Self-Supported Film Based on Intermetallic PtCu Nanowire Clusters, Preparation Method Thereof, and Application Thereof

Abstract

The present invention belongs to the technical field of hydrogen fuel cell catalysis, and particularly relates to an intermetallic PtCu nanowire cluster self-supporting film and its preparation method and application. The preparation method of the intermetallic PtCu nanowire cluster self-supporting film of the present invention: preparing a precursor solution → obtaining a PtCu alloy nanowire cluster catalyst → obtaining a self-supporting PtCu nanowire cluster film → preparing a self-supporting PtCu nanowire cluster film with a surface-coated SiO2 protective layer (immersing the self-supporting PtCu nanowire cluster film in a solution of tetraethyl orthosilicate and formic acid and drying to obtain) → obtaining an intermetallic PtCu nanowire cluster self-supporting film (heating the self-supporting PtCu nanowire cluster film with a surface-coated SiO2 protective layer under a reducing atmosphere, and the heat treatment temperature is 400-800 °C to obtain). The self-supporting film provided by the present invention has high mechanical strength, mild method conditions, and improves the output power of the fuel cell.

Description

Technical Field

[0001] The present invention belongs to the technical field of hydrogen fuel cell catalysis, and particularly relates to a self-supporting film based on intermetallic PtCu nanowire clusters, a preparation method thereof, and an application thereof. Background Art

[0002] Proton exchange membrane fuel cells belong to clean and sustainable energy conversion technologies. However, due to the slow oxygen reduction reaction (ORR) of traditional carbon-supported electrodes, their industrialization still faces problems such as too high catalyst costs (the usage amount of precious metal platinum > 0.2 mg / cm 2 ) and short lifespan. Therefore, as a complex system involving electrocatalytic reactions, charge migration, and mass transfer, it is very important to measure the enhancement and balance of electrochemical processes from different dimensions, understand the construction of electrode structures, and form effective "solid-liquid-gas" three-phase transport channels to drive the sustainable progress of cathode ORR.

[0003] Platinum, as the most effective ORR catalyst, the structure and morphology controllable preparation, electronic structure regulation, and the structure-activity relationship between them and the electrochemical performance based on thin film glassy carbon electrodes have been widely studied. Recently reported intermetallic catalysts, the periodic and ordered arrangement of platinum atoms and transition metal atoms makes the intermetallic compounds have stronger 3d-5d orbital interactions and electronic effects, thereby enhancing the ORR activity and stability. In addition, nano-based metal films with large-scale ordered arrangement structures constructed based on high aspect ratio nanowires will bring new properties or enhanced performance to electrode catalytic materials. Currently, most catalysts are in powder form. In order to evaluate the electrochemical performance of a three-electrode system, catalyst powders are usually mixed with conductive carbon materials, and the highly conductive glassy carbon substrate eliminates the influence of electrode resistivity on electrochemical performance, and the sufficient proton concentration in the electrolyte in the three-electrode system greatly weakens the influence of proton transport limitation on electrochemical performance. Optimizing the electrode catalytic layer structure can effectively achieve high catalyst utilization and enhance the gas / liquid transport performance in actual membrane electrode assemblies. Traditionally, the catalytic layer is prepared by methods such as coating the catalyst on a gas diffusion layer electrode or coating the catalyst on a membrane. Due to its dense and disordered structure, it leads to low gas / liquid mass transfer efficiency and insufficient catalyst utilization; high potential carbon carrier corrosion causes the pore structure and skeleton of the catalytic layer to collapse; the discontinuous proton transport network limits the effective transport of protons in the cathode catalytic layer; and the two-dimensional interface structure of traditional membrane electrodes results in poor mass transfer and stability at the interface between the cathode catalytic layer and the proton exchange membrane.

[0004] To circumvent these problems, researchers have been working on binder-free self-supporting electrodes: ordered arrays, nano-porous metal ordered carrier thin films, electrospun fiber membranes, template-packed electrodes such as PS, SiO2, and K2CO3. Among them, the electrospun fiber membrane electrode process is suitable for mass production. However, using polymer fibers as the support and after carbonization treatment, the membrane has poor mechanical strength and flexibility, and extremely strong hydrophobicity, which is not suitable for constructing the reaction three-phase interface. Template-packed electrodes can effectively construct multi-scale porous structure electrodes, but the preparation process is complex and the pore structure is prone to collapse. The nano-porous metal thin film prepared by the dealloying method has a double continuity of ligaments and pores in its structure, which is conducive to the orderly transport of electrons and protons.

[0005] Patent CN117476960A discloses a nano-porous Pt thin film, its preparation method, and its application in fuel cell electrodes. The prepared Pt thin film has high electrocatalytic activity. When applied to fuel cell electrodes, it can improve the battery output power and stable performance output. Ordered carrier arrays such as CNTs, nickel foam, and metal oxides are most commonly used because of their porous structure, easy availability, and low cost. The catalytic active substance is directly sprayed / grown on the ordered substrate. However, there are still some problems in the actual later applications: the preparation process of the CNT array is relatively complex and not suitable for mass production; the conductivity of the metal oxide array is poor; the cathode prepared with a conductive polymer as an ordered carrier faces serious flooding, etc. Therefore, traditional porous metal electrodes have limitations, and self-supporting electrodes are difficult to apply under harsh conditions.

