A catalyst for fuel cells and a method for producing the same

Abstract

The application discloses a kind of catalysts for fuel cell and its preparation method, it is related to fuel cell technical field.The application provides a kind of zirconium carbon composite carrier and catalyst preparation process, platinum colloid and platinum supported catalyst are prepared using distribution method, and platinum particle size can be controlled, uniformly dispersed on carrier;The preparation method of the present application is simple, easy to operate, and can realize batch production;With the catalyst prepared by the application, the catalytic activity is good and has good resistance to monomer poisoning performance.

Description

Technical Field

[0001] This invention relates to the field of fuel cell technology, and specifically to a catalyst for fuel cells and its preparation method. Background Technology

[0002] A proton exchange membrane fuel cell (PEMFC) is a device that generates power through an electrochemical reaction between hydrogen and oxygen. Its byproduct is primarily water, making it a clean power generation system with a low environmental impact. In a fuel cell, an electromotive force is generated by supplying hydrogen-containing gaseous fuel to the anode side and an oxygen-containing oxidant to the cathode side. The anode side undergoes an oxidation reaction, while the cathode side undergoes a reduction reaction, providing an electromotive force to the external circuit. It features green environmental protection, high specific energy, rapid low-temperature start-up, and highly stable operation, and is considered an ideal power source to replace internal combustion engines.

[0003] A fuel cell stack system mainly consists of a catalyst, a gas diffusion layer, and a proton exchange membrane. The catalyst accounts for the highest proportion of the stack cost, primarily due to the limited variety of commercially available catalysts. The catalyst is one of the key materials in the membrane electrode assembly (MEA) of a proton exchange membrane fuel cell, determining the cell's discharge performance and lifespan. Since PEMFCs operate at temperatures below 100℃, they require very high catalyst activity. Platinum (Pt) catalysts possess excellent molecular adsorption and dissociation characteristics, making them the most ideal and currently the only commercially available catalyst material. However, platinum metal is expensive, and my country's reserves are very limited. Therefore, improving PEMFC performance and reducing system costs mainly involves the following approaches: one is to reduce the amount of precious metal Pt used by modifying the support and preparing alloy catalysts, thereby improving catalyst activity and stability, from the perspective of intrinsic catalyst activity.

[0004] Platinum-based catalysts are one of the key materials in fuel cells, and their intrinsic properties determine the performance, lifespan, and cost of the fuel cell system. Currently, commercial precious metal catalysts mainly use carbon as a support, which has relatively weak acid and alkali resistance, generally operating at temperatures between 60-90 degrees Celsius. Catalyst performance is prone to degradation during high-temperature operation because low-temperature fuel cell systems require hydrogen with a purity of over 99.9% and very low CO toxicity. In 2019, the Japan Fuel Cell Industrialization Promotion Association proposed that fuel cells would be able to operate at temperatures up to 150 degrees Celsius with stronger acid and alkali resistance to suit a wider range of applications. De-platinization is a fundamental way to address the high cost of fuel cells, but achieving low-platinum membrane electrodes still faces many technical challenges. These include a sharp deterioration in high-current performance, accelerated catalyst degradation, and a significant increase in ion resistance under low humidity conditions.

[0005] In the traditional catalyst slurry preparation process, the perfluorosulfonic acid ionomers, especially Nafion series derivatives, which play a proton transfer role in the catalyst layer, are directly in contact with the Pt catalyst surface after ultrasonic dispersion. In the dried catalyst layer, the ionomers existing in the form of a thin film covering the Pt surface can be directly contacted by the sulfonic acid groups (-SO) at the end of the side chains. 3- Oxygen atoms in sulfonic acid groups specifically adsorb onto the Pt surface. The poisoning effect of sulfonic acid groups on the Pt surface can lead to a loss of up to 80% of the catalyst's mass activity. Therefore, reducing the surface toxicity of sulfonic acid groups to Pt catalysts to achieve low platinum treatment and improve fuel cell performance is of great significance. Summary of the Invention

[0006] In view of this, the present invention provides a fuel cell catalyst and its preparation method. During the catalyst reaction, oxygen atoms readily coordinate with metal atoms, adsorbing onto oxygen vacancies on the metal surface, forming chemisorption. The present invention aims to modify a carbon support with zirconium, a transition metal with extremely strong adsorption capacity for oxygen atoms, to prepare a Pt / Zr-C catalyst, thereby improving the membrane electrode's resistance to ionomer poisoning and enhancing fuel cell performance.

