Pt-ultra-short carbon nanotube composite catalyst powder, preparation method thereof and fuel cell membrane electrode

Abstract

This invention discloses a Pt-ultrashort carbon nanotube composite catalyst powder, its preparation method, and a fuel cell membrane electrode assembly, belonging to the field of fuel cell technology. The composite catalyst powder comprises Pt or Pt alloy nanoparticles, and multi-walled carbon nanotubes formed by in-situ induced growth of the Pt or Pt alloy nanoparticles, wherein the average length of the multi-walled carbon nanotubes is 50-200 nm. The composite catalyst powder can be mixed with proton-conducting ionomers and a dispersion medium to form a catalyst slurry, which can be used to prepare fuel cell catalyst layers and membrane electrode assemblies. By allowing Pt or Pt alloy nanoparticles to exist prior to carbon nanotubes and inducing in-situ growth of carbon nanotubes, this invention improves the bonding stability between Pt particles and the carbon support, the dispersibility of the catalyst slurry, and the discharge performance of the membrane electrode assembly in high current density regions.

Description

Technical Field

[0001] This invention belongs to the field of fuel cell technology, specifically relating to a Pt-ultra-short carbon nanotube composite catalyst powder for proton exchange membrane fuel cells (PEMFC), its preparation method, a catalyst slurry containing the composite catalyst powder, a membrane electrode assembly, and a proton exchange membrane fuel cell. Background Technology

[0002] Proton exchange membrane fuel cells (PEMFCs) are an important clean energy technology due to their high energy conversion efficiency, zero emissions, and rapid start-up at low temperatures. The membrane electrode assembly (MEA) is the core component of a fuel cell, and its performance directly determines the cell's output power, lifespan, and cost.

[0003] Currently, commercial MEAs typically use carbon black (such as Vulcan XC-72) supported on platinum (Pt) or platinum alloy nanoparticles as catalysts. However, this system suffers from the following problems: low platinum utilization, as carbon black has limited conductivity and irregular pore structure, with some platinum particles located in "dead zones," failing to form an effective three-phase reaction interface; high mass transfer resistance, as the microporous structure formed by traditional carbon black support stacking is complex, and liquid water easily clogs the pores during high current density operation of the battery, making it difficult for reactant gases (especially oxygen) to transport to active sites, causing severe concentration polarization; insufficient stability, under fuel cell start-up, shutdown, and load variations, potential cycling easily leads to carbon black support corrosion, as well as the migration, aggregation, and loss of platinum nanoparticles, causing irreversible degradation of catalyst performance; and carbon black support usually only serves as a physical support, contributing little to the improvement of the intrinsic activity of the catalyst.

[0004] Carbon nanotubes (CNTs) are considered ideal alternative catalyst supports due to their high conductivity, high specific surface area, excellent chemical stability, and unique one-dimensional tubular structure. Their tubular structure facilitates the formation of through-holes, promoting mass transfer; their high conductivity facilitates rapid electron transport. However, current techniques for directly loading platinum onto commercial carbon nanotubes still have significant drawbacks: uneven platinum particle dispersion and uncontrollable size; the inert surface of carbon nanotubes necessitates strong acid oxidation to introduce defects or functional groups before platinum can be loaded, a process that disrupts the intrinsic structure and conductivity of CNTs; high interfacial contact resistance, with physical adsorption being the primary mode of interaction between physically mixed or post-loaded platinum particles and CNTs, resulting in weak interfacial bonding; and excessively long carbon nanotubes, typically in the micrometer or even millimeter range, which easily entangle and aggregate in the catalyst layer, blocking pores and hindering uniform coating of ionomers and proton transport, thus reducing the effective utilization rate of the catalyst layer.

[0005] Therefore, developing a composite catalyst material that can achieve high dispersion, high stability, and high utilization of platinum catalysts, while also possessing excellent mass transfer and conductivity capabilities, is key to breaking through the current performance and cost bottlenecks of fuel cells. Summary of the Invention

[0006] The technical problem this invention aims to solve is to address the issues of low platinum utilization, high mass transfer resistance, poor stability, and weak interfacial bonding between platinum and the support in existing fuel cell membrane electrode catalysts. This invention provides a novel Pt-ultrashort carbon nanotube composite catalyst powder and its preparation method. This composite catalyst powder utilizes an in-situ growth strategy to achieve a relatively stable bond between platinum nanoparticles and ultrashort carbon nanotubes, which is beneficial for constructing a conductive network and mass transfer channels.

