Process for the preparation of platinum-cobalt alloy catalysts and use thereof

Abstract

The application provides a preparation method of a platinum-cobalt alloy catalyst, which comprises the following steps: preparing a hexadecyl trimethyl ammonium bromide clear solution; preparing a platinum compound, a transition metal cobalt salt and a dimethyl imidazole dispersion solution; adding the dispersion solution into the hexadecyl trimethyl ammonium bromide clear solution in sequence, stirring, adding a carbon black, a ketchen black, a cabot black or a carbon nanotube slurry, and continuously stirring to obtain a mixed solution I; then centrifuging, vacuum drying and grinding the mixed solution I to obtain an intermediate powder; then performing a different temperature staged calcination on the intermediate powder under a reducing / inert atmosphere to obtain an ordered low platinum-cobalt alloy catalyst powder; and then performing an acid washing, suction filtration, vacuum drying and grinding on the ordered low platinum-cobalt alloy catalyst powder to obtain a catalyst product which can be used in a fuel cell. The platinum-cobalt alloy catalyst prepared by the application can be applied to a proton exchange membrane fuel cell as a cathode oxygen reduction catalyst, and the platinum-cobalt alloy catalyst can improve the utilization rate, catalytic activity and durability of the noble metal Pt in the fuel cell cathode ORR catalyst, and can reduce the manufacturing cost and use cost of the fuel cell.

Description

Technical Field

[0001] This invention belongs to the field of new energy materials technology, specifically relating to a method for preparing and applying a platinum alloy catalyst for fuel cells. Background Technology

[0002] In recent years, with the large-scale use of fossil fuels and the increasingly severe environmental pollution and climate change, the development of green, efficient renewable energy and new energy storage and conversion devices has become urgent. Fuel cells are considered the third generation of energy power systems after steam engines and internal combustion engines, and are of great significance in solving the two major problems of energy shortage and environmental pollution. Proton exchange membrane fuel cells (PEMFCs) are one type of green fuel cell, essentially equivalent to the "reverse" device of water electrolysis. A single cell consists of an anode, a cathode, and a proton exchange membrane. The anode is where hydrogen fuel is oxidized, and the cathode is where the oxidant is reduced. Both electrodes contain catalysts that accelerate the electrochemical reactions, and the proton exchange membrane serves as the electrolyte. During operation, it functions like a direct current power source, with the anode being the negative terminal and the cathode the positive terminal. PEMFCs possess advantages such as high energy conversion efficiency, zero emissions, simple structure, high reliability, excellent safety, and low noise, making them the best alternative to internal combustion engines as a power source for automobiles.

[0003] However, the slow oxygen reduction reaction (ORR) at the cathode of proton exchange membrane fuel cells severely hinders the practical application of fuel cells, thus requiring catalysts to improve reaction kinetics. Platinum-based materials are considered ideal oxygen reduction electrocatalysts in practical applications. However, the scarcity, high cost, and poor durability of platinum limit its widespread use in renewable energy technologies. Numerous studies have shown that forming alloy catalysts with Pt and transition metals can not only reduce the amount of precious metal Pt used, but also enhance catalytic performance and stability by adjusting the electronic and geometric structures to change the binding strength between Pt and oxygen intermediates. Pt alloys with transition metals have been well-proven as highly efficient catalysts for improving oxygen reduction activity; however, the disorder of Pt-transition metal alloys leads to the easy leaching of transition metal elements during electrochemical reactions, reducing their catalytic activity and stability. Currently, the methods for preparing carbon-supported Pt-based alloy catalysts involve first preparing a Pt alloy and then supporting it on a carbon support. The interaction between the Pt alloy and the support is weak, resulting in decreased catalyst activity and stability, and easily causing problems such as alloy detachment. The commonly used impregnation reduction method involves fully immersing the support in a solution containing different metal salts, and then heating and reducing the metal ions adsorbed on the support under a reducing atmosphere. Supported nano-alloy catalysts can also be prepared by wet chemical reduction. However, these methods are difficult to obtain catalysts with uniform dispersion and ideal particle size, and the processes are complex, costly, and difficult to mass-produce.

[0004] Therefore, it is necessary to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and to provide a method for preparing a platinum-cobalt alloy catalyst.

[0006] The method for preparing the platinum-cobalt alloy catalyst provided by the present invention includes the following steps:

[0007] S1. Hexadecyltrimethylammonium bromide was dissolved in deionized water and stirred to obtain a clear solution;

[0008] S2 Dissolves platinum compound, transition metal cobalt salt, and dimethylimidazole in deionized water and disperses them by ultrasonication to obtain platinum compound dispersion, transition metal cobalt salt dispersion, and dimethylimidazole dispersion.

