Acid pickling method for improving activity and durability of platinum alloy catalyst

Abstract

The invention discloses a pickling method for improving the activity and durability of a platinum alloy catalyst. Relates to the technical field of nano materials and fuel cell catalysts. The preparation method comprises the following steps: uniformly stirring and mixing a carbon carrier, a chloroplatinic acid solution and a transition metal salt solution, vacuumizing the mixed solution under a stirring condition until the mixed solution becomes viscous, and freeze-drying; the obtained powder is subjected to high-temperature alloying in a reducing atmosphere and then cooled to the room temperature; alloyed powder is added into a dilute acid solution with hydrogen, low potential close to 0V is formed on the surfaces of platinum and platinum alloy through H2 / H < + >, large-particle or inadequately-alloyed transition metal and oxide thereof are dissolved in the acid pickling process, the dissolution speed of the transition metal in platinum alloy particles is effectively controlled, and therefore the transition metal and the oxide of the transition metal in the platinum alloy particles are effectively controlled. And meanwhile, dissolved platinum ions can be reduced to the surfaces of alloy particles again, and the low-potential environment on the surfaces of the alloy particles is beneficial to surface reconstruction of surface platinum and transition metal, so that the platinum alloy catalyst with improved activity and durability is obtained.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterials and fuel cell catalyst technology, specifically relating to an acid washing method for improving the activity and durability of platinum alloy catalysts. Background Technology

[0002] Energy shortages and environmental pollution have gradually become key constraints on socio-economic development. The rise of proton exchange membrane fuel cells (PEMFCs) and fuel cell power plants marks the arrival of the hydrogen energy era. PEMFCs directly convert the chemical energy of hydrogen and oxygen into electrical energy, and catalysts are essential in this process. Platinum-carbon catalysts are currently the most widely used fuel cell catalysts; however, as fuel cells demand increasingly higher catalyst activity and durability, platinum-carbon catalysts can no longer meet the efficiency and lifespan design requirements of next-generation high-power-density fuel cells. In recent years, significant progress has been made in the research of alloy catalysts. The catalytic activity of platinum alloy catalysts can reach 2-3 times that of platinum-carbon catalysts. Research has mainly focused on the morphology, size, and composition of platinum-based alloy nanoparticles to improve catalyst activity and durability.

[0003] The activity and durability of platinum alloy catalysts are directly related to the content and distribution of transition metals within the platinum alloy particles. Higher transition metal content generally results in higher catalyst activity; however, during prolonged operation, the performance of fuel cells significantly degrades due to the reduction in catalytic activity caused by transition metal dissolution and the substantial decrease in proton conductivity resulting from transition metals entering ionomers and proton exchange membranes. Therefore, improving the distribution of transition metals within the alloy particles and inhibiting their dissolution are effective ways to enhance the activity and durability of platinum alloy catalysts.

[0004] In existing technologies, platinum alloy catalysts are either left untreated with acid washing to maintain their activity, or they are acid-washed in air. Without acid washing, the dissolution of alloy ions leads to contamination of the membrane electrode assembly (MEA), resulting in severe mass transfer losses. Furthermore, the entry of alloying elements into the membrane and resin can trigger Fenton reactions, generating free radicals that attack resin side chains, leading to resin and membrane degradation over time. Direct acid washing and dealloying in air, due to the oxidizing effect of air, creates pores in the alloy particles as alloying elements dissolve, often resulting in significant roughness. Over time, with further dissolution of internal transition metals, the alloy structure gradually collapses, leading to loss of activity. Therefore, a new acid washing method that improves the activity and durability of alloy catalysts is crucial for maximizing their high catalytic activity. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide an acid washing method for improving the activity and durability of platinum alloy catalysts.

