Preparation method of carbon-coated cerium oxide-cobalt heterojunction oxygen electrocatalyst

Abstract

The invention discloses a method for preparing a carbon-coated cerium oxide cobalt heterojunction oxygen evolution electrocatalyst. First, 2-aminoterephthalic acid and sodium hydroxide are dispersed in water for mixing and freeze-drying to obtain 2-aminoterephthalic acid disodium salt; 2-aminoterephthalic acid disodium salt and cerium salt are then dispersed in water, and stirring reaction is performed at room temperature to obtain Ce-MOF; Ce-MOF, cobalt nitrate hexahydrate, and benzimidazole are then dispersed in dimethylformamide for hydrothermal reaction. After the hydrothermal reaction is completed, the product is cleaned and dried to obtain a purple powdery precursor; finally, the precursor is placed in an inert atmosphere for heat treatment, thereby obtaining a carbon-coated cerium oxide cobalt heterojunction oxygen evolution electrocatalyst. The present invention forms a heterojunction by the intercalation of Co and CeO2, and by carbon-coating the heterojunction, significantly improving electrical conductivity, and the obtained oxygen evolution electrocatalyst has high activity and excellent stability.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation and application of new chemical materials, and in particular to a method for preparing a carbon-coated cerium oxide-cobalt heterojunction oxygen electrocatalyst. Background Art

[0002] Hydrogen energy, with its environmentally friendly, high energy density, and high calorific value, is a promising alternative to traditional fossil fuels. Hydrogen production from water splitting driven by renewable energy offers advantages such as high energy conversion efficiency and rapid reaction rates. However, the oxygen evolution reaction (OER) occurring at the anode in water electrolysis suffers from slow four-electron kinetics, resulting in low water splitting efficiency and hindering the development of energy conversion and storage. Therefore, the development of highly active OER electrocatalysts to improve reaction kinetics is a hot topic in energy research. Currently, catalysts widely used in the OER are primarily based on precious metals such as RuO2 and IrO2, but their low storage capacity, high cost, and poor stability significantly limit the development and application of water splitting. Notably, inexpensive CeO2 has attracted considerable attention as an electrocatalyst due to its rich electronic structure, but its catalytic activity needs to be improved. Utilizing heterojunction engineering strategies to construct low-cost, highly active, and long-term stable catalysts is of great significance for industrial water electrolysis and the efficient development and utilization of hydrogen energy. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a method for preparing a carbon-coated cerium oxide-cobalt heterojunction oxygen evolution electrocatalyst. A heterojunction is formed by the intercalation of Co and CeO2, and the conductivity is significantly improved by carbon coating the heterojunction. The obtained oxygen evolution electrocatalyst has high activity and excellent stability.

[0004] The technical solution of the present invention is:

[0005] A method for preparing a carbon-coated cerium oxide-cobalt heterojunction oxygen electrocatalyst comprises the following steps:

[0006] (1) dispersing 2-aminoterephthalic acid and sodium hydroxide in water, mixing, and freeze-drying to obtain 2-aminoterephthalic acid disodium salt;

[0007] (2) Dispersing 2-aminoterephthalic acid disodium salt and cerium salt in water, stirring and reacting at room temperature to obtain Ce-MOF;

[0008] (3) Ce-MOF, cobalt nitrate hexahydrate, and benzimidazole are dispersed in dimethylformamide for hydrothermal reaction. After the hydrothermal reaction is completed, the product is washed and dried to obtain a purple powder precursor;

[0009] (4) The precursor is placed in an inert atmosphere for heat treatment and then cooled naturally to room temperature to obtain a carbon-coated cerium oxide-cobalt heterojunction oxygen electrocatalyst.

[0010] In the step (1), the mass ratio of 2-aminoterephthalic acid to sodium hydroxide is 1:4-5.

[0011] In the step (1), the 2-aminoterephthalic acid and sodium hydroxide are mixed, the mixed solution is subjected to ultrasonic treatment, and then freeze-dried. The freeze-drying time is 20 to 24 hours and the freeze-drying temperature is -85 to -75°C.

