Modified catalyst, preparation method thereof, membrane electrode, fuel cell and application

Abstract

The invention provides a modified catalyst and a preparation method thereof, a membrane electrode, a fuel cell and application, the modified catalyst comprises a catalyst matrix and a modified layer loaded on the outer surface of the catalyst matrix, the catalyst matrix is a Pt / C catalyst, and the structural formula of the material of the modified layer is SiO2-(CH2) 3SH. By adopting the modified catalyst provided by the invention, on one hand, when the modified catalyst is applied to a membrane electrode, the coverage of an ionomer on catalyst nanoparticles can be reduced, so that active sites of the catalyst are increased, and the catalytic performance is improved; and on the other hand, the local oxygen mass transfer resistance in the cathode catalyst layer can be greatly reduced, so that the cathode catalyst layer has better catalytic activity and mass transfer rate, and the comprehensive performance is better.

Description

Technical Field

[0001] The present application relates to the technical field of fuel cells, and particularly to a modified catalyst, a preparation method thereof, a membrane electrode, a fuel cell and an application. Background Art

[0002] The cathode oxygen reduction reaction (ORR) and the anode hydrogen oxidation reaction (HOR) are two extremely important electrochemical reactions in proton exchange membrane fuel cells (PEMFCs) and metal-air batteries. Among them, due to the slow kinetics of the ORR reaction, an electrocatalyst with high catalytic activity is required to accelerate the reaction rate. Among them, the platinum / carbon catalyst (Pt / C) is still the mainstream commercial core material for the anode hydrogen oxidation and cathode oxygen reduction reactions in proton exchange membrane fuel cells, and its cost accounts for more than 40% of the cost of the fuel cell stack.

[0003] Moreover, compared with the rapid oxidation of hydrogen at the anode, the cathode oxygen reduction is a multi-electron reaction process with a complex reaction mechanism and slow kinetics, which determines that the electrochemical kinetic loss and Pt consumption in the cathode reaction in PEMFCs are relatively large. At present, the high platinum loading in the cathode catalyst layer, the slow electrocatalytic kinetics of oxygen reduction and the difficulty of oxygen mass transfer have become the key limiting factors for the cost, performance and life of the membrane electrode.

[0004] At present, for the optimization of the platinum / carbon catalyst, more attention is paid to the intrinsic activity and life of the catalyst, but its performance life parameters cannot effectively meet the requirements of low platinum loading and high current density operation in actual operating fuel cells, making it difficult to effectively reduce the platinum consumption in fuel cells and resulting in slow cost reduction. That is, the main reason is that only the intrinsic activity of the catalyst is considered without optimizing its mass transfer characteristics, and there is a lack of solutions to reduce the local oxygen mass transfer resistance from the perspective of catalyst design.

[0005] Therefore, in the existing proton exchange membrane fuel cell with a low platinum loading, due to its low platinum loading, the oxygen and proton transport in the cathode catalyst layer is incomplete and insufficient, which further leads to poor electrochemical performance of the fuel cell and further limits the battery performance and life. Especially when applied under high current, the catalyst with an ultra-low platinum loading in the proton exchange membrane fuel cell causes a rapid increase in the local oxygen mass transfer resistance, resulting in battery performance loss.

[0006] Based on this, in the face of the technical problems that the existing catalysts have poor catalytic activity or high local oxygen mass transfer resistance under high current and ultra-low platinum loading, resulting in poor electrochemical performance and short life of the fuel cell when applied to the fuel cell, there is an urgent need to provide a catalyst and a preparation method thereof to improve the above problems. Summary of the Invention

[0007] The main object of the present invention is to provide a modified catalyst, a preparation method thereof, a membrane electrode, a fuel cell and an application, so as to solve the technical problems that in the prior art, when the catalyst is under high current and ultra-low platinum loading, the catalytic activity is poor or the local oxygen mass transfer resistance is high, resulting in poor electrochemical performance and short service life of the fuel cell when it is applied to the fuel cell.

[0008] To achieve the above object, according to one aspect of the present invention, there is provided a modified catalyst, comprising a catalyst matrix and a modified layer loaded on the outer surface of the catalyst matrix; wherein, the catalyst matrix is a Pt / C catalyst, and the structural formula of the material of the modified layer is: SiO2-(CH2)3SH.