[0006] High platinum loading is one of the key challenges hindering the large-scale commercialization of fuel cells. This stems from the relatively low catalytic activity of platinum-carbon catalysts commonly used in existing fuel cells, leading to high costs. Introducing a second transition metal (such as Co, Mn, or Ni) can form an alloy with Pt, modulating the electronic and geometric structure of Pt and significantly enhancing the catalyst's activity by 2-3 times, thus reducing platinum usage in fuel cells by more than 50%. However, because fuel cells operate in an acidic, high-potential, and highly oxidizing environment, the transition metals in the platinum alloy gradually dissolve during prolonged operation. This leads to decreased catalyst activity and proton exchange membrane contamination, significantly reducing fuel cell performance and lifespan. Therefore, improving the activity and stability of platinum alloy catalysts is crucial.

[0007] This invention first involves evacuating a mixture of carbon powder, platinum salt, and transition metal salt. This process serves two purposes: firstly, the release of gas from the porous structure of the carbon support facilitates the entry of metal ions, regulating the distribution of alloy particles within and outside the pores; secondly, the vacuum process controls the viscosity of the mixture. Excessive moisture leads to uneven distribution of the material during subsequent freeze-drying, while insufficient moisture may cause salt segregation, also resulting in unevenness. Then, freeze-drying combined with a suitable viscous material (i.e., a state without significant liquid water) and rapid cooling with liquid nitrogen immobilize the metal ions in situ and uniformly within the carbon support. This facilitates the subsequent reduction process, resulting in uniformly distributed platinum alloy particles.

[0008] Furthermore, the low-potential pickling method for platinum alloy surfaces of the present invention utilizes hydrogen gas and hydrogen ions in the acid solution to form a low potential (~0V) on the Pt alloy surface. During the pickling process, the surface and interior of the platinum alloy are reconstructed, and a closed platinum-rich shell is formed on the surface to lock in the transition metal alloy components beneath the surface. Figure 2 This process significantly suppresses the outflow of metal cations. Simultaneously, as transition metals diffuse towards the surface, those located in the subsurface layer enhance catalyst activity by adjusting the electronic structure of platinum. Therefore, the acid-washing method of this invention enables platinum alloys to possess higher catalytic activity and better durability. It is worth noting that the low potential (hydrogen ion concentration) created by hydrogen and protons in this invention is crucial for the distribution of transition metals within the alloy and for the uniformity and density of platinum enrichment on the surface.

[0009] The objective of this invention is achieved through the following technical solution:

[0010] This invention provides an acid pickling method for improving the activity and durability of platinum alloy catalysts, the method comprising the following steps: Step 1: Add carbon support, chloroplatinic acid hexahydrate and transition metal salt to deionized water and stir to mix evenly to obtain mixed dispersion A; Step 2: Vacuum treatment of mixed dispersion A under stirring conditions until mixed dispersion A becomes viscous, stop vacuum treatment, and freeze dry for 12~48h to obtain black solid powder B; Step 3: Place the black solid powder B under a reducing atmosphere and heat it to 500~900℃ for 0.5~8h, then cool it to room temperature to obtain solid powder C; Step 4: Disperse solid powder C in a dilute acid solution that has been pre-deoxygenated with high-purity argon, then purged with high-purity hydrogen until saturation and continuously purged with hydrogen for acid washing treatment. After filtration, washing and drying, a platinum alloy catalyst with improved activity and durability is obtained.

[0011] As one implementation scheme, in step 1, the mass ratio of carbon support, chloroplatinic acid hexahydrate and transition metal salt is 1:0.5~2.5:0.25~1.5.

[0012] As one implementation, in step 1, the transition metal salt is one or two of the following: chloride, nitrate, acetate, sulfate, and acetylacetone salts of cobalt, nickel, manganese, and chromium.

[0013] As one implementation scheme, in step 2, the vacuum level of the vacuuming process is 10. 3 ~10 4 Pa, vacuuming is performed by heating to 50~70℃ and vacuuming time is 30~90min.

[0014] As one implementation scheme, in step 2, the freeze-drying is as follows: after cooling to room temperature, it is placed in liquid nitrogen for rapid cooling for 10 to 30 minutes, and then placed in a freeze-drying device for freeze-drying at -30℃ to -70℃ for 20 to 36 hours.

