A fuel cell catalyst and its preparation method and application

Abstract

The present invention discloses a fuel cell catalyst and its preparation method and application, and relates to the field of fuel cell technology. The present invention prepares a platinum-carbon catalyst by combining a liquid phase method and a colloid method, regulates the content and particle size distribution of platinum particles distributed on the surface and in the pores of the carbon carrier, and further improves the electrochemical performance (up to 65.9%) and durability (attenuation rate reduced by about 2 times) of the catalyst under different humidity in a single cell.

Description

Technical Field

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

[0002] A fuel cell is an energy conversion device that converts chemical energy in fuel and oxidant into electrical energy. Proton exchange membrane fuel cell is one of them. It uses sulfonic acid proton membrane as solid electrolyte and has the advantages of high energy conversion efficiency, no pollution, rapid start-up at room temperature, and high power density. Due to its advantages of low pollution and high energy density, it is considered to be one of the preferred clean and efficient energy conversion devices for future electric vehicles and other civilian occasions. The life of the catalyst is one of the core issues restricting the development of fuel cell technology. Commonly used catalysts are carbon-supported precious metal catalysts.

[0003] Due to its outstanding catalytic effect, Pt-based metals have become the most important catalyst in the current application of proton exchange membrane fuel cell catalysts. The Pt catalysts currently used are highly dispersed on amorphous carbon with a high specific surface area in the form of nano-scale particles; in actual operation, due to strong acid, high potential start-stop, air impurities and other reasons, the catalyst in the membrane electrode will undergo platinum dissolution, platinum migration, platinum agglomeration, platinum shedding, etc., which will cause the electrochemical active area (ECSA) to decrease, weaken the catalytic ability of the catalyst layer, intensify the activation polarization of the battery, increase the internal resistance, and ultimately lead to a decrease in the output power of the fuel cell. On the other hand, it will also have an impact on the proton membrane. The oxygen that permeates across the membrane reacts directly with the hydrogen in the proton membrane, and the generated H 2 O 2 The free radicals will directly act on the proton membrane, accelerating the chemical degradation of the proton membrane, but there is also another possibility, that is, oxygen and hydrogen will generate water under the catalytic action of Pt, playing a role of self-humidification. Therefore, it is very necessary to maintain the stability of the catalyst during operation.

[0004] There are many factors that affect the performance of catalysts, including carrier performance (specific surface area, pore structure, surface chemical properties, etc.), the content and particle size of active metals in the catalyst, and the distribution of active metals on the carrier. Existing commercial Pt / C generally uses amorphous carbon powder with high specific surface area to load Pt particles. Amorphous carbon powder has a certain amount of medium and large pores, which allows platinum to remain on the carrier surface and inside the pores during the loading process. In the actual operation of fuel cells, platinum particles on the surface are more likely to be coated and poisoned by sulfonic acid groups, resulting in a decrease in platinum active sites and weakened membrane electrode performance. Compared with surface platinum, the oxygen mass transfer process is less likely to occur in the catalysts in the pores, and the interaction between gas and platinum particles is weakened, which will also reduce the membrane electrode performance. Therefore, the dispersion control of metal particles is a problem worthy of attention, the purpose of which is to maintain the balance of particles contained in the pores and on the carbon surface. In addition, the platinum particles on the surface of the carbon carrier are roughly proportional to the electrochemical performance of the catalyst. The more platinum particles are evenly dispersed on the surface, the larger the electrochemical area of ​​the catalyst. Summary of the invention

[0005] Based on the deficiencies in the prior art, the present invention adopts the combined action of liquid phase reduction method and colloidal method to regulate the particle size of Pt particles on the carrier and the distribution content in the pores and on the surface, thereby improving the activity and stability of the catalyst during actual operation.

[0006] The technical solution adopted by the present invention is as follows:

[0007] The present invention provides a method for preparing a fuel cell catalyst, comprising the following steps:

[0008] (1) mixing a carbon carrier, an organic solvent and water, and dispersing them to obtain a first mixed solution;

[0009] (2) mixing the first mixed solution prepared in step (1), the first mass of the platinum salt precursor, the alkali solution and the reducing agent, and heating the mixture to react to obtain a first reaction solution;

[0010] (3) mixing a second mass of platinum salt precursor, an organic solvent, an alkali solution and a reducing agent and heating the mixture to react to obtain a second reaction solution;

[0011] (4) mixing the first reaction liquid obtained in step (2) and the second reaction liquid obtained in step (3), then dropping an acid solution to neutralize the mixture, and filtering the mixture to obtain the fuel cell catalyst.

