A platinum-based catalyst, its preparation method and use

Abstract

The application provides a platinum-based catalyst and a preparation method and application thereof, and belongs to the technical field of fuel cells. The preparation method comprises the following steps: mixing a polymer solution, a conductive agent and a zeolite imidazolate framework material to obtain an electrostatic spinning solution; electrostatic spinning is performed on the electrostatic spinning solution, and then heat treatment is performed to obtain composite nanofibers containing metal nanoparticles or metal oxide nanoparticles; the composite nanofibers, a platinum source and an organic solvent are mixed to perform a reduction reaction, and the platinum-based catalyst is obtained. The polymer solution, the conductive agent and the zeolite imidazolate framework material are mixed, and the uniform distribution of various components on the nanoscale can be ensured by means of the electrostatic spinning technology, which is beneficial to the formation of a stable and efficient three-phase interface; the metal nanoparticles or the metal oxide nanoparticles obtained by conversion are combined with platinum particles, so that more active sites of the catalyst are exposed, and the efficient performance of the catalytic reaction is promoted.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of fuel cells, and particularly relates to a platinum-based catalyst and a preparation method and application thereof. BACKGROUND

[0002] In many energy conversion and storage devices, such as fuel cells and metal-air batteries, the construction of a three-phase interface (gas phase, liquid phase, and solid phase) plays a key role in the efficient performance of catalytic reactions. Traditional three-phase interface catalytic layer preparation methods often have difficulty in precisely controlling the distribution of each phase, the pore structure, and the exposure degree of the catalytically active sites, thereby limiting the further improvement of catalytic performance. As an effective means for preparing continuous nanofiber materials, electrospinning technology has unique advantages in regulating the microstructure of materials. However, there are still many challenges in applying it to the construction of ideal three-phase interface catalytic layers, such as the uniform dispersion of different components in the fibers, the optimization of the synergistic effect of catalytically active substances and the fiber matrix, and the like.

[0003] Therefore, how to use electrospinning technology to construct a three-phase interface catalytic layer so that it can realize the uniform dispersion of different components in the fibers, optimize the synergistic effect of catalytically active substances and the fiber matrix, and further improve the catalytic performance is a technical problem to be solved. SUMMARY

[0004] In view of the deficiencies of the prior art, the purpose of the present application is to provide a platinum-based catalyst and a preparation method and application thereof. The polymer solution, the conductive agent, and the zeolite imidazolate framework material are mixed, and the uniform distribution of each component on the nanoscale can be ensured by means of electrospinning technology, which is conducive to the formation of a stable and efficient three-phase interface. The composite nanofiber after heat treatment has a unique microstructure, in which the carbon fiber matrix formed by the carbonization of the polymer can provide a good electronic conduction channel, the zeolite imidazolate framework material forms a high specific surface area porous structure, and metal nanoparticles or metal oxide nanoparticles are converted, and the bonding force between the conductive agent, the carbon fiber matrix, and the nanoparticles is stronger. Further, after loading platinum particles and compounding with the metal nanoparticles or metal oxide nanoparticles, the catalyst exposes more active sites, which is conducive to promoting the efficient performance of the catalytic reaction. When applied in a fuel cell, the power density and durability of the cell can be significantly improved.

[0005] To achieve the purpose of the present application, the following technical solutions are adopted:

[0006] In a first aspect, the present application provides a preparation method of a platinum-based catalyst, which comprises the following steps:

[0007] Mixing a polymer solution, a conductive agent, and a zeolite imidazolate framework material to obtain an electrospinning solution.

[0008] The electrostatic spinning solution is electrostatically spun, and then heat treated to obtain the composite nanofiber containing metal nanoparticles or metal oxide nanoparticles.

[0009] The composite nanofiber, a platinum source and an organic solvent are mixed to perform a reduction reaction, and the platinum-based catalyst is obtained.

[0010] The polymer solution, the conductive agent and the zeolitic imidazolate framework material are mixed, and the uniform distribution of the components in the nanoscale is ensured by means of the electrostatic spinning technology, which is beneficial to the formation of a stable and efficient three-phase interface; the composite nanofiber after heat treatment has a unique microstructure, in which the carbon fiber matrix formed by the carbonization of the polymer can provide a good electronic conduction channel, the zeolitic imidazolate framework material forms a high specific surface porous structure, and metal nanoparticles or metal oxide nanoparticles are converted, and the binding force between the conductive agent, the carbon fiber matrix and the nanoparticles is stronger; further, the platinum particles are loaded and combined with the metal nanoparticles or the metal oxide nanoparticles, so that the catalyst exposes more active sites, which is beneficial to the efficient promotion of the catalytic reaction. When applied in a fuel cell, the power density and the durability of the cell can be significantly improved.

[0011] Preferably, the polymer solution contains a fiber matrix material.

[0012] Preferably, the fiber matrix material includes any one of (PVDF), polyacrylonitrile (PAN), polyvinyl alcohol (PVA) or polyacrylic acid (PAA) or a combination of at least two thereof.

[0013] It should be noted that the organic solvent in the polymer solvent can be selected according to the solubility of the fiber matrix material, for example, PVDF can select a mixed solvent of N,N-dimethylformamide (DMF) and acetone, and PAN can select DMF, etc.

[0014] Preferably, the mass fraction of the polymer solution is 5-20%, for example, it can be 5%, 10%, 15% or 20%, etc.