[0007] To address the aforementioned technical problems, this invention provides a Pt-ultrashort carbon nanotube composite catalyst powder, comprising Pt or Pt alloy nanoparticles and multi-walled carbon nanotubes bonded to the Pt or Pt alloy nanoparticles. The multi-walled carbon nanotubes are carbon nanotubes induced to grow in situ by the Pt or Pt alloy nanoparticles, and the average length of the multi-walled carbon nanotubes is 50-200 nm. The Pt-ultrashort carbon nanotube composite catalyst powder is a powder capable of being mixed with proton-conducting ionomers and a dispersion medium to form a catalyst slurry.

[0008] In some embodiments, at least a portion of the Pt or Pt alloy nanoparticles are located at the root, end, or wall of the multi-walled carbon nanotube.

[0009] In some embodiments, the average particle size of the Pt or Pt alloy nanoparticles is 3-5 nm.

[0010] In some embodiments, the mass of the Pt or Pt alloy nanoparticles accounts for 45%-55% of the total mass of the Pt-ultra-short carbon nanotube composite catalyst powder, preferably 48%-52%, based on the total mass of the Pt or Pt alloy nanoparticles.

[0011] In some embodiments, the average length of the multi-walled carbon nanotubes is 80-150 nm.

[0012] In some embodiments, the Pt alloy nanoparticles include PtAu alloy nanoparticles, or alloy nanoparticles formed by Pt and at least one metal selected from Co, Ni, Fe, and Cu.

[0013] This invention also provides a method for preparing the above-mentioned Pt-ultrashort carbon nanotube composite catalyst powder, comprising the following steps: Provides a removable substrate; By loading Pt or Pt alloy nanoparticles onto the removable substrate, a substrate loaded with Pt or Pt alloy nanoparticles is obtained. The substrate loaded with Pt or Pt alloy nanoparticles is placed in a carbon-containing atmosphere, so that the carbon source is pyrolyzed at the Pt or Pt alloy nanoparticles and multi-walled carbon nanotubes are grown in situ. The average length of the multi-walled carbon nanotubes is controlled to be 50-200 nm. The removable substrate is removed to obtain the Pt-ultra-short carbon nanotube composite catalyst powder.

[0014] In some embodiments, the Pt or Pt alloy nanoparticles are prepared by a polyol reduction method. Exemplarily, a platinum precursor (such as chloroplatinic acid) is dissolved in an organic solvent (such as ethylene glycol), a surfactant (such as polyvinylpyrrolidone, PVP) and an alkaline solution (such as NaOH) are added, and the mixture is heated under reflux in a protective atmosphere to obtain a Pt nanoparticle sol.

[0015] In some embodiments, the removable substrate includes alumina nanoparticles, porous silicon wafers, MgO, or SiO2. Preferably, the removable substrate is γ-Al2O3 powder.

[0016] In some embodiments, the in-situ growth of multi-walled carbon nanotubes includes: pretreatment at 500-700°C in a reducing atmosphere (such as H2 / Ar), followed by introduction of a carbon source and reaction at 650-800°C for 5-30 min. The carbon source may be acetylene, ethylene, ethanol vapor, methane, or propylene.

[0017] In some embodiments, the step of removing the removable substrate includes treating the substrate loaded with multi-walled carbon nanotubes with an acid or alkali solution selected according to the material of the removable substrate, the acid or alkali solution including hydrochloric acid, nitric acid, or sodium hydroxide solution.

[0018] This invention also provides a fuel cell catalyst slurry, comprising the above-mentioned Pt-ultra-short carbon nanotube composite catalyst powder, a proton-conducting ionomer, and a dispersion medium. The proton-conducting ionomer may be a perfluorosulfonic acid resin, and the dispersion medium may include an alcohol solvent (such as isopropanol, n-propanol), water, or a water-alcohol mixture. The catalyst slurry can be formed by ultrasonic dispersion and stirring.

