Method for improving reduction catalytic performance of cobalt phthalocyanine electro-catalysis carbon dioxide through molecular co-adsorption strategy

Abstract

The invention relates to a method for improving the catalytic performance of cobalt phthalocyanine in electrocatalysis of carbon dioxide reduction through a molecular co-adsorption strategy, in particular to an efficient electrocatalysis carbon dioxide reduction system formed by co-adsorbing functional molecules melamine and cobalt phthalocyanine on the surface of a multi-walled carbon nanotube through pi-pi interaction, and belongs to the technical field of catalytic energy. According to the invention, cobalt phthalocyanine (CoPc) and melamine (MLA) are used, and CoPc and MLA are co-adsorbed on the surface of a multi-walled carbon nanotube (MWCNT) through a method of co-adsorption in a solution, so that the MWCNT-coated CoPc-MLA catalyst is formed. In the reaction of electrocatalytically reducing carbon dioxide into carbon monoxide, the adsorption of MLA molecules can regulate and control the electronic structure of the Co center, so that the Faraday efficiency of CO is improved. And the Faraday efficiency and the current density are remarkably improved under different overpotentials. The smooth implementation of the patent provides a universal, simple, convenient and efficient strategy for regulating and improving the Faraday efficiency (FE) of reducing carbon dioxide into carbon monoxide through electro-catalysis, solves the problem of unstable structure of the conventional system, and provides greater possibility for industrialization in the field of electro-catalysis carbon dioxide reduction.

Description

Technical Field

[0001] The present invention relates to a method for improving the electrocatalytic performance of cobalt phthalocyanine for carbon dioxide reduction by a molecular co-adsorption strategy, and particularly to an efficient electrocatalytic carbon dioxide reduction system formed by co-adsorbing a functional molecule and cobalt phthalocyanine on the surface of multi-walled carbon nanotubes through π-π interaction, belonging to the field of catalytic energy technology. Background Art

[0002] Electrochemical reduction of carbon dioxide (CO2) is a technical route with dual benefits. It can not only effectively reduce the concentration of CO2 in the atmosphere to alleviate the greenhouse effect, but also convert CO2 into high-value chemicals, providing an innovative solution to address climate change and energy crises. What makes this technology particularly attractive is its ability to use electricity generated from clean energy sources such as solar and wind energy as the reaction driving force. Based on these advantages, the electrocatalytic CO2 reduction reaction (CO2RR) has become a research hotspot in recent years. Currently, the catalytic systems developed in this field mainly cover three major types: inorganic nanomaterial catalysts, organic molecular catalysts, and porous crystalline materials such as metal-organic frameworks (MOFs) and covalent organic frameworks (COFs). Among them, organic molecular catalysts exhibit unique advantages due to their simple synthesis and outstanding structural tunability. However, it should be noted that to achieve industrial application, the current key issues still need to be addressed are the improvement of catalytic efficiency and selectivity.

[0003] Transition metal phthalocyanine complexes are regarded as a class of highly potential catalytic materials due to their excellent chemical stability. However, in practical applications, their catalytic performance still needs to be optimized. Research has shown that the catalytic activity and product selectivity can be effectively improved by precisely regulating the molecular structure. Traditional modification methods mainly rely on introducing specific functional groups into the complex, but this often requires cumbersome organic synthesis steps and usually needs to use organic solvents under harsh reaction conditions. It is worth noting that there is still significant room for improvement in the reaction rate and selectivity of existing metal phthalocyanine catalytic systems. Therefore, the development of molecular catalysts with simple synthesis and high-efficiency and directional conversion of CO2 has become the current research focus.