[0012] The ratio of the first mass to the second mass is 1:0.25-4.

[0013] The colloid method is a commonly used method for preparing platinum nanoparticles. Platinum colloids of different particle sizes are prepared by adjusting the reaction temperature and the reducing agent content. When the platinum-carbon catalyst is prepared by the liquid phase method, the platinum precursor is usually adsorbed on the surface or in the pores of the carbon carrier, and then nucleates and grows in situ under the action of the reducing agent. Due to the differences in carbon carriers and the choice of process, the content of platinum particles distributed on the surface and in the pores of the prepared catalysts varies greatly.

[0014] Preferably, the carbon carrier is conductive carbon black. The conductive carbon black can be conventional conductive carbon black, such as BP2000, DENTA, and XC-72R.

[0015] The conductive carbon black is selected from Cabot and Lion's Ketjen black. In the preferred embodiment of the present invention, Cabot FCX800 carbon black is particularly preferred, which has a large specific surface area (800-1000m 2 / g), and the average pore size is 3-6nm.

[0016] In the embodiment of the present invention, when the mass ratio of platinum particles of the colloid method to the liquid phase method is 3:2, the optimal electrochemical area (56.3 m 2 / g), the catalyst performance is good.

[0017] In a preferred embodiment of the present invention, the platinum salt in the platinum salt precursor is chloroplatinic acid or potassium chloroplatinate.

[0018] In a preferred embodiment of the present invention, the alkali solution is a sodium carbonate solution or a sodium hydroxide solution, with a mass fraction of 5%-20wt%;

[0019] The reducing agent is at least one of methanol and formaldehyde;

[0020] The organic solvent is at least one of ethylene glycol and n-propanol.

[0021] In step (2) and step (3), the temperature of the heating reaction is 65-90° C., and the heating reaction time is 3-5 hours. In step (1), the ultrasonic rod treatment time of the mixed solution is 1-2 hours.

[0022] After adding acid solution for neutralization, a third mixed solution is obtained, and a precipitate is obtained after filtering. The precipitate is vacuum dried at 60-80° C. for 2-3 hours, and the fuel cell catalyst is obtained after grinding.

[0023] The present invention also provides a fuel cell catalyst prepared by the method for preparing the fuel cell catalyst.

[0024] The present invention also provides application of the fuel cell catalyst, wherein the fuel cell catalyst is used as an anode catalyst or a cathode catalyst of a fuel cell.

[0025] Compared with the prior art, the technical effects of the present invention are mainly reflected in:

[0026] The present invention prepares a platinum-carbon catalyst by combining a liquid phase method and a colloidal method, regulates the content and particle size distribution of platinum particles distributed on the surface and in the pores of the carbon carrier, and further improves the electrochemical performance (up to 65.9%) and durability (the attenuation rate is reduced by about 2 times) of the catalyst under different humidity in a single cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is an experimental flow chart of an embodiment of the present invention;

[0028] Figure 2 CV test spectra of the embodiments of the present invention and the comparative examples in the electrolyte;

[0029] Figure 3 The electrochemical performance spectrum of the cathode catalyst layer of the catalyst single cell prepared in Example 4 of the present invention under different humidity conditions;

[0030] Figure 4 The electrochemical performance spectrum of the cathode catalyst layer of the catalyst single cell prepared in Comparative Example 1 of the present invention under different humidity conditions;

[0031] Figure 5 The electrochemical performance spectrum of the cathode catalyst layer of the catalyst single cell prepared in Comparative Example 2 of the present invention under different humidity conditions;

[0032] Figure 6 This is a graph of accelerated aging test of the cathode catalytic layer of the catalyst single cell prepared in Example 4 of the present invention;

[0033] Figure 7 This is a graph of accelerated aging test of the cathode catalytic layer of the catalyst single cell prepared in Comparative Example 1 of the present invention;

[0034] Figure 8 This is the accelerated aging test graph of the cathode catalytic layer of the catalyst single cell prepared in Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0035] Figure 1 This is an experimental flow chart of an embodiment of the present invention, and the specific implementation method is shown in the following embodiments.