[0015] Preferably, the conductive agent includes any one of carbon black, graphene, carbon nanotube or mesoporous carbon material or a combination of at least two thereof.

[0016] Preferably, the zeolitic imidazolate framework material includes any one of Co-ZIF, ZnCo-ZIF or Zn-ZIF.

[0017] Preferably, the mass ratio of the fiber matrix material to the conductive agent is 10:(0.1-5), for example, it can be 10:0.1, 10:0.5, 10:1, 10:2, 10:3, 10:4 or 10:5, etc.

[0018] In the present application, the mass ratio of the fiber matrix material and the conductive agent directly affects the electrical conductivity, specific surface area and platinum dispersion of the platinum-based catalyst, and a suitable ratio can optimize the three-dimensional structure of the electrode and improve the catalytic performance.

[0019] Preferably, the mass ratio of the fiber matrix material and the zeolitic imidazolate framework material is 10:(0.1-10), for example, it can be 10:0.1, 10:0.5, 10:1, 10:2, 10:3, 10:4, 10:5, 10:6, 10:7, 10:8, 10:9 or 10:10, etc.

[0020] In the present application, a suitable mass ratio of the fiber matrix material and the zeolitic imidazolate framework material helps to maintain the integrity of the nanofiber structure and reduce the generation of defects, improve the dispersion and stability of ZIF, adjust the pore structure, and enhance the catalytic activity.

[0021] Preferably, the mixing process is accompanied by stirring.

[0022] Preferably, the stirring method includes ultrasonic dispersion and / or mechanical stirring.

[0023] Preferably, the mixing method includes:

[0024] The polymer solution and the conductive agent are mixed, and then the zeolitic imidazolate framework material is added for mixing.

[0025] Preferably, the electrospinning parameters include:

[0026] The voltage is 10-30kV, for example, it can be 10kV, 15kV, 20kV, 25kV or 30kV, etc., the solution flow rate is 0.5-2mL / h, for example, it can be 0.5mL / h, 1mL / h, 1.5mL / h, 2mL / h, etc., the ambient temperature is 20-30℃, for example, it can be 20℃, 25℃ or 30℃, etc., the relative humidity is 30-60%, for example, it can be 30%, 40%, 50% or 60%, etc., the distance between the injection device and the receiving device is 10-20cm, for example, it can be 10cm, 15cm or 20cm, etc., the rotational speed of the receiving device is 200-500rpm, for example, it can be 200rpm, 300rpm, 400rpm or 500rpm, etc.

[0027] Under the joint limitation of the above parameters, the present application can ensure the uniformity and stability of the prepared fibers, improve the uniformity of fiber diameter and mechanical strength.

[0028] Preferably, the heat treatment is a step heat treatment, including a first heat treatment and a second heat treatment performed in sequence, the temperature of the first heat treatment is greater than the temperature of the second heat treatment.

[0029] Preferably, the temperature of the first heat treatment is 500-1000℃, for example, it can be 500℃, 600℃, 700℃, 800℃, 900℃ or 1000℃, etc., the holding time is 1-5h, for example, it can be 1h, 2h, 3h, 4h or 5h, etc., and the atmosphere is an inert atmosphere. For example, it can be a nitrogen atmosphere or an argon atmosphere, etc.

[0030] Preferably, the temperature of the second heat treatment is 150-250℃, for example, it can be 150℃, 200℃ or 250℃, etc., the holding time is 0.5-1.5h, for example, it can be 0.5h, 1h or 1.5h, etc., and the atmosphere is a reducing atmosphere. For example, it can be a hydrogen atmosphere, etc.

[0031] In the present application, the heat treatment is performed in a gradient cooling manner, the first heat treatment is performed in an inert atmosphere, which can stabilize the carbonization of the nanofiber matrix material, and at the same time, the ZIF structure is pyrolyzed to form a porous dodecahedron structure, thereby improving the porosity; the second heat treatment is performed in a reducing atmosphere, which can reduce the metal oxide to a metal with higher catalytic activity, remove the unstable surface oxygen-containing functional groups, optimize the interaction between the metal and the carbon nanofiber carrier, and improve the stability.

[0032] Preferably, the diameter of the composite nanofiber is 1-5μm, for example, it can be 1μm, 2μm, 3μm, 4μm or 5μm, etc.

[0033] Preferably, the composite nanofiber is a porous structure.

[0034] In the present application, the composite nanofiber is a porous structure, which can provide a good electronic conduction channel.

[0035] Preferably, the platinum source includes any one or a combination of at least two of chloroplatinates, platinum nitrate, platinum sulfate or platinum acetate.

[0036] Preferably, the chloroplatinates include chloroplatinic acid hexahydrate.

[0037] Preferably, the reduction reaction is a microwave reduction reaction.

[0038] Preferably, the parameters of the microwave reduction reaction include:

[0039] The microwave power is 400-600W, for example, can be 400W, 500W or 600W, etc., the reaction temperature is 100-200℃, for example, can be 100℃, 120℃, 140℃, 160℃, 180℃ or 200℃, etc., the holding time is 5-15min, for example, can be 5min, 10min or 15min, etc.

[0040] Preferably, the process of mixing the polymer solution, the conductive agent and the zeolitic imidazolate framework material also adds a modifier, and the modifier includes graphene quantum dots.