[0012] In the step (1), the freeze-dried powder obtained after freeze-drying is added to an appropriate amount of ethanol, fully stirred and dissolved to obtain a suspension, and the suspension is filtered and vacuum-dried to obtain 2-aminoterephthalic acid-disodium salt.

[0013] In the step (2), the cerium salt is cerium chloride hexahydrate, and the mass ratio of cerium chloride hexahydrate to 2-aminoterephthalic acid disodium salt is 1:1.0-1.3.

[0014] In the step (2), 2-aminoterephthalic acid disodium salt and cerium salt are dispersed in water to form a mixed solution. The mixed solution is subjected to ultrasonic dispersion treatment and then stirred at room temperature for 2 to 3 hours.

[0015] In the step (3), the mass ratio of Ce-MOF, cobalt nitrate hexahydrate, and benzimidazole is 1:3-5:2-4.

[0016] In the step (3), the temperature of the hydrothermal reaction is 140-160° C. and the time is 20-24 hours.

[0017] In the step (3), the product is washed with acetone and vacuum dried to obtain a precursor.

[0018] In the step (4), the heat treatment is to maintain the temperature at 450-550°C for 2 hours, then raise the temperature to 700-800°C and maintain the temperature for 2 hours.

[0019] Advantages of the present invention:

[0020] (1) The present invention significantly improves the activity of the anode oxygen evolution reaction during the water electrolysis process; at a current density of 10 mA cm -2 When the overpotential of RuO2 catalyst is 332mV, the overpotential of IrO2 catalyst is 310mV, and the overpotential of oxygen evolution electrocatalyst prepared by the present invention is as low as 210mV.

[0021] (2) The carbon-coated cerium oxide-cobalt heterojunction oxygen electrocatalyst prepared by the present invention exhibits long-lasting stability in a long-term constant current test; after 250 hours and a constant current of 100 mA / cm 2 After testing, the catalytic performance of the oxygen evolution electrocatalyst prepared by the present invention was only attenuated by 10%. 2 After testing, the oxygen evolution electrocatalyst prepared by the present invention showed no obvious catalytic performance degradation and exhibited good stability.

[0022] (3) In the carbon-coated cerium oxide-cobalt heterojunction oxygen evolution electrocatalyst prepared by the present invention, the cerium oxide-cobalt heterojunction is uniformly coated with carbon elements, which increases the conductivity and specific surface area of ​​the catalyst and avoids the aggregation and deactivation of nanocatalyst particles.

[0023] (4) The preparation method of the present invention is simple to operate, has a short preparation time, is easy to transplant and expand production, and is easy to prepare carbon-coated cerium oxide-cobalt heterojunction oxygen electrocatalysts in batches.

[0024] (5) The cost of preparing the oxygen evolution electrocatalyst of the present invention is low. The transition metal cobalt and the rare earth element cerium are relatively abundant in the earth and are inexpensive, which overcomes the shortcomings of high cost and low reserves of noble metal catalysts such as RuO2 and IrO2. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a scanning electron microscope image (SEM image) of the carbon-coated cerium oxide-cobalt heterojunction oxygen electrocatalyst prepared in Example 1 of the present invention.

[0026] Figure 2 This is a high-resolution surface transmission electron microscopy image (HRTEM image) of the carbon-coated cerium oxide-cobalt heterogeneous oxygen electrocatalyst prepared in Example 1 of the present invention.

[0027] Figure 3 It is a linear sweep voltammetry curve (LSV curve) of the OER performance test of the products obtained in Examples of the present invention and Comparative Examples 1 and 2.