[0036] Example 1

[0037] 1. Weigh 10 g of chloroplatinic acid and dissolve it in 190 g of ethylene glycol, and dissolve 25 g of anhydrous sodium carbonate in 225 g of deionized water to obtain a 5 wt % chloroplatinic acid precursor solution and a 10 wt % sodium carbonate alkaline solution;

[0038] 2. Weigh 0.5 g of carbon powder (Cabot Corporation, FCX800), 40 g of ethylene glycol, 40 g of n-propanol and 20 g of deionized water, stir and mix, place in an ultrasonic rod disperser with ice water circulation, and ultrasonically disperse for 60 min;

[0039] 3. Transfer the mixed solution after ultrasound to a three-necked flask, add 5.3 g of 5 wt% chloroplatinic acid precursor, 6 g of 10 wt% sodium carbonate and 0.2 g of methanol, and mix under magnetic stirring for 30 min at room temperature;

[0040] 4. Transfer the stirred solution to a water bath and stir the reaction at 75°C for 3 hours;

[0041] While dispersing carbon powder by liquid phase method, platinum nanoparticles with controllable particle size are prepared by colloid method;

[0042] 5. Weigh 21.1 g of 5 wt% chloroplatinic acid precursor, 50 g of ethylene glycol, 24 g of 10 wt% sodium carbonate and 0.8 g of methanol into a three-necked beaker and mix them under magnetic stirring at room temperature for 30 min;

[0043] 6. After stirring at room temperature, transfer the three-necked flask to a water bath and stir the reaction at 75°C for 3 hours until the solution completely changes color;

[0044] 7. After the liquid phase method reaction is completed, the solution is transferred to a 2L beaker and placed on a magnetic stirrer for cooling and stirring; at the same time, the platinum colloid prepared by the colloid method is slowly added to the beaker to mix the two solutions and continue stirring for 30 minutes;

[0045] 8. After stirring, add 3 g of concentrated sulfuric acid drop by drop, continue stirring, and when no bubbles are generated, add 1000 g of deionized water and stir for 12 hours; then let it stand for 24 hours;

[0046] 9. After standing, the precipitate is washed with deionizer and filtered to obtain the precipitate; then, it is dried in a vacuum drying oven at 70°C for 3 hours, and the desired electrocatalyst is obtained after grinding.

[0047] Example 2

[0048] 1. Weigh 0.5g of Cabot FCX800 carbon powder, 40g of ethylene glycol, 40g of n-propanol and 20g of deionized water, stir and mix, place in an ultrasonic rod disperser with ice water circulation, and ultrasonically disperse for 60min;

[0049] 2. Transfer the mixed solution after ultrasound to a three-necked flask, add 10.5g 5wt% chloroplatinic acid precursor, 12g 10wt% sodium carbonate and 0.4g methanol, and mix under magnetic stirring for 30min at room temperature;

[0050] 3. Transfer the stirred solution to a water bath and stir the reaction at 75°C for 3 hours;

[0051] While dispersing carbon powder by liquid phase method, platinum nanoparticles with controllable particle size are prepared by colloid method;

[0052] 4. Weigh 15.8 g of 5 wt% chloroplatinic acid precursor, 38 g of ethylene glycol, 18 g of 10 wt% sodium carbonate and 0.6 g of methanol into a three-necked beaker and mix them under magnetic stirring at room temperature for 30 min;

[0053] 5. After stirring at room temperature, transfer the three-necked flask to a water bath and stir the reaction at 75°C for 3 hours until the solution completely changes color;

[0054] 6. After the liquid phase method reaction is completed, the solution is transferred to a 2L beaker and placed on a magnetic stirrer for cooling and stirring; at the same time, the platinum colloid prepared by the colloid method is slowly added to the beaker to mix the two solutions and continue stirring for 30 minutes;

[0055] 7. After stirring, add 3 g of concentrated sulfuric acid drop by drop, continue stirring, and when no bubbles are generated, add 1000 g of deionized water and stir for 12 hours; then let it stand for 24 hours;

[0056] 8. After standing, the precipitate is washed with deionizer and filtered to obtain the precipitate; then, it is dried in a vacuum drying oven at 70°C for 3 hours, and the desired electrocatalyst is obtained after grinding.

