Method for modifying catalyst particles, catalyst particles and use thereof

Abstract

The application relates to the field of fuel cells, and provides a modification method of catalyst particles, the catalyst particles and application thereof, the modification method comprises the following steps: S1, placing the catalyst particles in a vacuum plasma device, treating the catalyst particles in an atmosphere of inert gas, and the treatment time is T1; S2, closing the vacuum plasma device, switching the inert gas into oxidizing gas, opening the vacuum plasma device after the oxidizing gas is balanced, and continuing to perform plasma treatment on the catalyst particles, and the treatment time is T2, so that the modified catalyst particles are obtained. Advantages: the catalyst particles are treated in the vacuum plasma device in the inert atmosphere, so that part of the surface active volatile components of the catalyst particles is volatilized; the moderate plasma treatment is further performed on the catalyst particles in the oxidizing atmosphere, a small amount of basic oxides is generated on the surface of the carbon black through slight oxidation, the surface charge distribution of the catalyst is adjusted, the excessive adsorption of the ionomer in the slurry is reduced, the ionomer distribution is optimized, and the performance of a membrane electrode is improved.

Description

Technical Field

[0001] This invention relates to the field of fuel cells, and more specifically, to a method for modifying catalyst particles, catalyst particles, and their applications. Background Technology

[0002] A proton exchange membrane fuel cell (PEMFC) consists of multiple single cells connected in series. A single cell mainly consists of a membrane electrode assembly (MEA) and bipolar plates. The MEA mainly consists of a catalyst layer, a proton exchange membrane, and a gas diffusion layer. The catalyst layer is the most critical component of the MEA, serving as both the site of electrochemical reactions and the channel for the transfer of substances such as gases, water, electrons, and protons.

[0003] The most crucial element in the catalyst layer is the three-phase interface, where reactant gases, electrons, and protons need to be transported to the catalyst surface to initiate the electrochemical reaction, while simultaneously carrying away the generated products and heat. Ionomers in the catalyst layer require proton transport 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 many ionomers are adsorbed onto the catalyst particles, it will affect the performance of the membrane electrode assembly (MEA). Therefore, regulating the interaction between the ionomers and the catalyst surface, as well as the distribution of ionomers on the catalyst surface, is essential for controlling the performance of the MEA.

[0004] Catalysts generally consist of a metal catalyst and a carbon support. For carbon black support materials, pH is a crucial property, directly affecting characteristics such as specific surface area, porosity, and surface charge. Typically, functional groups on the carbon black surface include hydroxyl, carboxyl, phenol, ether, and alcohol groups. The protonation or deprotonation of these functional groups on the carbon black surface influences its acid-base properties (pH). The pH of the carbon black surface is often determined by measuring the pH of the carbon black suspension. If the catalyst surface pH is too low, it indicates that the carbon black surface has numerous electron acceptors, allowing for the binding of more hydroxyl groups, resulting in a high hydrogen ion content around the particles and a low pH in the catalyst solution. Therefore, in fuel cell catalyst slurries, the interaction between ionomers with sulfonic acid ion groups on their side chains and the catalyst particles is related to the acidity or alkalinity of the catalyst particle surface. Low pH catalyst particles mean that excessive sulfonic acid groups in the slurry will adsorb onto their surface, leading to over-adsorption or coating of ionomers on the catalyst particles, affecting the mass transfer and performance of the membrane electrode assembly (MEA).

[0005] The giant aromatic fused-ring structure of carbon black forms an electron donor known as a Lewis base. When the oxygen bonding on the carbon black surface reaches a certain level, sufficient to offset the Lewis basicity while leaving a surplus, the carbon black surface becomes acidic. Current technology typically involves devolatilization of carbon black under inert atmosphere, high temperature, and high pressure conditions. This process removes volatile organic compounds from the carbon black, eliminating its acidity and making it alkaline, thus preventing excessive adsorption of ionomers. However, for fuel cell catalysts supported on platinum or other metals, high temperature and high pressure conditions may cause coarsening and changes in crystal structure within the catalyst particles, thereby affecting catalyst activity and stability. Summary of the Invention

[0006] The present invention aims to overcome at least one defect (deficiency) of the prior art and provide a method for modifying catalyst particles, catalyst particles and their applications, thereby reducing the adsorption of ionomers on the surface of catalyst particles.

