Modification method of catalyst particles, catalyst particles and application of catalyst particles

Abstract

The invention relates to the field of fuel cells, and provides a modification method of catalyst particles, the catalyst particles and application of the catalyst particles, the modification method comprises the following steps: S1, placing the catalyst particles in vacuum plasma equipment, and treating the catalyst particles in an inert gas atmosphere for T1; and S2, closing the vacuum plasma equipment, switching the inert gas into oxidizing gas, after the oxidizing gas is balanced, opening the vacuum plasma equipment, and continuously carrying out plasma treatment on the catalyst particles for T2 to obtain the modified catalyst particles. The method has the advantages that the catalyst particles are subjected to vacuum plasma treatment in an inert atmosphere, so that active volatile matters on the surfaces of the catalyst particles are partially volatilized; moderate plasma treatment is carried out again in the oxidizing atmosphere, slight oxidation can enable a small amount of basic oxide to be generated on the surface of the carbon black, surface charge distribution of the catalyst is adjusted, excessive adsorption of ionomers in the slurry is reduced, ionomer distribution is optimized, and therefore the performance of the membrane electrode is improved.

Description

Technical Field

[0001] The present invention relates to the field of fuel cells, and more particularly to a method for modifying catalyst particles, the catalyst particles and applications thereof. Background Art

[0002] A proton exchange membrane fuel cell (PEMFC) consists of multiple cells connected in series. Each cell primarily comprises a membrane electrode assembly (MEA) and bipolar plates. The MEA primarily consists of a catalyst layer, a proton exchange membrane, and a gas diffusion layer. The catalyst layer is the core component of the MEA, acting as both the site of the electrochemical reaction and the channel for the transfer of gases, water, electrons, protons, and other substances.

[0003] The three-phase interface is crucial in the catalytic layer: the reactant gases, electrons, and protons that must be transported to the catalyst surface for the electrochemical reaction to occur, while simultaneously carrying away the resulting products and heat. Ionomers in the catalytic layer must transport protons to the catalyst surface to complete the electrochemical reaction. However, the anionic structure of the ionomers can poison the catalyst, reducing its activity and efficiency. If too much ionomer is adsorbed on the catalyst particles, the performance of the membrane electrode can be compromised. Therefore, regulating the interaction between the ionomer and the catalyst surface, as well as the distribution of the ionomer on the catalyst surface, is crucial for controlling membrane electrode performance.

[0004] Catalysts generally consist of a metal catalyst and a carbon support supporting it. For carbon black support materials, pH is a critical property, often directly influencing properties such as specific surface area, porosity, and surface charge. Typically, functional groups on the carbon black surface include hydroxyl, carboxyl, phenol, ether, and alcohol. The protonation or deprotonation of these functional groups on the carbon black surface influences the pH of the carbon black's acid-base properties. Carbon black surface pH is often measured by measuring the pH of the carbon black suspension. A low catalyst surface pH indicates that the carbon black surface has a high number of electron acceptors, which can bind more hydroxide groups. This results in a high hydrogen ion concentration around the particles, manifesting as a low catalyst solution pH. Therefore, in fuel cell catalyst slurries, the interaction between ionomers with sulfonic acid ion groups on their side chains and catalyst particles is related to the acidity and alkalinity of the catalyst particle surface. A low catalyst particle pH indicates that excessive sulfonic acid groups in the slurry are adsorbed on the catalyst particle surface, leading to excessive adsorption or coating of the ionomer on the catalyst particle, affecting membrane electrode mass transfer and performance.

