Carbon-supported metal catalyst and preparation method therefor

Abstract

The present application relates to the technical field of fuel cells, and in particular to a carbon-supported metal catalyst and a preparation method therefor. The method comprises the steps of: dispersing platinum bis(acetylacetonate), transition-metal acetylacetonate, and a carbon material in a solvent, drying and removing the solvent to obtain a precursor, and performing first annealing in an air atmosphere to obtain a mixture; and performing second annealing on the mixture in a hydrogen-argon atmosphere, performing acid pickling after cooling, then drying after washing, and performing third annealing in the hydrogen-argon atmosphere to obtain the carbon-supported metal catalyst. In the present application, platinum and the transition metal acetylacetonate are used, directly undergo annealing in the air atmosphere after being uniformly impregnated, and then undergo two-step gas-phase reduction in the hydrogen-argon atmosphere to prepare platinum-based intermetallic compound nanoparticles wrapped by a controllable carbon layer, thereby effectively preventing particle agglomeration. The prepared catalyst has a high degree of order, fine particles, uniform distribution, and excellent activity.

Description

A carbon-supported metal catalyst and its preparation method Technical Field

[0001] This application relates to the field of fuel cell technology, and mainly to a carbon-supported metal catalyst and its preparation method. Background Technology

[0002] To achieve my country's "dual-carbon" goals, hydrogen energy has become an indispensable part of the future clean energy system. Currently proposed fuel cells can effectively convert hydrogen energy into electrical energy, showing promising application prospects in energy conversion devices and heavy-duty truck drives. Platinum and platinum-based alloys are essential catalyst materials for proton exchange membrane fuel cells (PEMFCs) and are also major factors affecting the conversion efficiency and application cost of PEMFCs. However, the platinum content used in currently commercial fuel cell vehicles is relatively high; for example, the platinum loading in the Toyota Mirai is approximately 36 g. This high application cost is a major factor limiting the widespread use of PEMFCs.

[0003] Currently, an effective strategy for reducing platinum loading is to alloy Pt with the first-row transition metals. This involves adding smaller transition metal atoms to the Pt-based alloy to induce beneficial strain and alloying effects, thereby increasing the oxygen reduction reaction (ORR) rate of the platinum alloy catalyst. For platinum-based alloy catalysts, the orderliness generally increases with increasing temperature, and this orderliness is positively correlated with catalyst activity. However, achieving high atomic orderliness often requires high-temperature annealing, which inevitably accelerates metal sintering, leading to nanoparticle agglomeration and reduced activity. Many preparation methods have been developed to prepare fine nanoparticles, especially for platinum-based catalyst materials used in fuel cells. These include coating with polymers or metal oxides before annealing to limit particle size, or using small-molecule-assisted impregnation. However, these methods are cumbersome, the thickness of the protective shell is difficult to control, and they can easily affect the activity of the platinum-based catalyst. Therefore, existing technologies require further improvement and development. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this application is to provide a carbon-supported metal catalyst and its preparation method, which aims to solve the problems that the existing methods for controlling the agglomeration of metal particles in catalysts are cumbersome to operate and easily affect the catalyst activity.

[0005] The technical solution of this application is as follows:

[0006] In a first aspect, this application provides a method for preparing a carbon-supported metal catalyst, comprising the following steps:

[0007] Platinum acetylacetonate, acetylacetonate salts of transition metals and carbon materials are dispersed in a solvent, and the precursor is obtained by drying to remove the solvent. After a first annealing in air atmosphere, a mixture is obtained.

[0008] The mixture was annealed a second time under a hydrogen-argon atmosphere, cooled, acid-washed, washed, and dried, and then annealed a third time under a hydrogen-argon atmosphere to obtain the carbon-supported metal catalyst.

[0009] This application utilizes platinum and transition metal acetylacetonate salts, followed by uniform impregnation and direct annealing in an air atmosphere, and then a two-step gas-phase reduction under a hydrogen-argon atmosphere. This process enables the preparation of platinum-based intermetallic compound nanoparticles encapsulated by a tunable carbon layer, effectively preventing particle agglomeration. This method yields carbon-supported metal catalysts with high order, fine and uniformly distributed catalyst particles, and excellent activity.

[0010] Furthermore, the temperature of the first annealing is 100-500℃, and the annealing time is 5-500 min;

[0011] The weight loss of the mixture before and after the first annealing is 1-50% wt.

[0012] In this application, a carbon layer is formed by acetylacetone groups. By controlling the temperature and weight loss rate of the first annealing, the thickness of the subsequently formed carbon layer and its encapsulation performance of the reduced metal particles can be controlled, which is beneficial to improving the catalytic effect of the catalyst.

