A carbon-supported platinum-based core-shell catalyst and a method for preparing the same

Abstract

The present application relates to the technical field of proton exchange membrane fuel cell, and particularly relates to a carbon-loaded core-shell type platinum-based catalyst and a preparation method thereof.The inner core of the core-shell type platinum-based catalyst is mainly PtM alloy, and the outer shell is mainly PtAu alloy.In the disclosed preparation method, first, the carbon-loaded platinum-based catalyst (PtM / C) is subjected to core-shell forming-alloying synchronous processing; then, gold atoms are used to replace transition metal atoms on the surface of the catalyst to form a dense platinum-gold alloy outer shell layer; the alloy outer shell layer can prevent the loss of transition metal atoms in the inner core and improve the stability of the catalyst.The introduction of Au also helps to balance the adsorption strength of OH ad on the surface of Pt, reduce the probability of Pt particle dissolution loss and ripening growth.The catalyst prepared by the present application can effectively improve the utilization rate of noble metals Pt and Au, and help to reduce the use amount of noble metals; the disclosed method is easy to realize batch production, and helps to control the cost of the catalyst.

Description

Technical Field

[0001] This invention relates to the field of proton exchange membrane fuel cell technology, and particularly to a carbon-supported platinum-based core-shell catalyst and its preparation method. Background Technology

[0002] Electrode catalysts are both the "active center" and the "cost center" of fuel cells. The "three-phase reaction interface" formed by the catalyst and ion-conducting polymers is the site of electrochemical reactions, and the activity and durability of the catalyst largely determine the performance and lifespan of the fuel cell stack. Improving the activity and durability of platinum-based catalysts is a bottleneck problem that urgently needs to be solved for the large-scale commercial application of fuel cells.

[0003] Currently, platinum-carbon catalysts remain the mainstream in commercial fuel cell electrode catalysts, and they are still predominantly high in platinum content. However, platinum-carbon catalysts suffer from low activity and poor durability, and future development will prioritize improving durability. Experimental and theoretical research on platinum-based catalysts has made rapid progress. For example, the intrinsic activity of the catalyst can be improved by doping with transition metals to form platinum-based alloys; the utilization rate of Pt can be improved by dispersing the noble metal Pt on the surface of nanoparticles to form a core-shell structure; or the catalyst surface morphology and dominant crystal faces can be controlled to enhance catalyst activity and durability.

[0004] Platinum-based alloys can improve the intrinsic activity of catalysts, but they suffer from poor durability. Transition metal elements in these catalysts are prone to dissolution during operation, leading to a decrease in catalyst activity. Furthermore, the dissolved transition metal ions react with H₂O₂, a byproduct of ORR (Orbital Reductant Ration), to generate reactive free radicals (Fenton's reagent), accelerating the degradation of ion-conducting polymers in the proton exchange membrane and catalyst layer, thus causing rapid degradation of battery performance.

[0005] Au nanoparticles exhibit good electrochemical stability, and their introduction into electrocatalysts can significantly improve the stability of the catalysts. However, on the one hand, Au itself has poor ORR catalytic activity, and its introduction into the catalyst may lead to a decrease in catalytic activity if it covers the active sites of Pt; on the other hand, Au is expensive, and excessive doping will significantly affect the cost of the catalyst.

[0006] Patents CN105914381A and CN105870469A disclose a method for preparing supported Au@Pt catalysts using underpotential deposition, which effectively improves the durability of fuel cells. However, this method is complex and difficult to control, making it unsuitable for mass production. Furthermore, the Pt layer on the catalyst surface is too thin, and the core uses a large amount of Au, resulting in poor stability of the Pt monolayer on the surface and excessively high catalyst costs. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing platinum-based alloy catalysts, such as poor durability and the complex preparation process and poor stability of the Pt monolayer on the surface, in preparing supported Au@Pt catalysts using underpotential deposition. This invention provides a carbon-supported platinum-based core-shell catalyst and its preparation method.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A carbon-supported platinum-based core-shell catalyst (PtM@PtAu / C) comprises a core and a shell, wherein the core is a PtM alloy and the shell is a PtAu alloy shell mainly composed of Pt, where M represents a transition metal.