[0019] This invention also provides a fuel cell membrane electrode assembly, comprising a proton exchange membrane, an anode catalyst layer disposed on one side of the proton exchange membrane, and a cathode catalyst layer disposed on the other side of the proton exchange membrane. At least one of the anode and cathode catalyst layers comprises the aforementioned Pt-ultrashort carbon nanotube composite catalyst powder, or is formed from the aforementioned fuel cell catalyst slurry through spraying, transfer printing, or direct coating. The catalyst slurry can be coated on the surface of the proton exchange membrane or on the surface of the gas diffusion layer, and then assembled with the proton exchange membrane to form the membrane electrode assembly. The membrane electrode assembly can be obtained through hot pressing.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: The size and loading of platinum particles are controllable: By pre-preparing monodisperse platinum sol, the initial size of platinum particles can be ensured to be controllable. By adjusting the precursor concentration, the mass fraction of platinum in the final composite catalyst can be directly controlled, and the process repeatability is good.

[0021] It facilitates the formation of a more stable interfacial bond: the in-situ growth of carbon nanotubes using platinum particles as "seeds" promotes the formation of a more stable bonding structure between the platinum particles and carbon nanotubes. This structure helps to inhibit the migration, aggregation, and loss of platinum particles during electrochemical cycling, thereby improving the stability of the catalyst.

[0022] Constructing an ultrashort CNT conductive network: The 100-nanometer-long CNTs help avoid the entanglement problem of long CNTs, allowing them to be uniformly dispersed in the catalyst layer and interconnected to form a conductive network and porous structure. Short, straight channels help reduce mass transfer resistance between gas and products, and are beneficial for performance at high current densities.

[0023] It is beneficial to improve the utilization rate of platinum: the smaller platinum particle size, higher dispersion, good electronic conductivity with the support, and the abundant porosity brought by the composite structure are all conducive to improving the utilization rate of platinum atoms.

[0024] The process is scalable: the method can flexibly control the length and graphitization degree of CNTs by adjusting CVD parameters (temperature, time, carbon source), providing room for adjustment to optimize the catalyst layer structure. Attached Figure Description

[0025] The above features and advantages of the present invention will become clearer and more readily understood from the following description of exemplary embodiments thereof in conjunction with the accompanying drawings.

[0026] Figure 1 This is a transmission electron microscope (TEM) image of the Pt-ultrashort carbon nanotube composite catalyst powder obtained in Example 1 of the present invention.

[0027] Figure 2This is a TEM schematic diagram of the conventional Pt / C catalyst in Comparative Example 1.

[0028] Figure 3 The graph shows a comparison of the polarization curves of the membrane electrodes obtained in Examples 1 to 3 and Comparative Example 1. Detailed Implementation

[0029] The present invention will be further described below with reference to the accompanying drawings. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. For those skilled in the art, any equivalent substitutions or modifications made without departing from the concept of the present invention should fall within the scope of protection of the present invention.

[0030] Example 1

[0031] S1. Preparation of Platinum Sol: Weigh 100 mg of chloroplatinic acid (H₂PtCl₆·6H₂O) and dissolve it in 100 mL of ethylene glycol, then sonicate to dissolve. Add 100 mg of polyvinylpyrrolidone (PVP) with a molecular weight of 40,000 as a stabilizer, and stir magnetically for 30 minutes. Then, add 10 mL of 0.5 M NaOH ethylene glycol solution dropwise, and heat the mixture to 160 °C under argon protection, then reflux for 3 hours. The solution color changes from yellow to black, yielding a platinum nanoparticle sol with a particle size of approximately 3.5 nm. Remove excess PVP by centrifugation and washing (ethanol / acetone mixture), then redisperse in 50 mL of ethanol for later use.

