A method for preparing a high-performance PtRu / C catalyst

Abstract

This invention discloses a method for preparing a high-performance PtRu / C catalyst, comprising: firstly, dispersing a pretreated carbon support in N,N-dimethylformamide to form a uniform suspension; preparing platinum salt solutions and ruthenium salt solutions, and adding them to the suspension to load platinum-ruthenium precursors onto the carbon support; adding sodium borohydride to the suspension to react and obtain a suspension of platinum-ruthenium metal particles loaded on the carbon support; further heating the suspension to 140-145°C and stirring the reaction under nitrogen protection for 6-7 hours; and obtaining the alloyed PtRu / C catalyst by centrifugation, washing, and drying. The preparation method of this invention simplifies the process and reduces costs while fundamentally inhibiting particle migration and sintering, maintaining a small particle size of 4±0.5 nm, and promoting ordered atomic rearrangement and inducing the formation of a stable structure, thereby significantly improving the oxygen reduction activity and cycle stability of the catalyst.

Description

Technical Field

[0001] This invention belongs to the field of fuel cell catalyst technology, and particularly relates to a method for preparing a high-performance PtRu / C catalyst. Background Technology

[0002] In the field of fuel cell catalyst preparation, platinum-ruthenium-carbon (PtRu / C) catalysts have become a research hotspot. They have excellent methanol oxidation and oxygen reduction performance. Compared with pure Pt catalysts, the addition of Ru can reduce the amount of Pt used while maintaining or improving catalytic performance. Furthermore, the bimetallic synergistic effect significantly improves the catalytic efficiency per unit mass of precious metal, thereby reducing the cost of the catalyst.

[0003] Currently, the mainstream preparation process for PtRu / C catalysts adopts the polyol reduction method. This method uses a mixed solvent of polyols such as ethylene glycol and propylene glycol to disperse carbon powder in the polyol, add Pt / Ru salt and reducing agent, and then heat and reflux for in-situ reduction, so that Pt and Ru particles are deposited on the carbon surface in situ. Finally, the alloying degree and stability are improved by annealing.

[0004] However, in conventional preparation processes, due to the significant difference in reduction temperatures between platinum and ruthenium, platinum and ruthenium may not be reduced simultaneously, resulting in the formation of a single metallic phase. Liquid-phase reduction is complex and time-consuming and costly to ensure complete alloy formation of the metal salt. Furthermore, traditional annealing processes are all gas-phase annealing, which suffers from uneven heat transfer, easily leading to nanoparticle migration, aggregation, and sintering. This results in increased particle size (typically from 3-4 nm to 5-8 nm) and a decrease in active area (30-50% loss of specific surface area), making it difficult to balance small particle size with high thermal stability.

[0005] Based on this, a novel preparation process for PtRu / C catalysts has been developed to obtain uniform ruthenium-platinum alloy catalyst particles, avoid particle size growth of ruthenium-platinum particles, and improve the quality activity and cycle stability of oxygen reduction. Summary of the Invention

[0006] Objective of the invention: This invention provides a method for preparing a high-performance PtRu / C catalyst with small particle size and high stability.

[0007] Technical solution: The preparation method of the highly active iridium oxide catalyst of the present invention includes the following steps:

[0008] (1) The pretreated carbon support is dispersed in N,N-dimethylformamide to form a uniform suspension;

[0009] (2) Prepare platinum salt solution and ruthenium salt solution respectively, add them to the suspension heated to 85-95℃ and protected by nitrogen, and keep warm and stir for 1-2 hours so that the platinum and ruthenium precursors are loaded on the carbon support;

[0010] (3) Add sodium borohydride to the suspension at room temperature, and then stir the reaction at pH 8-12 and 85-95℃ for 3-4 hours to obtain a suspension of carbon support loaded with platinum and ruthenium metal particles.

[0011] (4) Continue heating the suspension to 140-145℃ and stir the reaction under nitrogen protection for 6-7 hours. After centrifugation, washing and drying, the alloyed PtRu / C catalyst is obtained.

[0012] Furthermore, in the preparation step (1) of the catalyst, the pretreatment method of the carbon support is: calcining the carbon support at 800-900℃ under an inert atmosphere for 2-4 hours.

[0013] Furthermore, in step (1) of the catalyst preparation, the carbon support is selected from Ketjen black or conductive carbon black, and its addition amount is to achieve a target metal loading of 20-25%.

[0014] Furthermore, in step (2) of the catalyst preparation, the molar ratio of platinum to ruthenium in the platinum salt solution and the ruthenium salt solution is (1-3):1.

