High-durability catalyst slurry as well as preparation method and application thereof

Abstract

The invention provides high-durability catalyst slurry as well as a preparation method and application thereof. The catalyst slurry comprises a carbon-supported Pt-based catalyst, perfluorinated sulfonic acid resin, a solvent and a free radical quenching agent. According to the present invention, the catalytic coating in the proton membrane prepared from the catalyst slurry contains the free radical quenching agent, such that the attack of the free radical on the perfluorinated sulfonic acid resin in the catalytic coating is reduced, and the chemical durability of the catalytic coating is significantly improved; the free radical quenching agent is nano-scale particles and is dispersed on the carbon-supported Pt-based catalyst, so that the functions of separating Pt particles and preventing the Pt particles from growing up are achieved, and the service life of the carbon-supported Pt-based catalyst is further prolonged.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery manufacturing, and in particular relates to a high-durability catalyst slurry, a preparation method thereof, and an application thereof. Background Art

[0002] Fossil fuels are non-renewable energy sources and contain large amounts of chemical elements, such as sulfur and nitrogen, that can cause environmental pollution. Extensive use of fossil fuels has led to serious energy crises and environmental pollution. Finding a new, renewable, clean energy source to replace fossil fuels is of great significance.

[0003] Fuel cells use hydrogen as their raw material, generating electricity through an electrochemical reaction between hydrogen and oxygen, with the only product being water. This reaction process is not restricted by the Carnot cycle, resulting in higher energy conversion efficiency. Therefore, hydrogen fuel cells offer zero pollution and high energy efficiency, making them an important new energy technology.

[0004] The electrochemical reaction in hydrogen fuel cells must occur under the action of a catalyst. Currently, the most widely used catalyst is a carbon-supported Pt-based catalyst. To meet the needs of electrochemical reaction scenarios in fuel cells, the carbon-supported Pt-based catalyst needs to form a porous layered structure between the gas diffusion layer and the proton exchange membrane. A common method is to coat the catalyst on the surface of the proton exchange membrane to form a catalyst-coated proton membrane CCM (catalyst coating membrane, abbreviated as CCM). A single carbon-supported Pt-based catalyst is a nano-sized particle that is not easy to bond with each other and cannot be formed on the surface of the proton exchange membrane. The electrochemical reaction on the catalyst surface in hydrogen fuel cells also involves the transfer of protons, which is not possible with carbon-supported Pt-based catalysts. Therefore, perfluorosulfonic acid resin and carbon-supported Pt-based catalysts are usually mixed to form a slurry, which is then coated on the surface of the proton exchange membrane to form a porous catalytic layer, providing a place for the electrochemical reaction.

[0005] During hydrogen fuel cell operation, hydrogen peroxide is produced, which in turn generates hydroxyl radicals and hydrogen peroxide radicals. These radicals attack unstable groups and non-fluorine atoms in the PFSA molecule, such as the sulfonic acid groups and ether bonds in the resin molecule, ultimately leading to the degradation of the perfluorosulfonic acid resin. Degradation of the perfluorosulfonic acid resin in the catalytic layer deprives it of its ability to bind to the carbon-supported Pt-based catalyst and conduct protons, depriving the hydrogen fuel cell of a suitable electrochemical reaction site. Degradation of the perfluorosulfonic acid resin is one of the main factors affecting the life of the catalytic layer.

[0006] In addition, hydrogen fuel cells experience catalyst aging during operation: (1) The active platinum nanoparticles on the platinum-based catalyst migrate and aggregate during long-term battery operation, causing the platinum nanoparticles to increase in size and reduce the electrochemically active specific surface area (ECSA) of the catalyst; (2) Ostwald ripening occurs, and small platinum nanoparticles tend to deposit on larger platinum nanoparticles, causing the platinum nanoparticles to grow larger and the ECSA to decrease. Catalyst aging is another culprit that affects the life of the catalyst layer. Summary of the Invention

[0007] To address the issue of hydrogen fuel cell lifespan degradation caused by the degradation of perfluorosulfonic acid resin in the membrane electrode catalyst layer (MEC) of hydrogen fuel cells, the present invention has developed a catalyst slurry containing a free radical quencher. The catalyst layer produced with this slurry is resistant to free radical attack, maintaining a stable structure and performance over time. Furthermore, the addition of the nanoscale free radical quencher separates Pt nanoparticles and hinders their growth, thereby extending the catalyst's lifespan.

[0008] The polarization properties of CCM made from this slurry are consistent with those of conventional CCM, and the addition of free radical quencher does not affect the performance of CCM.

