A method for preparing lanthanide composite porous carbon and its application in electrocatalytic reduction of CO2.

Abstract

The application discloses a preparation method of a lanthanide compound composite porous carbon and application of the lanthanide compound composite porous carbon in electrocatalytic reduction of CO2. The method comprises the following steps: mixing a certain amount of porous carbon, a lanthanide nitrate and a complexing agent and stirring; centrifuging the mixed solution, drying the precipitate and performing high-temperature pyrolysis treatment; and performing acid pickling, filtering and drying of the product to obtain a catalytic material. The lanthanide compound composite porous carbon prepared by the method has excellent catalytic activity in electrocatalytic reduction of CO2, and the CO Faraday efficiency can reach more than 90% in a wide potential interval and has long-term stability at a high potential. In addition, the raw material source is wide, the cost is low, the preparation process is simple and efficient, the method can be used for large-scale industrial production process, and has high practical application value.

Description

Technical Field

[0001] This invention relates to the fields of lanthanides, porous carbon materials, and catalysis, specifically to a method for preparing lanthanide composite porous carbon and its application in the electrocatalytic reduction of CO2. Background Technology

[0002] CO2 is an important C1 resource, and the electrocatalytic reduction of CO2 into high-value-added chemicals can improve resource utilization and environmental protection. CO2 is a linearly configured molecule, with the oxygen and carbon atoms bonded together by sp hybrid orbitals, making it a thermodynamically stable molecule. Therefore, the electrochemical reduction rate of CO2 is relatively slow. The electrochemical reduction of CO2 is a multi-electron coupling process, resulting in highly complex products. Generally, the ECRR reaction involves 2–18 electron transfer steps, producing a wide variety of products. These include one-carbon products such as carbon monoxide (CO), formic acid (HCOOH), and methane (CH4); two-carbon products such as ethylene (C2H4), ethanol (C2H5OH), and ethane (C2H6); and small amounts of three-carbon products such as propanol (C3H7OH). Furthermore, the electrochemical hydrogen evolution reaction (HER) is a competing reaction for CO2 reduction; therefore, it is necessary to study efficient electrocatalysts to improve the Faraday efficiency of ECRR and reduce the occurrence of the HER.

[0003] Noble metal-based catalysts (such as gold, silver, and platinum) have exhibited excellent electrocatalytic CO2 reduction performance. However, the high price, low reserves, poor stability, and susceptibility to poisoning and deactivation of noble metals severely limit their large-scale application. On the other hand, most transition metals are highly reactive, and their active sites are easily corroded and oxidized, losing their electrocatalytic CO2 reduction activity, which is detrimental to large-scale applications. Furthermore, competitive electrochemical hydrogen evolution reactions easily occur on the surface of transition metal clusters, further reducing their electrocatalytic CO2 reduction activity and selectivity. Therefore, further research into non-noble metal-based active sites with high stability, corrosion resistance, and good selectivity is crucial for improving electrocatalytic CO2 reduction activity and realizing industrial applications.

[0004] Lanthanide metal complexes possess diverse crystal and electronic structures, demonstrating excellent potential as alternatives to noble metal-based materials. Furthermore, my country is a major rare earth producer with abundant and varied rare earth reserves. Due to the lanthanide contraction effect, the physicochemical properties of different lanthanide elements are relatively similar. The inner-shell charge of lanthanide atoms exerts a significant electron shielding effect on the outer-shell electrons, weakening the attraction of the nucleus to the outer electrons and making them easier to lose. Using lanthanide compounds as active centers and leveraging the different electron-withdrawing abilities of O, F, P, and S to regulate the crystal and electronic structures of the metals holds promise for improving the activity, selectivity, and stability of electrocatalytic CO2 reduction. Summary of the Invention

[0005] One of the objectives of this invention is to provide a method for preparing lanthanide compound composite porous carbon, which uses inexpensive and readily available raw materials, is simple to prepare, is environmentally friendly, and produces composite porous carbon with high catalytic activity.

[0006] The second objective of this invention is to provide the application of lanthanide compound composite porous carbon prepared by the above method in the electrocatalytic reduction of CO2.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing lanthanide compound composite porous carbon, comprising the following steps:

[0008] Step 1: Dissolve porous carbon and lanthanide nitrate hydrate together in deionized water, denoted as material A; dissolve the complexing agent in an ethanol aqueous solution, denoted as material B; the addition ratio of porous carbon and lanthanide nitrate hydrate is 0.1g:0.5-2.0mmol; the molar ratio of complexing agent and lanthanide nitrate hydrate is 4:0.15;

[0009] Step 2: Stir material A at 50°C, slowly pour material B into material A, then add 5% perfluorosulfonic acid-polytetrafluoroethylene copolymer (Nafion) solution dropwise, mix and stir for 1 hour, and record as material C; the addition ratio of the 5% perfluorosulfonic acid-polytetrafluoroethylene copolymer solution and the lanthanide nitrate hydrate is 1-5 mL: 0.25-1.25 mmol;

[0010] Step 3: Transfer material C to a centrifuge and centrifuge to remove the filtrate. Dry the precipitate and record it as material D.

