A preparation method of a nitrogen-doped carbon-supported platinum-cobalt intermetallic compound catalyst

Abstract

The application provides a preparation method of a nitrogen-doped carbon-supported platinum-cobalt intermetallic compound catalyst. The method comprises the following steps: (1) stirring and mixing a nitrogen-doped carbon carrier with an alcohol solvent to obtain a uniformly dispersed system A; (2) uniformly mixing a metal precursor with an alcohol solution by ultrasonic mixing to obtain a uniformly dispersed system B; (3) uniformly stirring and mixing the system A and the system B, then performing oil bath heating, and then performing washing and drying to obtain a nitrogen-doped carbon-supported platinum-cobalt alloy; and (4) placing the product obtained in step (3) into a porcelain boat, annealing the product in an inert atmosphere at a high temperature, and cooling the product to room temperature to obtain the nitrogen-doped carbon-supported platinum-cobalt intermetallic compound catalyst. The nitrogen-doped carbon-supported platinum-cobalt intermetallic compound catalyst prepared by the method has a uniform particle distribution and exhibits good catalytic activity and stability in an oxygen reduction reaction (ORR) of a fuel cell.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of fuel cell catalysts, in particular to a preparation method of nitrogen-doped carbon supported platinum-cobalt intermetallic compound catalyst and its application in oxygen reduction reaction in fuel cell cathode. BACKGROUND

[0002] With the rapid growth of global population and the increasing survival risks caused by climate change, the demand for clean and sustainable energy in human society has significantly increased. It is essential to develop diversified and renewable advanced fuel systems from traditional single fossil fuel systems to mitigate global climate warming. Obviously, among all the current renewable clean energy technologies, fuel cells have attracted considerable attention. It can directly convert chemical energy into electrical energy. Compared with other power generation equipment, fuel cells have incomparable advantages, such as high energy conversion efficiency, low pollution, faster start-up speed, etc. However, the further development of fuel cell technology still faces many challenges. On the one hand, the high cost of platinum metal as the cathode catalyst needs to be reduced. On the other hand, the widely used platinum-based electrocatalyst lacks durability in the start-up and shutdown state of the battery. Therefore, the development of high-activity and durable catalysts to meet the kinetic requirements of fuel cells remains one of the most important challenges.

[0003] One of the effective ways to solve the above problems is to prepare intermetallic compounds of platinum and transition metals. From the perspective of thermodynamics, intermetallic compounds following strict stoichiometric ratios are more stable than disordered solid solution alloys. At the same time, its unique crystal structure can provide high-activity reaction sites for oxygen reduction reaction. Generally, the synthesis process of intermetallic compounds can be simply summarized as two steps: the generation of disordered structure phase and the transformation of disordered structure to ordered structure. The second step is the key step, which can only be carried out in high-temperature annealing process above 600 DEG C. Although high-temperature treatment can not only accelerate the ordering process, but also promote the formation of Pt-rich layer on the surface. But high temperature will inevitably lead to the agglomeration and sintering of nanoparticles, which will reduce the active sites and seriously affect the ORR activity of the catalyst. Therefore, measures must be taken to inhibit the agglomeration of particles, so as to effectively control the catalyst particle size. In the patent CN110465652A, a method for inhibiting the agglomeration of PtFe nanoparticles at high temperature by using organic matter containing amino groups such as monocyamine, dicyandiamide and melamine as coating layer is disclosed. Sun et al. (Kim J, Lee Y, Sun S. Journal of the American Chemical Society, 2010, 132(14): 4996-4997.) wrapped magnesium oxide on the surface of fcc-PtFe nanoparticles to inhibit their agglomeration at high temperature. Qi et al. (Qi Z, Xiao C, Liu C, et al. Journal of the American Chemical Society, 2017, 139(13): 4762-4768.) used mesoporous silica as a protective layer to prevent PtZn nanoparticle agglomeration.

[0004] The processes involved in the above methods are relatively complex and the cost is not low. Therefore, developing a simple and easy, low-cost, and intermetallic compound catalyst synthesis method that can inhibit the agglomeration of disordered phase nanoparticles during high-temperature annealing process has good promotional significance for the preparation of ORR electrocatalysts. SUMMARY

[0005] The purpose of the present application is to solve the problems of low activity and stability of Pt / C catalyst and agglomeration of nanoparticles in the preparation process of intermetallic compounds, and to provide a simple and effective, low-cost synthesis scheme of nitrogen-doped carbon-supported platinum-cobalt intermetallic compound catalyst.

