Polymetallic phthalocyanine-coated nitrogen-doped porous hollow carbon spheres and preparation method and use thereof

Abstract

The present invention relates to polymetallic phthalocyanine encapsulated nitrogen-doped porous hollow carbon spheres and their preparation methods and uses. In the present invention, dopamine hydrochloride is used as the nitrogen source and carbon source, and SiO₂ spheres are used as the template. By optimizing the carbonization temperature, the regulation of the physical and chemical properties of NHCSs is achieved, thereby optimizing the activity of metal sites. The metal salts used in the present invention are one of cobalt chloride, nickel chloride and ferric chloride. By regulating the precursor ratio and hydrothermal synthesis conditions, specific M (M = Co, Fe and Ni) PPC / NHCSs heterogeneous molecular catalyst materials are obtained, realizing the electrocatalytic conversion of CO₂ into CO.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of catalytic materials for electrocatalytic reduction of CO2 to CO, specifically to polymetallic phthalocyanine-coated nitrogen-doped porous hollow carbon spheres and their preparation methods, and their application in anion exchange membrane electrolytic cells for electrocatalytic conversion of CO2 to CO at high current. Background Art

[0002] Electrochemically reducing CO2 into C1 chemicals and fuels such as carbon monoxide (CO), formic acid (HCOOH), and methane (CH4) by electrical energy converted from renewable energy, thereby reducing greenhouse gas emissions. Among them, CO, as a product of simple two-electron transfer, has been proven to be a product with the potential for industrialization because it can be directly utilized or reprocessed, as well as its satisfactory productivity and low electricity cost (Adv. Mater. 2021, 33(41): 2102212). Currently, the emergence of high current (>100 mA cm –2 ) for the reduction product has pointed the way for industrial CO2 electrocatalytic reduction reaction (CO2RR) (Adv. Funct. Mater. 2023, 33(4): 2208781). However, to achieve industrialization of CO2RR, it is still affected by the high activation barrier (806 kJ mol –1 , Angew. Chem. Int. Ed. 2021, 60: 2–24.) of CO2 molecules with stable C═O bonds, and the low solubility of CO2 molecules in aqueous electrolytes. In addition, the competitive hydrogen evolution reaction (HER) also poses a huge challenge to improving the Faraday efficiency (FE) of the reduction product. Developing electrocatalytic CO2 reduction catalysts with high activity, high selectivity, and high stability and electrolytic cells with industrial application prospects remains a hot issue in recent research.

[0003] Existing commercial electrochemical technologies provide a blueprint for electrocatalytic CO2RR. Anion exchange membrane electrolyzers are most similar to water electrolyzers for producing hydrogen and oxygen in terms of both electrocatalytic conversion principles and electrolyzer components. There is a zero gap between the anode and cathode, which greatly reduces the ohmic resistance of the reaction and saves energy consumption. Currently, companies such as Siemens, Proton Onsite, Teledyne, Nel Hydrogen, and Hydrogenics are selling commercial-scale water electrolyzers. Moreover, products for electrocatalytic CO2RR already exist in many petrochemical supply chains, so the chemical industry infrastructure is more adaptable to electrocatalytic CO2RR. Meanwhile, more industrially mature electrocatalytic technologies, such as chlor-alkali cells, hydrogen electrolyzers, and fuel cells, provide examples and directions for the development of CO2 electrochemical synthesis from the laboratory scale to the commercial scale. However, various problems may occur during the operation of AEM at high current densities, leading to a decrease in the stability of the electrolyzer, and most of the tested stabilities are less than 10 h (J. Am. Chem. Soc. 2022, 144: 10446–10454, Angew. Chem. Int. Ed. 2022, 61, e202202298, Energy & Environmental Science, 2023). Developing catalysts for electrocatalytic CO2 reduction with high activity, high selectivity, and high stability is an important guarantee for its high-current operation and stable operation. Summary of the Invention

[0004] The present invention relates to a preparation method and use of a catalytic material for electrocatalytic reduction of CO2 to CO, specifically a preparation method of polymetallic phthalocyanine (MPPc)-coated nitrogen-doped porous hollow carbon spheres (NHCSs) and their application in anion exchange membrane electrolyzers for high-current electrocatalytic CO2→CO.