[0007] The technical solution of the present invention is as follows:

[0008] On one hand, the present invention provides a method for preparing a zirconium carbon composite support for fuel cell catalysts, comprising the following steps:

[0009] (1) Dissolve the zirconium salt in a solvent to prepare a mixed solution;

[0010] (2) Add carbon black to the mixed solution in step (1), then add an alcohol dispersant for dispersion, and then add an alkaline solution for precipitation reaction;

[0011] (3) The precipitate after the precipitation reaction in step (2) is dried and calcined under an inert gas to obtain the zirconium carbon composite carrier.

[0012] In one embodiment of the first aspect, in step (1), the zirconium salt is at least one of zirconium nitrate and zirconium dichloride; the solid content in the mixed solution is 5%-25%. The solvent is water.

[0013] In one embodiment of the first aspect, in step (2), the carbon black is at least one of Cabot FCX800 and Toyo Carbon MH-1800;

[0014] The alcohol dispersant is at least one of n-butanol and isopropanol;

[0015] The concentration of the alkaline solution is 10wt% to 20wt%, and the alkaline solution is at least one of sodium hydroxide solution and sodium carbonate solution.

[0016] In one embodiment of the first aspect, in step (3), the inert gas is hydrogen and argon, with a volume percentage of 5%;

[0017] The calcination temperature is 600-900℃, and the calcination time is 3-6 hours.

[0018] In a second aspect, the present invention also provides a zirconium carbon composite support prepared by the preparation method described above, the zirconium carbon composite support comprising carbon and zirconium, wherein the mass fraction of zirconium is 5%-15%.

[0019] In a third aspect, the present invention also provides a catalyst for a fuel cell, the catalyst comprising the zirconium carbon composite support and an active component supported on the zirconium carbon composite support, the active component being platinum.

[0020] In one embodiment of the third aspect, the loading of the active component is 50%.

[0021] In a fourth aspect, the present invention also provides a method for preparing the catalyst for a fuel cell, comprising the following steps:

[0022] S1: The chloride precursor solution, alkaline solution, ethylene glycol and reducing agent are mixed and stirred under inert gas to obtain reaction solution 1;

[0023] S2: Mix and disperse the zirconium carbon composite carrier and alcohol dispersant to obtain reaction solution 2;

[0024] S3: Add reaction solution 1 dropwise to reaction solution 2 to obtain a mixed solution. Then add acid solution dropwise to the mixed solution. After filtration and drying, the catalyst for fuel cells is obtained.

[0025] In one embodiment of the fourth aspect, in step S1, the platinum salt precursor solution is at least one of chloroplatinic acid and platinum nitrate.

[0026] The alkaline solution is at least one of sodium carbonate, ammonia, and sodium bicarbonate.

[0027] The reducing agent is at least one of methanol and formic acid;

[0028] The reaction temperature is 70-90℃, and the reaction time is 3-6 hours;

[0029] In step S2, the alcohol dispersant is at least one of anhydrous ethanol, n-butanol, and isopropanol.

[0030] In one embodiment of the fourth aspect, in step S3, the acid solution is at least one of sulfuric acid and nitric acid, and the mass fraction of the acid solution is 5wt%-10wt%.

[0031] Preferably, the cooling and stirring time of reaction solution 1 in the magnetic stirrer is 1-2 hours; the stirring and dispersion time of reaction solution 2 in the magnetic stirrer is 1-2 hours.

[0032] Preferably, after adding reaction solution 1 dropwise to reaction solution 2, stirring is continued for 0.5-1 hour. After adding acid, the mixture is stirred for 6-8 hours and then allowed to settle overnight.

[0033] The drying temperature is 70-100℃, and the drying time is 3-6 hours.