[0009] S3 The platinum compound dispersion, the transition metal cobalt salt dispersion, and the dimethylimidazole dispersion are added dropwise to the hexadecyltrimethylammonium bromide clear solution in sequence, the dropping rate is controlled, and after stirring, carbon black, Ketjen black, Cabot black, or carbon nanotube slurry is added and stirring is continued to obtain mixture I;

[0010] S4 The intermediate powder is obtained by centrifuging, vacuum drying, grinding, and then collecting the mixture I.

[0011] S5 The intermediate powder is calcined in stages at different temperatures under a reducing / inert atmosphere to obtain ordered low-platinum-cobalt alloy catalyst powder.

[0012] S6 The catalyst powder obtained in step S5 is acid washed, filtered, vacuum dried, and ground to obtain a catalyst product that can be used in fuel cells.

[0013] The method for preparing the platinum-cobalt alloy catalyst provided by this invention involves a one-step process in which a platinum compound, a transition metal cobalt salt, and dimethylimidazole are sequentially added to an aqueous solution of hexadecyltrimethylammonium bromide to form an intermediate at room temperature. The intermediate has an eggshell-like hollow sphere structure, with the shell surface composed of a platinum compound-supported metal-organic framework material (ZIF-67). When hexadecyltrimethylammonium bromide is completely dissolved in deionized water, it forms a bilayered vesicle structure with hydrophobic chains stacked together. The metal-organic framework material (ZIF-67) then self-assembles and grows outward to form the surface "eggshell" within the eggshell-like hollow sphere, allowing the platinum compound to be uniformly distributed inside and outside this "eggshell." This intermediate structure ensures uniform dispersion of the various elements and achieves a relatively ideal particle size. During the subsequent heating and reduction process, the "eggshell" (ZIF-67) breaks down, exposing cobalt atoms to the reduced platinum alloy on the surface. During continuous holding at temperature, the platinum alloy gradually undergoes an ordered transformation. Simultaneously, the carbon nitride derived from the pyrolysis of ZIF-67 coats the ordered platinum-cobalt alloy. This structure alleviates the particle aggregation and enlargement phenomenon caused by Oswald ripening of platinum-based particles at high temperatures. Furthermore, this carbon nitride shell enhances the bonding force between the platinum-based particles and the support, significantly improving catalyst stability. Adding carbon black, Ketjen black, Cabot black, or carbon nanotube slurry during intermediate formation can further reduce the platinum loading while improving the catalyst's conductivity.

[0014] The method for preparing the platinum-cobalt alloy catalyst in this application improves the utilization rate of platinum in the catalyst, reduces the consumption of platinum, enhances catalytic activity through alloying, and improves catalyst stability through nitrogen-carbon shell coating. As a result, the catalyst of this invention has both high ORR oxygen catalytic performance and good stability.

[0015] This invention obtains a chemically ordered platinum-cobalt alloy through high-temperature reduction without the need for a reducing agent. Furthermore, the heating process employs segmented calcination at different temperatures to remove hexadecyltrimethylammonium bromide, effectively preventing platinum loss and the introduction of other entrained elements, thus ensuring the quality of the prepared platinum alloy catalyst.

[0016] The preparation method of this invention is simple and the process is short. It can reduce the amount of platinum metal used in the catalyst while improving the stability of the catalyst, and significantly reduce the cost of the catalyst.

[0017] This invention also provides the application of the platinum-cobalt alloy catalyst prepared by the above method as a cathode oxygen reduction catalyst in a proton exchange membrane fuel cell.

[0018] Applying this catalyst to fuel cells can reduce fuel cell costs, improve fuel cell performance stability, and promote the commercial application of fuel cells. Attached Figure Description

[0019] Figure 1 The powder X-ray diffraction (XRD) pattern of the platinum-cobalt alloy catalyst prepared in Example 1 compared with that of a 20 wt% commercial Pt / C catalyst.

[0020] Figure 2 The image shows the SEM image of the intermediate of the platinum-cobalt alloy catalyst prepared in Example 1.

[0021] Figure 3 The graph shows the oxygen reduction reaction (ORR) polarization curves of the platinum-cobalt alloy catalyst prepared in Example 1 compared to a 20 wt% commercial Pt / C catalyst.

[0022] Figure 4 The graph shows the oxygen reduction reaction (ORR) polarization curves of the platinum-cobalt alloy catalyst prepared in Example 2 compared to a 20 wt% commercial Pt / C catalyst.

[0023] Figure 5 The graph shows the oxygen reduction reaction (ORR) polarization curves of the platinum-cobalt alloy catalyst prepared in Example 3 compared to a 20 wt% commercial Pt / C catalyst.

[0024] Figure 6 Cyclic voltammetry (CV) curves and ORR polarization curves of a 20 wt% commercial Pt / C catalyst before and after 10,000 cycles.

[0025] Figure 7 The images show the cyclic voltammetry (CV) curves and ORR polarization curves of the platinum-cobalt alloy catalyst prepared in Example 1 before and after 10,000 cycles.