[0057] Example 3

[0058] 1. Weigh 0.5g of Cabot FCX800 carbon powder, 40g of ethylene glycol, 40g of n-propanol and 20g of deionized water, stir and mix, place in an ultrasonic rod disperser with ice water circulation, and ultrasonically disperse for 60min;

[0059] 2. Transfer the mixed solution after ultrasound to a three-necked flask, add 13.2g of 5wt% chloroplatinic acid precursor, 15g of 10wt% sodium carbonate and 0.5g of methanol, and mix under magnetic stirring for 30min at room temperature;

[0060] 3. Transfer the stirred solution to a water bath and stir the reaction at 75°C for 3 hours;

[0061] While dispersing carbon powder by liquid phase method, platinum nanoparticles with controllable particle size are prepared by colloid method;

[0062] 4. Weigh 13.2 g of 5 wt% chloroplatinic acid precursor, 31 g of ethylene glycol, 15 g of 10 wt% sodium carbonate and 0.5 g of methanol into a three-necked beaker and mix them under magnetic stirring at room temperature for 30 min;

[0063] 5. After stirring at room temperature, transfer the three-necked flask to a water bath and stir the reaction at 75°C for 3 hours until the solution completely changes color;

[0064] 6. After the liquid phase method reaction is completed, the solution is transferred to a 2L beaker and placed on a magnetic stirrer for cooling and stirring; at the same time, the platinum colloid prepared by the colloid method is slowly added to the beaker to mix the two solutions and continue stirring for 30 minutes;

[0065] 7. After stirring, add 3 g of concentrated sulfuric acid drop by drop, continue stirring, and when no bubbles are generated, add 1000 g of deionized water and stir for 12 hours; then let it stand for 24 hours;

[0066] 8. After standing, the precipitate is washed with deionizer and filtered to obtain the precipitate; then, it is dried in a vacuum drying oven at 70°C for 3 hours, and the desired electrocatalyst is obtained after grinding.

[0067] Example 4

[0068] 1. Weigh 0.5g of Cabot FCX800 carbon powder, 40g of ethylene glycol, 40g of n-propanol and 20g of deionized water, stir and mix, place in an ultrasonic rod disperser with ice water circulation, and ultrasonically disperse for 60min;

[0069] 2. Transfer the mixed solution after ultrasound to a three-necked flask, add 15.8 g of 5 wt% chloroplatinic acid precursor, 18 g of 10 wt% sodium carbonate and 0.6 g of methanol, and mix under magnetic stirring for 30 min at room temperature;

[0070] 3. Transfer the stirred solution to a water bath and stir the reaction at 75°C for 3 hours;

[0071] While dispersing carbon powder by liquid phase method, platinum nanoparticles with controllable particle size are prepared by colloid method;

[0072] 4. Weigh 10.5 g of 5 wt% chloroplatinic acid precursor, 25 g of ethylene glycol, 12 g of 10 wt% sodium carbonate and 0.4 g of methanol into a three-necked beaker and mix them under magnetic stirring at room temperature for 30 min;

[0073] 5. After stirring at room temperature, transfer the three-necked flask to a water bath and stir the reaction at 75°C for 3 hours until the solution completely changes color;

[0074] 6. After the liquid phase method reaction is completed, the solution is transferred to a 2L beaker and placed on a magnetic stirrer for cooling and stirring; at the same time, the platinum colloid prepared by the colloid method is slowly added to the beaker to mix the two solutions and continue stirring for 30 minutes;

[0075] 7. After stirring, add 3 g of concentrated sulfuric acid drop by drop, continue stirring, and when no bubbles are generated, add 1000 g of deionized water and stir for 12 hours; then let it stand for 24 hours;

[0076] 8. After standing, the precipitate is washed with deionizer and filtered to obtain the precipitate; then, it is dried in a vacuum drying oven at 70°C for 3 hours, and the desired electrocatalyst is obtained after grinding.

