A silicon carbide whisker-carbon nanofiber composite fuel cell catalyst and its preparation method

Abstract

The present invention discloses a preparation method of a silicon carbide whisker-carbon nanofiber composite fuel cell catalyst, comprising the following steps: respectively weighing silicon powder, graphite powder and cobalt tetroxide powder and mixing them to obtain a first mixture; mixing the first mixture evenly with a solvent, adding polyvinylidene fluoride, grinding evenly and then drying to obtain a second mixture; shaping the second mixture and placing it in a calcination device, calcining it under a mixed atmosphere of argon, hydrogen and methane, and cooling to obtain a finished product. The preparation method provided by the present invention can effectively reduce the use of Pt, reduce the catalyst preparation cost, and is suitable for its large-scale application. The prepared silicon carbide whisker-carbon nanofiber composite fuel cell catalyst has high oxygen reduction activity and can effectively improve the catalytic reaction efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and particularly to a silicon carbide whisker-carbon nanofiber composite fuel cell catalyst and a preparation method thereof. Background Art

[0002] Among many new energy sources, as a driving device for energy vehicles, fuel cells have the advantages of high efficiency, high energy conversion rate, and zero emission of harmful gases by directly converting chemical energy into electrical energy. Since water and a small amount of heat are the only by-products during the reaction process without carbon emissions, fuel cells are of great significance in the process of reducing carbon emissions and achieving "carbon neutrality". However, the reaction rates of the two half-reactions of fuel cells are different, which hinders the application of fuel cells. The anodic hydrogen oxidation reaction has a high current density, and its reaction overpotential can be almost ignored. On the contrary, the cathodic oxygen reduction reaction is very slow kinetically, and its reaction rate is about six orders of magnitude slower than the hydrogen oxidation reaction. Therefore, the oxygen reduction reaction is the most important catalytic process in fuel cell research.

[0003] Currently, commercially available Pt / C materials with high Pt metal loading are used as cathode catalytic materials in commerce to reduce the reaction overpotential and increase the reaction rate. However, the cost of the catalyst is high, accounting for about 40% of the total cost of fuel cells. In order to reduce costs and achieve large-scale application, it is necessary to minimize or avoid the use of platinum or platinum group metals as oxygen reduction catalysts in fuel cell production.

[0004] In current research, the development and design of non-precious metal electrocatalysts have received extensive attention. A large number of non-precious metal catalytic materials have been screened out, and these materials exhibit high catalytic activity and stability, such as metal oxides, metal sulfides, metal carbides, etc. The material cost is only a small part of that of precious metal electrocatalysts, enabling these electrocatalysts to be widely used in commercial fuel cells. Therefore, the development and research of new non-precious metal oxygen reduction catalysts are of great significance for controlling the cost of fuel cells and achieving the "carbon neutrality" goal.

[0005] Non-precious metal electrocatalysts include metal carbide catalysts, metal nitride catalysts, transition metal cluster catalysts, transition metal chelate catalysts, etc. Among them, metal carbide catalysts are known as "quasi-platinum catalysts". Silicon carbide whiskers are single crystal fibers with few defects and a certain aspect ratio. They are carbides with quite good high-temperature resistance and very high strength. Silicon carbide whiskers are often used as carriers for non-precious metal electrocatalysts due to their excellent properties. However, silicon carbide whiskers have the defect of insufficient conductivity and cannot obtain sufficient electron transport channels, resulting in slow reaction efficiency. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a preparation method of a silicon carbide whisker carbon nanofiber composite fuel cell catalyst, which can effectively reduce the preparation cost of the catalyst and is suitable for large-scale applications.

[0007] Another technical problem to be solved by the invention is to provide a silicon carbide whisker carbon nanofiber composite fuel cell catalyst, which has high oxygen reduction activity, good cycle stability and high anti-poisoning ability, and can effectively improve the catalytic reaction efficiency.

[0008] Another technical problem to be solved by the invention is to provide an application of a silicon carbide whisker carbon nanofiber composite fuel cell catalyst in a fuel cell, which can reduce the cost of the battery and improve the performance and stability of the battery.

[0009] To solve the above technical problems, the present invention provides a preparation method of a silicon carbide whisker carbon nanofiber composite fuel cell catalyst, which includes the following steps:

[0010] Weigh silicon powder, graphite powder and cobalt tetroxide powder respectively and mix them to obtain a first mixture;

[0011] Mix the first mixture evenly with a solvent, add polyvinylidene fluoride, grind evenly and then dry to obtain a second mixture;

[0012] After the second mixture is formed, it is placed in a calcination device and calcined in a mixed atmosphere of argon, hydrogen and methane, and the finished product is obtained after cooling.