[0013] Furthermore, the temperature of the first annealing is 176°C, and the annealing time is 20-40 minutes;

[0014] The weight loss of the mixture before and after the first annealing is 1-30% wt.

[0015] In this application, the acetylacetone group was modified to improve catalytic activity at 176°C and a weight loss rate of no more than 30%.

[0016] Furthermore, the conditions for the second annealing are annealing at 400-1100℃ for 10 min-8 h.

[0017] In this application, by annealing under an argon-hydrogen atmosphere, the acetylacetone group can decompose and form a carbon layer, which encapsulates the reduced nano-metal particles and effectively prevents particle aggregation.

[0018] Furthermore, the pickling conditions are as follows: pickling in sulfuric acid with a concentration of 0.1-1 mol / L at 60°C for 12 hours.

[0019] Furthermore, the conditions for the third annealing are annealing at 100-500℃ for 10 min-6 h.

[0020] In this application, a third annealing process can stabilize the metal structure between platinum and the transition metal, thereby improving stability.

[0021] Furthermore, the carbon material includes graphitized carbon or commercially available carbon materials;

[0022] The graphitized carbon is prepared by heating amorphous carbon materials at 1200-3000℃ for 10 min-6 h in an inert or nitrogen atmosphere, and then naturally cooling to room temperature.

[0023] The commercially available carbon material is one of Vulcan XC72, KB300, KB600, BP 2000, or Toray carbon.

[0024] Further, the transition metal acetylacetone salt is one or more of the following: iron acetylacetone, nickel acetylacetone, molybdenum acetylacetone, vanadium acetylacetone, copper acetylacetone, manganese acetylacetone, zinc acetylacetone, titanium acetylacetone, tungsten acetylacetone, chromium acetylacetone, and zirconium acetylacetone.

[0025] Furthermore, the platinum loading in the carbon-supported metal catalyst is 1-60 wt%.

[0026] Secondly, this application also provides a carbon-supported metal catalyst, which includes a carbon support on which metal nanoparticles are distributed and loaded, and the surface of the metal nanoparticles is coated with a carbon layer.

[0027] The carbon support is either a solid nanoparticle or a porous continuous structure, and the particle size of the solid nanoparticle is 1 nm-300 μm.

[0028] The particle size of the metal nanoparticles is 1-20 nm;

[0029] The pore structure in the carbon layer is one of loose porous, microporous, or closed non-porous;

[0030] The coating can be one of no coating, partial coating, or full coating;

[0031] The thickness of the carbon layer is 0.001 nm - 50 nm;

[0032] The number of carbon layers is 0-50.

[0033] Beneficial effects: By using platinum and transition metal acetylacetonate salts, after uniform impregnation, the platinum-based intermetallic compound nanoparticles can be directly annealed in an air atmosphere and then subjected to a two-step gas-phase reduction in a hydrogen-argon atmosphere. This process can effectively prevent particle agglomeration and produce carbon-supported metal catalysts with high order, fine and uniformly distributed catalyst particles, and excellent activity. Attached Figure Description

[0034] Figure 1a is an electron microscope image of the particle distribution of the graphitized carbon supported metal catalyst in Example 1 of this application.

[0035] Figure 1b is an electron microscope image of the graphitized carbon supported metal catalyst particles of Example 1 of this application.

[0036] Figure 2 shows the XRD test results of the graphitized carbon supported metal catalyst in Example 1 of this application.

[0037] Figure 3 shows the TGA curve of the precursor of Example 1 of this application obtained by heating it in air at 5°C / min.

[0038] Figure 4a is an electron microscope image of the particle distribution of the graphitized carbon-supported metal catalyst of Example 2 of this application after annealing in an air atmosphere at 152°C.

[0039] Figure 4b is an electron microscope image of the particle distribution of the graphitized carbon-supported metal catalyst of Example 2 of this application after annealing in an air atmosphere at 164°C.

[0040] Figure 4c is an electron microscope image of the particle distribution of the graphitized carbon-supported metal catalyst of Example 2 of this application after annealing in an air atmosphere at 188°C.

[0041] Figure 4d shows the ORR polarization curves of the graphitized carbon-supported metal catalysts annealed in air at 152°C, 164°C, 176°C, and 188°C in Examples 1 and 2 of this application, respectively.

[0042] Figure 5 shows the XRD test results of the graphitized carbon supported metal catalysts prepared in Example 2 of this application by annealing in air at 152°C, 164°C and 188°C respectively.