[0006] The technical scheme adopted by the present application to achieve the above purpose is as follows:

[0007] A preparation method of a nitrogen-doped carbon-supported platinum-cobalt intermetallic compound catalyst, comprising the following steps:

[0008] (1) Stir the nitrogen-doped carbon carrier in an alcohol solution for 0.5-2 hours to obtain a smooth and uniform system A.

[0009] (2) Ultrasonically mix the metal precursor in an alcohol solution for 1-2 hours to obtain a uniformly dispersed system B.

[0010] (3) After stirring and uniformly mixing system A and system B, heat in an oil bath, keep warm for a certain period of time, cool to room temperature, and then wash and dry to obtain a nitrogen-doped carbon-supported platinum-cobalt alloy.

[0011] (4) Put the product obtained in step (3) into a porcelain boat and perform high-temperature treatment and annealing under an inert atmosphere. After cooling to room temperature, a nitrogen-doped carbon-supported platinum-cobalt intermetallic compound catalyst with uniform particle distribution is obtained.

[0012] Preferably, the nitrogen-doped carbon carrier in step (1) can be EC-300J, EC-600JD, Vulcan XC-72R, or carbon nanotubes after heat treatment at 500-1000°C under ammonia.

[0013] Preferably, the alcohol solution in step (1) is one or more of diethylene glycol, triethylene glycol, ethylene glycol, and pentaerythritol.

[0014] Preferably, the alcohol solution concentration of the carbon carrier in step (1) is 5-15 g / L.

[0015] Preferably, the metal precursor in step (2) includes a platinum precursor and a cobalt precursor. The platinum precursor can be one or more of chloroplatinic acid, platinum acetylacetone, and potassium chloroplatinate. The cobalt precursor can be one or more of cobalt nitrate, cobalt chloride, cobalt acetylacetone, cobalt formate, and cobalt acetate.

[0016] Preferably, the molar ratio of the platinum precursor to the cobalt precursor in step (2) is 2.5:1-3.5:1.

[0017] Preferably, the alcohol solution concentration of the metal precursor in step (2) is 0.1-10 mmol / L.

[0018] Preferably, the alcohol solution in step (2) is one or more of diethylene glycol, triethylene glycol, ethylene glycol, and pentaerythritol.

[0019] Preferably, the oil bath heating temperature in step (3) is 140-200°C.

[0020] Preferably, the holding time in step (3) is 4-12 hours.

[0021] Preferably, the washing solution in step (3) is an aqueous solution, and the washing frequency can be 4-6 times.

[0022] Preferably, the drying temperature in step (3) is 40-80℃; the drying time is 8-12h.

[0023] Preferably, the inert atmosphere in step (4) can be N2, Ar, one of N2 containing 5-10Vol% H2, one of Ar containing 5-10Vol% H2.

[0024] Preferably, the temperature of high-temperature treatment in step (4) is 700-1000℃; the high-temperature treatment time is 2-10h.

[0025] The application also provides the catalyst prepared by the preparation method.

[0026] Compared with the prior art, the application uses polyhydric alcohol as a solvent and a reducing agent to prepare a disordered alloy. No toxic and difficult-to-remove reaction solvent is involved, which is green and environmentally friendly. Water is used as a washing solution of the reaction product, which effectively reduces the preparation cost. Ammonia gas is used for nitrogen-doping treatment of the carbon carrier, which is simple and easy to operate. The nitrogen-doped carbon-supported platinum-cobalt intermetallic compound catalyst prepared by the application has uniform particle dispersion under transmission electron microscope observation. In the rotating disc electrode test system, the activity and stability of the catalyst in an acidic environment are better than those of a commercial Pt / C catalyst. The preparation method involved in the application is green and environmentally friendly, simple and effective, and has strong operability, and can be popularized to other intermetallic compound preparation fields. BRIEF DESCRIPTION OF DRAWINGS

[0027] The application will be further described below in combination with the drawings and examples.