[0004] Herein, the present invention proposes a novel and convenient strategy to improve the catalytic performance of CoPc in electrochemical CO2RR. We co-adsorb the modified molecule melamine (MLA) and CoPc on MWCNT, and significantly improve the catalytic activity and Faraday efficiency for CO by changing the electronic structure of the central Co atom through the modified molecule. Summary of the Invention

[0005] The technical problem solved by the present invention is: a method for improving the electrocatalytic performance of cobalt phthalocyanine for carbon dioxide reduction. The MWCNT@CoPc-MLA catalyst of the present invention has a Faradaic efficiency of up to 92% for CO at an overpotential of -1.33 V vs Ag|AgCl. The adsorption of MLA molecules can change the electronic structure of Co in CoPc, promote the adsorption of *CO on Co, inhibit the reaction activity of the hydrogen evolution reaction (HER), lower the reaction energy barrier of CO2RR, accelerate the reaction kinetics, and improve the reaction stability of the catalyst. The photocatalyst MWCNT@CoPc-MLA of the present invention has better catalytic activity than the latest catalysts reported currently.

[0006] To solve the above technical problems, the technical solution proposed by the present invention is: a method for improving the electrocatalytic performance of cobalt phthalocyanine for carbon dioxide reduction by a molecular co-adsorption strategy. Different masses of cobalt phthalocyanine and modified molecular powder are dissolved in 1 mL of DMF to obtain a mixed solution with a modified molecular content of 0% - 40%. 1 mg of catalytic support is added to the mixed solution, and after ultrasonic dispersion and centrifugation, it is washed with DMF and ethanol to form a composite material co-adsorbed on the surface of the catalytic support. The electrocatalytic carbon dioxide reduction reaction experiment is carried out in a 60 mL H-type reactor, and the overpotential is provided by an electrochemical workstation.

[0007] Preferably, the preparation process of the MWCNT@CoPc-MLA catalyst: 0.04 mg of CoPc and 18 μL of 0.1 mmol melamine are dissolved in 1 mL of DMF and ultrasonicated for 30 minutes. Then, 1 mg of MWCNT is added to this solution and ultrasonicated again for 30 minutes. The obtained product is washed twice with DMF and then twice with ethanol. The washed product is finally dissolved in 1 mL of ethanol to finally obtain the MWCNT@CoPc-MLA catalyst.

[0008] Preferably, the MWCNT@CoPc-MLA is finally loaded on carbon paper for the reaction: 3 μL of 5% Nafion solution is added to the prepared 1 mL of MWCNT@CoPc-MLA catalyst, and then ultrasonicated for 30 minutes to obtain a black suspension. This suspension is used as the composite catalyst. 400 μL of the obtained MWCNT@CoPc-MLA catalyst suspension is drop-coated on a 1 cm 2 carbon paper for deposition. The drop-coated electrode is dried in air at 140 °C for 10 minutes.

[0009] Preferably, the process of the electrocatalytic carbon dioxide reduction experiment is as follows: A standard H-type electrolytic cell (dual-chamber design, single-chamber volume 60 mL) is used, and the experimental system is controlled by an electrochemical workstation (CHI 630E, Shanghai Chenhua Instrument). The test system adopts a three-electrode configuration: the catalyst-modified electrode is the working electrode, and the platinum wire electrode and the Ag|AgCl electrode are used as the counter electrode and the reference electrode respectively. To isolate the anode and cathode chambers, a Nafion N117 perfluorosulfonic acid proton exchange membrane (product of DuPont Company, USA) is used for separation. In the experiment, 0.1 M potassium bicarbonate (KHCO3) solution is selected as the electrolyte, and high-purity CO2 gas is continuously introduced for 15 minutes before the test to ensure the saturation of the solution. During the formal test, 25 mL of CO2-saturated electrolyte is injected into each chamber of the electrolytic cell, and then a preset potential is applied for electrochemical performance characterization. After the reaction for 15 min, off-line gas chromatography (GC-9860 5CNJ, Nanjing Haerpu Analytical Equipment Co., Ltd.) is used for gas analysis.

[0010] Advantages of the present invention:

[0011] 1. The adsorption of MLA can change the electronic structure of Co in CoPc, enhance the catalytic activity of the Co central atom, and promote its charge separation. In addition, the adsorption of MLA molecules can also inhibit the reaction activity of HER and reduce the occurrence of side reactions.

[0012] 2. The method for adsorbing MLA molecules is very simple and convenient, making this composite material have great potential value in many practical applications. The successful implementation of this patent will provide a simple and efficient strategy for enhancing the activity of the electrocatalytic carbon dioxide reduction reaction, and solve the problem that the previous regulation of CoPc in this system relied on organic synthesis methods, reducing the synthesis difficulty of this type of catalyst and providing the possibility for efficient and stable electrocatalytic carbon dioxide reduction reaction.