[0006] Nano-wires, nano-tubes, and nano-rods prepared by methods such as solvothermal reduction are sprayed to prepare an ultra-thin catalytic layer, the thickness, composition, and pore size of which are controllable and adjustable. However, the connection between the nano-wires, nano-tubes, and nano-rods is only a simple physical superposition contact, which is not conducive to the transport of protons between the nano-wires in the catalytic layer, and thus affects the efficient transport and distribution of protons between and within the planes. Therefore, although the catalytic layer composed of nano-wires, tubes, and rods has excellent electrochemical performance and excellent mass transport performance brought by the open structure, its battery performance is always poor. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the above-mentioned defects existing in the prior art and provide a self-supporting thin film based on intermetallic PtCu nanowire clusters, which has excellent open pores, flexibility, and mechanical strength. The present invention also provides a preparation method thereof, with mild preparation conditions and a simple process. Applying the self-supporting thin film of intermetallic PtCu nanowire clusters prepared by the present invention to fuel cells can improve the battery output power and stable performance output.

[0008] The preparation method of the self-supporting film based on the intermetallic PtCu nanowire clusters of the present invention includes the following steps: preparing a metal salt precursor solution → obtaining a PtCu alloy nanowire cluster catalyst → obtaining a self-supporting PtCu nanowire cluster film → preparing a self-supporting PtCu nanowire cluster film with a surface-coated SiO2 protective layer → obtaining an intermetallic PtCu nanowire cluster self-supporting film;

[0009] The specific steps for preparing the self-supporting PtCu nanowire cluster film with a surface-coated SiO2 protective layer are as follows: immersing the self-supporting PtCu nanowire cluster film in a solution of tetraethyl orthosilicate and formic acid to coat its surface with a SiO2 coating layer, and then drying to obtain the self-supporting PtCu nanowire cluster film with a surface-coated SiO2 protective layer; the volume ratio of tetraethyl orthosilicate to formic acid is 1 to 10, the immersion temperature is 40 to 60 °C, and the immersion time is 2 to 6 h.

[0010] The specific steps for obtaining the intermetallic PtCu nanowire cluster self-supporting film are as follows: heat-treating the self-supporting PtCu nanowire cluster film with a surface-coated SiO2 protective layer under a reducing atmosphere, the heat-treatment temperature is 400 to 800 °C, and the heat-treatment time is 2 to 10 h, to obtain the intermetallic PtCu nanowire cluster self-supporting film. The reducing atmosphere is 5% H2 / N2 (volume ratio).

[0011] The specific steps for preparing the metal salt precursor solution are as follows: dissolving platinum and copper precursors in water to obtain a precursor solution with a concentration of 50 to 200 mmol / L, then adding a reducing agent, a structure-directing agent, and an organic solvent, adjusting the pH of the solution to 10 to 14, controlling the atomic ratio of platinum to copper to be 1:1, and stirring until a clear, transparent, and homogeneous metal salt precursor solution is formed. The precursors are chloroplatinic acid, potassium chloroplatinate, copper chloride, and copper nitrate. Potassium hydroxide is used to adjust the pH.

[0012] The reducing agent is glucose, urea, ascorbic acid, or sodium citrate; the structure-directing agent is N,N-dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylenediamine, or hexamethylphosphoric triamide; the organic solvent is ethylene glycol, glycerol, 1,3-propanediol, propylene glycol, diethylene glycol, or methanol.

[0013] The added mass of the reducing agent is 50 wt% to 200 wt% of platinum and palladium, the added volume of the structure-directing agent is 2 to 10 mL, the added volume of the organic solvent is 4 to 12 mL, and the total added volume of the structure-directing agent and the organic solvent is 10% to 50% of the total volume of the reaction kettle. The organic solvent, as the solvent main body and the structure-directing agent, has a much larger added volume and is usually not calculated by mass ratio.

[0014] The specific steps for preparing the PtCu alloy nanowire cluster catalyst are as follows: Heat and keep the metal salt precursor solution warm to form a black colloidal solution precipitate, add a solvent and centrifuge to obtain the PtCu alloy nanowire cluster catalyst. Heat to 140 - 200 °C and keep warm for 6 - 12 h. The solvent is absolute ethanol, and centrifuge and wash 3 - 5 times.

[0015] The specific steps for preparing the self - supported PtCu nanowire cluster thin film are as follows: Add the PtCu alloy nanowire cluster catalyst to ethanol and disperse it by ultrasonic treatment for 0.5 - 4 h until a black and homogeneous suspension with a concentration of 0.4 - 5 mg / mL is formed, and then perform vacuum evaporation to obtain the self - supported PtCu nanowire cluster thin film; The vacuum evaporation temperature is 30 - 60 °C, and the evaporation time is 24 - 48 h.

[0016] An intermetallic PtCu nanowire cluster self - supported thin film is prepared by the preparation method of the intermetallic PtCu nanowire cluster self - supported thin film described above.

[0017] Transfer the intermetallic PtCu nanowire cluster self - supported thin film to a mica sheet or a PET substrate, and use the hot - pressing method to transfer the intermetallic PtCu nanowire cluster self - supported thin film from the substrate surface to the Nafion membrane surface and assemble it into a hydrogen fuel cell.

[0018] Specifically, the preparation method of the intermetallic PtCu nanowire cluster self - supported thin film includes the following steps:

[0019] (1) Dissolve platinum and copper precursors in water to prepare a precursor solution with a concentration of 50 - 200 mmol / L, add a reducing agent, a structure - directing agent, and a solvent, adjust the pH to 10 - 14, control the atomic ratio of platinum to copper to be 1:1, and magnetically stir to form a clear, transparent, and homogeneous metal salt precursor solution;

[0020] (2) Transfer the metal salt precursor solution to a 25 - mL reaction kettle, heat it in an oven to 140 - 200 °C, keep warm for 6 - 12 h, and a black colloidal solution precipitate is formed at the bottom of the solvent - thermal kettle. Centrifuge it with an ethanol solution 3 - 5 times, collect the above - mentioned black colloidal catalyst, and obtain a PtCu alloy nanowire cluster catalyst with a Pt / Cu atomic ratio of 1:1;