[0026] Figure 8 TEM image of the platinum-cobalt alloy catalyst prepared in Example 1 Figure 1 .

[0027] Figure 9 TEM image of the platinum-cobalt alloy catalyst prepared in Example 1 Figure 2 .

[0028] Figure 10 The image shows a TEM image of the platinum-cobalt alloy catalyst prepared in Comparative Example 1.

[0029] Figure 11 The image shows a TEM image of the platinum-cobalt alloy catalyst prepared in Comparative Example 2. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0031] The method for preparing the platinum-cobalt alloy catalyst provided by the present invention includes the following steps:

[0032] S1. Dissolve hexadecyltrimethylammonium bromide (CTAB) in deionized water and stir at a temperature of 30-40℃ and a stirring speed of 900-1000 rpm until the solution becomes clear.

[0033] This step utilizes hexadecyltrimethylammonium bromide (CTAB), which improves the dispersibility of platinum acid ions in deionized water during subsequent mixing with platinum compounds, resulting in a more uniform dispersion of platinum metal in the prepared catalyst product. After complete dissolution in deionized water, CTAB forms bilayer vesicles with hydrophobic chains stacked together. This unique vesicle structure induces the nucleation of nearby transition metal cobalt salts and dimethylimidazoles added in subsequent processes at the vesicle sites. The resulting surface metal-organic framework material allows acid acid ions from the platinum compounds added in subsequent processes to uniformly aggregate on the vesicle surface, providing nucleation sites for the outward growth of crystals. The metal-organic framework material then self-assembles and grows outward, ensuring a strong bond between the platinum alloy and the metal-organic framework material, preventing alloy detachment, and improving the catalyst's activity and stability. Furthermore, hexadecyltrimethylammonium bromide is easily removed during subsequent calcination, simplifying the process and avoiding the introduction of other entrained elements, thus improving the purity of the platinum-cobalt alloy.

[0034] S2 Dissolves platinum compound, transition metal cobalt salt, and dimethylimidazole in deionized water, and then disperses them by ultrasonication to obtain platinum compound dispersion, transition metal cobalt salt dispersion, and dimethylimidazole dispersion.

[0035] In this step, the platinum compound is chloroplatinic acid, chloroplatinic acid hexahydrate, or potassium chloroplatinate, preferably chloroplatinic acid; the transition metal cobalt salt specifically includes cobalt nitrate hexahydrate, cobalt chloride hexahydrate, or cobalt acetate tetrahydrate; the dimethylimidazole serves as an organic synthesis intermediate, used to form a ZIF-67 metal-organic framework structure with the cobalt salt. This structure, on the one hand, allows cobalt and platinum to form an ordered alloy during subsequent heat treatment; on the other hand, after pyrolysis, this metal-organic framework material forms a nitrogen-carbon shell that encapsulates the platinum alloy, simultaneously providing carbon, nitrogen, and metal sources. The ZIF-67 metal-organic framework can provide cobalt, carbon, and nitrogen sources. The improved activity of the formed ordered platinum-cobalt catalyst is due to two reasons: firstly, the geometric effect—the atomic radius of the added Co is smaller than that of Pt, resulting in lattice compression after alloy formation, leading to a shorter Pt-Pt bond length, which facilitates the breaking of O2O bonds, thereby promoting the dissociation and adsorption of oxygen. Secondly, there is the electronic effect. The addition of Co causes a negative shift in the d-band center of Pt, which weakens the adsorption energy of oxygen-containing intermediates, thereby improving the catalytic activity and stability of the catalyst.

[0036] S3 The platinum compound dispersion, the transition metal cobalt salt dispersion, and the dimethylimidazole dispersion are added dropwise in sequence to the hexadecyltrimethylammonium bromide aqueous ion clear solution. The dropping rate is controlled, and after stirring, carbon black, Ketjen black, Cabot black, or carbon nanotube slurry is added and stirring is continued to obtain mixture I.

[0037] In this step, the molar ratio of platinum compound to transition metal cobalt salt in the synthesis phase is 1:1 to 1:5, and the molar ratio of transition metal cobalt salt to dimethylimidazole is 1:20 to 1:50. Within this range, the formation of the metal-organic framework material ZIF-67 can be guaranteed, and the platinum alloy catalyst particles can obtain a smaller particle size, thereby enabling the catalyst to obtain excellent electrochemical performance. Adding slurries such as carbon black, Ketjen black, Cabot black, or carbon nanotubes can reduce the platinum loading while improving the catalyst's conductivity.

[0038] Platinum compound dispersion, cobalt salt dispersion and dimethylimidazole dispersion were added dropwise to the hexadecyltrimethylammonium bromide clear solution in step S1 in sequence, with the dropping rate controlled at 1-2 mL / min. After stirring continuously at room temperature for 4-5 h, carbon black, Ketjen black, Cabot black or carbon nanotube slurry was added and stirred for another 1-2 h to obtain mixture I.