[0041] In the application, after the introduction of graphene quantum dots, it can be strongly combined with the zeolitic imidazolate framework material through π-π interaction, and after heat treatment, it can form an "ion-electron dual channel" network, which is conducive to optimizing the three-phase interface and improving the mass transfer rate of the catalyst.

[0042] Preferably, the mass ratio of the graphene quantum dots to the zeolitic imidazolate framework material is (0.05-0.3):1, for example, can be 0.05:1, 0.1:1, 0.15:1, 0.2:1, 0.25:1 or 0.3:1, etc.

[0043] In the application, if the mass ratio of graphene quantum dots to zeolitic imidazolate framework material is too small, the graphene quantum dots are dispersed and isolated, and cannot form an effective electron channel, and the electron conduction resistance increases; if the mass ratio of graphene quantum dots to zeolitic imidazolate framework material is too large, it will lead to the collapse of the porous structure after carbonization and destroy the ion transport channel.

[0044] Preferably, the preparation method comprises the following steps:

[0045] (1) The cobalt-based metal salt solution (for example, can be Co(NO3)2·6H2O solution, etc.), zinc-based metal salt solution (for example, can be Zn(NO3)2·6H2O solution, etc.), ligand (for example, can be 2-methyl imidazole, etc.) and basic control agent are mixed and reacted to obtain Co-ZIF powder; wherein the basic control agent includes triethylamine.

[0046] (2) The fiber matrix material and the organic solvent are stirred and mixed to obtain a polymer solution with a mass fraction of 5-20%.

[0047] The polymer solution and the conductive agent are mixed, the Co-ZIF powder is added after ultrasonic dispersion for 30-120 min (for example, 30 min, 50 min, 70 min, 90 min or 120 min, etc.) and mechanical stirring for 1-6 h (for example, 1 h, 2 h, 3 h, 4 h, 5 h or 6 h, etc.), and then ultrasonic dispersion for 20-60 min (for example, 20 min, 30 min, 40 min, 50 min or 60 min, etc.) and mechanical stirring for 0.5-3 h (for example, 0.5 h, 1 h, 2 h or 3 h, etc.) to obtain an electrospinning solution.

[0048] (3) The electrospinning solution is electrospun, and then subjected to a ladder-type heat treatment to obtain a composite nanofiber containing metal nanoparticles or metal oxide nanoparticles.

[0049] The parameters of the electrospinning include that the voltage is 10-30 kV, the solution flow rate is 0.5-2 mL / h, the ambient temperature is 20-30 DEG C, the relative humidity is 30-60%, and the distance between the injection device and the receiving device is 10-20 cm; the ladder-type heat treatment includes a first-order heat treatment and a second-order heat treatment performed in sequence; the temperature of the first-order heat treatment is 500-1000 DEG C, the holding time is 1-5 h, and the atmosphere is an inert atmosphere; the temperature of the second-order heat treatment is 150-250 DEG C, the holding time is 0.5-1.5 h, and the atmosphere is a reducing atmosphere.

[0050] (4) The composite nanofiber is ground, dispersed in an organic solvent, and then a platinum source is added, ultrasonic dispersion and mechanical stirring are performed, a pH adjusting agent (for example, a sodium hydroxide solution, etc.) is added to adjust the pH to 9-12 (for example, 9, 10, 11 or 12, etc.), a microwave reduction reaction is performed, the solution is cooled to room temperature after the reaction is completed, an acid solution (for example, a nitric acid solution, etc.) is used to adjust the pH of the solution to 2-3 (for example, 2, 2.2, 2.4, 2.6, 2.8 or 3, etc.), washed, dried, and a platinum-based catalyst is obtained.

[0051] The parameters of the microwave reduction reaction include that the microwave power is 400-600 W, the reaction temperature is 100-200 DEG C, and the holding time is 5-15 min.

[0052] The purpose of introducing the zinc-based metal salt solution in the preparation of the Co-ZIF powder is to form an ordered MOF framework as a template so that the cobalt ions are replaced by Zn at the original position to obtain Co-ZIF.

[0053] The basic regulating agent introduced in the application is a weak base, which can promote the deprotonation of the ligand, inhibit the hydrolysis of cobalt ions, and ensure the uniform replacement of cobalt ions on the zinc site.

[0054] In the second aspect, the application provides a platinum-based catalyst prepared by the preparation method of the first aspect.

[0055] In the third aspect, the application provides the use of the platinum-based catalyst of the second aspect in a cathode catalyst layer of a proton exchange membrane fuel cell.

[0056] Preferably, in the cathode catalyst layer, the loading of the metal or metal oxide other than platinum is 5-30wt%, for example, it can be 5wt%, 10wt%, 15wt%, 20wt%, 25wt% or 30wt% and the like.

[0057] In the application, the loading of the metal or metal oxide other than platinum in the cathode catalyst layer is limited to 5-30wt%, which is beneficial to reduce the cost of the catalyst layer while improving the catalytic performance of the catalyst layer.

[0058] The numerical range in the application not only includes the point values listed above, but also includes any point values between the above numerical ranges that are not listed. Due to the limited space and for the sake of simplicity, the application will not list the specific point values included in the range.

