Cathode catalyst for fuel cell, preparation method of cathode catalyst and membrane electrode comprising cathode catalyst

Abstract

The invention provides a cathode catalyst for a fuel cell, a preparation method of the cathode catalyst and a membrane electrode containing the cathode catalyst, and relates to the technical field of fuel cells. According to the preparation method of the cathode catalyst for the fuel cell, a spherical urea-formaldehyde resin carbon carrier is adopted as a carbon carrier precursor, and the spherical urea-formaldehyde resin carbon carrier has the advantages of high mechanical strength and large packing density and also has rich surface functional groups and rich nitrogen elements. Therefore, the spherical urea-formaldehyde resin carbon is used as a carbon carrier precursor to synthesize the fuel cell catalyst, the obtained catalyst is high in mechanical strength and stable in structure, and the problem that pores of a catalyst layer become smaller in the hot pressing process of the fuel cell catalyst layer can be effectively solved. Besides, the cathode catalyst is prepared by adopting a microwave heating method, the obtained noble metal particles are small and uniform in particle size, relatively narrow in particle size distribution range and good in catalytic activity, and the microsphere morphology of the spherical urea-formaldehyde resin carbon can be fully reserved by adopting the microwave heating method.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and in particular to a cathode catalyst for a fuel cell, a preparation method thereof, and a membrane electrode containing the cathode catalyst. Background Art

[0002] Fuel cell reaction catalysts refer to materials that accelerate and increase the speed of electrochemical reactions and shorten the reaction time during the reaction process between the positive and negative electrodes of the battery. Most fuel cells choose platinum, a precious metal with high stability, high activity and low pollution, as catalysts. The preparation technology of membrane electrode catalyst layers has undergone three generations of development and can be roughly divided into three types: hot pressing, transfer printing or direct coating, and ordered membrane electrode.

[0003] Among them, the transfer method is a method for preparing a membrane electrode assembly by indirectly coating the catalytic layer on the proton exchange membrane. The transfer method has the technical advantages of simple preparation process, good bonding between the catalyst layer and the proton exchange membrane, not easy to peel off, high catalyst utilization rate, long membrane electrode life, and the proton exchange membrane does not come into contact with any solvent during the preparation process, which effectively avoids the swelling problem of the membrane.

[0004] However, the membrane electrode transfer process requires high temperature and pressure to promote the effective combination of the catalyst layer and the proton exchange membrane. The high temperature and pressure transfer process will make the catalyst pores smaller, causing the catalyst layer to be too tight to prevent gas from passing through, thereby reducing the performance of the fuel cell. Some solutions are also given in the prior art, for example: CN113991125A provides a proton exchange membrane fuel cell catalyst slurry and its preparation method and application. In this application, the proton exchange membrane fuel cell catalyst slurry contains a pore-reducing agent with a hollow spherical structure, which solves the problem that the catalyst pores of the catalyst layer become smaller after hot pressing, causing the catalyst layer to be too tight to prevent gas from passing through. However, the addition of the pore-reducing agent will weaken the pore support layer of the membrane electrode, which will also affect the performance of the membrane electrode.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] The first purpose of the present invention is to provide a method for preparing a cathode catalyst for a fuel cell. The cathode catalyst prepared by this method has the technical effects of high mechanical strength and stable structure, and can effectively reduce the problem of smaller pores in the catalyst layer during hot pressing of the fuel cell catalyst layer.

[0007] The second object of the present invention is to provide a cathode catalyst for a fuel cell, which is prepared by the above-mentioned preparation method.

[0008] The third object of the present invention is to provide a membrane electrode, the cathode catalyst layer of which is prepared from the cathode catalyst for fuel cell

[0009] To achieve the above object of the present invention, the following technical solutions are specifically adopted:

[0010] A preparation method of a cathode catalyst for a fuel cell provided by the present invention, the preparation method comprising:

[0011] Adding a carbon support precursor into a noble metal precursor solution and mixing evenly, then using microwave heating method to prepare a reaction product, and washing and drying the reaction product in sequence to obtain a cathode catalyst for a fuel cell;

[0012] The carbon support precursor is a spherical urea-formaldehyde resin carbon support.

[0013] Further, the spherical urea-formaldehyde resin carbon support is mainly prepared by carbonizing and activating urea-formaldehyde resin microspheres in sequence.