[0028] Figure 4 It is a constant current test curve diagram of the products obtained in the embodiment of the present invention and comparative examples 1 and 2. DETAILED DESCRIPTION

[0029] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0030] Example

[0031] A method for preparing a carbon-coated cerium oxide-cobalt heterojunction oxygen electrocatalyst comprises the following steps:

[0032] (1) Weigh 181.15 mg of 2-aminoterephthalic acid and 800 mg of sodium hydroxide, disperse them in 50 mL of deionized water, and ultrasonicate for 3 h to obtain a uniform and stable solution. Then, place the above solution in a freeze dryer and freeze-dry it at -80°C for 24 h. Grind it to obtain a freeze-dried powder. Finally, add the freeze-dried powder to an appropriate amount of ethanol, stir it thoroughly to dissolve it, obtain a suspension, filter it, and vacuum dry it to obtain 2-aminoterephthalic acid disodium salt.

[0033] (2) Weigh 708.5 mg of 2-aminoterephthalic acid disodium salt prepared in step (1) and 620.48 mg of CeCl3·6H2O and disperse them in 50 mL of water. Ultrasonication is used to completely disperse them. Stirring is continued for 3 h. The mixture is filtered and dried to obtain Ce-MOF.

[0034] (3) Weigh 177.28 mg of Ce-MOF prepared in step (2), 700 mg of cobalt nitrate hexahydrate (Co(NO3)2·6H2O), and 568 mg of benzimidazole (C7H6N2), and then ultrasonically disperse the three in 60 mL of dimethylformamide (DMF). After hydrothermal reaction at 140°C for 24 h, the obtained product is washed with acetone and vacuum-dried to obtain a purple powder precursor;

[0035] (4) The precursor prepared in step (3) was placed in a tube furnace under an argon atmosphere at 5°C·min -1 The heating rate was increased from room temperature to 500°C and kept at this temperature for 2 hours; the temperature was further increased to 750°C and kept at this temperature for 2 hours; and finally the temperature was naturally cooled to room temperature to obtain the product - carbon-coated cerium oxide-cobalt heterojunction oxygen evolution electrocatalyst, marked as CeO2-Co@C.

[0036] Figure 1 The SEM image of the carbon-coated cerium oxide-cobalt heterojunction oxygen electrocatalyst prepared in Example 1 is Figure 1 It can be seen that the oxygen evolution electrocatalyst is in the shape of nano-pillars; Figure 2 HRTEM image of the oxygen evolution electrocatalyst prepared in Example Figure 2 It can be seen that carbon elements are evenly coated on the heterojunction of CeO2 and Co.

[0037] Comparative Example 1

[0038] Compared with the embodiment, the difference of comparative example 1 is that: steps (1) and (2) are omitted, Ce-MOF is not added in step (3), step (4) is the same as that of the embodiment, and the product prepared is Co@C.

[0039] Comparative Example 2

[0040] Compared with the embodiment, the difference of comparative example 2 is that no cobalt nitrate hexahydrate is added in step (3), the other steps are the same as those in the embodiment, and the product prepared is CeO2.

[0041] The products obtained in Example 1, Comparative Example 2 were subjected to OER performance tests. All performance tests were performed on a CHI-760E electrochemical workstation equipped with a typical three-electrode system. The oxygen evolution performance test was performed in an electrolyte of 1M KOH solution. A carbon rod was used as the counter electrode and a mercury oxide electrode was used as the reference electrode. 5 mg of the prepared product powder was weighed and added to 1 mL of a mixed solution of water and ethanol (V 水 :V 乙醇 =3:1) was thoroughly sonicated, and 30 μL of a perfluorosulfonic acid polymer solution (Nafion solution) was added. After further sonication for 30 minutes, 5 μL was dripped onto a 3 mm radius glassy carbon electrode using a micropipette and allowed to air dry, serving as the working electrode. A linear voltammetric sweep test was performed on the working electrode at a sweep rate of 10 mV / s.

[0042] from Figure 3 It can be seen that when the current density is 10mA·cm - 2, the overpotential of the carbon-coated cerium oxide-cobalt heterojunction oxygen evolution electrocatalyst prepared in Example 1 is as low as 210 mV, the overpotential of the Co@C electrocatalyst prepared in Comparative Example 1 is 280 mV, and the overpotential of the CeO2 electrocatalyst prepared in Comparative Example 2 is higher. Therefore, it can be concluded that the carbon-coated cerium oxide-cobalt heterojunction oxygen evolution electrocatalyst prepared in Example has excellent catalytic activity for oxygen evolution reaction.