[0021] (3) Prepare the self - supported PtCu nanowire cluster thin film by the solvent evaporation - induced self - assembly process. Disperse the PtCu nanowire cluster catalyst prepared in step (2) in ethanol, ultrasonically disperse it for 0.5 - 4 h until a black and homogeneous suspension is formed with a concentration of 0.4 - 5 mg / mL, and then pour 0.5 mL - 10 mL of the catalyst suspension into a 2 polytetrafluoroethylene mold, and slowly evaporate the solvent in a 30 - 60 °C vacuum oven for 24 - 48 h to obtain the self - supported PtCu nanowire cluster thin film;

[0022] (4) The self-supporting PtCu nanowire cluster film is immersed in a solution of tetraethyl orthosilicate (TEOS) and formic acid with a volume ratio of 1 to 10 at 40 to 60 °C for 2 to 6 h to coat a SiO2 coating layer on its surface, and then dried in a vacuum oven for 12 h to obtain a self-supporting PtCu nanowire cluster film with a SiO2 protective layer on its surface;

[0023] (5) The self-supporting SiO2-coated PtCu nanowire cluster film obtained in step (4) is placed in a tubular furnace with a reducing atmosphere of 5% H2 / N2 and heat-treated at 400 to 800 °C for 2 to 10 h to obtain an intermetallic PtCu nanowire cluster self-supporting film.

[0024] Specifically, the intermetallic PtCu nanowire cluster self-supporting film is first subjected to an electrochemical test: The self-supporting intermetallic PtCu film material is cut into circular pieces with a diameter of 4 mm and placed on a glassy carbon electrode coated with a 0.5 wt% Nafion membrane solution on its surface. The surface of the electrode covered with the film is dried with nitrogen to fix the film, obtaining a glassy carbon electrode with the self-supporting intermetallic PtCu film, and then an electrochemical test of a three-electrode system is carried out to characterize the electrochemical active area and oxygen reduction performance of the film material.

[0025] Specifically, the application of the intermetallic PtCu nanowire cluster self-supporting film in a hydrogen fuel cell electrode: The intermetallic PtCu nanowire cluster self-supporting film is transferred onto a mica sheet or a PET substrate, and by using a hot pressing method, with a pressure of 2 to 15 MPa, a temperature of 50 to 200 °C, and a time of 0.5 to 10 min, the intermetallic PtCu nanowire cluster self-supporting film is transferred from the substrate surface to the Nafion membrane surface and assembled into a hydrogen fuel cell fixture for single cell performance testing.

[0026] The intermetallic PtCu nanowire cluster self-supporting film of the present invention first prepares PtCu alloy nanowire clusters with a Pt / Cu atomic ratio of 1:1 by a solvothermal synthesis method. Using a structure-directing agent, the PtCu nanowires form nanowire clusters according to the oriented attachment mechanism. Then, it is ultrasonically dispersed in ethanol to form a catalyst slurry, and the PtCu nanowire clusters are induced to stack by the slow evaporation of the ethanol solution to form a self-supporting film material with a certain area. Using the TEOS solution method, formic acid is used to adjust the solution pH, and silicic acid molecules react with the surface hydroxyl groups of TiO2 to form a continuous SiO2 film as a protective layer, which uniformly coats the surface of the PtCu nanowire clusters, restricting the coarsening of the PtCu nanowire clusters during the heat treatment process. Finally, it is treated in a reducing atmosphere using the confined thermal effect to induce the diffusion and rearrangement of Cu and Pt atoms to grow into a chemically ordered structure, obtaining an intermetallic PtCu nanowire cluster self-supporting film with adjustable pore size and thickness, and having a certain flexibility and mechanical strength. The intermetallic PtCu is a face-centered cubic ordered intermetallic compound.

[0027] Aiming at the problems in the prior art that porous metal films are applied to self-supporting electrodes of hydrogen fuel cells, such as the easy corrosion, dissolution, shedding, and agglomeration of metal-based oxygen reduction electrocatalysts in acidic media, resulting in high costs, low activity, and poor stability of the catalysts. The porous film electrode formed by the interpenetrating and overlapping of the intermetallic PtCu nanowire clusters prepared by the present invention has an adjustable catalytic layer loading and thickness, an easily adjustable pore size, a strong binding force with the proton exchange membrane, and a small interfacial resistivity. The method has a wide application range and is used in the field of electrocatalysis of self-supporting film electrodes for hydrogen fuel cells, improving the battery output power and stable output performance.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] (1) For the intermetallic PtCu nanowire cluster self-supporting film prepared by the present invention, the Pt loading of the catalyst is controllable, the thickness is uniform, the pore size is easily adjustable, the binding force with the Nafion membrane is strong, and the interfacial resistance is small. The intermetallic PtCu nanowire cluster self-supporting film has an area that can be customized according to requirements as an electrode (such as 1×1 cm 2 , 2×2 cm 2 , 5×5 cm 2 sizes), meeting the actual application requirements of the electrodes of fuel cells.

[0030] (2) For the intermetallic PtCu nanowire cluster self-supporting film prepared by the present invention, the intermetallic PtCu nanowire clusters have a high aspect ratio, and the film formed by their interpenetration has open pores, flexibility, and mechanical strength; it has a fixed stoichiometric ratio and a highly ordered atomic structure. The Pt and Cu metal atoms are bonded to each other through strong d-d orbital interactions, which can inhibit the dissolution of non-precious metals and improve the structural stability of the catalyst.

[0031] (3) The preparation method of the intermetallic PtCu nanowire cluster self-supporting film of the present invention uses non-noble metal Cu as a doping atom, and combines a solvothermal synthesis method, a solvent evaporation-induced self-assembly process, and a confined heat treatment method to prepare the intermetallic PtCu nanowire cluster self-supporting film, which has the characteristics of low cost, environmental friendliness, simple steps, and mild preparation conditions.