[0014] Furthermore, the urea-formaldehyde resin microspheres are mainly prepared by an addition reaction of urea and formaldehyde in an acidic medium;

[0015] Preferably, the molar ratio of formaldehyde to urea is 3-1:1, preferably 1.6:1.

[0016] Furthermore, the carbonization includes:

[0017] Adding the urea-formaldehyde resin microspheres into a carbonization furnace, and heating up to 200-700 °C at a heating rate of 0.5-8 °C / min for carbonization for 1-3 h to complete carbonization, obtaining carbonized material of urea-formaldehyde resin microspheres;

[0018] Preferably, the carbonization is carried out under a nitrogen protection atmosphere.

[0019] Furthermore, the activation includes:

[0020] Mixing the carbonized material of urea-formaldehyde resin microspheres and an activator evenly at a mass ratio of 1:1-5, then heating up to 600-900 °C in an activation furnace for activation for 1-4 h to obtain a spherical urea-formaldehyde resin carbon support;

[0021] Preferably, the activation is carried out under a nitrogen protection atmosphere.

[0022] Further, the noble metal precursor includes at least one of chloroplatinic acid, trimethylplatinum, and trimethylacetylacetone platinum.

[0023] Further, the solvent in the noble metal precursor solution is at least one of ethylene glycol, glycerol, and acetone;

[0024] The concentration of the noble metal precursor solution is 14-20 wt%.

[0025] Further, the weight ratio of the noble metal precursor solution to the carbon support precursor is 4 to 15:1. A cathode catalyst for a fuel cell prepared by the method for preparing a cathode catalyst for a fuel cell according to the above.

[0026] A membrane electrode provided by the present invention, wherein the cathode catalyst layer of the membrane electrode is prepared from the above cathode catalyst for a fuel cell.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] The method for preparing a cathode catalyst for a fuel cell provided by the present invention uses a spherical urea-formaldehyde resin carbon support as the carbon support precursor. This spherical urea-formaldehyde resin carbon support has the advantages of high mechanical strength, large packing density, rich surface functional groups and rich nitrogen elements. Therefore, in this application, the above spherical urea-formaldehyde resin carbon is used as the carbon support precursor to synthesize a fuel cell catalyst. The obtained catalyst has high mechanical strength and stable pore structure, and can effectively reduce the problem of pore reduction in the catalyst layer during the hot pressing process of the fuel cell catalyst layer. In addition, the microwave heating method is used to prepare the cathode catalyst in this application. The obtained noble metal particles have small and uniform particle size, and the particle size distribution range is also relatively narrow, with good catalytic activity. Moreover, the microwave heating method can also fully retain the microspherical morphology of the spherical urea-formaldehyde resin carbon.

[0029] The cathode catalyst for a fuel cell provided by the present invention is prepared by the method for preparing a cathode catalyst for a fuel cell as described above, and has the technical advantages of stable catalyst structure and can effectively reduce the problem of pore reduction in the catalyst layer during the hot pressing process of the fuel cell catalyst layer.

[0030] The membrane electrode provided by the present invention can effectively alleviate the problem of performance degradation of the membrane electrode caused by pore reduction after hot pressing of the catalyst layer. Description of the Drawings

[0031] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0032] Figure 1 It is the SEM diagram of the spherical urea-formaldehyde resin carbon provided in Example 1 of the present invention. Detailed Embodiments

[0033] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0034] According to one aspect of the present invention, a method for preparing a cathode catalyst for a fuel cell, the preparation method comprising:

[0035] Adding a carbon support precursor into a noble metal precursor solution and mixing evenly, then using a microwave heating method to prepare a reaction product, and washing and drying the reaction product in sequence to obtain a cathode catalyst for a fuel cell;

[0036] The carbon support precursor is a spherical urea-formaldehyde resin carbon support.

[0037] The preparation method of the cathode catalyst for a fuel cell provided by the present invention uses a spherical urea-formaldehyde resin carbon support as the carbon support precursor. This spherical urea-formaldehyde resin carbon support has the advantages of high mechanical strength and large packing density; it also has rich surface functional groups and rich nitrogen elements. Among them, the surface functional groups of the spherical urea-formaldehyde resin carbon support can effectively improve the three-phase site reaction of the catalyst, and the nitrogen-containing functional groups can promote the ability of Pt to donate electrons, and at the same time promote the adsorption of oxygen and the decomposition of intermediate peroxides. Therefore, using the above spherical urea-formaldehyde resin carbon support as the carbon support precursor can significantly improve the activity of the catalyst.