[0043] Figure 6 is an electron microscope image of the particle distribution of the graphitized carbon supported metal catalyst in Example 3 of this application.

[0044] Figure 7 shows the XRD test results of the graphitized carbon supported metal catalyst in Example 3 of this application.

[0045] Figure 8 is an electron microscope image of the particle distribution of the KB600-supported platinum-based intermetallic compound catalyst of Example 4 of this application.

[0046] Figure 9 shows the XRD test results of the KB600 supported platinum-based intermetallic compound catalyst of Example 4 of this application.

[0047] Figure 10a is an electron microscope image of the particle distribution of the catalyst in Comparative Example 1 of this application.

[0048] Figure 10b is an electron microscope image of the particles of Comparative Example 1 of this application.

[0049] Figure 11 shows the XRD test results of the catalyst of Comparative Example 1 of this application.

[0050] Figure 12 shows the ORR polarization curves of the graphitized carbon supported metal catalyst of Example 1 and the commercial platinum-carbon catalyst of Comparative Example 2.

[0051] Figure 13 shows the ORR polarization curves of the KB600 supported platinum-based intermetallic compound catalyst of Example 4 of this application and the commercial platinum-carbon catalyst of Comparative Example 2.

[0052] Figure 14 shows the ORR polarization curves of the graphitized carbon supported metal catalyst of Example 1 and the graphitized carbon supported catalyst of Comparative Example 1.

[0053] Figure 15 is a bar chart comparing the specific activity values ​​of Example 1, Comparative Example 1, and Comparative Example 2 of this application. Detailed Implementation

[0054] This application provides a carbon-supported metal catalyst and its preparation method. To make the objectives, technical solutions, and effects of this application clearer and more explicit, the following provides a more detailed description. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0055] Currently, platinum-based intermetallic compound catalysts typically require high-temperature annealing to achieve a high degree of order. The degree of order of platinum-based intermetallic compound catalysts is positively correlated with their catalytic performance. However, high-temperature annealing inevitably accelerates metal sintering, producing larger microcrystals, which leads to the aggregation of nanoparticles in platinum-based intermetallic compound catalysts, reducing the specific surface area and mass specific activity, thereby greatly reducing the activity and stability of the catalyst.

[0056] To address this problem, this application provides a method for preparing a carbon-supported metal catalyst, comprising the following steps:

[0057] S1. Platinum acetylacetonate, transition metal acetylacetonate salts and carbon materials are dispersed in a solvent, dried to remove the solvent to obtain a precursor, and then annealed for the first time to obtain a mixture.

[0058] S2. The mixture is annealed for the second time under a hydrogen-argon atmosphere, cooled, acid-washed, washed and dried, and then annealed for the third time under a hydrogen-argon atmosphere to obtain a carbon-supported metal catalyst.

[0059] This application utilizes platinum and transition metal acetylacetonate salts, followed by uniform impregnation and direct annealing in an air atmosphere, and then a two-step gas-phase reduction under a hydrogen-argon atmosphere. This process enables the preparation of platinum-based intermetallic compound nanoparticles encapsulated by a tunable carbon layer, effectively preventing particle agglomeration. This method yields carbon-supported metal catalysts with high order, fine and uniformly distributed catalyst particles, and excellent activity.

[0060] The ratio of platinum to transition metal is 1:0.1-10, preferably 1:1-1.2.

[0061] Specifically, in this application, by directly using platinum and transition metal acetylacetone salts, the acetylacetone groups are directly used as carbon layer raw materials. The acetylacetone groups can limit the occurrence of agglomeration by decomposing and reorganizing to form a carbon layer that encapsulates platinum-based intermetallic compound nanoparticles, thereby obtaining a catalyst material with uniformly distributed nanoparticles and high activity.

[0062] In step S1, after platinum acetylacetonate, transition metal acetylacetonate salts and graphitized carbon are dispersed in a solvent, they can be mixed uniformly by ultrasonication and then dried by rotary evaporation.

[0063] Furthermore, the carbon material includes graphitized carbon or commercial carbon materials. Graphitized carbon is prepared by heating an amorphous carbon material at 1200-3000°C for 10 minutes to 6 hours in an inert or nitrogen atmosphere, followed by natural cooling to room temperature. Specifically, graphitized carbon can be replaced with commonly used commercial carbon materials, such as Vulcan XC72, KB300 (Ketjen Black 300), KB600 (Ketjen Black 600), BP 2000, or Toray carbon, depending on the requirements. Graphitized carbon is preferred as it exhibits stronger corrosion resistance compared to other carbon materials in high-temperature acidic environments. However, graphitized carbon has fewer surface defect sites, making it unable to effectively load metal nanoparticles. Therefore, traditional chloroplatinic acid impregnation can lead to particle agglomeration. The adjustments made in this application effectively address this particle agglomeration problem.