[0032] (4) The intermetallic PtCu nanowire cluster self-supporting film prepared by the present invention is not only applicable to electrochemical catalytic half-reactions, but can also be directly applied to fuel cell membrane electrodes as a self-supporting electrode to improve the output power and stable output performance of the battery. Description of the Drawings

[0033] Figure 1 It is a transmission electron microscope image of the microscopic morphology of the intermetallic PtCu nanowire cluster self-supporting film prepared in Example 1.

[0034] Figure 2 It is a scanning electron microscope image of the microscopic morphology of the intermetallic PtCu nanowire cluster self-supporting film prepared in Example 1.

[0035] Figure 3 It is the XRD spectra of the self-supporting PtCu nanowire cluster film (disordered) obtained in step (3) and the intermetallic PtCu nanowire cluster self-supporting film (ordered) obtained after step (5) prepared in Example 1.

[0036] Figure 4 It is the BET nitrogen adsorption and desorption curve of the intermetallic PtCu nanowire cluster self-supporting film prepared in Example 1.

[0037] Figure 5 It is the cyclic voltammogram of the initial and after 3000 cycles in the electrochemical test in Application 1.

[0038] Figure 6 It is the oxygen reduction polarization curve of the initial state and after 3000 cycles in the electrochemical test in Application 1.

[0039] Figure 7 It is the polarization curve of the hydrogen / air fuel cell prepared in Application 2 at 30 °C, 60 °C, and 80 °C.

[0040] Figure 8 It is a scanning electron microscope image of the microscopic morphology of the film prepared in Comparative Example 1. Detailed Description of the Invention

[0041] The present invention will be further described below in conjunction with specific embodiments.

[0042] The raw materials and auxiliaries used in the following examples and comparative examples are all commercially available products. Copper chloride is calculated as anhydrous copper chloride according to a molecular weight of 135. Chloroplatinic acid is hexahydrate chloroplatinic acid, and the molecular weight is calculated as 518. The Nafion membrane is a proton exchange membrane of DuPont.

[0043] Example 1

[0044] The preparation method of the self-supporting film based on intermetallic PtCu nanowire clusters includes the following steps:

[0045] (1) Dissolve 0.518 g of chloroplatinic acid and 0.135 g of copper chloride in 20 mL of water respectively to prepare a precursor solution with a concentration of 50 mmol / L. Add 6 mL of ethylene glycol and 4 mL of N,N-dimethylformamide, and adjust the pH to 10 with potassium hydroxide. Stir magnetically to form a clear, transparent and homogeneous metal salt precursor solution;

[0046] (2) Each time, take 0.2 mL of the metal salt precursor solution and perform multiple preparations according to the following steps: Transfer it to a 25 mL reaction kettle, heat it in an oven to 170 °C, keep it warm for 8 h, and a black colloidal solution precipitate is formed at the bottom of the solvothermal kettle. Centrifuge it 3 times with an ethanol solution, and collect the black colloidal catalysts obtained multiple times to obtain a PtCu alloy nanowire cluster catalyst with a Pt / Cu atomic ratio of 1:1;

[0047] (3) Prepare a self-supporting PtCu nanowire cluster film by solvent evaporation-induced self-assembly process. Take 10 mg of the PtCu alloy nanowire cluster catalyst prepared in step (2) and disperse it in 25 mL of ethanol. Ultrasonically disperse it for 0.5 h to form a black and homogeneous suspension with a concentration of 0.4 mg / mL. Then pour 0.5 mL of the catalyst suspension into a 2 polytetrafluoroethylene mold with a bottom area of 1×1 cm, and evaporate ethanol in a vacuum oven at 30 °C for 48 h to obtain a self-supporting PtCu nanowire cluster film;

[0048] (4) Immerse 0.2 mg of the self-supporting PtCu nanowire cluster film in TEOS and formic acid with a volume ratio of 2 at 40 °C for 6 h to completely impregnate it, so that a SiO2 coating layer is coated on its surface, and then dry it in a vacuum oven for 12 h to obtain a self-supporting PtCu nanowire cluster film with a SiO2 protective layer coated on its surface;

[0049] (5) Place the self-supporting PtCu nanowire cluster film with a SiO2 protective layer coated on its surface obtained in step (4) in a tubular furnace with a reducing atmosphere of 5% (volume ratio) H2 / N2, and heat-treat it at 600 °C for 4 h to obtain an intermetallic PtCu nanowire cluster self-supporting film.

[0050] The transmission electron microscope image of the microscopic morphology of the prepared intermetallic PtCu nanowire cluster self-supporting film is asFigure 1 As shown, it can be seen that it is composed of metal nanowire clusters. The scanning electron microscope image of the microscopic morphology of the prepared intermetallic PtCu nanowire cluster self-supporting film is as Figure 2 shown. It can be seen that it shows a high aspect ratio of 300-400 nanowire cluster structural units. The constructed self-supporting film has an open pore structure, an accurate Pt / Cu atomic ratio (1:1), a high porosity, has a certain flexibility, and can be separated from the mold without damage to its integrity, demonstrating that the film has a certain mechanical strength. The XRD spectrum of the prepared intermetallic PtCu nanowire cluster self-supporting film is as Figure 3 the ordered spectrum. The self-supporting PtCu nanowire cluster film obtained after step (3) is disordered, as Figure 3 shown in the disordered spectrum in Figure 3 It can be seen that the disordered PtCu nanowire cluster film maintains the face-centered cubic (fcc) structure of the Pt crystal (ICDD standard powder diffraction PDF database PDF#04-0802). The XRD diffraction peaks of PtCu (ordered) after heat treatment match well with the PtCu intermetallic structure (ICDD standard powder diffraction PDF database PDF#42-1326). The BET nitrogen adsorption-desorption isotherm curve of the prepared intermetallic PtCu nanowire cluster self-supporting film is as Figure 4 shown. BET pore size analysis shows that the large surface area (about 90 m 2 / g), high porosity of 76%, and two concentrated bands of pore size distribution of 20-60 nm and 60 nm-300 nm of the PtCu nanowire cluster assembly construct a large electrochemically accessible surface area and a fast mass transfer flux, which can significantly improve the electrocatalytic performance.