[0038] Therefore, in this application, the above spherical urea-formaldehyde resin carbon is used as the carbon support precursor to synthesize a fuel cell catalyst. The obtained catalyst has a stable structure and can effectively reduce the problem of the decrease in the pores of the catalyst layer during the hot pressing process of the fuel cell catalyst layer. In addition, this application uses a microwave heating method to prepare the cathode catalyst. The obtained noble metal particles have small and uniform particle size, and the particle size distribution range is also relatively narrow, with good catalytic activity. Moreover, the microwave heating method can also fully retain the microspherical morphology of the spherical urea-formaldehyde resin carbon.

[0039] In a preferred embodiment of the present invention, the spherical urea-formaldehyde resin carbon support is mainly prepared by successively carbonizing and activating urea-formaldehyde resin microspheres.

[0040] As a preferred embodiment, the technical solution of successively carbonizing and activating the above urea-formaldehyde resin microspheres can obtain activated carbon microspheres with a high specific surface area, which is beneficial to the loading of platinum metal during subsequent catalyst synthesis.

[0041] In a preferred embodiment of the present invention, the urea-formaldehyde resin microspheres are mainly prepared by an addition reaction of urea and formaldehyde in an acidic medium;

[0042] It should be noted that the selection of the acidic medium in the addition reaction of urea and formaldehyde in this application lies in that since the strong acidic medium is not easy to control the reaction rate, weak acids such as formic acid and acetic acid are preferably used as the acidic medium in the addition reaction of urea and formaldehyde in this application.

[0043] At the same time, since the acidic medium is only added as a medium solution and does not participate in the addition reaction. Therefore, there is no special limitation on the amount of the acidic medium in this application, and it can maintain the pH value of the solution in the acidic solution (pH value 1.0 - 5.0) during the addition reaction.

[0044] In the above preferred embodiment, the molar ratio of formaldehyde to urea is 3 - 1:1, preferably 1.6:1.

[0045] As a preferred embodiment, the urea - formaldehyde resin microspheres prepared at a molar ratio of formaldehyde to urea of 3 - 1:1 have a better spherical structure. When the molar ratio of formaldehyde to urea is greater than 3:1, the formed urea - formaldehyde resin microspheres are prone to fragmentation. When the molar ratio of formaldehyde to urea is less than 1:1, the formed urea - formaldehyde resin microspheres have a layered network aggregation structure and are prone to adhesion between microspheres.

[0046] Furthermore, through experimental verification, when preparing urea - formaldehyde resin microspheres at a molar ratio of formaldehyde to urea of 1.6:1, the condensation reaction is rapid at this time, and the effect of generating solid microspheres with a smooth surface is the best.

[0047] In the above preferred embodiment, the carbonization includes:

[0048] Adding the urea - formaldehyde resin microspheres into a carbonization furnace, heating at a heating rate of 0.5 - 8 °C / min to 200 - 700 °C for carbonization for 1 - 3 h to complete carbonization, and obtaining the carbonized material of urea - formaldehyde resin microspheres;

[0049] Preferably, the carbonization is carried out under a nitrogen - protection atmosphere.

[0050] Furthermore, preferably, the carbonization temperature is 500 °C and the heating rate is 0.5 °C / min. If the heating rate is too fast, the urea - formaldehyde resin microspheres are prone to melting, merging, and adhesion.

[0051] In the above preferred embodiment, the activation includes:

[0052] Mixing the carbonized material of urea - formaldehyde resin microspheres and the activator evenly at a mass ratio of 1:1 - 5, and then heating to 600 - 900 °C in an activation furnace for activation for 1 - 4 h to obtain the spherical urea - formaldehyde resin carbon carrier;

[0053] Preferably, the carbonization and activation are carried out under a nitrogen protection atmosphere. Under the nitrogen protection atmosphere, the oxidation reaction during the preparation of the spherical urea-formaldehyde resin carbon support of the present application can be avoided, thereby effectively ensuring the stability of the carbonization and activation processes.

[0054] Preferably, the activator is sodium hydroxide powder or potassium hydroxide powder.

[0055] In a preferred embodiment of the present invention, the noble metal precursor includes at least one of chloroplatinic acid, trimethylplatinum, and platinum acetylacetonate trimethyl.

[0056] In a preferred embodiment of the present invention, the solvent in the noble metal precursor solution is at least one of ethylene glycol, glycerol, and acetone;

[0057] The concentration of the noble metal precursor solution is 14-20 wt%.