[0005] The technical solution provided by the present invention is as follows:

[0006] The preparation method of the polymetallic phthalocyanine material for high-current electrocatalytic CO2→CO according to the present invention specifically comprises the following steps:

[0007] (1) Using tetraethyl orthosilicate (TEOS) under alkaline conditions to generate silica spheres (SiO2) as templates. Hydrochloric acid dopamine (DA) is used as the precursor of the spherical shell, and under alkaline conditions, it polymerizes and grows on the surface of the SiO2 spheres to form polydopamine (PDA)@SiO2 spheres (SiO2@PDA). The SiO2@PDA is then calcined at high temperature under inert conditions and treated with hydrogen fluoride (HF) to obtain nitrogen-doped porous hollow carbon spheres (NHCSs).

[0008] (2) NHCSs, metal salts, and 1,2,4,5-tetracyanobenzene were successively added to the solvent, and the material ratios among NHCSs, metal salts, and 1,2,4,5-tetracyanobenzene were regulated. Under hydrothermal conditions, the metal ions and 1,2,4,5-tetracyanobenzene underwent a polymerization reaction to form polymetallic phthalocyanine on the surface of NHCSs. After vacuum filtration, rinsing, and drying, the MPPc / NHCSs material was obtained. The solvent, hydrothermal time, and temperature were regulated to optimize the structure of the polymetallic phthalocyanine molecules and their polymerization structure on the surface of NHCSs, thereby realizing the optimization of the active sites, improving the stability of the central sites, and meeting the requirements of the cathode catalyst material for the long-term stable operation of the anion exchange membrane electrolytic cell at high currents.

[0009] In the present invention, dopamine hydrochloride was used as the nitrogen source and carbon source, and SiO2 spheres were used as the template. By optimizing the carbonization temperature, the regulation of the physicochemical properties of NHCSs was realized, thereby achieving the optimization of the activity of the metal sites. The metal salts used in the present invention were one of cobalt chloride, nickel chloride, and ferric chloride. By regulating the precursor ratio and hydrothermal synthesis conditions, a specific M (M = Co, Fe, and Ni) PPc / NHCSs heterogeneous molecular catalyst material was obtained.

[0010] Preferably, in step (1), the size of SiO2 was controlled at 200 - 500 nanometers (nm); the size of NHCSs was controlled at 200 - 500 nm, and the surface mesopore size was controlled at 2 - 4 nm; the inert condition refers to using nitrogen, argon, or helium as the inert protective gas.

[0011] Preferably, in step (2), the metal salt was any one of cobalt chloride, nickel chloride, and ferric chloride; the solvent was selected from any one of ethanol and water; NHCSs was 50 - 150 milligrams (mg), the metal salt was 10 - 40 mg, and 1,2,4,5-tetracyanobenzene was 56 - 225 mg. The hydrothermal temperature was 140 - 200 degrees Celsius (°C), the time was 6 - 8 hours (h), and the solvent volume was 40 - 50 milliliters (mL).

[0012] The present invention also provides the use of the polymetallic phthalocyanine-coated nitrogen-doped porous hollow carbon spheres as a cathode catalyst material for the electrocatalytic reduction of CO2 to CO.

[0013] The preparation method of the polymetallic phthalocyanine-coated nitrogen-doped porous hollow carbon spheres of the present invention as a cathode catalytic material is as follows: The MPPc / NHCSs material obtained in the above steps is mixed with a certain amount of ionomer and solvent to prepare an electrode ink, which is coated on an electrode carrier to construct a cathode gas diffusion electrode (GDE). First, it is used in an "H"-type electrolytic cell to carry out the reaction of electrocatalytic reduction of CO2 to prepare CO, and the electrocatalytic performance of the material is tested. Specifically, a Pt electrode is used as the counter electrode, the cathode gas diffusion electrode is used as the working electrode, an Ag / AgCl electrode is used as the reference electrode, and a CO2-saturated aqueous salt solution is used as the electrolyte. The "H"-type electrolytic cell is connected to an electrochemical workstation (CHI1140C) to carry out the test reaction of electrocatalytic reduction of CO2 to CO, and the types and contents of the products are monitored and analyzed by on-line gas chromatography and liquid chromatography, and the Faraday efficiency of electrochemical conversion is calculated.