[0009] Further, the material form of the modified layer is particles, and its average particle size is 3-50 nm.

[0010] Further, the catalyst matrix comprises a Pt active component and a carbon carrier, and the content of the Pt active component is 10-70 wt%.

[0011] Further, in the catalyst, the content of the material of the modified layer is 1-15 wt%.

[0012] Further, in the catalyst matrix, the Pt active component is in the form of nanoparticles, and its average particle size is 3-10 nm.

[0013] Further, the structural morphology of the nanoparticles of the Pt active component is selected from one or more of spherical, rhombic, flower-shaped or polyhedral structural morphologies.

[0014] Further, the carbon carrier is selected from one or more of carbon black, graphite carbon, nano-carbon or graphene; preferably, the nano-carbon is selected from one or more of carbon nanotubes, carbon nanospheres or carbon nanosheets.

[0015] To achieve the above object, according to one aspect of the present invention, there is provided a preparation method of a modified catalyst, the preparation method comprising: providing a catalyst matrix; coating a modified layer on the outer surface of the catalyst matrix to obtain a modified catalyst.

[0016] Further, the preparation method comprises: Step S1: taking the catalyst matrix and performing first dispersion in a first solvent to obtain a catalyst matrix dispersion liquid; Step S2: taking a modifier, performing second dispersion in a second solvent, and then adding the catalyst matrix dispersion liquid for heat treatment to obtain a modified catalyst.

[0017] Further, the modifier is a silane containing a mercapto functional group; preferably, the modifier is 3-mercaptopropyltriethoxysilane.

[0018] Further, by weight percentage, the weight ratio of the catalyst matrix to the modifier is (3 to 15):1; preferably, the molar concentration of the modifier is 0.05 to 0.2 mmol.

[0019] Further, in step S2, after the heat treatment, ammonia water needs to be added to the heated material to adjust the pH value to 9 to 11; preferably, after adding ammonia water, hydrolysis, centrifugation, washing, and drying treatments need to be carried out in sequence.

[0020] Further, the first solvent is a mixed solution of ethanol and water, wherein the mass ratio of ethanol to water is (0.2 to 1.2):1.

[0021] Further, the first dispersion is carried out in an ultrasonic instrument, the ultrasonic frequency is 20 to 100 kHz, the ultrasonic temperature is 0 to 25 °C, and the ultrasonic time is 1 to 4 h.

[0022] Further, the second solvent is selected from one or more of ethanol, isopropanol, n-propanol, or water.

[0023] Further, the second dispersion is carried out in a blender, the stirring speed is 100 to 2000 rpm, the stirring temperature is 50 to 80 °C, and the stirring time is 0.5 to 6 h.

[0024] Further, the heating temperature is 60 to 70 °C, and the heating time is 0.5 to 6.0 h.

[0025] According to another aspect of the present invention, a membrane electrode is provided, which includes the modified catalyst according to the above, or the modified catalyst obtained by the preparation method of the above modified catalyst.

[0026] According to another aspect of the present invention, a fuel cell is provided, which includes a membrane electrode, and the membrane electrode is the above membrane electrode.

[0027] According to another aspect of the present invention, an application of the above fuel cell in the fields of transportation, shipbuilding, distributed energy, and standby power supply is provided.

[0028] Applying the technical solution of the present invention, on the one hand, the modified catalyst reduces the coverage of the ionomer on the catalyst nanoparticles when applied in the membrane electrode, increasing the active sites of the catalyst and improving the catalytic performance; on the other hand, it can also greatly reduce the local oxygen mass transfer resistance in the cathode catalyst layer, making it take into account both catalytic activity and mass transfer rate, and having better comprehensive performance. Description of the Drawings

[0029] The drawings here are incorporated into the specification and form a part of this specification, showing the embodiments in line with this application, and are used together with the specification to explain the principles of this application. In the drawings:

[0030] Figure 1 The polarization curve graphs of the catalysts prepared in Example 1 and Comparative Example 1 of the present invention applied to a membrane electrode are shown;

[0031] Figure 2 The curve graphs of the total oxygen mass transfer resistance of the catalysts prepared in Example 1 and Comparative Example 1 of the present invention applied to a membrane electrode are shown;

[0032] Figure 3 The local oxygen mass transfer resistance curve graphs of the catalysts prepared in Example 1 and Comparative Example 1 of the present invention applied to a membrane electrode are shown; and

[0033] Figure 4 The TEM graph of the modified catalyst prepared in Example 1 of the present invention is shown. Detailed implementation manners

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the protection scope of the present application.

