A method for dispersing a catalyst slurry for a fuel cell

Abstract

The present invention provides a method for dispersing a fuel cell catalyst slurry, comprising the following steps: S1. mixing a catalyst, water, an organic alcohol, and a perfluorosulfonic acid resin solution to form a catalyst mixture; S2. adding a certain amount of zirconium oxide ball milling beads to the catalyst mixture; and S3. placing the catalyst mixture containing the ball milling beads in an ultrasonic generator for ultrasonication to obtain a uniformly dispersed catalyst slurry. The present invention combines the advantages of ultrasonic dispersion and ball milling dispersion. The ball milling beads are first added to the slurry, followed by ultrasonic dispersion. This method not only utilizes the ultrasonic cavitation effect of ultrasound on the slurry, but also utilizes the collision, extrusion, and grinding effects of the ball milling beads on the catalyst slurry under the action of ultrasound. Furthermore, the high-intensity bouncing of the ball milling beads simultaneously solves the problems of coagulation in the early stages of dispersion and foaming during the dispersion process of high-solids slurries.

Description

Technical Field

[0001] The present invention relates to the field of fuel cells, and in particular to a method for dispersing catalyst slurry for fuel cells. Background Art

[0002] A fuel cell is an electrochemical power generation device. Hydrogen on the anode side and oxygen on the cathode side undergo oxidation and reduction reactions respectively under the catalytic action of the anode catalyst and cathode catalyst, generating external current while producing water. Its green and efficient advantages have made fuel cell technology widely concerned by the society.

[0003] At present, the catalytic layer in the membrane electrode, the core component of fuel cells, is formed by evenly coating the catalyst slurry on the substrate and then drying it. Among them, the quality of the catalyst slurry plays a decisive role in the quality of the catalytic layer. Only by preparing a slurry with small particle size and uniform particle size distribution can the active sites of the catalyst be exposed as much as possible and the catalytic ability of the catalyst be exerted. Therefore, the dispersion method of the catalyst slurry is crucial.

[0004] Commonly used catalyst slurry dispersion methods include ultrasonic dispersion and ball milling. Ultrasonic dispersion uses ultrasonic waves generated by an ultrasonic generator to induce cavitation in the liquid within the slurry. The enormous energy released when the cavitation bubbles burst can achieve uniform mixing of the heterogeneous components within the slurry. Ball milling, on the other hand, utilizes moving ball mill beads to impact, squeeze, and grind the slurry components to achieve dispersion. For large-scale commercial production of catalyst slurries, the solids content of the catalyst must be increased to achieve a high catalyst loading in a single coating. However, the aforementioned dispersion methods are not very effective for catalyst slurries with high solids contents.

[0005] The catalyst slurry is composed of a porous carbon-supported platinum catalyst, a dispersant and a perfluorosulfonic acid resin solution. The porous carbon-supported platinum catalyst has a very strong water absorption due to the high specific surface area of its carrier, and the slurry becomes very thick and almost solidified; coupled with the hydrophilic and hydrophobic structure and high molecular weight of the perfluorosulfonic acid resin, it is very easy to produce numerous stable and tiny bubbles during the slurry dispersion process. Combined with the strong water absorption of the carbon carrier, ultrasonic dispersion and ball milling dispersion make it difficult to disperse the catalyst slurry evenly or even impossible to disperse it, resulting in poor quality of the subsequent coated catalytic layer. Therefore, proposing an efficient dispersion method for high-solid content catalyst slurry is of great significance to the development of the industry. Summary of the Invention

[0006] The purpose of the present invention is to overcome and supplement the deficiencies in the prior art by providing a method for dispersing a catalyst slurry for a fuel cell, thereby obtaining a high-solids catalyst slurry with small catalyst particle size and uniform particle size distribution. The technical solution adopted by the present invention is:

[0007] A method for dispersing a catalyst slurry for a fuel cell, comprising the following steps:

[0008] S1. The catalyst, water, organic alcohol and perfluorosulfonic acid resin solution are mixed to form a catalyst mixture;

[0009] S2. adding a certain amount of zirconia ball milling beads to the catalyst mixture;

[0010] S3. Place the catalyst mixture containing ball mill beads in an ultrasonic generator and ultrasonicate to obtain a uniformly dispersed catalyst slurry.