[0014] In the present invention, the design and optimization of the anion exchange membrane electrolytic cell are based on the previous anion exchange membrane electrolytic cell construction technology (the use of a metal aerogel catalytic material for the electrocatalytic reduction of CO2 reaction in an anion exchange membrane electrolytic cell, application number: 202110759115.9). An anion exchange membrane electrolytic cell was independently constructed and the size of the mold was optimized. The specific model is shown in Figure 1 . The overall reaction volume of the electrolytic cell is controlled at 7 cm × 7 cm × 5 cm. From left to right, there are a metal baffle (with a thickness of 1 cm), a cathode serpentine gas flow field plate (with a thickness of 1.5 cm), a silica gel sealing sheet, a cathode electrode gas diffusion electrode, an anion exchange membrane (AEM membrane), an anode electrode, a silica gel sealing sheet, an anode liquid flow field plate (with a thickness of 1.5 cm), and a metal baffle (with a thickness of 1 cm). The cathode reaction area is 1 cm × 1 cm, the control area of the serpentine gas flow field is 1 cm × 1 cm, and the depth is controlled at 0.5 cm. Follow the principle of connecting the inlet gas at the top and the outlet gas at the bottom. The gas inlet at the upper part of the flow field is connected to humidified CO2 gas, and the lower side is the outlet for collecting the product gas and on-line gas chromatography for monitoring the product. An anion exchange membrane (AEM membrane) with a size of 1.5 cm × 1.5 cm is used as the separation membrane and is placed between the cathode and anode electrodes. The back side of the cathode electrode (the side opposite to the side closely attached to the AEM membrane) is connected to a conductive copper foil, which is used as a current collector. The silica gel sealing sheet, the cathode electrode, and the AEM membrane are sealed together with non-conductive tape, so that when disassembling and assembling the device and flushing the serpentine channel, the cathode electrode will not be damaged. Using nickel foam (NF) as the substrate, a NiFe / LDH / NF electrode is prepared by the traditional electrostatic deposition method (Nature Communications 6 (2015): 1-7) and used as the anode of the membrane electrolytic cell. The upper end of NiFe / LDH / NF is connected to a copper foil, which extends outside the flow field and is used as a current collector. The assembly sequence of the anion exchange membrane electrolytic cell is shown in Figure 1After the assembly of the anion exchange membrane electrolytic cell is completed, humidified CO2 is connected to the external field of the cathode. At the gas outlet, a liquid collection bottle is connected to collect the overflowing liquid. The flow rate of the outlet of the on-line gas chromatograph is measured to quantitatively analyze the components of the reduced gas. A flowing electrolyte is applied to the anode side, and a peristaltic pump is used to control the liquid flow rate. A Shanghai Chenhua (CHI 1140C) electrochemical workstation is connected to an on-line gas chromatograph for testing. The working lines of the reference electrode and the counter electrode are connected to the anode, and the working electrode is connected to the cathode to construct an MPPc / NHCSs / CC||FeNi / LDH / NF system to test the electrocatalytic reduction reaction activity and stability of CO2→CO in the anion exchange membrane electrolytic cell.

[0015] Preferably, for the cathode made of MPPc / NHCSs material, the electrode support is one of carbon paper, carbon felt, carbon cloth, and carbon fiber. Preferably, the electrode support does not participate in the electrocatalytic CO2 reduction reaction, has good conductivity, and can ensure the uniform dispersion of the catalyst material.

[0016] Preferably, for the method of making the cathode from MPPc / NHCSs, a commercial perfluorinated acid resin Nafion solution (5wt%) is used as the ionomer to stabilize the catalyst on the surface of the electrode. The catalyst (2 - 4 mg), Nafion solution (20 - 60 μL) are added to an ethanol (1 - 3 mL) solution, and ultrasonically mixed for 1 h to obtain a uniform electrode ink. The electrode ink is coated on the electrode support and dried to obtain the cathode.

