Preparation method and application of carbon-supported nanoscale cerium oxide electrocatalyst with controllable oxygen vacancy content

Abstract

The application discloses a preparation method and application of carbon-loaded nanoscale cerium oxide electrocatalyst with controllable oxygen vacancy content, and belongs to the technical field of electrocatalysts. The cerium oxide nanoparticles uniformly dispersed on the surface of carbon material are prepared by a chemical precipitation method, and then the cerium oxide nanoparticles with oxygen vacancies are obtained by treatment in a reducing environment. The oxygen vacancy content in the electrocatalyst is controlled by adjusting the mass fraction of cerium oxide on the carbon material and the temperature of the reducing atmosphere and other factors. The cerium oxide nanoparticles prepared by the application have uniform size, the average particle size is about 3nm, and are uniformly dispersed on the surface of the carbon carrier. The peak power density of an ascorbic acid fuel cell assembled by using the electrocatalyst can reach 46.5mW cm ‑2 , and the performance is better than that of reported electrocatalysts. The preparation method of the electrocatalyst is green and environmentally friendly, and the steps are simple, and can be applied in the field of direct ascorbic acid fuel cells.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalyst technology, and relates to a method for preparing and applying a carbon-supported nanoscale cerium oxide electrocatalyst with controllable oxygen vacancy content for direct ascorbic acid fuel cells. Background Technology

[0002] Given that fossil fuels such as coal, oil, and natural gas in the current global energy structure produce large amounts of harmful substances after use, posing a significant threat to the environment, proton exchange membrane fuel cells (PEMFCs) are power generation devices that directly convert the chemical energy stored in fuel into electrical energy. They have attracted widespread attention due to their environmental friendliness, high specific energy, and high energy conversion efficiency. However, their anode fuel is primarily high-purity hydrogen, which poses potential risks during storage and transportation. Furthermore, the electrocatalyst used in their anodes is typically commercially available Pt / C, resulting in high costs. Direct ascorbic acid fuel cells, on the other hand, use ascorbic acid as their anode fuel, offering advantages such as safe storage and transportation and low cost. Therefore, the research and development of direct ascorbic acid fuel cells has gradually become a hot topic.

[0003] Fujiwara et al. (Naoko Fujiwara, et al. Electrochem. Commun., 2006, 8, 720-724) found that carbon black possesses excellent electrocatalytic oxidation activity for ascorbic acid, far exceeding that of noble metals such as platinum, palladium, and gold. However, overall, the electrocatalytic oxidation activity of carbon black for ascorbic acid remains at a relatively low level (31 mW cm⁻¹). -2 (Qiu Chenxi, et al. Hydrogen Energy, 2018, 43, 21908-21917). Therefore, modifying carbon black with other species to enhance its activity has become a promising approach. In 2011, Ye Eun Kim et al. (Ye Eun Kim, et al. Electrocatalysis, 2011, 200-206) found that modifying carbon with titanium dioxide could enhance the electrocatalytic oxidation activity of carbon for ascorbic acid. This is because titanium dioxide increases the proportion of oxygen-containing groups on carbon, promotes the electron transfer rate on the carbon surface, and thus enhances the catalytic activity of the electrocatalyst.

[0004] CeO2, as a rare earth metal oxide, has excellent oxygen storage capabilities. However, it readily generates chemical defects, specifically oxygen vacancies (CeO2). 3+ To Ce 4+Cerium oxides are widely used in electrocatalytic reactions (e.g., for the conversion of oxygen vacancies). For example, cerium oxides can be used as free radical quenchers (Choi CH, et al. Energy & Environmental Science, 2018, 3176-3182); they are also used in the electrocatalytic oxidation of organic compounds such as methanol (Salarizadeh, P., et al. J. Phys. Chem. Solids, 2020, 109442-109449) and ethanol (Kumar, PM, et al. ACS Sustain. Chem. Eng., 2017, 11290-11299). Cerium oxides with oxygen vacancies can promote electron transfer in electrocatalytic reactions and facilitate the conversion of intermediate species, thereby improving fuel cell performance. However, existing cerium oxides generally have large particle sizes, and methods for controlling oxygen vacancy content are cumbersome, which is detrimental to mass transfer and application in electrocatalytic reactions. For example, in 2019, An Taicheng et al. (CN110975857 A) invented a method for preparing a three-dimensional ordered macroporous oxygen-deficient cerium dioxide catalyst. However, the preparation process is cumbersome and does not control the oxygen vacancy content. In 2022, Jiang Lilong et al. (202211075996.3) invented a method for preparing ultra-small particle size cerium dioxide and applied it to desulfurization. However, their preparation process uses some organic reagents such as silane coupling agents and triethanolamine, which are not environmentally friendly.