[0009] Specifically, the present invention provides the following technical solutions:

[0010] A catalyst slurry comprises a carbon-supported Pt-based catalyst, a perfluorosulfonic acid resin, a solvent and a free radical quencher.

[0011] According to an embodiment of the present invention, the free radical quencher is selected from at least one of cerium oxide, manganese oxide, zirconium oxide and tungsten oxide or hydrates thereof.

[0012] According to a preferred embodiment of the present invention, the free radical quencher is selected from at least one of hydrated nano-cerium oxide, hydrated nano-manganese oxide, hydrated nano-zirconium oxide, and hydrated nano-tungsten oxide.

[0013] According to a preferred embodiment of the present invention, the free radical quencher is in the form of colloidal particles.

[0014] According to an embodiment of the present invention, the colloidal particle size of the free radical quencher may be 1 nm-10 nm, preferably 3 nm-4 nm.

[0015] According to an embodiment of the present invention, the Pt loading in the carbon-supported Pt-based catalyst may be 5%-70%, preferably 8%-60%, further preferably 10%-50%, 20%-40%, and more preferably 40%-60%, for example 60%. In the present invention, the Pt loading refers to the mass percentage of Pt in the carbon-supported Pt-based catalyst.

[0016] According to an embodiment of the present invention, the carbon-supported Pt-based catalyst is, for example, a supported catalyst of platinum supported on activated carbon, and its Pt loading is 5%-70%; preferably 8%-60%, further preferably 10-50%, 20-40%, more preferably 40%-60%, for example 60%.

[0017] According to an embodiment of the present invention, the solvent is selected from a mixture of alcohol and water. Preferably, the alcohol is selected from at least one of ethanol, n-propanol, and isopropanol. Preferably, the mass ratio of alcohol to water in the solvent is 10:0.1-7.0, preferably 10:0.2-5.0; or 10:0.5-3.0; more preferably 7:1.

[0018] According to an embodiment of the present invention, in the catalyst slurry, the mass ratio of the carbon-supported Pt-based catalyst, the perfluorosulfonic acid resin, the free radical quencher and the solvent can be 100-500:20-300:0.1-500:10000-50000, preferably 150-450:30-250:1-400:15000-40000; further preferably 200-400:50-150:10-300:20000-30000; for example, 294:100:1:25860.

[0019] The present invention also provides a method for preparing the catalyst slurry, the method comprising:

[0020] (1) mixing a free radical quencher and a dispersion containing a perfluorosulfonic acid resin to obtain a first dispersion;

[0021] (2) mixing the carbon-supported Pt-based catalyst and the wetting agent, ball milling the mixture, and then adding a solvent to obtain a second dispersion;

[0022] (3) The first dispersion liquid and the second dispersion liquid are mixed to obtain the catalyst slurry.

[0023] According to an embodiment of the present invention, the free radical quencher, perfluorosulfonic acid resin, carbon-supported Pt-based catalyst and solvent have the meanings as described above.

[0024] According to an embodiment of the present invention, in step (1), the dispersion containing perfluorosulfonic acid resin includes a dispersion of perfluorosulfonic acid resin and n-propanol, isopropanol and water; wherein the concentration of perfluorosulfonic acid resin is 1-30%, for example, 20%.

[0025] According to an embodiment of the present invention, in step (1), the mass ratio of the free radical quencher to the perfluorosulfonic acid resin in the first dispersion is 20-300:0.1-500, for example, 100:1.

[0026] According to an embodiment of the present invention, in step (2), the solid content of the carbon-supported Pt-based catalyst in the second dispersion is 0.1%-5%, for example, 1.5%.

[0027] According to an embodiment of the present invention, in step (2), the ball milling can be performed using conditions known in the art, and the present invention does not specifically limit this.

[0028] According to an embodiment of the present invention, in step (2), the wetting agent is selected from at least one of deionized water and ultrapure water.

[0029] According to an embodiment of the present invention, in step (3), the mass ratio of the carbon-supported Pt-based catalyst in the second dispersion to the perfluorosulfonic acid resin in the first dispersion is 100-500:20-300, for example, 294:100:1.

[0030] According to an embodiment of the present invention, in steps (1) to (3), the mixing can be performed by methods known in the art, such as mixing by ultrasonic dispersion.

[0031] According to an embodiment of the present invention, the mass ratio of the total amount of water added in steps (1) to (3) to the alcohol in step (2) is 0.1-7:10, preferably 1:7.

