A catalyst slurry for fuel cells and its preparation method

Abstract

This invention provides a catalyst slurry for fuel cells and its preparation method, relating to the field of fuel cells. The catalyst slurry for fuel cells, by weight, comprises catalyst particles, perfluorosulfonic acid resin ionomer, ultrapure water, lower alcohol, and carbon powder. By employing porous carbon powder with specific properties, which interacts with the perfluorosulfonic acid resin ionomer, this invention can significantly improve the viscosity and stability of the catalyst slurry. Furthermore, the CCM formed after coating this catalyst slurry exhibits good performance and will not produce any adverse effects when in contact with the carbon in the microporous layer of the gas diffusion layer during fuel cell use.

Description

Technical Field

[0001] This invention relates to the field of fuel cells, and more specifically, to a catalyst slurry for fuel cells and a method for preparing the same. Background Technology

[0002] Proton exchange membrane fuel cells (PEMFCs) are characterized by high energy conversion efficiency, environmental friendliness, low operating noise, convenient maintenance, and readily available fuels. They can directly convert the chemical energy of fuel into electrical energy without an intermediate combustion process, making them safe and reliable. The membrane electrode assembly (MEA) is the core of the PEMFC, and the proton exchange membrane catalyst coating (CCM) within the MEA is obtained by coating a catalyst slurry onto the proton exchange membrane. Therefore, the stability and dispersibility of the catalyst slurry directly affect the performance of the CCM, and ultimately, the performance of the PEMFC.

[0003] Currently, there are many methods for preparing CCMs, such as spraying, transfer printing, chemical deposition, electrochemical deposition, physical sputtering deposition, dry powder spraying, printing, and slot coating. Traditional film electrode fabrication processes, such as spraying, deposition, and hot-press transfer, are not suitable for continuous production or have low production line speeds (<1m / min), making them difficult to apply to large-scale industrial production. Slot coating technology, however, is one of the most effective methods for industrial-scale CCM preparation due to its advantages such as high coating speed (linear speed ≥5m / min), good coating uniformity, continuous production capability, and wide coating window.

[0004] Membrane electrode assembly (MEAs) prepared by directly coating a slurry (containing catalyst, resin, and solvent) onto a proton exchange membrane (PEM) on both sides exhibits better performance and lower cost compared to MEAs prepared using the Gas Diffusion Electrode (GDE) method (where the catalyst layer is first coated onto the gas diffusion layer and then hot-pressed onto the PEM). This is due to the lower interfacial contact resistance between the catalyst layer and the PEM, and the fewer production steps involved. However, direct coating presents challenges. Since the wet membrane coating is formed in a single step, if the slurry viscosity is too low (<50 cps), and the catalyst used in the PEM fuel cell is typically a Pt-containing carbon-supported catalyst, a high-density metal, it tends to settle to the bottom of the catalyst slurry. This results in a higher resin content on the coating surface and a higher platinum-carbon particle content in the bottom layer. Furthermore, the surface layer's contact with the gas diffusion layer is insufficient, and if the resin layer is too dense, it can even hinder gas-liquid conduction. The catalyst particles are also more concentrated at the bottom of the coating, affecting proton conduction. Insufficient gas supply further impacts the catalytic reaction. Therefore, many studies have focused on thickening the slurry.

[0005] In the existing technology, most methods increase the viscosity of the slurry by adding thickeners or changing the preparation process. However, the following problems exist: (1) The additives need to be in a certain amount to work, which will affect the performance of the fuel cell. At the same time, the additives are not stable enough in the fuel cell, which will also have a certain impact on the life of the fuel cell; (2) The preparation process is complicated and the stability of the slurry is limited, which cannot meet the requirements of mass production of catalyst slurry and effective performance of catalyst. Summary of the Invention

[0006] The present invention aims to overcome at least one defect (deficiency) of the prior art and provides a catalyst slurry for fuel cells and a method for preparing the same. The catalyst slurry has good stability, and the catalyst layer coated on the proton exchange membrane has good uniformity and good electrochemical performance.

[0007] Another object of the present invention is to provide a method for preparing a catalyst slurry for fuel cells.