[0034] The beneficial effects of this invention are:

[0035] This invention provides a zirconium carbon composite support and a catalyst preparation process. Platinum colloids and platinum-supported catalysts are prepared by a distribution method, and the particle size of platinum particles is controllable and uniformly dispersed on the support. This preparation method is simple, easy to operate, and can achieve mass production. The catalyst prepared by this invention has good catalytic activity and good resistance to ionomer poisoning. Attached Figure Description

[0036] Figure 1 The CV performance diagrams of the catalysts prepared in Examples 1-4 and Comparative Example 1 of this invention are shown in the electrolyte.

[0037] Figure 2 The images show the electrochemical test spectra on the cathode side at different I / C ratios when the catalyst of Example 2 is used as the cathode catalyst.

[0038] Figure 3 The images show the electrochemical spectra of the cathode side at different I / C ratios when the catalyst of Comparative Example 1 is used as the cathode catalyst.

[0039] Figure 4 The graphs show the polarization curves of the membrane electrode at different I / C ratios when the catalyst of Example 2 is used as the cathode catalyst.

[0040] Figure 5 The graphs show the polarization curves of the membrane electrode at different I / C ratios when the catalyst of Comparative Example 1 is used as the cathode catalyst. Detailed Implementation

[0041] Example 1

[0042] This invention provides a method for preparing a zirconium carbon composite support and its catalyst, comprising the following steps;

[0043] Step 1: Weigh 1.28g of a 10% zirconium dichloride aqueous solution, 20g of anhydrous ethanol, and 0.95g of Cabot FCX800 carbon black into a beaker, stir, and then place the beaker in a sand mill and disperse at 1600rpm for 30 minutes.

[0044] Step 2: Place the dispersed solution in a three-necked flask, put it in a water bath, set the temperature to 75℃, add 2.5g of 10wt% sodium hydroxide solution while stirring, and continue stirring for 1 hour.

[0045] Step 3: After the reaction is complete, let the solution stand for 3 hours, then filter it and dry it in an air drying oven at 100°C for 3 hours.

[0046] Step 4: Place the dried solid in a quartz boat and put it into a high-temperature atmosphere furnace. After evacuation, introduce a 5% (v / v) H2 / Ar mixed gas at a flow rate of 100 ml / min. Heat the solid at a rate of 10 °C / min and calcine it at 700 °C for 3 hours. After natural cooling, the desired zirconium carbon is obtained and labeled as 5 wt% Zr-C.

[0047] Step 5: Weigh 6.6g of 20wt% ethylene glycol solution, add 80g of ethylene glycol, 1g of methanol, and 5g of 20wt% sodium carbonate solution into a three-necked flask, stir for 10 minutes, then place in a water bath and react at 85℃ for 3 hours under nitrogen purging. During this period, the solution color changes from pale yellow to black.

[0048] Step 6: Weigh 0.5g of carbon zirconium, 25g of n-butanol and 25g of ethylene glycol, place them in a sand mill, and disperse them at 1800rpm for 1 hour. During this time, the sand mill is kept warm by circulating cooling water. After the reaction is complete, place the solution in a beaker and continue stirring on a magnetic stirrer.

[0049] Step 7: Place the platinum colloid obtained in step 5 into a beaker, stir and cool for 2 hours under magnetic stirring; then slowly pour the cooled colloidal solution into the zirconium carbon slurry obtained in step 6, and continue to stir the mixture at room temperature for 0.5 hours.

[0050] Step 8: Add 10g of 10wt% H2SO4 solution dropwise to the mixture stirred at room temperature in Step 7, then continue stirring for 6 hours, and finally let it settle overnight;

[0051] Step 9: Filter the settled solution and then place it in a vacuum drying oven and dry it at 80°C for 6 hours to obtain the desired catalyst; labeled as 50% Pt / 5wt% Zr-C.

[0052] Example 2

[0053] This invention provides a method for preparing a zirconium carbon composite support and its catalyst, comprising the following steps;

[0054] Step 1: Weigh 2.56g of a 10% zirconium dichloride aqueous solution, 20g of ethanol, and 0.9g of Cabot FCX800 carbon black into a beaker, stir, and then place the beaker in a sand mill and disperse at 1600rpm for 30 minutes.

