure 16A Figure 16D Instruction Manual Drawings 30 / 80 Pages 50 CN 121428575 Figure 16E Figure 17 Instruction Manual Drawings 31 / 80 Pages 51 CN 121428575 Figure 18A Figure 18B Instruction Manual Drawings 32 / 80 Pages 52 CN 121428575 Figure 20A Instruction Manual Drawings 33 / 80 Pages 53 CN 121428575 Figure 20B Figure 20C Instruction Manual Drawings 34 / 80 Pages 54 CN 121428575 Figure 20D Figure 20E Instruction Manual Drawings 35 / 80 Pages 55 CN 121428575 Figure 20F Figure 21A Instruction Manual Drawings 36 / 80 Pages 56 CN 121428575 Figure 21B Figure 21C Instruction Manual Drawings 37 / 80 Pages 57 CN 121428575 Figure Figure 21D Figure 21E Instruction Manual Drawings, Page 38 / 80, 58 CN 121428575 A Figure 22A Figure 22B Instruction Manual Drawings, Page 39 / 80, 59 CN 121428575 A Figure 23A Figure 23B Instruction Manual Drawings, Page 40 / 80, 60 CN 121428575 A Figure 23C Figure 23D Instruction Manual Drawings, Page 41 / 80, 61 CN 121428575 A Figure 23E Figure 23F Instruction Manual Drawings, Page 42 / 80, 62 CN 121428575 A Figure 24A Figure 24B Instruction Manual Drawings, Page 43 / 80, 63 CN121428575 A Figure 24C Figure 24D Instruction Manual Drawings 44 / 80 Page 64 CN 121428575 A Figure 24E Figure 25A Instruction Manual Drawings 45 / 80 Page 65 CN 121428575 A Figure 25B Figure 26A Instruction Manual Drawings 46 / 80 Page 66 CN 121428575 A Figure 26B Figure 26C Instruction Manual Drawings 47 / 80 Page 67 CN 121428575 A Figure 26D Figure 26E Instruction Manual Drawings 48 / 80 Page 68 CN 121428575 A Figure 26F Figure 27A Instruction Manual Drawings 49 / 80 Page 69 CN 121428575 A Figure 27B Figure 27C Instruction Manual Drawings 50 / 80 Page 70 CN 121428575 A Figure 27D Figure 27E Instruction Manual Drawings 51 / 80 Page 71 CN 121428575 A Figure 28A Figure 28B Instruction Manual Drawings 52 / 80 Page 72 CN 121428575 A Figure 29A Figure 29B Instruction Manual Drawings 53 / 80 Page 73 CN 121428575 A Figure 29C Instruction Manual Drawings 54 / 80 Page 74 CN 121428575 A Figure 29D Instruction Manual Drawings 55 / 80 Page 75 CN 121428575 A Figure 29E Figure 29F Instruction Manual Drawings 56 / 80 Page 76 CN 121428575 A Figure 30A Figure 30B Instruction Manual Drawings 57 / 80 Page 77 CN 121428575 A Figure 30C Figure 30D Instruction Manual Drawings 58 / 80 Page 78 CN 121428575 A Figure 30E Figure 31 Instruction Manual Drawings 59 / 80 Page 79 CN 121428575 A Figure 32A Instruction Manual Drawings, Page 60 / 80, 80 CN 121428575 A Figure 32B Instruction Manual Drawings, Page 61 / 80, 81 CN 121428575 A Figure 32C Figure 32D Instruction Manual Drawings, Page 62 / 80, 82 CN 121428575 A Figure 32E Figure 32F Instruction Manual Drawings, Page 63 / 80, 83 CN 121428575 A Figure 32G Figure 32H Instruction Manual Drawings, Page 64 / 80, 84 CN 121428575 A Figure 32I Figure 32J Instruction Manual Drawings, Page 65 / 80, 85 CN 121428575Figure 33A, Instruction Manual Drawing, Page 66 / 80, CN 121428575; Figure 33B, Instruction Manual Drawing, Page 67 / 80, CN 121428575; Figure 34, Figure 35A, Instruction Manual Drawing, Page 68 / 80, CN 121428575; Figure 35B, Figure 35C, Instruction Manual Drawing, Page 69 / 80, CN 121428575; Figure 36A, Figure 36B, Instruction Manual Drawing, Page 70 / 80, CN 121428575; Figure 37A, Figure 37B, Instruction Manual Drawing, Page 71 / 80, CN 121428575; Figure 38, Figure 39A, Instruction Manual Drawing, Page 72 / 80, CN 121428575; Figure 39B, Figure 40A, Instruction Manual Drawing, Page 73 / 80, CN 121428575; Figure 40B Figure 40C Appendix to the Instruction Manual, Page 74 / 80, 94 CN 121428575 A Figure 40D Figure 40E Appendix to the Instruction Manual, Page 75 / 80, 95 CN 121428575 A Figure 40F Figure 41A Appendix to the Instruction Manual, Page 76 / 80, 96 CN 121428575 A Figure 41B Figure 41C Appendix to the Instruction Manual, Page 77 / 80, 97 CN 121428575 A Figure 41D Appendix to the Instruction Manual, Page 78 / 80, 98 CN 121428575 A Figure 41E Figure 42 Appendix to the Instruction Manual, Page 79 / 80, 99 CN 121428575 A Figure 43 Appendix to the Instruction Manual, Page 80 / 80, 100 CN 121428575 A Abstract: Abdominal ultrasound examination method, system and device. The present invention provides a method for electrochemically converting carbon dioxide (CO2) to methanol in an acidic electrolyte environment (pH < 100). 6). The method involves the use of an electrochemical cell equipped with a cathode provided with a modifiedcatalyst, which includes a metal phthalocyanine covalently functionalized with cationic iminium groups. These introduced functional groups create a hydrophobic and aerophilic interface that enhances local carbon monoxide (CO) availability at the catalyst surface while simultaneously suppressing the competing hydrogen evolution reaction (HER). By applying an appropriate electrical potential, the electrochemical cell effectively performs selective and efficient CO2-to-methanol conversion under strongly acidic conditions.

