Carbon-coated cerium oxide material with excellent electrocatalytic oxygen reduction performance

Abstract

The application discloses a carbon-coated cerium oxide material with excellent electrocatalytic oxygen reduction performance, and relates to the technical fields of materials, chemistry and electrocatalysis. The preparation method comprises the following steps: S100, preparation of a cerium oxide precursor; and S200, preparation of the carbon-coated cerium oxide. The amorphous carbon coating technology is used to introduce a carbon layer with high electron density, so that the cerium oxide core is effectively protected from corrosion or decomposition in the reaction process, the stability and service life of the catalyst are significantly improved, the mechanical strength of the catalyst is improved due to the existence of the carbon layer, the particle aggregation and abrasion between particles are reduced, the durable time of the catalyst is further prolonged, the interaction between the amorphous carbon coating and the cerium oxide promotes the generation of more oxygen vacancies and defects, the vacancies and defects serve as active sites, the oxygen reduction reaction is accelerated, and the selectivity to hydrogen peroxide generation is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of materials, chemistry and electrocatalysis, in particular to a carbon-coated cerium oxide material with excellent electrocatalytic oxygen reduction performance. BACKGROUND

[0002] In recent years, the large consumption of fossil energy has caused a series of problems such as energy shortage. The electrocatalytic oxygen reduction reaction is an important step in fuel cells and metal-air batteries, and has been increasingly concerned. In recent years, hybrid electrocatalysts of transition metal oxides and carbon materials have been widely used in the study of electrocatalytic oxygen reduction reaction, in which carbon materials play a role of promoter in most cases. Carbon-based materials have been widely concerned in the application of electrocatalytic oxygen reduction to hydrogen peroxide due to their good electrical conductivity, low cost, stability and other characteristics. The ability of carbon-based materials to electrochemically generate hydrogen peroxide can be improved by doping non-metallic heteroatoms or creating structural defects and modifying the surface. The electrocatalytic activity of carbon-based materials can be optimized by strategies such as the construction of porous structures and the creation of special functional groups, which can accelerate mass transfer and expose more active sites. For example, samples containing rich C=O functional groups show more positive potential than samples containing C-O-C functional groups. More notably, cerium oxide, as a rare earth metal oxide, has been widely used in various catalytic fields. The origin of the electrocatalytic activity of cerium oxide is the redox pair, which can undergo rapid transformation and produce rich oxygen vacancies. When the catalytic reaction occurs, cerium oxide can promote the activation of reactants as a reaction site, and can also improve the specific surface area to expose more active sites in the catalytic boundary to increase the electrocatalytic activity. In addition, cerium oxide has excellent oxygen storage capacity and electronic / ionic conductivity. The redox pair can undergo rapid transformation and produce rich oxygen vacancies. When the catalytic reaction occurs, cerium oxide can promote the activation of reactants as a reaction site, and can also improve the specific surface area to expose more active sites in the catalytic boundary to increase the electrocatalytic activity. In addition, cerium oxide has excellent oxygen storage capacity and electronic / ionic conductivity. and The redox pair can undergo rapid transformation and produce rich oxygen vacancies. When the catalytic reaction occurs, cerium oxide can promote the activation of reactants as a reaction site, and can also improve the specific surface area to expose more active sites in the catalytic boundary to increase the electrocatalytic activity. In addition, cerium oxide has excellent oxygen storage capacity and electronic / ionic conductivity.