[0017] As a preference, in the H-type electrolytic cell test, the loading amount of the poly-metallophthalocyanine encapsulated nitrogen-doped porous hollow carbon sphere material on the electrode support is 0.1 - 1 mg cm -2 。

[0018] As a preference, in the anion exchange membrane electrolytic cell, the loading amount of the poly-metallophthalocyanine encapsulated nitrogen-doped porous hollow carbon sphere material on the electrode support is 0.1 - 2 mg cm -2 。

[0019] The technical progress achieved by the present invention using the above technical solution compared with the existing technology lies in:

[0020] (1) The poly-metallophthalocyanine encapsulated nitrogen-doped porous hollow carbon spheres prepared in the present invention optimize the binding mode between the catalytic sites of the poly-metallophthalocyanine molecules and the substrate compared with the traditional non-covalent fixation technology, which is beneficial to stabilizing the macrocyclic molecules on the surface of the substrate, inhibiting the precipitation problem of the poly-metallophthalocyanine molecular catalyst during the electrocatalytic CO2 process, and improving the stability of the catalyst under high current operation.

[0021] (2) The poly-metallophthalocyanine encapsulated nitrogen-doped porous hollow carbon spheres prepared by the present invention are used for the electrocatalytic CO2→CO reaction. In an H-type electrolytic cell, the optimal composition of the poly-metallophthalocyanine molecular catalyst encapsulated nitrogen-doped porous hollow carbon spheres can not only achieve high selectivity for the electrocatalytic CO2→CO reaction (the Faraday efficiency of CO can reach >95% at most), but also the molecular active sites are evenly dispersed, greatly improving the utilization rate of the catalyst and saving costs. In the anion exchange membrane electrolytic cell test, the test current range is 20 - 150 mA cm -2 , and the Faraday efficiency of the optimal catalyst for the electrocatalytic CO2→CO reaction is >95%; under the test conditions of a constant current of -100 mA cm -2 , the optimal catalyst can stably operate for up to 110 h, and the Faraday efficiency of CO is stable above 80%. Description of the Drawings

[0022] Figure 1 is a model diagram of the anion exchange membrane electrolytic cell.

[0023] Figure 2 is the infrared spectrum diagram of CoPPc in the material of Example 1.

[0024] Figure 3 is the scanning electron microscope (SEM) photograph (left figure) and high-angle annular dark-field scanning (HADDF-TEM, right figure) of CoPPc / NHCSs in the material of Example 1, and the scales are 100 nm and 50 nm respectively.

[0025] Figure 4 is the aberration-corrected transmission electron microscope (AC HADDF-TEM) photograph of CoPPc / NHCSs in the material of Example 1, and the scale is 5 nm.

[0026] Figure 5 is the synchrotron radiation data diagram of CoPPc / NHCSs and Co foil standard sample in the material of Example 1.

[0027] Figure 6 is the test performance diagram of CoPPc / NHCSs in the H-cell electrolytic cell in the material of Example 1.

[0028] Figure 7 is the test performance diagram of CoPPc / NHCSs in the anion exchange membrane electrolytic cell in the material of Example 1.

[0029] Figure 8 is the test stability diagram of CoPPc / NHCSs in the anion exchange membrane electrolytic cell in the material of Example 1.

[0030] Figure 9SEM image of CoPPc / NHCSs-2 in the material of Example 2. The scale bar is 1 μm.

[0031] Figure 10 SEM image of NiPPc / NHCSs in the material of Example 3.

[0032] Figure 11 SEM image of FePPc / NHCSs in the material of Example 4.

[0033] Figure 12 Test performance graph of NiPPc / NHCSs in the H-cell electrolytic cell for the material of Example 3.

[0034] Figure 13 Test performance graph of FePPc / NHCSs in the H-cell electrolytic cell for the material of Example 4. Detailed implementation manners

[0035] Example 1:

[0036] Preparation of NHCSs sample: Add 35 mL of deionized water, 5 mL of ammonia water (25 - 28 wt%), and 100 mL of ethanol into a 250 mL single-neck flask. After stirring for 30 minutes, a homogeneous solution is obtained. Immediately, add 5 mL of TEOS to the above mixed solution, continuously stir for 1 h to obtain a SiO2 sphere suspension, and then ultrasonicate for 3 min. Then add 0.5 g of hydrochloric acid dopamine and continuously stir for 12 h. Under alkaline conditions, hydrochloric acid dopamine will undergo a polymerization reaction and grow on the surface of SiO2. The sample is collected by centrifuging at 7000 rpm for 3 min. The sample is washed with water once and with alcohol once, and finally dried at 60 °C to obtain the SiO2@PDA sample. Immediately, the SiO2@PDA sample is carbonized at a high temperature of 400 °C for 2 h under a nitrogen inert atmosphere, with a heating rate of 1 °C / min. Then, at a high temperature of 800 °C, it is carbonized for 3 h, with a heating rate of 5 °C / min. The obtained carbonized sample is then treated with 4 mol / L HF for 72 h to remove the SiO2 hard template. The NHCSs sample is collected by vacuum filtration, rinsed with clear water 30 times, and then rinsed with ethanol 3 times to remove the residual acid, and finally dried at 60 °C. The obtained NHCSs have a size of 394 ± 31 nm and a surface mesopore size of ~3.74 nm.

