Catalyst for fuel cell as well as preparation method and application of catalyst

Abstract

The invention belongs to the technical field of fuel cells, and particularly relates to a catalyst for a fuel cell as well as a preparation method and application thereof. Modifying the oxidized carbon nanotube by using a carboxylic acid modifier containing N or S atoms to obtain a modified carbon nanotube; adding the ionic liquid solution into the platinum complex solution to obtain a platinum precursor solution; then adding a platinum precursor solution into the dispersion liquid containing the modified carbon nanotubes, stirring and standing to obtain slurry; and reducing the slurry in a hydrogen atmosphere, purifying and drying to obtain the catalyst for the fuel cell. The carbon nanotube carrier is treated by introducing the carboxylic acid modifier which can be tightly combined with platinum ions, so that the interaction between the carrier and the active component platinum is remarkably enhanced, platinum metal particles are effectively prevented from being agglomerated in the use process, and the activity and stability of the catalyst are effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of fuel cells, and in particular relates to a catalyst for fuel cells and a preparation method and application thereof. Background Art

[0002] Proton exchange membrane fuel cells (PEMFCs) have gained wide attention due to their low-carbon, green, efficient, and sustainable environmental characteristics, and have become a representative of new energy conversion equipment to replace traditional fossil power sources. During the operation of PEMFC, the dissolution of platinum (Pt) nanoparticles at the cathode, the particle enlargement and agglomeration caused by the Oswald ripening effect, and the corrosion of the carbon carrier are the main reasons for the reduction of fuel cell life. In order to solve this problem, improving the durability of the catalyst has become an important strategy to effectively extend the working life of PEMFC.

[0003] Patent CN115548354A discloses a method for preparing a highly durable platinum-carbon catalyst, which effectively deposits zirconium oxide on an activated carbon substrate and uses the steric hindrance effect of zirconium oxide to create a stable anchor point for subsequent platinum particles. This design improves the durability and stability of the catalyst by limiting the migration and agglomeration of platinum particles during preparation and use; however, the surface of the carbon carrier contains a large number of defects and unsaturated bonds, which are easily oxidized and corroded under operating conditions, causing the platinum particles to fall off and the catalyst activity to decrease. Summary of the invention

[0004] In view of the above problems existing in the prior art, the present invention provides a fuel cell catalyst and a preparation method and application thereof, which can ensure the stable existence of platinum in the catalyst and solve the problem of platinum ion shedding.

[0005] To achieve the above object, the technical solution provided by the present invention is as follows: In a first aspect, the present application provides a method for preparing a fuel cell catalyst, comprising the following steps: S1: oxidizing the carbon nanotubes to obtain oxidized carbon nanotubes; S2: mixing the oxidized carbon nanotubes with an aqueous solution of a carboxylic acid modifier containing N or S atoms and reacting them at 60-100° C. for 10-15 hours, and washing and drying the reaction product to obtain modified carbon nanotubes; S3: mixing the ionic liquid with the first solvent to obtain an ionic liquid solution; mixing the platinum complex with the second solvent to obtain a platinum complex solution, and adding the ionic liquid solution to the platinum complex solution under stirring to obtain a platinum precursor solution; S4: dispersing the modified carbon nanotubes in a third solvent to obtain a dispersion, then adding a platinum precursor solution to the dispersion, stirring and standing to obtain a slurry; reducing the slurry in a hydrogen atmosphere, purifying and drying to obtain the fuel cell catalyst.

[0006] Optionally, the carboxylic acid modifier containing N or S atoms is selected from one or more of the following modifiers: .

[0007] Optionally, the concentration of the aqueous solution of the carboxylic acid modifier containing N or S atoms is 0.5-2 mol / L, and the mass ratio of the oxidized carbon nanotubes to the aqueous solution of the carboxylic acid modifier containing N or S atoms is 1:(5-20).

[0008] Optionally, the oxidation reaction of the carbon nanotubes comprises the following specific steps, based on parts by mass: adding 1 part of the carbon nanotubes to 10-30 parts of concentrated nitric acid, adding 40-80 parts of concentrated sulfuric acid thereto, ultrasonically shaking for 2-10 minutes, and refluxing at 120° C. for 2-6 hours under stirring conditions.

[0009] Optionally, the ionic liquid is tributylmethylammonium chloride, tributylethylphosphonium bromide or tetraphenylphosphonium bromide, and the mass fraction of the ionic liquid solution is 2-20%; the platinum complex is hexachloroplatinic acid, platinum nitrate or dichlorotetraamineplatinum, and the mass fraction of the platinum complex solution is 2%-8%; the mass dosage ratio of the ionic liquid solution to the platinum complex solution is 1:(2-2.5).