[0013] In one embodiment, the mass ratio between the silicon powder and the graphite powder is 1:(1.2 - 2).

[0014] In one embodiment, the mass ratio between the cobalt tetroxide powder and the silicon powder is 1:(100 - 200).

[0015] In one embodiment, the solvent is selected as N-methylpyrrolidone.

[0016] In one embodiment, the addition amount ratio of the polyvinylidene fluoride to the addition amount of the silicon powder is 1:(80 - 100).

[0017] In one embodiment, the calcination temperature of the calcination is 1100°C - 1500°C, and the calcination time is 6h - 12h.

[0018] In one embodiment, in the mixed atmosphere of argon, hydrogen and methane, by volume ratio, argon:hydrogen:methane = (50 - 80):1:1.

[0019] To solve the above problems, the present invention provides a silicon carbide whisker-carbon nanofiber composite fuel cell catalyst, which is prepared by the preparation method of the silicon carbide whisker-carbon nanofiber composite fuel cell catalyst described above.

[0020] Correspondingly, the present invention also provides the application of the above-mentioned silicon carbide whisker-carbon nanofiber composite fuel cell catalyst in a fuel cell.

[0021] Implementing the present invention has the following beneficial effects:

[0022] The present invention provides a preparation method of a silicon carbide whisker-carbon nanofiber composite fuel cell catalyst. This method uses the high-temperature calcination method to directly prepare fluorine / cobalt-doped silicon carbide whiskers supporting carbon nanofibers in one step, and uses it as a fuel cell catalyst. The silicon carbide whisker-carbon nanofiber composite fuel cell catalyst prepared by the above method has the following advantages:

[0023] (1) The present invention avoids the use of Pt-based catalysts, greatly reducing the cost of fuel cell catalysts. At the same time, a one-dimensional fluorine / cobalt-doped silicon carbide whisker structure is designed. Fluorine comes from polyvinylidene fluoride, and cobalt comes from cobalt tetroxide powder. The introduction of heteroatoms will introduce defect structures in the dense lattice of silicon carbide, enhancing its reaction activity, catalyzing the cracking of oxygen, and improving its oxygen reduction catalytic ability.

[0024] (2) Compared with other non-precious metal electrocatalysts, the preparation method provided by the present invention is simple. By directly calcining in one step, a silicon carbide whisker-carbon nanofiber composite fuel cell catalyst with a structure of fluorine / cobalt-doped silicon carbide whiskers supporting carbon nanofibers is obtained. It has low cost, simple process parameters, and is convenient for large-scale industrial production, providing the possibility for the large-scale application of fuel cells.

[0025] (3) In the process of preparing silicon carbide whiskers, the present invention introduces cobalt and methane as the carbon nanofiber catalyst and carbon source respectively, loads a large amount of carbon nanofibers on the surface of silicon carbide whiskers, improves the defect of insufficient conductivity of single silicon carbide whiskers, constructs an electron rapid transmission channel, and enhances the reaction efficiency.

[0026] Therefore, the catalyst of the present invention can effectively reduce the use of precious metals, reduce costs, and has high oxygen reduction activity, good cycle stability, and high anti-poisoning ability, and can effectively improve the catalytic reaction efficiency. When it is used to make fuel cells, it can reduce the cost of the cells, improve the performance and stability of the cells, and greatly broaden the commercial application range of fuel cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a transmission electron microscope picture of the silicon carbide whisker-carbon nanofiber composite fuel cell catalyst prepared in Example 1 of the present invention;

[0028] Figure 2 This is the LSV curve of the oxygen reduction activity of the silicon carbide whisker-carbon nanofiber composite fuel cell catalyst obtained in Example 1 of the present invention. Detailed implementation manners

[0029] To make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below.

[0030] Unless otherwise stated or there are contradictions, the terms or phrases used in this article have the following meanings:

[0031] In the present invention, "its combination", "any combination thereof", "any combination mode thereof", etc. include all suitable combination modes of any two or more of the listed items.

[0032] In the present invention, "preferred" only describes the implementation manners or embodiments with better effects, and it should be understood that it does not constitute a limitation to the protection scope of the present invention.

[0033] In the present invention, among the technical features described in an open-ended manner, it includes a closed technical solution composed of the listed features, and also includes an open technical solution containing the listed features.

[0034] In the present invention, regarding the numerical range, unless otherwise specified, it includes the two endpoints of the numerical range.