[0015] As one implementation scheme, in step 4, the dilute acid is one or two of dilute sulfuric acid, dilute hydrochloric acid, and dilute acetic acid.

[0016] As one implementation scheme, in step 4, the concentration of hydrogen ions in the dilute acid used for pickling is 0.01~6 mol / L; including 0.01~2 mol / L, 2~4 mol / L, 4~6 mol / L, etc.

[0017] As one implementation scheme, in step 4, during pickling, high-purity hydrogen gas is continuously introduced.

[0018] As one implementation scheme, in step 4, the pickling treatment involves stirring at a temperature controlled at 50-80℃ for 6-48 hours. That is, the acid solution temperature is controlled at 50-80℃. Pickling temperatures include 50-60℃, 60-70℃, and 70-80℃.

[0019] As one implementation, in step 4, during acid washing, the concentration of the platinum alloy catalyst in dilute acid is 2~20 g / L.

[0020] The platinum alloy catalyst obtained by the above method also falls within the scope of protection of this invention.

[0021] Compared with the prior art, the present invention has the following beneficial effects: This invention involves adding alloying powder to a dilute acid solution purged with hydrogen gas, utilizing the H2 / H2O ratio... + By creating a low potential close to 0V on the surface of platinum and platinum alloys, large particles or insufficiently alloyed transition metals and their oxides are dissolved during the pickling process, effectively controlling the dissolution rate of transition metals in platinum alloy particles. At the same time, the dissolved platinum ions can be restored back to the surface of the alloy particles. Since the low potential environment on the surface of the alloy particles is conducive to the surface reconstruction of platinum and transition metals, a platinum alloy catalyst with improved activity and durability is obtained. Attached Figure Description

[0022] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a schematic diagram of the diffusion of platinum and cobalt during the acid washing process of platinum alloy catalysts. Figure 2 These are the actual TEM and STEM images of the platinum alloy catalyst after acid washing. Detailed Implementation

[0023] The technical solution of the present invention will be described in detail below with reference to the embodiments. These embodiments are preferred application examples of the carbon-based Trichoderma spore granules of the present invention and are only used to illustrate the present invention and not to limit its scope of protection. For those skilled in the art, other technical solutions obtained based on the technical solution of the present invention without inventive effort should fall within the scope of protection of the present invention. Unless otherwise specified, the raw materials and equipment used in the embodiments are all conventional products that can be purchased from the market.

[0024] Example 1 The prepared Pt3Co alloy catalyst was acid-washed as follows. The catalyst contained 40.0 wt.% Pt and 4.03 wt.% Co (this content refers to the Pt and Co content in step 4). The specific steps included: 1) Weigh 10.67 g of chloroplatinic acid hexahydrate and 3.0 g of cobalt nitrate hexahydrate, add them to 100 mL of deionized water, and stir at 300 rpm until completely dissolved; then add 5.6 g of carbon powder, and stir thoroughly at 500 rpm for 60 min to make the mixture evenly dispersed, to obtain mixed dispersion A. 2) While stirring the mixed dispersion A at 500 rpm, heat it to 60°C and perform vacuum treatment, controlling the vacuum degree at 1×10⁻⁶. 3 Pa, vacuuming time is 50min; observe the state of the slurry, and when the mixed dispersion becomes viscous, stop heating and vacuuming, and wait for it to cool to room temperature. Place it in liquid nitrogen for rapid cooling for 20min, and then place it in a freeze-drying device. Freeze-dry at -70℃ for 24h to obtain black solid powder B. 3) Black solid powder B was placed under a 10% H2 / Ar mixed gas and kept at 900℃ for 2 hours, with the heating rate controlled at 5℃ / min. Then it was cooled to room temperature to obtain black solid powder C. 4) Disperse 10g of black solid powder C in a 0.5 mol / L dilute sulfuric acid solution that has been pre-deoxygenated with high-purity argon for 60 min, then purged with high-purity hydrogen until saturated and continuously purged with hydrogen for acid washing. The volume of the dilute sulfuric acid solution is 1L, the temperature is controlled at 70℃, and the stirring speed is 300rpm for 24 h. After filtration, washing with deionized water, and drying (80℃, 12 h), a platinum alloy catalyst with improved activity and durability is obtained.