[0055] Step 2: Place the dispersed solution in a three-necked flask, put it in a water bath, set the temperature to 75°C, add 3g of 10wt% sodium hydroxide solution while stirring, and continue stirring for 1 hour.

[0056] Step 3: After the reaction is complete, let the solution stand for 3 hours, then filter it and dry it in an air drying oven at 100°C for 3 hours.

[0057] Step 4: Place the dried solid in a quartz boat and put it into a high-temperature atmosphere furnace. After evacuation, introduce a 5% (v / v) H2 / Ar mixed gas at a flow rate of 100 ml / min. Heat the solid at a rate of 10 °C / min and calcine it at 700 °C for 3 hours. After natural cooling, the desired zirconium carbon is obtained and labeled as 10 wt% Zr-C.

[0058] Step 5: Weigh 6.6g of 20wt% ethylene glycol solution, add 80g of ethylene glycol, 1g of methanol, and 5g of 20wt% sodium carbonate solution into a three-necked flask, stir for 10 minutes, then place in a water bath and react at 85℃ for 3 hours under nitrogen purging. During this period, the solution color changes from pale yellow to black.

[0059] Step 6: Weigh 0.5g of carbon zirconium, 25g of n-butanol and 25g of ethylene glycol, place them in a sand mill, and disperse them at 1800rpm for 1 hour. During this time, the sand mill is kept warm by circulating cooling water. After the reaction is complete, place the solution in a beaker and continue stirring on a magnetic stirrer.

[0060] Step 7: Place the platinum colloid obtained in step 5 into a beaker, stir and cool for 2 hours under magnetic stirring; then slowly pour the cooled colloidal solution into the zirconium carbon slurry obtained in step 6, and continue to stir the mixture at room temperature for 0.5 hours.

[0061] Step 8: Add 10g of 10wt% H2SO4 solution dropwise to the mixture stirred at room temperature in Step 7, then continue stirring for 6 hours, and finally let it settle overnight;

[0062] Step 9: Filter the settled solution and then place it in a vacuum drying oven and dry it at 80°C for 6 hours to obtain the desired catalyst; labeled as 50% Pt / 10wt% Zr-C.

[0063] Example 3

[0064] This invention provides a method for preparing a zirconium carbon composite support and its catalyst, comprising the following steps;

[0065] Step 1: Weigh 3.84g of a 10% zirconium dichloride aqueous solution, 20g of ethanol, and 0.85g of Cabot FCX800 carbon black into a beaker, stir, and then place the beaker in a sand mill and disperse at 1600rpm for 30 minutes.

[0066] Step 2: Place the dispersed solution in a three-necked flask, put it in a water bath, set the temperature to 75℃, add 3.5g of 10wt% sodium hydroxide solution while stirring, and continue stirring for 1 hour.

[0067] Step 3: After the reaction is complete, let the solution stand for 3 hours, then filter it and dry it in an air drying oven at 100°C for 3 hours.

[0068] Step 4: Place the dried solid in a quartz boat and put it into a high-temperature atmosphere furnace. After evacuation, introduce a 5% (v / v) H2 / Ar mixed gas at a flow rate of 100 ml / min. Heat the solid at a rate of 10 °C / min and calcine it at 700 °C for 3 hours. After natural cooling, the desired zirconium carbon is obtained and labeled as 15 wt% Zr-C.

[0069] Step 5: Weigh 6.6g of 20wt% ethylene glycol solution, add 80g of ethylene glycol, 1g of methanol, and 5g of 20wt% sodium carbonate solution into a three-necked flask, stir for 10 minutes, then place in a water bath and react at 85℃ for 3 hours under nitrogen purging. During this period, the solution color changes from pale yellow to black.

[0070] Step 6: Weigh 0.5g of carbon zirconium, 25g of n-butanol and 25g of ethylene glycol, place them in a sand mill, and disperse them at 1800rpm for 1 hour. During this time, the sand mill is kept warm by circulating cooling water. After the reaction is complete, place the solution in a beaker and continue stirring on a magnetic stirrer.