[0064] In step S1, acetone can be used as the solvent, with a volume ranging from 6 to 10 ml. The amount can be selected according to the different carbon materials. Specifically, 150 mg of carbon material corresponds to 6-10 ml of acetone. Since different carbon materials have different volumes after soaking in the solvent, it is only necessary for the acetone to completely submerge the carbon material for dispersion. In this application, acetylacetone salt and carbon material are uniformly dispersed in acetone to obtain a homogeneous solution, which allows for subsequent gas-phase reduction of uniformly distributed nanoparticles on a carbon support.

[0065] Acetone is removed through rotary drying. As a solvent for the precursor, acetone acts as a dispersant and does not participate in the synthesis of the material. Failure to remove it would lead to uneven dispersion of the precursor, resulting in particle agglomeration.

[0066] Furthermore, the first annealing is performed in air at a temperature of 100-500°C for 5-500 minutes. Currently, methods for introducing carbon layers using conventional organic ligands require the addition of other substances, potentially introducing impurities, and are more complex and costly. This application uses an acetylacetone salt as the target metal in an organometallic salt, resulting in a simpler composition, and the carbon layer formed through the acetylacetone group is simpler and purer.

[0067] Preferably, the first annealing is performed in air at 176°C for 20-40 minutes. Specifically, the platinum-based intermetallic compound nanoparticles are encapsulated with a carbon layer to prevent agglomeration under high-temperature annealing conditions. However, the encapsulated carbon layer should not be too thick, otherwise it will affect the catalytic activity of the catalyst. In this application, controlling the first annealing temperature at 176°C is specifically for the acetylacetone group. Pre-oxidation intervention in air at 176°C allows for the regulation of subsequent decomposition and recombination of the acetylacetone group, optimizing the formed carbon layer. The catalyst encapsulated by this carbon layer can achieve uniform distribution on the graphitized carbon support, which is beneficial for obtaining a carbon-supported metal catalyst with excellent oxygen reduction reaction performance.

[0068] Furthermore, the weight loss rate of the mixture before and after the first annealing is 1-50% wt. The weight loss rate can be controlled by the annealing time and temperature. Carbon reacts at high temperatures; generally, the longer the time or the higher the temperature, the less carbon remains, and the higher the weight loss rate. More specifically, annealing in an air atmosphere oxidizes some acetylacetone groups, affecting the content of the surface carbon layer. The weight loss rate of the mixture before and after the first annealing affects the carbon layer performance. If the weight loss is too low, the carbon layer is too thick, and fewer active sites are exposed. Conversely, increasing the weight loss rate leads to a thinner carbon layer or even prevents its formation, causing particle agglomeration and a decrease in performance.

[0069] More preferably, the weight loss of the mixture before and after the first annealing is no more than 30% wt. If the weight loss exceeds 30% wt, the particles are more likely to become larger, which will more easily affect the catalytic performance. By controlling the weight loss within a suitable range, it is easier to achieve a better balance between active sites and carbon layer thickness.

[0070] Furthermore, the second annealing conditions are annealing at 400-1100℃ for 10 min-8 h, preferably 700℃ for 6 h. In this application, by performing high-temperature annealing under a hydrogen-argon atmosphere, the acetylacetone platinum and transition metal acetylacetone salts in the mixture can be reduced in situ to nano-metal particles. Then, at high temperature, the acetylacetone groups decompose and recombine upon heating. After continuous high-temperature maintenance and the continuous outflow of hydrogen-argon atmosphere, the decomposed acetylacetone groups decompose into small molecular fragments at high temperature, forming a carbon layer that simultaneously encapsulates the nano-metal particles, restricting particle growth and effectively preventing particle agglomeration or sintering. At the same time, the reduced nano-metal particles can also obtain high orderliness at high temperature, thereby obtaining a catalyst material with uniform particle distribution and high activity. The operation is simple, does not introduce other impurities and elements, and the alloy has higher orderliness, improving stability and performance. Smaller particles also result in better performance.

[0071] Furthermore, the pickling conditions are as follows: pickling in sulfuric acid with a concentration of 0.1-1 mol / L, preferably 0.25 mol / L, at 60°C for 12 hours. In this application, pickling removes additional transition metal atoms from the surface of the metal particles, which is beneficial for improving stability.