[0032] The present invention also provides use of the catalyst slurry in preparing a composite proton membrane, preferably in preparing a composite proton membrane for a hydrogen fuel cell.

[0033] The present invention also provides a composite proton membrane, which comprises a proton exchange membrane substrate and a catalyst coating located on the surface of the substrate; the catalyst coating is a coating layer of the catalyst slurry.

[0034] According to an embodiment of the present invention, the proton exchange membrane substrate may be selected from perfluorosulfonic acid proton exchange membrane. Preferably, the proton exchange membrane substrate may have a thickness of 8 μm-15 μm, for example, 10 μm.

[0035] According to an embodiment of the present invention, the mass content of platinum on the surface of the substrate of the catalyst is 0.01-1 mg / cm 2 , for example 0.4 mg / cm 2 Preferably, the mass content of platinum on the surface of the substrate of the catalyst of the present invention includes the total platinum content on both sides of the substrate. For example, the mass content of platinum on the surface of the substrate is 0.4 mg / cm 2 , where the platinum loading near the anode side is 0.1 mg / cm 2 , the platinum loading near the cathode side is 0.3 mg / cm 2 .

[0036] The present invention also provides application of the composite proton membrane in a hydrogen fuel cell.

[0037] The present invention has the following beneficial effects:

[0038] The present invention develops a catalyst slurry for a composite proton membrane that can be used in hydrogen fuel cells. The catalyst slurry contains a nanoscale free radical quencher. Because the nanoscale free radical quencher is in a colloidal state, it is highly dispersed in the catalyst slurry and does not settle. The catalytic coating in the proton membrane made using the catalyst slurry of the present invention, because it contains the free radical quencher, reduces free radical attack on the perfluorosulfonic acid resin in the catalytic coating, significantly improving the chemical durability of the catalytic coating. The free radical quencher used in the present invention is in the form of nanoscale particles dispersed on the carbon-supported Pt-based catalyst, which serves to separate the Pt particles and hinder their growth, further extending the lifespan of the carbon-supported Pt-based catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Actual photos of CCM-1 and CCM-2 after being soaked in Fenton's reagent in Example 3.

[0040] Figure 2 SEM images of the surface morphology of CCM-1 and CCM-2 before and after immersion in Fenton's reagent in Example 3. DETAILED DESCRIPTION

[0041] The technical solutions of the present invention will be described in further detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are encompassed within the scope of protection that the present invention is intended to protect.

[0042] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0043] Comparative Example 1

[0044] Comparative catalyst slurry was prepared according to the following steps:

[0045] (1) Weigh 0.5 g of carbon-supported Pt-based catalyst (manufacturer: Johnson Matthey, model: Hispec9100, Pt loading of 60%) and place it in a beating box. After adding the first portion of deionized water to moisten it, pour in zirconium beads and place it in a vacuum degassing mixer for ball milling.

[0046] (2) After the ball milling is completed, take out the mixture and add the second portion of deionized water and add isopropanol in batches, and ultrasonically disperse for 8-10 minutes; in this process, the residual catalyst in the beating box needs to be rinsed clean with isopropanol several times and transferred to a transparent beaker; (3) Nafion D2020CS resin dispersion (the solvent is n-propanol, isopropanol and water, and the resin concentration is 20%) is added, the ultrasonic voltage is 0.5A, and ultrasonic dispersion is carried out for more than 30 minutes. During the ultrasonic process, the beaker is shaken to prevent sedimentation until the slurry becomes ink-like, and a comparative catalyst slurry is obtained;

[0047] In the comparative catalyst slurry prepared in step (3), the mass ratio of the carbon-supported Pt-based catalyst, the perfluorosulfonic acid resin and the solvent is: 294:100:25860; wherein the solvent includes water and isopropanol; and the mass ratio of the total amount of deionized water in steps (1)-(3) to isopropanol is 1:7.

[0048] Comparative Example 2

[0049] The comparative composite proton membrane was prepared according to the following steps:

[0050] (1) The proton exchange membrane substrate is perfluorosulfonic acid proton exchange membrane (manufacturer: Gore, model:

[0051] M788.12) Attach the frames on both sides to obtain a blank membrane electrode with a sandwich structure;

[0052] (2) The blank membrane electrode prepared in step (1) was adsorbed and leveled on an adsorption platform of an ultrasonic sprayer at a temperature of 100°C;

[0053] (3) Using a syringe pump, draw an appropriate amount of the comparative catalyst slurry prepared in Comparative Example 1, ultrasonically spray 3 layers on the anode side of the blank membrane electrode, remove it, turn it over, and spray 8 layers on the cathode side to obtain a catalyst coating. Finally, close the adsorption station to obtain a comparative composite proton membrane, named CCM-1, wherein the content of the catalyst coating is 0.1 mg / cm3 and the anode platinum loading is 0.1 mg / cm3. 2 , the cathode platinum loading is 0.3 mg / cm 2 .