[0043] from Figure 4 It can be seen that the Co@C electrocatalyst prepared in Comparative Example 1 and the CeO2 electrocatalyst prepared in Comparative Example 2 decay rapidly under constant current, while the carbon-coated cerium oxide-cobalt heterojunction oxygen evolution electrocatalyst prepared in Example 1 decays rapidly under constant current. -2 After 1000 h of constant current treatment, there was no significant degradation in performance. Therefore, it was concluded that the carbon-coated cerium oxide-cobalt heterojunction oxygen evolution electrocatalyst prepared in the example had good oxygen evolution reaction stability.

[0044] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a carbon-coated cerium oxide-cobalt heterojunction oxygen electrocatalyst, characterized by: The specific steps include: (1) dispersing 2-aminoterephthalic acid and sodium hydroxide in water, mixing, and freeze-drying to obtain 2-aminoterephthalic acid disodium salt; (2) Dispersing 2-aminoterephthalic acid disodium salt and cerium salt in water, stirring and reacting at room temperature to obtain Ce-MOF; (3) Ce-MOF, cobalt nitrate hexahydrate, and benzimidazole are dispersed in dimethylformamide for hydrothermal reaction. After the hydrothermal reaction is completed, the product is washed and dried to obtain a purple powder precursor; the mass ratio of Ce-MOF, cobalt nitrate hexahydrate, and benzimidazole is 1:3-5:2-4, the hydrothermal reaction temperature is 140-160°C, and the time is 20-24h; (4) The precursor is placed in an inert atmosphere for heat treatment and then cooled naturally to room temperature to obtain a carbon-coated cerium oxide-cobalt heterojunction oxygen electrocatalyst.

2. The method for preparing a carbon-coated cerium oxide-cobalt heterojunction oxygen electrocatalyst according to claim 1, characterized in that: In the step (1), the mass ratio of 2-aminoterephthalic acid to sodium hydroxide is 1:4-5.

3. The method for preparing a carbon-coated cerium oxide-cobalt heterojunction oxygen electrocatalyst according to claim 1, characterized in that: In the step (1), the 2-aminoterephthalic acid and sodium hydroxide are mixed, the mixed solution is subjected to ultrasonic treatment, and then freeze-dried. The freeze-drying time is 20 to 24 hours and the freeze-drying temperature is -85 to -75°C.

4. The method for preparing a carbon-coated cerium oxide-cobalt heterojunction oxygen electrocatalyst according to claim 1, characterized in that: In the step (1), the freeze-dried powder obtained after freeze-drying is added to an appropriate amount of ethanol, fully stirred and dissolved to obtain a suspension, and the suspension is filtered and vacuum-dried to obtain 2-aminoterephthalic acid-disodium salt.

5. The method for preparing a carbon-coated cerium oxide-cobalt heterojunction oxygen electrocatalyst according to claim 1, characterized in that: In the step (2), the cerium salt is cerium chloride hexahydrate, and the mass ratio of cerium chloride hexahydrate to 2-aminoterephthalic acid disodium salt is 1:1.0-1.

3.

6. The method for preparing a carbon-coated cerium oxide-cobalt heterojunction oxygen electrocatalyst according to claim 1, characterized in that: In the step (2), 2-aminoterephthalic acid disodium salt and cerium salt are dispersed in water to form a mixed solution. The mixed solution is subjected to ultrasonic dispersion treatment and then stirred at room temperature for 2 to 3 hours.

7. The method for preparing a carbon-coated cerium oxide-cobalt heterojunction oxygen electrocatalyst according to claim 1, characterized in that: In the step (3), the product is washed with acetone and vacuum dried to obtain a precursor.

8. The method for preparing a carbon-coated cerium oxide-cobalt heterojunction oxygen electrocatalyst according to claim 1, characterized in that: In the step (4), the heat treatment is to maintain the temperature at 450-550°C for 2 hours, then raise the temperature to 700-800°C and maintain the temperature for 2 hours.

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