[0051] Example 2

[0052] The preparation method of the intermetallic PtCu nanowire cluster self-supporting film described above includes the following steps:

[0053] (1) Dissolve 1.036 g of chloroplatinic acid and 0.27 g of copper chloride in 20 mL of water respectively to prepare a precursor solution with a concentration of 100 mmol / L. Add 0.31 g of glucose, 5 mL of dimethylacetamide, and 7 mL of glycerol. Add potassium hydroxide to adjust the pH to 11, and stir magnetically to form a clear, transparent, and homogeneous metal salt precursor solution;

[0054] (2) Take 0.1 mL of the metal salt precursor solution each time and perform multiple preparations according to the following steps: Transfer it to a 25 mL reaction kettle, heat it in an oven to 140 °C, keep it warm for 12 h, generate a black colloidal solution precipitate at the bottom of the solvothermal kettle, centrifuge it 3 times with an ethanol solution, and collect the black colloidal catalyst obtained multiple times to obtain a PtCu alloy nanowire cluster catalyst with a Pt / Cu atomic ratio of 1:1;

[0055] (3) Prepare a self-supporting PtCu nanowire cluster film by using a solvent evaporation-induced self-assembly process. Disperse 10 mg of the PtCu alloy nanowire cluster catalyst prepared in step (2) into 20 mL of ethanol, and ultrasonically disperse for 2 h until a black and homogeneous suspension is formed with a concentration of 0.5 mg / mL. Then pour 6.4 mL of the catalyst suspension into a polytetrafluoroethylene mold with a bottom area of 2×2 cm 2 and evaporate the ethanol in a vacuum oven at 40 °C for 48 h to obtain a self-supporting PtCu nanowire cluster film;

[0056] (4) Immerse 3.2 mg of the self-supporting PtCu nanowire cluster film in a solution of TEOS and formic acid with a volume ratio of 5 at 60 °C for 2 h to completely coat its surface with a SiO2 coating layer, and then dry it in a vacuum oven for 12 h to obtain a self-supporting PtCu nanowire cluster film with a SiO2 protective layer on its surface;

[0057] (5) Place the self-supporting PtCu nanowire cluster film with a SiO2 protective layer on its surface obtained in step (4) in a tubular furnace with a reducing atmosphere of 5% (volume ratio) H2 / N2, and heat-treat it at 400 °C for 10 h to obtain an intermetallic PtCu nanowire cluster self-supporting film.

[0058] Example 3

[0059] The preparation method of the intermetallic PtCu nanowire cluster self-supporting film includes the following steps:

[0060] (1) Dissolve 1.036 g of chloroplatinic acid and 0.27 g of copper chloride in 20 mL of water respectively to prepare a precursor solution with a concentration of 100 mmol / L. Add 0.31 g of urea, 5 mL of N-methylpyrrolidone, and 6 mL of 1,3-propanediol, and adjust the pH to 12 with potassium hydroxide, and magnetically stir to form a clear, transparent, and homogeneous metal salt precursor solution;

[0061] (2) Take 0.1 mL of the metal salt precursor solution each time and perform multiple preparations according to the following steps: transfer it to a 25 mL reaction kettle, heat it in an oven to 200 °C, and keep it warm for 6 h to form a black colloidal solution precipitate at the bottom of the solvothermal kettle. Centrifuge it with an ethanol solution 3 times, and collect the black colloidal catalysts obtained multiple times to obtain a PtCu alloy nanowire cluster catalyst with a Pt / Cu atomic ratio of 1:1;

[0062] (3) Prepare a self-supporting PtCu nanowire cluster film by using a solvent evaporation-induced self-assembly process. Disperse 10 mg of the PtCu alloy nanowire cluster catalyst prepared in step (2) into 20 mL of ethanol, and ultrasonically disperse for 3 h until a black and homogeneous suspension is formed with a concentration of 0.5 mg / mL. Then pour 4 mL of the catalyst suspension into a polytetrafluoroethylene mold with a bottom area of 2×2 cm2 In a polytetrafluoroethylene mold, the solvent ethanol was evaporated in a vacuum oven at 60 °C for 24 h to obtain a self-supporting PtCu nanowire cluster film;

[0063] (4) 2 mg of the self-supporting PtCu nanowire cluster film was placed in TEOS and formic acid with a volume ratio of 10 and completely impregnated at 45 °C for 4 h to coat a SiO2 coating layer on its surface, and then dried in a vacuum oven for 12 h to obtain a self-supporting PtCu nanowire cluster film with a SiO2 protective layer on its surface;

[0064] (5) The self-supporting PtCu nanowire cluster film with a SiO2 protective layer on its surface obtained in step (4) was placed in a tubular furnace with a reducing atmosphere of 5% (volume ratio) H2 / N2 and heat-treated at 500 °C for 8 h to obtain an intermetallic PtCu nanowire cluster self-supporting film.