[0059] Compared with the prior art, the application has the following beneficial effects:

[0060] (1) In the application, the polymer solution, the conductive agent and the zeolite imidazolate framework material are mixed, and the uniform distribution of each component on the nanoscale can be ensured by the electrospinning technology, which is beneficial to form a stable and efficient three-phase interface; the composite nanofiber after heat treatment has a unique microstructure, in which the carbon fiber matrix formed by the carbonization of the polymer can provide a good electronic conduction channel, the zeolite imidazolate framework material forms a high specific surface porous structure, and metal nanoparticles or metal oxide nanoparticles are converted, and the binding force between the conductive agent, the carbon fiber matrix and the nanoparticles is stronger; further, after loading of platinum particles, the platinum particles are combined with the metal nanoparticles or the metal oxide nanoparticles, so that the catalyst exposes more active sites, which is beneficial to promote the efficient performance of the catalytic reaction.

[0061] (2) When the catalyst layer finally prepared based on the catalyst provided by the application is in contact with gas (such as oxygen, hydrogen) and liquid electrolyte in the actual application in energy conversion or storage devices, due to the porous structure of the fiber and the reasonable distribution of each component, the catalyst layer has higher catalytic activity and stability, so that an efficient three-phase interface can be formed, the catalytic reaction is promoted, and the power density and durability of the battery can be significantly improved. BRIEF DESCRIPTION OF DRAWINGS

[0062] Figure 1 SEM image of the surface of the cathode catalytic layer prepared in Example 1 of the present application.

[0063] Figure 2 TEM image of the cathode catalytic layer prepared in Example 1 of the present application.

[0064] Figure 3 HRTEM image of the cathode catalytic layer prepared in Example 1 of the present application.

[0065] Figure 4 Single cell performance comparison chart of the fuel cell prepared based on Example 1 and Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0066] The technical solutions of the present application will be further illustrated by specific embodiments. It should be understood by those skilled in the art that the embodiments are only to help understand the present application and should not be regarded as specific limitations of the present application.

[0067] It should be noted that the following room temperature refers to 25℃.

[0068] Example 1

[0069] The present embodiment provides a preparation method of a platinum-based catalyst, which comprises the following steps:

[0070] (1) 0.58 g of Co(NO3)2·6H2O was dissolved in 20 mL of methanol to obtain a Co(NO3)2·6H2O solution, 1.3 g of Zn(NO3)2·6H2O was dissolved in 30 mL of methanol to obtain a Zn(NO3)2·6H2O solution, and 3.3 g of 2-methylimidazole was dissolved in 50 mL of methanol to obtain a ligand solution.

[0071] The Co(NO3)2·6H2O solution, the Zn(NO3)2·6H2O solution, the ligand solution and 20 μL of triethylamine were mixed and allowed to stand for 2 h of reaction, and after the reaction was completed, washed with methanol for 2 times, and then dried at 70℃ to obtain a Co-ZIF powder.

[0072] (2) 10 g of PVDF was dissolved in a mixed solvent composed of 80 mL of DMF and 20 mL of acetone, and stirred and mixed at 50℃ for 3 h to obtain a polymer solution with a mass fraction of 10%.

[0073] The polymer solution and the conductive agent are mixed, the Co-ZIF powder is added and mixed after 60 min of ultrasonic dispersion and 3 h of mechanical stirring (temperature is 40℃), and the electrospinning solution is obtained after 60 min of ultrasonic dispersion and 3 h of mechanical stirring (temperature is 40℃).

[0074] The conductive agent is conductive carbon black, the mass ratio of PVDF and the conductive agent is 10:0.5, and the mass ratio of PVDF and the Co-ZIF powder is 10:0.5.

[0075] (3) The electrospinning solution is loaded into a metal needle syringe with an inner diameter of 0.5 mm, a high-voltage power supply of 15 kV is connected, electrospinning is performed on an aluminum foil receiving device, and then a stepwise heat treatment is performed to obtain a composite nanofiber containing Co nanoparticles.

[0076] The parameters of the electrospinning include: a solution flow rate of 1 mL / h, an ambient temperature of 25℃, a relative humidity of 40%, a distance between the injection device and the receiving device of 15 cm, and a rotating speed of the receiving device of 300 rpm; the stepwise heat treatment includes a first-order heat treatment and a second-order heat treatment performed in sequence; the temperature of the first-order heat treatment is 700℃, the holding time is 3 h, and the atmosphere is a nitrogen atmosphere; the temperature of the second-order heat treatment is 200℃, the holding time is 1 h, and the atmosphere is a hydrogen atmosphere; the diameter of the composite nanofiber is 2 μm; and the composite nanofiber has a porous structure.

[0077] (4) The composite nanofiber is ground and then added to 2 L of ethylene glycol for dispersion, 1.5 g of chloroplatinic acid hexahydrate is then added, ultrasonic dispersion is performed for 30 min and mechanical stirring is performed for 1.5 h, a sodium hydroxide solution is then added to adjust the pH to 10, and then the mixture is transferred to a microwave reactor for microwave reduction reaction, the solution is cooled to room temperature after the reaction is completed, a 5 mol / L nitric acid solution is then used to adjust the pH of the solution to 3, and then the mixture is stirred with ultrapure water for 30 min, followed by suction filtration and washing until the conductivity of the filtrate is 100 μS / cm, the filter cake is dried, and a platinum-based catalyst is obtained.