[0032] S2. Loading and Drying: Weigh 2g of γ-Al2O3 powder with an average particle size of 50nm (specific surface area ~150m²). 2 The platinum particles were added to the above platinum sol and stirred at room temperature for 12 hours to allow for full adsorption. Then, the ethanol was removed by rotary evaporation at 80°C to obtain platinum-loaded Al₂O₃ powder. The Pt loading in the obtained Pt-loaded Al₂O₃ powder can be adjusted according to the Pt content in the target composite catalyst; in this example, it is approximately 5 wt%.

[0033] S3. In-situ growth of carbon nanotubes: The above powder was placed in a quartz boat and then placed in a tube CVD furnace. Under an atmosphere of 200 sccm argon and 100 sccm hydrogen, the temperature was increased to 600℃ at a rate of 10℃ / min and held for 30 minutes to reduce platinum and activate the surface. Subsequently, the temperature was increased to 720℃, and a mixture of the carbon source gas acetylene (C2H2, 20 sccm) and the carrier gases argon (200 sccm) and hydrogen (50 sccm) was introduced into the reaction chamber for 10 minutes. After the reaction was completed, the acetylene was turned off, and the mixture was cooled to room temperature under argon protection.

[0034] S4. Separation and Purification of the Composite Catalyst: The sample was taken out and placed in a 6M hydrochloric acid solution, and stirred in a 60℃ water bath for 24 hours to dissolve the Al2O3 substrate. The mixture was centrifuged, washed with deionized water until neutral, and finally dried in a vacuum drying oven at 80℃ for 12 hours to obtain a black platinum-ultrashort carbon nanotube composite catalyst powder. ICP-AES testing showed that the platinum content was 49.8% by mass.

[0035] To confirm that the growth of carbon nanotubes was mainly caused by the catalysis of Pt nanoparticles, the obtained composite catalyst powder was analyzed by inductively coupled plasma mass spectrometry. The contents of conventional carbon nanotube catalytic metal impurities such as Fe, Co, and Ni were not detected or were below the instrument detection limit.

[0036] S5. Catalyst Slurry Preparation and Membrane Electrode Preparation: Weigh 50 mg of the above-mentioned composite catalyst powder, and mix it with 0.95 g of 5 wt% perfluorosulfonic acid resin (Nafion) solution (solvent is a water / alcohol mixture) (calculated based on the ionomer to carbon mass ratio I / C = 0.8) and 3 mL of isopropanol. Sonicate in an ice-water bath for 2 hours, then magnetically stir for 6 hours to form a homogeneous slurry. Use an ultrasonic sprayer to uniformly spray the slurry onto both sides of a 25 μm thick reinforced proton exchange membrane (such as Gore-SELECT®), with an anode platinum loading of 0.1 mg / cm². 2 The cathode platinum loading is 0.2 mg / cm³. 2 The coated film was dried at 80°C and then hot-pressed at 135°C and 1MPa for 90 seconds to obtain membrane electrode A.

[0037] Example 2

[0038] The process was essentially the same as in Example 1, except for the CVD growth parameters in step S3: the carbon source was changed to ethylene (C2H4, 30 sccm), the growth temperature was adjusted to 680℃, and the growth time was extended to 15 minutes. The aim was to obtain CNTs with a slightly higher degree of graphitization and slightly longer length. The final measured platinum content was 50.5%, and membrane electrode B was prepared using the same process.

[0039] Example 3

[0040] The process is essentially the same as in Example 1, except that in step S1, a small amount of chloroauric acid (H2AuCl4) is introduced during the preparation of the platinum sol, resulting in PtAu alloy nanoparticles (Au atoms accounting for 10%). The growth temperature in step S3 is adjusted to 700℃. The final product is a platinum alloy-ultra-short carbon nanotube composite catalyst with a total platinum mass content of 51.2% (of which Pt accounts for 46.1%). The membrane electrode C is prepared using the same process.

[0041] Comparative Example 1 (Conventional Pt / C catalyst) Purchase a commercially available 50wt% Pt / C catalyst (Johnson Matthey). Weigh 250mg of this catalyst (containing 125mg Pt), mix it with 0.4g of 5wt% Nafion solution (I / C = 0.8) and 3mL of isopropanol, and prepare a slurry by ultrasonication and stirring as in the example. Using the exact same spraying and hot-pressing process as in the example, prepare membrane electrode D on the same proton exchange membrane. The platinum loading at the anode and cathode remains consistent with the example (0.1mg / cm³). 2 / 0.2mg / cm 2 ).

