Rapid conversion method of platinum oxidation state-highly metallic state of hafnium-doped platinum catalyst

Abstract

The invention provides a rapid conversion method of a platinum oxidation state and a highly metallic state of a hafnium-doped platinum catalyst, and belongs to the technical field of new energy catalytic materials. According to the method, a commercial carbon-supported platinum catalyst, hafnium salt and super-hydride are mixed in a high-boiling-point solvent, high reduction potential of hafnium is overcome by utilizing a strong reduction environment and chemical energy released by violent decomposition of the super-hydride, high-valence platinum is reduced into a metal state, and meanwhile reduced hafnium atoms are inlaid on the surfaces or subsurfaces of platinum nanoparticles. Through the synergistic effect of the superhydride and the hafnium salt, the oxidation state on the surface of the platinum is rapidly and efficiently removed, the d-band center of the platinum is optimized through the electronic effect and geometric effect of hafnium, and the oxygen reduction reaction activity and stability of the catalyst are remarkably improved. The method is simple to operate, low in cost and suitable for large-scale production, and the prepared catalyst has excellent performance and good application prospects in hydrogen fuel cells.

Description

Technical Field

[0001] This invention relates to the field of new energy catalytic materials and application technology, specifically to a rapid conversion method for platinum oxidation state to highly metallic state in a hafnium-doped platinum catalyst. Background Technology

[0002] In hydrogen fuel cells, the oxygen reduction reaction (ORR) is a critical cathode reaction, and its efficiency directly affects the overall performance of the fuel cell. Therefore, developing efficient and stable oxygen reduction electrocatalysts is of paramount importance.

[0003] Platinum-carbon catalysts supported on carbon-platinum nanoparticles have become one of the most widely used commercial oxygen reduction electrocatalysts due to their excellent catalytic activity and stability. However, nanoparticles possess a much larger specific surface area compared to bulk materials of the same mass. This means that a higher proportion of atoms are exposed on the surface. These surface atoms, not being fully coordinated with surrounding atoms as atoms within the material, are in a high-energy, unstable state, i.e., possessing high "surface energy." To lower their own energy, these highly reactive surface atoms readily react with other molecules in the environment (such as oxygen and water) to form more stable oxides.

[0004] The formation of platinum oxide has a dual negative impact on catalyst performance. First, it directly leads to a decrease in catalytic activity. The main active site of ORR is zero-valent metallic platinum (Pt). 0 PtO forms on the surface. x Layers, especially PtO2, possess insulating or semiconductor properties, physically cover these active sites and alter the surface's electronic structure, severely hindering oxygen molecule adsorption and electron transfer processes, leading to a sharp decline in ORR activity. Secondly, the formation and reduction cycle of platinum oxide accelerates the irreversible degradation of the catalyst. Under dynamic operating conditions such as fuel cell start-up, shutdown, or load changes, the electrode potential fluctuates frequently. This potential cycling causes repeated oxidation and reduction on the platinum surface, disrupting the original crystal lattice structure of platinum atoms and increasing the platinum dissolution rate. Dissolved platinum ions (PtO2)... 2+ The platinum nanoparticles migrate into the electrolyte and then redeposit elsewhere, leading to an increase in size (i.e., Ostwald ripening) and aggregation of the platinum nanoparticles. This ultimately results in a permanent loss of the electrochemically active surface area (ECSA) and an irreversible decline in catalyst performance.

[0005] Therefore, developing a simple, efficient, and rapid technique to convert oxidized platinum into a metallic state is of great significance for improving the performance and stability of the catalyst. This technique can effectively convert platinum oxide species on the surface of commercial platinum carbon-oxygen reduction electrocatalysts while maintaining the structural integrity of the catalyst and the dispersibility of platinum particles. Summary of the Invention

[0006] To address the shortcomings of easily oxidized metal nanoparticle surfaces and high oxidized platinum content on carbon-supported platinum catalyst surfaces, the present invention aims to provide a rapid conversion method for platinum oxidation state to highly metallic state in hafnium-doped platinum catalysts.