[0071] Step 7: Place the platinum colloid obtained in step 5 into a beaker, stir and cool for 2 hours under magnetic stirring; then slowly pour the cooled colloidal solution into the zirconium carbon slurry obtained in step 6, and continue to stir the mixture at room temperature for 0.5 hours.

[0072] Step 8: Add 10g of 10wt% H2SO4 solution dropwise to the mixture stirred at room temperature in Step 7, then continue stirring for 6 hours, and finally let it settle overnight;

[0073] Step 9: Filter the settled solution and then place it in a vacuum drying oven and dry it at 80°C for 6 hours to obtain the desired catalyst; labeled as 50% Pt / 15wt% Zr-C.

[0074] Example 4

[0075] This invention provides a method for preparing a zirconium carbon composite support and its catalyst, comprising the following steps;

[0076] Step 1: Weigh 5.12g of a 10% zirconium dichloride aqueous solution, 20g of ethanol, and 0.8g of Cabot FCX800 carbon black into a beaker, stir, and then place the beaker in a sand mill and disperse at 1600rpm for 30 minutes.

[0077] Step 2: Place the dispersed solution in a three-necked flask, put it in a water bath, set the temperature to 75℃, add 4g of 10wt% sodium hydroxide solution while stirring, and continue stirring for 1 hour.

[0078] Step 3: After the reaction is complete, let the solution stand for 3 hours, then filter it and dry it in an air drying oven at 100°C for 3 hours.

[0079] Step 4: Place the dried solid in a quartz boat and put it into a high-temperature atmosphere furnace. After evacuation, introduce a 5% (v / v) H2 / Ar mixed gas at a flow rate of 100 ml / min. Heat the solid at a rate of 10 °C / min and calcine it at 700 °C for 3 hours. After natural cooling, the desired zirconium carbon is obtained and labeled as 20 wt% Zr-C.

[0080] Step 5: Weigh 6.6g of 20wt% ethylene glycol solution, add 80g of ethylene glycol, 1g of methanol, and 5g of 20wt% sodium carbonate solution into a three-necked flask, stir for 10 minutes, then place in a water bath and react at 85℃ for 3 hours under nitrogen purging. During this period, the solution color changes from pale yellow to black.

[0081] Step 6: Weigh 0.5g of carbon zirconium, 25g of n-butanol and 25g of ethylene glycol, place them in a sand mill, and disperse them at 1800rpm for 1 hour. During this time, the sand mill is kept warm by circulating cooling water. After the reaction is complete, place the solution in a beaker and continue stirring on a magnetic stirrer.

[0082] Step 7: Place the platinum colloid obtained in step 5 into a beaker, stir and cool for 2 hours under magnetic stirring; then slowly pour the cooled colloidal solution into the zirconium carbon slurry obtained in step 6, and continue to stir the mixture at room temperature for 0.5 hours.

[0083] Step 8: Add 10g of 10wt% H2SO4 solution dropwise to the mixture stirred at room temperature in Step 7, then continue stirring for 6 hours, and finally let it settle overnight;

[0084] Step 9: Filter the settled solution and then place it in a vacuum drying oven and dry it at 80°C for 6 hours to obtain the desired catalyst; labeled as 50% Pt / 20wt% Zr-C.

[0085] Comparative Example 1

[0086] Using Cabot FCX800 as a support, a 50% Pt / C catalyst was prepared by a colloidal method. The specific steps were as follows: 6.6 g of 20 wt% ethylene glycol solution was weighed, and 80 g of ethylene glycol, 1 g of methanol, and 5 g of 20 wt% sodium carbonate solution were added to a three-necked flask. After stirring for 10 minutes, the flask was placed in a water bath and reacted at 85°C for 3 hours under nitrogen purging. During this period, the solution color changed from pale yellow to black. 0.5 g of… FCX800 carbon black, 25g n-butanol, and 25g ethylene glycol were placed in a sand mill and dispersed at 1800 rpm for 1 hour, with cooling water circulating in the mill during the reaction. After the reaction, the solution was placed in a beaker and stirred on a magnetic stirrer. The resulting platinum colloid was placed in a beaker and cooled under magnetic stirring for 2 hours. The cooled colloidal solution was then slowly poured into the carbon slurry, and the mixture was stirred at room temperature for 0.5 hours. 10g of 10wt% H2SO4 solution was added dropwise to the mixture after stirring at room temperature, and stirring was continued for 6 hours. The mixture was then allowed to settle overnight. The settled solution was filtered and then placed in a vacuum drying oven and dried at 80°C for 6 hours to obtain the desired catalyst, labeled as 50% Pt / C.