[0025] The prepared platinum alloy catalyst consists of a platinum-cobalt binary alloy. After acid washing, ICP testing showed that the atomic ratio of Pt to Co was 3:1, with the cobalt alloy supported on a carbon support (Pt3Co / C). TEM showed that the size of the platinum-cobalt alloy nanoparticles was 4.5 nm. The catalyst achieved a catalytic activity of 0.471 A / mg Pt@0.9 V. After 30,000 cycles of high and low potentials from 0.6 V (3 s) to 0.95 V (3 s), the mass-specific activity decreased by 17.6%.

[0026] Example 2 The prepared Pt3Co alloy catalyst was acid-washed as follows. The catalyst contained 40.0 wt.% Pt and 4.03 wt.% Co. The specific steps included are as follows: 1) Weigh 10.67 g of chloroplatinic acid hexahydrate and 3.0 g of cobalt nitrate hexahydrate, add them to 100 mL of deionized water, and stir at 300 rpm until completely dissolved; then add 5.6 g of carbon powder, and stir thoroughly at 500 rpm for 60 min to make the mixture evenly dispersed, to obtain mixed dispersion A. 2) While stirring the mixed dispersion A at 500 rpm, heat it to 60°C and perform vacuum treatment, controlling the vacuum degree at 1×10⁻⁶. 3 Pa, vacuuming time is 50 min; observe the state of the slurry, and when the mixed dispersion becomes viscous, stop heating and vacuuming, and wait for it to cool to room temperature. Then put it into liquid nitrogen for rapid cooling for 20 min, and then put it into a freeze-drying device and freeze-dry at -70℃ for 24 h to obtain black solid powder B. 3) Black solid powder B was placed under a 10% H2 / Ar mixed gas and kept at 900℃ for 2 hours, with the heating rate controlled at 5℃ / min. Then it was cooled to room temperature to obtain black solid powder C. 4) Disperse 10g of black solid powder C in a 1 mol / L sulfuric acid solution that has been pre-deoxygenated with high-purity argon for 60 min, then purged with high-purity hydrogen until saturated and continuously purged with hydrogen for acid washing. The volume of the dilute sulfuric acid solution is 1L, the temperature is controlled at 70℃, and the stirring speed is 300rpm for 24 h. After filtration, washing, and drying (80℃, 12 h), a platinum alloy catalyst with improved activity and durability is obtained.

[0027] The prepared platinum alloy catalyst consists of a platinum-cobalt binary alloy. After acid washing, the atomic ratio of Pt to Co is 3:1, and it is supported on a carbon support (Pt3Co / C). The size of the platinum-cobalt alloy nanoparticles is 4.6 nm. The catalyst has a catalytic activity of 0.533 A / mg Pt@0.9 V. After 30,000 high and low potential cycles at 0.6 V (3 s) to 0.95 V (3 s), the mass-specific activity decay rate is 22.5%.

[0028] Example 3 The prepared Pt3Co alloy catalyst was acid-washed as follows. The catalyst contained 40.0 wt.% Pt and 4.03 wt.% Co. The specific steps included are as follows: 1) Weigh 10.67 g of chloroplatinic acid hexahydrate and 3.0 g of cobalt nitrate hexahydrate, add them to 100 mL of deionized water, and stir at 300 rpm until completely dissolved; then add 5.6 g of carbon powder, and stir thoroughly at 500 rpm for 60 min to make the mixture evenly dispersed, to obtain mixed dispersion A. 2) While stirring the mixed dispersion A at 500 rpm, heat it to 60°C and perform vacuum treatment, controlling the vacuum degree at 1×10⁻⁶. 3Pa, vacuuming time is 50 min; observe the state of the slurry, and when the mixed dispersion becomes viscous, stop heating and vacuuming, and wait for it to cool to room temperature. Then put it into liquid nitrogen for rapid cooling for 20 min, and then put it into a freeze-drying device and freeze-dry at -70℃ for 24 h to obtain black solid powder B. 3) Black solid powder B was placed under a 10% H2 / Ar mixed gas and kept at 900℃ for 2 hours, with the heating rate controlled at 5℃ / min. Then it was cooled to room temperature to obtain black solid powder C. 4) Disperse 10g of black solid powder C in a 2mol / L dilute sulfuric acid solution that has been deoxygenated with high-purity argon for 60min, and then purged with high-purity hydrogen until saturated and continuously purged with hydrogen for acid washing treatment. The amount of dilute sulfuric acid solution is 1L, the temperature is controlled at 70℃, and the stirring speed is 300rpm for 24h. Then filter, wash and dry (80℃, 12h) to obtain a platinum alloy catalyst with improved activity and durability.