[0003] Therefore, the present application proposes a carbon-coated cerium oxide material with excellent electrocatalytic oxygen reduction performance, which exhibits excellent performance in the cathode oxygen reduction reaction of fuel cells. SUMMARY

[0004] The present application aims to make up for the shortcomings of the prior art, and provides a carbon-coated cerium oxide material with excellent electrocatalytic oxygen reduction performance, which utilizes amorphous carbon coating technology to introduce a carbon layer with high electron density, effectively protecting the cerium oxide core from corrosion or decomposition during the reaction process, significantly improving the stability and service life of the catalyst, and the presence of the carbon layer also improves the mechanical strength of the catalyst, reduces particle aggregation and wear, further prolongs the service life of the catalyst, the interaction between the amorphous carbon coating and the cerium oxide promotes the generation of more oxygen vacancies and defects, which act as active sites to accelerate the oxygen reduction reaction and improve the selectivity of hydrogen peroxide generation, and the electronic structure of the carbon layer optimizes the charge distribution on the surface of the catalyst, making it easier for electrons to transfer to the reactant molecules, reducing the activation energy of the oxygen reduction reaction and improving the reaction efficiency.

[0005] To solve the above technical problems, the present application provides the following technical solutions: on the one hand, a carbon-coated cerium oxide material with excellent electrocatalytic oxygen reduction performance, the preparation method comprising: step S100 preparation of cerium oxide precursor and step S200 preparation of carbon-coated cerium oxide, wherein the specific steps of step S100 preparation of cerium oxide precursor are:

[0006] S101, material preparation: weigh an appropriate amount of cerium nitrate hexahydrate ( ), ensure the required molar amount,

[0007] Prepare deionized water for dissolving cerium nitrate and subsequent washing steps, and prepare sodium hydroxide (NaOH) solution, the concentration of which is adjusted according to the reaction requirements;

[0008] S102, mixing: in a suitable container, slowly add cerium nitrate hexahydrate powder to deionized water while stirring, until completely dissolved, forming a uniform solution, slowly add sodium hydroxide solution to the cerium nitrate solution while continuously stirring, to ensure thorough mixing, this process will produce a white precipitate, which is the initial formation of cerium hydroxide ( );

[0009] S103, heating: place the mixed solution in a heating device and heat to a certain temperature for a period of time to promote the complete formation and aging of cerium hydroxide;

[0010] S104, centrifugation and drying: centrifuge the heated solution to separate the solid precipitate, wash the precipitate with deionized water several times to remove residual ions and impurities, centrifuge the washed precipitate to remove excess water, and dry the centrifuged solid in an oven at an appropriate temperature (such as 80-120℃) overnight to obtain the cerium oxide precursor;

[0011] The specific steps of the step S200 of preparing the carbon-coated cerium oxide are as follows:

[0012] S201, preparation of a glucose solution: a proper amount of glucose is weighed and added to deionized water, heated and stirred until completely dissolved to form a glucose solution;

[0013] S202, mixing and heating: the cerium oxide precursor powder obtained in the step S100 is added to the glucose solution, stirred uniformly to ensure that the precursor particles are fully wrapped by the glucose solution, and the mixed solution is placed in a heating device and heated to a certain temperature for a period of time, so that the glucose is carbonized at high temperature and coated on the surface of the cerium oxide;

[0014] S203, centrifugation and dialysis: the heated solution is subjected to centrifugal treatment to separate out the solid product, the solid product is washed with deionized water to remove the unreacted substances attached to the surface, and the washed solid product is placed in a dialysis membrane and subjected to dialysis treatment with deionized water to remove the residual glucose and other small molecular substances, the dialysis time is determined according to actual needs, until no glucose is detected in the dialysate;

[0015] S204, freeze-drying and crushing: the dialyzed sample is placed in a freeze-drying machine for freeze-drying treatment to remove the water in the sample and retain its porous structure, after the freeze-dried sample is taken out, a proper amount of deionized water is added, and crushing treatment is performed in a cell crusher to refine the particles and increase the specific surface area, and centrifugal drying treatment is performed again to remove excess water, to obtain the final carbon-coated cerium oxide electrocatalyst.

[0016] Further, during the heating process in the step S103, inert gas (such as nitrogen, argon) is also introduced into the heating device for protection, to prevent the cerium oxide precursor from being oxidized at high temperature, thereby improving the purity and catalytic performance of the product.