[0072] Furthermore, the third annealing conditions are annealing at 100-500℃ for 10 min-6 h, preferably at 200℃ for 1.5 h. In this application, by performing a third annealing, the metal structure strength between platinum and the transition metal can be stabilized, and the stability can be improved.

[0073] In the second and third annealing processes, the argon-hydrogen ratio in the hydrogen-argon atmosphere can be maintained within a safe range of 99:1-80:20.

[0074] Furthermore, the transition metal acetylacetone salt is one or more of the following: iron acetylacetone, nickel acetylacetone, molybdenum acetylacetone, vanadium acetylacetone, copper acetylacetone, manganese acetylacetone, zinc acetylacetone, titanium acetylacetone, tungsten acetylacetone, chromium acetylacetone, and zirconium acetylacetone. Preferably, the transition metal acetylacetone salt is cobalt acetylacetone. Platinum-cobalt alloys have high performance among currently reported platinum-based alloys and are also a commonly used alloy choice for alloy catalysts. Using platinum-cobalt alloys is beneficial for improving the performance of the catalyst.

[0075] Specifically, when chloroplatinic acid is used as the platinum source, it decomposes at high temperatures, leading to agglomeration. Currently, the common practice is to first reduce the metal particles at low temperatures, then add substances to limit particle agglomeration before high-temperature treatment. These added substances often remain after high-temperature annealing, requiring further processing. Furthermore, this process can affect the properties of the formed carbon layer, hindering solution diffusion on the catalyst surface and impacting catalytic efficiency. In contrast, this application uses acetylacetone as the metal source. The acetone used is highly volatile and does not volatilize. Through high-temperature treatment with graphitized carbon, the acetylacetone decomposes at high temperatures, and the decomposed substances form a carbon layer that encapsulates the particles, limiting agglomeration. Compared to existing methods, this approach allows for preparation in fewer steps, is simpler to synthesize, and has lower costs.

[0076] Furthermore, the platinum loading in the carbon-supported metal catalyst is 1-60 wt%, preferably 5-60 wt%.

[0077] This application also provides a carbon-supported metal catalyst, which includes a carbon support on which metal nanoparticles are distributed and loaded, and the surface of the metal nanoparticles is coated with a carbon layer.

[0078] Specifically, in the provided carbon-supported metal catalyst, metal nanoparticles are uniformly distributed on the carbon support, and each metal particle on the carbon support is wrapped by a carbon layer.

[0079] Furthermore, the carbon support can be either solid nanoparticles or a porous continuous structure, with the solid nanoparticles having a particle size of 1 nm-300 μm. The solid nanoparticles or porous continuous structure carbon supports include commercial carbon materials and graphitized carbon.

[0080] Furthermore, the particle size of the metal nanoparticles is 1-20 nm, preferably 3-5 nm. Specifically, the metal nanoparticles can be one or more intermetallic compounds selected from platinum, iron, nickel, molybdenum, vanadium, copper, manganese, zinc, titanium, tungsten, chromium, and zirconium, with platinum nanoparticles and platinum-based intermetallic compound nanoparticles being more preferred. The particle size of the metal nanoparticles can be determined by observing the STEM image or XRD test results of the carbon-supported metal catalyst.

[0081] Furthermore, the pore structure in the carbon layer can be one of loose porous, microporous, or closed non-porous. More preferably, the pore structure in the carbon layer is loose porous, which provides a larger electrochemical contact area and is beneficial for improving electrochemical performance.

[0082] Specifically, the distribution of pores in the coated carbon layer can be observed through STEM images of carbon-supported metal catalysts, or it can be judged based on electrochemical data. A loose and porous structure has a good electrochemical contact area, so excellent electrochemical performance reflects that the coated carbon layer has a loose and porous structure.

[0083] Furthermore, the coating can be no coating, partial coating, or full coating, with full coating being preferred. The degree of carbon layer coating can be observed using STEM images of the carbon-supported metal catalyst.

[0084] Furthermore, the thickness of the carbon layer is 0.001-50 nm, preferably 0.01 nm-3 nm. The thickness of the carbon layer can be obtained by observing the STEM image of the carbon-supported metal catalyst.

[0085] Furthermore, the number of carbon layers is 0-50, preferably 1-2. The number of carbon layers can be determined by observing the STEM image of the carbon-supported metal catalyst.