[0008] The technical solution adopted by this invention is a catalyst slurry for fuel cells, comprising the following components, in parts by weight:

[0009] 1-2 parts of catalyst particles;

[0010] 0.5-1.5 parts of perfluorosulfonic acid resin ionomer;

[0011] 4-5 parts ultrapure water;

[0012] 0.5 to 1.5 parts of lower alcohols;

[0013] 0.005~0.1 parts of toner;

[0014] The lower alcohol is an alcohol with 3 or fewer carbon atoms.

[0015] The catalyst slurry for fuel cells of this invention uses carbon-supported catalyst particles. Simultaneously, carbon powder is added to the catalyst slurry to increase its viscosity and improve its stability. Since the catalyst support is carbon, the addition of carbon powder improves the slurry's properties and does not adversely affect the membrane electrode assembly after coating. When carbon powder particles are added to the catalyst slurry, after physical and mechanical stirring and pre-dispersion, followed by high-speed shearing, they embed themselves between the molecular chains of the ionomers, resulting in a disordered molecular chain state. This disordered state increases the viscosity of the slurry system, thus maintaining good stability of the catalyst slurry.

[0016] Furthermore, the carbon powder is a porous carbon powder with a specific surface area of ​​300~660m². 2 / g.

[0017] Porous carbon powder has a large specific surface area. In catalyst slurry, the large specific surface area of ​​carbon powder is needed to disperse catalyst particles. However, carbon powder with an excessively large specific surface area has a small pore size, which is too different from the size of ionomers and particles in the slurry. This makes it difficult for ionomer particles to enter the pore size of carbon powder, resulting in less interaction and an insignificant thickening effect.

[0018] Furthermore, the pore size of the carbon powder is in the range of 50~150 nm.

[0019] Furthermore, the particle size of the toner is 4~6 μm.

[0020] Furthermore, the catalyst particles are one or more of the following: platinum / carbon catalyst particles, platinum alloy / carbon catalyst particles, platinum / metal oxide catalyst particles, and platinum alloy / metal oxide catalyst particles.

[0021] Preferably, the platinum alloy in the catalyst particles is one of platinum-cobalt alloy, platinum-cobalt-nickel alloy, or platinum-nickel alloy, and the metal oxide in the catalyst particles is one of tin oxide or cerium oxide.

[0022] Furthermore, the content of platinum or platinum alloy in the catalyst particles is 20-60%.

[0023] When the metal content in the catalyst particles is too high, the catalyst layer is too thin, and the quality of the CCM coating is difficult to control. When it is too low, the catalyst layer is too thick, and the coated catalyst layer is easy to fall off the membrane.

[0024] Furthermore, the ion exchange equivalent of the perfluorosulfonic acid resin ionomer is 700~1100.

[0025] When the ion exchange equivalent is below 700, the perfluorosulfonic acid resin swells significantly, which can clog the pores of the catalyst layer and increase the gas diffusion resistance. When it is above 1100, the acid content in the perfluorosulfonic acid resin is too low, resulting in low proton conductivity.

[0026] Furthermore, the lower alcohol is one or more of methanol, ethanol, ethylene glycol, propanol, isopropanol, and glycerol.

[0027] A method for preparing a catalyst slurry for fuel cells includes the following steps:

[0028] Step 1: Prepare a perfluorosulfonic acid resin ionomer solution by mixing solid perfluorosulfonic acid resin with 1 / 3 to 2 / 3 of a lower alcohol and 1 / 2 of ultrapure water, and stirring on a magnetic stirrer for 12 to 48 hours to obtain a perfluorosulfonic acid resin ionomer solution.

[0029] Step 2: Add the perfluorosulfonic acid resin ionomer solution prepared in Step 1, carbon powder, catalyst particles, and the remaining lower alcohol to the remaining ultrapure water in sequence, and use a mechanical stirrer to initially mix them for 0.5-1h, and then place them on a magnetic stirrer to stir for 0.5-1h.