[0007] This method utilizes the strong reducing environment and chemical energy released by the vigorous decomposition of superhydrides to overcome the high reduction potential of hafnium, reducing high-valence platinum to the metallic state, while simultaneously embedding the reduced hafnium atoms into the surface or subsurface of platinum nanoparticles. This application achieves rapid and efficient removal of the oxidized state from the platinum surface through the synergistic effect of superhydrides and hafnium salts, and optimizes the d-band center of platinum using the electronic and geometric effects of hafnium, significantly improving the oxygen reduction reaction activity and stability of the catalyst.

[0008] This method is simple to operate, low in cost, and suitable for large-scale production. The catalyst produced meets the requirements of hydrogen fuel cells for efficient and stable oxygen reduction electrocatalysts, and has excellent performance and good application prospects in hydrogen fuel cells.

[0009] This application provides a rapid conversion method for platinum oxidation state to highly metallic state using a hafnium-doped platinum catalyst, comprising the following steps: S1. The carbon-supported platinum catalyst to be treated is pre-soaked in dilute acid for 10-30 minutes, and then centrifuged and washed until neutral; S2. The carbon-supported platinum catalyst pretreated in step S1 is dispersed in a high-boiling-point solvent and ultrasonically dispersed to form a uniform dispersion. S3. The dispersion is heated to 200-350°C in an oil bath under turbulent stirring and inert gas protection; the mixed powder of hafnium salt and superhydride is added to the above reaction system, and stirring and heating are stopped after 5-30 min of heat preservation; S4. After the product from step S3 has cooled, it is subjected to solid-liquid separation, washing, drying, and grinding to obtain a catalyst with highly metallic platinum on the surface. S5. The catalyst obtained in step S4 is dispersed in an ethanol solution containing benzotriazole for surface passivation treatment, followed by solid-liquid separation, washing, drying, and grinding to obtain a stable platinum catalyst with a highly metallic surface. S6. The catalyst obtained in step S5 is washed with dilute hydrochloric acid to remove boron residue, and then subjected to solid-liquid separation, washing, drying, and grinding to obtain the final finished catalyst.

[0010] Furthermore, in step S3, the amount of hafnium salt added is calculated as platinum, and the mass ratio of platinum to hafnium is (5-15):1.

[0011] Furthermore, the final product catalyst is a hafnium-doped platinum catalyst.

[0012] Further, in step S3, the mass ratio of the catalyst to be treated to the superhydride is 1 g: (0.02~2) g.

[0013] Furthermore, the hafnium salt is one of hafnium oxalate, hafnium chloride, and hafnium sulfate.

[0014] Furthermore, the superhydride is one of sodium borohydride, potassium borohydride, lithium borohydride, and triethyllithium borohydride.

[0015] Further, in step S2, the high-boiling-point solvent is one of glycerol, ethylene glycol, butanediol, and triethylene glycol; the solid-liquid ratio of the carbon-supported platinum catalyst to be treated to the high-boiling-point solvent is 1 g: (500~1000) ml.

[0016] Furthermore, in step S3, the inert gas is nitrogen or argon.

[0017] Furthermore, the carbon-supported platinum catalyst to be treated is one of Johnson Matthey HISPEC3000, HISPEC4000, HISPEC9100, Tanaka Precious Metals TEC10E40E, or TEC10E20E.

[0018] Furthermore, the dilute acid is HNO3.