[0010] Optionally, the reduction conditions in S4 are: hydrogen pressure of 3MPa-8MPa, temperature of 150°C-100°C, stirring speed of 1000rpm-2000rpm, and reaction time of 3h-8h.

[0011] Optionally, the slurry is obtained by the following method: adding a platinum precursor solution to a dispersion at 0-5° C., stirring for 30-60 min, and standing for 24-30 h to obtain a slurry.

[0012] Optionally, the specific surface area of ​​the carbon nanotubes is 80-120 m 2 / g; the pore volume is 0.5-1cc / g; the pore diameter is 2-3nm.

[0013] In a second aspect, the present invention further provides a catalyst for a fuel cell, which is prepared by the method described in the first aspect.

[0014] In a third aspect, the present application also provides the use of the catalyst described in the second aspect in a fuel cell.

[0015] Compared with the prior art, this application has at least the following beneficial effects: The present invention uses carbon nanotubes with high specific surface area to replace traditional carbon materials as carriers, which can not only improve the catalyst performance but also facilitate the recovery and utilization of precious metals due to its unique structure; by introducing a carboxylic acid modifier that can tightly bind to platinum ions and treating the carbon nanotube carrier, not only the interaction between the carrier and the active ingredient platinum is significantly enhanced, but also the platinum metal particles are effectively prevented from agglomerating during use, thereby effectively improving the activity and stability of the catalyst. DETAILED DESCRIPTION

[0016] The present invention is described in further detail below: The experimental methods used in the embodiments of the present invention are conventional methods unless otherwise specified.

[0017] The reagents and materials used in this example can all be purchased conventionally. The quantitative experiments involved in the examples were repeated at least three times, and the results were averaged.

[0018] Source of raw materials: Concentrated nitric acid: mass fraction 68%; concentrated sulfuric acid: mass fraction 98%. Example

[0019] This embodiment provides a fuel cell catalyst, including a modified carbon nanotube carrier and metal platinum supported on the modified carbon nanotube carrier, and the preparation method is as follows: 1) Add 2.5g of untreated carbon nanotubes (CNT-1) to 37.5g of concentrated nitric acid, then add 125.0g of concentrated sulfuric acid, ultrasonically shake for 7min, and reflux at 120℃ for 5h under stirring. After the reflux reaction is completed, filter, wash with deionized water, and vacuum dry at 120℃ for 24h to obtain oxidized carbon nanotubes (oCNT-2). The surface area of ​​the raw carbon nanotube CNT-1 is 100.4m 2 / g; the pore volume is 0.75cc / g; the pore diameter is 2.53nm.

[0020] 2) 2.02 g of oxidized carbon nanotubes were added to 20.2 g of 0.75 mol / L 2-phenylpyridine-5,4'-dicarboxylic acid aqueous solution, stirred at 60° C. for 10 h, filtered, washed with deionized water, and vacuum dried at 80° C. for 24 h to obtain modified carbon nanotubes.

[0021] 3) Dissolve 3.25 g of tributyl methyl ammonium chloride in 37.4 g of ethanol to obtain a tributyl methyl ammonium chloride solution; dissolve 4.56 g of hexachloroplatinic acid in 109.4 g of water to obtain a platinum complex solution; add the tributyl methyl ammonium chloride solution dropwise to the platinum complex solution under stirring, and continue stirring after the addition is completed to obtain a platinum precursor solution.

[0022] 4) Disperse 3.25g of modified carbon nanotubes in 325g of ethanol to obtain a dispersion, stir at 5°C, drop the platinum precursor solution obtained in step 3 into the dispersion, continue stirring for 30min, and let stand for 24h to obtain a slurry. Reduce the slurry with hydrogen in a high-pressure reactor at a hydrogen pressure of 5MPa, a temperature of 150°C, a stirring speed of 1000rpm, and a reaction time of 4h. After cooling to room temperature, filter, wash alternately with ultrapure water and anhydrous ethanol, and cool and dry to obtain a fuel cell catalyst. Example

[0023] This embodiment provides a fuel cell catalyst, including a modified carbon nanotube carrier and metal platinum supported on the modified carbon nanotube carrier, and the preparation method is as follows: 1) Add 3.25g of untreated carbon nanotubes (CNT-2) to 65g of concentrated nitric acid, then add 195.0g of concentrated sulfuric acid, ultrasonically shake for 10min, and reflux at 120℃ for 4h under stirring. After the reflux reaction is completed, filter, wash with deionized water, and vacuum dry at 120℃ for 24h to obtain oxidized carbon nanotubes (oCNT-1). The surface area of ​​the raw carbon nanotube CNT-2 is 110.4m 2 / g; the pore volume is 0.82cc / g; the pore diameter is 2.67nm.