[0058] In a preferred embodiment of the present invention, the weight ratio of the noble metal precursor solution to the carbon support precursor is 4-15:1. Preferably, the method for preparing the cathode catalyst for a fuel cell includes:

[0059] Step 1, synthesize urea-formaldehyde resin microspheres: (prepared by the hydroxymethylation addition reaction of urea and formaldehyde in an acidic medium).

[0060] (1), prepare the prepolymer:

[0061] Add urea in two batches to formaldehyde according to a molar ratio of 1:1-3 to prepare the prepolymer.

[0062] Among them:

[0063] The first addition amount is 50-80 wt% of the total amount of urea, and the reaction is carried out for 10-60 min.

[0064] The second addition amount is 20-50 wt% of the total amount of urea, and the reaction is continued for 10-30 min to prepare the prepolymer;

[0065] The purity of the urea is greater than 98 wt%;

[0066] (2), add a 50% formic acid solution to the prepolymer in step (1) to adjust the pH value to 1.0-5.0. When particles precipitate in the solution, add 1-4 mol / L hydrochloric acid to solidify for 48 hours, then centrifuge and wash, and dry to obtain urea-formaldehyde resin microspheres;

[0067] Step 2, carbonize and activate the urea-formaldehyde resin microspheres:

[0068] Add the urea - formaldehyde resin microspheres into a carbonization furnace. Under the protection of nitrogen gas, heat up to 200 - 700 °C at a heating rate of 0.5 - 8 °C / min, and carbonize for 1 - 3 h to obtain the carbonized material of urea - formaldehyde resin microspheres. Grind and screen the carbonized material, and add the carbonized material and the activator into a crucible at a mass ratio of carbon to alkali of 1:(1 - 5). Mix evenly for 10 min - 20 min, transfer to an activation furnace. Under the protection of nitrogen, heat up to 600 °C - 900 °C, carry out the activation reaction for 1 h - 4 h, cool down and discharge to obtain spherical urea - formaldehyde resin carbon.

[0069] Step 3: Preparation of the cathode catalyst:

[0070] Prepare the cathode catalyst by microwave - assisted ethylene glycol reduction method. Mix the spherical urea - formaldehyde resin carbon carrier with ethylene glycol and the noble metal precursor, and ultrasonically make the suspension evenly mixed. Microwave heat for 30 - 90 s, repeat the heating 2 - 6 times, take out and cool to room temperature, wash with acetone and deionized water 2 - 6 times, dry and reserve to obtain the cathode catalyst.

[0071] Furthermore, the noble metal precursor includes but is not limited to one or more of the following: chloroplatinic acid, trimethylplatinum, platinum acetylacetonate trimethyl, etc.

[0072] According to one aspect of the present invention, a cathode catalyst for a fuel cell prepared by the preparation method of the cathode catalyst for a fuel cell as described above.

[0073] The cathode catalyst for a fuel cell provided by the present invention is prepared by the preparation method of the cathode catalyst for a fuel cell as described above, and has the technical advantages of stable catalyst structure and can effectively reduce the reduction of the pores in the catalyst layer during the hot - pressing process of the fuel cell catalyst layer.

[0074] According to one aspect of the present invention, a membrane - electrode, the cathode catalyst layer of the membrane - electrode is prepared from the cathode catalyst for a fuel cell as described above.

[0075] The membrane - electrode provided by the present invention can effectively alleviate the problem of the decline in the performance of the membrane - electrode caused by the reduction of pores after hot - pressing of the catalyst layer.

[0076] The technical solution of the present invention will be further described below in conjunction with embodiments.

[0077] Example 1

[0078] A preparation method of a cathode catalyst for a fuel cell, the preparation method includes:

[0079] (1) Urea was added to formaldehyde in two batches according to a molar ratio of 1:1.6 to prepare a prepolymer. Among them: the addition amount of the first batch was 75 wt% of the total amount of urea, and the reaction was carried out for 60 min; the addition amount of the second batch was 25 wt% of the total amount of urea, and the reaction was continued for 10 min to prepare the prepolymer;

[0080] Subsequently, a formic acid solution with a concentration of 50% was added to adjust the pH value to 1.0. When particles precipitated in the solution, 2 mol / L hydrochloric acid was added for curing for 48 hours, followed by centrifugal washing;

[0081] The purity of the urea was greater than 98 wt%.