[0029] Figure 1 This is a schematic diagram of the diffusion of platinum and cobalt during the acid washing process of the platinum alloy catalyst in this embodiment. As can be seen from the figure, the introduction of high-purity hydrogen gas into the surface during the acid washing process and the protons in the acid form a low potential on the surface of the platinum alloy, which is beneficial to the surface reconstruction of platinum-cobalt alloy nanoparticles. Figure 2 These are the actual TEM and STEM images of the platinum alloy catalyst after acid washing; it can be seen in the high-resolution STEM image that Pt atoms form a platinum shell of 1-2 atomic layers on the outside.

[0030] The prepared platinum alloy catalyst consists of a platinum-cobalt binary alloy. After acid washing, the atomic ratio of Pt to Co is 3:1, and it is supported on a carbon support (Pt3Co / C). The size of the platinum-cobalt alloy nanoparticles is 4.2 nm. The catalyst has a catalytic activity of 0.621 A / mg Pt@0.9V. After 30,000 high and low potential cycles at 0.6V(3s)~0.95V(3s), the mass-specific activity decay rate is 16.9%.

[0031] Example 4 The prepared Pt3Co alloy catalyst was acid-washed as follows. The catalyst contained 40.0 wt.% Pt and 4.03 wt.% Co. The specific steps included are as follows: 1) Weigh 10.67 g of chloroplatinic acid hexahydrate and 3.0 g of cobalt nitrate hexahydrate, add them to 100 mL of deionized water, and stir at 300 rpm until completely dissolved; then add 5.6 g of carbon powder, and stir thoroughly at 500 rpm for 60 min to make the mixture evenly dispersed, to obtain mixed dispersion A. 2) While stirring the mixed dispersion A at 500 rpm, heat it to 60°C and perform vacuum treatment, controlling the vacuum degree at 1×10⁻⁶. 3 Pa, vacuuming time is 50 min; observe the state of the slurry, and when the mixed dispersion becomes viscous, stop heating and vacuuming, and wait for it to cool to room temperature. Then put it into liquid nitrogen for rapid cooling for 20 min, and then put it into a freeze-drying device and freeze-dry at -70℃ for 24 h to obtain black solid powder B. 3) Black solid powder B was placed under a 10% H2 / Ar mixed gas and kept at 900℃ for 2 hours, with the heating rate controlled at 5℃ / min. Then it was cooled to room temperature to obtain black solid powder C. 4) Disperse 10g of black solid powder C in a 2 mol / L dilute sulfuric acid solution that has been pre-deoxygenated with high-purity argon for 60 min, then purged with high-purity hydrogen until saturated and continuously purged with hydrogen for acid washing treatment. The volume of the dilute sulfuric acid solution is 1L, the temperature is controlled at 50℃, and the stirring speed is 300rpm for 24h. After filtration, washing, and drying (80℃, 12h), a platinum alloy catalyst with improved activity and durability is obtained.