[0065] Example 4

[0066] The preparation method of the intermetallic PtCu nanowire cluster self-supporting film includes the following steps:

[0067] (1) 1.554 g of chloroplatinic acid and 0.405 g of copper chloride were respectively dissolved in 20 mL of water to prepare a precursor solution with a concentration of 150 mmol / L. 0.54 g of sodium citrate, 4 mL of N,N-dimethylformamide, and 6 mL of ethylene glycol were added, and potassium hydroxide was added to adjust the pH to 13, and magnetic stirring was carried out to form a clear, transparent and homogeneous metal salt precursor solution;

[0068] (2) Each time 0.067 mL of the metal salt precursor solution was taken and prepared multiple times according to the following steps: transferred to a 25 mL reaction kettle, heated in an oven to 180 °C, and kept warm for 9 h. A black colloidal solution precipitate was formed at the bottom of the solvothermal kettle, and it was centrifuged 5 times with an ethanol solution. The black colloidal catalysts obtained multiple times were collected to obtain a PtCu alloy nanowire cluster catalyst with a Pt / Cu atomic ratio of 1:1;

[0069] (3) A self-supporting PtCu nanowire cluster film was prepared by a solvent evaporation-induced self-assembly process. 10 mg of the PtCu alloy nanowire cluster catalyst prepared in step (2) was dispersed in 5 mL of ethanol and ultrasonically dispersed for 4 h to form a black homogeneous suspension with a concentration of 2 mg / mL. Then, 4.5 mL of the catalyst suspension was poured into a polytetrafluoroethylene mold with a bottom area of 3×3 cm 2 In a polytetrafluoroethylene mold, the solvent ethanol was evaporated in a vacuum oven at 30 °C for 48 h to obtain a self-supporting PtCu nanowire cluster film;

[0070] (4) Immerse 9 mg of the self-supporting PtCu nanowire cluster film in a solution of TEOS and formic acid with a volume ratio of 6 at 50 °C for 5 h to completely coat its surface with a SiO2 coating layer, and then dry it in a vacuum oven for 12 h to obtain a self-supporting PtCu nanowire cluster film with a SiO2 protective layer on its surface;

[0071] (5) Place the self-supporting PtCu nanowire cluster film with a SiO2 protective layer obtained in step (4) in a tubular furnace with a reducing atmosphere of 5% (volume ratio) H2 / N2, and heat-treat it at 700 °C for 5 h to obtain an intermetallic PtCu nanowire cluster self-supporting film.

[0072] Example 5

[0073] The preparation method of the intermetallic PtCu nanowire cluster self-supporting film described above includes the following steps:

[0074] (1) Dissolve 1.036 g of chloroplatinic acid and 0.27 g of copper chloride in 10 mL of water respectively to prepare a precursor solution with a concentration of 200 mmol / L. Add 0.31 g of ascorbic acid, 4 mL of N,N-dimethylformamide, and 8 mL of ethylene glycol, and adjust the pH to 14 with potassium hydroxide, and magnetically stir to form a clear, transparent, and homogeneous metal salt precursor solution;

[0075] (2) Each time, take 0.1 mL of the metal salt precursor solution and perform multiple preparations according to the following steps: Transfer it to a 25 mL reaction kettle, heat it in an oven to 160 °C, and keep it warm for 9 h to generate a black colloidal solution precipitate at the bottom of the solvothermal kettle. Centrifuge it 5 times with an ethanol solution, and collect the black colloidal catalysts obtained multiple times to obtain a PtCu alloy nanowire cluster catalyst with a Pt / Cu atomic ratio of 1:1;

[0076] (3) Prepare a self-supporting PtCu nanowire cluster film by solvent evaporation-induced self-assembly process. Disperse 10 mg of the PtCu alloy nanowire cluster catalyst prepared in step (2) in 20 mL of ethanol, and ultrasonically disperse it for 1 h to form a black and homogeneous suspension with a concentration of 0.5 mg / mL. Then pour 12.8 mL of the catalyst suspension into a 2 polytetrafluoroethylene mold with a bottom area of 4×4 cm, and evaporate the solvent ethanol in a 40 °C vacuum oven for 24 h to obtain a self-supporting PtCu nanowire cluster film;

[0077] (4) Immerse 6.4 mg of the self-supporting PtCu nanowire cluster film in a solution of TEOS and formic acid with a volume ratio of 1 at 60 °C for 2 h to completely coat its surface with a SiO2 coating layer, and then dry it in a vacuum oven for 12 h to obtain a self-supporting PtCu nanowire cluster film with a SiO2 protective layer on its surface;

[0078] (5) The self-supporting PtCu nanowire cluster film with an SiO2 protective layer on the surface obtained in step (4) was placed in a tubular furnace with a reducing atmosphere of 5% (volume ratio) H2 / N2 and heat-treated at 600 °C for 3 h to obtain an intermetallic PtCu nanowire cluster self-supporting film.

[0079] Comparative Example 1

[0080] This comparative example was the same as Example 1, except that step (4) was removed, and step (5) only retained "The self-supporting PtCu nanowire cluster film was placed in a tubular furnace with a reducing atmosphere of 5% H2 / N2 and heat-treated at 600 °C for 4 h". The results showed that during the heat treatment of the intermetallic PtCu nanowire clusters without the SiO2 surface coating layer, the nanostructure and morphology of the nanowire clusters underwent severe agglomeration, reducing the electrochemically active area, and the pore size and porosity of the pore structure decreased significantly, further hindering the mass transfer during the electrocatalytic process. The scanning electron micrograph of its structure and morphology is as Figure 8 shown.

[0081] Comparative Example 2

[0082] This comparative example was the same as Example 1, except that step (3) was removed, and the other step parameters were the same. The final results showed that for the film prepared without the solvent evaporation-induced self-assembly process, the nanostructure units of the nanowire clusters were arranged loosely and could not form a self-supporting film with certain flexibility and mechanical strength, thus affecting the testing of the glassy carbon three-electrode system and the membrane electrode system and reducing the battery performance.