Claims

1. A method of electrochemical reduction of carbon dioxide to produce methanol in an acidic electrolyte, characterized in that, Comprising: providing an electrochemical cell comprising a cathode, an anode, and an acidic electrolyte having a pH value lower than 6; providing a modified molecular catalyst on the cathode, wherein the modified molecular catalyst comprises a metal phthalocyanine functionalized with a cationic imine group covalently attached; applying an electric potential to the electrochemical cell to drive a conversion reaction of carbon dioxide to methanol at the cathode; wherein the surface of the modified molecular catalyst has a hydrophobic-glypohilic interface to increase the local availability of carbon monoxide and suppress hydrogen evolution reaction.

2. The method of claim 1, wherein the conversion reaction of carbon dioxide to methanol can achieve a methanol faradaic efficiency of at least 60% and a methanol partial current density of at least 130 mA / cm -2 2. The method of claim 1, wherein the conversion reaction of carbon dioxide to methanol can achieve a methanol faradaic efficiency of at least 60% and a methanol partial current density of at least 130 mA / cm -2 2. The method of claim 1, wherein the conversion reaction of carbon dioxide to methanol can achieve a 3. The method of claim 1, wherein the metal phthalocyanine comprises one or more of cobalt phthalocyanine, nickel phthalocyanine, iron phthalocyanine, and derivatives thereof.

4. The method of claim 1, wherein the cationic imine group comprises an alkyl chain having at least 6 carbon atoms.

5. The method of claim 4, wherein the alkyl chain comprises 6 or 10 carbon atoms.

6. The method of claim 1, wherein the hydrophobic-glypohilic interface increases the surface coverage of carbon monoxide through van der Waals interaction forces and suppresses the reduction of hydronium ions through electrostatic repulsion forces.

7. The method of claim 1, wherein the electric potential ranges between -1.2 volts and -1.5 volts relative to the potential of a reversible hydrogen electrode.

8. A catalyst for electrochemical carbon dioxide reduction reaction, characterized by, Comprising: a layered nanosheet structure of a metal phthalocyanine comprising one or more of cobalt phthalocyanine, nickel phthalocyanine, iron phthalocyanine, and derivatives thereof; wherein the layered nanosheet structure of the metal phthalocyanine is post-synthetically modified by a cationic imine group of an alkyl chain having at least 6 carbon atoms covalently grafted; wherein the cationic imine group forms a hydrophobic-glypohilic interface on the surface of the catalyst; and wherein the catalyst suppresses hydrogen evolution reaction and enhances methanol selectivity under acidic conditions.

9. The catalyst of claim 8, wherein the alkyl chain comprises 6 or 10 carbon atoms.

10. The catalyst of claim 8, wherein the layered nanosheet structure of the metal phthalocyanine has a thickness of 1 nanometer to 2 nanometers.

11. A system for electrochemical conversion of carbon dioxide to methanol, characterized in that, Comprising: an electrochemical cell comprising a cathode, an anode, and a liquid electrolyte having a pH value lower than 6, wherein the cathode is provided with the catalyst of claim 8; a gas supply device that continuously provides carbon dioxide to the cathode; and a power source that applies an electric potential between the cathode and the anode; wherein the system achieves a methanol partial current density of at least 130 mA / cm -2 2.

12. The system of claim 11, wherein the system can be operated continuously and the Faradaic efficiency of methanol is over 60%.

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