[0054] Example 1

[0055] Prepare the catalyst slurry according to the following steps:

[0056] (1) Hydrated nano-cerium oxide (free radical quencher) in colloidal form was mixed with a Nafion D2020CS resin dispersion (the solvent was n-propanol, isopropanol, and water, and the resin concentration was 20%) to obtain a dispersion of perfluorosulfonic acid resin containing a free radical quencher; wherein the solid content of the hydrated nano-cerium oxide was 5.0%.

[0057] (2) Weigh 0.5 g of carbon-supported Pt-based catalyst (manufacturer: Johnson Matthey, model: Hispec9100, Pt loading of 60%) and place it in a beating box. After adding the first portion of deionized water to moisten it, pour in zirconium beads and place it in a vacuum degassing mixer for ball milling.

[0058] (3) After the ball milling is completed, take out the water and add the second part of deionized water and isopropanol in batches, and ultrasonically disperse for 8-10 minutes. During this process, the residual catalyst in the beating box needs to be rinsed with isopropanol several times and transferred to a transparent beaker.

[0059] (4) adding the dispersion of the perfluorosulfonic acid resin containing a free radical quencher in step (1), ultrasonically dispersing at an ultrasonic voltage of 0.5 A for more than 30 minutes, and shaking the beaker during the ultrasonic process to prevent sedimentation until the slurry becomes ink-like to obtain a catalyst slurry.

[0060] In the catalyst slurry prepared in this embodiment, the mass ratio of the carbon-supported Pt-based catalyst, the perfluorosulfonic acid resin, the hydrated nano-cerium oxide, and the solvent is 294:100:5:25860; wherein the solvent includes water and isopropanol; and the mass ratio of the total amount of deionized water in steps (1) to (3) to isopropanol is 1:7.

[0061] Example 2

[0062] A composite proton membrane was prepared with reference to Comparative Example 2, except that, in step (3), the catalyst slurry prepared in Example 1 was used instead of the comparative catalyst slurry in Comparative Example 1 to prepare a composite proton membrane, which was named CCM-2.

[0063] Example 3

[0064] Add FeSO4 to 30% H2O2 to make Fe 2+ The concentration of Fenton's reagent was 20 ppm. CCM-1 and CCM-2 prepared in Comparative Example 1 and Example 1 were immersed in 100 ml of the Fenton's reagent, then placed in an 80°C water bath for 4 hours. CCM-1 and CCM-2 were removed and dried at 80°C for 2 hours. The CCM-1 and CCM-2 soaked in the Fenton's reagent were named CCM-1F and CCM-2F, respectively.

[0065] After taking photos of the above CCM-1F and CCM-2F, the actual pictures are as follows Figure 1 The above CCM-1, CCM-2, CCM-1F and CCM-2F were photographed under a scanning electron microscope, and their surface morphologies are shown as follows. Figure 2 shown.

[0066] like Figure 1As shown, CCM-1 without a free radical quencher showed obvious catalyst coating shedding after being soaked in the Fenton reagent, while CCM-2 with a free radical quencher was not found to have catalyst coating shedding after being soaked in the Fenton reagent. Therefore, CCM-1F showed obvious cracks, while CCM-2F did not show any cracks. This shows that under the attack of hydroxyl radicals (generated by the Fenton reagent), the perfluorosulfonic acid resin in CCM-1 was obviously degraded, resulting in weak adhesion of the catalyst coating, shedding of the catalyst coating, and fracture; while CCM-2F containing a free radical quencher did not show any apparent damage. This shows that the catalyst slurry and CCM-2 provided by the present invention have obvious anti-free radical properties.

[0067] Example 4

[0068] Fresh CCM-1 from Comparative Example 1 and CCM-2 from Example 1 were used as separators to assemble a cell, where both the positive and negative electrodes were graphite plates. The prepared CCM was stacked with carbon paper (SGL22BB) and a rubber sealing gasket, placed between the graphite bipolar plates in the serpentine flow channel, and secured to the cell with a preload of 4 N·m. The ECSA of the catalytic coating on the composite proton membrane surface was measured, followed by a square wave test:

[0069] ① The battery temperature is 80°C, the relative humidity on both the anode and cathode sides is 100%; the anode hydrogen flow rate is 200 sccm, and the cathode nitrogen flow rate is 75 sccm;

[0070] ② In the external circuit, 0.6V (3s) and 0.95V (3s) are applied between the cathode and anode of the battery in sequence. The potential step time is less than 0.5s, and one cycle is formed between each two potential steps.