[0019] The beneficial effects of this application are as follows: 1. This application disperses a purified commercial carbon-supported platinum catalyst in a high-boiling-point solvent. A large amount of superhydride containing hafnium salt is added under heating and turbulent stirring. The large amount of chemical energy released by the vigorous decomposition of the superhydride in the high-boiling-point solvent, along with the extremely strong reducing environment, is utilized to overcome the thermodynamically high reduction potential of Hf. 4+ Restore to Hf 0 The system provides the necessary energy, breaking the limitations of conventional chemical reduction. In the reducing environment created by the superhydride, hafnium ions are reduced. The platinum nanoparticles present in the system act as "trapping traps," and newly generated hafnium atoms immediately deposit and embed themselves on the platinum surface or subsurface, forming a stable Pt-Hf structure and preventing the self-aggregation of hafnium atoms. Simultaneously, the large amount of hydrogen bubbles generated by the decomposition of the superhydride acts as a vigorous stirrer in the high-boiling-point viscous solvent, facilitating the uniform migration of hafnium atoms on the platinum surface. This forms a nanoparticle catalytic layer composed of hafnium single atoms embedded on the highly metallic platinum surface, converting the oxidized platinum into a highly metallic state and maintaining its metallic stability through surface passivation.

[0020] That is, this method utilizes the energy and reducing power provided by superhydrides to overcome the high reduction potential of hafnium, and successfully introduces high-melting-point, high-oxidation-resistant hafnium atoms into the platinum surface, thereby obtaining a catalyst with unique electronic and geometric structures.

[0021] 2. In this application, the addition of hafnium alters the electronic structure of the platinum surface. Hafnium atoms are located in the platinum subsurface layer (i.e., embedded below the platinum surface). Due to the difference in atomic radius between hafnium and platinum, a strong lattice strain is generated on the platinum surface. This strain can also adjust the position of the platinum d-band center, optimizing its adsorption strength for reaction intermediates and improving intrinsic activity. The interaction between the d-electron orbitals of hafnium and platinum causes the platinum d-band center to shift downward. This weakens the adsorption energy of platinum for oxygen-containing intermediates (such as OH, O), reducing the coverage of these intermediates on the platinum active sites, thereby accelerating the rate-determining steps of ORR (usually the breaking of OO bonds or the desorption of oxygen-containing intermediates).

[0022] 3. Platinum is prone to dissolution (Pt->Pt) during fuel cell start-up, shutdown, idling, or high-potential operation. 2+ + 2e - In this application, the presence of hafnium and its oxides, such as HfO2, formed under acidic conditions can alter the local potential environment. Hafnium oxides have a lower Fermi level, attracting electrons and thus reducing the potential of catalyst particles under harsh conditions such as reverse polarity, preventing platinum from reaching a high dissolution potential. Furthermore, the hafnium oxide layer formed on the platinum surface or at the platinum / carbon interface can act as a physical barrier, hindering the dissolution and migration of platinum atoms. By reducing the platinum dissolution rate, hafnium indirectly reduces the opportunity for dissolved platinum ions to redeposit on the carbon support or migrate to other platinum particles, thereby inhibiting the aggregation and growth of platinum particles.

[0023] 4. The rapid conversion method for platinum oxidation state to highly metallic state using hafnium-doped platinum catalysts provided in this application is simple to operate, low in cost, requires minimal equipment, and is applicable to commercially available catalysts, thus showing good commercial application prospects.

[0024] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0026] Figure 1 The XRD patterns are those of the catalysts treated in Examples 1-3 and the commercial Pt / C catalyst (Johnson & Johnson HISPEC 3000).

[0027] Figure 2 The results of X-ray photoelectron spectroscopy (XPS) of the Pt 4f orbital of the catalyst treated in Example 1 and commercial Pt / C, as well as the peak fitting results, are shown.

[0028] Figure 3 The results of X-ray photoelectron spectroscopy (XPS) of the Pt 4f orbital of the catalyst treated in Example 2 and commercial Pt / C are shown, along with the peak fitting results.

[0029] Figure 4 The results of X-ray photoelectron spectroscopy (XPS) of the Pt 4f orbital of the catalyst treated in Example 3 and commercial Pt / C are shown, along with the peak fitting results.

[0030] Figure 5 The figures show the cyclic voltammetry (CV) plots of the catalysts treated in Examples 1-3 and commercial Pt / C, as well as the electrochemical specific surface area (ECSA) values ​​calculated from the hydrogen adsorption-desorption peak area; where (a) is Example 1, (b) is Example 2, (c) is Example 3, and (d) is commercial Pt / C.