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

[0008] S1. Place the catalyst particles in a vacuum plasma device and treat them in an inert gas atmosphere for a duration of T1.

[0009] 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 to continue plasma treatment of the catalyst particles for a duration of T2 to obtain modified catalyst particles.

[0010] In one or more embodiments of the present invention, the catalyst particles comprise a metal catalyst and a carbon support thereon. The oxidizing gas balance in step S2 refers to the complete replacement of the inert gas by the oxidizing gas after a certain period of time, with the gas pressure or vacuum reaching a set value. The present invention employs a two-step plasma treatment method 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 volatiles on the catalyst particle surface; then the instrument is turned off, and an oxidizing atmosphere such as air or oxygen is introduced, followed by a moderate plasma treatment under the oxidizing atmosphere. Slight oxidation can generate a small amount of alkaline oxides on the carbon black surface, adjusting the surface charge distribution of the catalyst, thereby reducing excessive adsorption of ionomers in the slurry, optimizing the ionomer distribution, and thus improving the membrane electrode performance.

[0011] Furthermore, in step S1, the flow rate of the inert gas is 50–100 mL / min; in step S2, the flow rate of the oxidizing gas is 10–30 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 25–35 min.

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

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

[0016] Further, 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 the active volatiles on their surface; in step S2, low-power plasma treatment of the catalyst particles is beneficial for the formation of alkaline oxides on the surface of the catalyst particles.

[0017] Another object of the present invention is to provide catalyst particles, which are obtained by any of the above-described 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 catalyst particles described above.

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

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention employs a two-step plasma treatment method for catalyst particles. The catalyst particles are subjected to vacuum plasma treatment under an inert atmosphere, causing partial volatilization of the active volatiles on the catalyst particle surface; a second, moderate plasma treatment is performed under an oxidizing atmosphere. Slight oxidation generates a small amount of alkaline oxides on the carbon black surface, adjusting the surface charge distribution of the catalyst, reducing excessive adsorption of ionomers in the slurry, significantly reducing the poisoning effect of ionomers on the catalyst particles, improving the catalytic efficiency of the catalyst particles, optimizing the ionomer distribution to improve membrane electrode performance, and simultaneously increasing the utilization rate of catalyst particles while saving costs. Attached Figure Description

[0021] Figure 1 The AFM test phase diagram is shown for the cathode catalyst layer corresponding to Example 1.

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

[0023] Figure 3 The graphs show the performance of membrane electrodes prepared for the catalyst particles of Examples 1-3 and Comparative Examples 1-4. Detailed Implementation

[0024] To enable those skilled in the art to better understand the technical solutions of this application, the application will be further described in detail below with reference to specific embodiments.

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

[0026] S1. Place the catalyst particles in a vacuum plasma device and treat them in an inert gas atmosphere for a duration of T1.

[0027] 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 to continue plasma treatment of the catalyst particles for a duration of T2 to obtain modified catalyst particles.

[0028] Furthermore, in step S1, the flow rate of the inert gas is 50–100 mL / min; in step S2, the flow rate of the oxidizing gas is 10–30 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 25–35 min.

[0031] Further, 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. Further, in step S1, the vacuum degree during processing is 10–30 Pa; in step S2, the vacuum degree during processing is 5–15 Pa.

[0032] Further, 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 the active volatiles on their surface; in step S2, low-power plasma treatment of the catalyst particles is beneficial for the formation of alkaline oxides on the surface of the catalyst particles.

[0033] Another object of the present invention is to provide a catalyst particle, which is obtained by any of the above-described 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 catalyst particles described above.

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

[0036] Example 1

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

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

[0039] The plasma was placed in a vacuum plasma treatment machine (Nanotech, NE-OIC04), and the treatment conditions were set as follows: helium atmosphere, gas flow rate of 75 mL / min, radio frequency of 13.56 MHz, vacuum degree of 15 Pa, treatment power of 800 W, and treatment time of 20 min.