[0078] The parameters of the microwave reduction reaction include: a microwave power of 500 W, a reaction temperature of 150℃, and a holding time of 10 min.

[0079] The embodiment also provides a cathode catalyst layer, which comprises the platinum-based catalyst as described above; in the cathode catalyst layer, the loading amount of Co is 15 wt%.

[0080] Figure 1 A surface SEM image of the cathode catalyst layer prepared in the embodiment is shown, and it can be known from the image that a stable and continuous nanofiber structure is formed.

[0081] Figure 2 The TEM image of the cathode catalytic layer prepared in the embodiment is shown, and it can be seen from the image that the catalyst particles are uniformly exposed on the surface of the nanofiber, which is beneficial to form a good three-phase interface.

[0082] Figure 3 The HRTEM image of the cathode catalytic layer prepared in the embodiment is shown, and alloy nanoparticles can be clearly observed, and the catalyst particles are not agglomerated.

[0083] Embodiment 2

[0084] The embodiment provides a preparation method of a platinum-based catalyst, and the preparation method comprises the following steps:

[0085] (1) 0.58 g of Co(NO3)2·6H2O is dissolved in 20 mL of methanol to obtain a Co(NO3)2·6H2O solution, 1.3 g of Zn(NO3)2·6H2O is dissolved in 30 mL of methanol to obtain a Zn(NO3)2·6H2O solution, and 3.3 g of 2-methylimidazole is dissolved in 50 mL of methanol to obtain a ligand solution.

[0086] The Co(NO3)2·6H2O solution, the Zn(NO3)2·6H2O solution, the ligand solution and 20 μL of triethylamine are mixed, and the reaction is allowed to stand for 2 h, then washed with methanol twice, and then dried at 70 ℃ to obtain a Co-ZIF powder.

[0087] (2) 5 g of PVDF is dissolved in a mixed solvent composed of 80 mL of DMF and 20 mL of acetone, and the mixture is stirred at 50 ℃ for 3 h to obtain a polymer solution with a mass fraction of 5%.

[0088] The polymer solution and the conductive agent are mixed, and after ultrasonic dispersion for 30 min and mechanical stirring (at a temperature of 40 ℃) for 6 h, the Co-ZIF powder is added and mixed, and after ultrasonic dispersion for 20 min and mechanical stirring (at a temperature of 40 ℃) for 3 h, an electrospinning solution is obtained.

[0089] The conductive agent is graphene, the mass ratio of PVDF to the conductive agent is 10:2, and the mass ratio of PVDF to the Co-ZIF powder is 10:2.

[0090] (3) The electrospinning solution is loaded into a metal needle syringe with an inner diameter of 0.5 mm, a high-voltage power supply of 10 kV is connected, electrospinning is performed on an aluminum foil receiving device, and then stepwise heat treatment is performed to obtain composite nanofibers containing Co nanoparticles.

[0091] The electrostatic spinning parameter includes: a solution flow rate is 0.5 mL / h, an ambient temperature is 25 DEG C, a relative humidity is 30%, a distance between an injection device and a receiving device is 10 cm, and a rotating speed of the receiving device is 200 rpm; the stepwise heat treatment includes a first-order heat treatment and a second-order heat treatment which are sequentially performed; the first-order heat treatment has a temperature of 500 DEG C, a holding time of 5 h, and a nitrogen atmosphere; the second-order heat treatment has a temperature of 150 DEG C, a holding time of 1.5 h, and a hydrogen atmosphere; the composite nanofiber has a diameter of 1 micron; and the composite nanofiber has a porous structure.

[0092] (4) The composite nanofiber is ground and then added into 2 L of ethylene glycol for dispersion, and then 1.5 g of chloroplatinic acid hexahydrate is added, after ultrasonic dispersion for 30 min and mechanical stirring for 1.5 h, a sodium hydroxide solution is added to adjust the pH to 9, and then the mixture is transferred into a microwave reactor for microwave reduction reaction, after the reaction is completed, the temperature is lowered to room temperature, then a 5 mol / L nitric acid solution is used to adjust the pH of the solution to 3, and then after stirring with ultrapure water for 30 min, the mixture is filtered and washed until the conductivity of the filtrate is 100 muS / cm, and then the filter cake is dried to obtain a platinum-based catalyst.

[0093] The microwave reduction reaction parameter includes: a microwave power is 400 W, a reaction temperature is 100 DEG C, and a holding time is 15 min.

[0094] The embodiment also provides a cathode catalytic layer, which comprises the platinum-based catalyst as described above; in the cathode catalytic layer, the loading amount of Co is 20 wt%.

[0095] Example 3

[0096] The embodiment provides a preparation method of a platinum-based catalyst, which comprises the following steps:

[0097] (1) 2.32 g of Co(NO3)2·6H2O is dissolved in 80 mL of methanol to obtain a Co(NO3)2·6H2O solution, 5.2 g of Zn(NO3)2·6H2O is dissolved in 120 mL of methanol to obtain a Zn(NO3)2·6H2O solution, and 13.2 g of 2-methylimidazole is dissolved in 200 mL of methanol to obtain a ligand solution.

[0098] The Co(NO3)2·6H2O solution, the Zn(NO3)2·6H2O solution, the ligand solution and 80 muL of triethylamine are mixed and subjected to a standing reaction for 2 h, after the reaction is completed, the mixture is washed with methanol twice, and then dried at 70 DEG C to obtain a Co-ZIF powder.