[0005] In summary, the reported cerium oxide electrocatalysts still have the following problems: (1) generally large particle size; (2) complicated preparation process; (3) uncontrollable oxygen vacancy content.

[0006] Based on this, the present invention provides a method for preparing carbon-supported nanoscale cerium oxide electrocatalysts with controllable oxygen vacancy content and their applications. The reagents used in the preparation process are green and environmentally friendly, and the steps are simple. Summary of the Invention

[0007] The present invention aims to provide a method for preparing carbon-supported nanoscale cerium oxide electrocatalysts with controllable oxygen vacancy content and their applications. The invention prepares cerium oxide nanoparticles uniformly dispersed on the surface of a carbon material via chemical precipitation, and then obtains cerium oxide nanoparticles with oxygen vacancies through treatment in a reducing atmosphere. This method is simple, convenient, mild, and easy to control; the obtained cerium oxide particles have an average particle size of 2.5-3.5 nm, and the particles are uniformly distributed on the carbon support, which is beneficial for mass transfer. Furthermore, the oxygen vacancy ratio in the electrocatalyst can be controlled by adjusting factors such as the mass fraction of cerium oxide on the carbon material and the temperature of the reducing atmosphere heat treatment. The resulting carbon-supported cerium oxide electrocatalyst can be applied in the field of direct ascorbic acid fuel cells, exhibiting high ascorbic acid electrocatalytic oxidation activity.

[0008] A method for preparing a carbon-supported nanoscale cerium oxide electrocatalyst with controllable oxygen vacancy content, comprising the following steps:

[0009] (1) Disperse the carbon material in deionized water to a concentration of 1-4 mg / mL. -1 Preferably 1-2 mg / mL -1 Then add a concentration of 10-100 mmol / L. -1 (preferably 20-50 mmol L) -1 Aqueous solutions of cerium salt precursors with concentrations of 0.5-3 mol / L -1 An aqueous solution of the precipitant is stirred at room temperature for 30-120 min, then filtered and dried to obtain carbon-supported cerium hydroxide. The molar ratio of the precipitant to the cerium salt precursor is 20-40:1, preferably 40:1; the loading (mass fraction) of the carbon-supported cerium hydroxide is 2-20%.

[0010] (2) The solid (carbon-supported cerium hydroxide) in step (1) is heated to 150-400°C in a tube furnace filled with gas and held for more than 30 minutes (preferably 30-60 minutes) to obtain a carbon-supported cerium oxide catalyst.

[0011] (3) The solid (carbon-supported cerium oxide catalyst) obtained in step (2) is heated to 200-500°C in a reducing atmosphere in a tube furnace and held for more than 30 min (preferably 30-90 min), or held in a reducing aqueous solution for more than 30 min (preferably 30-90 min) to obtain a carbon-supported cerium oxide electrocatalyst containing oxygen vacancies.

[0012] The aforementioned carbon material is one of carbon black, multi-walled carbon nanotubes, and graphene oxide, wherein the carbon black is one of BP2000, EC600, EC300, and VXC-72.

[0013] The aforementioned cerium salt precursor is one of cerium nitrate, cerium sulfate, or cerium chloride aqueous solution.

[0014] The precipitant mentioned above is one of sodium hydroxide, potassium hydroxide, potassium bicarbonate, sodium bicarbonate, sodium carbonate, potassium carbonate, or ammonia water.