[0031] Figure 6 The LSV polarization curves are for the catalysts treated in Examples 1-3 and for commercial Pt / C.

[0032] Figure 7 The results show the stability test results of the catalysts treated in Example 1, Comparative Examples 1-4, and commercial Pt / C catalysts.

[0033] Figure 8 This is a TEM image of the finished catalyst obtained in Example 1.

[0034] Figure 9 The image shows a TEM image of the finished catalyst obtained in Comparative Example 1.

[0035] Figure 10 The image shows a TEM image of the finished catalyst obtained in Comparative Example 2.

[0036] Figure 11 The image shows a TEM image of the finished catalyst obtained in Comparative Example 3.

[0037] Figure 12 LSV curves for both the example and commercial Pt / C at the initial and 20,000 potential cycles.

[0038] Figure 13 The polarization curves are for fuel cells with the catalyst treated in Example 2 and a commercial Pt / C catalyst as the cathode. Detailed Implementation

[0039] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0041] This application provides a rapid conversion method for platinum oxidation state to highly metallic state using a hafnium-doped platinum catalyst, comprising the following steps: S1. The carbon-supported platinum catalyst to be treated is pre-soaked in dilute acid for 10-30 minutes, and then centrifuged and washed until neutral; The carbon-supported platinum catalyst to be treated is one of Johnson Matthey HISPEC3000, HISPEC4000, HISPEC9100, Tanaka Precious Metals TEC10E40E, or TEC10E20E.

[0042] S2. The carbon-supported platinum catalyst pretreated in step S1 is dispersed in a high-boiling-point solvent and ultrasonically dispersed to form a uniform dispersion. The high-boiling-point solvent is one of glycerol, ethylene glycol, butanediol, and triethylene glycol, and the solid-liquid ratio of the carbon-supported platinum catalyst to be treated to the high-boiling-point solvent is 1 g: (500~1000) ml.

[0043] S3. The dispersion is heated to 200-350°C in an oil bath under turbulent stirring and inert gas protection; the mixed powder of hafnium salt and superhydride is added to the above reaction system, and stirring and heating are stopped after 5-30 min of heat preservation; The mass ratio of the catalyst to be treated to the superhydride is 1 g: (0.02~2) g.

[0044] The amount of hafnium salt added is calculated based on platinum, and the mass ratio of platinum to hafnium is (5-15):1.

[0045] Among them, hafnium salt is one of hafnium oxalate, hafnium chloride, and hafnium sulfate.

[0046] The superhydride is one of sodium borohydride, potassium borohydride, lithium borohydride, and triethyllithium borohydride.

[0047] In step S3, the inert gas is nitrogen or argon.

[0048] S4. After the product from step S3 has cooled, it is subjected to solid-liquid separation, washing, drying, and grinding to obtain a catalyst with highly metallic platinum on the surface. S5. The catalyst obtained in step S4 is dispersed in an ethanol solution containing benzotriazole for surface passivation treatment, followed by solid-liquid separation, washing, drying, and grinding to obtain a stable platinum catalyst with a highly metallic surface. S6. The catalyst obtained in step S5 is washed with dilute hydrochloric acid to remove boron residue, and then subjected to solid-liquid separation, washing, drying, and grinding to obtain the final finished catalyst.

[0049] The final product catalyst is a hafnium-doped platinum catalyst.

[0050] The catalyst obtained by the rapid conversion method of platinum oxidation state to highly metallic state of the hafnium-doped platinum catalyst can be applied to the oxygen reduction reaction of hydrogen fuel cells.

[0051] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0052] Example 1 This embodiment provides a rapid conversion method for platinum oxidation state to highly metallic state using a hafnium-doped platinum catalyst, comprising the following steps: S1. Add 25 mg of Johnson Matthey HISPEC 3000 catalyst to 0.1 M HNO3, stir for 30 minutes, filter and wash until neutral, vacuum dry at 60°C for 6 hours and grind into powder.