[0030] Step 3: Pour the pre-dispersed catalyst slurry from Step 2 into a high-pressure shearing machine for high-pressure shearing dispersion to obtain the target catalyst slurry.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows: by using porous carbon powder with specific properties to interact with perfluorosulfonic acid resin ionomer, the viscosity and stability of the catalyst slurry can be significantly improved; and the CCM formed after the catalyst slurry is coated has good performance and will not produce any adverse effects when it comes into contact with the carbon in the microporous layer of the gas diffusion layer during fuel cell use. Attached Figure Description

[0032] Figure 1 The graph shows a comparison of the single-cell performance curves of membrane electrode samples prepared from the catalyst slurries of Example 1 and Comparative Examples 1-5.

[0033] Figure 2 The graph shows a comparison of the single-cell performance curves of membrane electrode samples prepared from the catalyst slurry of Examples 1-4 and Comparative Example 1.

[0034] Figure 3 This is an optical microscope image of the cathode catalyst layer in Comparative Example 5.

[0035] Figure 4 This is an optical microscope image of the cathode catalyst layer in Example 1. Detailed Implementation

[0036] The accompanying drawings are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0037] Chinese Patent 201911393214 discloses a method for preparing an anti-settling fuel cell catalyst slurry, which obtains a stable catalyst slurry through magnetic stirring, ultrasonic dispersion, high-pressure shearing, and stirring with a homogenizer in a vacuum. This preparation method is complex, the slurry stability is limited, and it is difficult to mass-produce.

[0038] Chinese Patent 201210193830 discloses a fuel cell catalyst slurry and its preparation method. The method involves adding a polymer dispersant to the catalyst slurry, wherein the polymer dispersant is one or a mixture of two or more of polyvinylpyrrolidone, polyvinyl alcohol, sodium carboxymethyl cellulose, polyethylene oxide, and polyacrylamide, thereby improving the dispersibility and stability of the catalyst slurry. However, the slurry obtained by this preparation method has limited stability, and the polymer additives used are unstable under fuel cell operating conditions, which can negatively impact the performance and lifespan of the fuel cell.

[0039] Chinese Patent 201010176562 discloses a catalyst slurry for preparing a fuel cell catalytic membrane electrode and its preparation. By controlling the catalyst slurry to be in a colloidal state and changing the composition and addition order of the organic solvents in the slurry, a liquid catalyst slurry is first prepared using isopropanol, ethanol, ethylene glycol, etc., and then the formed slurry is dropwise added to butyl acetate under ultrasonic oscillation, thereby forming a colloidal catalyst slurry and improving its stability. This preparation method requires multiple solvents and is complex, making it unsuitable for mass production.

[0040] The embodiments of the present invention are improvements made based on the defects existing in the prior art, and specifically include the following embodiments.

[0041] Example 1

[0042] A catalyst slurry for fuel cells, comprising, by weight, the following components:

[0043] 1 part catalyst particles;

[0044] 1 part of perfluorosulfonic acid resin ionomer;

[0045] 4 parts ultrapure water;

[0046] 1.5 parts of lower alcohols;

[0047] 0.1 parts toner.

[0048] The catalyst particles are platinum-carbon catalyst particles with a platinum content of 50%, the ion exchange equivalent of the perfluorosulfonic acid resin ionomer is 700, the lower alcohol is ethanol, and the specific surface area of ​​the carbon powder is 300 m². 2 / g, pore size is 150nm, particle size is 5μm.

[0049] The specific preparation steps of the catalyst slurry in this embodiment are as follows:

[0050] Step 1: Prepare a perfluorosulfonic acid resin ionomer solution by mixing solid perfluorosulfonic acid resin with 1 / 3 ethanol and 1 / 2 ultrapure water and stirring on a magnetic stirrer for 48 hours to obtain a perfluorosulfonic acid resin ionomer solution.

[0051] Step 2: Add the perfluorosulfonic acid resin ionomer solution prepared in Step 1, carbon powder, catalyst particles, and the remaining ethanol to the remaining ultrapure water in sequence, and use a mechanical stirrer to initially mix them for 1 hour, and then place them on a magnetic stirrer to stir for 0.5 hours.

[0052] Step 3: Pour the pre-dispersed catalyst slurry from Step 2 into a high-pressure shearing machine for high-pressure shearing dispersion to obtain the target catalyst slurry.