[0082] (2) After drying, the urea-formaldehyde resin microspheres were added to a carbonization furnace. Under the protection of nitrogen gas, the temperature was raised to 500 °C at a heating rate of 0.5 °C / min for carbonization for 1 h to obtain carbonized urea-formaldehyde resin microspheres;

[0083] The carbonized material was ground and sieved. The carbonized material and the activator (sodium hydroxide powder) were added to a crucible according to a carbon-to-alkali mass ratio of 1:3, and evenly mixed for 10 min. Then it was transferred to an activation furnace. Under the protection of nitrogen, the temperature was raised to 800 °C, and the activation reaction was carried out for 2 h. After cooling, the product was discharged to obtain spherical urea-formaldehyde resin carbon;

[0084] Figure 1 This is the SEM image of the spherical urea-formaldehyde resin carbon provided in this example.

[0085] As Figure 1 can be seen, the spherical urea-formaldehyde resin carbon prepared in this example has uniform particle size and smooth surface.

[0086] (3) A cathode catalyst was prepared by microwave-assisted ethylene glycol reduction method: A solution of H2PtCl6 (hexahydrate chloroplatinic acid) dissolved in ethylene glycol was provided. The spherical urea-formaldehyde resin carbon support was added to the solution and mixed evenly. Ultrasonic treatment was used to make the suspension evenly mixed. Microwave heating was carried out for 60 s, and the heating was repeated 5 times. Then it was taken out and cooled to room temperature, and washed 5 times with acetone and deionized water to obtain the cathode catalyst for fuel cells.

[0087] The concentration of the solution of H2PtCl6 dissolved in ethylene glycol was 17 wt%.

[0088] The weight ratio of the solution of H2PtCl6 dissolved in ethylene glycol to the spherical urea-formaldehyde resin carbon was 10:1.

[0089] Example 2

[0090] A preparation method of a cathode catalyst for fuel cells, the preparation method comprising:

[0091] (1) Add urea in two batches to formaldehyde in a molar ratio of 1:1 to prepare a prepolymer. Among them: the addition amount of the first batch is 50 wt% of the total amount of urea, and the reaction is carried out for 10 min; the addition amount of the second batch is 50 wt% of the total amount of urea, and the reaction is continued for 10 min to prepare a prepolymer;

[0092] Subsequently, add a 50% formic acid solution to adjust the pH value to 3.0. When particles precipitate in the solution, add 1 mol / L hydrochloric acid to cure for 48 hours and then centrifuge and wash;

[0093] The purity of the urea is greater than 98 wt%.

[0094] (2) After drying, add the urea-formaldehyde resin microspheres to a carbonization furnace. Under the protection of nitrogen gas, heat up to 200 °C at a heating rate of 0.5 °C / min for carbonization for 3 h to obtain carbonized urea-formaldehyde resin microsphere materials;

[0095] Grind and sieve the carbonized materials. Add the carbonized materials and an activator (sodium hydroxide powder) to a crucible in a carbon-to-alkali mass ratio of 1:1, mix evenly for 10 min, transfer to an activation furnace, under the protection of nitrogen, heat up to 600 °C, carry out an activation reaction for 4 h, cool down and discharge to obtain spherical urea-formaldehyde resin carbon;

[0096] (3) Prepare a cathode catalyst by microwave-assisted ethylene glycol reduction method: Provide a solution of H2PtCl6 (hexahydrate chloroplatinic acid) dissolved in ethylene glycol. Add the spherical urea-formaldehyde resin carbon carrier to the solution and mix well. Ultrasonic to make the suspension mix evenly, microwave heat for 30 s, repeat the heating 6 times, take out and cool to room temperature, wash 6 times with acetone and deionized water to obtain a cathode catalyst for fuel cells.

[0097] The concentration of the solution of H2PtCl6 dissolved in ethylene glycol is 20 wt%.

[0098] The weight ratio of the solution of H2PtCl6 dissolved in ethylene glycol to the spherical urea-formaldehyde resin carbon is 4:1.

[0099] Example 3

[0100] A preparation method of a cathode catalyst for fuel cells, the preparation method comprising:

[0101] (1) Add urea in two batches to formaldehyde in a molar ratio of 1:3 to prepare a prepolymer. Among them: the addition amount of the first batch is 80 wt% of the total amount of urea, and the reaction is carried out for 60 min; the addition amount of the second batch is 20 wt% of the total amount of urea, and the reaction is continued for 30 min to prepare a prepolymer;

[0102] Subsequently, add a 50% formic acid solution to adjust the pH value to 5.0. When particles precipitate in the solution, add 4 mol / L hydrochloric acid to cure for 48 hours and then centrifuge and wash;

[0103] The purity of the urea is greater than 98 wt%.