[0013] 3. The MWCNT@CoPc-MLA prepared by this patent has a Faraday efficiency of up to 92% for CO at an overpotential of 1.33 V vs Ag|AgCl. In addition, the catalyst is stable after 50 hours of catalytic cycling, greatly improving the stability of the original electrocatalyst. The catalytic activity and stability of our composite photocatalyst are superior to the reported CoPc-based catalysts. Description of the Drawings

[0014] The present invention will be further described below with reference to the drawings.

[0015] Figure 1 It is a schematic diagram of the highly efficient carbon dioxide reduction reaction of the MWCNT@CoPc-MLA structure.

[0016] Figure 2The morphology of MWCNT@CoPc-MLA. (a) TEM image of MWCNT@CoPc-MLA; (b) TEM-EDS image of MWCNT@CoPc-MLA.

[0017] Figure 3 Surface structure analysis of MWCNT@CoPc-MLA. (a) Co 2p XPS image; (b) UV-vis image

[0018] Figure 4 This is the performance test of the electrocatalytic carbon dioxide of MWCNT@CoPc-MLA. (a) Faradaic efficiency of CO of MWCNT@CoPc-MLA at different voltages; (b) Local reaction current density of CO of MWCNT@CoPc-MLA at different voltages; (c)

[0019] Figure 5 It is the stability test of MWCNT@CoPc-MLA in the flow electrolytic cell.

[0020] Figure 6 is the electrocatalytic performance of MWCNT@CoPc with different MLA contents. DETAILED DESCRIPTION

[0021] Example 1

[0022] The synthesis of MWCNT@CoPc-MLA is to dissolve 0.04 mg of CoPc and 18 μL of 0.1 mmol of melamine in 1 mL of DMF and sonicate for 30 minutes. Then, 1 mg of MWCNT is added to the solution and sonicated again for 30 minutes. The resulting product is washed twice with DMF and then twice with ethanol. The washed product is finally dissolved in 1 mL of ethanol. Next, 3 μL of 5% Nafion solution is added, followed by sonication for 30 minutes to obtain a black suspension, which is used as a composite catalyst. Take 400 μL of the obtained MWCNT@CoPc-MLA catalyst suspension and drop it on a 1 cm 2 The electrode was then dried in air at 140 °C for 10 min.

[0023] Our electrocatalytic carbon dioxide reduction experimental process is:

[0024] The experiment was carried out using a standard H-type electrolytic cell (double-chamber design, single-chamber volume 60 mL), and the experimental system was controlled by an electrochemical workstation (CHI 630E, Shanghai Chenhua Instrument). The test system adopted a three-electrode configuration: the catalyst-modified electrode was the working electrode, and the platinum wire electrode and Ag / AgCl electrode were used as the counter electrode and reference electrode respectively. To isolate the anode and cathode chambers, a Nafion N117 perfluorosulfonic acid proton exchange membrane (product of DuPont Company, USA) was used for separation. 0.1 M potassium bicarbonate (KHCO3) solution was selected as the electrolyte for the experiment, and high-purity CO2 gas was continuously introduced for 15 minutes before the test to ensure the solution was saturated. During the formal test, 25 mL of CO2-saturated electrolyte was injected into each chamber of the electrolytic cell, and then a preset potential was applied for electrochemical performance characterization. After the reaction for 15 min, gas analysis was carried out using an off-line gas chromatograph (GC-9860 5CNJ, Nanjing Haerpu Analytical Equipment Co., Ltd.).

[0025] As Figure 1 is a schematic diagram of the highly efficient carbon dioxide reduction reaction of the MWCNT@CoPc-MLA structure. The adsorption of MLA improves the reaction activity of CO2RR.