[0037] Preparation of cathode catalytic material CoPPc / NHCSs: Weigh 100 mg of NHCSs, 16 mg of cobalt chloride, and 90 mg of 1,2,4,5-tetracyanobenzene, add them to 50 mL of ethanol solution, ultrasonicate for 30 min, stir for 30 min, then transfer to a 100 mL hydrothermal autoclave and hydrothermally react at 180 °C for 8 h. Finally, through vacuum filtration, the sample is rinsed successively with 2 mol / L hydrochloric acid and hot ethanol (60 °C) solution, and finally rinsed with deionized water and ethanol (at room temperature), and dried at 60 °C to finally obtain cobalt phthalocyanine-coated nitrogen-doped porous hollow carbon spheres—CoPPc / NHCSs.

[0038] Performance test of H-type electrolytic cell: Take 3 mg of the obtained CoPPc / NHCSs sample, add 30 μL of Nafion (5 wt%) ionomer and 3 mL of ethanol, ultrasonicate for 1 h to obtain catalyst ink. The obtained ink is coated on a commercial carbon paper of 3 cm × 1 cm, and the coating area is 1 cm 2 , and the catalyst loading is 0.45 mg cm -2 . Dry at room temperature to prepare a working electrode. It is combined with an Ag / AgCl reference electrode and a Pt counter electrode to form a three-electrode system, and all the measured potentials are converted to a reversible hydrogen electrode (RHE). The linear sweep voltammetry range is -0.2 to -1.16 V vs. RHE, and the scan rate is 5 mV s -1 . The test potentials are -0.5, -0.6, -0.7, -0.75, -0.8, -0.85, -0.9, and -1.0 V vs. RHE, and the products are monitored by on-line gas chromatography. The potentiostatic test is set at -0.8 V vs. RHE, and the electrolyte is replaced every 20 h, and the electrode surface is rinsed with deionized water.

[0039] Performance test of anion exchange membrane electrolytic cell: Weigh 3 mg of CoPPc / NHCSs catalyst, add it to 3 mL of ethanol containing 50 μL of Nafion (5 wt%) solution and mix, ultrasonicate for 1 h to obtain a uniform catalyst ink. A low content of Nafion is used to stabilize the catalyst on the electrode surface and at the same time has a conductive effect. Then use an airbrush to spray the catalytic ink onto a commercial hydrophobic carbon paper (CC), and the hydrophobic carbon paper serves as a gas diffusion layer, and dry at 50 °C to obtain a cathode gas diffusion electrode, and the catalyst loading is 2 mg cm -2. NiFe / LDH / NF was used as the anode on the anode side, and Ni and Fe metal salts were deposited onto commercial nickel foam by the traditional electrostatic deposition method (Nature Communications 6 (2015): 1-7). The commercial nickel foam was pre-cut into 1.5 cm × 1.5 cm and cleaned with 2 mol / L hydrochloric acid and ethanol, respectively. The NiFe / LDH / NF sample after electrostatic deposition was rinsed with deionized water and ethanol, dried at room temperature, and used as the anode of the anion membrane electrolysis cell. The cathode was connected to humidified CO2 externally, and the flow gas flow rate was controlled at 20 sccm. A flowing electrolyte (1MKHCO3) was added to the anode side, and a peristaltic pump was used to control the gas flow rate to 20 sccm. The test was carried out using a Shanghai Chenhua (CHI 1140C) electrochemical workstation, with the working lines of the reference and counter electrodes connected to the anode, and the working electrode connected to the cathode. The test adopts the constant current test model, and the test current is: 20, 50, 75, 90, 100, 125 and 150mA cm -2 The test duration was 1200s. The stability of the constant current test was 110h. During the test period, the solution was changed every 3-5h. The anion membrane electrolyzer was disassembled, and the serpentine gas channel and the back of the electrode were rinsed with deionized water to remove salt precipitation. The electrode was then reassembled and 100mA cm was applied. -2 The constant current test was performed.