[0104] (2) After drying, the urea-formaldehyde resin microspheres are added to a carbonization furnace. Under the protection of nitrogen gas, the temperature is raised to 700 °C at a heating rate of 8 °C / min and carbonized for 1 h to obtain carbonized urea-formaldehyde resin microsphere material.

[0105] The carbonized material is ground and sieved. The carbonized material and the activator (sodium hydroxide powder) are added to a crucible at a carbon-to-alkali mass ratio of 1:5, uniformly mixed for 20 min, transferred to an activation furnace, and under the protection of nitrogen, the temperature is raised to 900 °C, the activation reaction is carried out for 1 h, and then cooled and discharged to obtain spherical urea-formaldehyde resin carbon.

[0106] (3) A cathode catalyst is prepared by a microwave-assisted ethylene glycol reduction method: A solution of H2PtCl6 (hexahydrate chloroplatinic acid) dissolved in ethylene glycol is provided. The spherical urea-formaldehyde resin carbon support is added to the solution and mixed evenly. Ultrasonic treatment is used to make the suspension mix evenly. Microwave heating is carried out for 90 s, and the heating is repeated 2 times. Then it is taken out and cooled to room temperature, and washed 2 times with acetone and deionized water to obtain the cathode catalyst for fuel cells.

[0107] The concentration of the solution of H2PtCl6 dissolved in ethylene glycol is 14 wt%.

[0108] The weight ratio of the solution of H2PtCl6 dissolved in ethylene glycol to the spherical urea-formaldehyde resin carbon is 15:1.

[0109] Example 4

[0110] A preparation method of a cathode catalyst for fuel cells, the preparation method comprising:

[0111] (1) Urea is added to formaldehyde in two batches according to a molar ratio of 1:0.5 to prepare a prepolymer. Among them: the amount added in the first batch is 75 wt% of the total amount of urea, and the reaction is carried out for 60 min; the amount added in the second batch is 25 wt% of the total amount of urea, and the reaction is continued for 10 min to prepare a prepolymer;

[0112] Subsequently, a formic acid solution with a concentration of 50% is added to adjust the pH value to 1.0. When particles precipitate in the solution, 2 mol / L hydrochloric acid is added for curing for 48 hours, and then centrifuged and washed;

[0113] The purity of the urea is greater than 98 wt%.

[0114] (2) The same as in Example 1;

[0115] (3) The same as in Example 1.

[0116] The difference between this example and Example 1 is that in step (1), the molar ratio of formaldehyde to urea is 0.5:1.

[0117] Example 5

[0118] A preparation method of a cathode catalyst for a fuel cell, the preparation method comprising:

[0119] (1) Urea is added to formaldehyde in two batches according to a molar ratio of 1:4 to prepare a prepolymer. Among them: the addition amount of the first batch is 75 wt% of the total amount of urea, and the reaction is carried out for 60 min; the addition amount of the second batch is 25 wt% of the total amount of urea, and the reaction is continued for 10 min to prepare a prepolymer;

[0120] Subsequently, a formic acid solution with a concentration of 50% is added to adjust the pH value to 1.0. When particles precipitate in the solution, 2 mol / L hydrochloric acid is added for curing for 48 hours, and then centrifuged and washed;

[0121] The purity of the urea is greater than 98 wt%.

[0122] (2) The same as Example 1;

[0123] (3) The same as Example 1.

[0124] The difference between this example and Example 1 is that the molar ratio of formaldehyde to urea in step (1) is 4:1.

[0125] Example 6

[0126] Except that step (2) of this example is:

[0127] “(2) After drying, the urea-formaldehyde resin microspheres are added to a carbonization furnace. Under the protection of nitrogen gas, the temperature is raised to 500 °C at a heating rate of 9 °C / min for carbonization for 1 h to obtain carbonized urea-formaldehyde resin microspheres;

[0128] The carbonized material is ground and sieved. The carbonized material and the activator (sodium hydroxide powder) are added to a crucible according to a carbon-alkali mass ratio of 1:3, uniformly mixed for 10 min, transferred to an activation furnace, and under the protection of nitrogen, the temperature is raised to 800 °C, and the activation reaction is carried out for 2 h, and then cooled and discharged to obtain spherical urea-formaldehyde resin carbon”, the rest is the same as Example 1.