[0005] The electron donor formed by the large aromatic fused ring structure of carbon black is a Lewis base. When the oxygen on the carbon black surface bonds to a certain degree, sufficient to offset the Lewis base and with a residual amount, the carbon black surface becomes acidic. In the prior art, carbon black is generally devolatilized under inert atmosphere, high temperature, and high pressure conditions. This removes the volatile organic compounds from the carbon black, which eliminates the acidity of the carbon black and makes the devolatilized carbon black alkaline, thereby preventing excessive adsorption of ionomers. However, for fuel cell catalysts loaded with platinum or other metals, high temperature and high pressure conditions may cause the metal crystals in the catalyst particles to coarsen and change their crystal form, thereby affecting the catalyst activity and stability. Summary of the Invention

[0006] The present invention aims to overcome at least one defect (shortcoming) of the above-mentioned prior art, and provides a method for modifying catalyst particles, catalyst particles and applications thereof, so as to reduce the adsorption of ionomers on the surface of the catalyst particles.

[0007] An object of the present invention is to provide a method for modifying catalyst particles, comprising the following steps:

[0008] S1, placing the catalyst particles in a vacuum plasma device and treating them under an inert gas atmosphere for a treatment time of T1;

[0009] S2. Turn off the vacuum plasma equipment, switch the inert gas to the oxidizing gas, wait for the oxidizing gas to be balanced, turn on the vacuum plasma equipment, and continue to perform plasma treatment on the catalyst particles for a treatment time of T2 to obtain modified catalyst particles.

[0010] In one or more embodiments of the present invention, the catalyst particles include a metal catalyst and a carbon carrier supporting the metal catalyst. The oxidizing gas balance in step S2 means that after the oxidizing gas is introduced for a certain period of time, the oxidizing gas completely replaces the inert gas, and the gas pressure or vacuum degree reaches the set value. The present invention adopts a two-step plasma treatment for the catalyst particles. In step S1, the catalyst particles are subjected to vacuum plasma treatment under an inert atmosphere to partially volatilize the active volatile components on the surface of the catalyst particles; then the instrument is turned off, and an oxidizing atmosphere such as air, oxygen, etc. is introduced, and a moderate plasma treatment is performed again under an oxidizing atmosphere. Slight oxidation can produce a small amount of alkaline oxide on the surface of the carbon black, adjust the charge distribution on the catalyst surface, thereby reducing the excessive adsorption of ionomers in the slurry, optimizing the ionomer distribution, and thus improving the membrane electrode performance.

[0011] Furthermore, in step S1, the gas flow rate of the inert gas is 50 to 100 mL / min; and in step S2, the gas flow rate of the oxidizing gas is 10 to 30 mL / min.

[0012] Furthermore, T1 is 10 min to 30 min, and T2 is 1 min to 5 min.

[0013] Furthermore, in step S2, the oxidizing gas equilibrium time is 25 to 35 minutes.

[0014] Furthermore, in step S1, the radio frequency during processing is 40 KHz or 13.56 MHz; in step S2, the radio frequency during processing is 13.56 MHz or 2.45 GHz.

[0015] Furthermore, in step S1, the vacuum degree during the treatment is 10-30 Pa; in step S2, the vacuum degree during the treatment is 5-15 Pa.

[0016] Furthermore, in step S1, the processing power is 800-1000 W; in step S2, the processing power is 200-500 W. In step S1, high-power plasma treatment of the catalyst particles is beneficial for removing active volatiles on their surfaces; in step S2, low-power plasma treatment of the catalyst particles is beneficial for generating alkaline oxides on the surfaces of the catalyst particles.

[0017] Another object of the present invention is to provide catalyst particles obtained by modification using any of the above modification methods, wherein the pH of the catalyst particles is 3.5 to 4.5.

[0018] Another object of the present invention is to provide a catalyst slurry comprising ultrapure water, a resin solution, an organic solvent and the above-mentioned catalyst particles.

[0019] Another object of the present invention is to provide a catalytic layer prepared from the above-mentioned catalyst slurry.

[0020] Compared with the prior art, the present invention has the following advantages: The present invention utilizes a two-step plasma treatment process for catalyst particles. The catalyst particles are subjected to vacuum plasma treatment in an inert atmosphere to partially volatilize the active volatile components on the catalyst particle surface. A further moderate plasma treatment is then performed in an oxidizing atmosphere. This slight oxidation produces a small amount of alkaline oxide on the carbon black surface, adjusting the charge distribution on the catalyst surface, reducing excessive adsorption of ionomers in the slurry, significantly reducing the ionomer poisoning effect on the catalyst particles, improving the catalytic efficiency of the catalyst particles, and optimizing the ionomer distribution, thereby enhancing membrane electrode performance. This also increases the utilization rate of the catalyst particles and saves costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the AFM test phase image of the cathode catalyst layer corresponding to Example 1.