[0099] (2) 20 g of PAN was dissolved in 100 mL of DMF organic solvent, and the mixture was stirred at 50℃ for 3 h to obtain a polymer solution with a mass fraction of 20%.

[0100] The polymer solution and the conductive agent were mixed, and after 120 min of ultrasonic dispersion and 1 h of mechanical stirring (at a temperature of 40℃), the Co-ZIF powder was added and mixed, and after 40 min of ultrasonic dispersion and 1.5 h of mechanical stirring (at a temperature of 40℃), an electrospinning solution was obtained.

[0101] The conductive agent is mesoporous carbon, the mass ratio of PAN to the conductive agent is 10:5, and the mass ratio of PAN to the Co-ZIF powder is 10:5.

[0102] (3) The electrospinning solution was loaded into a metal needle syringe with an inner diameter of 0.5 mm, connected to a high-voltage power supply of 30 kV, and electrospun on an aluminum foil receiving device, followed by stepwise heat treatment to obtain a composite nanofiber containing Co nanoparticles.

[0103] The parameters of the electrospinning include a solution flow rate of 2 mL / h, an ambient temperature of 30℃, a relative humidity of 60%, a distance between the injection device and the receiving device of 20 cm, and a rotating speed of the receiving device of 500 rpm. The stepwise heat treatment includes a first-order heat treatment and a second-order heat treatment performed in sequence. The temperature of the first-order heat treatment is 1000℃, the holding time is 1 h, and the atmosphere is nitrogen atmosphere. The temperature of the second-order heat treatment is 250℃, the holding time is 0.5 h, and the atmosphere is hydrogen atmosphere. The diameter of the composite nanofiber is 2.5 μm. The composite nanofiber has a porous structure.

[0104] (4) The composite nanofiber was ground and then added to 2 L of ethylene glycol for dispersion, followed by the addition of 5 g of chloroplatinic acid hexahydrate, 30 min of ultrasonic dispersion, and 1.5 h of mechanical stirring. Then, a sodium hydroxide solution was added to adjust the pH to 12, and the mixture was transferred to a microwave reactor for microwave reduction reaction. After the reaction was completed, the temperature was lowered to room temperature. Then, a 5 mol / L nitric acid solution was used to adjust the pH of the solution to 2. After stirring with ultrapure water for 30 min, the mixture was filtered and washed until the conductivity of the filtrate was 100 μS / cm. The filter cake was dried to obtain a platinum-based catalyst.

[0105] The parameters of the microwave reduction reaction include a microwave power of 600 W, a reaction temperature of 200℃, and a holding time of 5 min.

[0106] The embodiment also provides a cathode catalyst layer, which comprises the platinum-based catalyst as described above. In the cathode catalyst layer, the loading of Co is 30 wt%.

[0107] Example 4

[0108] The difference between this example and Example 1 is that graphene quantum dots are added in the process of adding the Co-ZIF powder for mixing in step (2), and the mass ratio of the graphene quantum dots to the Co-ZIF powder is 0.15:1.

[0109] The rest of the preparation method and parameters remain consistent with Example 1.

[0110] Example 5

[0111] The difference between this example and Example 1 is that graphene quantum dots are added in the process of adding the Co-ZIF powder for mixing in step (2), and the mass ratio of the graphene quantum dots to the Co-ZIF powder is 0.05:1.

[0112] The rest of the preparation method and parameters remain consistent with Example 1.

[0113] Example 6

[0114] The difference between this example and Example 1 is that graphene quantum dots are added in the process of adding the Co-ZIF powder for mixing in step (2), and the mass ratio of the graphene quantum dots to the Co-ZIF powder is 0.3:1.

[0115] The rest of the preparation method and parameters remain consistent with Example 1.

[0116] Example 7

[0117] The difference between this example and Example 4 is that the mass ratio of the graphene quantum dots to the Co-ZIF powder is 0.5:1.

[0118] The rest of the preparation method and parameters remain consistent with Example 4.

[0119] Example 8

[0120] The difference between this example and Example 1 is that the mass ratio of the PVDF to the conductive agent in step (2) is 10:20.

[0121] The rest of the preparation method and parameters remain consistent with Example 1.

[0122] Example 9

[0123] The difference between this example and Example 1 is that the mass ratio of the PVDF to the conductive agent in step (2) is 10:0.05.

[0124] The rest of the preparation method and parameters remain consistent with Example 1.

[0125] Example 10

[0126] The difference between this example and Example 1 is that the relative humidity in the electrospinning parameters in step (3) is 20%.

[0127] The rest of the preparation method and parameters remain the same as in Example 1.

[0128] Example 11

[0129] The difference between this example and Example 1 is that the relative humidity in the electrospinning parameters in step (3) is 70%.

[0130] The rest of the preparation method and parameters remain the same as in Example 1.

[0131] Example 12

[0132] The difference between this example and Example 1 is that the step (3) ladder heat treatment is replaced by one-step heat treatment, the temperature is 700℃, the holding time is 4h, and the atmosphere is air atmosphere.

[0133] The rest of the preparation method and parameters remain the same as in Example 1.

[0134] Example 13

[0135] The difference between this example and Example 1 is that the step (3) ladder heat treatment is replaced by one-step heat treatment, the temperature is 700℃, the holding time is 4h, and the atmosphere is air atmosphere.