[0015] The drying conditions were as follows: drying at 60°C for 6 hours in a vacuum oven.

[0016] The gas mentioned above is one of air, argon, nitrogen, and carbon dioxide.

[0017] The reducing atmosphere described above is a mixture of gas 2 and gas 3. Gas 2 is one of hydrogen, carbon monoxide, hydrogen sulfide, ammonia, and sulfur monoxide. Gas 3 is a mixture of nitrogen, argon, and carbon dioxide. Gas 2 accounts for 3%-10% of the volume of the mixture.

[0018] The reducing aqueous solution mentioned above is an aqueous solution of one of sodium borohydride, ascorbic acid, sodium ascorbate, and potassium bromide, with a concentration of 0.1-1 mol / L. -1 .

[0019] This invention relates to carbon-supported nanoscale cerium oxide electrocatalysts with controllable oxygen vacancy content prepared by the above-described method. The controllable oxygen vacancy content is 0.1-0.7, and the average particle size of the cerium oxide nanoparticles ranges from 2.5-3.5 nm. The mass fraction of cerium oxide on the carbon material is 2-20%.

[0020] The aforementioned carbon-supported cerium oxide electrocatalyst exhibits high electrocatalytic oxidation activity for ascorbic acid and can be applied in direct ascorbic acid fuel cells. Specifically, the obtained catalyst is fabricated into a membrane electrode assembly and assembled into a battery fixture to obtain a direct ascorbic acid fuel cell. When used as the anode catalyst in an ascorbic acid fuel cell, the obtained catalyst achieves a maximum peak power density of 46.5 mW / cm³. -2 This is consistent with previously reported data (31 mW cm). -2 )1.5 times.

[0021] The beneficial effects of this invention are as follows: This preparation method regulates the oxygen vacancy ratio in the electrocatalyst by adjusting factors such as the mass fraction of cerium oxide on the carbon material and the reducing atmosphere temperature. The preparation method of this electrocatalyst is green and environmentally friendly, with simple steps and inexpensive and readily available raw materials. It has the potential for large-scale production. The cerium oxide nanoparticles prepared by this invention have uniform size, with an average particle size of approximately 3 nm, and are uniformly dispersed on the carbon support surface. Furthermore, the introduction of cerium oxide enhances the ascorbic acid electrocatalytic oxidation activity of the carbon material, and the peak power density of the ascorbic acid fuel cell can reach 46.5 mW / cm³. -2 The performance is superior to that of previously reported electrocatalysts. This method provides a new design approach for the preparation of high-performance direct ascorbic acid fuel cell anode catalysts. Attached Figure Description

[0022] This invention appendix Figure 9 Size:

[0023] Figure 1 Thermogravimetric curve of sample in Example 1;

[0024] Figure 2 Transmission electron microscope images of the sample in Example 1, with the inset showing a statistical chart of sample particle size;

[0025] Figure 3 X-ray photoelectron spectroscopy of the sample in Example 1;

[0026] Figure 4 Polarization curves and power density curves of carbon materials and samples in single cells in Example 1;

[0027] Figure 5 Thermogravimetric curve of sample in Example 7;

[0028] Figure 6 Transmission electron microscope images of the sample in Example 10, with the inset showing a statistical chart of sample particle size;

[0029] Figure 7 Thermogravimetric curve of sample 11 in Example 11;

[0030] Figure 8 Transmission electron microscope image of sample 1 (Comparative Example 1);

[0031] Figure 9 Transmission electron microscope image of sample 2 (Comparative Example 2). Detailed Implementation

[0032] The specific embodiments of the present invention are described below with reference to the accompanying drawings and technical solutions.