[0039] In this step, dispersions of platinum compounds, transition metal cobalt salts, and dimethylimidazole are sequentially added dropwise to a clear solution of hexadecyltrimethylammonium bromide. Under continuous magnetic stirring and with the dropping rate controlled by a dropper, suspension mixture I is obtained. This method ensures thorough and uniform mixing of the platinum compounds and transition metal cobalt salts. Furthermore, it allows the intermediate (dimethylimidazole) to rapidly crosslink and attach to the transition metal cobalt salt, facilitating the rapid synthesis of the metal-organic framework material ZIF-67 on the intermediate. This provides a guarantee for the subsequent formation of ordered platinum-cobalt alloys and the generation of pyrolytically derived carbon from the metal-organic framework material. After mixing a platinum compound dispersion, a cobalt salt dispersion, and a dimethylimidazole dispersion with a clarified hexadecyltrimethylammonium bromide solution, the bilayer vesicles formed by the hydrophobic chains of hexadecyltrimethylammonium bromide combine with the metal-organic framework material ZIF-67 to form hollow eggshell-like spheres. The anions in the platinum compound aggregate on the surface of these "eggshells" (vesicles), distributed uniformly inside and out. Furthermore, the "eggshell" itself is the metal-organic framework material (ZIF-67), allowing the platinum compound to be uniformly loaded onto the metal-organic framework support, thus reducing the amount of platinum used in the catalyst. During subsequent pyrolysis, the hexadecyltrimethylammonium bromide in the metal-organic framework material (ZIF-67) is removed, leading to the exposure of cobalt atoms and surface reduction of platinum alloying. During high-temperature holding, the platinum alloy gradually becomes ordered, and the carbon nitride derived from the pyrolysis of ZIF-67 coats the ordered platinum-cobalt alloy, significantly enhancing structural stability and improving catalyst lifespan.

[0040] S4 The intermediate powder is obtained by centrifuging, vacuum drying, grinding, and then centrifuging the mixture I.

[0041] In this step, mixture I is centrifuged at 8000-10000 rpm for 5-10 minutes. Centrifugal force separates the solid particles from the liquid in suspension I. The product after centrifugation does not require washing with deionized water, avoiding the loss of platinum compounds and the potential for partial hydrolysis of ZIF-67 when left to stand in deionized water, which could disrupt the intermediate structure. This reduces the loss of platinum compounds and improves the retention rate of platinum metal.

[0042] The centrifuged purple intermediate slurry was placed in an oven at 60℃~70℃ and dried under low temperature vacuum for 12~24 hours. After grinding, purple powder (intermediate powder) was obtained.

[0043] S5 The intermediate powder obtained in step S4 is calcined in stages at different temperatures under a reducing / inert atmosphere to obtain ordered low-platinum-cobalt alloy catalyst powder.

[0044] The intermediate material obtained in step S4 is placed in a tube furnace and heated at a temperature of 280–300°C. Under a reducing atmosphere of 5%–10% hydrogen and nitrogen mixture (5%–10% H2 / N2), it is first calcined for 30–60 minutes, then heated to 700°C–900°C at a rate of 5°C / min, and then calcined for another 2–4 hours.

[0045] In the above temperature parameters, the first stage calcination temperature is controlled between 280℃ and 300℃ to melt the platinum-cobalt metal. Within this temperature range, hexadecyltrimethylammonium bromide decomposes into smaller molecules for removal, ensuring the purity of the subsequent platinum-cobalt alloy phase. If the temperature rises too quickly, the hexadecyltrimethylammonium bromide may not burn completely or will form carbon deposits that remain in the alloy phase, affecting the oxygen reduction performance and stability of the prepared catalyst. The second temperature stage is controlled between 700℃ and 900℃, and calcination for 2–4 hours allows the platinum-cobalt alloy to form an ordered alloy phase, ensuring the formation of an ordered metallic alloy phase structure.

[0046] S6 obtains a catalyst product that can be used in fuel cells by acid washing, filtration, vacuum drying, and grinding of the obtained platinum-cobalt alloy catalyst powder.

[0047] The catalyst powder obtained in step S5 was placed in a 2 mol / L H2SO4 solution for 12–24 h to perform acid washing. This process ensures that the metal-organic framework-derived carbon support has uniform particle size, ideal particle size, and no surface impurities. The acid washing also removes excess cobalt. After acid washing, the powder was filtered and then vacuum dried at 60–70 °C for 12–24 h. Finally, it was ground to obtain a catalyst product suitable for fuel cells.