[0011] Step 4: Pyrolyze material D in an inert gas-protected tubular furnace at an inert gas flow rate of 5℃ / min and a pyrolysis temperature of 700-900℃ for 2 hours. Then, cool the material to 300℃ and allow it to cool naturally to room temperature. The product is then acid-washed, washed with water until the filtrate is neutral, and dried to obtain lanthanide compound composite porous carbon.

[0012] Preferably, the ratio of porous carbon to lanthanide nitrate hydrate added in step one is 0.1g:0.75mmol.

[0013] Preferably, the lanthanide nitrate hydrates mentioned in step one are one or more of the following: lanthanum nitrate, cerium nitrate, praseodymium nitrate, neodymium nitrate, samarium nitrate, europium nitrate, gadolinium nitrate, terbium nitrate, dysprosium nitrate, holmium nitrate, erbium nitrate, thulium nitrate, ytterbium nitrate, and lutetium nitrate hydrates.

[0014] Preferably, the amount of complexing agent in step one is 20 mmol.

[0015] Preferably, the complexing agent is 2-methylimidazole.

[0016] Preferably, the addition ratio of the 5% perfluorosulfonic acid-polytetrafluoroethylene copolymer solution and the lanthanide nitrate hydrate added in step two is 1 mL: 0.25 mmol.

[0017] Preferably, the centrifugation speed in step three is 5000 rpm and the centrifugation time is 5 min.

[0018] Preferably, the pyrolysis temperature in step four is 700℃.

[0019] This invention also provides the application of the lanthanide compound composite porous carbon prepared by the above method in the field of electrocatalytic CO2 reduction. The method is as follows: 5 mg of the prepared sample, 20 μL of Nafion solution, and 480 μL of N,N-dimethylformamide (DMF) are mixed, and then sonicated for 30 min to form a uniform dispersion. Then, 40 μL of the above-prepared dispersion is drop-coated onto a 0.5 cm² surface. 2 The carbon paper is dried naturally to obtain the working electrode.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. Porous carbon materials are excellent supports. This invention combines lanthanide metal active centers with porous carbon supports. On the one hand, this improves the dispersion of metal active centers, avoids metal accumulation, and generates more abundant electrocatalytic active sites. On the other hand, the rich pore structure of the porous carbon support also facilitates the transport and transfer of substances, further enhancing catalytic activity.

[0022] 2. This invention utilizes inexpensive raw materials and employs a series of green and safe preparation strategies to produce lanthanide compound composite porous carbon materials with highly efficient electrocatalytic CO2 reduction activity. The experimental steps are simple and environmentally friendly, achieving effective utilization of carbon resources in the atmosphere and protecting the environment.

[0023] 3. This invention achieves highly efficient electrocatalytic CO2 reduction to CO using lanthanide compound composite porous carbon, and the method is simple and highly innovative.

[0024] 4. Based on the material properties, this invention discovered that the crystal and electronic structures of lanthanide metals regulated by different heteroelements have a significant impact on the electrocatalytic activity of CO2 reduction to CO. Among them, the active sites of metals regulated by F, which possesses the strongest electron-withdrawing properties, exhibited high electrocatalytic CO2 reduction activity. This provides some exploratory and reference value for the regulation of electronic structure. Attached Figure Description

[0025] Figure 1 The image shows a transmission electron microscope (TEM) image of the lanthanum fluoride composite porous carbon material prepared in Example 1.

[0026] Figure 2 High-resolution transmission electron microscope (HRTEM) image of the lanthanum fluoride composite porous carbon material prepared in Example 1;

[0027] Figure 3 The isothermal (77K) nitrogen adsorption-desorption curve of the lanthanum fluoride composite porous carbon material prepared in Example 1 is shown below.

[0028] Figure 4 X-ray photoelectron spectroscopy (XPS) of the lanthanum fluoride composite porous carbon material prepared in Example 1, specifically the La 3d... 5 / 2 Peak spectrum;

[0029] Figure 5 The Faraday efficiency curves of CO in the lanthanide composite porous carbon materials prepared in Example 1 and Comparative Examples 1-3 are shown.