[0083] Comparative Example 3

[0084] This comparative example was the same as Example 1, and the heat treatment process in step (5) was modified to heat treatment at 380 °C for 4 h in a tubular furnace with a reducing atmosphere of 5% H2 / N2, and the other steps were the same. The results showed that heat treatment at a temperature below 400 °C could not cause the transformation of PtCu nanowire clusters from an atomic disordered state to an ordered structure, accelerating the structurally destructive dissolution of Cu atoms in the catalyst in an acidic electrolyte system, thus being unfavorable for the stability of the film.

[0085] Comparative Example 4

[0086] This comparative example was the same as Example 1, and the solvothermal synthesis process in step (2) was modified to heat in an oven to 130 °C and keep warm for 12 h. The results showed that at a synthesis temperature below 140 °C, even if the synthesis reaction time was extended, nanowire clusters constructed by ultrafine nanowire units could not be formed, and there was obvious particle accumulation, which was not conducive to the preparation of a self-supporting film with flexibility and mechanical strength.

[0087] The thin films obtained from the above Examples 1 to 5 and Comparative Examples 1 to 4 were fabricated into supported thin film electrodes, and Experiments 1 and 2 were carried out. The specific fabrication method is as follows:

[0088] (1)The self-supported thin film of intermetallic PtCu nanowire clusters was respectively cut into two shapes: a circle with an area of 0.1256 cm 2 (applied to a glassy carbon electrode with Φ4 mm) and a square with 1 cm 2 (applied to a membrane electrode of a fuel cell with 1 cm×1 cm). The circular thin film cut to 0.1256 cm 2 was covered on the surface-cleaned glassy carbon electrode, fixed with Nafion solution, dried at room temperature, and subjected to subsequent electrochemical three-electrode system tests.

[0089] (2)The square thin film cut to 1 cm 2 was transferred to the proton exchange membrane by hot pressing to obtain a 1 cm 2 square electrode, and subsequent membrane electrode tests of the fuel cell system were carried out.

[0090] Experiment 1:

[0091] Electrochemical tests were carried out using the self-supported thin film of intermetallic PtCu nanowire clusters prepared in Example 1: Cyclic voltammetry characterization was performed. A three-electrode system was composed of a glassy carbon electrode with the thin film catalyst as the working electrode, a saturated calomel electrode as the reference electrode, and a carbon rod electrode as the counter electrode. 0.1 molL -1 of HClO4 saturated with N2 was used as the electrolyte solution. The electrochemical workstation was connected, and cyclic voltammetry technology was selected. In the potential range of -0.24 - 0.9 V vs SCE, cyclic scanning tests were carried out at a scanning rate of 50 mV s -1 . The cyclic voltammograms in the initial state and after 3000 cycles are as shown in Figure 5 . It can be seen that the nanowire cluster thin film exhibits obvious hydrogen absorption / desorption peaks, indicating the existence of an ordered surface atomic structure. The electrochemically active area (ECSA) of the thin film in the present invention was estimated by integrating the charge amount of the hydrogen absorption / desorption process to be 51.8 m 2 / g. After 3000 accelerated stability cycle tests, the ECSA of the intermetallic PtCu nanowire cluster thin film only lost 8%. The oxygen reduction polarization curves in the initial state and after 3000 cycles are as shown in Figure 6 . As can be seen from Figure 6 , the limiting current of the curve after cycling decreases and the current density corresponding to 0.9 V decreases significantly, demonstrating good intrinsic activity stability. Therefore, the above tests show that the structure of the self-supported thin film has significant advantages in the oxygen reduction reaction.

[0092] Experiment 2:

[0093] The application of the self-supporting intermetallic PtCu nanowire cluster thin film prepared in Example 1 in a fuel cell electrode was subjected to hydrogen-oxygen fuel cell performance testing. The intermetallic PtCu nanowire cluster thin film transferred to the Nafion 211 membrane by hot pressing was used as the cathode, and the catalyst loading was 0.2 mg / cm 2 , which was placed between the prepared anode and cathode electrodes to form a sandwich structure. Under a pressure of 0.75 MPa, it was hot pressed on a hot press at 135 °C. The hot pressing was carried out with positive pressure and negative pressure, each for 90 s, to obtain a membrane electrode with an area of 1 cm 2 . During the single cell performance test, after connecting the membrane electrode, gas pipelines, and pressure devices, first, humidified high-purity N2 was introduced into the anode and cathode of the cell to discharge the impurity gases in the cell. The gas flow rate was 200 mL / min -1 , and it was continuously introduced into the cell for 50 min. Then, a back pressure of 0.5 bar and 1.5 bar required for the anode and cathode during battery testing was applied to the cell. Then, humidified high-purity H2 and air were introduced into the anode and cathode sides respectively, with a flow rate of 200 mL / min -1 . Then, the fuel cell test system was used to complete the test of the I-V curve of the cell performance under the specified temperature and conditions. The polarization curves of the prepared hydrogen / air fuel cell at 30 °C, 60 °C, and 80 °C are as shown in Figure 7 . The I-V curve showed a normal open circuit voltage of 0.95 - 0.98 V, indicating that the self-supporting thin film cathode catalyst layer had good impedance hydrogen permeability and good oxygen reduction performance. Test conditions: The anode electrode was a commercially purchased 0.1 mg Pt cm -2 Pt / C (40 wt%) electrode. At temperatures of 30 °C, 60 °C, and 80 °C, and a back pressure of 1.5 bar, the peak power densities reached 232 mW / cm -2 , 407 mW / cm -2 and 615 mW / cm -2 respectively. After cyclic scanning 5000 times in the voltage range of 0.6 - 1 V, the peak power density of the cell at 60 °C only decreased by 5%, showing good hydrogen fuel cell performance overall.