[0086] Preferably, the provided carbon-supported metal catalyst can also be prepared by the method described above. The preparation method provided in this application maintains the structure and properties of the carbon support, and preparation can be carried out on the desired carbon support as needed. The obtained carbon-supported metal catalyst has metal nanoparticles fully coated with a loose, porous carbon layer, the thickness of which is less than 3 nm, and the number of carbon layers is less than two. The thickness and number of carbon layers formed by acetylacetone groups can be controlled by adjusting the annealing conditions. The particle size of the metal nanoparticles is 1-20 nm. This carbon-supported metal catalyst exhibits good catalytic performance, high stability, and high cycling performance.

[0087] The following specific examples provide further details.

[0088] Example 1

[0089] The graphitized carbon-supported platinum-cobalt intermetallic compound of Example 1 of this application includes the following steps:

[0090] Platinum acetylacetonate, cobalt acetylacetonate, and 150 mg of graphitized carbon were dispersed in 7 ml of acetone and sonicated until homogeneous. The platinum loading was controlled at 30 wt% and the cobalt loading at 30 wt%. The mixture was dried by rotary evaporation to remove acetone, and the precursor of Example 1 was obtained. The precursor was then annealed at 176 °C in air for 20 min to obtain the mixture.

[0091] The mixture was annealed for a second time at 700°C for 6 hours in a hydrogen-argon atmosphere. After cooling, it was placed in 0.25 mol / L sulfuric acid and acid-washed at 60°C for 12 hours. After acid washing, the catalyst was washed with deionized water and then dried in a vacuum oven at 65°C. After drying, it was annealed for a third time at 200°C for 1.5 hours in a hydrogen-argon atmosphere to obtain the graphitized carbon supported platinum-cobalt intermetallic compound catalyst of Example 1.

[0092] In Example 1, the graphitized carbon was prepared by heating an amorphous carbon material at 1800°C for 75 min in an argon atmosphere and then naturally cooling it to room temperature.

[0093] The particle distribution and STEM images of the graphitized carbon-supported platinum-cobalt intermetallic compound catalyst in Example 1 are shown in Figures 1a and 1b, respectively. It can be observed that the particles are uniformly distributed on the surface of the graphitized carbon. The carbon support supports the platinum-cobalt intermetallic compound particles, with a thin carbon layer covering the entire particle surface, the thickness of which is less than 2.5 nm. The XRD test results of Example 1 are shown in Figure 2, indicating the successful preparation of Pt1Co1 (a platinum-cobalt intermetallic compound with a platinum-cobalt atomic ratio of 1:1). Furthermore, observation of the STEM images and XRD results shows that the particle size of the carbon-coated platinum-cobalt intermetallic compound is 4-5 nm. The TGA curve of the precursor containing acetylacetone salt and graphitized carbon in Example 1, obtained by heating in air at 5 °C / min, is shown in Figure 3.

[0094] Example 2

[0095] The preparation method of the graphitized carbon-supported platinum-cobalt intermetallic compound catalyst in Example 2 is basically the same as that in Example 1, except that three precursors were prepared in Example 2, and the first annealing temperatures were set to 152℃, 164℃, and 188℃, respectively, and designated as Example 2a, Example 2b, and Example 2c. STEM and XRD tests were performed on the graphitized carbon-supported platinum-cobalt intermetallic compound catalyst prepared in Example 2. The particle distribution obtained by STEM is shown in Figures 4a, 4b, and 4c. It can be observed that the particles are uniformly distributed on the surface of the graphitized carbon, and the carbon support is loaded with platinum-cobalt intermetallic compound particles, with a thin carbon layer completely covering the particle surface. The performance of the carbon layer is slightly different. The graphitized carbon-supported platinum-cobalt intermetallic compound catalysts prepared in Examples 1 and 2 were tested for activity. Oxygen reduction reaction experiments were conducted in an electrochemical cell saturated with oxygen in 0.1M perchloric acid solution, with a scan rate of 20 mV / s. -1 The ORR performance tests for Examples 1 and 2 are shown in Figure 4d. It can be seen that the ORR performance of the sample annealed at 176℃ in Example 1 is relatively better. The XRD test results are shown in Figure 5. Observation shows that the particles become larger with increasing temperature, and the main peak shows the peak of the solid solution. The small bifurcations of the peaks may be due to some particles not being fully bonded. It can be seen that the temperature of the first annealing also affects the bonding effect of the platinum-based metal. As the temperature increases, the effect of the carbon layer in restricting particle growth decreases, resulting in larger particles.

