Preparation method of catalyst layer for improving mass transfer polarization of Pt-transition metal alloy catalyst of fuel cell

Abstract

The invention relates to the technical field of fuel cell membrane electrode assemblies, in particular to a preparation method of a catalyst layer for improving mass transfer polarization of a Pt-transition metal alloy catalyst of a fuel cell. The method comprises the following steps: (1) mixing a Pt-transition metal alloy catalyst and a Pt / C catalyst, adding a dispersing agent, ultrasonically dispersing uniformly, adding a perfluorosulfonic acid ionomer solution, stirring, and shearing by adopting a high-speed shearing machine to obtain catalyst slurry; and (2) spraying the catalyst slurry obtained in the step (1) to form the fuel cell catalyst layer. According to the catalyst layer prepared by the invention, the relatively strong activity of the Pt-M / C catalyst is exerted in a low-current-density region in a polarization curve, and the mass transfer polarization phenomenon of the catalyst layer is also greatly improved in a high-current-density region.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cell membrane electrode assemblies, and in particular to a method for preparing a catalytic layer for improving mass transfer polarization of a Pt-transition metal alloy catalyst in a fuel cell. Background Art

[0002] Proton exchange membrane fuel cells are a promising technology that can provide clean and sustainable electricity, especially in the field of transportation. Their high efficiency, scalable power and energy density demonstrate their promise as a clean energy conversion technology. As an important component of proton exchange membrane fuel cells, membrane electrode (MEA) consists of a catalyst layer, a proton exchange membrane and a gas diffusion layer. The catalyst layer is the core site of the electrochemical reaction of the fuel cell. Therefore, the performance of the catalyst in the catalyst layer directly affects the output power and life of the entire cell. At present, the most commercially used catalyst is still Pt / C. However, due to the high price of Pt, reducing the amount of Pt in the catalyst is the only way for future development. At present, there are also many Pt-transition metal alloy catalysts (Pt-M / C; M is: transition metals such as Co, Ni, Fe, etc.) commercially used. The use of Pt-M / C catalysts can not only reduce the amount of Pt, but also effectively improve the dispersion and specific activity of Pt atoms due to the geometric effect, electronic effect and synergistic effect between the alloy metal and Pt.

[0003] However, although the Pt-M / C catalyst can show a high mass specific activity, in practical applications, due to the strong acid environment of the battery, the transition metal dissolves and poisons the ionomer in the catalyst layer. These pollutant cations will preferentially exchange with the protons in the ionomer, hindering the sulfonate groups (-SO 3 - ) conducts protons and suppresses the O 2 Transmission (such as Figure 1 shown).

[0004] In recent years, most studies have focused on adjusting the resin or dispersant content in the catalyst layer slurry or adding some inorganic or organic additives, including polytetrafluoroethylene (PTFE), hexadecyltrimethylammonium bromide dispersant, functional additives, etc. to improve the performance and coating state of the catalyst layer.

[0005] However, the catalyst layer in these studies did not distinguish between Pt / C and Pt-M / C catalysts. In fact, the dissolution of alloy atoms will be related to the -SO 3 - Too many alloy ion sites make the ionomer structure compact or even distorted, which will cause O 2The resistance to passing through the ionomer increases, which results in severe mass transfer polarization in the use of Pt-M / C catalysts. Summary of the invention

[0006] The purpose of the present invention is to provide a method for preparing a catalyst layer for improving the mass transfer polarization of a Pt-transition metal alloy catalyst in a fuel cell. By adding an appropriate amount of a Pt / C catalyst with a high Pt content during the preparation of the Pt-M / C catalyst layer slurry, the element molar ratio of Pt to the alloy element M in the entire catalyst layer is regulated, and the introduction of the alloy can be effectively reduced while ensuring that the Pt loading of the catalyst layer remains unchanged, thereby preventing a large amount of alloy ions from dissolving and poisoning the ionomer; in addition, the introduction of the Pt / C catalyst with a high Pt content can reduce the thickness of the catalyst layer, thereby further reducing the bulk mass transfer resistance of the catalyst layer.