[0032] The prepared platinum alloy catalyst consists of a platinum-cobalt binary alloy. After acid washing, the atomic ratio of Pt to Co is 3:1, and it is supported on a carbon support (Pt3Co / C). The size of the platinum-cobalt alloy nanoparticles is 3.8 nm. The catalyst has a catalytic activity of 0.654 A / mg Pt@0.9 V. After 30,000 high and low potential cycles at 0.6 V (3 s) to 0.95 V (3 s), the mass-specific activity decay rate is 12.3%.

[0033] Example 5 The prepared Pt3Co alloy catalyst was acid-washed as follows. The catalyst contained 40.0 wt.% Pt and 4.03 wt.% Co. The specific steps included are as follows: 1) Weigh 10.67 g of chloroplatinic acid hexahydrate and 3.0 g of cobalt nitrate hexahydrate, add them to 100 mL of deionized water, and stir at 300 rpm until completely dissolved; then add 5.6 g of carbon powder, and stir thoroughly at 500 rpm for 60 min to make the mixture evenly dispersed, to obtain mixed dispersion A. 2) While stirring the mixed dispersion A at 500 rpm, heat it to 60°C and perform vacuum treatment, controlling the vacuum degree at 1×10⁻⁶. 3Pa, vacuuming time is 50 min; observe the state of the slurry, and when the mixed dispersion becomes viscous, stop heating and vacuuming, and wait for it to cool to room temperature. Then put it into liquid nitrogen for rapid cooling for 20 min, and then put it into a freeze-drying device and freeze-dry at -70℃ for 24 h to obtain black solid powder B. 3) Black solid powder B was placed under a 10% H2 / Ar mixed gas and kept at 900℃ for 2 hours, with the heating rate controlled at 5℃ / min. Then it was cooled to room temperature to obtain black solid powder C. 4) Disperse 10g of black solid powder C in a 2mol / L dilute sulfuric acid solution that has been deoxygenated with high-purity argon for 60min, then purged with high-purity hydrogen until saturated and continuously purged with hydrogen for acid washing treatment. The volume of dilute sulfuric acid solution is 1L, the temperature is controlled at 80℃, and the stirring speed is 300rpm for 24h. After filtration, washing and drying (80℃, 12h), a platinum alloy catalyst with improved activity and durability is obtained.

[0034] The prepared platinum alloy catalyst consists of a platinum-cobalt binary alloy. After acid washing, the atomic ratio of Pt to Co is 3:1, and it is supported on a carbon support (Pt3Co / C). The size of the platinum-cobalt alloy nanoparticles is 4.0 nm. The catalyst has a catalytic activity of 0.562 A / mg Pt@0.9V. After 30,000 high and low potential cycles at 0.6V(3s)~0.95V(3s), the mass-specific activity decay rate is 21.9%.

[0035] Example 6 The following describes the preparation of Pt3Co 0.8 Mn 0.2 The alloy catalyst was acid-washed. The catalyst contained 40.0 wt.% Pt, 2.41 wt.% Co, and 0.6 wt.% Mn. The specific steps included: 1) Weigh 10.67 g of chloroplatinic acid hexahydrate, 3.0 g of cobalt nitrate hexahydrate and 0.5 g of manganese chloride tetrahydrate, add them to 100 mL of deionized water, and stir at 300 rpm until completely dissolved; then add 5.6 g of carbon powder, and stir thoroughly at 500 rpm for 60 min to ensure uniform dispersion, thus obtaining mixed dispersion A; 2) While stirring the mixed dispersion A at 500 rpm, heat it to 60°C and perform vacuum treatment, controlling the vacuum degree at 1×10⁻⁶. 3Pa, vacuuming time is 50 min; observe the state of the slurry, and when the mixed dispersion becomes viscous, stop heating and vacuuming, and wait for it to cool to room temperature. Then put it into liquid nitrogen for rapid cooling for 20 min, and then put it into a freeze-drying device and freeze-dry at -70℃ for 24 h to obtain black solid powder B. 3) Black solid powder B was placed under a 10% H2 / Ar mixed gas and kept at 900℃ for 2 hours, with the heating rate controlled at 5℃ / min. Then it was cooled to room temperature to obtain black solid powder C. 4) Disperse 10g of black solid powder C in a 2 mol / L dilute sulfuric acid solution that has been pre-deoxygenated with high-purity argon for 60 min, then purged with high-purity hydrogen until saturated and continuously purged with hydrogen for acid washing treatment. The volume of the dilute sulfuric acid solution is 1L, the temperature is controlled at 50℃, and the stirring speed is 300rpm for 24h. After filtration, washing, and drying (80℃, 12h), a platinum alloy catalyst with improved activity and durability is obtained.