[0017] Further, in the step S202 of mixing and heating, the heating rate is further controlled to be no more than 5℃ per minute, to ensure that the glucose is uniformly and slowly carbonized and coated on the surface of the cerium oxide precursor to form a uniform carbon layer, thereby improving the stability and durability of the catalyst.

[0018] Further, after the step S203 of centrifugation and dialysis, the dialyzed solid product is also subjected to acid washing treatment to further remove the impurities and incompletely reacted organic substances attached to the surface, the acid washing treatment uses a dilute acid solution (such as dilute nitric acid, dilute hydrochloric acid), and after soaking at room temperature for a certain period of time, the dialyzed solid product is washed with deionized water to neutralize, to obtain a more pure carbon-coated cerium oxide material.

[0019] Further, before the freeze-drying step S204, the sample after dialysis and acid washing is further subjected to ultrasonic treatment to further break the agglomeration between particles, increase the specific surface area and active sites of the catalyst, the ultrasonic treatment is carried out in a suitable solvent including ethanol or acetone, and the ultrasonic time and power are controlled to avoid particle breakage.

[0020] Further, the concentration of the prepared sodium hydroxide in step S101 is 1-10 mol / L, the volume ratio of water to sodium hydroxide in step S102 is 1:(1-20), the reaction time is 1-100 min, the heating temperature in step S103 is 50-150℃, and the heating time is 12-36 h.

[0021] Further, the mass ratio of the prepared cerium oxide precursor powder to glucose in step S201 is 1:(1-10), the heating temperature in step S202 is 100-200℃, the heating time is 1-10 h, and the cell crushing time in step S204 is 1-5 h.

[0022] Further, the drying temperature in steps S104 and S204 is 50-100℃, and the drying time is 10-24 h.

[0023] In another aspect, an electrocatalyst for electrocatalytic oxygen reduction production of hydrogen peroxide, the electrocatalyst being a carbon-coated rare earth metal oxide, is prepared according to the above preparation method.

[0024] Compared with the prior art, the carbon-coated cerium oxide material with excellent electrocatalytic oxygen reduction performance has the following beneficial effects:

[0025] Firstly, the amorphous carbon coating technology introduced in the present application can effectively protect the cerium oxide core by introducing a carbon layer with high electron density, preventing it from being corroded or decomposed during the reaction process, thereby significantly improving the stability and service life of the catalyst.

[0026] Secondly, the application promotes the generation of more oxygen vacancies and defects by utilizing the interaction between amorphous carbon coating and cerium oxide, which acts as active sites to accelerate the oxygen reduction reaction and improve the selectivity of hydrogen peroxide generation, the electronic structure of the carbon layer optimizes the charge distribution on the catalyst surface, making it easier for electrons to transfer to the reactant molecules, reducing the activation energy of the oxygen reduction reaction, thereby improving the reaction efficiency, freeze-drying and crushing further refine the catalyst particles, increasing the specific surface area and the number of active sites, providing more reaction sites for the oxygen reduction reaction, and further improving the catalytic performance.

[0027] Thirdly, in the preparation process, the catalyst surface impurities and incompletely reacted organic matter are effectively removed through multiple purification steps such as centrifugation, dialysis, acid washing and ultrasonic treatment, improving the purity and quality of the product, the heating process under inert gas protection prevents the oxidation of cerium oxide precursor at high temperature, avoiding the generation of harmful oxides, improving the safety and environmental friendliness of the product, and the finally obtained carbon-coated cerium oxide electrocatalyst has excellent catalytic performance and stability, which can efficiently and stably generate hydrogen peroxide in the electrocatalytic oxygen reduction reaction, providing reliable technical support for the industrial production of related fields.