[0035] As described in the background art part of the present invention, the catalysts in the prior art have problems such as poor catalytic activity or high local oxygen mass transfer resistance under the conditions of high current and ultra-low platinum loading amount, resulting in poor electrochemical performance and short lifespan of the fuel cell when applied to the fuel cell. Based on this, the present invention provides a modified catalyst, which includes a catalyst matrix and a modified layer loaded on the outer surface of the catalyst matrix; wherein, the catalyst matrix is a Pt / C catalyst, and the structural formula of the material of the modified layer is: SiO2-(CH2)3SH.

[0036] Based on the prior art, the optimization and modification of Pt / C catalysts are mostly used to improve the intrinsic activity and service life of the catalysts. However, the above parameters cannot effectively meet the actual requirements of fuel cells, namely high current density and low Pt loading, resulting in a significant increase in the local oxygen mass transfer resistance during the application of the catalysts, and being unable to balance the intrinsic activity of the catalysts and the local oxygen mass transfer rate inside the catalyst layer. Therefore, the present invention adopts a new catalyst, which includes a catalyst matrix and a modified layer loaded on the outer surface of the catalyst matrix. Among them, the catalyst matrix is a Pt / C catalyst. In particular, the structural formula of the material of the modified layer is: SiO2-(CH2)3SH. The loading of this modified layer material on the catalyst surface enables the catalyst to be combined with the ionomer (perfluorosulfonic acid resin) in the form of intermolecular interaction by means of SiO2 in the modified layer material during subsequent application to fuel cells, making their binding force stronger; the mercapto functional group in the modified layer material is further combined with the Pt (platinum) particles in the catalyst matrix in the form of chemical bonds. As a result, when this modified catalyst is applied to fuel cells, it further reduces the coverage of the perfluorosulfonic acid resin in the catalyst layer on the active components of the catalyst to further increase the active sites of the catalyst, and can also further reduce the local oxygen mass transfer resistance in the cathode catalyst layer. In summary, by using the modified catalyst of the present invention, on the one hand, the modified layer thereon can increase the active sites of the catalyst and improve the catalytic activity when applied to the membrane electrode; on the other hand, it can also greatly reduce the local oxygen mass transfer resistance in the cathode catalyst layer, making it balance the catalytic activity and mass transfer rate, and having better comprehensive performance.

[0037] In a preferred embodiment, the material form of the modified layer is particles, and its particle size is 3-50 nm; to further improve the catalytic activity and reduce the local oxygen mass transfer resistance in the cathode catalyst layer; preferably, the catalyst matrix includes Pt active components and a carbon carrier, and the content of the Pt active components is 10-70 wt%.

[0038] In order to further reduce the coverage of the electrolyte (perfluorosulfonic acid resin) in the catalyst layer on the active components of the catalyst to further increase the active sites of the catalyst, the content of the material of the modified layer is preferably 1-15 wt% (for example, the content of the material of the modified layer can be 1 wt%, 3 wt%, 5 wt%, 7 wt%, 9 wt%, 12 wt% and 15 wt%).

[0039] In order to further reduce the local oxygen mass transfer resistance in the cathode catalyst layer, preferably, the form of the Pt active components in the catalyst matrix is nanoparticles, and their average particle size is 3-10 nm; more preferably, the structural morphology of the nanoparticles of the Pt active components is selected from one or more of spherical, rhombic, flower-shaped or polyhedral structural morphologies.

[0040] In order to further provide the active sites of the catalyst and enhance the catalytic effect of the reaction, it is preferred that the carbon support is selected from one or more of carbon black, graphite carbon, nano-carbon or graphene; more preferably, the nano-carbon is selected from one or more of carbon nanotubes, carbon nanospheres or carbon nanosheets.