[0028] Figure 1 TEM image of the nitrogen-doped carbon-supported platinum-cobalt intermetallic compound catalyst prepared in Example 1.

[0029] Figure 2 X-ray diffraction pattern of the nitrogen-doped carbon-supported platinum-cobalt intermetallic compound catalyst prepared in Example 1.

[0030] Figure 3 LSV curve graph of the nitrogen-doped carbon-supported platinum-cobalt intermetallic compound catalyst prepared in Example 1 and a commercial JM Pt / C catalyst. DETAILED DESCRIPTION

[0031] In order to make the experimental scheme involved in the application clearer and more understandable, the application will be further described in detail below in combination with the drawings and specific examples, but the protection scope of the application includes but is not limited to the following examples.

[0032] Example 1:

[0033] (1) Take 2 g Vulcan XC-72R carbon powder and place it in a porcelain boat, and then place it in a tube furnace and heat it to 1000°C under an ammonia atmosphere, keep it for 5 h, and then cool it to room temperature to obtain nitrogen-doped carbon powder.

[0034] (2) Take 600 mg of nitrogen-doped Vulcan XC-72R carbon powder in (1) and place it in a 250 mL round-bottom flask, then add 50 mL of diethylene glycol, stir for 1 h, until the solution is uniform.

[0035] (3) Take 732.74 mg of platinum acetylacetonate and 221.24 mg of cobalt acetylacetonate and place them in a 250 mL beaker, then add 40 mL of diethylene glycol to it, and ultrasonic it for 1 h, until the solution is uniform.

[0036] (4) Stir and mix the solutions in (2) and (3) for 2 h, so that they are fully dispersed.

[0037] (5) Place the reaction system in (4) in an oil bath and react at 160°C for 10 h, then cool it to room temperature, wash it with deionized water 5 times, place the product in a vacuum drying oven and dry it at 80°C for 12 h, then take it out and grind it into a powder with a mortar for use.

[0038] (6) Take 100 mg of the powder in (5) and place it in a porcelain boat, then place it in a tube furnace and heat it at 800°C under a nitrogen atmosphere for 2 h, and then cool it to room temperature to obtain a nitrogen-doped carbon-supported platinum-cobalt intermetallic compound catalyst with a metal loading of 40%.

[0039] Example 2:

[0040] (1) Take 2 g Vulcan XC-72R carbon powder and place it in a porcelain boat, and then place it in a tube furnace and heat it to 1000°C under an ammonia atmosphere, keep it for 5 h, and then cool it to room temperature to obtain nitrogen-doped carbon powder.

[0041] (2) Take 600 mg of nitrogen-doped Vulcan XC-72R carbon powder in (1) and place it in a 250 mL round-bottom flask, then add 50 mL of pentaerythritol, stir for 1 h, until the solution is uniform.

[0042] (3) Take 732.74 mg of platinum acetylacetonate and 221.24 mg of cobalt acetylacetonate and place them in a 250 mL beaker, then add 40 mL of pentaerythritol to it, and ultrasonic it for 1 h, until the solution is uniform.

[0043] (4) Stir and mix the solutions in (2) and (3) for 2 h, so that they are fully dispersed.

[0044] (5) The reaction system in (4) was placed in an oil bath, and reacted at 200 °C for 10 h. After cooling to room temperature, the product was washed with deionized water for 5 times. The product was placed in a vacuum drying oven and dried at 80 °C for 12 h. After taking out, the product was ground into powder with a mortar for standby.

[0045] (6) 100 mg of the powder in (5) was placed in a porcelain boat, and placed in a tube furnace for heat treatment at 800 °C for 2 h under a nitrogen atmosphere. After cooling to room temperature, a nitrogen-doped carbon-supported platinum-cobalt intermetallic compound catalyst with a metal loading of 40% was obtained.

[0046] Example 3:

[0047] (1) 2 g of Vulcan XC-72R carbon powder was placed in a porcelain boat, and placed in a tube furnace for heating to 1000 °C under an ammonia atmosphere for 5 h to obtain nitrogen-doped carbon powder.

[0048] (2) 600 mg of the nitrogen-doped Vulcan XC-72R carbon powder in (1) was placed in a 250 mL round-bottom flask, and 50 mL of ethylene glycol was added. After stirring for 1 h, the solution was uniform.