[0011] Preferably, in the method for dispersing a catalyst slurry for a fuel cell, the solid content of the catalyst mixture in step S1 is 5 to 30%.

[0012] Preferably, in the method for dispersing the catalyst slurry for fuel cells, the mass of the zirconium oxide ball milling beads in step S2 accounts for 20 to 80% of the total mass of the catalyst mixture and the ball milling beads.

[0013] Preferably, in the method for dispersing the catalyst slurry for fuel cells, the diameter of the zirconia ball milling beads in step S2 is 0.5 to 10 mm; and zirconia ball milling beads of one or more diameters are added to the catalyst mixture.

[0014] Preferably, in the method for dispersing the catalyst slurry for a fuel cell, the power of the ultrasonic generator in step S3 is 100 to 10,000 W.

[0015] Preferably, in the method for dispersing the catalyst slurry for a fuel cell, the ultrasonic time in step S3 is 10 to 300 minutes; and cooling water is used during the ultrasonic process to control the ultrasonic temperature to 20° C. to 25° C.

[0016] Advantages of the present invention:

[0017] The method for dispersing catalyst slurry for fuel cells of the present invention combines the advantages of ultrasonic dispersion and ball milling dispersion. Ball milling beads are first added to the slurry and then ultrasonic dispersion is performed. This not only brings into play the ultrasonic cavitation effect of ultrasound on the slurry, but also utilizes the collision, extrusion and grinding effects of the ball milling beads on the catalyst slurry under the action of ultrasound. The coagulation problem of high-solid content slurry in the early stage of dispersion and the foaming problem during the dispersion process are simultaneously solved under the high-intensity beating of the ball milling beads. Not only can the coagulated slurry be stirred and the combination of the catalyst and perfluorosulfonic acid resin be promoted, so that water adsorbed on the porous carbon support is separated and the slurry is converted into a liquid state, but the tiny and stable bubbles generated in the slurry can also be eliminated by collision, and finally a high-solid content catalyst slurry with small catalyst particle size and uniform particle size distribution is obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The following are actual pictures of the catalyst slurries of Example 1, Comparative Example 1 and Comparative Example 3.

[0019] Figure 2 The diagram shows the actual coating effect of the catalyst slurry of Example 1, Comparative Example 1 and Comparative Example 3.

[0020] Figure 3 The cell performance diagram of the catalytic layer prepared with the catalyst slurry of Example 1, Comparative Example 1 and Comparative Example 3. DETAILED DESCRIPTION

[0021] The present invention will be further described below with reference to specific drawings and embodiments.

[0022] Example 1

[0023] A method for dispersing a catalyst slurry for a fuel cell, comprising the following steps:

[0024] S1. Pt / C catalyst, ultrapure water, n-propanol and Aquivion D72 perfluorosulfonic acid resin solution were mixed to form a catalyst mixture having a solid content of 5%;

[0025] S2. 0.5 mm zirconia ball milling beads were added to the catalyst mixture, the mass of the ball milling beads accounting for 20% of the total mass of the catalyst mixture and the ball milling beads;

[0026] S3. The catalyst mixture was placed in an ultrasonic generator with an ultrasonic power of 100 W and an ultrasonic time of 10 minutes. During the ultrasonic period, cooling water was used to control the ultrasonic temperature to 20°C. After ultrasonication, a uniformly dispersed catalyst slurry was obtained.

[0027] The manufacturer of Aquivion D72 perfluorosulfonic acid resin solution is Solvay.

[0028] Example 2

[0029] A method for dispersing a catalyst slurry for a fuel cell, comprising the following steps:

[0030] S1. PtCo / C catalyst, ultrapure water, isopropanol and Aquivion D79 perfluorosulfonic acid resin solution were mixed to form a catalyst mixture having a solid content of 10%;

[0031] S2. 2 mm zirconium oxide ball milling beads and 4 mm zirconium oxide ball milling beads were added to the catalyst mixture, the mass of the ball milling beads accounting for 40% of the total mass of the catalyst mixture and the ball milling beads;

[0032] S3. The catalyst mixture was placed in an ultrasonic generator with an ultrasonic power of 2000 W and an ultrasonic time of 50 minutes. During the ultrasonic period, cooling water was used to control the ultrasonic temperature to 20°C. After ultrasonication, a uniformly dispersed catalyst slurry was obtained.