[0010] The alloy catalyst of this invention, by introducing Au, eliminates or reduces the presence of easily lost transition metal atoms on the catalyst surface. Simultaneously, the denser surface of the platinum-gold alloy prevents the loss of transition metal atoms from the platinum-transition metal alloy core, thus improving catalyst stability. The introduction of Au also helps to balance OH at higher potentials. ad The adsorption strength of (adsorbed OH) on the Pt surface is increased, which reduces the probability of Pt particle dissolution and loss and Oswald ripening and growth, thus ensuring the stability of the catalyst.

[0011] As a preferred embodiment of the present invention, in the carbon-supported platinum-based core-shell catalyst, the transition metal M is any one of Fe, Co, and Ni.

[0012] Since Au itself has poor catalytic activity, excessively high Au content can easily lead to a decrease in catalytic activity, while excessively low Au content has limited effect on improving catalyst durability. As a preferred embodiment of the present invention, in the carbon-supported platinum-based core-shell catalyst, the molar ratio of platinum to gold is 10~100:1; preferably, the molar ratio of platinum to gold is 20~30:1. In the outer shell layer, the atomic molar ratio between platinum and gold is 1~50:1; the molar ratio between metallic platinum and metallic gold is 2~10:1. The technical solution of this invention controls the distribution of Au on the surface of nanoparticles, thereby improving its utilization rate.

[0013] A method for preparing a carbon-supported platinum-based core-shell catalyst includes the following preparation steps: Step 1: The carbon-supported platinum-based catalyst PtM / C is heat-treated at high temperature in a reducing mixed atmosphere to obtain a carbon-supported platinum-based alloy catalyst in which core-shell formation and alloying occur simultaneously. Step 2: The carbon-supported platinum-based alloy catalyst obtained in Step 1 is placed in an aqueous solution of Au salt precursor. Through a displacement reaction, a PtAu alloy layer is formed on the surface of the PtM nanoparticles. After filtration, washing, and drying, the carbon-supported platinum-based core-shell catalyst PtM@PtAu / C is obtained.

[0014] In this invention, an alloyed PtM / C catalyst is mixed with an aqueous solution of an Au salt precursor. Using the reduction potential difference between Au and the transition metal M as the driving force, a substitution reaction replaces the transition metal atoms on the surface of the PtM / C nanoparticles with Au, forming a PtAu alloy with Pt as the main component on the surface and a PtM alloy structure with M as the main component inside. This invention utilizes the principle of surface segregation to perform core-shell alloying treatment on the PtM / C catalyst. On the one hand, this forms PtM alloyed nanoparticles; on the other hand, the presence of hydrogen induces atomic reconstruction on the nanoparticle surface, forming a surface structure dominated by Pt and supplemented by transition metals. This is also key to controlling the ultra-low Au content in the PtM@PtAu / C alloy catalyst. By introducing Au atoms, there are almost no easily lost transition metal atoms on the catalyst surface. Furthermore, the denser platinum-gold alloy surface effectively prevents the loss of transition metal atoms from the core, greatly improving the catalyst's stability. On the other hand, the introduction of Au helps balance the OH groups at higher potentials. ad The adsorption strength at Pt active sites is increased, while the probability of Pt particle dissolution and loss and Oswald ripening and growth is reduced, thereby improving the stability of the catalyst.

[0015] Temperature has a certain influence on atomic reconstruction. When the temperature is too low, disordered alloys tend to form, while excessively high temperatures can cause the agglomeration and growth of nanoparticles. As a preferred embodiment of the present invention, in step 1, the temperature range of the high-temperature heat treatment is 300-1000℃. More preferably, the temperature range of the high-temperature heat treatment is 600-800℃.