[0048] The platinum-cobalt alloy catalyst prepared by the above method uses a metal-organic framework-derived carbon material as a support and deionized water as a solvent. Through the induction of hexadecyltrimethylammonium bromide, self-sacrificing eggshell-shaped hollow spheres are formed, constructing an intermediate material with a special morphology. This allows the platinum compound to be uniformly distributed on the inner and outer surfaces of the metal-organic framework material (ZIF-67). Further high-temperature reduction yields a chemically ordered platinum-cobalt alloy. Simultaneously, the pyrolysis-derived nitrogen-carbon material of ZIF-67 coats the formed platinum-cobalt alloy, effectively preventing Oswald ripening and growth of particles. The heating process employs segmented heat treatment, using low temperatures to remove hexadecyltrimethylammonium bromide, avoiding platinum loss and the introduction of other entrained elements during water washing. Finally, a uniform nitrogen-carbon shell-coated ordered platinum-cobalt alloy catalyst is obtained. The ordered structure of the platinum-cobalt alloy of this invention effectively slows down particle aggregation during cycling, and the ordered structure further resists particle agglomeration, ensuring uniform dispersion of catalyst particles with a relatively ideal particle size. ICP-OES testing revealed that the Pt content in the catalyst prepared in this application was only 11.8 wt%, far lower than the platinum content of 20 wt% in commercial Pt / C. Therefore, the catalyst prepared in this invention exhibits high ORR oxygen catalytic performance and high cycling stability.

[0049] The platinum-cobalt alloy catalyst prepared by this invention can be used as a cathode oxygen reduction catalyst in proton exchange membrane fuel cells, which improves the utilization rate of the noble metal Pt in the cathode ORR catalyst of fuel cells, as well as its catalytic activity and durability, and can reduce the manufacturing cost and operating cost of fuel cells.

[0050] The preparation method of the above-mentioned platinum-cobalt alloy catalyst will be further described in detail below with reference to specific embodiments.

[0051] Example 1:

[0052] The preparation method of the platinum-cobalt alloy catalyst in Example 1 includes the following specific steps:

[0053] S1 Dissolve 1g of cetyltrimethylammonium bromide (CTAB) in 200mL of deionized water and stir at 30℃ and 1000rpm until a clear solution is obtained.

[0054] S2 is prepared by dissolving chloroplatinic acid (H2PtCl6), cobalt nitrate hexahydrate (Co(NO3)2·6H2O), and dimethylimidazole (C4H6N2) in deionized water and then dispersing them by ultrasonication to obtain:

[0055] Chloroplatinic acid dispersion: 6 mL of chloroplatinic acid aqueous solution with a concentration of 40 mg / mL;

[0056] Cobalt nitrate hexahydrate dispersion: 290 mg of cobalt nitrate hexahydrate dissolved in 10 mL of deionized water;

[0057] Dimethylimidazole dispersion: 2.5 g of dimethylimidazole dissolved in 20 mL of deionized water.

[0058] S3. The chloroplatinic acid dispersion, cobalt nitrate hexahydrate dispersion, and dimethylimidazole dispersion were sonicated for 10 min each, and then gradually added dropwise to the hexadecyltrimethylammonium bromide aqueous solution prepared in step S1. The dropping rate was controlled at 1 mL / min with a dropper. After stirring magnetically at room temperature for 4 h, Ketjen black slurry (60 mg Ketjen black dissolved in 10 mL deionized water) was added, and the mixture was stirred for another 1 h to obtain mixture I.

[0059] S4 The mixture I was centrifuged at 10,000 rpm for 10 minutes, dried under vacuum at 60°C for 12 hours, and then ground to obtain a purple intermediate powder.

[0060] S5. The purple powder obtained in step S4 was placed in a tube furnace. The quartz tube was evacuated, and a mixture of hydrogen and nitrogen (5%–10% H2 / N2) was introduced into the quartz tube. The gas flow rate was controlled within 200 sccm, and the gas was repeatedly purged three times. The temperature was raised to 300℃ using a program, held for 30 minutes, then raised to 850℃ and heat-treated for 2 hours. The temperature was then cooled to room temperature. The heating rate was 5℃ / min, and finally, an ordered low-platinum-cobalt alloy catalyst powder was obtained.

[0061] S6 The catalyst powder obtained in step S5 was placed in a 2 mol / L H2SO4 solution for 12 h, the catalyst powder was acid washed, filtered, and then vacuum dried at 60 °C for 24 h. After grinding, a catalyst product that can be used in fuel cells was obtained.

[0062] The structure and performance characterization of this embodiment 1 are as follows:

[0063] like Figure 1 As shown in the XRD curves, compared to the 20 wt% commercial Pt / C catalyst, the characteristic diffraction peaks of the ordered platinum-cobalt alloy catalyst prepared in Example 1 shift to higher angles, indicating that Pt and cobalt form an alloy. The peak positions are consistent with the standard card (PDF#04-002-0887). TEM results are as follows. Figure 8 As shown, the surface of the platinum-cobalt particles is covered by a nitrogen-carbon shell. Figure 9 The ordered platinum-cobalt particles have a particle size of 3-5 nm and a relatively uniform particle distribution.