[0087] Test Example 1

[0088] The catalysts prepared in Examples 1-4 and Comparative Example 1 were subjected to electrochemical performance tests under the same conditions. The test method was as follows: 5 mg of catalyst was accurately weighed into a 25 ml brown glass bottle, and 5 ml of prepared Nafion isopropanol solution (Nafion mass fraction of 0.13%) was added; the mixture was ultrasonically dispersed in ice water for 30 minutes to ensure uniform mixing; 5 μl of the dispersed slurry was transferred by pipette and evenly dropped onto the surface of a smooth and clean glassy carbon disk electrode, and completely dried under an infrared lamp to serve as the working electrode; the electrode was placed in a 5-cell electrolytic cell to form a three-electrode system. The reference electrode was a calomel electrode, the counter electrode was a Pt wire electrode, and the electrolyte was a 0.5 mol / L H2SO4 solution saturated with N2.

[0089] Cyclic voltammetry testing: First, the catalyst was activated for 10 cycles at a scan rate of 200 mV / s within a voltage range of 0.4–1.4 V (relative to the RHE electrode). Then, it was scanned for 4 cycles at a scan rate of 50 mV / s within a potential range of 0.05 V–1.15 V (relative to the RHE electrode). The stabilized cyclic voltammetry curve was then selected, as shown below. Figure 1As shown in Table 1, the hydrogen desorption peak area was integrated, and then the electrochemical active area (ECSA) of the catalyst was calculated according to the formula.

[0090] Table 1. Electrochemical active areas of the catalysts prepared in Examples 1-4 and Comparative Example 1

[0091] Experimental Example catalyst <![CDATA[Electrochemical surface area m 2 / g]]> Example 1 50% Pt / 5wt% Zr-C 56.8 Example 2 50% Pt / 10wt% Zr-C 63.2 Example 3 50% Pt / 15wt% Zr-C 58.3 Example 4 50% Pt / 20wt% Zr-C 48 Comparative Example 1 50% Pt / C 53

[0092] Depend on Figure 1 As shown in Table 1, for Examples 1-4, the electrochemical performance of platinum supported on Zr-C composite supports with different zirconium contents varied. Among them, the catalyst prepared in Example 2 exhibited the best electrochemical performance, with a value of 65.2 m. 2 / g, the electrochemical area of ​​the catalyst prepared in Example 4 is 48m². 2 / g, compared to 53m of the catalyst prepared in Comparative Example 1 2 / g, the performance is somewhat reduced; for platinum-based supported catalysts, their electrochemical performance is mainly related to the degree of platinum dispersion on the support. The larger the specific surface area of ​​the support, the more active sites there are for anchoring platinum particles, and the better the dispersion effect of platinum on the support surface; after a certain amount of zirconium is combined with carbon black, its specific surface area decreases accordingly. However, the interaction between the transition metal Zr and Pt increases the number of anchoring sites that can be used for platinum particles. Therefore, for Zr-C composite supports, there is an optimal addition value for zirconium. While ensuring minimal surface area loss, the number of anchoring sites should be increased as much as possible; in this invention, in the Zr-C composite support, when the mass fraction of zirconium is 10%, the catalyst performance after loading platinum particles is optimal, indicating that the composite support has a large specific surface area and suitable anchoring sites at this time.

[0093] Test Example 2

[0094] To verify the resistance of the prepared catalyst membrane electrode to ionomer poisoning, catalysts from Example 2 and Comparative Example 1 were selected as cathodes and sprayed onto membrane electrodes with the same loading. The electrochemical performance of the catalyst layer was tested at different ionomer contents. The ionomer content was measured by its mass ratio to the carbon particles in the catalyst and labeled as I / C. The I / C ratios were 0.8, 1.1, and 1.3, respectively. Then, the electrochemical properties of the cathode-side catalyst layer and the polarization curves of the membrane electrode were tested at different I / C ratios.