[0016] As a preferred technical solution of the present invention, in step 1, the reducing mixed atmosphere includes a reducing gas and a balancing gas. The reducing gas includes, but is not limited to, any one of hydrogen, ammonia, and carbon monoxide, and the balancing gas is any one of nitrogen, argon, etc. The volume ratio of the reducing gas in the reducing mixed atmosphere is 0.5~20%.

[0017] The heat treatment atmosphere also has a certain impact on atomic reconstruction. When the hydrogen concentration is too low, the interaction between Pt and hydrogen is weak, and the "surface segregation" phenomenon is not obvious. However, when the hydrogen concentration is too high, the "methanation" of the carbon support is easily generated, which significantly reduces the carbon content in the catalyst. As a preferred technical solution of the present invention, in step 1, the volume ratio of hydrogen in the heat treatment atmosphere is 3-10%.

[0018] As a preferred embodiment of the present invention, in step 2, the Au precursor aqueous solution includes any one of chloroauric acid, potassium chloroaurate, and gold chloride, and the concentration of the Au precursor aqueous solution is 0.01–0.5 mol·L⁻¹. -1 .

[0019] As a preferred embodiment of the present invention, the PtM / C catalyst can be prepared according to the following preparation method: A Pt precursor salt solution and a transition metal precursor salt solution were mixed evenly to form a mixed solution. Sodium citrate aqueous solution was added dropwise to the mixed solution while stirring. Then, carbon support dispersion was mixed with the mixed solution and ultrasonically dispersed evenly. Under rapid stirring, excess NaBH4 aqueous solution was added dropwise. After the addition was completed, stirring was continued for 2 hours. The PtM / C catalyst was obtained by filtration, washing and drying.

[0020] As a preferred embodiment of the present invention, the molar ratio between platinum and transition metal elements is 1:3 to 5:1. More preferably, the molar ratio between platinum and transition metal elements is 1:3 to 3:1.

[0021] Preferably, the Pt precursor solution includes any one of chloroplatinic acid, potassium chloroplatinate, chloroplatinic acid, potassium chloroplatinate, platinum nitrate, and platinum chloride.

[0022] Preferably, the transition metal precursor salt solution includes nitrates, sulfates, acetates, or halides corresponding to the transition metal ions.

[0023] The transition metal is specifically Fe, Co, or Ni.

[0024] A catalytic membrane electrode comprising the aforementioned carbon-supported platinum-based core-shell catalyst.

[0025] A fuel cell comprising the catalytic membrane electrode.

[0026] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: 1. The PtM@PtAu / C alloy catalyst of the present invention modifies Au by chemical substitution, without the need for additional reducing agent. The method is simple, the environment is mild, the gold precursor solution can be reused, and mass production can be achieved, which helps to control the cost of the catalyst.

[0027] 2. In the PtM@PtAu / C alloy catalyst of the present invention, the catalyst surface layer is a PtAu alloy mainly composed of Pt, and the core is a PtM alloy. The active components are more distributed on the catalyst surface, which is beneficial to improving the utilization rate of Pt.

[0028] 3. The durability of the PtM@PtAu / C alloy catalyst is significantly improved. On one hand, the catalyst surface contains little or no easily leached transition metal atoms, and the denser platinum-gold alloy surface prevents the loss of transition metal atoms from the platinum-transition metal alloy core. On the other hand, the introduction of Au helps balance the OH groups at higher potentials. ad The adsorption strength on the Pt surface reduces the probability of Pt particles dissolving and leaching, as well as Oswald ripening and growth.