[0022] Figure 2 This is the AFM test phase image of the cathode catalyst layer corresponding to Comparative Example 1.

[0023] Figure 3 The performance curves of membrane electrodes prepared corresponding to the catalyst particles of Examples 1 to 3 and Comparative Examples 1 to 4 are shown. DETAILED DESCRIPTION

[0024] In order to enable those skilled in the art to better understand the technical solution of the present application, the present application is further described in detail below in conjunction with specific embodiments.

[0025] An object of the present invention is to provide a method for modifying catalyst particles, comprising the following steps:

[0026] S1, placing the catalyst particles in a vacuum plasma device and treating them under an inert gas atmosphere for a treatment time of T1;

[0027] S2. Turn off the vacuum plasma equipment, switch the inert gas to the oxidizing gas, wait for the oxidizing gas to be balanced, turn on the vacuum plasma equipment, and continue to perform plasma treatment on the catalyst particles for a treatment time of T2 to obtain modified catalyst particles.

[0028] Furthermore, in step S1, the gas flow rate of the inert gas is 50 to 100 mL / min; and in step S2, the gas flow rate of the oxidizing gas is 10 to 30 mL / min.

[0029] Furthermore, T1 is 10 min to 30 min, and T2 is 1 min to 5 min.

[0030] Furthermore, in step S2, the oxidizing gas equilibrium time is 25 to 35 minutes.

[0031] Furthermore, in step S1, the RF frequency during treatment is 40 KHz or 13.56 MHz; in step S2, the RF frequency during treatment is 13.56 MHz or 2.45 GHz. Furthermore, in step S1, the vacuum degree during treatment is 10-30 Pa; in step S2, the vacuum degree during treatment is 5-15 Pa.

[0032] Furthermore, in step S1, the processing power is 800-1000 W; in step S2, the processing power is 200-500 W. In step S1, high-power plasma treatment of the catalyst particles is beneficial for removing active volatiles on their surfaces; in step S2, low-power plasma treatment of the catalyst particles is beneficial for generating alkaline oxides on the surfaces of the catalyst particles.

[0033] Another object of the present invention is to provide a catalyst particle obtained by modification using any one of the above modification methods, wherein the pH of the catalyst particle is 3.5 to 4.5.

[0034] Another object of the present invention is to provide a catalyst slurry comprising ultrapure water, a resin solution, an organic solvent and the above-mentioned catalyst particles.

[0035] Another object of the present invention is to provide a catalytic layer prepared from the above-mentioned catalyst slurry.

[0036] Example 1

[0037] This embodiment provides a method for modifying catalyst particles, comprising the following steps:

[0038] TEC10E50E catalyst (Pt / C catalyst with 50% platinum content) produced by Tanaka Precious Metals (TKK) of Japan

[0039] Place it in a vacuum plasma processor (Nan Technology, NE-OIC04), set the processing conditions to helium atmosphere, gas flow rate of 75 mL / min, radio frequency frequency of 13.56 MHz, vacuum degree of 15 Pa, processing power of 800 W, and processing time of 20 min.

[0040] Turn off the vacuum plasma processor, switch the gas to oxygen with a flow rate of 20 mL / min, and after introducing oxygen for 30 minutes, evacuate the chamber to a vacuum degree of 10 Pa, and allow the gas to reach equilibrium. Turn on the vacuum plasma processor, set the RF frequency to 2.45 GHz, the vacuum degree to 10 Pa, the processing power to 400 W, and the processing time to 3 minutes to finally obtain modified catalyst particles.