[0049] (3) 732.74 mg of platinum acetylacetonate and 221.24 mg of cobalt acetylacetonate were placed in a 250 mL beaker, and 40 mL of ethylene glycol was added. After ultrasonic treatment for 1 h, the solution was uniform.

[0050] (4) The solutions in (2) and (3) were stirred and mixed for 2 h to make them fully dispersed.

[0051] (5) The reaction system in (4) was placed in an oil bath, and reacted at 140 °C for 10 h. After cooling to room temperature, the product was washed with deionized water for 5 times. The product was placed in a vacuum drying oven and dried at 80 °C for 12 h. After taking out, the product was ground into powder with a mortar for standby.

[0052] (6) 100 mg of the powder in (5) was placed in a porcelain boat, and placed in a tube furnace for heat treatment at 700 °C for 5 h under a N2 atmosphere containing 5 Vol% H2. After cooling to room temperature, a nitrogen-doped carbon-supported platinum-cobalt intermetallic compound catalyst with a metal loading of 40% was obtained.

[0053] Comparative Example 1:

[0054] The Pt / C catalyst was a 40% platinum-carbon catalyst produced by Johnson Matthey Company.

[0055] The catalysts in Example 1 and Comparative Example 1 were tested for ORR activity in a three-electrode test system, and the specific test conditions were as follows:

[0056] 1. The working electrode is a glassy carbon electrode, the counter electrode is a platinum sheet electrode, and the reference electrode is a saturated calomel electrode.

[0057] 2. The test environment is 0.1M HCIO4 solution saturated with O2, the scanning potential range is -0.3-0.8V, the scanning speed is 10mV, and the working electrode rotation speed is 1600rpm.

[0058] 3. The catalyst durability test potential range is between 0.6-1.1V (vs. RHE), the scanning speed is 100mV / s, and the scanning circle number is 10000.

[0059] 4. The ink composition: 1.5mg catalyst, 790μL isopropyl alcohol, 200μL ultrapure water, and 10μL Nafion solution. All the above components are placed in a 2mL small glass bottle and ultrasonically treated in cold water for 10 minutes until the slurry is uniform.

[0060] 5. 10μL ink is dropped on the glassy carbon electrode, which is dried under an infrared lamp and then subjected to ORR activity test.

[0061] The nitrogen-doped carbon-supported platinum-cobalt intermetallic compound catalyst prepared in Example 1 is subjected to characterization analysis. Figure 1 The transmission electron microscope image thereof shows that the platinum-cobalt intermetallic compound particles are uniformly dispersed on the carrier. Figure 2 The XRD diffraction pattern thereof has diffraction peaks characteristic of face-centered tetragonal structure (fct), indicating that the intermetallic compound structure is formed. Figure 3 The LSV curve comparison chart of the prepared nitrogen-doped carbon-supported platinum-cobalt intermetallic compound catalyst and the commercial JM Pt / C catalyst shows that the half-wave potential and the limiting diffusion current density of the sample are superior to those of the commercial JM Pt / C catalyst, indicating that the ORR catalytic activity of the nitrogen-doped carbon-supported platinum-cobalt intermetallic compound catalyst is superior to that of the commercial JM Pt / C catalyst. After 10000 circle durability test, the activities of the two catalysts are attenuated to a certain extent. After normalizing the kinetic current of the two samples at 0.9V to the catalyst loading, it is known that the mass specific activity of the commercial JM Pt / C catalyst is attenuated by 53.77%, while the mass specific activity of the nitrogen-doped carbon-supported platinum-cobalt intermetallic compound catalyst is attenuated by only 14.89%.

[0062] The above description is only for the preferred embodiments of the present application, and therefore cannot limit the scope of the present application. Equivalent changes and modifications made according to the scope and content of the present patent should still be within the scope of the present application.