[0036] The prepared platinum alloy catalyst includes a platinum-cobalt binary alloy composition (Pt3Co). 0.8 Mn 0.2 / C), after acid washing, the atomic ratio of Pt to (Co+Mn) is 3:1, and it is loaded on a carbon support. The size of the platinum cobalt manganese alloy nanoparticles is 4.2nm. The catalytic activity of this catalyst reaches 0.671A / mg Pt@0.9V. After 30,000 high and low potential cycles of 0.6V(3s)~0.95V(3s), the decay rate of the mass specific activity is only 9.5%.

[0037] Comparative Example 1 In this comparative example, the Pt content is 40 wt% and the Co content is 3.02 wt%. The only difference from Example 3 is that hydrogen gas was not introduced during acid washing in step 4. All other operations are exactly the same.

[0038] The platinum-cobalt alloy nanoparticles have a size of 4.4 nm. The catalytic activity of this catalyst is 0.352 A / mg Pt@0.9V. After 30,000 high and low potential cycles at 0.6V(3s)~0.95V(3s), the mass-specific activity decreases by 33.5%.

[0039] Comparative Example 2 In this comparative example, the Pt content is 40 wt% and the Co content is 3.02 wt%. The only difference from Example 3 is that argon gas was introduced instead of hydrogen gas during acid washing in step 4. All other operations are exactly the same.

[0040] The platinum-cobalt alloy nanoparticles have a size of 4.2 nm, and the catalyst has a catalytic activity of 0.311 A / mg Pt@0.9V. After 30,000 high and low potential cycles at 0.6V(3s)~0.95V(3s), the mass-specific activity decay rate reaches 28.2%.

[0041] Comparative Example 3 In this comparative example, the Pt content is 40 wt% and the Co content is 3.02 wt%. The only difference from Example 3 is that the acid solution temperature during pickling in step 4 is 30°C. All other operations are completely the same.

[0042] The platinum-cobalt alloy nanoparticles have a size of 4.3 nm, and the catalyst has a catalytic activity of 0.421 A / mg Pt@0.9V. After 30,000 high and low potential cycles at 0.6V(3s)~0.95V(3s), the mass-specific activity decay rate reaches 23.6%.

[0043] Comparative Example 4 In this comparative example, the Pt content is 40 wt% and the Co content is 3.02 wt%. The only difference from Example 3 is that there is no liquid nitrogen quenching step in step 2; that is, after cooling to room temperature, it is placed in the freeze-drying equipment and freeze-dried at -70°C for 24 hours. All other operations are exactly the same.

[0044] The platinum-cobalt alloy nanoparticles have a size of 4.8 nm. The catalytic activity of this catalyst is 0.437 A / mg Pt@0.9 V. After 30,000 high and low potential cycles at 0.6 V (3 s) to 0.95 V (3 s), the mass-specific activity decreases by 28.5%.

[0045] Table 1. Catalytic activity and durability data of the catalysts prepared in Examples 1-6 and Comparative Examples 1-4

[0046] As shown in Table 1, compared with Comparative Examples 1, 2, 3 and 4, the platinum alloy catalysts prepared in Examples 1 to 6 all exhibited higher catalyst activity and durability, demonstrating excellent catalyst performance.