[0029] 4. By inducing the formation of a Pt-based transition metal-based structure on the surface of alloy particles through heat treatment in a hydrogen atmosphere, the Au content entering the catalyst can be effectively controlled during the chemical replacement step. Furthermore, the Au atoms are all located on the surface of the alloy nanoparticles, effectively improving their utilization rate. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the structure of the PtM@PtAu / C alloy catalyst of the present invention; Figure 2 These are the XRD patterns of the catalysts prepared in Example 3 and Comparative Examples 1-3; Figure 3 These are the IV polarization curves of the catalysts prepared in Example 3 and Comparative Examples 1-2 before and after stability testing in the membrane electrode; Figure 4 These are TEM images of the catalysts prepared in Example 3 and Comparative Example 1 before and after stability testing in the membrane electrode. Detailed Implementation

[0031] The present invention will now be described in detail with reference to the accompanying drawings.

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0033] Example 1 (PtFe@PtAu / C alloy catalyst) A method for preparing a PtFe@PtAu / C alloy catalyst includes the following steps: S1: Preparation of PtFe nanoparticles: Prepare chloroplatinic acid aqueous solution and ferric nitrate precursor solution (where the molar ratio of Pt to Fe is 3:1) and mix them evenly. Then, add sodium citrate aqueous solution dropwise to the above mixture while stirring. Mix the pre-dispersed carbon support solution with the above mixture and disperse it evenly by ultrasonication. Add excess NaBH4 aqueous solution dropwise under rapid stirring. After the addition is completed, continue stirring for 2 hours. Then filter, wash and dry to obtain PtFe / C catalyst. S2: PtFe nanoparticle alloying: The PtFe / C catalyst obtained in step S1 was heat-treated at 600°C in a 5 vol.% hydrogen / nitrogen atmosphere to obtain an alloyed PtFe / C catalyst with Pt-rich surface. S3: Introduction of Au element by chemical substitution method: The alloyed PtFe / C catalyst obtained in step S2 is dispersed in an aqueous solution of chloroauric acid, stirred for 2 hours, and then filtered, washed and dried to obtain the PtFe@PtAu / C alloy catalyst.

[0034] Example 2 PtNi@PtAu / C alloy catalyst A method for preparing a PtNi@PtAu / C alloy catalyst includes the following steps: S1: Preparation of PtNi nanoparticles: Prepare chloroplatinic acid aqueous solution and nickel nitrate precursor solution (where the molar ratio of Pt to Ni is 3:1) and mix them evenly. Then, add sodium citrate aqueous solution dropwise to the above mixture while stirring. Mix the pre-dispersed carbon support solution with the above mixture and disperse it evenly by ultrasonication. Add excess NaBH4 aqueous solution dropwise under rapid stirring. After the addition is completed, continue stirring for 2 hours. Then filter, wash and dry to obtain PtNi / C catalyst.

[0035] S2: PtNi nanoparticle alloying: The PtNi / C catalyst obtained in step S1 is heat-treated at 700℃ in a 5 vol.% hydrogen / nitrogen atmosphere to obtain an alloyed PtNi / C catalyst with Pt-rich surface.

[0036] S3: Introduction of Au element by chemical substitution method: The alloyed PtNi / C catalyst obtained in step S2 is dispersed in an aqueous solution of chloroauric acid, stirred for 2 hours, and then filtered, washed and dried to obtain the PtNi@PtAu / C alloy catalyst.

[0037] Example 3 PtCo@PtAu / C alloy catalyst (1#) S1: Preparation of PtCo nanoparticles: Prepare chloroplatinic acid aqueous solution and cobalt nitrate precursor solution (where the molar ratio of Pt to Co is 3:1) and mix them evenly. Then, add sodium citrate aqueous solution dropwise to the above mixture while stirring. Mix the pre-dispersed carbon support solution with the above mixture and disperse it evenly by ultrasonication. Add excess NaBH4 aqueous solution dropwise under rapid stirring. After the addition is completed, continue stirring for 2 hours. Then filter, wash and dry to obtain PtCo / C catalyst.