[0015] Furthermore, the platinum salt solution used in the preparation of this catalyst is a 0.05-0.1 mol / L H2PtCl6-N,N-dimethylformamide solution, and the ruthenium salt solution is a 0.05-0.1 mol / L RuCl3-N,N-dimethylformamide solution.

[0016] Furthermore, in step (3) of the catalyst preparation, the number of moles of sodium borohydride added is (5-15) times the total number of moles of platinum and ruthenium.

[0017] Furthermore, in step (3) of the catalyst preparation, the pH value is adjusted using a methanol solution of tetramethylammonium hydroxide.

[0018] Beneficial effects: Compared with the prior art, the significant advantage of the present invention is that the preparation process uses DMF to construct a dispersion, reduction and uniform annealing environment, which simplifies the process and reduces costs, while inhibiting particle migration and sintering from the source, maintaining a small particle size of 4±0.5nm, and promoting ordered atomic rearrangement and inducing the formation of a stable structure, thereby significantly improving the oxygen reduction quality activity and cycle stability of the catalyst. Attached Figure Description

[0019] Figure 1 The cyclic voltammetry results are shown for the PtRu / C catalyst prepared in Example 1 of this invention.

[0020] Figure 2 This is an electron micrograph of the PtRu / C catalyst prepared in Example 1;

[0021] Figure 3 This is an electron microscope image of the PtRu / C catalyst prepared in Example 2. Detailed Implementation

[0022] The technical solution of the present invention will be further described in detail below with reference to the embodiments and accompanying drawings.

[0023] It should be noted that the pH adjuster used in the following embodiments and comparative examples of the present invention is a methanol solution of tetramethylammonium hydroxide. In the following embodiments and comparative examples of the present invention, the formed platinum salt solution is a 0.1 mol / L H₂PtCl₆-N,N-dimethylformamide solution, and the ruthenium salt solution is a 0.1 mol / L RuCl₃-N,N-dimethylformamide solution.

[0024] All raw materials used in this invention are commercially available, and the carbon support selected is model ECP600JD (specific surface area 1200 m²). 2 / g) or model Vulcan XC-72 (specific surface area 254 m²) 2 / g); the model ECP600JD used in the examples and comparative examples has a specific surface area of ​​1200 m². 2 / g.

[0025] The raw material information used in the following embodiments is as follows:

[0026] Table 1. Sources of raw materials

[0027] Example 1

[0028] The preparation method of the PtRu / C catalyst in Example 1 includes the following steps:

[0029] (1) The carbon support was pretreated at 800℃ in an argon atmosphere for 2 hours with a heating rate of 5℃ / min to obtain the pretreated carbon support.

[0030] (2) With a target metal loading of 20wt% and a Pt:Ru molar ratio of 1:1, weigh out chloroplatinic acid, ruthenium chloride and carbon support respectively; disperse the carbon support in anhydrous N,N-dimethylformamide and ultrasonically disperse for 30 min to form a uniform carbon support suspension; heat the carbon support suspension in an oil bath to 85℃ and keep it at that temperature, introduce nitrogen gas for protection, and continuously stir to provide reduction conditions.

[0031] (3) Dissolve chloroplatinic acid and ruthenium chloride in DMF to form platinum salt solution and ruthenium salt solution respectively; add platinum salt solution and ruthenium salt solution to carbon support suspension for 15 min; after addition, stir and react for 1 h to allow the metal precursor to be fully adsorbed on the carbon support surface.

[0032] (4) Add 0.1M NaBH4-DMF solution (the number of moles of sodium borohydride is 10 times the total number of moles of platinum and ruthenium) to step (3) at room temperature, and then stir the reaction for 3 hours at pH 10 and 85℃ to complete the reduction of metal ions and obtain a suspension of carbon support loaded with platinum and ruthenium metal particles.

[0033] (5) Continue heating the suspension to 140°C, stir the reaction under nitrogen protection for 6 hours, add ten times the volume of deionized water to the reaction system, centrifuge the product at 8000 rpm, wash it with deionized water and ethanol alternately 4 times, and vacuum dry it at 70°C for 16 hours to obtain PtRu / C catalyst particles.

[0034] Example 2

[0035] The preparation method of the high-performance PtRu / C catalyst in Example 2 includes the following steps:

[0036] (1) The carbon support was pretreated at 800℃ in an argon atmosphere for 2 hours with a heating rate of 5℃ / min to obtain the pretreated carbon support.

[0037] (2) With a target metal loading of 25wt% and a Pt:Ru molar ratio of 2:1, weigh out chloroplatinic acid, ruthenium chloride and carbon support respectively; disperse the carbon support in anhydrous N,N-dimethylformamide and ultrasonically disperse for 30 min to form a uniform carbon support suspension; heat the carbon support suspension in an oil bath to 90℃ and keep it at that temperature, introduce nitrogen gas for protection, and continuously stir to provide reduction conditions.