[0033] Example 1

[0034] Disperse 50 mg of BP2000 carbon black in 50 mL of deionized water, then add 0.927 mL of 20 mmol L. -1 Cerium nitrate solution and 0.37 mL 2 mol L -1 Potassium hydroxide solution. After stirring at room temperature for 60 min, the solution was filtered under reduced pressure through a Buchner funnel until the filtrate was neutral and a solid was obtained. This solid was dried in a vacuum oven at 60 °C for 6 h to obtain carbon-supported cerium hydroxide. The obtained solid was heated to 250 °C and held for 60 min in an air-filled tube furnace to obtain a carbon-supported cerium oxide catalyst. The carbon-supported cerium oxide was then held at 250 °C for 60 min in a reducing atmosphere of a mixture of hydrogen and argon (5% hydrogen). Figure 1 Thermogravimetric analysis (TGA) curves show that a carbon-supported cerium oxide electrocatalyst with oxygen vacancies and a mass fraction of 6% was obtained. Transmission electron microscopy images are shown (see...). Figure 2 Cerium oxide nanoparticles are uniformly distributed on carbon materials, with an average particle size of 2.8 ± 0.9 nm. In cerium oxide, Ce... 3+ Representing oxygen vacancies, hence Ce 3+ / Ce 4+ This indicates the proportion of oxygen vacancies. X-ray photoelectron spectroscopy results show (see...) Figure 3The oxygen vacancy ratio of the carbon-supported cerium oxide electrocatalyst is 0.48. The prepared carbon-supported cerium oxide electrocatalyst and BP2000 carbon black were used as anode catalysts in direct ascorbic acid fuel cells to prepare membrane electrode assemblies. Figure 4 As shown, the peak power density of the cerium oxide-loaded membrane electrode can reach up to 46.5 mW / cm². -2 Superior performance compared to carbon materials. It has been demonstrated that the addition of cerium oxides containing oxygen vacancies can enhance the ascorbic acid electrocatalytic oxidation activity of carbon black.

[0035] Example 2

[0036] The reducing atmosphere temperature in Example 1 was adjusted to 200°C, while the other parameters remained unchanged.

[0037] Example 3

[0038] The reducing atmosphere temperature in Example 1 was adjusted to 300°C, while the other parameters remained unchanged.

[0039] Example 4

[0040] The reducing atmosphere temperature in Example 1 was adjusted to 350°C, while the other parameters remained unchanged.

[0041] Example 5

[0042] The reducing atmosphere temperature in Example 1 was adjusted to 400°C, while the other parameters remained unchanged.

[0043] The comparison of the proportion of oxygen vacancies in the cerium oxides prepared in Examples 1-5 is shown in Table 1.

[0044] Table 1. Oxygen vacancy ratio in carbon-supported cerium oxide catalysts (at temperature of reducing atmosphere)

[0045] Oxygen vacancy ratio Example 1 0.48 Example 2 0.26 Example 3 0.41 Example 4 0.50 Example 5 0.64

[0046] Example 6

[0047] The 20 mmol L from Example 1 -1 Cerium nitrate solution and 2 mol L -1 The amount of potassium hydroxide solution added was adjusted to 0.31 mL and 0.12 mL, respectively. All other parameters remained unchanged. This yielded a carbon-supported cerium oxide electrocatalyst with oxygen vacancies and a mass fraction of 2%.

[0048] Example 7

[0049] The 20 mmol L from Example 1 -1 Cerium nitrate solution and 2 mol L -1 The amounts of potassium hydroxide solution added were adjusted to 0.62 mL and 0.25 mL, respectively. All other parameters remained unchanged. Figure 5 The thermogravimetric curves show that a carbon-supported cerium oxide electrocatalyst with oxygen vacancies and a mass fraction of 4% was obtained.

[0050] Example 8

[0051] The 20 mmol L from Example 1 -1 Cerium nitrate solution and 2 mol L -1 The amount of potassium hydroxide solution added was adjusted to 1.24 mL and 0.50 mL, respectively. All other parameters remained unchanged. This yielded a carbon-supported cerium oxide electrocatalyst with oxygen vacancies and a mass fraction of 8%.

[0052] Example 9

[0053] The 20 mmol L from Example 1 -1 Cerium nitrate solution and 2 mol L -1 The amounts of potassium hydroxide solution added were adjusted to 1.55 mL and 0.625 mL, respectively. All other parameters remained unchanged. This yielded a carbon-supported cerium oxide electrocatalyst with oxygen vacancies and a mass fraction of 10%.