[0096] Example 3

[0097] The preparation method of the graphitized carbon-supported platinum-cobalt intermetallic compound catalyst in Example 3 is basically the same as that in Example 1, except that the second annealing condition in Example 3 is in a hydrogen-argon atmosphere and held at 700°C for 2 hours. STEM and XRD tests were performed on the obtained graphitized carbon-supported platinum-cobalt intermetallic compound catalyst of Example 3. The particle distribution observed by STEM is shown in Figure 6. It can be seen that the particle distribution on the graphitized carbon surface is slightly poor, and the carbon support loads the platinum-cobalt intermetallic compound particles, with a carbon layer completely covering the particle surface. The XRD test results are shown in Figure 7. Electron microscopy shows that the particles are uniformly distributed; however, the XRD test shows peaks of a solid solution, indicating that the annealing time was only two hours, resulting in lower orderliness, which is slightly inferior to Example 1.

[0098] Example 4

[0099] The preparation method of the carbon-supported platinum-cobalt intermetallic compound catalyst in Example 4 is basically the same as that in Example 1, except that the graphitized carbon used for support in Example 4 is replaced with porous KB600. STEM and XRD tests were performed on the KB600-supported platinum-cobalt intermetallic compound catalyst of Example 4. The STEM test results are shown in Figure 8. It can be observed that the particles are uniformly distributed on the surface of the graphitized carbon, and the carbon support supports the platinum-cobalt intermetallic compound particles, with a thin layer of carbon completely coating the particle surface. The XRD test results are shown in Figure 9. Electron microscopy shows that the particles are uniformly distributed, but the degree of order is slightly lower than that of Example 1 using graphitized carbon.

[0100] Comparative Example

[0101] Comparative Example 1

[0102] The preparation method of the graphitized carbon supported catalyst of Comparative Example 1 includes the following steps:

[0103] Platinum acetylacetonate, cobalt acetylacetonate, and graphitized carbon were dispersed in 7 ml of acetone and sonicated until homogeneous. The platinum loading was controlled at 30 wt%, and the mixture was dried by rotary evaporation. After drying to remove the acetone, the precursor of Comparative Example 1 was obtained.

[0104] The precursor was annealed at 700°C for 6 hours in a hydrogen-argon atmosphere, cooled, and then placed in 0.25 mol / L sulfuric acid. It was then acid-washed at 60°C for 12 hours. After acid washing, the catalyst was washed with deionized water and dried in a vacuum oven at 65°C. After drying, it was annealed at 200°C for 1.5 hours in a hydrogen-argon atmosphere to obtain the graphitized carbon-supported platinum-cobalt intermetallic compound catalyst of Comparative Example 1.

[0105] The raw materials and preparation method of Comparative Example 1 are basically the same as those of Example 1, except that the precursor of Comparative Example 1 does not undergo a first annealing treatment in an air atmosphere. STEM and XRD tests were performed on the graphitized carbon-supported catalyst prepared in Comparative Example 1. The particle distribution and electron microscope images obtained by STEM are shown in Figures 10a and 10b, respectively. STEM shows that the particles are uniformly distributed, with a carbon layer completely covering the particle surface. Compared to Example 1, the carbon layer thickness is greater than 5 nm. The XRD test results are shown in Figure 11. It can be found that the unannealed sample has a lower degree of material order, resulting in a much lower activity than the air-annealed example.

[0106] Comparative Example 2

[0107] A commercially available Pt / C catalyst with a platinum loading of 40 wt% was used, with a loading of 20.0 μg Pt / cm. 2 .

[0108] The graphitized carbon-supported platinum-cobalt intermetallic compound catalyst of Example 1 and the commercial Pt / C catalyst of Comparative Example 2 were subjected to the same activity tests as in Example 2. The activity test results are shown in Figure 12. By comparing the polarization curves of the graphitized carbon-supported platinum-cobalt intermetallic compound catalyst and the commercial Pt / C catalyst, it can be found that the MA of the catalyst of Example 1, which has undergone air annealing pretreatment, is as high as 3162 mA / mgPt, while the MA of the commercial Pt / C catalyst is 430 mA / mgPt. The comparison results show that the MA of the graphitized carbon-supported platinum-cobalt intermetallic compound of Example 1 is 7-8 times that of the commercial platinum-carbon catalyst. The platinum-based intermetallic compound catalyst prepared by the method of this application has a significant activity advantage.

[0109] The KB600-supported platinum-cobalt intermetallic compound catalyst of Example 4 and the commercial Pt / C catalyst of Comparative Example 2 were subjected to the same activity tests as in Example 2. The activity test results are shown in Figure 13. By comparing the polarization curves of the KB600-supported platinum-cobalt intermetallic compound catalyst and the commercial Pt / C catalyst, it can be found that the MA of the catalyst of Example 4, which has undergone air annealing pretreatment, is as high as 2030 mA / mgPt, while the MA of the commercial Pt / C catalyst is 400 mA / mgPt. The comparison results show that the activity is still much higher than that of the commercial platinum-carbon catalyst. The platinum-based intermetallic compound catalyst prepared by the method of this application has a significant activity advantage.