[0064] The electrochemical performance of the ordered platinum-cobalt alloy catalyst was tested using a standard three-electrode system, with a platinum sheet as the counter electrode and a saturated calomel electrode as the reference electrode. Oxygen reduction reaction (ORR) tests were conducted in an oxygen-saturated 0.1 M perchloric acid electrolyte at a rotation speed of 1600 rpm and a scan rate of 10 mV / s. Polarization curves (e.g., [image of polarization curves]) were obtained. Figure 3 The results showed that the half-wave potential of the ordered platinum-cobalt alloy catalyst was 0.948 V (vs. RHE), which was significantly better than that of the 20 wt% commercial Pt / C catalyst.

[0065] Stability testing of the ordered platinum-cobalt alloy catalyst: The prepared working electrode was subjected to initial cyclic voltammetry and oxygen reduction polarization curve testing. Then, the working electrode was placed in oxygen-saturated 0.1 M perchloric acid electrolyte, and a full potential range scan of 0.6–1.1 V (vs. RHE) was performed at a scan rate of 200 mV / s. After 10,000 cycles, oxygen was continuously introduced during the cycling process, and the initial cyclic voltammetry and oxygen reduction polarization curve testing were performed again. Before and after 10,000 cycles: the CV curve of the ordered platinum-cobalt alloy catalyst showed little change. Figure 7 ), while 20 wt% commercial Pt / C catalyst ( Figure 6 The area under the CV curve of the ordered platinum-cobalt alloy catalyst decreased significantly; the half-wave potential of the ORR polarization curve of the ordered platinum-cobalt alloy catalyst showed almost no decay. Figure 7 ), while 20 wt% commercial Pt / C catalyst ( Figure 6 The ORR polarization curve showed a decrease of approximately 70 mV in half-wave potential. These results indicate that the prepared platinum-cobalt alloy porous nanosphere electrocatalyst exhibits excellent cycling stability.

[0066] The above performance tests demonstrate that the platinum-cobalt alloy catalyst used as the cathode oxygen reduction catalyst in the proton exchange membrane fuel cell of Example 1 has good electrocatalytic activity and stability. Example 2:

[0067] The preparation method of the platinum-cobalt alloy catalyst in Example 2 includes the following specific steps:

[0068] S1 Dissolve 1g of hexadecyltrimethylammonium bromide (CTAB) in 200mL of deionized water and stir at 30℃ and 900rpm until a clear solution is obtained.

[0069] S2 Chloroplatinic acid hexahydrate (H2PtCl6·6H2O), cobalt nitrate hexahydrate (Co(NO3)2·6H2O), and dimethylimidazole (C4H6N2) were dissolved in deionized water and then ultrasonically dispersed to obtain:

[0070] Chloroplatinic acid hexahydrate dispersion: 3 mL of chloroplatinic acid hexahydrate aqueous solution with a concentration of 40 mg / mL;

[0071] Cobalt nitrate hexahydrate dispersion: 290 mg of cobalt nitrate hexahydrate dissolved in 30 mL of deionized water;

[0072] Dimethylimidazole dispersion: 2.25 g of dimethylimidazole was dissolved in 30 mL of deionized water.

[0073] S3. The dispersions of chloroplatinic acid hexahydrate, cobalt nitrate hexahydrate, and dimethylimidazole were all sonicated for 30 min. Then, they were gradually added dropwise to the hexadecyltrimethylammonium bromide aqueous solution prepared in step S1. The dropping rate was controlled at 2 mL / min with a dropper. After stirring magnetically at room temperature for 5 h, carbon black slurry (60 mg of carbon black dissolved in 10 mL of deionized water) was added, and the mixture was stirred for another 2 h to obtain mixture I.

[0074] S4 centrifuged mixture I at 8000 rpm for 10 minutes, dried it under vacuum at 70°C for 16 hours, and then ground it to obtain a purple intermediate powder.

[0075] S5. The purple powder obtained in step S4 was placed in a tube furnace. The quartz tube was evacuated, and a mixture of hydrogen and nitrogen (5%–10% H2 / N2) was introduced into the quartz tube. The flow rate of the gas was controlled within 200 sccm, and the gas was repeatedly purged three times. The temperature was raised to 280℃ using a program and held for 60 minutes. Then, the temperature was raised to 750℃ and heat-treated for 3 hours. The temperature was then cooled to room temperature. The heating rate was 5℃ / min. Finally, an ordered low-platinum-cobalt alloy catalyst powder was obtained.