[0028] Other advantages, objects and features of the present application will be in part apparent and in part pointed out hereinafter in the specification, and in part will be learned from the practice of the application. BRIEF DESCRIPTION OF DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0030] Figure 1 is the X-ray diffraction pattern of carbon-coated cerium oxide and cerium oxide material prepared by the method of the present application;

[0031] Figure 2 is the scanning electron microscope image of the carbon-coated cerium oxide material prepared by the method of the present application;

[0032] Figure 3 is the transmission electron microscope image of the carbon-coated cerium oxide material prepared by the method of the present application;

[0033] Figure 4 is the hydrogen peroxide selectivity graph of carbon-coated cerium oxide and cerium oxide material prepared by the method of the present application. DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0035] Embodiment one

[0036] Preparation of / C

[0037] Step one: Preparation of the precursor

[0038] Solution preparation: first, 0.8 g of cerium nitrate hexahydrate (Ce(NO3)3·6H2O) is weighed and added to 5 mL of deionized water, and fully stirred with a magnetic stirrer or glass rod until completely dissolved, forming a uniform cerium nitrate solution. Then, 35 mL of sodium hydroxide (NaOH) solution with a concentration of 6 mol / L is quickly poured into the above cerium nitrate solution and immediately stirred vigorously for 30 minutes. The purpose of this step is to make ions react with ions to form precipitates.

[0039] Hydrothermal reaction: the above mixed solution is carefully transferred into a 100 mL high-pressure reaction kettle (lined with polytetrafluoroethylene to prevent corrosion), ensuring good sealing, and then the reaction kettle is placed in an oven for constant temperature reaction at 100°C for 24 hours. The hydrothermal reaction helps to crystallize and control the morphology of the precipitates.

[0040] Washing and drying: after the reaction is completed, the reaction kettle is naturally cooled to room temperature, and the precipitate is taken out. The precipitate is washed with deionized water and anhydrous ethanol alternately for three times to remove excess ions and impurities. Then, the yellow solid is placed in a constant temperature oven at 65°C for drying overnight until completely dry. Finally, the dried solid is ground into powder, and the precursor is obtained.

[0041] Step two: Preparation of / C composite material

[0042] Glucose solution mixing: 0.1 g of precursor powder is weighed and added to 4 mL of glucose solution with a concentration of 0.1 g / mL. By vigorous stirring, it is ensured that the powder is uniformly dispersed in the glucose solution.

[0043] ​Secondary hydrothermal reaction: The above mixed solution was transferred to a 10 mL high-pressure reactor (also using a PTFE liner), sealed, and placed in an oven at 160°C for 3 hours. This step aims to carbonize the glucose at high temperature and coat it with... Particle surface;

[0044] Purification and Drying: After the reaction was completed, the reaction vessel was allowed to cool naturally to room temperature. The reaction product was then removed and dialyzed using a dialysis membrane (with a molecular weight cutoff of approximately 2000 Da) for two days to remove unreacted glucose and other small molecule impurities. After dialysis, the solution was freeze-dried to remove moisture, yielding the desired product. / C composite materials;

[0045] Grinding and post-processing: The freeze-dried material... The / C composite material is mixed with an appropriate amount of deionized water and pulverized for 1.5 hours using a cell disruptor or ball mill to improve its dispersibility and particle size distribution. After pulverization, the suspension is centrifuged to remove larger particles or undispersed agglomerates. Finally, the solid obtained by centrifugation is dried in a constant temperature oven to obtain the final product. / C composite material sample.

[0046] Example 2

[0047] Preparation

[0048] Step 1: Solution preparation: First, accurately weigh 0.8g of cerium nitrate hexahydrate ( Add 4 mL of cerium nitrate hexahydrate to 4 mL of deionized water and stir thoroughly with a magnetic stirrer or glass rod until the cerium nitrate hexahydrate is completely dissolved to form a homogeneous solution. Then, quickly and evenly pour 35 mL of 6 mol / L sodium hydroxide (NaOH) solution into the cerium nitrate solution, stirring vigorously throughout the process to ensure thorough mixing and uniform reaction. Stir for approximately 30 minutes to allow the solution to fully dissolve. Ions and Ions react completely to form precipitation;