[0053] S2. Add the above powder to 20 mL of ethylene glycol and ultrasonically disperse for 30 min to obtain a uniform dispersion.

[0054] S3. The above dispersion was heated to 200°C in an oil bath while maintaining a stirring speed of 800 rpm and a continuous purging of argon gas. A reflux condenser was used to prevent solvent evaporation. Subsequently, a mixture of 5 mg of sodium borohydride and 1.45 mg of HfCl4 powder was rapidly added to the reaction system. The solution immediately produced a large number of bubbles, indicating that the sodium borohydride was undergoing vigorous decomposition. After maintaining the temperature for 10 min, the heating was turned off, and the container was removed from the oil bath and cooled.

[0055] S4. After the mixed solution in the oil bath device has cooled, it is filtered and washed with deionized water and ethanol. Then, it is dried and ground in an oven at 60°C to obtain a black powder.

[0056] S5. The above black powder was dispersed in an ethanol solution containing 1% benzotriazole (BTA) and stirred for 30 minutes. It was then filtered and washed with deionized water. After drying in a vacuum oven, it was ground to obtain a stable platinum catalyst with a highly metallic surface.

[0057] S6. The catalyst obtained in step S5 is washed three times with 0.1M HCl solution to remove boron residue, filtered and washed with deionized water; then dried in a vacuum oven, and ground to obtain the final product catalyst.

[0058] In Example 1, the mass ratio of platinum to hafnium was 6.19:1.

[0059] Example 2 The main difference from Example 1 is: In step S2, the solvent is triethylene glycol; In step S3, the heating temperature is 250℃, the stirring speed is 600rpm, the added mixed powder is 15 mg potassium borohydride and 1.6 mg HfCl4, and the temperature is maintained for 15 min.

[0060] The rest is largely the same as in Example 1, and will not be repeated here.

[0061] In Example 2, the mass ratio of platinum to hafnium was 5.6:1.

[0062] Example 3 The main difference from Example 1 is: In step S2, the solvent is triethylene glycol; In step S3, the heating temperature is 220℃, the stirring speed is 600rpm, and the gas introduced is nitrogen; the added mixed powder is 8.8 mg potassium borohydride and 1 mg HfCl4, and the temperature is maintained for 20 min.

[0063] In Example 3, the mass ratio of platinum to hafnium was 9:1.

[0064] Example 4 The main difference from Example 1 is: In step S2, the solvent is triethylene glycol; In step S3, the heating temperature is 220℃, the stirring speed is 600rpm, and the gas introduced is nitrogen; the added mixed powder is 8.8 mg potassium borohydride and 0.6 mg HfCl4, and the temperature is maintained for 20 min.

[0065] In Example 4, the mass ratio of platinum to hafnium was 15:1.

[0066] Comparative Example 1 The main difference between Comparative Example 1 and Example 1 is that in step S3, only 5 mg of sodium borohydride was added, and HfCl4 was not added. The rest is largely the same as in Example 1 and will not be repeated here.

[0067] Comparative Example 2 The main difference between Comparative Example 2 and Example 1 is that the hafnium salt is replaced with a niobium salt; specifically, in step S3, the added mixed powder is replaced by 5 mg of sodium borohydride and 1.45 mg of HfCl4 with 5 mg of sodium borohydride and 1.22 mg of NbCl5. The rest is largely the same as in Example 1 and will not be repeated here.

[0068] Comparative Example 3 The main difference between Comparative Example 3 and Example 1 is that in step S3, the added mixed powder is 5 mg of sodium borohydride and 2.25 mg of HfCl4; that is, the mass ratio of Pt:Hf is 4:1. Everything else is largely the same as in Example 1 and will not be repeated here.

[0069] Comparative Example 4 The main difference between Comparative Example 4 and Example 1 is that in step S1, the amount of the carbon-supported platinum catalyst to be treated is adjusted to 65 mg; that is, the mass ratio Pt:Hf is 16.1:1. Everything else is largely the same as in Example 1 and will not be repeated here.