[0136] The rest of the preparation method and parameters remain the same as in Example 1.

[0137] Comparative Example 1

[0138] This comparative example provides a commercial catalyst, which is a Pt / C catalyst (the mass ratio of platinum is 60wt%).

[0139] This comparative example also provides a preparation method of a catalytic layer, which comprises the following steps:

[0140] (1) Take 0.5g of the Pt / C catalyst, add 3.5g of water, 2.8g of Nafion and 65.9g of ethanol, then perform cell crushing treatment for 40min, and then ultrasonic dispersion for 30min to obtain a catalytic layer slurry.

[0141] (2) Spray the catalytic layer slurry on both sides of the proton exchange membrane, and dry to obtain a catalytic layer.

[0142] Figure 4The single cell performance comparison chart of the fuel cell prepared based on the catalyst layer prepared in Example 1 and Comparative Example 1 of the present application is shown in the figure, and it can be seen from the figure that the peak power density of the membrane electrode prepared in the present application is significantly greater than that of Comparative Example 1, and the single cell performance is better than that of Comparative Example 1 as a whole.

[0143] Performance test

[0144] Based on the catalyst layer prepared in the above examples and comparative examples, a proton exchange membrane fuel cell was prepared, and then power density and durability tests were performed.

[0145] The test method of power density and durability refers to GB / T 20042.5-2024 Proton Exchange Membrane Fuel Cell Part 5: Membrane Electrode Test Method.

[0146] The test results are shown in Table 1.

[0147] Table 1

[0148]

[0149] Analysis:

[0150] As can be seen from Table 1, when the catalyst layer finally prepared based on the catalyst provided in the present application is used in a proton exchange membrane fuel cell, due to the porous structure of the fiber and the reasonable distribution of the components, the catalyst layer has higher catalytic activity and stability, so that a high-efficiency three-phase interface can be formed to promote the catalytic reaction, and the power density and durability of the cell can be significantly improved.

[0151] As can be seen from the comparison between Example 1 and Example 4, if graphene quantum dots are also added during the mixing process of step (2) of adding the Co-ZIF powder, they can be strongly combined with Co-ZIF through π-π interaction, and after heat treatment, a "ion-electron dual channel" network can be formed, which is beneficial to optimizing the three-phase interface and improving the mass transfer rate of the catalyst, and ultimately the power density and durability of the cell can be further improved.

[0152] As can be seen from the comparison between Example 4 and Example 7, if the mass ratio of graphene quantum dots and Co-ZIF powder is too large, i.e., the amount of graphene quantum dots added is too much, it will cause the collapse of the porous structure after carbonization, destroy the ion transport channel, and affect the improvement of the power density and durability of the cell.

[0153] It can be seen from the comparison of Example 1 and Examples 8-9 that if the mass ratio of PVDF and conductive agent in step (2) is too small, i.e. the conductive agent is too much, the nano-fiber structure will be destroyed, the porous structure will be blocked, the mass transfer effect will be affected, and then the battery performance and durability will be affected; if the mass ratio of PVDF and conductive agent in step (2) is too large, i.e. the conductive agent is too little, the Pt active sites will be annihilated, the electronic conductivity of the catalyst will be affected, and the performance of the catalyst layer will be reduced.

[0154] It can be seen from the comparison of Example 1 and Examples 10-11 that if the relative humidity in the electrospinning parameters is too small, the spinning process will occur, the uniform and complete nano-fiber layer cannot be obtained, the pore structure will collapse after carbonization, and the power density and durability improvement of the battery will be affected; if the relative humidity in the electrospinning parameters is too large, liquid leakage, dripping and other phenomena will occur, the nano-fiber structure will have a curtain-shaped defect, the catalyst particle loading after carbonization will be affected, the catalyst activity will be reduced, and the battery performance will be affected.

[0155] It can be seen from the comparison of Example 1 and Examples 12-13 that if the stepwise heat treatment is replaced by one-step heat treatment, the metal oxide cannot be reduced to a metal with higher catalytic activity, the catalytic activity is reduced, and the surface oxygen-containing functional groups increase the instability of the catalyst; if the two-step heat treatment is performed first, and then the one-step heat treatment is performed, the Co-ZIF will not be reduced completely, and the surface functional groups cannot be removed; when the one-step heat treatment is performed, part of the reduced Co may sinter, the bonding force between the metal and the carrier is poor, and the durability of the battery is reduced.

[0156] It can be seen from the comparison of Example 1 and Comparative Example 1 that in the conventional commercial Pt / C catalyst, the platinum utilization rate is low, the peak power of the battery is low, and the durability is poor.

[0157] It should be noted that the process method of the present application is illustrated by the above examples, but the present application is not limited to the above process steps, i.e. it does not mean that the present application must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvement of the present application, equivalent replacement of the materials selected by the present application, addition of auxiliary ingredients, selection of specific methods, etc. fall within the scope of protection and disclosure of the present application.