[0129] The difference between this example and Example 1 is that the heating rate of carbonization of the urea-formaldehyde resin microspheres is 9 °C / min.

[0130] Example 7

[0131] Except that step (2) of this example is:

[0132] “(2) After drying, the urea-formaldehyde resin microspheres are added to a carbonization furnace. Under the protection of nitrogen gas, the temperature is raised to 500 °C at a heating rate of 0.5 °C / min for carbonization for 1 h to obtain carbonized urea-formaldehyde resin microspheres;

[0133] The carbonized material is ground and sieved. The carbonized material and the activator (sodium hydroxide powder) are added to a crucible in a carbon-to-alkali mass ratio of 1:1, uniformly mixed for 10 min, transferred to an activation furnace, heated to 800 °C under nitrogen protection, subjected to an activation reaction for 2 h, cooled and discharged to obtain spherical urea-formaldehyde resin carbon. Except for this, the rest is the same as in Example 1.

[0134] The difference between this example and Example 1 is that the carbon-to-alkali mass ratio of the carbonized material to the activator is 1:1.

[0135] Comparative Example 1

[0136] Commercially available TKK-TEC 10E50E catalyst.

[0137] Comparative Example 2

[0138] A membrane electrode catalyst for a proton exchange membrane fuel cell, comprising the following steps:

[0139] Step 1: Prepare a pore-forming agent: Take 1 g of ammonium carbonate and place it in a beaker, grind it until it is in a finely dispersed state of particles, dropwise add 3 g of PTFE solution, and ultrasonically stir in an ice bath for 20 min while dropping; put it in an oven to evaporate to dryness, and perform heat treatment at 300 °C for 20 min.

[0140] Step 2: Prepare a catalyst slurry: Weigh 50 mg of a platinum-carbon catalyst with a platinum content of 40%, moisten it with 1.5 g of deionized water, then dropwise add 50 mg of 5% Nafion, ultrasonically stir evenly in an ice bath and then dropwise add 5 g of isopropanol, and finally add 5 mg of the pore-forming agent, ultrasonically stir and mix evenly in an ice bath; use a high-speed shear machine for strong dispersion for 20 min to obtain a catalyst slurry, the dispersion speed is 10,000 r / min, and the catalyst is prepared.

[0141] Comparative Example 3

[0142] A preparation method of a cathode catalyst for a fuel cell, the preparation method comprising:

[0143] (1) The same as in Example 1;

[0144] (2) The same as in Example 1;

[0145] (3) Prepare a cathode catalyst by a hydrothermal synthesis method: Take a certain amount of urea-formaldehyde resin microsphere carbon carrier, add a certain amount of deionized water, ultrasonically stir for 15 min to make a carbon slurry, add a certain amount of chloroplatinic acid, then add a certain amount of thioacetamide and sodium hydroxide solution, mix evenly and pour them into a high-pressure reaction kettle together, and place it in a constant temperature oven for hydrothermal reaction for several hours. After the reaction, take it out and cool, filter, and repeatedly rinse with deionized water, and then dry in vacuum at 80 °C for 3 h. The dried catalyst is treated with hydrogen under nitrogen protection in a tubular furnace for a certain time to obtain the product.

[0146] Experimental Example 1

[0147] To demonstrate the technical effects of the cathode catalyst for fuel cells prepared in this application, the cathode catalysts prepared in Examples 1-7 and Comparative Examples 1-3 were fabricated into 50 cm2 membrane electrodes according to the same process for electrochemical performance testing.

[0148] Test conditions: temperature 75 °C, humidity (anode 40% / cathode 50%), pressure (anode 260 KPa / cathode 250 KPa), stoichiometric ratio (anode 2.0 / cathode 2.4)

[0149] The results of the electrochemical test are shown in Table 1.

[0150] Table 1 Electrochemical test results:

[0151]

[0152] As can be seen from the above table, compared with the commercially available TKK-TEC 10E50E catalyst in Comparative Example 1 and the catalyst prepared with a pore hydrophobic agent containing a hollow spherical structure in Comparative Example 2, the urea-formaldehyde resin microsphere carbon catalyst prepared in Examples 1-3 of this application has high oxidation activity, can increase the triple-phase reaction point, and effectively reduces the performance degradation caused by the reduction of pores after hot pressing of the catalyst layer.