[0038] S2: PtCo nanoparticle alloying: The PtCo / C catalyst obtained in step S1 is heat-treated at 800°C in a 5 vol.% hydrogen / nitrogen atmosphere to obtain an alloyed PtCo / C catalyst with Pt-rich surface.

[0039] S3: Introduction of Au element by chemical substitution: The alloyed PtCo / C catalyst obtained in step S2 was dispersed in an aqueous solution of chloroauric acid, stirred for 2 hours, and then filtered, washed and dried to obtain the PtCo@PtAu / C alloy catalyst (1#). Its structure is as follows Figure 1 As shown.

[0040] Example 4 PtCo@PtAu / C alloy catalyst (2#) S1: Preparation of PtCo nanoparticles: Prepare chloroplatinic acid aqueous solution and cobalt nitrate precursor solution (where the molar ratio of Pt to Co is 1:1) and mix them evenly. Then, add sodium citrate aqueous solution dropwise to the above mixture while stirring. Mix the pre-dispersed carbon support solution with the above mixture and disperse it evenly by ultrasonication. Add excess NaBH4 aqueous solution dropwise under rapid stirring. After the addition is completed, continue stirring for 2 hours. Then filter, wash and dry to obtain PtCo / C catalyst. S2: PtCo nanoparticle alloying: The PtCo / C catalyst obtained in step S1 was heat-treated at 800°C in a 5 vol.% hydrogen / nitrogen atmosphere to obtain a PtCo / C ordered alloy catalyst with Pt-rich surface.

[0041] S3: Introduction of Au element by chemical substitution method: The alloyed PtCo / C catalyst obtained in step S2 is dispersed in an aqueous solution of chloroauric acid, stirred for 2 hours, filtered, washed and dried to obtain PtCo@PtAu / C alloy catalyst (2#).

[0042] Example 5 PtCo@PtAu / C alloy catalyst (3#) S1 Preparation of PtCo nanoparticles: Prepare aqueous solutions of chloroplatinic acid and cobalt nitrate precursor solutions (with a molar ratio of Pt to Co of 5:1) and mix them evenly. Then, add sodium citrate aqueous solution dropwise to the mixture while stirring. Mix the pre-dispersed carbon support solution with the mixture and ultrasonically disperse it evenly. Add excess NaBH4 aqueous solution dropwise under rapid stirring. After the addition is complete, continue stirring for 2 hours. Then filter, wash, and dry to obtain the PtCo / C catalyst.

[0043] S2 PtCo nanoparticle alloying: The PtCo / C catalyst obtained in step S1 was heat-treated at 800℃ in a 5 vol.% hydrogen / nitrogen atmosphere to obtain a PtCo / C ordered alloy catalyst with Pt-rich surface.

[0044] S3 Chemical substitution method to introduce Au element: The alloyed PtCo / C catalyst obtained in step S2 is dispersed in chloroauric acid aqueous solution, stirred for 2 hours, filtered, washed and dried to obtain PtCo@PtAu / C alloy catalyst (3#).

[0045] Example 6 PtCo@PtAu / C alloy catalyst (4#) S1 Preparation of PtCo nanoparticles: Prepare aqueous solutions of chloroplatinic acid and cobalt nitrate precursor solution, and mix them evenly. Then, add sodium citrate aqueous solution dropwise to the mixture while stirring. Mix the pre-dispersed carbon support solution with the mixture and disperse it evenly by ultrasonication. Add excess NaBH4 aqueous solution dropwise under rapid stirring. After the addition is complete, continue stirring for 2 hours. Then filter, wash and dry to obtain PtCo / C catalyst.

[0046] S2 PtCo nanoparticle alloying: The PtCo / C catalyst obtained in step S1 was heat-treated at 500℃ in a 5 vol.% hydrogen / nitrogen atmosphere to obtain a PtCo / C ordered alloy catalyst with Pt-rich surface.