[0110] The graphitized carbon-supported platinum-cobalt intermetallic compound catalyst of Example 1 and the graphitized carbon-supported catalyst of Comparative Example 1 were subjected to the same activity tests as in Example 2. The activity test results are shown in Figure 14. It can be found that the specific MA of Comparative Example 1 (without annealing) is 882 mA / mgPt, which is lower than that of Example 1. The electrochemical performance of Comparative Example 1, which has a thicker carbon layer, is lower than that of Example 1. It can be seen that the properties of the carbon layer affect the electrochemical activity. Furthermore, the porosity of the carbon layer in Comparative Example 1 is lower than that in Example 1, which also indicates that the pre-oxidation treatment in air according to this application can improve the activity of the catalyst. The bar graph comparing the specific activity values ​​of Example 1, Comparative Example 1, and 2 is shown in Figure 15. The electrochemical performance of Example 1 is good, and the loose and porous carbon layer has a good electrochemical contact area. The preparation method provided in this application can effectively improve the catalyst activity.

[0111] It should be understood that the application of this application is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of this application.

Claims

1. A method for preparing a carbon-supported metal catalyst, characterized in that, Includes the following steps: Platinum acetylacetonate, acetylacetonate salts of transition metals and carbon materials are dispersed in a solvent, and the precursor is obtained by drying to remove the solvent. After a first annealing in air atmosphere, a mixture is obtained. The mixture was annealed a second time under a hydrogen-argon atmosphere, cooled, acid-washed, washed, and dried, and then annealed a third time under a hydrogen-argon atmosphere to obtain the carbon-supported metal catalyst.

2. The method for preparing the carbon-supported metal catalyst according to claim 1, characterized in that, The temperature of the first annealing is 100-500℃, and the annealing time is 5-500 min; The weight loss of the mixture before and after the first annealing is 1-50% wt.

3. The method for preparing the carbon-supported metal catalyst according to claim 2, characterized in that, The temperature of the first annealing is 176℃, and the annealing time is 20-40 min; The weight loss of the mixture before and after the first annealing is 1-30% wt.

4. The method for preparing the carbon-supported metal catalyst according to claim 1, characterized in that, The conditions for the second annealing are annealing at 400-1100℃ for 10 min-8 h.

5. The method for preparing the carbon-supported metal catalyst according to claim 4, characterized in that, The pickling conditions are as follows: pickling in sulfuric acid with a concentration of 0.1-1 mol / L at 60°C for 12 hours.

6. The method for preparing the carbon-supported metal catalyst according to claim 1, characterized in that, The conditions for the third annealing are annealing at 100-500℃ for 10 min-6 h.

7. The method for preparing the carbon-supported metal catalyst according to claim 1, characterized in that, The carbon material includes graphitized carbon or commercial carbon materials; The graphitized carbon is prepared by heating amorphous carbon materials at 1200-3000℃ for 10 min-6 h in an inert or nitrogen atmosphere, and then naturally cooling to room temperature. The commercially available carbon material is one of Vulcan XC72, KB300, KB600, BP 2000, or Toray carbon.

8. The method for preparing the carbon-supported metal catalyst according to claim 1, characterized in that, The transition metal acetylacetone salt is one or more of the following: iron acetylacetone, nickel acetylacetone, molybdenum acetylacetone, vanadium acetylacetone, copper acetylacetone, manganese acetylacetone, zinc acetylacetone, titanium acetylacetone, tungsten acetylacetone, chromium acetylacetone, and zirconium acetylacetone.

9. The method for preparing the carbon-supported metal catalyst according to claim 1, characterized in that, The platinum loading in the carbon-supported metal catalyst is 1-60 wt%.

10. A carbon-supported metal catalyst, characterized in that, Including carbon supports on which metal nanoparticles are distributed and loaded, with the surface of the metal nanoparticles coated with a carbon layer; The carbon support is either a solid nanoparticle or a porous continuous structure, and the particle size of the solid nanoparticle is 1 nm-300 μm. The particle size of the metal nanoparticles is 1-20 nm; The pore structure in the carbon layer is one of loose porous, microporous, or closed non-porous; The coating can be one of no coating, partial coating, or full coating; The thickness of the carbon layer is 0.001-50 nm; The number of carbon layers is 0-50.

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