[0035] Aiming at the defects of poor oxygen reduction reaction kinetics, insufficient cycle stability, low anti-poisoning ability and high cost of the existing fuel cell electrocatalyst, the present invention provides a preparation method of a silicon carbide whisker-carbon nanofiber composite fuel cell catalyst, including the following steps:

[0036] S1. Weigh silicon powder, graphite powder and cobalt tetroxide powder respectively and mix them to obtain a first mixture;

[0037] The silicon powder and the graphite powder are added to the formula to prepare silicon carbide whiskers. Excessive addition of the silicon powder or excessive addition of the graphite powder will result in ineffective formation of a stoichiometric structure of silicon carbide. In one implementation manner, the mass ratio between the silicon powder and the graphite powder is 1:(1.2 - 2).

[0038] The purpose of adding the cobalt tetroxide powder to the formula is to introduce cobalt, and the introduction of cobalt atoms has a dual effect. Firstly, cobalt atoms will introduce defect structures into the dense lattice of silicon carbide, enhance its reactivity, catalyze the cracking of oxygen, and improve the oxygen reduction catalytic ability. Secondly, cobalt is introduced as a carbon nanofiber catalyst during the preparation of silicon carbide whiskers to achieve the loading of a large amount of carbon nanofibers on the surface of silicon carbide whiskers, improve the defect of insufficient conductivity of single silicon carbide whiskers, construct an electron rapid transmission channel, and enhance the reaction efficiency. Excessive addition of the cobalt tetroxide powder will cause damage to the silicon carbide crystal structure and prevent the formation of complete silicon carbide whiskers; too little addition of the cobalt tetroxide powder will result in the inability to effectively improve the oxygen reduction catalytic ability of silicon carbide whiskers. In one embodiment, the mass ratio between the cobalt tetroxide powder and the silicon powder is 1:(100 - 200).

[0039] S2. Mix the first mixture with a solvent evenly, add polyvinylidene fluoride, grind evenly and then dry to obtain a second mixture.

[0040] In one embodiment, the solvent is selected as N-methylpyrrolidone. The addition of polyvinylidene fluoride not only acts as a binder, but more importantly, introduces fluorine atoms into the formula. The introduction of fluorine atoms will introduce defect structures into the dense lattice of silicon carbide, enhance its reactivity, catalyze the cracking of oxygen, and improve its oxygen reduction catalytic ability. Excessive addition of the polyvinylidene fluoride will lead to a decrease in the content of effective active substances in the synthesized product; too little addition of the polyvinylidene fluoride will result in the inability to effectively improve the oxygen reduction catalytic ability of silicon carbide whiskers. In one embodiment, the ratio of the addition amount of the polyvinylidene fluoride to the addition amount of the silicon powder is 1:(80 - 100).

[0041] Therefore, the present invention designs a one-dimensional fluorine / cobalt-doped silicon carbide whisker structure. The fluorine is derived from polyvinylidene fluoride, and the cobalt is derived from cobalt tetroxide powder. The fluorine and cobalt heteroatoms occupy different crystallographic positions in the silicon carbide crystal, introducing more defect structures into the dense lattice of silicon carbide compared with single-element doping, enhancing its reactivity, catalyzing the cracking of oxygen, and improving its oxygen reduction catalytic ability.

[0042] S3. After the second mixture is formed, place it in a calcination device and calcine it in a mixed atmosphere of argon, hydrogen and methane, and obtain the finished product after cooling.

[0043] The present invention directly prepares a silicon carbide whisker-carbon nanofiber composite fuel cell catalyst with a structure of fluorine / cobalt-doped silicon carbide whiskers supporting carbon nanofibers by using a one-step calcination method. Excessive calcination temperature or too long calcination time will lead to unnecessary energy waste; too low calcination temperature or too short calcination time will result in the inability to convert raw materials into target products. In one embodiment, the calcination equipment can be a tube furnace, but is not limited thereto. The calcination temperature is 1100°C to 1500°C, and the calcination time is 6h to 12h.

[0044] Meanwhile, in order to make up for the defect of insufficient conductivity of silicon carbide whiskers, methane is introduced as a carbon source in the preparation process of silicon carbide whiskers to realize the loading of a large amount of carbon nanofibers on the surface of silicon carbide whiskers, improve the defect of insufficient conductivity of single silicon carbide whiskers, construct an electron rapid transmission channel, and enhance the reaction efficiency. In one embodiment, in the mixed atmosphere of argon, hydrogen and methane, by volume, argon: hydrogen: methane = (50 - 80):1:1. Under the above mixed atmosphere, an appropriate loading amount of carbon nanofibers can be formed on the surface of the fluorine / cobalt-doped silicon carbide whiskers to improve the electrical conductivity of the silicon carbide whiskers.