[0041] Another aspect of the present invention provides a method for preparing a modified catalyst, the preparation method comprising: providing a catalyst matrix; coating a modified layer on the outer surface of the catalyst matrix to obtain a modified catalyst.

[0042] Those skilled in the art can first obtain the catalyst matrix, and then coat the modified layer on the outer surface of the catalyst matrix to obtain the modified catalyst. For the modified catalyst prepared by the present invention, on the one hand, the modified layer thereon can increase the active sites of the catalyst and improve the catalytic activity; on the other hand, it can also greatly reduce the local oxygen mass transfer resistance in the cathode catalyst layer, making it take into account both the catalytic activity and the mass transfer rate, and the comprehensive performance is better.

[0043] In a preferred embodiment, the method for preparing the modified catalyst comprises: Step S1: taking the catalyst matrix and performing a first dispersion treatment in a first solvent to obtain a catalyst matrix dispersion; Step S2: taking the modifier and performing a second dispersion in a second solvent, and then adding the catalyst matrix dispersion for heat treatment to obtain a modified catalyst.

[0044] Those skilled in the art first take the catalyst matrix and perform a first dispersion treatment in a first solvent to obtain a catalyst matrix dispersion; then take the modifier and perform a second dispersion in a second solvent, and then add the above catalyst matrix dispersion for heat treatment to obtain a modified catalyst. The preparation method of the modified catalyst provided by the present invention has simple preparation steps, convenient operation, is suitable for large-scale production, and has broad industrial application prospects.

[0045] In order to further improve the binding force between the modified layer and the electrolyte when applied to the membrane electrode, increase the active sites of the catalyst and improve the catalytic activity, it is preferred that the modifier is a silane containing a mercapto functional group, and the modifier is 3-mercaptopropyltriethoxysilane; by weight percentage, it is preferred that the weight ratio of the catalyst matrix to the modifier is (3-15):1 (for example, the weight ratio is 3:1, 5:1, 7:1, 9:1, 11:1, 13:1 or 15:1), and the molar concentration of the modifier is 0.05-0.2 mmol.

[0046] In order to further promote the hydrolysis of the modifier to better play its role, it is preferred that after the heat treatment, ammonia water needs to be added to the heated material to adjust the pH value to 9-11; it is preferred that after adding ammonia water, hydrolysis, centrifugation, washing and drying treatments need to be carried out in sequence to further avoid the influence of impurities on the product performance and improve its comprehensive performance.

[0047] In a preferred embodiment, the first solvent is a mixed solution of ethanol and water, where the mass ratio of ethanol to water is (0.2 - 1.2):1; preferably, the first dispersion is carried out in an ultrasonic instrument, with an ultrasonic frequency of 20 - 100 kHz, an ultrasonic temperature of 0 - 25 °C, and an ultrasonic time of 1 - 4 h, so as to make the catalyst matrix dispersion more uniform and stable, thereby preparing for the preparation of the modified catalyst and improving the comprehensive performance of the modified catalyst.

[0048] In order to further improve the comprehensive performance of the modified catalyst and make the modifier better dissolve in the above catalyst matrix dispersion, preferably, the second solvent is selected from one or more of ethanol, isopropanol, n-propanol, or water; the second dispersion is carried out in a stirrer, with a stirring speed of 100 - 2000 rpm, a stirring temperature of 50 - 80 °C, and a stirring time of 0.5 - 6 h; more preferably, the heating temperature is 60 - 70 °C and the heating time is 0.5 - 6.0 h, so as to make the modifier better act with the catalyst matrix and improve the local oxygen mass transfer resistance in the cathode catalyst layer of the modified catalyst.

[0049] On the other hand, the present invention also provides a membrane electrode, which includes the above modified catalyst, or a modified catalyst obtained by the preparation method of the above modified catalyst. As described above, this membrane electrode has good electrochemical performance and excellent comprehensive performance.