[0040] like Figure 2 As shown, the characteristic infrared absorption spectrum of CoPPc in Example 1 proves that CoPPc has been successfully synthesized.

[0041] like Figure 3 As shown in a, the CoPPc / NHCSs catalyst of Example 1 has a uniform spherical structure. Figure 3 As shown in b, the spherical shell surface of CoPPc / NHCSs is rich in mesoporous structure.

[0042] Figure 4 Obvious bright spots can be seen in the figure, indicating that the metal has reached atomic-level distribution, proving the formation of monodisperse CoPPc sites.

[0043] Figure 5Figure (a) shows the near-edge X-ray absorption spectra of CoPPc / NHCSs and Co foil. As can be seen, CoPPc / NHCSs exhibits a different pre-edge structure than Co foil. Figure (b) shows the Fourier transform extended X-ray absorption structure of the CoPPc / NHCSs sample, and Figure (c) shows the fitting curve. Analysis of Figures (b) and (c) indicates that the coordination configuration of Co in CoPPc / NHCS is a Co-N₄ structure. Figure (d) compares the theoretical and experimental spectra, with the inset showing the spatial configuration of the CoPPc structure. These characterizations fully demonstrate the successful synthesis of CoPPc and its surface loading on the NHCS substrate.

[0044] Figure 6 The figure shows the performance of CoPPc / NHCSs as cathode material in an “H” type electrolytic cell. Figure 6 As shown in a, CoPPc / NHCSs exhibited specific electrocatalytic performance for CO2 reduction. At a test potential of -0.8 V vs. RHE, the overall current density reached ∼45 mA cm -2 .like Figure 6 As shown in b, the constant potential test data found that at the test potential of -0.8V vs.RHE, the Faradaic efficiency (FE) of CoPPc / NHCSs electrocatalytic CO2 reduction to CO CO ) reaches its maximum value of 95.46%. At the same time, the partial current density of CO (j CO )like Figure 6 c shows that at -0.8 V vs. RHE potential, j CO The value is 36.31 mA cm -2 The constant potential test of CoPPc / NHCSs is as follows: Figure 6 As shown in (d), the selectivity of CoPPc / NHCSs for CO was maintained above 80% when tested at a constant potential of -0.8 V vs. RHE for up to 135 h, indicating the excellent stability of CoPPc / NHCSs.

[0045] Figure 7 The constant current test diagram of CoPPc / NHCSs as cathode material in anion membrane electrolysis cell, the test currents are 20, 50, 75, 90, 100, 125 and 150 mA cm -2 . When the test current is 90mA cm -2 When , the selectivity of CO reaches up to 95.22%.

[0046] Constant current stability test Figure 8 As shown, by replacing the electrolyte and flushing the electrodes, the final result is 100mAcm -2Under a constant current density, it operates stably for 110 h, and the Faraday efficiency of CO is stable above 80%.

[0047] Example 2:

[0048] The NHCSs sample was prepared in the same way as in Example 1. Weigh 100 mg of the obtained NHCSs, 32 mg of cobalt chloride, and 180 mg of 1,2,4,5 - tetracyanobenzene, add them into 50 mL of ethanol solution, ultrasonic for 30 min, stir for 30 min, then transfer them into a 100 mL hydrothermal reactor, and hydrothermal react at 180 °C for 8 h. Finally, through vacuum filtration, and rinse the sample successively with 2 mol / L hydrochloric acid and hot ethanol (60 °C) solution, and finally rinse the sample with deionized water and ethanol (room temperature), and dry at 60 °C to finally obtain cobalt phthalocyanine - coated porous nitrogen - doped hollow carbon spheres—CoPPc / NHCSs - 2.

[0049] Characterize the morphology of CoPPc / NHCSs - 2 by field - emission scanning electron microscopy.

[0050] As Figure 9 shown, the CoPPc / NHCSs - 2 catalyst of Example 2 is a spherical structure, and there are CoPPc aggregates in the substrate.