[0024] 2) 2.75 g of oxidized carbon nanotubes were added to 41.25 g of 0.8 mol / L 2,2'-bipyridine-5,5'-dicarboxylic acid aqueous solution, stirred at 70° C. for 12 h, filtered, washed with deionized water, and vacuum dried at 80° C. for 24 h to obtain modified carbon nanotubes.

[0025] 3) Dissolve 4.12 g of tributyl methyl ammonium chloride in 18.77 g of ethanol to obtain a tributyl methyl ammonium chloride solution; dissolve 4.33 g of hexachloroplatinic acid in 70.84 g of water to obtain a platinum complex solution; add the tributyl methyl ammonium chloride solution dropwise to the platinum complex solution under stirring, and continue stirring after the addition is completed to obtain a platinum precursor solution.

[0026] 4) Disperse 2.06g of modified carbon nanotubes in 206g of ethanol to obtain a dispersion, and dropwise add the platinum precursor solution obtained in step 3 to the dispersion under stirring at 0°C, continue stirring for 40min, and stand for 24h to obtain a slurry. Reduce the slurry with hydrogen in a high-pressure reactor at a hydrogen pressure of 6MPa, a temperature of 200°C, a stirring speed of 1200rpm, and a reaction time of 5h. After cooling to room temperature, filter, wash alternately with ultrapure water and anhydrous ethanol, and cool and dry to obtain a fuel cell catalyst. Example

[0027] This embodiment provides a fuel cell catalyst, including a modified carbon nanotube carrier and metal platinum supported on the modified carbon nanotube carrier, and the preparation method is as follows: 1) Add 4.38g of untreated carbon nanotubes (CNT-3) to 109.5g of concentrated nitric acid, then add 306.6g of concentrated sulfuric acid, ultrasonically shake for 10min, and reflux at 120℃ for 6h under stirring. After the reflux reaction is completed, filter, wash with deionized water, and vacuum dry at 120℃ for 24h to obtain oxidized carbon nanotubes (oCNT-3). The surface area of ​​carbon nanotubes CNT-3 is 118.4m2 / g; the pore volume is 0.93cc / g; and the pore diameter is 2.88nm.

[0028] 2) Add 2.75 g of oxidized carbon nanotubes to 41.25 g of 1.9 mol / L [2,2',6',2''-terpyridine]-3',4'-dicarboxylic acid aqueous solution, stir at 70° C. for 12 h, filter, wash with deionized water, and vacuum dry at 80° C. for 24 h to obtain modified carbon nanotubes.

[0029] 3) Dissolve 5.01 g of tetraphenylphosphonium bromide in 90.18 g of ethanol solution to obtain a tetraphenylphosphonium bromide solution; dissolve 3.72 g of platinum nitrate in 42.78 g of ethanol to obtain a platinum complex solution; add the tetraphenylphosphonium bromide solution dropwise to the platinum complex solution under stirring, continue stirring after the addition is completed, and obtain a platinum precursor solution.

[0030] 4) Disperse 2.27g of modified carbon nanotubes in 227g of ethanol to obtain a dispersion, and drop the platinum precursor solution obtained in step 3 into the dispersion under stirring at 0°C, continue stirring for 50min, and stand for 24h to obtain a slurry. Reduce the slurry with hydrogen in a high-pressure reactor at a hydrogen pressure of 7MPa, a temperature of 170°C, a stirring speed of 1500rpm, and a reaction time of 7h. After cooling to room temperature, filter, wash alternately with ultrapure water and anhydrous ethanol, and cool and dry to obtain a fuel cell catalyst.

[0031] Comparative Example: This embodiment provides a catalyst for a fuel cell, including a carbon nanotube carrier and metal platinum supported on the carbon nanotube carrier, and the preparation method is as follows: 1) Dissolve 3.25 g of tributyl methyl ammonium chloride in 37.4 g of ethanol to obtain a tributyl methyl ammonium chloride solution; dissolve 4.56 g of hexachloroplatinic acid in 109.4 g of water to obtain a platinum complex solution; add the tributyl methyl ammonium chloride solution dropwise to the platinum complex solution under stirring, and continue stirring after the addition is completed to obtain a platinum precursor solution.

[0032] 2) Disperse 3.25g of untreated carbon nanotubes (CNT-1) in 325g of ethanol to obtain a dispersion. Add the platinum precursor solution obtained in step 1 to the dispersion under stirring at 5°C, continue stirring for 30min, and let stand for 24h to obtain a slurry. Reduce the slurry with hydrogen in a high-pressure reactor at a hydrogen pressure of 5MPa, a temperature of 150°C, a stirring speed of 1000rpm, and a reaction time of 4h. After cooling to room temperature, filter, wash alternately with ultrapure water and anhydrous ethanol, and cool and dry to obtain a fuel cell catalyst.