[0054] The comparison of the proportion of oxygen vacancies in the cerium oxides prepared in Examples 6-12 is shown in Table 2.

[0055] Table 2. Oxygen vacancy ratio in carbon-supported cerium oxide electrocatalysts (mass fraction of cerium oxide on carbon)

[0056] Oxygen vacancy ratio Example 6 0.12 Example 7 0.29 Example 8 0.36 Example 9 0.45

[0057] Example 10

[0058] Take 50 mg of BP2000 carbon black, place it in 50 mL of deionized water, and add 0.927 mL of 20 mmol L. -1 Cerium chloride solution and 0.37 mL 2 mol L -1 Potassium hydroxide solution. Stirred at room temperature for 100 min, filtered under reduced pressure using a Buchner funnel until the filtrate was neutral, and the resulting solid was dried in a vacuum oven at 60 °C for 6 h to obtain carbon-supported cerium hydroxide. The carbon-supported cerium hydroxide was kept in an air-filled tube furnace at 250 °C for 60 min, and then dissolved in a reducing aqueous solution (0.5 mol / L). -1 Treatment with sodium borohydride aqueous solution for 60 min yielded a carbon-supported cerium oxide electrocatalyst with an oxygen vacancy ratio of 0.51 and a mass fraction of 6%. Transmission electron microscopy showed (see...) Figure 6 The cerium oxide nanoparticles are uniformly distributed on the carbon material, with an average particle size of 3.0 ± 0.9 nm.

[0059] Example 11

[0060] Take 50 mg of EC300 carbon black and place it in 50 mL of deionized water, then add 1.025 mL of 50 mmol L. -1 Cerium chloride solution and 2.05 mL of 1 mol L -1 Sodium hydroxide solution. Stir at room temperature for 60 min, filter under reduced pressure using a Buchner funnel until the filtrate is neutral, and dry the resulting solid in a vacuum oven at 60 °C for 6 h to obtain carbon-supported cerium hydroxide. Hold the carbon-supported cerium hydroxide at 400 °C for 40 min in a tube furnace filled with nitrogen, then hold it at 300 °C for 30 min in a reducing atmosphere of a mixture of carbon monoxide and argon (carbon monoxide accounting for 8%). Figure 7 The thermogravimetric curves show that a carbon-supported cerium oxide electrocatalyst with an oxygen vacancy ratio of 0.41 and a mass fraction of 15% was obtained.

[0061] Example 12

[0062] Take 50 mg of multi-walled carbon nanotubes and place them in 50 mL of deionized water, then add 0.927 mL of 20 mmol L⁻¹. -1 Cerium nitrate solution and 0.37 mL 2 mol L -1 Potassium hydroxide solution. Stirred at room temperature for 60 min, filtered through a Buchner funnel until the filtrate was neutral, and the resulting solid was dried in a vacuum oven at 60 °C for 6 h to obtain carbon-supported cerium hydroxide. The carbon-supported cerium hydroxide was kept at 300 °C for 60 min in a tube furnace filled with carbon dioxide, and then dissolved in a reducing aqueous solution (1 mol L⁻¹). -1 The cerium oxide electrocatalyst with a carbon-supported oxygen vacancy ratio of 0.44 and a mass fraction of 6% was obtained by keeping it in an aqueous solution of ascorbic acid for 60 min.

[0063] Comparative Example 1

[0064] Take 50 mg of BP2000 carbon black and place it in 50 mL of deionized water, then add 0.927 mL of 20 mmol L. -1 Cerium nitrate solution and 0.37 mL 2 mol L -1 Potassium hydroxide solution. Stirred at room temperature for 60 min, filtered through a Buchner funnel until the filtrate was neutral, and the resulting solid was dried in a vacuum oven at 60 °C for 6 h to obtain carbon-supported cerium hydroxide. The carbon-supported cerium hydroxide was held in an air-filled tube furnace at 250 °C for 60 min, and then held in a reducing atmosphere of a mixture of hydrogen and argon (5% hydrogen) at 600 °C for 60 min to obtain a carbon-supported cerium oxide electrocatalyst containing oxygen vacancies. Transmission electron microscopy image (…). Figure 8 The results show that cerium oxide particles agglomerate on carbon materials and the particle distribution is uneven.