[0076] S6 The catalyst powder obtained in step S5 was placed in a 2 mol / L H2SO4 solution for 20 h, acid-washed, filtered, and then vacuum-dried at 70 °C for 12 h. After grinding, a catalyst product suitable for fuel cells was obtained.

[0077] The electrochemical performance characterization of Example 2 is as follows:

[0078] The electrochemical performance of Example 2 was tested using a standard three-electrode system, with a platinum sheet as the counter electrode and a saturated calomel electrode as the reference electrode. The oxygen reduction reaction was tested in an oxygen-saturated 0.1 M perchloric acid electrolyte at a rotation speed of 1600 rpm and a scan rate of 10 mV / s. The polarization curves (e.g., [image of polarization curve]) are shown below. Figure 4 The results showed that the half-wave potential of the ordered platinum-cobalt alloy catalyst was 0.911 V (vs. RHE), which was significantly better than that of the 20 wt% commercial Pt / C catalyst.

[0079] Example 3:

[0080] The preparation method of the platinum-cobalt alloy catalyst in Example 3 includes the following specific steps:

[0081] S1 Dissolve 1g of hexadecyltrimethylammonium bromide (CTAB) in 200mL of deionized water and stir at 40℃ and 900rpm until a clear solution is obtained.

[0082] S2 Potassium chloroplatinate (K2PtCl6), cobalt acetate tetrahydrate (C2H3CoO2·4H2O), and dimethylimidazole (C4H6N2) were dissolved in deionized water and then ultrasonically dispersed to obtain:

[0083] Potassium chloroplatinate dispersion: 6 mL of potassium chloroplatinate aqueous solution with a concentration of 40 mg / mL;

[0084] Cobalt acetate tetrahydrate dispersion: 122 mg of cobalt acetate tetrahydrate dissolved in 10 mL of deionized water;

[0085] Dimethylimidazole dispersion: 2.25 mg of dimethylimidazole dissolved in 20 mL of deionized water.

[0086] S3. The potassium chloroplatinate dispersion, cobalt acetate tetrahydrate dispersion, and dimethylimidazole dispersion were sonicated for 10 min each, and then gradually added dropwise to the hexadecyltrimethylammonium bromide aqueous solution prepared in step S1. The dropping rate was controlled at 1 mL / min with a dropper. After stirring magnetically at room temperature for 4 h, Cabot Black slurry (60 mg Cabot Black dissolved in 10 mL deionized water) was added, and the mixture was stirred for another 1.5 h to obtain mixture I.

[0087] S4 The mixture I was centrifuged at 9000 rpm for 8 minutes, dried under vacuum at 70°C for 12 hours, ground, and then the purple intermediate powder was collected.

[0088] S5. The purple powder obtained in step S4 was placed in a tube furnace. The quartz tube was evacuated, and a mixture of hydrogen and nitrogen (5%–10% H2 / N2) was introduced into the quartz tube. The flow rate of the gas was controlled within 200 sccm, and the gas was repeatedly purged three times. The temperature was raised to 300℃ using a program, held for 45 minutes, then raised to 800℃ and heat-treated for 2.5 hours. The temperature was then cooled to room temperature. The heating rate was 5℃ / min, and finally, an ordered low-platinum-cobalt alloy catalyst powder was obtained.

[0089] S6 The catalyst powder obtained in step S5 was placed in a 2 mol / L H2SO4 solution for 15 h, the catalyst powder was acid washed, filtered, and then vacuum dried at 60 °C for 24 h. After grinding, a catalyst product that can be used in fuel cells was obtained.

[0090] The electrochemical performance characterization of Example 3 is as follows:

[0091] The electrochemical performance of Example 3 was tested using a standard three-electrode system, with a platinum sheet as the counter electrode and a saturated calomel electrode as the reference electrode. The oxygen reduction reaction was tested in an oxygen-saturated 0.1 M perchloric acid electrolyte at a rotation speed of 1600 rpm and a scan rate of 10 mV / s. The polarization curves (e.g., [image of polarization curve]) are shown below. Figure 5 The results showed that the half-wave potential of the ordered platinum-cobalt alloy catalyst was 0.905 V (vs. RHE), which was significantly better than that of the 20 wt% commercial Pt / C catalyst.

[0092] Comparative Example 1:

[0093] The preparation method of Comparative Example 1, steps S1-S2 and S4-S6, and process parameters are the same as those of Example 1. The difference is that in step S3 of Comparative Example 1, the chloroplatinic acid dispersion, cobalt nitrate hexahydrate dispersion, and dimethylimidazole dispersion are ultrasonicated for 10 min, and then gradually added dropwise to the hexadecyltrimethylammonium bromide aqueous solution prepared in step S1. The dropping rate is controlled at 1 mL / min with a dropper, and then stirred for 1.5 h to obtain mixture I.