[0038] (3) Dissolve chloroplatinic acid and ruthenium chloride in DMF to form platinum salt solution and ruthenium salt solution respectively; add platinum salt solution and ruthenium salt solution to carbon support suspension for 15 min; after addition, stir and react for 1 h to allow the metal precursor to be fully adsorbed on the carbon support surface.

[0039] (4) Add 0.1M NaBH4-DMF solution (the number of moles of sodium borohydride is 8 times the total number of moles of platinum and ruthenium) to step (3) at room temperature, and then stir the reaction for 3 hours at pH 8 and 90℃ to complete the reduction of metal ions and obtain a suspension of carbon support loaded with platinum and ruthenium metal particles.

[0040] (5) Continue heating the suspension to 145°C, stir the reaction under nitrogen protection for 6 hours, add ten times the volume of deionized water to the reaction system, centrifuge the product at 8000 rpm, wash it with deionized water and ethanol alternately 4 times, and dry it under vacuum at 70°C for 16 hours to obtain PtRu / C catalyst particles.

[0041] Example 3

[0042] The preparation method of the high-performance PtRu / C catalyst in Example 3 includes the following steps:

[0043] (1) The carbon support was pretreated at 800℃ in an argon atmosphere for 2 hours with a heating rate of 5℃ / min to obtain the pretreated carbon support.

[0044] (2) With a target metal loading of 22wt% and a Pt:Ru molar ratio of 3:1, chloroplatinic acid, ruthenium chloride and carbon support were weighed respectively; the carbon support was dispersed in anhydrous N,N-dimethylformamide and ultrasonically dispersed for 30 min to form a uniform carbon support suspension; the carbon support suspension was heated to 95℃ in an oil bath and kept at that temperature, nitrogen gas was introduced for protection, and continuous stirring was carried out to provide reduction conditions.

[0045] (3) Dissolve chloroplatinic acid and ruthenium chloride in DMF to form platinum salt solution and ruthenium salt solution respectively; add platinum salt solution and ruthenium salt solution to carbon support suspension for 15 min; after addition, stir and react for 1 h to allow the metal precursor to be fully adsorbed on the carbon support surface.

[0046] (4) Add 0.1M NaBH4-DMF solution (the number of moles of sodium borohydride is 12 times the total number of moles of platinum and ruthenium) to step (3) at room temperature, and then stir the reaction for 3 hours at pH 12 and 95℃ to complete the reduction of metal ions and obtain a suspension of carbon support loaded with platinum and ruthenium metal particles.

[0047] (5) Continue heating the suspension to 145°C, stir the reaction under nitrogen protection for 6 hours, add ten times the volume of deionized water to the reaction system, centrifuge the product at 8000 rpm, wash it with deionized water and ethanol alternately 4 times, and dry it under vacuum at 70°C for 16 hours to obtain PtRu / C catalyst particles.

[0048] Comparative Example 1

[0049] The PtRu / C catalyst of Comparative Example 1 was prepared by the following steps:

[0050] (1) The carbon support was pretreated at 800℃ in an argon (air) atmosphere for 2 hours with a heating rate of 5℃ / min to obtain the pretreated carbon support.

[0051] (2) With a target metal loading of 20wt% and a Pt:Ru molar ratio of 1:1, weigh out chloroplatinic acid, ruthenium chloride and carbon support respectively; disperse the carbon support in anhydrous ethanol and ultrasonically disperse for 30 min to form a uniform carbon support dispersion.

[0052] (3) Dissolve chloroplatinic acid and ruthenium chloride in ethanol to form a platinum-ruthenium salt solution; add the platinum-ruthenium salt solution dropwise to the carbon support dispersion for 15 min; adjust the pH to 10 with 2 mol / L sodium hydroxide ethanol solution, and react for 2 h in an oil bath at 180 °C to obtain a platinum-ruthenium / carbon catalyst.

[0053] (4) Place the washed and dried platinum-ruthenium / carbon catalyst in a quartz boat, purge it with argon gas in a tube furnace, heat it to 400°C at 5°C / min, and anneal it for 4 hours.

[0054] (5) Wash with deionized water and ethanol alternately 4 times, and dry under vacuum at 70°C for 16 h to obtain PtRu / C catalyst particles.

[0055] Comparative Example 2

[0056] The PtRu / C catalyst of Comparative Example 2 was prepared by the following steps:

[0057] (1) The carbon support was pretreated at 800℃ in an argon (air) atmosphere for 2 hours with a heating rate of 5℃ / min to obtain the pretreated carbon support.