[0094] The self-supporting nanowire cluster thin films prepared in the above examples and comparative examples were subjected to detection of the electrochemically active area, retention rate after cycling, peak power density of the membrane electrode, and stability performance under accelerated testing according to standards such as catalyst loading, nanowire cluster size, and porosity. The detection results are shown in Table 1.

[0095] Table 1 Detection Results

[0096]

[0097] The results of Example 1 and Comparative Example 1 show that, on the premise that other conditions are the same, during the heat treatment of the intermetallic PtCu nanowire clusters without SiO2 protective layer coating, the structural morphology of the nanowire clusters undergoes severe agglomeration. The scanning electron micrograph is as shown in Figure 8 . The electrochemically active area is reduced, the pore size and porosity of the pore structure are significantly reduced, further hindering the mass transfer during the electrocatalysis process. The SiO2 protective layer acts as a nanoreactor to promote the transformation from disorder to order and can also serve as a scaffold to mitigate the degradation of nanostructures. The results of Example 1 and Comparative Example 2 show that for the film prepared without the solvent evaporation-induced self-assembly process, the unit structure of the nanowire clusters is arranged loosely and cannot provide a self-supporting film with certain flexibility and mechanical strength, making it impossible to construct an interpenetrating pore and catalyst skeleton structure during the electrochemical and membrane electrode tests, resulting in poor stability. The results of Example 1 and Comparative Example 3 show that after reducing the heat treatment temperature under a reducing atmosphere, the transformation of PtCu nanowire clusters from an atomic disordered to an ordered structure cannot be achieved, indicating that high-temperature heat treatment provides energy to overcome the activation energy, enabling the atomic directional migration to specific positions to form an ordered structure, thus resulting in low stability. The results of Example 1 and Comparative Example 4 show that after reducing the temperature of the solvothermal synthesis, the nanowire cluster structure composed of ultrafine nanowires cannot be successfully prepared. Most of the prepared films are composed of particle accumulation, showing low open porosity and low activity and stability when applied to electrochemistry and membrane electrodes.

Claims

1. A preparation method of a self-supporting film based on an intermetallic PtCu nanowire cluster, characterized in that: It includes the following steps: Prepare a metal salt precursor solution → Obtain a PtCu alloy nanowire cluster catalyst → Obtain a self-supported PtCu nanowire cluster thin film → Prepare a self-supported PtCu nanowire cluster thin film with a SiO2 protective layer on the surface → Obtain an intermetallic PtCu nanowire cluster self-supported thin film; The specific steps for obtaining the PtCu alloy nanowire cluster catalyst are: Heat the metal salt precursor solution to 140 - 200 °C and keep it warm for 6 - 12 h to form a black colloidal solution precipitate, add a solvent and centrifuge to obtain the PtCu alloy nanowire cluster catalyst; The specific steps for obtaining the self-supported PtCu nanowire cluster thin film are: Add the PtCu alloy nanowire cluster catalyst to ethanol and disperse it by ultrasonic treatment until a black homogeneous suspension is formed, and then perform vacuum evaporation to obtain the self-supported PtCu nanowire cluster thin film; The vacuum evaporation temperature is 30 - 60 °C, and the evaporation time is 24 - 48 h; For the preparation of the self-supported PtCu nanowire cluster thin film with a SiO2 protective layer on the surface, the specific steps are: Immerse the self-supported PtCu nanowire cluster thin film in a solution of tetraethyl orthosilicate and formic acid to coat a SiO2 coating on its surface, and then dry it to obtain the self-supported PtCu nanowire cluster thin film with a SiO2 protective layer on the surface; The specific steps for obtaining the intermetallic PtCu nanowire cluster self-supported thin film are: Heat-treat the self-supported PtCu nanowire cluster thin film with a SiO2 protective layer on the surface in a reducing atmosphere at a heat-treatment temperature of 400 - 800 °C to obtain the intermetallic PtCu nanowire cluster self-supported thin film.

2. The preparation method of the self-supporting film based on the intermetallic PtCu nanowire clusters according to claim 1, wherein: The specific steps for preparing the metal salt precursor solution are: Dissolve platinum and copper precursors in water to obtain a precursor solution with a concentration of 50 - 200 mmol / L, then add a structure-directing agent and an organic solvent, adjust the pH of the solution to 10 - 14, and stir until a clear, transparent and homogeneous metal salt precursor solution is formed.

3. The preparation method of the self-supporting film based on the intermetallic PtCu nanowire clusters according to claim 2, characterized in that: In the said precursor solution, add a structure-directing agent, an organic solvent, and a reducing agent, and then adjust the pH of the solution.

4. The preparation method of the self-supporting film based on the intermetallic PtCu nanowire clusters according to claim 3, wherein: The structure-directing agent is N,N-dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylenediamine or hexamethylphosphoric triamide; the organic solvent is ethylene glycol, glycerol, 1,3-propanediol, propylene glycol, diethylene glycol or methanol; the reducing agent is glucose, urea, ascorbic acid or sodium citrate.

5. The preparation method of the self-supporting film based on the intermetallic PtCu nanowire clusters according to claim 1, wherein: The volume ratio of tetraethyl orthosilicate to formic acid is 1 - 10, the immersion temperature is 40 - 60 °C, and the immersion time is 2 - 6 h.

6. A self-supporting film based on intermetallic PtCu nanowire clusters, characterized in that It is obtained by the preparation method of the intermetallic PtCu nanowire cluster self-supported thin film according to any one of claims 1 - 5.

7. An application of the self-supporting film based on intermetallic PtCu nanowire clusters as described in claim 6, characterized in that: Transfer the intermetallic PtCu nanowire cluster self-supported thin film to a mica sheet or a PET substrate, and use a hot pressing method to transfer the intermetallic PtCu nanowire cluster self-supported thin film from the substrate surface to the Nafion membrane surface, and assemble it into a hydrogen fuel cell fixture.

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