[0041] Example 2

[0042] This embodiment provides a method for modifying catalyst particles, comprising the following steps:

[0043] TEC10E50E catalyst (Pt / C catalyst with 50% platinum content) produced by Tanaka Precious Metals (TKK) of Japan

[0044] The sample was placed in a vacuum plasma processor (Nan Technology, NE-OIC04), and the treatment conditions were set to helium atmosphere, gas flow rate of 50 mL / min, radio frequency frequency of 40 kHz, vacuum degree of 10 Pa, treatment power of 800 W, and treatment time of 10 min.

[0045] Turn off the vacuum plasma processor, switch the gas to oxygen with a flow rate of 30 mL / min, and after introducing oxygen for 30 minutes, evacuate the gas to a vacuum degree of 10 Pa and allow the gas to reach equilibrium. Turn on the vacuum plasma processor, set the RF frequency to 2.45 GHz, the processing power to 500 W, and the processing time to 1 minute to finally obtain modified catalyst particles.

[0046] Example 3

[0047] This embodiment provides a method for modifying catalyst particles, comprising the following steps:

[0048] TEC10E50E catalyst (Pt / C catalyst with 50% platinum content) produced by Tanaka Precious Metals (TKK) of Japan

[0049] Place it in a vacuum plasma processor (Nan Technology, NE-OIC04), set the processing conditions to helium atmosphere, gas flow rate of 100 mL / min, radio frequency frequency of 13.56 MHz, vacuum degree of 30 Pa, processing power of 1000 W, and processing time of 30 min.

[0050] The vacuum plasma processor was turned off, and the gas was switched to oxygen at a flow rate of 30 mL / min. After oxygen was introduced for 30 minutes, the vacuum was evacuated to a vacuum degree of 10 Pa, and the gas reached a balanced state. The vacuum plasma processor was turned on, and the RF frequency was set to 2.54 GH MHz, the processing power was set to 200 W, and the processing time was set to 5 minutes to finally obtain modified catalyst particles.

[0051] Comparative Example 1

[0052] This comparative example provides a catalyst particle, which is a TEC10E50E catalyst (Pt / C catalyst with 50% platinum content) produced by Tanaka Precious Metals (TKK) of Japan.

[0053] Comparative Example 2

[0054] This comparative example provides a method for modifying catalyst particles, comprising the following steps:

[0055] The TEC10E50E catalyst (Pt / C catalyst with 50% platinum content) produced by Tanaka Precious Metals (TKK) of Japan was placed in a vacuum plasma processor (Nan Technology, NE-OIC04), and the treatment conditions were set to helium atmosphere, gas flow rate of 100 mL / min, radio frequency frequency of 13.56 MHz, vacuum degree of 30 Pa, treatment power of 1000 W, and treatment time of 30 min, and finally modified catalyst particles were obtained.

[0056] Comparative Example 3

[0057] This comparative example provides a method for modifying catalyst particles, comprising the following steps:

[0058] The TEC10E50E catalyst (Pt / C catalyst with 50% platinum content) produced by Tanaka Precious Metals (TKK) of Japan was placed in a vacuum plasma processor (Nan Technology, NE-OIC04), and the treatment conditions were set to helium atmosphere, gas flow rate of 75 mL / min, radio frequency frequency of 13.56 MHz, vacuum degree of 15 Pa, treatment power of 800 W, and treatment time of 20 min.

[0059] Turn off the vacuum plasma processor, switch the gas to oxygen with a flow rate of 100 mL / min, and after introducing oxygen for 30 minutes, evacuate the chamber to a vacuum degree of 10 Pa and allow the gas to reach equilibrium. Turn on the vacuum plasma processor, set the RF frequency to 2.45 GHz, the processing power to 1000 W, and the processing time to 30 minutes to finally obtain modified catalyst particles.

[0060] Comparative Example 4

[0061] This comparative example provides a method for modifying catalyst particles, comprising the following steps:

[0062] The TEC10E50E catalyst (Pt / C catalyst with 50% platinum content) produced by Tanaka Precious Metals (TKK) of Japan was placed in a vacuum plasma processor (Nan Technology, NE-OIC04), and the treatment conditions were set to helium atmosphere, gas flow rate of 120 mL / min, radio frequency frequency of 40 kHz, vacuum degree of 40 Pa, treatment power of 1200 W, and treatment time of 60 min.