[0058] (2) With a target metal loading of 25wt% and a Pt:Ru molar ratio of 2:1, weigh out chloroplatinic acid, ruthenium chloride and carbon support respectively; disperse the carbon support in anhydrous ethanol and ultrasonically disperse for 30 min to form a uniform carbon support dispersion.

[0059] (3) Dissolve chloroplatinic acid and ruthenium chloride in ethanol to form a platinum-ruthenium salt solution; add the platinum-ruthenium salt solution dropwise to the carbon support dispersion for 15 min; adjust the pH to 10 with 2 mol / L sodium hydroxide ethanol solution, and react for 2 h in an oil bath at 180 °C to obtain a platinum-ruthenium / carbon catalyst.

[0060] (4) Place the washed and dried platinum-ruthenium / carbon catalyst in a quartz boat, purge it with argon gas in a tube furnace, heat it to 400°C at 5°C / min, and anneal it for 4 hours.

[0061] (5) Wash with deionized water and ethanol alternately 4 times, and dry under vacuum at 70°C for 16 h to obtain PtRu / C catalyst particles.

[0062] Performance testing

[0063] The performance of the catalyst particles prepared in Examples 1 to 3, Comparative Example 1 and Comparative Example 2 was tested, as follows.

[0064] Oxygen reduction performance was tested using a rotating disk electrode (RDE) in a 0.1 mol / L HClO4 solution at a rotation speed of 1600 rpm and a scan rate of 5 mV / s. Cyclic voltammetry was performed with parameters of 0–1.0 V vs RHE in a N2-saturated 0.1 mol / L HClO4 solution. The performance test results are shown in Table 2 below.

[0065] Table 2 Performance test results of the examples and comparative examples

[0066] As demonstrated in Examples 1 to 3, this invention utilizes DMF to construct a dispersion, reduction, and uniform annealing environment. Employing a one-step method, it not only simplifies the preparation of PtRu / C catalyst particles but also, compared to existing conventional methods (Comparative Examples 1 and 2), produces catalyst particles with smaller particle sizes (smaller particle sizes result in larger specific surface areas and higher oxygen reduction activity), higher alloying degree at a lower temperature of 140-145°C (higher alloying degree further improves cycle stability), and improved orderliness (higher orderliness means more regular catalyst crystal structure and better stability). In short, the process of this invention can prepare PtRu / C catalyst particles with small particle size, high orderliness, and high stability. Furthermore, the process is simple, low-cost, highly controllable, and suitable for large-scale industrial application.

[0067] The PtRu / C catalysts prepared in Examples 1 and 2 were further characterized structurally, and the results obtained are as follows: Figure 2 and Figure 3 As shown, low-magnification TEM image ( Figure 2 (Scale bar 50 nm) shows that Pt-Ru nanoparticles are uniformly loaded on the carbon support surface without obvious agglomeration, indicating that the metal particles are well dispersed on the support. High-magnification TEM image ( Figure 3 Further analysis (scale bar 10 nm) revealed the particle size information: the catalyst particles were nearly spherical with a uniform size distribution, concentrated in the range of 2-5 nm, and no obviously large particles, indicating that the preparation process effectively controlled the growth and aggregation of metal particles. Catalytic experiments were further conducted on the PtRu / C catalyst of Example 1, and the results are as follows... Figure 1As shown, the catalyst exhibits typical characteristics of a Pt-based electrocatalyst within the 0-1.0 V (vs. RHE) potential window: a significant hydrogen adsorption-desorption current is observed in the low potential region (0-0.4 V), while a significant oxidation peak appears at approximately 0.5-0.7 V. This is consistent with the electro-oxidation behavior of small molecule CO by the Pt-Ru alloy, indicating that the catalyst has good electrocatalytic activity. The core advantage of the Pt-Ru alloy catalyst is its resistance to CO poisoning, and the CO stripping test is the standard for directly verifying this advantage. It not only provides the active surface area of ​​the catalyst but also intuitively reflects the promoting effect of the introduction of Ru on CO oxidation kinetics, making it an important characterization method for establishing the structure-performance relationship of the catalyst. As can be seen from the figure, the catalyst prepared in this invention has a high peak current for methanol oxidation, a low reaction potential, excellent methanol electrocatalytic oxidation activity, and reversible surface redox, possessing a good catalytic foundation.