Claims

1. A method for the preparation of a platinum-based catalyst, characterized in that, The preparation method comprises the following steps: mixing a polymer solution, a conductive agent and a zeolitic imidazolate framework material to obtain an electrospinning solution; electrospinning the electrospinning solution and then performing heat treatment to obtain a composite nanofiber containing metal nanoparticles or metal oxide nanoparticles; the heat treatment is stepwise heat treatment, comprising first-order heat treatment and second-order heat treatment performed in sequence, the temperature of the first-order heat treatment is higher than that of the second-order heat treatment; the atmosphere of the first-order heat treatment is inert atmosphere; the atmosphere of the second-order heat treatment is reducing atmosphere; the diameter of the composite nanofiber is 1-5 μm; mixing the composite nanofiber, a platinum source and an organic solvent to perform a reduction reaction to obtain the platinum-based catalyst; the polymer solution contains a fiber matrix material; the fiber matrix material comprises any one or a combination of at least two of polyvinylidene fluoride, polyacrylonitrile, polyvinyl alcohol or polyacrylic acid; the zeolitic imidazolate framework material is Co-ZIF.

2. The production method according to claim 1, characterized by, the mass fraction of the polymer solution is 5-20%; and / or, the conductive agent comprises any one or a combination of at least two of carbon black, graphene, carbon nanotube or mesoporous carbon material; and / or, the mass ratio of the fiber matrix material to the conductive agent is 10:(0.1-5); and / or, the mass ratio of the fiber matrix material to the zeolitic imidazolate framework material is 10:(0.1-10).

3. The preparation method according to claim 1, characterized in that, the mixing process is accompanied by stirring; the stirring mode comprises ultrasonic dispersion method and / or mechanical stirring method; and / or, the mixing mode comprises: mixing a polymer solution and a conductive agent, and then adding a zeolitic imidazolate framework material for mixing.

4. The production method according to claim 1, characterized by, the parameters of the electrospinning comprise: the voltage is 10-30 kV, the solution flow rate is 0.5-2 mL / h, the ambient temperature is 20-30 ℃, the relative humidity is 30-60%, the distance between the injection device and the receiving device is 10-20 cm, and the rotating speed of the receiving device is 200-500 rpm.

5. The preparation method according to claim 1, characterized in that, the temperature of the first-order heat treatment is 500-1000 ℃, and the holding time is 1-5 h; and / or, the temperature of the second-order heat treatment is 150-250 ℃, and the holding time is 0.5-1.5 h; and / or, the composite nanofiber is a porous structure.

6. The method of claim 1, wherein, the platinum source comprises any one or a combination of at least two of chloroplatinates, platinum nitrate, platinum sulfate or platinum acetate; the chloroplatinates comprise chloroplatinic acid hexahydrate; and / or, the reduction reaction is a microwave reduction reaction; and / or, the parameters of the microwave reduction reaction comprise: the microwave power is 400-600 W, the reaction temperature is 100-200 ℃, and the holding time is 5-15 min.

7. The preparation method according to claim 1, characterized in that, a modifier is added during the mixing of the polymer solution, the conductive agent and the zeolitic imidazolate framework material, and the modifier comprises graphene quantum dots; and / or, the mass ratio of the graphene quantum dots to the zeolitic imidazolate framework material is (0.05-0.3):

1.

8. The method of claim 1, wherein, the preparation method comprises the following steps: (1) mixing a cobalt-based metal salt solution, a zinc-based metal salt solution, a ligand and a basic control reagent to react, to obtain a Co-ZIF powder; wherein the basic control reagent comprises triethylamine; (2) mixing a fiber matrix material and an organic solvent to obtain a polymer solution with a mass fraction of 5-20%; mixing the polymer solution and a conductive agent, after ultrasonic dispersion for 30-120 min and mechanical stirring for 1-6 h, adding the Co-ZIF powder to mix, after ultrasonic dispersion for 20-60 min and mechanical stirring for 0.5-3 h, to obtain an electrospinning solution; (3) electrospinning the electrospinning solution, and then performing ladder-type heat treatment, to obtain a composite nanofiber containing metal nanoparticles or metal oxide nanoparticles; wherein the parameters of electrospinning include: a voltage of 10-30 kV, a solution flow rate of 0.5-2 mL / h, an ambient temperature of 20-30℃, a relative humidity of 30-60%, and a distance between an injection device and a receiving device of 10-20 cm; the ladder-type heat treatment comprises a first-order heat treatment and a second-order heat treatment performed in sequence; the temperature of the first-order heat treatment is 500-1000℃, the holding time is 1-5 h, and the atmosphere is an inert atmosphere; the temperature of the second-order heat treatment is 150-250℃, the holding time is 0.5-1.5 h, and the atmosphere is a reducing atmosphere; (4) grinding the composite nanofiber, then dispersing it in an organic solvent, subsequently adding a platinum source, after ultrasonic dispersion and mechanical stirring, adding a pH adjusting agent to adjust the pH to 9-12, performing a microwave reduction reaction, after the reaction, cooling to room temperature, then using an acid solution to adjust the pH of the solution to 2-3, washing, drying, to obtain a platinum-based catalyst; wherein the parameters of the microwave reduction reaction include: a microwave power of 400-600 W, a reaction temperature of 100-200℃, and a holding time of 5-15 min.

9. A platinum-based catalyst characterized in that, The platinum-based catalyst is prepared by the preparation method of any one of claims 1-8.

10. A proton exchange membrane fuel cell characterized by The cathode catalyst layer of the proton exchange membrane fuel cell comprises the platinum-based catalyst of claim 9. In the cathode catalyst layer, the loading of metals or metal oxides other than platinum is 5-30 wt%.

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