[0063] Turn off the vacuum plasma processor, switch the gas to oxygen with a flow rate of 20 mL / min, and after introducing oxygen for 30 minutes, evacuate the chamber to a vacuum degree of 10 Pa and allow the gas to reach equilibrium. Turn on the vacuum plasma processor, set the RF frequency to 2.45 GHz, the processing power to 400 W, and the processing time to 3 minutes to finally obtain modified catalyst particles.

[0064] The catalyst particles obtained in Examples 1 to 3 and Comparative Examples 2 to 4, as well as the catalyst particles provided in Comparative Example 1, were prepared into a catalytic layer using the following method:

[0065] Weigh 5.10g of catalyst particles, 8.53g of 20wt% solid content D2020 resin solution, 7.20g of ethanol, and 39.00g of ultrapure water. Slowly add the catalyst to the stirred water and stir for 5 minutes. Then add the resin solution and stir for 2 minutes. Then add ethanol and continue stirring for 2 minutes to complete the slurry pre-dispersion. The pre-dispersed slurry is dispersed twice by a high-pressure homogenizer at a dispersion pressure of 2000psi to obtain a catalyst slurry. Apply it to one side of the proton exchange membrane by slot coating and dry at 80°C to obtain the membrane electrode cathode catalyst layer.

[0066] Test experiment:

[0067] Test 1: The pH of the catalyst particles of Examples 1 to 3 and Comparative Examples 1 to 4 was measured with reference to GB / T 3780.7-2016. The test results are shown in Table 1.

[0068] Table 1 pH test results of catalyst particles in Examples and Comparative Examples

[0069] sample Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 pH 3.8 3.5 4.5 2.9 3.7 2.1 4.8

[0070] Test 2: Atomic force microscopy (AFM) was used to test the cathode catalyst layer prepared corresponding to the catalyst particles of Example 1 and Comparative Example 1, and the phase diagram of the catalyst particles and ionomers was obtained. The results are as follows: Figure 1 and Figure 2 shown.

[0071] Test 3: The membrane electrode catalyst layers obtained in Examples 1 to 3 and Comparative Examples 1 to 4 were used to prepare membrane electrodes, and the polarization performance curve of the membrane electrode single cell was tested using the 850e fuel cell test system. The test conditions were 75°C and 75% RH. The test results are as follows: Figure 3 As shown, the electrical properties of the membrane electrodes corresponding to Examples 1 to 3 are all higher than those of Comparative Examples 1 to 4.

[0072] Figure 1 and Figure 2 The AFM test phase diagrams of Example 1 and Comparative Example 1 are respectively. The composition, hardness, viscoelastic properties, etc. of the sample will affect the AFM phase diagram test results. The catalytic layer is a composite of catalyst particles and ionomers. The dark area in the phase diagram indicates that the area is harder and more rigid, which may be exposed catalyst particles or catalyst particles with less adsorbed ionomers; the bright area indicates that the area is more sticky and soft, which may be a thicker ionomer area or an ionomer bonding area on the catalyst. Figure 2 There are a lot of unevenly distributed thick ionomer adsorption or aggregation in the middle. Figure 1 The phase diagram shows that the ionomer distribution in Example 1 is more uniform, and there is less excessive adsorption of ionomer on the catalyst particles.

[0073] Combined with Table 1 and Figures 1 to 3 According to the test results of the catalyst particles of Examples 1 to 3 and Comparative Example 1, the pH value of the surface of the catalyst particles treated by the modification method of the present invention is improved compared with the untreated catalyst particles. This reduces the excessive adsorption of the ionomer on the catalyst particles to a certain extent, reduces its poisoning effect on the catalyst, improves the mass transfer in the catalytic layer, and thus improves the performance of the membrane electrode.