[0033] The manufacturer of Aquivion D79 perfluorosulfonic acid resin solution is Solvay.

[0034] Example 3

[0035] A method for dispersing a catalyst slurry for a fuel cell, comprising the following steps:

[0036] S1. PtNi / C catalyst, ultrapure water, n-butanol and Nafion D2020 perfluorosulfonic acid resin solution were mixed to form a catalyst mixture with a solid content of 20%.

[0037] S2. 6 mm zirconium oxide ball milling beads and 8 mm zirconium oxide ball milling beads were added to the catalyst mixture, the mass of the ball milling beads accounting for 60% of the total mass of the catalyst mixture and the ball milling beads;

[0038] S3. The catalyst mixture was placed in an ultrasonic generator with an ultrasonic power of 5000 W and an ultrasonic time of 150 min. During the ultrasonic period, cooling water was used to control the ultrasonic temperature to 20°C. After ultrasonication, a uniformly dispersed catalyst slurry was obtained.

[0039] Nafion D2020 perfluorosulfonic acid resin solution is manufactured by Chemours.

[0040] Example 4

[0041] S1. PtNiCu / C catalyst, ultrapure water, glycerol and Nafion D2020 perfluorosulfonic acid resin solution were mixed to form a catalyst mixture with a solid content of 30%;

[0042] S2. 2 mm zirconia milling beads, 6 mm zirconia milling beads, and 10 mm zirconia milling beads were added to the catalyst mixture, the mass of the milling beads accounting for 80% of the total mass of the catalyst mixture and the milling beads;

[0043] S3. The catalyst mixture was placed in an ultrasonic generator with an ultrasonic power of 10,000 W and an ultrasonic time of 300 minutes. During the ultrasonic period, cooling water was used to control the ultrasonic temperature to 20°C. After the ultrasonic treatment, a uniformly dispersed catalyst slurry was obtained.

[0044] Nafion D2020 perfluorosulfonic acid resin solution is manufactured by Chemours.

[0045] Comparative Example 1

[0046] The difference from Example 1 is that ball milling beads are not added in step S2, and the remaining steps are the same as Example 1.

[0047] Comparative Example 2

[0048] The difference from Example 2 is that ball milling beads are not added in step S2, and the remaining steps are the same as Example 2.

[0049] Comparative Example 3

[0050] Steps S1 and S2 are the same as those in Example 3. Step S3: Place the catalyst mixture in a ball mill at a rotation speed of 250 r / min for 240 minutes. During the ball milling, cooling water is used to control the ball milling temperature at 20°C.

[0051] Comparative Example 4

[0052] Steps S1 and S2 are the same as those in Example 4. Step S3: Place the catalyst mixture in a ball mill at a rotation speed of 500 r / min for 120 minutes. During the ball milling, cooling water is used to control the ball milling temperature at 20°C.

[0053] The viscosity of the catalyst slurries prepared in Examples 1-4 and Comparative Examples 1-4 was tested at a shear rate of 20 s -1 Specific values are shown in Table 1. The smaller viscosity value indicates that the water adsorbed by the carbon carrier in the slurry is more thoroughly discharged and the adsorption and bonding of the resin and the catalyst are more sufficient; and the more stable viscosity value also proves that the slurry is more evenly dispersed and there are no large agglomerates causing viscosity deviations; as can be seen from Table 1, under the same slurry components, compared with only ultrasonic dispersion or only ball milling dispersion, the dispersion method of adding ball milling beads to the slurry and then ultrasonicating proposed in this patent can obtain a slurry with lower viscosity and more stability.