[0045] Correspondingly, the present invention also provides a silicon carbide whisker-carbon nanofiber composite fuel cell catalyst prepared according to the above preparation method. Preferably, the silicon carbide whisker-carbon nanofiber composite fuel cell catalyst is nanoparticles, and the morphology design of the nanoparticles can provide a large number of reaction active sites for the oxygen reduction reaction, improving the catalytic reaction efficiency. The silicon carbide whisker-carbon nanofiber composite fuel cell catalyst can be used for the preparation of fuel cells. When it is used to make fuel cells, it can reduce the cost of the battery, improve the performance and stability of the battery, and greatly broaden the commercial application range of fuel cells.

[0046] In summary, the silicon carbide whisker-carbon nanofiber composite fuel cell catalyst prepared by the present invention uses fluorine / cobalt-doped silicon carbide whiskers as the catalytic main body, which can realize the efficient oxygen capture and catalytic decomposition. Loading carbon nanofibers on the fluorine / cobalt-doped silicon carbide whiskers makes up for the defect of insufficient conductivity of silicon carbide whiskers and provides a rapid channel for electron transmission. The two work together to achieve an efficient oxygen reduction reaction.

[0047] The following further illustrates the present invention with specific examples:

[0048] Example 1

[0049] This example provides a preparation method of a silicon carbide whisker-carbon nanofiber composite fuel cell catalyst, including the following steps:

[0050] S1. Weigh silicon powder, graphite powder and cobalt tetroxide powder respectively and mix them to obtain a first mixture;

[0051] Among them, the mass ratio between the silicon powder and the graphite powder is 1:1.5, and the mass ratio between the cobalt tetroxide powder and the silicon powder is 1:100;

[0052] S2. Mix the first mixture evenly with N-methylpyrrolidone, add polyvinylidene fluoride, grind evenly and then dry to obtain a second mixture.

[0053] Among them, the ratio of the addition amount of the polyvinylidene fluoride to the addition amount of the silicon powder is 1:100.

[0054] S3. After the second mixture is formed, place it in a calcination device and calcine it under a mixed atmosphere of argon, hydrogen and methane, and obtain the finished product after cooling.

[0055] The calcination temperature of the calcination is 1300 °C, and the calcination time is 12 h; in the mixed atmosphere of argon, hydrogen and methane, by volume ratio, argon: hydrogen: methane = 60:1:1.

[0056] Example 2

[0057] This example provides a preparation method of a silicon carbide whisker carbon nanofiber composite fuel cell catalyst, including the following steps:

[0058] S1. Weigh silicon powder, graphite powder and cobalt tetroxide powder respectively and mix them to obtain a first mixture;

[0059] Among them, the mass ratio between the silicon powder and the graphite powder is 1:2, and the mass ratio between the cobalt tetroxide powder and the silicon powder is 1:200;

[0060] S2. Mix the first mixture evenly with N-methylpyrrolidone, add polyvinylidene fluoride, grind evenly and then dry to obtain a second mixture.

[0061] Among them, the ratio of the addition amount of the polyvinylidene fluoride to the addition amount of the silicon powder is 1:80.

[0062] S3. After the second mixture is formed, place it in a calcination device and calcine it under a mixed atmosphere of argon, hydrogen and methane, and obtain the finished product after cooling.

[0063] The calcination temperature of the calcination is 1500 °C, and the calcination time is 12 h; in the mixed atmosphere of argon, hydrogen and methane, by volume ratio, argon: hydrogen: methane = 80:1:1.

[0064] Example 3

[0065] This example provides a preparation method of a silicon carbide whisker carbon nanofiber composite fuel cell catalyst, including the following steps:

[0066] S1. Weigh silicon powder, graphite powder and cobalt tetroxide powder separately and mix them to obtain a first mixture;

[0067] Among them, the mass ratio between the silicon powder and the graphite powder is 1:1.8, and the mass ratio between the cobalt tetroxide powder and the silicon powder is 1:150;

[0068] S2. Mix the first mixture evenly with N-methylpyrrolidone, add polyvinylidene fluoride, grind evenly and then dry to obtain a second mixture.

[0069] Among them, the addition amount ratio of the polyvinylidene fluoride to the addition amount of the silicon powder is 1:90.

[0070] S3. After the second mixture is formed, place it in a calcination device and calcine it in a mixed atmosphere of argon, hydrogen and methane, and obtain the finished product after cooling.

[0071] The calcination temperature of the calcination is 1100 °C, and the calcination time is 6 h; in the mixed atmosphere of argon, hydrogen and methane, by volume ratio, argon: hydrogen: methane = 50:1:1.