[0068] Based on the experimental results, further reasoning reveals that this invention uses N,N-dimethylformamide (DMF) as a solvent to construct an environment for dispersion, reduction, and uniform annealing, achieving the reduction and alloying of platinum and ruthenium in the same system. This not only simplifies the catalyst preparation process but also, through the N,N-dimethylformamide solution system, it can act as an aid or weak ligand in the reduction process, coordinating with platinum and ruthenium salts to change the reduction potential of platinum and ruthenium, avoiding asynchronous reduction, the presence of impurities, and improving purity. Under these conditions, the reduced ruthenium and platinum in this solution system, while undergoing heat treatment annealing, also benefit from the fact that the molecular structure of DMF, through steric hindrance and coordination, can effectively prevent nanoparticle aggregation, assisting in the formation of fine-sized, uniformly distributed platinum and ruthenium nanoparticles, ensuring that the metal nanoparticles are highly dispersed on the carbon support. On the other hand, during the heat treatment annealing process, DMF provides a near-boiling-point high-temperature liquid phase environment, which gives the surface metal atoms sufficient kinetic energy (thermodynamic driving force) to migrate and interdiffusion within the lattice, so that the segregated Pt and Ru atoms can rearrange to form a uniform PtRu solid solution, achieving alloying while promoting the regularity of the crystal form.

[0069] Furthermore, the addition of sodium borohydride, a strong reducing agent, significantly suppresses the hydrolysis rate of sodium borohydride under alkaline conditions (pH 8-12), significantly improving its stability and allowing for the stable and continuous release of electrons. The slow decomposition (producing hydrogen gas and active hydrogen species) continuously creates a highly reducing liquid-phase microenvironment throughout the annealing process. This effectively prevents newly formed highly active, high surface energy metal nanoparticles from being oxidized by trace amounts of dissolved oxygen or impurities in the solvent at high temperatures, and may provide a "cleaner" surface for atomic diffusion and alloying processes. This allows metal atoms to nucleate uniformly and slowly at defect sites on the carbon support, resulting in nanoparticles with extremely small (4±0.5 nm) and highly uniform distribution.

[0070] The preparation process of this invention simplifies the process and reduces costs, while fundamentally inhibiting particle migration and sintering, maintaining a small particle size of 4±0.5nm, and promoting ordered atomic rearrangement and inducing the formation of a stable structure, thereby significantly improving the oxygen reduction quality activity and cycle stability of the catalyst.

[0071] In addition to the above embodiments, it should be noted that the technical effects claimed by the present invention can be achieved by using the preparation process and the limited parameter range of the present invention, and therefore no further examples will be provided to support these claims.

Claims

1. A method for preparing a high-performance PtRu / C catalyst, characterized in that, Includes the following steps: (1) The pretreated carbon support is dispersed in N,N-dimethylformamide to form a uniform suspension; (2) Prepare platinum salt solution and ruthenium salt solution respectively, add them to the suspension heated to 85-95℃ and protected by nitrogen, and keep warm and stir for 1-2 hours so that the platinum and ruthenium precursors are loaded on the carbon support; (3) Add sodium borohydride to the suspension at room temperature, and then stir the reaction at pH 8-12 and 85-95℃ for 3-4 hours to obtain a suspension of carbon support loaded with platinum and ruthenium metal particles. (4) Continue heating the suspension to 140-145℃ and stir the reaction under nitrogen protection for 6-7 hours. After centrifugation, washing and drying, the alloyed PtRu / C catalyst is obtained.

2. The method for preparing the high-performance PtRu / C catalyst according to claim 1, characterized in that, In step (1), the pretreatment method of the carbon support is to calcine the carbon support at 800-900℃ under an inert atmosphere for 2-4 hours.

3. The method for preparing the high-performance PtRu / C catalyst according to claim 1, characterized in that, In step (1), the carbon support is selected from Ketjen black or conductive carbon black, and its addition amount is 20-25% to achieve the target metal loading.

4. The method for preparing the high-performance PtRu / C catalyst according to claim 1, characterized in that, In step (2), the molar ratio of platinum to ruthenium in the platinum salt solution and the ruthenium salt solution is (1-3):

1.

5. The method for preparing the high-performance PtRu / C catalyst according to claim 1 or 4, characterized in that, The platinum salt solution is a 0.05-0.1 mol / L H2PtCl6-N,N-dimethylformamide solution, and the ruthenium salt solution is a 0.05-0.1 mol / L RuCl3-N,N-dimethylformamide solution.

6. The method for preparing the high-performance PtRu / C catalyst according to claim 4, characterized in that, The number of moles of sodium borohydride added is (5-15) times the total number of moles of platinum and ruthenium.

7. The method for preparing the high-performance PtRu / C catalyst according to claim 1 or 4, characterized in that, In step (3), the pH value is adjusted using a methanol solution of tetramethylammonium hydroxide.

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