[0049] Step 2: Hydrothermal reaction: [The following text appears to be a separate, unrelated section:] ...containing The precipitated mixture was carefully transferred to a 100 mL high-pressure reactor, which should be lined with PTFE to prevent corrosion. After ensuring the reactor was well sealed, it was placed in an oven and reacted at 100°C for 24 hours. Hydrothermal reaction is beneficial. The crystallization of the precipitate forms a more stable crystal. Precursor;

[0050] Washing and centrifugation: after the reaction is completed, the reactor is naturally cooled to room temperature, the reactor is opened, the precipitate is taken out, and the precipitate is washed and centrifuged alternately with deionized water and anhydrous ethanol, and after each washing, centrifugal separation is required to remove residual ions and impurities, and this process is repeated three times to ensure that the precipitate is thoroughly washed;

[0051] Drying and grinding: the washed yellow solid is placed in a constant temperature oven at 65°C and dried overnight until the solid is completely dried without residual moisture, then the dried solid is taken out and ground using a mortar or a ball mill until a fine powder is obtained;

[0052] Product collection: the ground powder is collected to obtain the final product.

[0053] Example three

[0054] Electrocatalytic oxygen reduction test and systematic characterization of carbon-coated cerium oxide material:

[0055] 3mg of catalyst was weighed and dispersed in a mixed solution of isopropanol, water and Nafion, and after ultrasonic treatment, a uniformly dispersed solution was obtained, then an appropriate amount was dropped on a glassy carbon electrode, dried, and the test system was a three-electrode system, which was Ag / AgCl (reference electrode), platinum mesh (counter electrode) and glassy carbon electrode (working electrode) with catalyst dropped; the test electrolyte was 0.1M KOH solution saturated with oxygen, the potential scanning range was 0.2-1.0V vs. reversible hydrogen electrode, the scanning speed was 5mV / s, the rotation speed of the rotating disc was 1600rpm, and the carbon-coated cerium oxide material was characterized by XRD, SEM and TEM.

[0056] It is obvious to those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or essential characteristics of the present application. Therefore, the embodiments should be regarded as exemplary and non-limiting, and the scope of the present application is defined by the appended claims rather than the above description, and therefore all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present application. Any reference signs in the claims should not be regarded as limiting the claims involved.

Claims

1. A method for preparing a carbon-coated cerium oxide material having excellent electrocatalytic oxygen reduction performance, characterized by, The preparation method comprises the steps of: step S100 of preparing a cerium oxide precursor and step S200 of preparing a carbon-coated cerium oxide, wherein the specific steps of the step S100 of preparing a cerium oxide precursor are: S101, material preparation: weigh an appropriate amount of cerium nitrate hexahydrate to ensure the required molar amount, Prepare deionized water, and prepare a sodium hydroxide solution; S102, mixing: in a suitable container, slowly add cerium nitrate hexahydrate powder to deionized water while stirring, until completely dissolved, forming a uniform solution, slowly add the sodium hydroxide solution to the cerium nitrate solution while continuously stirring, to ensure thorough mixing and uniformity, this process will produce a white precipitate, which is the initial formation of cerium hydroxide; S103, heating: place the mixed solution in a high-pressure reaction kettle and heat to 60-150℃ for 15-35h to promote the complete formation and aging of cerium hydroxide; S104, centrifugation and drying: centrifuge the heated solution to separate the solid precipitate, wash the precipitate with deionized water several times to remove residual ions and impurities, centrifuge the washed precipitate to remove excess water, and dry the centrifuged solid in an oven at a temperature of 80-120℃ overnight to obtain a cerium oxide precursor; The specific steps of the step S200 of preparing a carbon-coated cerium oxide are: S201, preparation of a glucose solution: weigh an appropriate amount of glucose and add it to deionized water, heat and stir until completely dissolved to form a glucose solution; S202, mixing and heating: add the cerium oxide precursor powder obtained in step S100 to the glucose solution and stir until uniform, ensuring that the precursor particles are fully coated with the glucose solution, place the mixed solution in a high-pressure reaction kettle and heat to 100-180℃ for 1-5h to carbonize the glucose at high temperature and coat the cerium oxide surface; S203, centrifugation and dialysis: centrifuge the heated solution to separate the solid product, wash the solid product with deionized water to remove surface-attached unreacted substances, place the washed solid product in a dialysis membrane and dialyze with deionized water to remove residual glucose and other small molecular substances, the dialysis time is determined according to actual needs until no glucose is detected in the dialysate; S204, freeze-drying and crushing: place the dialyzed sample in a freeze-dryer for freeze-drying treatment to remove water from the sample and preserve its porous structure, after removing the freeze-dried sample, add an appropriate amount of deionized water and crush it in a cell crusher to refine the particles and increase the specific surface area, then perform centrifugal drying treatment again to remove excess water and obtain the final carbon-coated cerium oxide electrocatalyst.