[0040] The vacuum plasma processor was turned off, and the gas was switched to oxygen at a flow rate of 20 mL / min. After 30 min of oxygen introduction, the vacuum was evacuated to a vacuum level of 10 Pa, and the gas reached equilibrium. The vacuum plasma processor was then turned on, and the radio frequency was set to 2.45 GHz, the vacuum level to 10 Pa, the processing power to 400 W, and the processing time to 3 min, finally yielding modified catalyst particles.

[0041] Example 2

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

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

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

[0045] The vacuum plasma processor was turned off, and the gas was switched to oxygen at a flow rate of 30 mL / min. After 30 min of oxygen introduction, the vacuum was evacuated to a vacuum level of 10 Pa, and the gas reached equilibrium. The vacuum plasma processor was then turned on, and the radio frequency was set to 2.45 GHz, the processing power to 500 W, and the processing time to 1 min, finally yielding modified catalyst particles.

[0046] Example 3

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

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

[0049] The plasma was placed in a vacuum plasma treatment machine (Nanotech, NE-OIC04), and the treatment conditions were set as follows: helium atmosphere, gas flow rate of 100 mL / min, radio frequency of 13.56 MHz, vacuum degree of 30 Pa, treatment power of 1000 W, and treatment 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 30 min of oxygen introduction, the vacuum was evacuated to a vacuum level of 10 Pa, and the gas reached equilibrium. The vacuum plasma processor was then turned on, and the radio frequency was set to 2.54 GH MHz, the processing power to 200 W, and the processing time to 5 min, finally yielding modified catalyst particles.

[0051] Comparative Example 1

[0052] This comparative example provides a catalyst particle, which is the TEC10E50E catalyst (50% platinum content Pt / C catalyst) manufactured 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 (a Pt / C catalyst with 50% platinum content) produced by Tanaka Precious Metals (TKK) of Japan was placed in a vacuum plasma treatment machine (Nanotech, NE-OIC04). The treatment conditions were set as follows: helium atmosphere, gas flow rate of 100 mL / min, radio frequency of 13.56 MHz, vacuum degree of 30 Pa, treatment power of 1000 W, and treatment time of 30 min, finally obtaining modified catalyst particles.

[0056] Comparative Example 3

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

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

[0059] The vacuum plasma processor was turned off, and the gas was switched to oxygen at a flow rate of 100 mL / min. After 30 minutes of oxygen introduction, the vacuum was evacuated to a vacuum level of 10 Pa, and the gas reached equilibrium. The vacuum plasma processor was then turned on, and the radio frequency was set to 2.45 GHz, the processing power to 1000 W, and the processing time to 30 minutes, finally yielding 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 (50% platinum content Pt / C catalyst) produced by Tanaka Precious Metals (TKK) of Japan was placed in a vacuum plasma treatment machine (Nanotech, NE-OIC04). The treatment conditions were set as follows: helium atmosphere, gas flow rate of 120 mL / min, radio frequency of 40 kHz, vacuum degree of 40 Pa, treatment power of 1200 W, and treatment time of 60 min.

[0063] The vacuum plasma processor was turned off, and the gas was switched to oxygen at a flow rate of 20 mL / min. After 30 min of oxygen introduction, the vacuum was evacuated to a vacuum level of 10 Pa, and the gas reached equilibrium. The vacuum plasma processor was then turned on, and the radio frequency was set to 2.45 GHz, the processing power to 400 W, and the processing time to 3 min, finally yielding 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 used to prepare a catalyst layer using the following method:

[0065] Weigh out 5.10 g of catalyst particles, 8.53 g of 20 wt% solid content D2020 resin solution, 7.20 g of ethanol, and 39.00 g of ultrapure water. Slowly add the catalyst to the water while stirring for 5 min. Then add the resin solution and stir for 2 min. Finally, add the ethanol and continue stirring for 2 min to complete the pre-dispersion of the slurry. Disperse the pre-dispersion slurry twice using a high-pressure homogenizer at a dispersion pressure of 2000 psi to obtain the catalyst slurry. Coat the proton exchange membrane with the slit coating method 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 in Examples 1-3 and Comparative Examples 1-4 was determined according to GB / T 3780.7-2016. The test results are shown in Table 1.