[0042] Comparative Example 2 (Commercial CNT Post-Load Pt Comparative Example) Purchase commercially available multi-walled carbon nanotubes (purity >95%, length 1-5 μm, diameter 10-30 nm). Weigh 1 g of the CNTs and place them in 6 M nitric acid solution, reflux at 80 °C for 4 hours to introduce oxygen-containing functional groups on the surface. After cooling, centrifuge and wash repeatedly with deionized water until the filtrate is neutral. Then, vacuum dry at 80 °C for 12 hours to obtain acid-treated CNTs.

[0043] 500 mg of the acid-treated CNTs were dispersed in 100 mL of ethylene glycol and sonicated for 1 hour. An ethylene glycol solution containing chloroplatinic acid (H₂PtCl₆·6H₂O) equivalent to the target Pt loading (50 wt%) was added, and the mixture was magnetically stirred for 30 minutes. The pH was adjusted to approximately 11 by dropwise addition of 0.5 M NaOH ethylene glycol solution. The mixture was heated to 160 °C under argon protection and refluxed for 3 hours. After cooling, the mixture was centrifuged, washed alternately with deionized water and ethanol, and finally dried under vacuum at 80 °C for 12 hours to obtain a commercially available CNT-supported Pt catalyst powder (denoted as catalyst E).

[0044] Weigh 50 mg of the above catalyst powder and mix it with 0.95 g of 5 wt% Nafion perfluorosulfonic acid resin solution (calculated based on an ionomer to carbon mass ratio of I / C = 0.8) and 3 mL of isopropanol. Sonicate the mixture in an ice-water bath for 2 hours, then magnetically stir for 6 hours to form a homogeneous slurry. Using an ultrasonic sprayer, uniformly spray the slurry onto both sides of a 25 μm thick reinforced proton exchange membrane, maintaining the same platinum loading at the anode and cathode as in Example 1. Dry the sprayed membrane at 80 °C, then hot-press it at 135 °C and 1 MPa for 90 seconds to obtain membrane electrode E.

[0045] The membrane electrode E and the gas diffusion layer are assembled to form an effective area of ​​5 cm². 2 The single cell was tested for performance under the exact same test conditions as in Example 1.

[0046] Characterization and performance testing Material characterization: The composite catalyst obtained in Example 1 was characterized by TEM. Figure 1 As can be seen, a large number of short, straight, multi-walled carbon nanotubes are present in the sample; according to multi-field random statistics, the length of the multi-walled carbon nanotubes is approximately 150 nm. High electronic contrast nanoparticles are visible in the tube walls and end regions of the carbon nanotubes; according to statistics of hundreds of particles in multiple regions, the average particle size of the nanoparticles is in the range of 3 nm to 5 nm, and the particle size distribution is relatively narrow.

[0047] Comparative Example 1: TEM morphology of commercial Pt / C catalyst as shown in Figure 1. Figure 2 As shown, platinum particles are loaded onto the surface of a carbon black carrier. Statistical analysis using the same method revealed that the platinum particles in Comparative Example 1 have a particle size distribution ranging from 2 nm to 6 nm, and exhibit some particle agglomeration.

[0048] The composite catalyst obtained in Example 2 was characterized by TEM. Multi-field random sampling revealed a large number of short, straight carbon nanotubes in the sample. Statistical analysis of hundreds of carbon nanotubes across multiple regions showed that the average length of the carbon nanotubes was approximately 130 nm, with the overall length falling within the range of 80 nm to 150 nm.

[0049] Elemental content testing: ICP-AES analysis showed that the Pt mass percentage in Example 1 was 49.8 wt%; the Pt mass percentage in Example 2 was 50.5 wt%; and the total precious metal content in Example 3 was 51.2 wt%, of which Pt content was 46.1 wt% and Au content was 5.1 wt%, with Au atoms accounting for 10.02% of the total precious metal atoms. The measured Pt content in Comparative Example 1 (commercial Pt / C) was 49.6 wt%; and the measured Pt content in Comparative Example 2 (catalyst E) was 48.9 wt%.