[0070] Figure 1 The images show the XRD patterns of the catalysts obtained in Examples 1-3 and the commercial Pt / C catalyst.

[0071] It can be seen that the diffraction peaks of Pt(111), Pt(200), Pt(220) and Pt(311) of the catalysts obtained by the method of this application after treatment are not significantly different from the diffraction peaks of platinum, and the peak positions and half-peak widths are not significantly different from those of the Pt / C catalyst before treatment, which confirms that the conversion method of this application does not change the structure of the catalyst.

[0072] Figures 2 to 4 The images show the Pt 4f XPS spectra from Examples 1-3, and the Pt... 0 Pt 2+ Pt 4+ The three species were calibrated with a binding energy of 285 eV for C 1s and peak fitting was performed. The relative contents of the different platinum species are recorded in Table 1.

[0073] Table 1 As can be seen, after processing by the transformation method of this application, Pt 0 The relative content of Pt increased, while the relative content of Pt increased. x+The oxidation state of the species decreased. This indicates that the processing method of this application successfully transformed the oxidized platinum into highly active and stable metallic platinum.

[0074] Figure 5 The table shows a comparison of rotating disk CV (chemical velocity) in acidic media between the catalysts obtained in Examples 1-3 and the commercial Pt / C catalyst. The electrolyte solution was 0.1 M HClO4 saturated with N2; the scan rate was 50 mV / s; and the scan voltage range was -0.25 ~ 0.8 V. The ECSA (electrochemically active area) calculated from the hydrogen adsorption / desorption peak area is recorded in Table 2.

[0075] Table 2 Figure 6 This is a comparison of the rotating disk polarization curves in acidic media of the catalysts obtained in Examples 1-3 and the commercial Pt / C catalyst. The electrolyte solution was 0.1 M HClO4 saturated with O2; the scan rate was 10 mV / s; the scan voltage range was -0.25 ~ 0.8 V; and the rotation speed was 1600 rpm.

[0076] As can be seen from the polarization curves after iR compensation, the half-wave potential of the catalyst treated by this method in Example 1 is 0.945V, which exceeds the untreated Pt / C catalyst by 50mV (0.895V). In addition, the half-wave potentials of Examples 2 and 3 also exceed the untreated Pt / C catalyst by 46mV and 35mV, respectively.

[0077] Figure 7 This is a comparison of the rotating disk polarization curves of the catalysts obtained in Example 1 and Comparative Examples 1-4 in acidic media. The electrolyte solution was 0.1 M HClO4 saturated with O2; the scan rate was 10 mV / s; the scan voltage range was -0.25 ~ 0.8 V; and the rotation speed was 1600 rpm.

[0078] Figure 8-11 The images shown are TEM images of the finished catalysts obtained in Example 1 and Comparative Examples 1-3, respectively.

[0079] The polarization curves after iR compensation show that the half-wave potentials of Comparative Examples 1-4 are 0.902V, 0.911V, 0.875V, and 0.907V, respectively, all of which are less than the half-wave potential of 0.945V in Example 1. Among them, in Comparative Example 3, the performance was actually worse than that of the commercial Pt / C catalyst due to the excessive addition of hafnium salt.

[0080] Among them, the half-wave potential of Comparative Example 1 was 0.902V, which is an improvement over commercial Pt / C, but much lower than that of Example 1, indicating that without Hf anchoring, the reduced Pt is prone to agglomeration, and the performance improvement is limited.

[0081] Specifically, due to the absence of hafnium salt, under turbulent stirring and localized high temperatures, the highly activated platinum atoms are prone to migration and aggregation without the anchoring of external hafnium atoms, leading to the growth of platinum nanoparticle size (Ostwald ripening or aggregation), thereby reducing the electrochemical active area. At the same time, it is easy to cause damage to the catalyst carbon support. Excessive strong reducing environment and high-energy bubble impact may cause excessive erosion or pore collapse of the surface structure of the carbon support, affecting electron conduction and mass transfer.