[0074] Combined with Table 1 and Figures 1 to 3According to the test results of the catalyst particles of Examples 1 to 3 and Comparative Example 2, it can be seen that in Comparative Example 2, only the first step of inert atmosphere high-power plasma treatment is performed on the catalyst particles. The pH test result of the catalyst after treatment is 3.7. However, due to the lack of the second step of oxidizing atmosphere low-power plasma treatment, no additional alkaline oxides are generated on the surface of the catalyst particles, which affects the surface charge of the catalyst. Although the performance is slightly improved compared with Comparative Example 1, it is still worse than that of Examples 1 to 3.

[0075] Combined with Table 1 and Figures 1 to 3 According to the test results of the catalyst particles of Examples 1 to 3 and Comparative Example 3, it can be seen that in Comparative Example 3, due to the excessive high gas flow and high power treatment of the second step plasma in an oxidizing atmosphere, not only alkaline oxides are generated on the surface of the catalyst particles, but more catalyst carriers are over-oxidized to regenerate acidic oxides, and the catalyst pH is too low, resulting in a decrease in membrane electrode performance.

[0076] Combined with Table 1 and Figures 1 to 3 According to the test results of the catalyst particles of Examples 1 to 3 and Comparative Example 4, it can be seen that the comparative example 4 is due to excessive treatment of the first step plasma at high flow and high power, which leads to excessive volatilization of acidic active volatiles, making the active functional groups on the catalyst surface too low and the pH too high, thereby affecting the adsorption and distribution of the ionomer, resulting in reduced membrane electrode performance.

[0077] Combined with the test results of Examples 1 to 3 and Comparative Examples 1 to 4, moderate two-step plasma treatment can effectively adjust the pH and surface charge of catalyst particles, thereby optimizing the adsorption of ionomers in the slurry and the distribution of ionomers in the catalyst layer, and improving membrane electrode performance.

[0078] Obviously, the above embodiments of the present invention are merely examples for the purpose of clearly illustrating the technical solutions of the present invention, and are not intended to limit the specific implementation methods of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the claims of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. A method for modifying catalyst particles, characterized in that: The following steps are involved: S1, placing the catalyst particles in a vacuum plasma device and treating them in an inert gas atmosphere for a treatment time of T1; S2. Turn off the vacuum plasma equipment, switch the inert gas to the oxidizing gas, and after the oxidizing gas is balanced, turn on the vacuum plasma equipment and continue to perform plasma treatment on the catalyst particles for a treatment time of T2 to obtain modified catalyst particles.

2. The method for modifying catalyst particles according to claim 1, characterized in that: In step S1, the gas flow rate of the inert gas is 50 to 100 mL / min; in step S2, the gas flow rate of the oxidizing gas is 10 to 30 mL / min.

3. The method for modifying catalyst particles according to claim 1, characterized in that: T1 is 10min~30min, and T2 is 1min~5min.

4. The method for modifying catalyst particles according to claim 1, characterized in that: In step S2, the duration of oxidizing gas equilibrium is 25 to 35 minutes.

5. The method for modifying catalyst particles according to claim 1, characterized in that: In step S1, the radio frequency during processing is 40 KHz or 13.56 MHz; in step S2, the radio frequency during processing is 13.56 MHz or 2.45 GHz.

6. The method for modifying catalyst particles according to claim 1, characterized in that: In step S1, the vacuum degree during the treatment is 10-30Pa; in step S2, the vacuum degree during the treatment is 5-15Pa.

7. The method for modifying catalyst particles according to any one of claims 1 to 6, characterized in that: In step S1, the processing power is 800-1000W; in step S2, the processing power is 200-500W.

8. A catalyst particle, characterized in that: The catalyst particles are modified by the modification method according to any one of claims 1 to 7, and the pH of the catalyst particles is 3.5 to 4.

5.

9. A catalyst slurry, characterized in that: The method comprises ultrapure water, a resin solution, an organic solvent and the catalyst particles according to claim 8.

10. A catalytic layer, characterized in that: Prepared from the catalyst slurry described in claim 9.

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