[0050] Specific surface area and pore structure testing: According to BET testing, the BET specific surface area of ​​the catalyst powder in Example 1 is 138 m². 2 / g, with an average pore size of 12.6 nm; Comparative Example 1: Commercial Pt / C has a BET specific surface area of ​​105 m² / g. 2 / g, with an average pore size of 22.3 nm; the BET specific surface area of ​​catalyst E in Comparative Example 2 is 117 m². 2 / g, with an average pore size of 18.5 nm.

[0051] Electrochemical active area (ECA) measurement: A three-electrode system was used in 0.1 M HClO4 solution, and the ECA was calculated via hydrogen adsorption / desorption. The Pt ECA of the catalyst in Example 1 was 85.2 m. 2 / g, Comparative Example 1 is 72.5 m 2 / g indicates that the catalyst of Example 1 has a high electrochemical active area under the test conditions.

[0052] Single-cell performance testing: Membrane electrodes A, B, C, D, and E were assembled with a gas diffusion layer to form an effective area of ​​5 cm². 2 A single cell was tested. The test conditions were: H2 / Air, back pressure 150 kPa, cell temperature 80℃, gas humidification temperature 75℃, and anode / cathode stoichiometric ratio 1.5 / 2.0. The result was achieved at 2 A / cm². 2 At a current density of 2 A / cm², the voltages of membrane electrodes A, B, C, and E are 0.624 V, 0.655 V, 0.610 V, and 0.618 V, respectively, all higher than the 0.534 V of membrane electrode D. Membrane electrode A at 2 A / cm²... 2 The power density at that time was 1.25 W / cm². 2 The membrane electrode D is 1.07 W / cm². 2 The above results indicate that, under the test conditions, the membrane electrode prepared using the composite catalyst of the present invention exhibits higher output voltage and power density in the high current density region compared to the conventional Pt / C membrane electrode.

[0053] Accelerated durability testing: Potential cycling (ADT) was performed on the cathodes of membrane electrode A and the comparative membrane electrode D on a single-cell test platform. The test conditions were 0.6 V ↔ 0.95 V, triangular wave, scan rate 500 mV / s, under an N2 atmosphere. After 3000 cycles, the ECA of membrane electrode A decreased from 85.2 mV / s. 2 / g decreased to 79.8 m 2 / g, with an attenuation rate of 6.3%; the ECA of the membrane electrode D decreased from 72.5 m 2 / g decreased to 52.1 m 2 / g, with a decay rate of 28.1%. After ADT, the current density of membrane electrode A at 0.6 V decreased by 8.5%, and that of membrane electrode D decreased by 32.7%. These results indicate that under the test conditions, membrane electrode A exhibits better ECA retention and performance retention trend compared to the conventional Pt / C membrane electrode.

[0054] Table 1 shows the electrochemical active area (ECA) and decay rate of the membrane electrodes prepared in Example 1 and Comparative Example 1 before and after accelerated durability testing (ADT).

[0055]

[0056] The above examples and comparative examples demonstrate that the in-situ grown Pt-ultrashort carbon nanotube composite catalyst powder provided by this invention, through its unique structural design, achieves improvements in platinum particle size control, dispersibility, interfacial bonding strength, conductive network construction, and mass transfer optimization. The prepared membrane electrode exhibits superior electrochemical activity, output power, and durability compared to traditional Pt / C membrane electrodes under the indicated test conditions.

[0057] This invention is not limited to the specific embodiments described above. Ordinary variations and substitutions made by those skilled in the art within the scope of the technical solution of this invention should be included within the protection scope of this invention. For example, platinum nanoparticles can be replaced with alloys of platinum with metals such as cobalt, nickel, iron, and copper; the carbon source can be other hydrocarbons such as methane and propylene; the substrate material can be acid / alkali soluble substances such as MgO and SiO2; and the type of ionomer can also be changed.