[0077] Example 5

[0078] 1. Weigh 0.5g of Cabot FCX800 carbon powder, 40g of ethylene glycol, 40g of n-propanol and 20g of deionized water, stir and mix, place in an ultrasonic rod disperser with ice water circulation, and ultrasonically disperse for 60min;

[0079] 2. Transfer the mixed solution after ultrasound to a three-necked flask, add 21.1 g of 5 wt% chloroplatinic acid precursor, 24 g of 10 wt% sodium carbonate and 0.8 g of methanol, and mix under magnetic stirring for 30 min at room temperature;

[0080] 3. Transfer the stirred solution to a water bath and stir the reaction at 75°C for 3 hours;

[0081] While dispersing carbon powder by liquid phase method, platinum nanoparticles with controllable particle size are prepared by colloid method;

[0082] 4. Weigh 5.3 g of 5 wt% chloroplatinic acid precursor, 13 g of ethylene glycol, 6 g of 10 wt% sodium carbonate and 0.2 g of methanol into a three-necked beaker and mix them under magnetic stirring at room temperature for 30 min;

[0083] 5. After stirring at room temperature, transfer the three-necked flask to a water bath and stir the reaction at 75°C for 3 hours until the solution completely changes color;

[0084] 6. After the liquid phase method reaction is completed, the solution is transferred to a 2L beaker and placed on a magnetic stirrer for cooling and stirring; at the same time, the platinum colloid prepared by the colloid method is slowly added to the beaker to mix the two solutions and continue stirring for 30 minutes;

[0085] 7. After stirring, add 3 g of concentrated sulfuric acid drop by drop, continue stirring, and when no bubbles are generated, add 1000 g of deionized water and stir for 12 hours; then let it stand for 24 hours;

[0086] 8. After standing, the precipitate is washed with deionizer and filtered to obtain the precipitate; then, it is dried in a vacuum drying oven at 70°C for 3 hours, and the desired electrocatalyst is obtained after grinding.

[0087] Comparative Example 1 Preparation of Catalyst by Liquid Phase Method

[0088] 1. Weigh 0.5g of Cabot FCX800 carbon powder, 40g of ethylene glycol, 40g of n-propanol and 20g of deionized water, stir and mix, place in an ultrasonic rod disperser with ice water circulation, and ultrasonically disperse for 60min;

[0089] 2. Transfer the mixed solution after ultrasound into a three-necked flask, add 26.3g 5wt% chloroplatinic acid precursor, 30g 10wt% sodium carbonate and 1g methanol, and mix under magnetic stirring for 30min at room temperature;

[0090] 3. Transfer the stirred solution to a water bath and stir the reaction at 75°C for 3 hours;

[0091] 4. After the reaction is completed, transfer the solution to a 2L beaker and place it on a magnetic stirrer and stir for 30 minutes at low temperature;

[0092] 5. After stirring, add 3 g of concentrated sulfuric acid drop by drop, continue stirring, and when no bubbles are generated, add 1000 g of deionized water and stir for 12 hours; then let it stand for 24 hours;

[0093] 6. After standing, the precipitate is washed with deionizer and filtered to obtain the precipitate; then, it is dried in a vacuum drying oven at 70°C for 3 hours, and the desired electrocatalyst is obtained after grinding.

[0094] Comparative Example 2 Preparation of Catalyst by Colloidal Method

[0095] 1. Weigh 26.3 g of 5 wt% chloroplatinic acid precursor, 63 g of ethylene glycol, 30 g of 10 wt% sodium carbonate and 1 g of methanol into a three-necked beaker and mix them under magnetic stirring at room temperature for 30 min;

[0096] 2. After stirring, transfer the three-necked flask to a water bath and stir the reaction at 75°C for 3 hours until the solution completely changes color;

[0097] 3. Weigh 0.5g of Cabot FCX800 carbon powder, 40g of ethylene glycol, 40g of n-propanol and 20g of deionized water, stir and mix, place in an ultrasonic rod disperser with ice water circulation, and ultrasonically disperse for 60 minutes; after the ultrasonication is completed, transfer to a 2L beaker and continue stirring;

[0098] 4. After the platinum colloid reaction is completed, slowly transfer the solution to a 2L beaker containing carbon powder and place it on a magnetic stirrer to cool and stir for 30 minutes;

[0099] 5. After stirring, add 3 g of concentrated sulfuric acid drop by drop, continue stirring, and when no bubbles are generated, add 1000 g of deionized water and stir for 12 hours; then let it stand for 24 hours;

[0100] 6. After standing, the precipitate is washed with deionizer and filtered to obtain the precipitate; then, it is dried in a vacuum drying oven at 70°C for 3 hours, and the desired electrocatalyst is obtained after grinding.