[0072] Example 4

[0073] This example provides a preparation method of a silicon carbide whisker-carbon nanofiber composite fuel cell catalyst, including the following steps:

[0074] S1. Weigh silicon powder, graphite powder and cobalt tetroxide powder separately and mix them to obtain a first mixture;

[0075] Among them, the mass ratio between the silicon powder and the graphite powder is 1:1.2, and the mass ratio between the cobalt tetroxide powder and the silicon powder is 1:150;

[0076] S2. Mix the first mixture evenly with N-methylpyrrolidone, add polyvinylidene fluoride, grind evenly and then dry to obtain a second mixture.

[0077] Among them, the addition amount ratio of the polyvinylidene fluoride to the addition amount of the silicon powder is 1:90.

[0078] S3. After the second mixture is formed, place it in a calcination device and calcine it in a mixed atmosphere of argon, hydrogen and methane, and obtain the finished product after cooling.

[0079] The calcination temperature of the calcination is 1100 °C, and the calcination time is 6 h; in the mixed atmosphere of argon, hydrogen and methane, by volume ratio, argon: hydrogen: methane = 50:1:1.

[0080] The morphology of the silicon carbide whisker carbon nanofiber composite fuel cell catalyst prepared in Example 1 was observed. Figure 1 It can be seen that the silicon carbide whisker carbon nanofiber composite fuel cell catalyst prepared in the present invention has a uniform and narrow particle size distribution, good dispersibility, and no serious agglomeration. This morphology can provide a large number of reactive sites for the oxygen reduction reaction and improve the catalytic reaction efficiency. Subsequently, the silicon carbide whisker carbon nanofiber composite fuel cell catalyst prepared in Example 1 was tested for oxygen reduction activity. The test was carried out at 0 2 Saturated 0.1 M HClO 4 The results were obtained by forward scanning at a scanning rate of 50 mV / s and a rotation speed of 1600 r / min in the solution. Figure 2 As shown. Figure 2 It can be seen that the silicon carbide whisker carbon nanofiber composite fuel cell catalyst prepared by the present invention has high oxygen reduction activity, can effectively improve the oxygen reduction reaction kinetics, and improve the catalytic reaction efficiency.

[0081] The above is a preferred embodiment of the invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle of the invention. These improvements and modifications are also considered to be within the scope of protection of the invention.

Claims

1. Preparation method of silicon carbide whisker-carbon nanofiber composite fuel cell catalyst, Characterized in that, It includes the following steps: Weigh silicon powder, graphite powder and cobalt tetroxide powder respectively and mix them to obtain a first mixture; Mix the first mixture evenly with a solvent, add polyvinylidene fluoride, grind evenly and then dry to obtain a second mixture; After the second mixture is formed, it is placed in a calcination device and calcined in a mixed atmosphere of argon, hydrogen and methane, and the finished product is obtained after cooling.

2. The preparation method of silicon carbide whisker-carbon nanofiber composite fuel cell catalyst according to claim 1, Characterized in that, The mass ratio between the silicon powder and the graphite powder is 1:(1.2~2).

3. The preparation method of silicon carbide whisker-carbon nanofiber composite fuel cell catalyst according to claim 1, Characterized in that, The mass ratio between the cobalt tetroxide powder and the silicon powder is 1:(100~200).

4. The preparation method of silicon carbide whisker-carbon nanofiber composite fuel cell catalyst according to claim 1, Characterized in that, The solvent is selected as N-methylpyrrolidone.

5. The preparation method of silicon carbide whisker-carbon nanofiber composite fuel cell catalyst according to claim 1, Characterized in that, The addition amount ratio of polyvinylidene fluoride to the addition amount of silicon powder is 1:(80~100).

6. The preparation method of silicon carbide whisker-carbon nanofiber composite fuel cell catalyst according to claim 1, Characterized in that, The calcination temperature of the calcination is 1100°C~1500°C, and the calcination time is 6h~12h.

7. The preparation method of silicon carbide whisker-carbon nanofiber composite fuel cell catalyst according to claim 1, Characterized in that, In the mixed atmosphere of argon, hydrogen and methane, by volume ratio, argon:hydrogen:methane=(50~80):1:

1.

8. A silicon carbide whisker-carbon nanofiber composite fuel cell catalyst, Characterized in that, It is prepared by the preparation method of silicon carbide whisker-carbon nanofiber composite fuel cell catalyst according to any one of claims 1~7.

9. Application of the silicon carbide whisker-carbon nanofiber composite fuel cell catalyst according to claim 8 in a fuel cell.

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