[0030] Figure 6 The current density curves of CO in the lanthanide compound composite porous carbon materials prepared in Example 1 and Comparative Examples 1-3 are shown. Detailed Implementation

[0031] The following embodiments further illustrate the innovative points and content of the present invention and should not be construed as limiting the present invention. Modifications to the methods, steps, and other conditions of the present invention that conform to the principles and content of the present invention are all within the scope of the present invention.

[0032] Example 1

[0033] 0.1 g of porous carbon and 0.75 mmol of lanthanum nitrate hexahydrate were dissolved in 15 mL of deionized water and stirred at 400 rpm in a water bath at 50 °C. 20 mmol of 2-methylimidazole was dissolved in 15 mL of deionized water and 3 mL of ethanol. The 2-methylimidazole solution was slowly poured into the above solution and mixed, followed by the addition of 3 mL of 5% Nafion solution. After stirring for 1 h, the mixture was centrifuged at 5000 rpm for 5 min, the supernatant was removed, and the precipitate was dried and then pyrolyzed in a tube furnace under inert gas (flow rate 5 °C / min). The pyrolysis was carried out at 700 °C for 2 h, then cooled to 300 °C and allowed to cool naturally to room temperature. The product was acid-washed, filtered through deionized water until the filtrate was neutral, and then dried to obtain the lanthanum fluoride composite porous carbon material.

[0034] 5 mg of the prepared sample was mixed with 20 μL of 5% Nafion solution and 480 μL of N,N-dimethylformamide (DMF), and then sonicated for 30 min to form a homogeneous dispersion. Then, 40 μL of the prepared dispersion was drop-coated onto a 0.5 cm² plate. 2The carbon paper was dried naturally to obtain the working electrode. The prepared working electrode was then electrochemically tested in an H-type electrolytic cell to evaluate its electrocatalytic CO2 reduction performance. A proton exchange membrane (Nafion 115) was used to separate the anode and cathode electrolytic chambers. A three-electrode system was used for electrochemical testing, with a platinum sheet as the counter electrode (CE) and 3.5M Ag / AgCl as the reference electrode (RE). 0.5M KHCO3 was used as the electrolyte. The electrochemical workstation was used for testing, and an online gas chromatography system equipped with a thermal conductivity detector (TCD) and a flame ionization detector (FID) was used to detect the composition and content of the products.

[0035] Comparative Example 1

[0036] 0.1 g of porous carbon and 0.75 mmol of lanthanum nitrate hexahydrate were dissolved in 15 mL of deionized water and stirred at 400 rpm in a water bath at 50 °C. 20 mmol of 2-methylimidazole was dissolved in 15 mL of deionized water and 3 mL of ethanol. The 2-methylimidazole solution was slowly poured into the above solution and mixed. After stirring for 1 h, the mixture was centrifuged at 5000 rpm for 5 min, the supernatant was removed, and the precipitate was dried and then pyrolyzed in a tube furnace under inert gas (flow rate 5 °C / min). The pyrolysis was carried out at 700 °C for 2 h, then cooled to 300 °C and allowed to cool naturally to room temperature. The product was acid-washed, filtered through deionized water until the filtrate was neutral, and then dried to obtain the lanthanum oxide composite porous carbon material.

[0037] The preparation method and electrochemical testing method of the working electrode of the lanthanum oxide composite porous carbon material electrocatalytic CO2 reduction catalyst in Comparative Example 1 are the same as those in Example 1.

[0038] Comparative Example 2

[0039] 0.1 g of porous carbon and 0.75 mmol of lanthanum nitrate hexahydrate were dissolved in 15 mL of deionized water and stirred at 400 rpm in a water bath at 50 °C. 20 mmol of sodium hexametaphosphate was dissolved in 15 mL of deionized water and 3 mL of ethanol. The sodium hexametaphosphate solution was slowly poured into the above solution and mixed. After stirring for 1 h, the mixture was centrifuged at 5000 rpm for 5 min, the supernatant was removed, and the precipitate was dried and then pyrolyzed in a tube furnace under inert gas (flow rate 5 °C / min). The pyrolysis was carried out at 700 °C for 2 h, then cooled to 300 °C and allowed to cool naturally to room temperature. The product was acid-washed, filtered through deionized water until the filtrate was neutral, and then dried to obtain the lanthanum phosphide composite porous carbon material.

[0040] The preparation method and electrochemical testing method of the working electrode of the lanthanum phosphide composite porous carbon material electrocatalytic CO2 reduction catalyst in Comparative Example 2 are the same as those in Example 1.