[0007] In order to achieve the above object, the technical solution of the present invention is as follows:

[0008] In one aspect, the present invention provides a method for preparing a catalytic layer for improving mass transfer polarization of a Pt-transition metal alloy catalyst for a fuel cell, the method comprising the following steps:

[0009] (1) mixing a Pt-transition metal alloy catalyst and a Pt / C catalyst, adding a dispersant, uniformly dispersing by ultrasonication, adding a perfluorosulfonic acid ionomer solution, stirring, and then shearing with a high-speed shearing machine to obtain a catalyst slurry;

[0010] (2) Spraying the catalyst slurry obtained in step (1) to form a fuel cell catalyst layer.

[0011] In the above technical solution, further, the dispersant is a mixture of one or more of water, ethanol, isopropanol, and propylene glycol.

[0012] In the above technical solution, further, in the perfluorosulfonic acid ionomer solution, the mass fraction of the perfluorosulfonic acid ionomer is 5wt%.

[0013] In the above technical solution, further, the Pt-transition metal alloy catalyst includes one of Pt-Co / C, Pt-Ni / C, and Pt-Fe / C.

[0014] In the above technical solution, further, in the catalyst layer, the molar ratio of Pt to transition metal is 5-8:1.

[0015] In the above technical solution, further, in the Pt-transition metal alloy catalyst, the Pt content is 30wt%-50wt%, and the transition metal content is 2wt%-5wt%; in the Pt / C catalyst, the Pt content is 50wt%-75wt%.

[0016] In the above technical solution, further, the ratio of the mass of the perfluorosulfonic acid ionomer to the total mass of the carbon carrier in the Pt-transition metal alloy catalyst and the Pt / C catalyst is 0.4 to 1.3:1.

[0017] Another aspect of the present invention provides a membrane electrode for a fuel cell, comprising a proton exchange membrane and a catalyst layer, wherein the catalyst layer is a catalyst layer prepared by the above preparation method; the Pt loading amount at the cathode in the catalyst layer is 0.1-0.3 mg / cm 2 , the Pt loading on the anode is 0.02~0.1mg / cm 2 .

[0018] The beneficial effects of the present invention are:

[0019] 1. Compared with the Pt / C catalyst layer, the Pt-M / C catalyst layer prepared by the present invention can not only reduce the amount of Pt, but also effectively improve the dispersion and specific activity of Pt atoms through the geometric effect, electronic effect and synergistic effect between the alloy metal and Pt. Compared with the traditional Pt-M / C catalyst layer, the present invention can not only effectively reduce the introduction of alloy atoms in the catalyst layer on the basis of ensuring the same Pt ​​loading amount of the catalyst layer by regulating the element molar ratio of Pt and alloy elements in the entire catalyst layer, but also reduce the thickness of the catalyst layer by introducing a Pt / C catalyst with a high Pt content, which is more conducive to mass transfer.

[0020] 2. The catalytic layer prepared by the present invention not only exerts the strong activity of the Pt-M / C catalyst in the low current density region of the polarization curve, but also greatly improves its mass transfer polarization phenomenon in the high current density region. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the structure of the traditional Pt-M / C cathode catalyst layer;

[0022] Figure 2 The polarization curves of Example 1, Comparative Example 1 and Comparative Example 2 are shown in FIG. DETAILED DESCRIPTION

[0023] The following examples may enable those skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0024] Unless otherwise specified, the materials used in the embodiments of the present invention can be obtained through commercial channels or prepared according to conventional methods well known to those skilled in the art.

[0025] Example 1

[0026] (1) 3.0 g of Pt-Co / C (wherein the Pt content is 30 wt % and the Co content is 2 wt %) catalyst and 1.0 g of Pt / C (wherein the Pt content is 60 wt %) catalyst were weighed and added into a beaker and mixed thoroughly, 120 g of a mixed solvent of water and isopropanol was added as a dispersant, and 30.0 g of a 5 wt % perfluorosulfonic acid ionomer solution was added, stirred for 10 min, and high-speed shear dispersion was performed for 60 min;

[0027] (2) coating the mixed slurry on both sides of the proton exchange membrane by ultrasonic spraying;

[0028] (3) Control the Pt loading of the cathode catalyst layer of CCM to 0.25 mg / cm 2 , the anode loading is 0.05 mg / cm 2 .