[0047] S3 Chemical substitution method to introduce Au element: The alloyed PtCo / C catalyst obtained in step S2 is dispersed in chloroauric acid aqueous solution, stirred for 2 hours, filtered, washed and dried to obtain PtCo@PtAu / C alloy catalyst (4#).

[0048] Example 7 PtCo@PtAu / C alloy catalyst (5#) S1: Purchase finished PtCo / C catalyst (PtCo molar ratio is 3:1); S2: PtCo nanoparticle alloying: The PtCo / C catalyst obtained in step S1 is heat-treated at 800℃ in a 5 vol.% hydrogen / nitrogen atmosphere to obtain a PtCo / C ordered alloy catalyst with Pt-rich surface.

[0049] S3: Introduction of Au element by chemical substitution method: The alloyed PtCo / C catalyst obtained in step S2 is dispersed in an aqueous solution of chloroauric acid, stirred for 2 hours, filtered, washed and dried to obtain PtCo@PtAu / C alloy catalyst (5#).

[0050] Comparative Example 1 S1 Preparation of PtCo nanoparticles: Prepare aqueous solutions of chloroplatinic acid and cobalt nitrate precursor solution, and mix them evenly. Then, add sodium citrate aqueous solution dropwise to the mixture while stirring. Mix the pre-dispersed carbon support solution with the mixture and disperse it evenly by ultrasonication. Add excess NaBH4 aqueous solution dropwise under rapid stirring. After the addition is complete, continue stirring for 2 hours. Then filter, wash and dry to obtain PtCo / C catalyst.

[0051] S2 Chemical substitution method to introduce Au element: The PtCo / C catalyst obtained in step S1 is dispersed in chloroauric acid aqueous solution, stirred for 2 hours, filtered, washed and dried to obtain unalloyed Au-PtCo / C catalyst.

[0052] Comparative Example 2 The catalyst obtained in Example 3 through steps S1 and S2 is a PtCo / C alloy catalyst.

[0053] Comparative Example 3 S1 Preparation of PtCoAu nanoparticles: Prepare aqueous solutions of chloroplatinic acid, cobalt nitrate, and chloroauric acid, and mix them evenly. Then, add sodium citrate aqueous solution dropwise to the mixture while stirring. Mix the pre-dispersed carbon support dispersion with the mixture and ultrasonically disperse it evenly. Add filtered NaBH4 aqueous solution dropwise under rapid stirring. After the addition is complete, continue stirring for 2 hours. Then filter, wash, and dry to obtain PtCoAu / C catalyst. S2 PtCoAu nanoparticle alloying: The PtCoAu / C catalyst obtained in step S1 is heat-treated at 800℃ in a 5 vol.% hydrogen / nitrogen atmosphere with inert gas as carrier gas to obtain alloyed PtCoAu / C catalyst.

[0054] The metal element content of each catalyst in Examples 1-7 and Comparative Examples 1-3 is summarized in Table 1 below.

[0055] Table 1 compares the metal element content in the catalysts of the examples and comparative examples. Case catalyst Pt content (wt.%) Transition metal content (wt.%) Au content (wt.%) Example 1 PtFe@PtAu / C 43.74 3.63 2.22 Example 2 PtNi@PtAu / C 43.67 3.80 2.28 Example 3 PtCo@PtAu / C(1#) 43.66 3.82 2.30 Example 4 PtCo@PtAu / C(2#) 40.08 11.14 4.13 Example 5 PtCo@PtAu / C(3#) 44.24 2.45 0.91 Example 6 PtCo@PtAu / C(4#) 40.39 4.18 1.05 Example 7 PtCo@PtAu / C (5#) 46.50 5.50 0.96 Comparative Example 1 Au-PtCo / C 40.87 2.01 8.10 Comparative Example 2 PtCo / C 44.39 4.49 / Comparative Example 3 PtCoAu / C 43.50 3.71 2.08 In Table 1, the difference between Examples 1-3 is that different transition metal elements were used; the rest of the preparation process is the same, and all of them use the catalyst preparation method proposed in this invention; the Au content can be controlled at about 2.2 wt.%.