[0053] Example 2

[0054] A catalyst slurry for fuel cells, comprising, by weight, the following components:

[0055] Two parts of catalyst particles;

[0056] 0.5 parts of perfluorosulfonic acid resin ionomer;

[0057] 5 parts ultrapure water;

[0058] 0.5 parts of lower alcohol;

[0059] 0.005 parts toner.

[0060] The catalyst particles are platinum-cobalt alloy / carbon catalyst particles with a platinum content of 50%; the ion exchange equivalent of the perfluorosulfonic acid resin ionomer is 1100; the lower alcohol is ethanol; and the specific surface area of ​​the carbon powder is 300 m². 2 / g, pore size is 150nm, particle size is 5μm.

[0061] The specific preparation steps of the catalyst slurry in this embodiment are as follows:

[0062] Step 1: Prepare a perfluorosulfonic acid resin ionomer solution by mixing solid perfluorosulfonic acid resin with 1 / 3 ethanol and 1 / 2 ultrapure water and stirring on a magnetic stirrer for 12 hours to obtain a perfluorosulfonic acid resin ionomer solution.

[0063] Step 2: Add the perfluorosulfonic acid resin ionomer solution prepared in Step 1, carbon powder, catalyst particles, and the remaining ethanol to the remaining ultrapure water in sequence, and use a mechanical stirrer to initially mix them for 0.5 hours, and then place them on a magnetic stirrer to stir for 0.6 hours.

[0064] Step 3: Pour the pre-dispersed catalyst slurry from Step 2 into a high-pressure shearing machine for high-pressure shearing dispersion to obtain the target catalyst slurry.

[0065] Example 3

[0066] A catalyst slurry for fuel cells, comprising, by weight, the following components:

[0067] 1.5 parts catalyst particles;

[0068] 1.5 parts of perfluorosulfonic acid resin ionomer;

[0069] 4.5 parts ultrapure water;

[0070] 1 part of lower alcohol;

[0071] 0.01 parts toner.

[0072] The catalyst particles are platinum-cobalt alloy / carbon catalyst particles with a platinum content of 30%; the ion exchange equivalent of the perfluorosulfonic acid resin ionomer is 1000; the lower alcohol is propanol; and the specific surface area of ​​the carbon powder is 300 m². 2 / g, pore size is 150nm, particle size is 5μm.

[0073] The specific preparation steps of the catalyst slurry in this embodiment are as follows:

[0074] Step 1: Prepare a perfluorosulfonic acid resin ionomer solution by mixing solid perfluorosulfonic acid resin with 2 / 3 propanol and 1 / 2 ultrapure water, and stirring on a magnetic stirrer for 15 hours to obtain a perfluorosulfonic acid resin ionomer solution.

[0075] Step 2: Add the perfluorosulfonic acid resin ionomer solution, carbon powder, catalyst particles, and the remaining propanol prepared in Step 1 to the remaining ultrapure water in sequence, and use a mechanical stirrer to initially mix them for 0.7 hours, and then place them on a magnetic stirrer to stir for 1 hour.

[0076] Step 3: Pour the pre-dispersed catalyst slurry from Step 2 into a high-pressure shearing machine for high-pressure shearing dispersion to obtain the target catalyst slurry.

[0077] Example 4

[0078] A catalyst slurry for fuel cells, comprising, by weight, the following components:

[0079] 1 part catalyst particles;

[0080] One part of perfluorosulfonic acid resin ionomer solution;

[0081] 4 parts ultrapure water;

[0082] 1.5 parts of lower alcohols;

[0083] 0.1 parts toner.

[0084] The catalyst particles are platinum-carbon catalyst particles with a platinum content of 50%, the ion exchange equivalent of the perfluorosulfonic acid resin ionomer is 700, the lower alcohol is methanol, and the specific surface area of ​​the carbon powder is 660 m². 2 / g, pore size 50nm, particle size 5μm.