[0068] Table 1. pH test results of catalyst particles in the 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 layers prepared corresponding to the catalyst particles of Example 1 and Comparative Example 1, obtaining phase diagrams of the catalyst particles and ionomers. The results are as follows: Figure 1 and Figure 2 As shown.

[0071] Test 3: Membrane electrodes were prepared by using the catalytic layers obtained in Examples 1-3 and Comparative Examples 1-4. The polarization performance curves of single-cell membrane electrodes were then tested using an 850e fuel cell testing system. The test conditions were 75°C and 75% RH. The test results are as follows: Figure 3 As shown, the electrical performance of the membrane electrodes corresponding to Examples 1 to 3 is higher than that of Comparative Examples 1 to 4.

[0072] Figure 1 and Figure 2 The AFM phase diagrams for Example 1 and Comparative Example 1 are shown below. The composition, hardness, and viscoelastic properties of the samples all affect the AFM phase diagram test results. The catalyst layer is a complex composed of catalyst particles and ionomers. Dark areas in the phase diagram indicate that the region is "harder" and "rigid," possibly representing exposed catalyst particles or catalyst particles with less adsorbed ionomers; bright areas indicate that the region is "stickier" and "softer," possibly representing regions with a thicker distribution of ionomers on the catalyst or ionomer-bonded regions. Compared to... Figure 2 In many areas, there is uneven distribution of relatively thick ionomers adsorbed or aggregated. Figure 1 The phase diagram shows that the ionomers in Example 1 are more evenly distributed, and there is less excessive adsorption of ionomers on the catalyst particles.

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

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

[0075] Combining Table 1 and Figures 1-3 According to the test results of the catalyst particles in Examples 1-3 and Comparative Example 3, it can be seen that in Comparative Example 3, due to the excessive processing of the second-step plasma under high gas flow and high power in an oxidizing atmosphere, not only were alkaline oxides generated on the surface of the catalyst particles, but more catalyst supports were also over-oxidized and regenerated into acidic oxides. The catalyst pH was too low, resulting in a decrease in membrane electrode performance.

[0076] Combining Table 1 and Figures 1-3 According to the test results of the catalyst particles in Examples 1-3 and Comparative Example 4, it can be seen that in Comparative Example 4, the excessive treatment of the first-step plasma under high flow and high power resulted in excessive volatilization of acidic active volatiles, which led to an excessively low number of active functional groups on the catalyst surface and an excessively high pH, ​​thereby affecting the adsorption and distribution of ionomers and reducing the performance of the membrane electrode.

[0077] Based on the test results of Examples 1-3 and Comparative Examples 1-4, a 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 the performance of the membrane electrode.

[0078] 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 method for modifying catalyst particles, characterized in that, Includes the following steps: S1. Place the catalyst particles in a vacuum plasma device and treat them in an inert gas atmosphere for a duration 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 to continue plasma treatment of the catalyst particles for a duration of T2 to obtain modified catalyst particles. In step S1, T1 is 10 min to 30 min; the inert gas flow rate is 50 to 100 mL / min; the processing power is 800 to 1000 W; in step S2, the oxidizing gas flow rate is 10 to 30 mL / min; the processing power is 200 to 500 W; T2 is 1 min to 5 min. Catalyst particles consist of a metal catalyst and a carbon support on which it is supported.

2. The method for modifying catalyst particles according to claim 1, characterized in that, In step S2, the oxidizing gas equilibrium time is 25~35 min.

3. 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.

4. The method for modifying catalyst particles according to claim 1, characterized in that, In step S1, the vacuum level during processing is 10~30 Pa; in step S2, the vacuum level during processing is 5~15 Pa.

5. A catalyst particle, characterized in that, The catalyst particles are obtained by modification according to any one of claims 1 to 4, and the pH of the catalyst particles is 3.5 to 4.

5.

6. A catalyst slurry, characterized in that, It includes ultrapure water, resin solution, organic solvent and catalyst particles as described in claim 5.

7. A catalyst layer, characterized in that, It is prepared from the catalyst slurry described in claim 6.

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