Claims

1. A method for preparing a nitrogen-doped carbon-supported platinum-cobalt intermetallic compound catalyst, characterized in that, An alcohol solution containing a metal precursor is mixed uniformly with an alcohol solution containing a nitrogen-doped carbon support. The mixture is then heated in an oil bath and washed and dried to obtain a nitrogen-doped carbon-supported platinum-cobalt alloy. This alloy is then subjected to high-temperature annealing under an inert atmosphere and cooled to room temperature to obtain a nitrogen-doped carbon-supported platinum-cobalt intermetallic compound catalyst with uniform particle distribution. The metal loading of the nitrogen-doped carbon-supported platinum-cobalt intermetallic compound catalyst is 40%–60%. The nitrogen-doped carbon support consists of EC-300J, EC-600JD, and Vulcan XC-72R carbon powder and carbon nanotubes that have undergone heat treatment with ammonia at 500–1000℃.

2. The method for preparing the nitrogen-doped carbon-supported platinum-cobalt intermetallic compound catalyst according to claim 1, characterized in that, Includes the following steps: (1) The nitrogen-doped carbon carrier was stirred and mixed in an alcohol solution to obtain a uniformly dispersed system A; (2) The metal precursor was ultrasonically mixed in an alcohol solution to obtain a uniformly dispersed system B; (3) Mix system A and system B evenly, heat in an oil bath, keep warm for a sufficient time, cool to room temperature, and then wash and dry to obtain nitrogen-doped carbon-supported platinum-cobalt alloy. (4) The product obtained after washing and drying in step (3) is placed in a porcelain boat, treated and annealed at high temperature under an inert atmosphere, and cooled to room temperature to obtain a nitrogen-doped carbon-supported platinum-cobalt intermetallic compound catalyst with uniform particle distribution.

3. The method for preparing the nitrogen-doped carbon-supported platinum-cobalt intermetallic compound catalyst according to claim 2, characterized in that, In step (1): The alcohol solution is one or more of diethylene glycol, triethylene glycol, ethylene glycol, and pentaerythritol; and / or The concentration of the alcohol solution of the carbon support is 5 g to 15 g / L; and / or The stirring time is 0.5 to 2 hours.

4. The method for preparing the nitrogen-doped carbon-supported platinum-cobalt intermetallic compound catalyst according to claim 2, characterized in that, In step (2): The metal precursor includes platinum precursors and cobalt precursors; and / or The platinum precursor is one or more of chloroplatinic acid, platinum acetylacetonate, and potassium chloroplatinate; and / or The cobalt precursor is one or more of cobalt nitrate, cobalt chloride, cobalt acetylacetone, cobalt formate, and cobalt acetate; and / or The molar ratio of the platinum precursor to the cobalt precursor is 2.5:1 to 3.5:1; and / or The concentration of the alcohol solution of the metal precursor is 0.1~10 mmol / L; and / or The alcohol solution is one or more of diethylene glycol, triethylene glycol, ethylene glycol, and pentaerythritol; and / or The ultrasound session lasts 1 to 2 hours.

5. The method for preparing the nitrogen-doped carbon-supported platinum-cobalt intermetallic compound catalyst according to claim 2, characterized in that, In step (3), the oil bath heating temperature is 140~200℃.

6. The method for preparing the nitrogen-doped carbon-supported platinum-cobalt intermetallic compound catalyst according to claim 2, characterized in that, In step (3), the heat preservation time is 4~12h.

7. The method for preparing the nitrogen-doped carbon-supported platinum-cobalt intermetallic compound catalyst according to claim 2, characterized in that, In step (3), the washing solution is an aqueous solution, and the washing is performed 4 to 6 times; the drying temperature is 40 to 80°C; and the drying time is 8 to 12 hours.

8. The method for preparing the nitrogen-doped carbon-supported platinum-cobalt intermetallic compound catalyst according to claim 2, characterized in that, In step (4), the inert atmosphere is at least one of N2, Ar, N2 containing 5~10 vol% H2, and Ar containing 5~10 vol% H2.

9. The method for preparing the nitrogen-doped carbon-supported platinum-cobalt intermetallic compound catalyst according to claim 2, characterized in that, In step (4), the temperature of the high-temperature treatment is 700~1000℃; the duration of the high-temperature treatment is 2~10h; and the metal loading of the obtained nitrogen-doped carbon-supported platinum-cobalt intermetallic compound catalyst is 40%~60%.

10. A nitrogen-doped carbon-supported platinum-cobalt intermetallic compound catalyst, prepared according to any one of claims 1 to 9.

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