[0050] On the other hand, the present invention also provides a preparation method of a membrane electrode, which includes: dissolving the modified catalyst in an organic solvent, and then further dispersing to obtain a modified catalyst solution; spraying the modified catalyst solution on the upper surface and the other surface of the proton exchange membrane to obtain a membrane electrode.

[0051] In order to further promote the uniformity of the membrane electrode, preferably, the organic solvent is a mixed solution of one of ethanol, isopropanol, and n-propanol and water; preferably, the spraying temperature is 60 - 70 °C.

[0052] On the other hand, the present invention also provides a fuel cell, which includes a membrane electrode, and this membrane electrode is the above membrane electrode. This fuel cell has good electrochemical performance and a long cycle life.

[0053] On the other hand, the present invention also provides an application of a fuel cell in the fields of transportation, ships, distributed energy, and standby power supplies.

[0054] The following further describes the present application in detail with specific embodiments, and these embodiments should not be construed as limiting the scope claimed by the present application.

[0055] Example 1

[0056] 300 mg of Pt / C catalyst was added to 30 mL of solvent (15 mL of water and 15 mL of ethanol), and ultrasonic dispersion was carried out for 1 h at an ultrasonic frequency of 50 kHz and an ultrasonic temperature of 25 °C to obtain a catalyst matrix dispersion. Then, 0.1 mmol of 3-mercaptopropyltriethoxysilane (MPTES) was taken and stirred in 45 mL of ethanol solvent for 1 h at a stirring temperature of 25 °C and a rotation speed of 500 rpm. The catalyst matrix dispersion was added thereto and heated to 60 °C for 0.5 h. Then, 700 μL of ammonia water solution was added thereto to adjust the pH value to 9, and the mixture was stirred and hydrolyzed at 60 °C for 2 h. The mixture was centrifuged, washed with ethanol and water three times, and dried at 60 °C to obtain a modified catalyst.

[0057] Among them, the structural formula of the modified layer in the modified catalyst is SiO2-(CH2)3SH, the particle size of the modified layer is 5 nm, and the content of the modified layer material in the modified catalyst is 4.3 wt%; the content of the Pt active component is 47.8 wt%, its average particle size is 5 nm, the Pt active component is nanoparticles, its structural morphology is spherical, the carbon carrier is an irregular aggregated form, and the carbon carrier is carbon black.

[0058] Preparation of membrane electrode: Weigh 50 mg of 50 wt% Pt / C catalyst, add 2 mL of deionized water to wet it, add 2 mL of isopropanol, and add 500 mg of 5 wt% perfluorinated resin solution (Nafion D520). The above mixture was ice-bathed and ultrasonically dispersed for 90 min to obtain ink. Set the spraying temperature at 65 °C, and spray the ink on one side of the proton exchange membrane to obtain the anode catalyst layer, with a Pt loading of 0.1 mg / cm 2 . Repeat the above operation on the other side of the proton exchange membrane as the cathode catalyst layer, and then attach the gas diffusion layer respectively to obtain the membrane electrode.

[0059] Comparative Example 1

[0060] The difference from Example 1 is that no modifier is added, and the catalyst is a commercial 50 wt% Pt / C catalyst.

[0061] Performance test:

[0062] 1) Electrochemical performance

[0063] The membrane electrodes prepared in the examples and comparative examples were assembled into a fuel cell fixture to obtain a single cell. After sufficient activation, the cell was under the conditions of 70 °C and 0.1 MPa, the electrode active area was 25 cm 2 , the excess coefficient of the anode was 1.3, the cathode was 2.0, the back pressure conditions were 100 kPa for the anode and 100 kPa for the cathode, the test humidity was 100% RH for the anode and 100% RH for the cathode, the polarization curve was tested, hydrogen was passed through the anode, and air was passed through the cathode. The test results are as shown in the appendixFigure 1 as shown

[0064] 2) Total oxygen mass transfer resistance

[0065] Oxygen molecules in the battery have to pass through the flow channel, gas diffusion layer and catalytic layer. Oxygen dissolves into the ionomer film on the surface of the catalyst agglomerates and then diffuses into the catalyst agglomerates. Among them, each component passed through will bring resistance to oxygen transport, so the total transport resistance can be written as the sum of the resistances of each step. The oxygen mass transfer rate can be regarded as the rate of oxygen consumption. The oxygen flow rate transferred from the channel to the Pt surface is proportional to the difference between the oxygen concentration at the channel inlet and the oxygen concentration on the Pt surface participating in the reaction. When the oxygen concentration on the Pt surface is zero, the current density under this condition can be considered as the limiting current density. The total oxygen mass transfer resistance (R total ) can be expressed as:

[0066] N O2 = i lim / 4F = C O2 / R total ; R total == 4FC O2 / i lim = 4F(P - P W )x O2 inlet / RTi lim .