[0047] In summary, this application provides an acid washing method for improving the activity and durability of platinum alloy catalysts. This invention constructs a low-potential acid washing method for platinum alloy surfaces. By utilizing hydrogen gas and hydrogen ions in the acid solution to create a low potential (~0V) on the Pt alloy surface, the surface and interior of the platinum alloy are reconstructed during the acid washing process. Under hydrogen gas conditions, transition metal ions diffuse and dissolve outwards. Simultaneously, the outward diffusion of internal transition metal ions to the subsurface layer affects the electronic structure of the surface platinum, improving catalyst activity. Simultaneously, internal platinum and trace amounts of dissolved platinum diffuse outwards and deposit on the surface, filling the voids left by the dissolution of transition metals, forming a Pt-rich layer on the surface, thus improving catalyst stability. The formation of a closed platinum-rich shell on the surface locks in the transition metal alloy components beneath the surface, greatly inhibiting the outflow of metal cations. Furthermore, as transition metals diffuse towards the surface, the transition metals in the subsurface layer improve catalyst activity by adjusting the electronic structure of platinum. Therefore, the acid washing method of this invention enables platinum alloys to possess higher catalytic activity and better durability.

[0048] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. An acid washing method for improving the activity and durability of platinum alloy catalysts, characterized in that, The method includes the following steps: Step 1: Add carbon support, chloroplatinic acid hexahydrate and transition metal salt to deionized water and stir to mix evenly to obtain mixed dispersion A; Step 2: Vacuum treatment of mixed dispersion A under stirring conditions until mixed dispersion A becomes viscous, stop vacuum treatment, and freeze dry for 12~48h to obtain black solid powder B; Step 3: Place the black solid powder B under a reducing atmosphere and heat it to 500~900℃ for 0.5~8h, then cool it to room temperature to obtain solid powder C; Step 4: Disperse solid powder C in a dilute acid solution that has been pre-deoxygenated with high-purity argon, then purged with high-purity hydrogen until saturation and continuously purged with hydrogen for acid washing treatment. After filtration, washing and drying, a platinum alloy catalyst with improved activity and durability is obtained.

2. The acid washing method for improving the activity and durability of platinum alloy catalysts according to claim 1, characterized in that, In step 1, the mass ratio of carbon support, chloroplatinic acid hexahydrate and transition metal salt is 1:0.5~2.5:0.25~1.

5.

3. The acid washing method for improving the activity and durability of platinum alloy catalysts according to claim 1, characterized in that, In step 1, the transition metal salt is one or two of the following: chloride, nitrate, acetate, sulfate, and acetylacetone salts of cobalt, nickel, manganese, and chromium.

4. The acid washing method for improving the activity and durability of platinum alloy catalysts according to claim 1, characterized in that, In step 2, the vacuum level during the vacuuming process is 10. 3 ~10 4 Pa, vacuuming is performed by heating to 50~70℃ and vacuuming time is 30~90min.

5. The acid washing method for improving the activity and durability of platinum alloy catalysts according to claim 1, characterized in that, In step 2, the freeze-drying process involves: cooling to room temperature and then rapidly cooling in liquid nitrogen for 10-30 minutes, followed by freeze-drying in a freeze-drying apparatus at -30℃ to -70℃ for 20-36 hours.

6. The acid washing method for improving the activity and durability of platinum alloy catalysts according to claim 1, characterized in that, In step 4, the dilute acid is one or two of dilute sulfuric acid, dilute hydrochloric acid, and dilute acetic acid; the concentration of hydrogen ions in the dilute acid is 0.01~6 mol / L.

7. The acid washing method for improving the activity and durability of platinum alloy catalysts according to claim 1, characterized in that, In step 4, during acid washing, high-purity hydrogen gas is continuously introduced.

8. The acid washing method for improving the activity and durability of platinum alloy catalysts according to claim 1, characterized in that, In step 4, the pickling process involves stirring at a temperature controlled at 50-80℃ for 6-48 hours at a stirring speed of 200-400 rpm.

9. The acid washing method for improving the activity and durability of platinum alloy catalysts according to claim 1, characterized in that, In step 4, during acid washing, the concentration of the platinum alloy catalyst in dilute acid is 2~20 g / L.

10. A platinum alloy catalyst obtained by the method according to any one of claims 1-9.

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