[0101] Test Example 1

[0102] (1) The electrochemical performance of the catalysts prepared in Examples 1-5 and Comparative Examples 1 and 2 was tested under the same conditions. The test method was as follows: 5 mg of the catalyst was accurately weighed into a 25 mL brown bottle, and 5 mL of the prepared Nafion isopropanol solution was added; ultrasonic dispersion was performed for 30 min to mix the slurry evenly; 5 μl of the dispersed slurry was transferred with a pipette and evenly dripped onto the smooth and clean surface of the glassy carbon electrode, which was completely dried under an infrared lamp and used as the working electrode; a calomel electrode was used as the reference electrode, a platinum electrode was used as the counter electrode, and the electrolyte was N 2 Saturated 0.5 mol / L sulfuric acid solution. Then the cyclic voltammetry curve test was carried out, and the hydrogen desorption peak of the curve was integrated to calculate the electrochemical area ECSA of the catalyst. The results are as follows Figure 2 As shown in Table 1;

[0103] Table 1 Catalyst electrochemical statistics (unit: m 2 / g)

[0104] Experiment No. Electrochemical ECSA Preparation process Example 1 49.5 Step-by-step preparation Example 2 50.8 Step-by-step preparation Example 3 52.4 Step-by-step preparation Example 4 56.3 Step-by-step preparation Example 5 53.2 Step-by-step preparation Comparative Example 1 38.4 Colloid method Comparative Example 2 44.5 Liquid Phase Method

[0105] In the electrolyte test, the Nafion solution mainly contacts the active sites of the platinum particles on the catalyst surface. Therefore, the more platinum exposed on the surface, the better the electrochemical performance of the catalyst. However, when too much platinum is dispersed on the carrier surface, the platinum particles are unevenly dispersed due to the limited specific surface area of ​​the carrier. When there is agglomeration on the surface, there is a certain surface platinum that cannot exert its catalytic performance. For example, the electrochemical area of ​​the catalyst in Comparative Example 1 prepared by the colloid method is 38.4 m 2 / g, the performance is poor, which may be due to the agglomeration of a large number of platinum nanoparticles with a particle size of about 4-5nm on the platinum surface, thereby affecting the electrochemical performance; for the catalyst of comparative example 2 prepared by the liquid phase method, its electrochemical area is 44.5m 2 / g, the performance of the catalyst in the electrolyte is poor, which may be due to the fact that during the liquid phase preparation process, a large amount of platinum precursors are adsorbed in the carrier pores, and then nucleate and grow during the reduction process. During the electrolyte test, Nafion cannot contact this part of the platinum particles, which leads to a small electrochemical area of ​​the catalyst; in Examples 1 to 5, due to the different contents of platinum particles prepared by the liquid phase method and the colloid method, the electrochemical active area of ​​the catalyst is different, among which Example 4 has the best electrochemical area, indicating that in this series of experiments, when the mass ratio of platinum particles prepared by the colloid method and the liquid phase method is 3:2, the catalyst performance is better;

[0106] (2) The catalysts prepared in Example 4 and Comparative Examples 1 and 2 were sprayed to prepare membrane electrodes, and then single cells were assembled to test the electrochemical performance of the single cells under different humidity conditions;

[0107] The anodes were all made of commercial 50% Pt / C catalyst with a loading of 0.1 mg / cm 2 . A homemade catalyst was selected as the cathode, and the specific preparation method is as follows: weigh 0.5g of the catalyst and place it in a 50mL beaker, transfer 2g of deionized water to wet the catalyst, then add 7g of n-propanol, 2g of 5wt% Nafion solution, 13g of deionized water, and ultrasonicate in an ice bath for 20min; then the mixture is treated by a dispersing and emulsifying homogenizer for 30 minutes to obtain a mixed catalytic layer ink. Using the direct spraying method, the above catalyst slurry is sprayed directly onto the surface of a 15μm proton exchange membrane to form a cathode and anode catalytic layer covering the membrane, and the amount of Pt nanoparticles loaded is controlled by weighing. The spraying process parameters are set as follows: nozzle flow rate 8mL / min, suction cup heating temperature 90°C, and nozzle height from the heating suction cup 40cm 2 .