[0026] As Figure 2 is the morphology of MWCNT@CoPc-MLA. The microscopic morphology of the MWCNT@CoPc-MLA composite material was observed by transmission electron microscopy (TEM). The results showed that the overall morphology of the carbon nanotubes was clearly visible, and their diameter range was between 20 nanometers and 50 nanometers. It was obvious from the TEM image that only a small amount of CoPc and MLA molecules were adsorbed on the surface of MWCNT, indicating that the adsorption process was controllable and did not cause a significant impact on the basic structure of the carbon nanotubes, and no obvious aggregation of CoPc was found. In addition, energy dispersive X-ray spectroscopy (EDS) analysis showed that cobalt (Co), carbon (C), and nitrogen (N) elements existed in the composite material, further confirming the successful preparation of the MWCNT@CoPc-MLA structure

[0027] As Figure 3 is the surface structure analysis of MWCNT@CoPc-MLA. By analyzing the Co 2p XPS spectra, it was found that the relative peak intensity of Co 3+ in the MWCNT@CoPc-MLA sample was significantly higher than that of the sample without co-adsorbed melamine. In addition, the binding energy of all deconvoluted peaks shifted about 0.65 eV towards higher energy, indicating that electrons transferred from Co atoms to the adsorbed molecules, that is, a charge transfer phenomenon occurred, resulting in an increase in the valence of Co in CoPc. Ultraviolet-visible (UV-vis) spectroscopy analysis showed that when MLA molecules were co-adsorbed, the absorption peak of CoPc-modified MWCNT underwent a 7 nm blue shift, also indicating a decrease in the electron density of the Co ion center in CoPc.

[0028] As Figure 4 is the FE of electrocatalytic CO2RR before and after melamine adsorption. The FE of the catalyst loaded with melamine for CO is always greater than that of the catalyst without melamine loading. However, the FE does not increase monotonically with the decrease of the applied potential. As the applied potential decreases from -1.03 V to -1.33 V vs Ag|AgCl, the FE for CO increases from 72% to 92%. Further decreasing the applied potential results in a decrease in FE. At an applied potential of -1.33 V vs Ag|AgCl, this FE is significantly greater than the maximum FE (85%) without melamine loading.

[0029] The electrocatalytic stability test of this experiment was carried out in a flow electrolytic cell with a reaction time of 50 hours. During these 50 hours, the flow rate of CO2 was maintained at 30 sccm, and samples were taken at intervals for analysis and testing on an off-line gas chromatograph (GC-98605CNJ, Nanjing Haerpu Analytical Equipment Co., Ltd.).

[0030] As Figure 5 The test results shown indicate that after 50 hours of electrocatalytic reaction, neither the reaction current nor the Faraday efficiency of CO of the MWCNT@CoPc-MLA catalyst has decreased significantly, confirming the high stability of this catalyst in the reaction.

[0031] Comparative Example 1

[0032] The adsorption of melamine molecules will affect the electronic structure of the catalyst and the electrocatalytic carbon dioxide reduction performance. We expect that it is feasible to regulate the electrocatalytic carbon dioxide reduction performance of the catalyst by adjusting the adsorption amount of melamine molecules. As Figure 6 We prepared MWCNT@CoPc-MLA catalysts with different loadings of melamine molecules, which represent the molecular percentage of MLA molecules among all the loaded molecules. At -1.23 V vs Ag|AgCl, it usually provides the best performance. As the loading of melamine molecules increases from 0 to 20%, the partial current density for generating CO increases significantly, approximately at -1.23 V vs Ag|AgCl. When the melamine loading is further increased, this current density will decrease instead. In addition, when the loading of MLA molecules is changed, the FE for CO also changes. When the loading of melamine increases from 0 to 20%, the FE for CO increases from 76% to 90%. Further increasing the melamine loading results in a decrease in the FE for CO. Therefore, the maximum output current density and the FE for CO are obtained when the melamine loading is 20%.

[0033] The present invention is not limited to the specific technical solutions described in the above embodiments. Any technical solutions formed by equivalent substitution are within the protection scope required by the present invention.