[0065] Comparative Example 2

[0066] Take 50 mg of EC600 carbon black and place it in 50 mL of deionized water, then add 0.927 mL of 20 mmol L⁻¹. -1 Cerium nitrate solution and 0.37 mL 5 mol L -1 Potassium hydroxide solution. Stirred at room temperature for 60 min, filtered through a Buchner funnel until the filtrate was neutral, and the resulting solid was dried in a vacuum oven at 60 °C for 6 h to obtain carbon-supported cerium hydroxide. The carbon-supported cerium hydroxide was kept in an air-filled tube furnace at 250 °C for 60 min, and then kept in a reducing atmosphere of a mixture of hydrogen and argon (5% hydrogen) at 250 °C for 60 min to obtain a carbon-supported cerium oxide electrocatalyst containing oxygen vacancies. Transmission electron microscopy image (see...) Figure 9 The results show that cerium oxide particles agglomerate on carbon materials and the particle distribution is uneven.

Claims

1. The application of a carbon-supported nanoscale cerium oxide electrocatalyst containing oxygen vacancies in a direct ascorbic acid fuel cell, characterized in that, The preparation method of the carbon-supported nanoscale cerium oxide electrocatalyst with controllable oxygen vacancy content includes the following steps: (1) Disperse the carbon material in deionized water, then add 10-100 mmol L -1 Aqueous solutions of cerium salt precursors and 0.5-3.0 mol L -1 The aqueous solution of the precipitant was stirred at room temperature for 30-120 min, filtered, and dried to obtain carbon-supported cerium hydroxide; wherein the molar ratio of the precipitant to the cerium salt precursor was 20-40:

1. (2) The carbon-supported cerium hydroxide obtained in step (1) is heated to 150-400°C in a gaseous atmosphere. o A carbon-supported cerium oxide catalyst is obtained by maintaining the gas at a temperature of C for at least 30 minutes; wherein the gas is one of air, nitrogen, argon, or carbon dioxide. (3) The carbon-supported cerium oxide catalyst obtained in step (2) is heated to 200-500 °C under a reducing atmosphere. o A carbon-supported cerium oxide electrocatalyst containing oxygen vacancies is obtained by holding the catalyst at C for more than 30 minutes, or by holding it in a reducing aqueous solution for more than 30 minutes.

2. The application according to claim 1, characterized in that, The cerium salt precursor is one of cerium nitrate, cerium sulfate, or cerium chloride aqueous solution.

3. The application according to claim 1, characterized in that, The precipitant is one of sodium hydroxide, potassium hydroxide, potassium bicarbonate, sodium bicarbonate, sodium carbonate, potassium carbonate, or ammonia water.

4. The application according to claim 1, characterized in that, The reducing atmosphere is a mixture of gas 2 and gas 3, wherein gas 2 is one of hydrogen or carbon monoxide, and gas 3 is one of nitrogen, argon or carbon dioxide, and gas 2 accounts for 3%-10% of the volume of the mixture.

5. The application according to claim 1, characterized in that, The reducing aqueous solution is an aqueous solution of one of sodium borohydride, ascorbic acid, sodium ascorbate, and potassium bromide, with a concentration of 0.1-1 mol / L. -1 .

6. The application according to claim 1, characterized in that, The carbon material is one of carbon black, multi-walled carbon nanotubes, and graphene oxide; the carbon black is one of BP2000, EC600, EC300, and VXC-72; the carbon material is dispersed in deionized water at a concentration of 1-2 mg / mL. -1 .

7. The application according to claim 1, characterized in that, The mass fraction of cerium oxide in carbon materials is 2-20%.

8. The application according to any one of claims 1-7, characterized in that, The particle size of cerium oxide nanoparticles is 2.5-3.5 nm.

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