[0071] ③ After 10,000 cycles, the electrochemically active surface areas (ECSAs) of CCM-1 and CCM-2 were compared with those at the initial stage. The results are shown in Table 1.

[0072] Table 1 ECSA of CCM-1 and CCM-2 before and after square wave cycling

[0073]

[0074] As shown in Table 1, after 10,000 square-wave cycles, the ECSA of CCM-2, which incorporates a durability additive, decreased by 17.1%. Under the same conditions, the ECSA of CCM-1, which does not incorporate a durability additive, decreased by 32.1%. This indicates that the Pt particles in CCM-2 are more stable and better retain their original properties. The Pt particles in CCM-1, unimpeded by the durability additive, migrated and grew, resulting in a greater ECSA decrease.

[0075] The above describes exemplary embodiments of the present invention. However, the scope of protection of this application is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc. made by those skilled in the art within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A catalyst slurry, characterized in that: The catalyst slurry comprises a carbon-supported Pt-based catalyst, a perfluorosulfonic acid resin, a solvent and a free radical quencher.

2. The catalyst slurry according to claim 1, characterized in that The free radical quencher is selected from at least one of cerium oxide, manganese oxide, zirconium oxide and tungsten oxide or hydrates thereof. Preferably, the free radical quencher is selected from at least one of hydrated nano-cerium oxide, hydrated nano-manganese oxide, hydrated nano-zirconium oxide and hydrated nano-tungsten oxide. Preferably, the free radical quencher is in the form of colloidal particles. Preferably, the colloidal particle size of the free radical quencher is 1 nm-10 nm.

3. The catalyst slurry according to claim 1 or 2, characterized in that In the carbon-supported Pt-based catalyst, the Pt loading is 5%-70%. Preferably, in the catalyst slurry, the mass ratio of the carbon-supported Pt-based catalyst, the perfluorosulfonic acid resin, the free radical quencher and the solvent is 100-500:20-300:0.1-500:10000-50000.

4. The method for preparing the catalyst slurry according to any one of claims 1 to 3, characterized in that: The preparation method comprises: (1) mixing a free radical quencher and a dispersion containing a perfluorosulfonic acid resin to obtain a first dispersion; (2) mixing the carbon-supported Pt-based catalyst and the wetting agent, ball milling the mixture, and then adding a solvent to obtain a second dispersion; (3) The first dispersion liquid and the second dispersion liquid are mixed to obtain the catalyst slurry.

5. The preparation method according to claim 4, characterized in that In step (1), the dispersion containing perfluorosulfonic acid resin comprises a dispersion of perfluorosulfonic acid resin, n-propanol, isopropanol and water; wherein the concentration of the perfluorosulfonic acid resin is 1-30%. Preferably, in step (1), the mass ratio of the free radical quencher to the perfluorosulfonic acid resin in the first dispersion is 20-300:0.1-500. Preferably, in step (2), the solid content of the carbon-supported Pt-based catalyst in the second dispersion is 0.1%-5%.

6. The preparation method according to claim 4 or 5, characterized in that In step (3), the mass ratio of the carbon-supported Pt-based catalyst in the second dispersion to the perfluorosulfonic acid resin in the first dispersion is 100-500:20-300. Preferably, the mass ratio of the total amount of water added in steps (1) to (3) to the alcohol in step (2) is 0.1-7:

10.

7. Use of the catalyst slurry according to any one of claims 1 to 3 in the preparation of a composite proton membrane.

8. A composite proton membrane, characterized in that The composite proton membrane comprises a proton exchange membrane substrate and a catalyst coating located on the surface of the substrate; the catalyst coating is a coating layer of the catalyst slurry according to any one of claims 1 to 3.

9. The composite proton membrane according to claim 8, characterized in that The proton exchange membrane substrate is selected from perfluorosulfonic acid proton exchange membrane. Preferably, the proton exchange membrane substrate has a thickness of 8 μm-15 μm. Preferably, the mass content of platinum on the substrate surface of the catalyst, i.e., the anode platinum loading, is 0.01 mg / cm 2 -1mg / cm 2 .

10. Use of the composite proton membrane according to any one of claims 1 to 3 in a hydrogen fuel cell.

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