[0082] The addition of hafnium salts transforms intense chemical energy into precise atomic-level structural control through a chain reaction of "energy dissipation-atomic deposition-interface modification".

[0083] In Example 1, under the enormous energy provided by the superhydride and the strong reducing atmosphere, Hf is reduced and rapidly forms a stable chemical bond with Pt (Pt-Hf). This process not only dissipates excess chemical energy and prevents Pt aggregation, but also directly constructs an active structure.

[0084] The oxygen reduction reaction (ORR) is extremely sensitive to the geometry of the catalyst. The relatively large atomic radius of Hf can generate optimal compressive strain on the Pt surface, compressing the Pt-Pt bond length and maximizing its catalytic activity. The atomic radius of Nb is similar to that of Pt, and it cannot produce this crucial geometric modification effect.

[0085] In Comparative Example 2, niobium salts were used. Due to the weak Nb-Pt interaction, even if Nb is reduced, it is difficult to stably "embed" on the Pt surface. It may be more prone to self-aggregation, or the formed Pt-Nb interface may be reconstructed or separated under severe turbulence and thermal shock. As a result, the energy of the superhydride fails to be converted into a stable and beneficial structure, and may instead lead to the ineffective aggregation of Pt or the waste of Nb.

[0086] In Comparative Example 3, the excess hafnium salt led to the reduction of a large amount of hafnium by the superhydride. Due to the excessively high concentration of hafnium atoms, they could no longer maintain a single-atom dispersed state. Hafnium atoms agglomerated on the platinum surface, forming a capping layer or multi-atom-thick clusters. The platinum surface is the site of the catalytic reaction; the excess hafnium physically covered the platinum atoms, reducing the number of active sites at the three-phase interface available for oxygen adsorption and reaction. The platinum surface, originally intended for catalysis, became a "hafnium surface," and pure hafnium (or its oxides) had almost no catalytic activity for the oxygen reduction reaction (ORR), resulting in a sharp decline in mass activity.

[0087] In Comparative Example 4, due to the insufficient addition of hafnium salt, a Pt-Hf active interface with adequate coverage could not be formed, resulting in the electronic structure modulation, geometric strain, and stability enhancement of platinum failing to reach the threshold for inducing performance transitions. Because there were too few hafnium atoms, most platinum atoms were too far from the nearest hafnium atom to experience this electronic modulation. From the perspective of the average electronic structure of the entire nanoparticle, it still closely resembles pure platinum.

[0088] The above comparison fully demonstrates the necessity of selecting hafnium salts and controlling their dosage within the range of (5~15):1 in this application.

[0089] Figure 12 The polarization curves of the catalyst obtained in Example 2 are compared before and after 20,000 potential cycles at a scan rate of 100 mA / s under conditions of 0.6 V to 0.95 V (vs. RHE). After 20,000 potential cycles, the half-wave potential of the catalyst in Example 2 decreased by 31 mV, while the untreated Pt / C, as a comparison, decreased by 45 mV under the same conditions. This demonstrates the excellent stability of the catalyst after treatment using this process.

[0090] Figure 13 These are the polarization curves and power densities of Example 2 and the untreated Pt / C catalyst in a hydrogen-air fuel cell. The test conditions were: cathode platinum loading of 0.3 mg / cm³. 2 The platinum loading at the anode is 0.2 mg / cm³. 2 Steady-state polarization curves collected under 100% humidification and 200 kPa back pressure.

[0091] It can be seen that the platinum mass ratio activity normalized to current at 0.9V when the catalyst processed by this process is used as the cathode of a fuel cell is 0.47 A mg. Pt -1 (Calculated based on the sum of platinum loadings at the anode and cathode), is the untreated Pt / C catalyst (0.17 A mg). Pt -1 It is 2.7 times that of other products, demonstrating good application potential.