[0094] The TEM results of Comparative Example 1 are as follows: Figure 10 As shown, it can be seen that without the addition of Ketjen black paste in step S3, the size of the platinum-cobalt particles varies greatly and the distribution is not very uniform. This indicates that adding a certain amount of Ketjen black paste can alleviate the Oswald curing of the particles.

[0095] Comparative Example 2:

[0096] The preparation method of Comparative Example 2, steps S1-S4 and S6, and process parameters are the same as those of Example 1. The difference is that in step S5 of Comparative Example 2, the purple powder is placed in a tube furnace and heated to 300°C, held for 45 minutes, then heated to 800°C and heat-treated for 5 hours, and then cooled to room temperature. The heating rate is 5°C / min, and finally ordered low platinum-cobalt alloy catalyst powder is obtained.

[0097] The TEM results of Comparative Example 2 are as follows: Figure 11 As shown, after increasing the high-temperature holding time, platinum-cobalt particles will agglomerate and grow in a certain area, which will lead to a decrease in catalyst performance.

[0098] The above embodiments of the present invention are only part of the preferred embodiments of the present invention and should not be construed as limiting the present invention. Any modifications, equivalent substitutions and improvements made by those skilled in the art without departing from the spirit of the present invention shall be within the protection scope of the present invention.

Claims

1. A method for preparing a platinum-cobalt alloy catalyst, characterized in that, Includes the following steps: S1. Hexadecyltrimethylammonium bromide is dissolved in deionized water and stirred at a temperature of 30-40°C and a speed of 900-1000 rpm to obtain a clear solution, thereby forming a bilayer vesicle structure of hydrophobic chains stacked together in the clear solution of hexadecyltrimethylammonium bromide. S2 Dissolves platinum compound, transition metal cobalt salt, and dimethylimidazole in deionized water and disperses them by ultrasonication to obtain platinum compound dispersion, transition metal cobalt salt dispersion, and dimethylimidazole dispersion. S3 The platinum compound dispersion, the transition metal cobalt salt dispersion, and the dimethylimidazole dispersion are added dropwise to the hexadecyltrimethylammonium bromide clear solution in sequence, according to the molar ratio of the transition metal cobalt salt to the dimethylimidazole being 1:20 to 1:50 and the molar ratio of the platinum compound to the transition metal cobalt salt being 1:1 to 1:

5. At room temperature, an intermediate with an eggshell-shaped hollow sphere structure is formed, with the shell surface being a metal-organic framework material supported by the platinum compound. The dropping speed is controlled, and after stirring, carbon black, Ketjen black, Cabot black, or carbon nanotube slurry is added and stirring is continued to obtain mixture I. S4 The intermediate powder is obtained by centrifuging, vacuum drying, grinding, and then collecting the mixture I. S5 The intermediate powder is placed in a tube furnace and calcined for 30 to 60 minutes under a 5% to 10% hydrogen reducing / inert atmosphere at a controlled temperature of 280 to 300°C to remove the hexadecyltrimethylammonium bromide. Then the temperature is raised to 700°C to 900°C at a rate of 5°C / min and calcined for another 2 to 4 hours to obtain an ordered low-platinum-cobalt alloy catalyst powder. S6 The catalyst powder obtained in step S5 is acid washed, filtered, vacuum dried, and ground to obtain a catalyst product that can be used in fuel cells.

2. The method for preparing the platinum-cobalt alloy catalyst as described in claim 1, characterized in that, The platinum compound in step S2 is sodium chloroplatinate hexahydrate, chloroplatinic acid, or potassium chloroplatinate.

3. The method for preparing the platinum-cobalt alloy catalyst as described in claim 1, characterized in that, The transition metal cobalt salt in step S2 is cobalt nitrate hexahydrate, cobalt chloride hexahydrate, or cobalt acetate tetrahydrate.

4. The method for preparing the platinum-cobalt alloy catalyst as described in claim 1, characterized in that, In step S3, the dropping rate is 1-2 mL / min, and after stirring continuously at room temperature for 4-5 h, carbon black, Ketjen black, Cabot black, or carbon nanotube slurry is added, and then stirred for another 1-2 h to obtain the mixture I.

5. The method for preparing the platinum-cobalt alloy catalyst as described in claim 1, characterized in that, In step S4, the mixture I is centrifuged and then vacuum dried at 60℃~70℃ for 12h~24h, and then ground and collected to obtain the intermediate powder.

6. The method for preparing the platinum-cobalt alloy catalyst as described in claim 1, characterized in that, In step S6, the catalyst powder obtained in step S5 is placed in a 2 mol / L H2SO4 solution for 12-24 hours, filtered, and then vacuum dried at 60-70°C for 12-24 hours, followed by grinding.

7. The application of the platinum-cobalt alloy catalyst prepared by any one of claims 1 to 6 as the cathode oxygen reduction catalyst in a proton exchange membrane fuel cell.

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