[0085] The specific preparation steps of the catalyst slurry in this embodiment are as follows:

[0086] Step 1: Prepare a perfluorosulfonic acid resin ionomer solution by mixing solid perfluorosulfonic acid resin with 1 / 3 methanol and 1 / 2 ultrapure water and stirring on a magnetic stirrer for 48 hours to obtain a perfluorosulfonic acid resin ionomer solution.

[0087] Step 2: Add the perfluorosulfonic acid resin ionomer solution prepared in Step 1, carbon powder, catalyst particles, and the remaining methanol to the remaining ultrapure water in sequence, and use a mechanical stirrer to initially mix them for 1 hour, and then place them on a magnetic stirrer to stir for 0.5 hours.

[0088] Step 3: Pour the pre-dispersed catalyst slurry from Step 2 into a high-pressure shearing machine for high-pressure shearing dispersion to obtain the target catalyst slurry.

[0089] Comparative Example 1

[0090] The difference between this comparative example and Example 1 is that the carbon powder is replaced with an equal part by weight of PTFE, while everything else remains the same as in Example 1. (The dispersants in the aforementioned prior art are unstable in fuel cells and are not suitable for use in fuel cells, while PTFE is chemically stable and can be used in fuel cells.)

[0091] Comparative Example 2

[0092] The difference between this comparative example and Example 1 is that the toner is replaced with a specific surface area of ​​1000 m². 2 / g, carbon powder with a pore size of 5nm and a particle size of 2μm, otherwise consistent with Example 1.

[0093] Comparative Example 3

[0094] The difference between this comparative example and Example 1 is that the toner is replaced with a material with a specific surface area of ​​1200 m². 2 / g, carbon powder with a pore size of 15nm and a particle size of 3μm, otherwise consistent with Example 1.

[0095] Comparative Example 4

[0096] The difference between this comparative example and Example 1 is that the amount of toner added is increased to 0.2 parts, while the rest remains the same as in Example 1.

[0097] Comparative Example 5

[0098] The difference between this comparative example and Example 1 is that no toner is added; otherwise, they are the same as in Example 1.

[0099] The viscosities of the catalyst slurries corresponding to Examples 1-4 and Comparative Examples 1-5 are shown in Table 1 (C1-C4 represent carbon powders with different specific properties):

[0100] Table 1. Viscosity comparison of catalyst slurries corresponding to Examples 1-4 and Comparative Examples 1-5

[0101]

[0102] Among them, C1~C4 are toners with different properties, and their property comparison is shown in Table 2:

[0103] Table 2 Comparison of toner characteristics for C1 to C4

[0104]

[0105] As shown in Tables 1 and 2, the thickening effect of additives is influenced by their properties and the amount added. At the same dosage, C1 and C4 showed better thickening effects (Examples 1 and 4), while C2 and C3 showed relatively weaker effects (Comparative Examples 2 and 3). This is because additives C2 and C3 have a larger specific surface area and smaller pore size, making it difficult for perfluorosulfonic acid resin in the slurry to enter the additives. The weak interaction between the additives and the perfluorosulfonic acid resin results in minimal viscosity change. The granular polymeric additive PTFE also has a limited effect on slurry viscosity, again because PTFE particles are not porous and have weak interaction with perfluorosulfonic acid resin.

[0106] Meanwhile, the viscosity of the slurry is greatly affected by the dosage. At low dosages (Examples 2 and 3), doubling the dosage does not significantly increase the viscosity, while at slightly higher dosages (Examples 1 and Comparative Example 4), doubling the dosage significantly increases the viscosity. However, excessive dosage will lead to excessive viscosity. During double-sided coating, if the slurry viscosity is too high (>300 cP), it will reduce the quality of CCM coating and thus affect the performance of CCM.

[0107] exist Figure 1 In the performance test results, the order of performance from high to low is: Example 1 > Comparative Example 4 = Comparative Example 1 > Comparative Example 2 > Comparative Example 5 > Comparative Example 3. As can be seen from the figure, the additive carbon powder can improve the performance of the membrane electrode. However, if the specific surface area of ​​the additive is too large, it will reduce the performance of the membrane electrode. This is because a large specific surface area results in a small interaction with the perfluorosulfonic acid resin, which affects the conduction of protons in the catalyst layer.