[0056] In Examples 3-5, the PtCo@PtAu / C catalysts were configured with different ratios of platinum and cobalt. The different PtCo ratios significantly affected the Au content in the finished product. As the PtCo ratio increased, the Au content decreased.

[0057] The catalyst preparation process in Example 6 was the same as in Example 3, except that the heating temperature during the high-temperature gas treatment was 500°C. The higher heat treatment temperature facilitates the formation of PtCo intermetallic compounds.

[0058] The catalyst preparation process in Example 7 is the same as that in Example 3, except that a commercial PtCo / C catalyst is used directly, wherein the molar ratio of Pt to Co in the PtCo / C catalyst is 3:1. The present invention also provides three comparative examples, wherein the Au-PtCo / C catalyst prepared in Comparative Example 1 is obtained by directly chemically replacing the PtCo / C catalyst with an aqueous solution of chloroauric acid without high-temperature gas alloying treatment.

[0059] In the Pt-Co / C catalyst prepared in Comparative Example 2, only high-temperature alloying treatment under a hydrogen / nitrogen atmosphere was involved, without gold substitution reaction. The alloying process was consistent with the parameters in Example 3.

[0060] Comparative Example 3 presents a method for preparing a directly alloyed PtCoAu / C catalyst.

[0061] The PtCo@PtAu / C catalyst prepared in Example 3 and the catalysts prepared in Comparative Examples 1-3 were characterized by XRD, and the results are as follows: Figure 2 As shown, XRD characterization tests reveal the following: The XRD characteristic diffraction peaks of the PtCo@PtAu / C catalyst prepared in Example 3 and the PtCo / C alloy catalyst prepared in Comparative Example 2 are almost identical, both showing that they are PtCo intermetallic compounds. However, no diffraction peak of Au was detected in Example 3, which may be because the relative content of Au in the catalyst is too low to be detected.

[0062] In contrast, Comparative Example 1 did not exhibit intermetallic compound characteristics, and a (111) diffraction peak of elemental Au appeared near 38.3°, indicating a significant increase in the relative Au content in the catalyst. This suggests that the core-shell alloying of PtCo nanoparticles during high-temperature treatment plays an important role in the formation of PtCo intermetallic compounds and the control of Au content. The (111) diffraction peak in Comparative Example 3 showed a significant negative shift compared to Example 3, corresponding to the characteristic diffraction peak of PtAuCo ternary alloying, indicating a higher relative Au content in the catalyst.

[0063] The catalysts of Example 3 and Comparative Examples 1-2 were used as cathode catalysts to prepare membrane electrodes, and their initial and stability IV polarization curves after stability tests (0.6-0.95V vs. RHE, 100 mV / s, 30 k cycles) were tested, as shown below. Figure 3 As shown, BOL represents fresh performance, and EOL represents performance after stability testing. The trends in the IV polarization curves show that Example 3 and Comparative Example 2 have similar fresh performance, but Example 3's performance after stability testing is significantly higher than Comparative Example 2. Comparative Example 1, due to the lack of high-temperature alloying treatment, introduced a large amount of Au onto the nanoparticle surface, leading to a decrease in initial performance. These results indicate that the PtCo@PtAu / C catalyst prepared by combining high-temperature induced core-shell alloying treatment with gold substitution exhibits excellent stability in membrane electrodes.

[0064] The catalysts prepared in Example 3 and Comparative Example 1 were characterized by TEM before and after the membrane electrode stability test. The results are as follows: Figure 4 As shown, the nanoparticles in both the fresh PtCo@PtAu / C and Au-PtCo / C catalysts are spherical with smooth surfaces and are relatively uniformly distributed on the carbon support. After stability testing, the nanoparticles in Au-PtCo / C showed severe aggregation, and their surfaces were no longer smooth, resulting in significant damage to the catalyst morphology. In contrast, the PtCo@PtAu / C catalyst, after the same stability test, did not show significant changes in morphology, with only a slight increase in nanoparticle size, indicating its good stability.