[0058] The Pt-ultrashort carbon nanotube composite catalyst powder of this invention can be prepared through processes such as sol preparation, substrate loading, CVD in-situ growth, substrate removal, and powder recovery. It can be mixed with proton-conducting ionomers and dispersion media to form a fuel cell catalyst slurry. This slurry can be used to prepare catalyst layers and membrane electrode assemblies through spraying, transfer printing, or direct coating, making it suitable for proton exchange membrane fuel cells and possessing industrial manufacturing and application value.

Claims

1. A Pt-ultra-short carbon nanotube composite catalyst powder, characterized by, Includes Pt or Pt alloy nanoparticles and multi-walled carbon nanotubes bonded to the Pt or Pt alloy nanoparticles; The multi-walled carbon nanotubes are carbon nanotubes formed by in-situ growth induced by the Pt or Pt alloy nanoparticles, and the average length of the multi-walled carbon nanotubes is 50-200 nm. The Pt-ultra-short carbon nanotube composite catalyst powder is a powder that can be mixed with proton-conducting ionomers and dispersion media to form a catalyst slurry.

2. The Pt-ultrashort carbon nanotube composite catalyst powder according to claim 1, characterized by, The average particle size of the Pt or Pt alloy nanoparticles is 3-5 nm, and the mass of the Pt or Pt alloy nanoparticles accounts for 45%-55% of the total mass of the Pt-ultra-short carbon nanotube composite catalyst powder.

3. The Pt-ultrashort carbon nanotube composite catalyst powder according to claim 1, characterized in that, The average length of the multi-walled carbon nanotubes is 80-150 nm.

4. The Pt-ultrashort carbon nanotube composite catalyst powder according to claim 1, characterized by, The Pt alloy nanoparticles include PtAu alloy nanoparticles, or alloy nanoparticles formed by Pt and at least one of the metals selected from Co, Ni, Fe, and Cu.

5. A method for preparing Pt-ultrashort carbon nanotube composite catalyst powder, characterized in that, Includes the following steps: Provides a removable substrate; By loading Pt or Pt alloy nanoparticles onto the removable substrate, a substrate loaded with Pt or Pt alloy nanoparticles is obtained. The substrate loaded with Pt or Pt alloy nanoparticles is placed in a carbon-containing atmosphere, so that the carbon source is pyrolyzed at the Pt or Pt alloy nanoparticles and multi-walled carbon nanotubes are grown in situ. The average length of the multi-walled carbon nanotubes is controlled to be 50-200 nm. The removable substrate is removed to obtain the Pt-ultra-short carbon nanotube composite catalyst powder.

6. The preparation method according to claim 5, characterized in that, The Pt or Pt alloy nanoparticles were prepared by polyol reduction method; The removable substrate includes alumina powder, porous silicon wafer, MgO or SiO2; The step of removing the removable substrate includes treating the substrate loaded with multi-walled carbon nanotubes with an acid or alkali solution selected according to the material of the removable substrate, wherein the acid or alkali solution includes hydrochloric acid, nitric acid, or sodium hydroxide solution.

7. The preparation method according to claim 5, characterized in that, The steps of in-situ growth of multi-walled carbon nanotubes include: pretreatment at 500-700℃ in an H2 / Ar atmosphere, followed by introduction of a carbon source and reaction at 650-800℃ for 5-30 min; the carbon source includes acetylene, ethylene, ethanol vapor, methane or propylene.

8. A fuel cell catalyst slurry, characterized in that, The powder includes the Pt-ultra-short carbon nanotube composite catalyst powder according to any one of claims 1 to 4, and also includes a proton-conducting ionomer and a dispersion medium.

9. A fuel cell membrane electrode assembly, characterized in that, The catalyst comprises a proton exchange membrane, an anode catalyst layer disposed on one side of the proton exchange membrane, and a cathode catalyst layer disposed on the other side of the proton exchange membrane, wherein at least one of the anode catalyst layer and the cathode catalyst layer comprises the Pt-ultra-short carbon nanotube composite catalyst powder according to any one of claims 1 to 4, or is formed by spraying, transferring or directly coating the fuel cell catalyst slurry according to claim 8.

10. A proton exchange membrane fuel cell, characterized in that, Includes the fuel cell membrane electrode assembly as described in claim 9.

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