[0153] Compared with the cathode catalyst for fuel cells prepared in Examples 1-3 and the cathode catalyst prepared in Example 4, the performance is significantly higher. This is mainly because the amount of formaldehyde added is too small, which affects the formation of urea-formaldehyde resin spheres, resulting in a low activity of the finally obtained catalyst;

[0154] Compared with the cathode catalyst for fuel cells prepared in Examples 1-3 and the cathode catalyst prepared in Example 5, the performance is significantly higher. This is mainly because the amount of formaldehyde added is too much, which causes the urea-formaldehyde resin spheres to rupture and affects the carbon carrier structure, resulting in a low activity of the finally obtained catalyst;

[0155] Comparing the cathode catalyst for fuel cells prepared in Examples 1-3 with Examples 6 and 7, it can be obtained that the cell components prepared from the membrane electrodes of proton exchange membrane fuel cells prepared in Examples 1-3 of the present invention have different degrees of voltage increase compared with the comparative examples at 0.2 A / cm 2 , 1.0 A / cm 2 , 1.8 A / cm 2 and 2.0 A / cm 2 . This shows that too fast carbonization heating rate and too small mass ratio of carbonized material to activator will affect the structure of urea-formaldehyde resin microspheres and ultimately affect the performance of the membrane electrode.

[0156] Comparing the cathode catalysts for fuel cells prepared in Examples 1 to 3 with Comparative Example 3, it can be obtained that the platinum distribution of the catalyst obtained by the microwave heating method matching this carbon support is more uniform, and the performance of the obtained membrane electrode is superior to that of the hydrothermal synthesis method.

[0157] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A preparation method of a cathode catalyst for a fuel cell, characterized in that, The preparation method includes: Adding a carbon carrier precursor into a noble metal precursor solution and mixing evenly, then using a microwave heating method to prepare a reaction product, and washing and drying the reaction product in sequence to obtain a cathode catalyst for a fuel cell; The carbon carrier precursor is a spherical urea-formaldehyde resin carbon carrier.

2. The preparation method of the cathode catalyst for a fuel cell according to claim 1, characterized in that, The spherical urea-formaldehyde resin carbon carrier is mainly prepared by carbonizing and activating urea-formaldehyde resin microspheres in sequence.

3. The preparation method of the cathode catalyst for fuel cells according to claim 2, characterized in that, The urea-formaldehyde resin microspheres are mainly prepared by an addition reaction of urea and formaldehyde in an acidic medium; Preferably, the molar ratio of formaldehyde to urea is 3 - 1:1, preferably 1.6:

1.

4. The preparation method of the cathode catalyst for a fuel cell according to claim 2, characterized in that, The carbonization includes: Adding the urea-formaldehyde resin microspheres into a carbonization furnace, heating at a heating rate of 0.5 - 8 °C / min to 200 - 700 °C for carbonization for 1 - 3 h to complete carbonization, and obtaining carbonized material of urea-formaldehyde resin microspheres; Preferably, the carbonization is carried out under a nitrogen protection atmosphere.

5. The preparation method of the cathode catalyst for a fuel cell according to claim 4, wherein, The activation includes: Mixing the carbonized material of urea-formaldehyde resin microspheres and an activator evenly at a mass ratio of 1:1 - 5, then heating to 600 - 900 °C in an activation furnace for activation for 1 - 4 h to obtain a spherical urea-formaldehyde resin carbon carrier; Preferably, the activation is carried out under a nitrogen protection atmosphere.

6. The preparation method of the cathode catalyst for a fuel cell according to claim 1, characterized in that, The noble metal precursor includes at least one of chloroplatinic acid, trimethylplatinum, and trimethylacetylacetone platinum.

7. The preparation method of the cathode catalyst for fuel cells according to claim 1, characterized in that, The solvent in the noble metal precursor solution is any one of ethylene glycol, glycerol, and acetone; The concentration of the noble metal precursor solution is 14 - 20 wt%.

8. The preparation method of the cathode catalyst for fuel cells according to claim 1, characterized in that, The weight ratio of the noble metal precursor solution to the carbon carrier precursor is 4 - 15:

1.

9. A cathode catalyst for a fuel cell prepared by the preparation method of the cathode catalyst for a fuel cell according to any one of claims 1 - 8.

10. A membrane electrode, characterized in that, The cathode catalyst layer of the membrane electrode is prepared from the cathode catalyst for a fuel cell according to claim 9.

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