[0054] Table 1 Viscosity values of catalyst slurries of Examples 1-4 and Comparative Examples 1-4

[0055]

[0056] Furthermore, the catalyst slurries prepared in Examples 1-4 and Comparative Examples 1-4 were tested for particle size distribution, and the specific values are shown in Table 2; D50 refers to the particle size value corresponding to 50% of the volume cumulative distribution, so a smaller D50 indicates that the particle size of the catalyst cluster aggregates in the slurry is smaller and the dispersion effect is more obvious; and the polydispersity index can reflect the uniformity of dispersion of the aggregates in the slurry, and the smaller the value, the more uniform the dispersion; it can be seen from Table 2 that under the same slurry components, compared with only ultrasonic dispersion or only ball milling dispersion, the dispersion method of adding zirconium beads to the slurry and then ultrasonicating proposed in this patent can obtain a catalyst slurry with a smaller particle size and a more uniform particle size distribution.

[0057] Table 2 Particle size distribution of catalyst slurries of Examples 1-4 and Comparative Examples 1-4

[0058]

[0059] pass Figure 1 It can be clearly seen from the actual picture of the slurry that compared with the slurry of comparative example 1 which only adopts ultrasonic dispersion and comparative example 3 which only adopts ball milling, more water is discharged from the carbon carrier in embodiment 1 which adopts the dispersion method of this patent, the slurry has better fluidity and no foaming phenomenon, which is consistent with the measured viscosity value and particle size distribution value.

[0060] The slurries prepared in Example 1, Comparative Example 1 and Comparative Example 3 were directly coated onto the PTFE substrate using an automatic coating machine. Figure 2 It can be seen that Example 1 has the best coating effect, and the coating is complete and flawless; the coating of Comparative Example 1 has some small defects. The small spots in the figure are caused by small bubbles in the slurry, which shows that ultrasonic dispersion alone cannot effectively eliminate the foaming effect caused by the ionomer; and Comparative Example 3 can be seen that the coating has obvious defects, not only the particle agglomeration phenomenon is serious, but also the cracks are dense, which will cause serious catalyst activation polarization and material transfer polarization.

[0061] Will Figure 2 The obtained coating was hot pressed with the membrane to form a catalyst coated membrane (CCM), and then a membrane electrode (MEA) was prepared to assemble a single cell for battery performance testing; the battery performance was as follows; Figure 3 As shown, the test conditions are: battery temperature 70°C, humidified H2 at the anode, relative humidity 50%, and an excess coefficient of 1.5, and humidified O2 at the cathode, relative humidity 50%, and an excess coefficient of 2.5; from the battery performance diagram, it is found that the battery performance corresponding to Example 1 is the best, and compared with Comparative Examples 1 and 3, the voltage polarization loss is smaller in the entire current density range, which indicates that the catalyst is fully utilized and the mass transfer loss is small, which is also a reflection that the catalyst slurry is evenly dispersed and the catalyst slurry dispersion method proposed in this patent is effective.

[0062] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for dispersing a catalyst slurry for a fuel cell, characterized in that: The following steps are involved: S1. The catalyst, water, organic alcohol and perfluorosulfonic acid resin solution are mixed to form a catalyst mixture; S2. adding a certain amount of zirconia ball milling beads to the catalyst mixture; S3. The catalyst mixture containing ball-milled beads was placed in an ultrasonic generator to obtain a uniformly dispersed catalyst slurry; The ultrasonic time in step S3 is 10 to 300 minutes; cooling water is used during the ultrasonic process to control the ultrasonic temperature to 20° C. to 25° C.

2. The method for dispersing a fuel cell catalyst slurry according to claim 1, wherein: The solid content of the catalyst mixture in step S1 is 5-30%.

3. The method for dispersing a fuel cell catalyst slurry according to claim 1, wherein: The mass of the zirconium oxide ball milling beads in step S2 accounts for 20 to 80% of the total mass of the catalyst mixture and the ball milling beads.

4. The method for dispersing a fuel cell catalyst slurry according to claim 1, wherein: The diameter of the zirconia ball milling beads in step S2 is 0.5 to 10 mm, and zirconia ball milling beads of one or more diameters are added to the catalyst mixture.

5. The method for dispersing a fuel cell catalyst slurry according to claim 1, wherein: The power of the ultrasonic generator in step S3 is 100 to 10,000 W.

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