[0041] Comparative Example 3

[0042] 0.1 g of porous carbon and 0.75 mmol of lanthanum nitrate hexahydrate were dissolved in 15 mL of deionized water and stirred at 400 rpm in a water bath at 50 °C. 20 mmol of thiophene was dissolved in 15 mL of deionized water and 3 mL of ethanol. The thiophene solution was slowly poured into the above solution and mixed. After stirring for 1 h, the mixture was centrifuged at 5000 rpm for 5 min, the supernatant was removed, and the precipitate was dried and then pyrolyzed in a tube furnace under inert gas (flow rate 5 °C / min). The pyrolysis was carried out at 700 °C for 2 h, then cooled to 300 °C and allowed to cool naturally to room temperature. The product was acid-washed, filtered through deionized water until the filtrate was neutral, and then dried to obtain the lanthanum sulfide composite porous carbon material.

[0043] The preparation method and electrochemical testing method of the working electrode of the lanthanum sulfide composite porous carbon material electrocatalytic CO2 reduction catalyst in Comparative Example 3 are the same as those in Example 1.

[0044] (1) Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) tests

[0045] The prepared lanthanum fluoride composite porous carbon material (Example 1) was placed under a transmission electron microscope (TEM). Figure 1 ) and high-resolution transmission electron microscopy ( Figure 2 Observe below. For example... Figure 1 As shown, the porous carbon material is relatively thin and lightweight with a uniform structure, indicating the successful fabrication of a porous carbon support with excellent structural properties. Furthermore, numerous nanorod-shaped metal clusters were successfully loaded onto the porous carbon support. Figure 2 As shown, the nanorods have obvious lattice stripes, indicating that the nanorods have a good crystal structure. This shows that after acid washing, the active metal centers still have a stable crystal structure, thus preparing stable nanorod-shaped lanthanum fluoride composite porous carbon.

[0046] (2) Nitrogen adsorption-desorption test

[0047] The nitrogen isothermal adsorption-desorption curves of Example 1 were tested using a nitrogen physical adsorption-desorption apparatus. Figure 3 As shown, a significant increase is observed in the region where p / p0 < 0.01, indicating the presence of abundant microporous structures. In the region where p / p0 > 0.45, a significant hysteresis loop is observed, indicating abundant mesoporous structures. When p / p0 > 0.90, the curve shifts significantly upwards, indicating the presence of macroporous structures. The isothermal adsorption-desorption curves show that the prepared Example 1 exhibits a good hierarchical pore structure, with a specific surface area of ​​366.19 m². 2 g -1 The pore volume is 0.29 cm. 3 g-1 This facilitates mass transfer, thereby increasing the electrochemical kinetics rate of the catalyst and improving the electrocatalytic CO2 reduction performance. Furthermore, TEM analysis reveals that the large specific surface area of ​​the porous carbon support promotes the dispersion of metal active centers, avoids cluster formation during preparation, and facilitates the creation of more active sites, thus enhancing the electrocatalytic CO2 reduction activity.

[0048] (3) X-ray photoelectron spectroscopy (XPS) test

[0049] X-ray photoelectron spectroscopy (XPS) was performed on Example 1. Figure 4 As shown, the 3d of La in Example 1 5 / 2 The fine spectrum shows peaks at 837.4 eV and 841.1 eV, which are the 3d peaks of La in LaF3, respectively. 5 / 2 The peaks and their satellite peaks were observed. Therefore, it can be confirmed that standard LaF3 crystals were formed in the sample of Example 1. TEM testing showed that LaF3 formed a stable nanorod structure, which is beneficial to improving the stability of the catalyst. Furthermore, based on the preparation of Comparative Example 1, it is known that adding an additional fluorine source will cause the metal active center to transform from lanthanum oxide to the more stable lanthanum fluoride during pyrolysis.

[0050] (4) Electrocatalytic CO2 reduction performance test

[0051] Working electrodes from Examples 1, 1, 2, and 3 were prepared according to the above method, forming a three-electrode system with a silver / silver chloride reference electrode and a platinum sheet counter electrode. 0.5 M KHCO3 was used as the electrolyte. To evaluate the activity and selectivity of the catalyst in electrocatalytic CO2 reduction, chronoamperometry was performed at potentials ranging from -0.6 V to -1.1 V vs. RHE. The gaseous product at 1800 s was passed through an online gas chromatography system (GC-TCD-FID) equipped with a thermal conductivity detector (TCD) and a flame ionization detector (FID) to detect the composition and content of the product. CO2 gas was continuously introduced for 30 minutes to saturate the CO2 concentration in the cathode electrolyte, with a CO2 gas flow rate of 10 mL / min. -1 .