[0108] The anode was prepared by spraying in the same way, and then made into a membrane electrode and assembled into a single cell for testing;

[0109] Single cell electrochemical test method: Install the assembled single cell on the fuel cell test platform and connect the pipeline to activate the single cell; then use high-purity nitrogen to purge the pipeline and reaction chamber; after completion, perform membrane electrode electrochemical performance test; test conditions are: single cell temperature 80℃, RH100% humidified hydrogen is passed into the anode at a flow rate of 50mL / min, and N with different humidity is passed into the cathode 2 , flow rate is 50mL / min; voltage scanning range is 0.05-0.6V, scanning rate is 50mv / s; the electrochemical area of ​​the cathode catalyst layer under different humidity is tested; the test results are as follows Figure 3-Figure 5 As shown in Table 2;

[0110] Table 2 Electrochemical statistics of cathode catalyst layer of single cell at different humidity / unit: m 2 / g

[0111] Experimental samples 30%RH 50%RH 100%RH Preparation process Example 4 55.5 61.0 68.5 Step-by-step preparation Comparative Example 1 36.9 39.3 41.3 Colloid method Comparative Example 2 44.9 46.3 56.1 Liquid Phase Method

[0112] The catalyst layer of a single cell is usually composed of a catalyst and its carrier, a polymer and pores, in which the main function of the polymer is proton conduction and bonding. In the three-phase region of the electrochemical reaction of the catalyst layer, the reaction gas needs to pass through the pores to reach the catalyst surface smoothly, and the proton needs to be transferred from the anode to the three-phase interface through the polymer; however, too much polymer on the surface of the cathode Pt catalyst will reduce the activity because the Pt catalyst adsorbs sulfonic acid and forms a dense polymer molecule layer near the Pt surface.

[0113] Polymers usually do not easily penetrate into the pores of the carrier, so avoiding direct contact between the catalyst surface and the polymer is one of the effective ways to change the catalyst poisoning caused by polymer coverage. However, compared with surface platinum, the oxygen mass transfer process is not easy to occur in the catalyst existing in the pores, the interaction between the gas and the platinum particles will be weakened, and the membrane electrode performance will also be reduced. Therefore, it is very important to regulate the balance of the content of platinum particles on the carrier surface and in the pores.

[0114] It can be seen from the test results that for the cathode catalyst layer of the single cell of Example 1 prepared by the colloid method, the increase in humidity cannot significantly improve the electrochemical performance of the catalyst layer. This may be due to the presence of a large number of large-size platinum particles on the surface of the carrier and the presence of a certain agglomeration phenomenon. In addition, the coverage of the platinum particles by the polymer causes the catalyst performance to not be alleviated with the increase in humidity. For the cathode catalyst layer of the single cell of Example 2 prepared by the liquid phase method, the electrochemical performance at 100% RH is significantly better than that at 30% RH, which indicates that some platinum particles exist in the pores of the carrier, and the increase in humidity improves the active sites of the platinum particles. Example 4 has the best electrochemical performance, and the electrochemical area increases significantly with the increase in humidity. This may be due to the reasonable content distribution of platinum particles on the surface and in the pores of the carrier, and the absence of agglomeration of platinum particles on the surface of the carrier, which results in fewer active sites not covered by the polymer. There is also no large amount of platinum particles in the pores of the carrier, which makes gas mass transfer difficult to occur, weakens the interaction between the platinum particles and the gas, and reduces the performance of the membrane electrode.

[0115] (3) Durability of the catalyst

[0116] The durability test of the cathode catalyst layer of a single cell was carried out on Example 4, Comparative Example 1 and Comparative Example 2. The experimental conditions were as follows: the initial BOL (Beginning of Life) test electrochemistry of the single cell was tested at high temperature as required; then the temperature controller was connected to the single cell and the temperature was set to 80°C; humidified nitrogen was passed through the cathode of the single cell with a relative humidity of 100% and a flow rate of 200ml / min, and humidified hydrogen was passed through the anode with a relative humidity of 100% and a flow rate of 75ml / min; a wavedriver electrochemical workstation was used, the working voltage was set to 0.6-1.0V triangle wave cycle, the scanning rate was 100mv / s, 8s / cycle, the number of experimental cycles was 10,000 cycles, and the electrochemical decay rate of the cathode catalyst layer was tested; the results are as follows Figure 6 , Figure 7 and Figure 8 As shown, the statistical table is shown in Table 3.