[0067] Among them, N O2 is the molar flux of O2 (mol·cm -2 ·s -1 ), i lim is the limiting current density (A / cm 2 ), F is the Faraday constant 96485 C / mol, C O2 is the inlet O2 molar concentration (mol / L), x O2 inlet is the mole fraction in the inlet gas, P is the total gas pressure (kPa), P w is the corresponding water vapor pressure (kPa), R is the gas constant 8.314 J·K -1 ·mol -1 , and T is the battery temperature.

[0068] 3) Local oxygen mass transfer resistance

[0069] The total oxygen mass transfer resistance includes the oxygen mass transfer resistance in the flow channel, the oxygen mass transfer resistance in the gas diffusion layer, and the oxygen mass transfer resistance in the catalyst layer. The oxygen mass transfer resistance in the catalyst layer can be further divided into the bulk oxygen mass transfer resistance and the local oxygen mass transfer resistance. Generally, the oxygen transfer resistance in the flow channel and the gas diffusion layer is linearly related to the absolute gas pressure, which can be called the molecular diffusion resistance. The oxygen transfer resistance in the catalyst layer is independent of the gas pressure and includes the Knudsen diffusion resistance and the local oxygen mass transfer resistance. Since the Knudsen diffusion resistance and the local oxygen mass transfer resistance have different sensitivities to temperature, the pressure-independent mass transfer resistance at different temperatures can be measured for quantitative fitting calculation. The specific principle formula is as follows:

[0070] R total =R CH +R GDL +R CL =R dif .P+R other ;

[0071] R other =R MPL Knudsen +R CL Knudsen +R ionomer =A T -1 / 2 +B T -1 e 17200 / RT ;

[0072] R MPL Knudsen +R CL Knudsen =A T -1 / 2 ;

[0073] R ionomer =B T -1 e 17200 / RT ;

[0074] Among them, R CH 、R GDL 、R CL respectively represent the oxygen mass transfer resistance in the flow channel, the oxygen mass transfer resistance in the gas diffusion layer, and the oxygen mass transfer resistance in the catalyst layer, and R total is the total oxygen mass transfer resistance; R dif .P represents the oxygen mass transfer resistance related to pressure (molecular diffusion resistance); R other represents the oxygen mass transfer resistance independent of pressure; R MPL Knudsen 、R CL Knudsen respectively represent the Knudsen mass transfer resistance in the microporous layer of the gas diffusion layer and the catalyst layer; R ionomer is the local oxygen mass transfer resistance; T is the battery temperature; A and B are fitting constants.

[0075] 4) Mass transfer resistance test method:

[0076] The oxygen transport resistance test was carried out using a 2 cm × 2 cm membrane electrode for test evaluation. The anode hydrogen gas flow rate was 2 L / min, the cathode 4% O2 + 96% N2 flow rate was 4 L / min, the gas humidity was 70%, and the limiting current density at back pressures of 0.05 MPa, 0.1 MPa, 0.15 MPa, and 0.2 MPa was measured respectively, and calculated according to the oxygen transport resistance formula; further, the limiting current density corresponding to different back pressures at 50 °C, 60 °C, and 70 °C was measured respectively, and the mass transfer resistance was calculated and the local oxygen mass transfer resistance was separated out.