[0092] In summary, this application successfully transformed oxidized platinum on the surface of a commercial Pt / C catalyst into a highly metallic platinum state through the synergistic effect of superhydrides and hafnium salts. Furthermore, the electronic and geometric structures of the catalyst were optimized using the hafnium embedding effect, thereby significantly improving the catalyst's ORR activity and stability. This method is simple to operate, low in cost, and highly effective, providing a new and efficient approach for the development of high-performance fuel cell catalysts.

[0093] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A rapid conversion method for platinum oxidation state to highly metallic state using a hafnium-doped platinum catalyst, characterized in that, Includes the following steps: S1. The carbon-supported platinum catalyst to be treated is pre-soaked in dilute acid for 10-30 minutes, and then centrifuged and washed until neutral; S2. The carbon-supported platinum catalyst pretreated in step S1 is dispersed in a high-boiling-point solvent and ultrasonically dispersed to form a uniform dispersion. S3. The dispersion is heated to 200-350°C in an oil bath under turbulent stirring and inert gas protection; the mixed powder of hafnium salt and superhydride is added to the above reaction system, and stirring and heating are stopped after 5-30 min of heat preservation; S4. After the product from step S3 has cooled, it is subjected to solid-liquid separation, washing, drying, and grinding to obtain a catalyst with highly metallic platinum on the surface. S5. The catalyst obtained in step S4 is dispersed in an ethanol solution containing benzotriazole for surface passivation treatment, followed by solid-liquid separation, washing, drying, and grinding to obtain a stable platinum catalyst with a highly metallic surface. S6. The catalyst obtained in step S5 is washed with dilute hydrochloric acid to remove boron residue, and then subjected to solid-liquid separation, washing, drying, and grinding to obtain the final finished catalyst.

2. The rapid conversion method for platinum oxidation state to highly metallic state using hafnium-doped platinum catalyst according to claim 1, characterized in that, In step S3, the amount of hafnium salt added is calculated as platinum, and the mass ratio of platinum to hafnium is (5-15):

1.

3. The rapid conversion method for platinum oxidation state to highly metallic state using hafnium-doped platinum catalyst according to claim 1, characterized in that, The final product catalyst is a hafnium-doped platinum catalyst.

4. The rapid conversion method for platinum oxidation state to highly metallic state using hafnium-doped platinum catalyst according to claim 1, characterized in that, In step S3, the mass ratio of the catalyst to be treated to the superhydride is 1 g: (0.02~2) g.

5. The rapid conversion method for platinum oxidation state to highly metallic state using hafnium-doped platinum catalyst according to claim 1, characterized in that, The hafnium salt is one of hafnium oxalate, hafnium chloride, and hafnium sulfate.

6. The rapid conversion method for platinum oxidation state to highly metallic state using hafnium-doped platinum catalyst according to claim 1, characterized in that, The superhydride is one of sodium borohydride, potassium borohydride, lithium borohydride, and triethyllithium borohydride.

7. The rapid conversion method for platinum oxidation state to highly metallic state using hafnium-doped platinum catalyst according to claim 1, characterized in that, In step S2, the high-boiling-point solvent is one of glycerol, ethylene glycol, butanediol, and triethylene glycol; the solid-liquid ratio of the carbon-supported platinum catalyst to be treated to the high-boiling-point solvent is 1 g: (500~1000) ml.

8. The rapid conversion method for platinum oxidation state to highly metallic state using hafnium-doped platinum catalyst according to claim 1, characterized in that, In step S3, the inert gas is nitrogen or argon.

9. The rapid conversion method for platinum oxidation state to highly metallic state using hafnium-doped platinum catalyst according to claim 1, characterized in that, The carbon-supported platinum catalyst to be treated is one of Johnson Matthey HISPEC3000, HISPEC4000, HISPEC9100, Tanaka Precious Metals TEC10E40E, or TEC10E20E.

10. The rapid conversion method for platinum oxidation state to highly metallic state in hafnium-doped platinum catalyst according to claim 1, characterized in that, The dilute acid is HNO3.

Images