[0095] The electrochemical performance testing conditions for the single-cell cathode are as follows: single-cell temperature 80℃; 100% RH humidified H2 is introduced at a flow rate of 100 ml / min at the anode; 100% RH N2 is introduced at a flow rate of 100 ml / min at the cathode; voltage scan range is 0.05-0.6 V, scan rate is 50 mV / s; the electrochemical area of ​​the cathode catalyst layer is measured, and the test results are as follows. Figure 2 , Figure 3 As shown.

[0096] The fuel cell catalyst layer is a porous electrode made of catalyst slurry. In the catalyst slurry, colloidal dispersions and ionomers of catalyst particles are dispersed in a solvent. The complex interactions between the components within the slurry ultimately determine the microstructure and electrochemical performance of the catalyst layer. Electrochemical performance is controlled by the amount of ionomers in contact with the catalyst sites: too many ionomers lead to high transport resistance and catalyst poisoning. This is mainly because the ionomers, existing in thin film form on the Pt surface, can pass through the sulfonic acid groups (-SO₄) at the end of their side chains. 3- Oxygen atoms in the polymer are specifically adsorbed onto the Pt surface; however, insufficient ionomer content leads to inadequate proton conduction in the slurry, thus affecting the performance of the catalyst and membrane electrode. Figure 2 It can be seen that when Example 2 is used as the cathode-side catalyst, the change in the ionomer content in the catalyst layer has little effect on the electrochemical performance of the catalyst layer. When the I / C ratio is 0.8, 1.1, and 1.3, the electrochemical area of ​​the cathode-side membrane electrode is 48.3.8 m² at high temperature. 2 / g, 51.5m 2 / g and 49.6m 2 / g. Figure 3 In the study, when Comparative Example 1 was used as the cathode-side catalyst, the electrochemical performance of the catalyst layer changed significantly with the change in ionomer. At I / C ratios of 0.8, 1.1, and 1.3, the electrochemical area of ​​the cathode-side membrane electrode was 42.5 m² at high temperatures. 2 / g, 39.6m 2 / g and 35.8m 2 / g.

[0097] During the catalytic reaction, oxygen atoms readily coordinate with metal atoms and adsorb onto oxygen vacancies on the metal surface, forming chemisorption. In this invention, after zirconium-modified carbon black, the oxygen on the ether group in the ionomer is more likely to combine with the zirconium on the support surface, thereby reducing the content of ionomers covering the surface of platinum particles and mitigating the poisoning of ionomers in the catalyst layer.

[0098] To further verify the effect of ionomer content on membrane electrode performance, polarization curve performance tests were conducted on membrane electrodes of Example 2 and Comparative Example 1 with different I / C ratios. The test conditions were as follows: single cell temperature 80°C, anode / cathode reaction gas Air / H2 stoichiometry ratio of 2 / 1.5; inlet air humidity of 40% / 50%, and gas inlet pressure of 150 kPa / 150 kPa, respectively. The test results are as follows. Figure 4 and Figure 5 As shown.