[0108] exist Figure 2 In the performance test results, the performance from high to low is as follows: Example 1 > Example 4 > Example 2 = Example 3 > Comparative Example 1. As can be seen from the figure, the performance improvement of the membrane electrode is not significant when the amount of additives is small. At the same time, the performance of the additives (C1 and C4) also affects the improvement of the membrane electrode performance, but the membrane electrode performance of carbon additives is significantly higher than that of polymer additives.

[0109] Low-viscosity catalyst slurries are unstable. Adding carbon powder with specific properties to increase the slurry viscosity can effectively improve its stability, further benefiting the coating of the membrane electrode catalytic layer and ensuring its uniformity. Simultaneously, high-viscosity catalyst slurries can effectively reduce crack formation during coating, thereby improving membrane electrode performance. However, while adding excessive carbon powder can more effectively increase the slurry viscosity, too much carbon powder can hinder the interaction between the metal catalyst and the reactant gas, preventing effective catalytic reaction and thus reducing membrane electrode performance. Furthermore, during double-sided coating, excessively high slurry viscosity (>300 cP) can negatively impact coating quality. Figure 3 (Comparative Example 5) and Figure 4 (Example 1) is an optical microscope image of the cathode catalyst layer. The appearance of the cathode catalyst layer prepared by other different types of carbon powder additives is similar to that of the coating in Example 1, and almost no cracks are observed.

[0110] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the technical solution of the present invention, and are not intended to limit the specific implementation of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the claims of the present invention should be included within the protection scope of the claims of the present invention.

Claims

1. A catalyst slurry for fuel cells, characterized in that, Includes the following components, by weight: 1-2 parts of catalyst particles; 0.5-1.5 parts of perfluorosulfonic acid resin ionomer; 4-5 parts ultrapure water; 0.5 to 1.5 parts of lower alcohols; 0.005~0.1 parts of toner; The lower alcohol is an alcohol with 3 or fewer carbon atoms; The carbon powder is a porous carbon powder with a specific surface area of ​​300~660m². 2 / g; The pore size of the carbon powder is 50~150nm; The particle size of the carbon powder is 4~6μm; The catalyst particles are one or more of the following: platinum / carbon catalyst particles, platinum alloy / carbon catalyst particles, platinum / metal oxide catalyst particles, and platinum alloy / metal oxide catalyst particles.

2. The catalyst slurry for fuel cells according to claim 1, characterized in that, The platinum alloy in the catalyst particles is one of platinum-cobalt alloy, platinum-cobalt-nickel alloy, or platinum-nickel alloy, and the metal oxide in the catalyst particles is one of tin oxide or cerium oxide.

3. The catalyst slurry for fuel cells according to claim 1, characterized in that, The catalyst particles contain 20-60% platinum or platinum alloy.

4. The catalyst slurry for fuel cells according to claim 1, characterized in that, The ion exchange equivalent of the perfluorosulfonic acid resin ionomer is 700~1100.

5. The catalyst slurry for fuel cells according to claim 1, characterized in that, The lower alcohol is one or more of methanol, ethanol, ethylene glycol, propanol, and glycerol.

6. A method for preparing a catalyst slurry for a fuel cell according to any one of claims 1 to 5, characterized in that, Includes the following steps: Step 1: Prepare a perfluorosulfonic acid resin ionomer solution by mixing solid perfluorosulfonic acid resin with 1 / 3 to 2 / 3 of a lower alcohol and 1 / 2 of ultrapure water, and stirring on a magnetic stirrer for 12 to 48 hours to obtain a perfluorosulfonic acid resin ionomer solution. Step 2: Add the perfluorosulfonic acid resin ionomer solution prepared in Step 1, carbon powder, catalyst particles, and the remaining low alcohol to the remaining ultrapure water in sequence, and use a mechanical stirring paddle to initially mix them, and then place them on a magnetic stirrer to stir for 0.5~1h. Step 3: Pour the pre-dispersed catalyst slurry from Step 2 into a high-pressure shearing machine for high-pressure shearing dispersion treatment for 0.5 hours to obtain the target catalyst slurry.

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