[0117] Table 3 Statistics of accelerated aging electrochemical tests of different samples (unit: m 2 / g)

[0118] Experimental samples BOL After 10,000 laps Decay rate Preparation process Example 4 67.8 57.9 14.6％ Step-by-step preparation Comparative Example 1 42.1 31.2 25.8％ Colloid method Comparative Example 2 57.2 33.1 42.1％ Liquid Phase Method

[0119] In the actual operation of the fuel cell, the catalyst performance will be greatly attenuated due to the dissolution of Pt nanoparticles, the agglomeration of Pt particles leading to an increase in particle size, which reduces the activity of the catalyst, and the corrosion of the carbon carrier or the weakening of the interaction between the Pt particles and the carbon carrier, which leads to the shedding of Pt. Compared with the electrolyte experiment at room temperature, the operation of a single cell at high temperature is more likely to lead to a decrease in the activity of the catalyst layer. The test results show that after accelerated aging, the catalytic layers of the three catalysts all experienced a certain degree of performance attenuation. After 10,000 cycles, the electrochemical performance attenuation rates were 14.6%, 25.8% and 42.1%, respectively. In Comparative Example 1, a large number of platinum particles exist on the surface of the carrier, and there is an agglomeration phenomenon. The occurrence of the phenomenon makes it easy for the platinum particles to migrate and re-deposit during the accelerated aging process; Comparative Example 2 adopts a liquid phase method to prepare the catalyst, and the platinum particles have a certain distribution on the carrier surface and in the pores. However, the particle size distribution of the platinum particles on the carrier surface is uneven, and the particle size deviation is large, which makes it easy for the platinum particles to dissolve, and then the performance of the catalytic layer is greatly attenuated; for Example 4, through the regulation of the preparation process, the platinum particles have a suitable content distribution on the carrier surface and in the pores, the platinum particles distributed on the carrier surface are highly evenly dispersed, and the particle size is highly concentrated at about 4-5nm. During the accelerated aging process, the dissolution and migration of the platinum particles are weakened, thereby improving the durability of the catalytic layer.

Claims

1. A method for preparing a fuel cell catalyst, It is characterized in that The following steps are involved: (1) mixing a carbon carrier, an organic solvent and water, and dispersing them to obtain a first mixed solution; (2) mixing the first mixed solution prepared in step (1), the first mass of the platinum salt precursor, the alkali solution and the reducing agent, and heating the mixture to react to obtain a first reaction solution; (3) mixing a second mass of platinum salt precursor, an organic solvent, an alkali solution and a reducing agent and heating the mixture to react to obtain a second reaction solution; (4) mixing the first reaction liquid obtained in step (2) and the second reaction liquid obtained in step (3), then dropping an acid solution to neutralize the mixture, and filtering the mixture to obtain the fuel cell catalyst. The ratio of the first mass to the second mass is 1:0.25-4.

2. The method for preparing a fuel cell catalyst according to claim 1, It is characterized in that The carbon carrier is conductive carbon black.

3. The method for preparing a fuel cell catalyst according to claim 1, It is characterized in that The platinum salt in the platinum salt precursor is chloroplatinic acid or potassium chloroplatinate.

4. The method for preparing a fuel cell catalyst according to claim 1, It is characterized in that The alkali solution is a sodium carbonate solution or a sodium hydroxide solution, with a mass fraction of 5wt%-20wt%; The reducing agent is at least one of methanol and formaldehyde; The organic solvent is at least one of ethylene glycol and n-propanol.

5. The method for preparing a fuel cell catalyst according to claim 1, It is characterized in that In step (2) and step (3), the heating reaction temperature is 65-90° C., and the heating reaction time is 3-5 h.

6. The method for preparing a fuel cell catalyst according to claim 1, It is characterized in that After adding acid solution for neutralization, a second mixed solution is obtained, and a precipitate is obtained after filtering. The precipitate is vacuum dried at 60-80° C. for 2-3 hours, and the fuel cell catalyst is obtained after grinding.

7. A fuel cell catalyst prepared by the method for preparing a fuel cell catalyst according to any one of claims 1 to 6.

8. Use of the fuel cell catalyst as claimed in claim 7, It is characterized in that The fuel cell catalyst is used as an anode catalyst or a cathode catalyst of a fuel cell.

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