[0029] Comparative Example 1

[0030] (1) Weigh 3 g of Pt / C catalyst (wherein the Pt content is 60 wt%) and add it to a beaker and mix thoroughly. Then, add 120 g of a mixed solvent of water and isopropanol as a dispersant, add 20 g of a 5 wt % perfluorosulfonic acid resin solution, stir for 10 min, and then perform high-speed shear dispersion for 60 min.

[0031] (2) coating the mixed slurry on both sides of the proton exchange membrane by ultrasonic spraying;

[0032] (3) Control the Pt loading of the cathode catalyst layer of CCM to 0.25 mg / cm 2 , the anode loading is 0.05 mg / cm 2 .

[0033] Comparative Example 2

[0034] (1) Weigh 3 g of Pt-Co / C (wherein the Pt content is 30 wt % and the Co content is 2 wt %) catalyst into a beaker, add 120 g of a mixed solvent of water and isopropanol as a dispersant, add 33 g of a 5 wt % perfluorosulfonic acid resin solution, stir for 10 min, and then perform high-speed shear dispersion for 60 min;

[0035] (2) coating the mixed slurry on both sides of the proton exchange membrane by ultrasonic spraying;

[0036] (3) Control the Pt loading of the cathode catalyst layer of CCM to 0.25 mg / cm 2 , the anode loading is 0.05 mg / cm 2 .

[0037] The prepared CCM, gas diffusion layer and polyester frame were hot pressed into MEA and assembled into a full-size single cell. Polarization curve tests were performed with a cell temperature of 80°C, anode humidification of 50%, cathode non-humidification, and back pressure of 150kPa on both sides. The test results are shown in the figure. Figure 2 shown.

[0038] Figure 2 The performance test diagram of the above-mentioned Example 1, Comparative Example 1 and Comparative Example 2 shows that the MEA prepared in Example 1 not only exerts the strong activity of the Pt-Co / C catalyst in the low current density region of the polarization curve, but also greatly improves its mass transfer polarization phenomenon in the high current density region; and after measurement, the catalyst layer thickness of Example 1 is 5 μm thinner than that of Comparative Example 2, which greatly reduces the bulk mass transfer resistance of the catalyst layer. It is worth emphasizing that due to the Pt-Co / C catalyst itself Co 2+ About SO 3 - The poisoning affects the proton conduction, and the polarization curve test is carried out under relatively dry conditions, which also seriously affects the contact of the three-phase interface. Therefore, Comparative Example 2 does not exert its excellent activity at low current density.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a catalytic layer for improving mass transfer polarization of a Pt-transition metal alloy catalyst for a fuel cell, characterized in that: The method comprises the following steps: (1) mixing a Pt-transition metal alloy catalyst and a Pt / C catalyst, adding a dispersant, uniformly dispersing by ultrasonication, adding a perfluorosulfonic acid ionomer solution, stirring, and then shearing with a high-speed shearing machine to obtain a catalyst slurry; (2) Spraying the catalyst slurry obtained in step (1) to form a fuel cell catalyst layer.

2. The preparation method according to claim 1, characterized in that: The dispersant is a mixture of one or more of water, ethanol, isopropanol and propylene glycol.

3. The preparation method according to claim 1, characterized in that: The Pt-transition metal alloy catalyst includes one of Pt-Co / C, Pt-Ni / C and Pt-Fe / C.

4. The preparation method according to claim 1, characterized in that: In the catalytic layer, the molar ratio of Pt to transition metal is 5-8:

1.

5. The preparation method according to claim 1, characterized in that: In the Pt-transition metal alloy catalyst, the content of Pt is 30wt%-50wt%, and the content of transition metal is 2wt%-5wt%; in the Pt / C catalyst, the content of Pt is 50wt%-75wt%.

6. The preparation method according to claim 1, characterized in that: The ratio of the mass of the perfluorosulfonic acid ionomer to the total mass of the carbon support in the Pt-transition metal alloy catalyst and the Pt / C catalyst is 0.4-1.3:

1.

7. A membrane electrode for a fuel cell, comprising a proton exchange membrane and a catalyst layer, characterized in that: The catalyst layer is a catalyst layer prepared by the preparation method according to any one of claims 1 to 6; the Pt loading on the cathode in the catalyst layer is 0.1 to 0.3 mg / cm 2 , the Pt loading on the anode is 0.02~0.1mg / cm 2 .

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