2. The method for preparing carbon-coated cerium oxide material with excellent electrocatalytic oxygen reduction performance according to claim 1, characterized in that, During the heating process in step S103, inert gas is also introduced into the heating device for protection to prevent the cerium oxide precursor from being oxidized at high temperature, thereby improving the purity and catalytic performance of the product.

3. The method for preparing carbon-coated cerium oxide material with excellent electrocatalytic oxygen reduction performance according to claim 1, characterized in that, In the mixing and heating process of step S202, the heating rate is further controlled to be no more than 5℃ per minute to ensure that the glucose uniformly and slowly carbonizes to coat the surface of the ceria precursor, forming a uniform carbon layer, thereby improving the stability and durability of the catalyst.

4. The method for preparing carbon-coated cerium oxide material with excellent electrocatalytic oxygen reduction performance according to claim 1, characterized in that, After the centrifugation and dialysis of step S203, the solid product after dialysis is further subjected to an acid washing treatment to further remove the impurities and incompletely reacted organic matter attached to the surface, the acid washing treatment uses a dilute acid solution, and after soaking for a certain time at room temperature, the product is washed with deionized water to neutralize, thereby obtaining a more pure carbon-coated ceria material.

5. The method for preparing carbon-coated cerium oxide material with excellent electrocatalytic oxygen reduction performance according to claim 1, characterized in that, Before the freeze-drying step S204, the sample after dialysis and acid washing is further subjected to ultrasonic treatment to further break the agglomeration between particles, increase the specific surface area and active sites of the catalyst, the ultrasonic treatment is carried out in a suitable solvent, including ethanol or acetone, and the ultrasonic time and power are controlled to avoid particle damage.

6. The method for preparing carbon-coated cerium oxide material with excellent electrocatalytic oxygen reduction performance according to claim 1, characterized in that, The concentration of the prepared sodium hydroxide in step S101 is 1-10 mol / L, the volume ratio of water to sodium hydroxide in step S102 is 1:(1-20), the reaction time is 1-100 min, the heating temperature in step S103 is 50-150℃, and the heating time is 12-36 h.

7. The method for preparing carbon-coated cerium oxide material with excellent electrocatalytic oxygen reduction performance according to claim 1, characterized in that, The mass ratio of the prepared ceria precursor powder to glucose in step S201 is 1:(1-10), the heating temperature in step S202 is 100-200℃, the heating time is 1-10 h, and the cell crushing time in step S204 is 1-5 h.

8. The method for preparing carbon-coated cerium oxide material with excellent electrocatalytic oxygen reduction performance according to claim 1, characterized in that, The drying temperature in steps S104 and S204 is 50-100℃, and the drying time is 10-24 h.

9. A carbon-coated cerium oxide material having excellent electrocatalytic oxygen reduction performance, characterized by, According to any one of claims 1-8. According to any one of claims 1-8.

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