[0033] The catalysts prepared in the examples and comparative examples were subjected to square wave cycling at two voltages of 0.6 V (3 s) for 30k cycles. Specific results are shown in the table below.

[0034] Table 1 Performance comparison of catalysts before and after square wave circulation catalyst <![CDATA[Initial ECSA (m 2 / g pt )]]> <![CDATA[Cycling 30K times of ECSA (m 2 / g pt )]]> <![CDATA[Initial MA (mA / mg pt )]]> <![CDATA[Loop 30K times MA (mA / mg pt )]]> Comparative Example 1 33.21 20.54 116.78 78.12 Example 1 70.65 63.56 311.34 280.34 Example 2 72.34 64.78 326.55 290.93 Example 3 75.67 67.52 352.46 324.48 According to Table 1, the catalyst for proton exchange membrane fuel cell prepared by the method of the present invention has a mass specific activity of more than 300 mA / mg and an electrochemical active area of ​​70 m 2 / g or more, which is significantly higher than the control example; in addition, the stability of the catalyst prepared by the method of the present invention is also significantly improved after being cycled 30k times; and the attenuation rate of the electrochemical active area of ​​the platinum-carbon catalyst after 30k cycles is within 10%. It can be seen that the catalyst prepared by the method of the present invention has higher electrochemical activity and stability, and can be used in proton exchange membrane fuel cells.

Claims

1. A method for preparing a catalyst for a fuel cell, characterized in that: The steps include: S1: oxidizing the carbon nanotubes to obtain oxidized carbon nanotubes; S2: mixing the oxidized carbon nanotubes with an aqueous solution of a carboxylic acid modifier containing N or S atoms and reacting them at 60-100° C. for 10-15 hours, and washing and drying the reaction product to obtain modified carbon nanotubes; S3: mixing the ionic liquid with the first solvent to obtain an ionic liquid solution; mixing the platinum complex with the second solvent to obtain a platinum complex solution, and adding the ionic liquid solution to the platinum complex solution under stirring to obtain a platinum precursor solution; S4: dispersing the modified carbon nanotubes in a third solvent to obtain a dispersion, then adding a platinum precursor solution to the dispersion, stirring and standing to obtain a slurry; reducing the slurry in a hydrogen atmosphere, purifying and drying to obtain the fuel cell catalyst.

2. The method for preparing a fuel cell catalyst according to claim 1, characterized in that: The carboxylic acid modifier containing N or S atoms is selected from one or more of the following modifiers: 。 3. The method for preparing a fuel cell catalyst according to claim 1, characterized in that: The concentration of the aqueous solution of the carboxylic acid modifier containing N or S atoms is 0.5-2 mol / L, and the mass ratio of the oxidized carbon nanotubes to the aqueous solution of the carboxylic acid modifier containing N or S atoms is 1:(5-20).

4. The method for preparing a fuel cell catalyst according to claim 1, characterized in that: The specific steps of the oxidation reaction of the carbon nanotubes include: adding 1 part of carbon nanotubes to 10-30 parts of concentrated nitric acid, adding 40-80 parts of concentrated sulfuric acid, ultrasonically shaking for 2-10 minutes, and refluxing at 120° C. for 2-6 hours under stirring.

5. The method for preparing a fuel cell catalyst according to claim 1, characterized in that: The ionic liquid is tributylmethylammonium chloride, tributylethylphosphonium bromide or tetraphenylphosphonium bromide, and the mass fraction of the ionic liquid solution is 2-20%; the platinum complex is hexachloroplatinic acid, platinum nitrate or dichlorotetraamineplatinum, and the mass fraction of the platinum complex solution is 2%-8%; the mass dosage ratio of the ionic liquid solution to the platinum complex solution is 1:(2-2.5).

6. The method for preparing a fuel cell catalyst according to claim 1, characterized in that: The reduction conditions in S4 are: hydrogen pressure of 3MPa-8MPa, temperature of 150°C-100°C, stirring speed of 1000rpm-2000rpm, and reaction time of 3h-8h.

7. The method for preparing a fuel cell catalyst according to claim 1, characterized in that: The slurry is obtained by the following method: a platinum precursor solution is added to a dispersion at 0-5° C., stirred for 30-60 minutes, and allowed to stand for 24-30 hours to obtain a slurry.

8. The method for preparing a fuel cell catalyst according to claim 1, characterized in that: The specific surface area of ​​the carbon nanotubes is 80-120 m 2 / g; the pore volume is 0.5-1cc / g; the pore diameter is 2-3nm.

9. A catalyst for a fuel cell, characterized in that: Prepared by the method according to any one of claims 1 to 9.

10. Use of the catalyst according to claim 9 in a fuel cell.

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