[0051] Example 3:

[0052] The NHCSs sample was prepared in the same way as in Example 1. Weigh 100 mg of the obtained NHCSs, 16 mg of nickel chloride, and 100 mg of 1,2,4,5 - tetracyanobenzene, add them into 50 mL of ethanol solution, ultrasonic for 30 min, stir for 30 min, then transfer them into a 100 mL hydrothermal reactor, and hydrothermal react at 180 °C for 8 h. Finally, through vacuum filtration, and rinse the sample successively with 2 mol / L hydrochloric acid and hot ethanol (60 °C) solution, and finally rinse the sample with deionized water and ethanol (room temperature), and dry at 60 °C to finally obtain nickel phthalocyanine - coated nitrogen - doped porous hollow carbon spheres—NiPPc / NHCSs.

[0053] H - type electrolytic cell performance test: Take 3 mg of the obtained NiPPc / NHCSs sample, and add 30 μL of Nafion (5 wt%) ionomer and 3 mL of ethanol, ultrasonic for 1 h to obtain catalyst ink. Coat the obtained ink on a 3 cm×1 cm commercial carbon paper, and the coating area is 1 cm 2 , and the catalyst loading is 0.45 mg cm -2 , dry at room temperature to prepare a working electrode. Together with an Ag / AgCl reference electrode and a Pt counter electrode, a three - electrode system is formed, and all the measured potentials are converted into a reversible hydrogen electrode (RHE). The voltammetric linear scanning range is - 0.2~ - 1.2 V vs. RHE, and the scan rate is 5 mV s-1 The test potentials were -0.5, -0.6, -0.7, -0.75, -0.8, -0.85, -0.9, and -1.0 V vs. RHE, and the products were monitored by on-line gas chromatography.

[0054] Example 4:

[0055] The NHCSs sample was prepared in the same way as in Example 1. Weigh 100 mg of the obtained NHCSs, 33.40 mg of ferric chloride, and 90 mg of 1,2,4,5-tetracyanobenzene, add them to 50 mL of an ethanol solution, ultrasonicate for 30 min, stir for 30 min, then transfer them to a 100 mL hydrothermal autoclave, and carry out hydrothermal treatment at 180 °C for 8 h. Finally, the sample was filtered by vacuum, rinsed successively with 2 mol / L hydrochloric acid and a hot ethanol (60 °C) solution, and finally rinsed with deionized water and ethanol (at room temperature), and dried at 60 °C to finally obtain iron phthalocyanine encapsulated nitrogen-doped porous hollow carbon spheres—FePPc / NHCSs.

[0056] Performance test of the H-type electrolytic cell: Take 3 mg of the obtained FePPc / NHCSs sample, add 30 μL of Nafion (5 wt%) ionomer and 3 mL of ethanol, ultrasonicate for 1 h to obtain the catalyst ink. The obtained ink was coated on a commercial carbon paper with a size of 3 cm × 1 cm, and the coating area was 1 cm 2 , and the catalyst loading was 0.45 mg cm -2 , dried at room temperature to prepare the working electrode. It was combined with an Ag / AgCl reference electrode and a Pt counter electrode to form a three-electrode system, and all the tested potentials were converted to the reversible hydrogen electrode (RHE). The linear sweep voltammetry range was -0.2 to -1.2 V vs. RHE, and the scan rate was 5 mV s -1 The test potentials were -0.5, -0.6, -0.7, -0.75, -0.8, -0.85, -0.9, and -1.0 V vs. RHE, and the products were monitored by on-line gas chromatography.

[0057] As Figure 10 shown, the NiPPc / NHCSs catalyst of this example was a spherical structure.

[0058] As Figure 11 shown, the FePPc / NHCSs catalyst of this example was a spherical structure.

[0059] As Figure 12 shown in a, under the condition that the test potential was -0.2 to -1.2 V (vs. RHE), the NiPPc / NHCSs prepared in Example 3 showed obvious activity for electrochemical CO2 reduction. As Figure 12As shown in Fig. b, the selectivity for CO reaches a maximum value of 98.7% at the test potential of -0.75 V (vs. RHE). As Figure 12 shown in Fig. c, j CO At the potential of -0.9 V vs. RHE, the maximum value reaches 27.82 mA cm -2 .