[0099] Depend on Figure 4 It can be seen that for the membrane electrode using Example 2 as the cathode catalyst, when the ionomer in the catalyst layer changes, the membrane electrode voltage does not change much at low current densities, 0.2 A / cm.2 When the I / C ratio is 0.8, 1.1, and 1.3, the membrane electrode voltages are 0.835V, 0.841V, and 0.839V, respectively. The intrinsic performance of the catalyst at low current densities is observed; the more active sites the catalyst has, the better the membrane electrode performance. However, if the ionomer strongly adsorbs onto the active platinum surface, catalyst poisoning will occur, significantly reducing the membrane electrode performance. Figure 5 As shown, when Comparative Example 1 is used as the cathode catalyst, at 0.2 A / cm 2 At current densities, as I / C increases from 0.8 to 1.3, the membrane electrode voltage decreases from 0.831V to 0.816V and 0.794V, with a maximum reduction of 37mV; in the high current region, at 2A / cm 2 At high current densities, high oxygen mass transfer requires more proton conduction. Therefore, generally speaking, the more ionomers present, the better the membrane electrode performance. However, high ionomer content is more likely to cause poisoning of platinum active sites, so the ionomer content needs to be maintained within a certain range. For the membrane electrode prepared using Example 2, at 2 A / cm 2 At current densities, as I / C increases from 0.8 to 1.3, the membrane electrode voltage increases from 0.635V to 0.641V and 0.651V; while for Figure 5 The membrane electrode prepared in Comparative Example 1, at 2 A / cm 2 At higher current densities, as the I / C ratio increased from 0.8 to 1.3, the membrane electrode voltage decreased from 0.618V to 0.603V and 0.586V. This may be because the platinum active sites in the catalyst layer were largely covered by ionomers, resulting in a significant reduction in catalyst performance. At high current densities, the catalyst could not provide enough active sites to support the operation of the membrane electrode. In conclusion, it is necessary to control the ionomer content in the catalyst layer to provide high proton conductivity while minimizing the poisoning of platinum active sites, thus better leveraging the catalyst's role.

Claims

1. A catalyst for a fuel cell, characterized by, The catalyst comprises a zirconium-carbon composite carrier and an active component supported on the zirconium-carbon composite carrier, and the active component is platinum. The preparation method of the zirconium-carbon composite carrier comprises the following steps: (1) dissolving a zirconium salt in a solvent to prepare a mixed solution; (2) adding carbon black to the mixed solution in step (1), then adding an alcohol dispersant for dispersion, and then adding an alkaline solution for a precipitation reaction; (3) drying the precipitate after the precipitation reaction in step (2), and then calcining under an inert gas to obtain the zirconium-carbon composite carrier; The calcination temperature is 600-900°C, and the calcination time is 3-6h; The zirconium-carbon composite carrier comprises carbon and zirconium, and the mass fraction of zirconium is 5%-15%; The preparation method of the catalyst comprises the following steps: S1: mixing a platinum salt precursor solution, an alkali solution, ethylene glycol, and a reducing agent, stirring for reaction under an inert gas to obtain a reaction liquid 1; S2: mixing and dispersing the zirconium-carbon composite carrier and an alcohol dispersant to obtain a reaction liquid 2; S3: adding the reaction liquid 1 dropwise into the reaction liquid 2 to obtain a mixed solution, then adding an acid solution dropwise into the mixed solution, and then filtering and drying to obtain the catalyst for fuel cells.

2. The catalyst for fuel cells as claimed in claim 1, characterized by In step (1), the zirconium salt is at least one of zirconium nitrate and zirconium dichloride; and the solid content in the mixed solution is 5%-25%.

3. The catalyst for fuel cells as claimed in claim 1, wherein In step (2), the carbon black is at least one of Cabot FCX800 and Toyo Carbon MH-1800; The alcohol dispersant is at least one of n-butanol and isopropyl alcohol; The concentration of the alkaline solution is 10 wt%-20 wt%, and the alkaline solution is at least one of a sodium hydroxide solution and a sodium carbonate solution.

4. The catalyst for fuel cells as claimed in claim 1, wherein The loading amount of the active component is 50%.

5. The catalyst for a fuel cell as claimed in claim 1, wherein In step S1, the platinum salt precursor solution is at least one of chloroplatinic acid and platinum nitrate; The alkali solution is at least one of sodium carbonate, ammonia, and sodium bicarbonate; The reducing agent is at least one of methanol and formic acid; The reaction temperature is 70-90°C, and the reaction time is 3-6h; In step S2, the alcohol dispersant is at least one of anhydrous ethanol, n-butanol, and isopropyl alcohol.

6. The catalyst for a fuel cell as claimed in claim 1, wherein In step S3, the acid solution is at least one of sulfuric acid and nitric acid, and the mass fraction of the acid solution is 5wt%-10wt%; The drying temperature is 70-100°C, and the drying time is 3-6h.

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