[0052] like Figure 5It can be seen that Example 1 exhibits excellent CO Faradaic efficiency at different voltages, with the CO Faradaic efficiency of Example 1 exceeding 90% between -0.8 and -1.0 V vs. RHE. Comparative Examples 1, 2, and 3 all showed poor catalytic activity. Comparative Example 3 showed the best Faradaic efficiency (46.8%) at -0.8 V vs. RHE, but its catalytic activity decreased continuously at higher voltages, demonstrating poor voltage tolerance. Comparative Examples 1 and 2 showed peak CO Faradaic efficiency at -0.7 V vs. RHE, but their electrocatalytic activity decreased continuously at higher voltages. This indicates that Example 1 possesses high electrocatalytic activity and stability for CO2 reduction.

[0053] Figure 6 The curves show the partial current density of CO at different locations. Figure 6 It can be seen that Example 1 exhibits a very high CO partial current density, and the CO partial current density only begins to decrease after the potential reaches -1.0V vs. RHE. In contrast, other lanthanide composite porous carbon materials regulated by heteroelement show very poor CO partial current density and voltage withstand capability. In summary, Example 1 not only possesses high electrocatalytic activity and selectivity but also strong voltage withstand capability, demonstrating excellent potential for large-scale applications.

[0054] This invention provides a strategy for preparing lanthanide composite porous carbon and its application in the field of electrocatalytic CO2 reduction. The optimal sample exhibits excellent electrocatalytic CO2 reduction to CO performance. Furthermore, the catalyst has widely available and low-cost raw materials, and the preparation process is simple and efficient, making it suitable for large-scale production processes and possessing high practical application value. This invention fills a research gap in the field of pure lanthanide metal electrocatalytic CO2 reduction and has high innovation and guiding significance.

Claims

1. A method for preparing lanthanum fluoride composite porous carbon, characterized in that, Includes the following steps: Step 1: Dissolve porous carbon and lanthanum nitrate hexahydrate together in deionized water, denoted as material A; dissolve the complexing agent in an ethanol aqueous solution, denoted as material B; the addition ratio of porous carbon and lanthanum nitrate hexahydrate is 0.1g:0.5-2.0mmol; the molar ratio of the complexing agent and lanthanum nitrate hexahydrate is 4:0.15; Step 2: Stir material A at 50°C, then slowly pour material B into material A, followed by dropwise addition of a 5% perfluorosulfonic acid-polytetrafluoroethylene copolymer solution. After mixing and stirring for 1 hour, this mixture is designated as material C. The addition ratio of the 5% perfluorosulfonic acid-polytetrafluoroethylene copolymer solution to the lanthanum nitrate hexahydrate is 1-5 mL. 0.25-1.25 mmol; Step 3: Transfer material C to a centrifuge and centrifuge to remove the filtrate. Dry the precipitate and record it as material D. Step 4: Pyrolyze material D in a tubular furnace under inert gas protection at an inert gas flow rate of 5℃ / min and a pyrolysis temperature of 700-900℃ for 2 hours. Then, cool the material to 300℃ and allow it to cool naturally to room temperature. The product is then acid-washed, washed with water until the filtrate is neutral, and dried to obtain lanthanum fluoride composite porous carbon.

2. The method for preparing lanthanum fluoride composite porous carbon according to claim 1, characterized in that, In step one, the ratio of porous carbon to lanthanum nitrate hexahydrate is 0.1 g: 0.75 mmol.

3. The method for preparing lanthanum fluoride composite porous carbon according to claim 1, characterized in that, The complexing agent mentioned in step one is 2-methylimidazole.

4. The method for preparing lanthanum fluoride composite porous carbon according to claim 1, characterized in that, In step two, the ratio of the 5% perfluorosulfonic acid-polytetrafluoroethylene copolymer solution added dropwise to the lanthanum nitrate hexahydrate is 1 mL: 0.25 mmol.

5. The method for preparing lanthanum fluoride composite porous carbon according to claim 1, characterized in that, The pyrolysis temperature mentioned in step four is 700℃.

6. The method for preparing lanthanum fluoride composite porous carbon according to claim 1, characterized in that, The centrifugation speed in step three is 5000 rpm, and the centrifugation time is 5 min.

7. The application of the lanthanum fluoride composite porous carbon prepared by the preparation method according to any one of claims 1 to 6 in the electrocatalytic reduction of CO2.

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