Claims

1. A method for improving the electrocatalytic performance of cobalt phthalocyanine in carbon dioxide reduction by a molecular co-adsorption strategy, characterized in that : Cobalt phthalocyanine and modifier molecules are co-adsorbed on the surface of the catalytic support by co-adsorption in solution to form the MWCNT@CoPc-MLA catalyst. Under an applied overpotential, the method for promoting the electrocatalytic reduction of carbon dioxide to carbon monoxide by co-adsorbing molecules on the catalyst surface is as follows: Dissolve different masses of cobalt phthalocyanine and modifier molecule powders in 1 mL of DMF to obtain a mixed solution with a modifier molecule content of 0% - 40%. Add 1 mg of the catalytic support to the mixed solution, disperse it by ultrasound and then centrifuge, and wash it with DMF and ethanol to form a composite material co-adsorbed on the surface of the catalytic support. The electrocatalytic carbon dioxide reduction reaction experiment is carried out in a 60 mL H-type reactor, and the overpotential is provided by an electrochemical workstation.

2. The method for improving the electrocatalytic performance of cobalt phthalocyanine for carbon dioxide reduction by the molecular co-adsorption strategy according to claim 1, characterized in that: Take different masses of cobalt phthalocyanine and modifier molecule powders and dissolve them in 1 mL of DMF. Add 1 mg of the catalytic support to the mixed solution, disperse it by ultrasound and then centrifuge. The electrocatalytic carbon dioxide reduction reaction experiment is carried out in a 60 mL H-type reactor.

3. The method for improving the electrocatalytic performance of cobalt phthalocyanine for carbon dioxide reduction by the molecular co-adsorption strategy according to claim 1, characterized in that: Melamine molecules and cobalt phthalocyanine are co-adsorbed on the surface of multi-walled carbon nanotubes through π-π conjugation.

4. The method for improving the electrocatalytic performance of cobalt phthalocyanine for carbon dioxide reduction by the molecular co-adsorption strategy according to claim 1, characterized in that: Dissolve 0.04 mg of the catalyst and 18 μL of 0.1 mmol molecules in 1 mL of DMF and sonicate for 30 minutes. Then, add 1 mg of the catalyst support to this solution and sonicate again for 30 minutes. The resulting product is washed twice with DMF and then twice with ethanol. The washed product is finally dissolved in 1 mL of ethanol. Then, add 3 μL of the binder and subsequently sonicate for 30 minutes to obtain a black suspension, which is used as the composite catalyst.

5. The method for improving the electrocatalytic performance of cobalt phthalocyanine for carbon dioxide reduction by the molecular co-adsorption strategy according to claim 1, characterized in that: The molecule is melamine, the main catalyst center is cobalt phthalocyanine, the catalyst reaction support is multi-walled carbon nanotubes, and the binder is a 5% nafion solution.

6. The method for improving the electrocatalytic performance of cobalt phthalocyanine for carbon dioxide reduction by the molecular co-adsorption strategy according to claim 1, characterized in that: The black suspension MWCNT@CoPc-MLA is finally loaded on carbon paper for the reaction.

7. The method for improving the electrocatalytic performance of cobalt phthalocyanine for carbon dioxide reduction by the molecular co-adsorption strategy according to claim 1, wherein: The process of the electrocatalytic carbon dioxide reduction experiment is as follows: It is carried out using a standard H-type electrolytic cell (double-chamber design, single-chamber volume 60 mL), and the experimental system is controlled by an electrochemical workstation (CHI 630E, Shanghai Chenhua Instrument). The test system adopts a three-electrode configuration: the catalyst-modified electrode is the working electrode, and the platinum wire electrode and the Ag|AgCl electrode are used as the counter electrode and the reference electrode respectively. To isolate the anode and cathode chambers, a Nafion N117 perfluorosulfonic acid proton exchange membrane (product of DuPont, USA) is used for separation. 0.1 M potassium bicarbonate (KHCO3) solution is selected as the electrolyte for the experiment, and high-purity CO2 gas is continuously introduced for 15 minutes before the test to ensure the solution is saturated. During the formal test, 25 mL of the CO2-saturated electrolyte is injected into each chamber of the electrolytic cell, and then the preset potential is applied for electrochemical performance characterization. After the reaction for 15 min, gas analysis is carried out using an off-line gas chromatograph (GC-9860 5CNJ, Nanjing Haerpu Analytical Equipment Co., Ltd.).

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