[0065] In summary, the test results from the above examples and comparative examples show that the catalyst preparation method of this invention utilizes the principle of surface segregation to first perform core-shell alloying treatment on the PtM / C catalyst. This process forms PtM alloyed nanoparticles, and the presence of hydrogen induces atomic reconstruction on the nanoparticle surface, forming a surface structure dominated by Pt and supplemented by transition metals. This is also key to controlling the ultra-low Au content in the PtM@PtAu / C alloy catalyst. By introducing Au atoms, the catalyst surface is almost free of easily lost transition metal atoms. Furthermore, the denser platinum-gold alloy surface effectively prevents the loss of transition metal atoms from the core, greatly improving the catalyst's stability. On the other hand, the introduction of Au helps balance the OH groups at higher potentials. ad The adsorption strength on the Pt surface is increased, while the probability of Pt particle dissolution and loss and Oswald ripening growth is reduced, thereby improving the stability of the catalyst.

[0066] In the catalyst and the method for preparing the catalyst of the present invention, a structure with Pt as the main component and transition metal as the auxiliary component is induced to form on the surface of the alloy particles by heat treatment in a hydrogen atmosphere. This effectively controls the Au content entering the catalyst in the chemical replacement step, and the Au atoms are all located on the surface of the alloy nanoparticles, effectively improving their utilization rate.

[0067] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A carbon-supported platinum-based core-shell catalyst, characterized in that, The carbon-supported platinum-based core-shell catalyst comprises a core and an outer shell. The core is a PtM alloy, and the outer shell is a PtAu alloy shell mainly composed of Pt, where M represents a transition metal; the transition metal M is any one of Fe, Co, and Ni. In the carbon-supported platinum-based core-shell catalyst, the molar ratio between platinum and gold is 20-30:1, and the atomic molar ratio between platinum and gold in the outer shell is 2-10:

1. The carbon-supported platinum-based core-shell catalyst is prepared according to the following method: Step 1: The carbon-supported platinum-based catalyst PtM / C is heat-treated at high temperature in a reducing mixed atmosphere to obtain a carbon-supported platinum-based alloy catalyst in which core-shell formation and alloying occur simultaneously. Step 2: The carbon-supported platinum-based alloy catalyst obtained in Step 1 is placed in an aqueous solution of Au salt precursor. Through a displacement reaction, a PtAu alloy layer is formed on the surface of the PtM nanoparticles. After filtration, washing, and drying, the carbon-supported platinum-based core-shell catalyst PtM@PtAu / C is obtained.

2. The carbon-supported platinum-based core-shell catalyst according to claim 1, characterized in that, In step 1, the temperature range for high-temperature heat treatment is 300-1000°C.

3. The carbon-supported platinum-based core-shell catalyst according to claim 1, characterized in that, In step 1, the reducing mixed atmosphere includes a reducing gas and a balancing gas. The reducing gas includes any one of hydrogen, ammonia, and carbon monoxide, and the balancing gas is any one of nitrogen and argon. The volume percentage of the reducing gas in the reducing mixed atmosphere is 0.5-20%.

4. The carbon-supported platinum-based core-shell catalyst according to claim 3, characterized in that, In step 2, the Au salt precursor aqueous solution includes any one of chloroauric acid, potassium chloroaurate, and gold chloride, and the concentration of the Au salt precursor aqueous solution is 0.01-0.5 mol / L.

5. A catalytic membrane electrode, characterized in that, The carbon-supported platinum-based core-shell catalyst comprising any one of claims 1-4.

6. A fuel cell comprising the catalytic membrane electrode of claim 5.

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