[0060] As Figure 13 shown in Fig. a, at the test potential of -0.2 to -1.2 V (vs. RHE), the FePPc / NHCSs prepared in Example 4 showed obvious electrocatalytic activity for CO2 reduction. As Figure 13 shown in Fig. b, at the applied potential of -0.5 V (vs. RHE), the selectivity for CO reaches a maximum value of 85.38%, and the maximum j CO is 1.36 mA cm -2 ( Figure 13 as shown in Fig. c).

[0061] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

Claims

1. Preparation method of polymetallic phthalocyanine-coated nitrogen-doped porous hollow carbon spheres, characterized in that, The specific steps are as follows: (1) Tetraethyl orthosilicate is used to generate silica spheres as templates under alkaline conditions; dopamine hydrochloride is used as the precursor of the spherical shell, and under alkaline conditions, it polymerizes and grows on the surface of the SiO2 spheres to form polydopamine (PDA)@SiO2 spheres (SiO2@PDA). The SiO2@PDA is then calcined at high temperature under inert conditions and treated with hydrogen fluoride (HF) to obtain nitrogen-doped porous hollow carbon spheres (NHCSs); (2) NHCSs, metal salts, and 1,2,4,5-tetracyanobenzene are successively added to the solvent, and the material ratios among NHCSs, metal salts, and 1,2,4,5-tetracyanobenzene are regulated; under hydrothermal conditions, the metal ions and 1,2,4,5-tetracyanobenzene undergo a polymerization reaction to form polymetallic phthalocyanine on the surface of NHCSs. After vacuum filtration, rinsing, and drying, the MPPc / NHCSs material is obtained; The solvent, hydrothermal time, and temperature are regulated to optimize the structure of the polymetallic phthalocyanine molecules and their polymerization structure on the surface of NHCSs, thereby realizing the optimization of the active sites, improving the stability of the central sites, and meeting the requirements of the cathode catalyst material for the long-term stable operation of the anion exchange membrane electrolytic cell under high current.

2. The preparation method of the polymetallic phthalocyanine-coated nitrogen-doped porous hollow carbon spheres according to claim 1, characterized in that, In step (1), the size of SiO2 is controlled within 200 - 500 nm; the size of NHCSs is controlled within 200 - 500 nm, and the surface mesopore size is controlled within 2 - 4 nm; the inert condition refers to using nitrogen, argon, or helium as the inert protective gas.

3. The preparation method of the polymetallic phthalocyanine-coated nitrogen-doped porous hollow carbon spheres according to claim 1, wherein, In step (2), the metal salt is any one of cobalt chloride, nickel chloride, and ferric chloride; the solvent is selected from any one of ethanol and water; NHCSs is 50 - 150 mg, the metal salt is 10 - 40 mg, 1,2,4,5-tetracyanobenzene is 56 - 225 mg; the hydrothermal temperature is 140 - 200 °C, the time is 6 - 8 h, and the solvent volume is 40 - 50 mL.

4. A preparation method of a poly-metallic phthalocyanine-coated nitrogen-doped porous hollow carbon sphere as a cathode catalytic material prepared by the preparation method described in claim 1, characterized in that: The MPPc / NHCSs material is mixed with a certain amount of ionomer and solvent to prepare an electrode ink, which is coated on the electrode carrier to construct a cathode gas diffusion electrode.

5. The preparation method according to claim 4, characterized in that, The electrode carrier is one of carbon paper, carbon felt, carbon cloth, and carbon fiber.

6. The preparation method according to claim 4, characterized in that, The ionomer uses a 5 wt% perfluorinated acid resin Nafion solution; the solvent uses an ethanol solution; 2 - 4 mg of MPPc / NHCSs, 20 - 60 μL of Nafion solution, and 1 - 3 mL of ethanol solution are ultrasonically mixed for 1 h.

7. The preparation method according to claim 4, characterized in that, In the H-type electrolytic cell test, the loading amount of the MPPc / NHCSs material on the electrode carrier is 0.1 - 1 mg cm -2 .

8. The preparation method according to claim 4, characterized in that, In the anion exchange membrane electrolytic cell, the loading amount of the MPPc / NHCSs material on the electrode support is 0.1 - 2 mg cm -2 .

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