[0077] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0078] From the test result graphs of the above embodiments and comparative examples, it can be found that when the modified catalyst prepared by the present invention is applied to the membrane electrode, the test results of its electrochemical performance are as Figure 1 shown in the polarization curve. The modified Pt / C catalyst has better performance; especially in Figure 2 and Figure 3 the total oxygen mass transfer resistance curve graph of the membrane electrode and the local oxygen mass transfer resistance curve graph of the membrane electrode, it is found that the mass transfer resistance of its total oxygen and local oxygen is significantly reduced. From Figure 4 the TEM graph results of the modified catalyst, it can be found that the distribution of S element and Pt element is highly consistent, indicating that the mercapto group can be adsorbed on the surface of Pt nanoparticles directionally, and the SiO2 nanoparticles are distributed around the Pt nanoparticles.

[0079] In summary, using the modified catalyst of the present invention, on the one hand, when applied to the membrane electrode, it can reduce the coverage of the ionomer on the catalyst nanoparticles, increase the active sites of the catalyst, and improve the catalytic performance; on the other hand, it can also greatly reduce the local oxygen mass transfer resistance in the cathode catalyst layer, making it take into account both catalytic activity and mass transfer rate, and the comprehensive performance is better.

[0080] Although this specification contains many specific implementation details, these should not be construed as limiting the scope of any invention or the scope of what is claimed, but are mainly used to describe the features of specific embodiments of a particular invention. Certain features described in multiple embodiments in this specification can also be combined and implemented in a single embodiment. On the other hand, various features described in a single embodiment can also be separately implemented in multiple embodiments or implemented in any suitable sub-combination. In addition, although features may function in certain combinations as described above and are even initially claimed as such, one or more features from the claimed combination can in some cases be removed from the combination, and the claimed combination can be directed to a sub-combination or a variant of the sub-combination.

[0081] Similarly, although operations are depicted in the figures in a particular order, this should not be construed as requiring that the operations be performed in the particular order shown or sequentially, or that all illustrated operations be performed to achieve the desired result. In some cases, multitasking and parallel processing may be advantageous. Additionally, the separation of various system modules and components in the above embodiments should not be construed as required in all embodiments, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products.

[0082] Accordingly, particular embodiments of the subject matter have been described. Other embodiments are within the scope of the appended claims. In some cases, the acts recited in the claims can be performed in a different order and still achieve the desired result. Additionally, the processes depicted in the figures are not necessarily in the particular order or sequential order shown to achieve the desired result. In some implementations, multitasking and parallel processing may be advantageous.

[0083] It should be noted that, in this document, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variation thereof is intended to cover a non-exclusive inclusion, such that a process, method, article or device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the presence of additional identical elements in the process, method, article or device comprising the element.

[0084] The above are only specific embodiments of the present application, which enable those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but rather to the broadest scope consistent with the principles and novel features claimed herein.

Claims

1. A modified catalyst, characterized in that, The modified catalyst includes a catalyst matrix and a modified layer loaded on the outer surface of the catalyst matrix; wherein, the catalyst matrix is a Pt / C catalyst, and the structural formula of the material of the modified layer is: SiO2-(CH2)3SH.

2. The modified catalyst according to claim 1, wherein The material of the modified layer is in the form of particles, and its average particle size is 3 to 50 nm.

3. The modified catalyst according to claim 1 or 2, characterized in that, The catalyst matrix includes a Pt active component and a carbon carrier, and the content of the Pt active component is 10 to 70 wt%.

4. The modified catalyst according to any one of claims 1 to 3, characterized in that, In the catalyst, the content of the material of the modified layer is 1 to 15 wt%.

5. The modified catalyst according to any one of claims 1 to 4, characterized in that, In the catalyst matrix, the Pt active component is in the form of nanoparticles, and its average particle size is 3 to 10 nm.

6. The modified catalyst according to any one of claims 1 to 5, characterized in that, The structural morphology of the nanoparticles of the Pt active component is selected from one or more of spherical, rhombic, flower-shaped or polyhedral structural morphologies.

7. The modified catalyst according to any one of claims 1 to 6, characterized in that, The carbon carrier is selected from one or more of carbon black, graphite carbon, nano-carbon or graphene; and / or The nano-carbon is selected from one or more of carbon nanotubes, carbon nanospheres or carbon nanosheets.

8. A method for preparing the modified catalyst according to any one of claims 1 to 7, characterized in that, The preparation method includes: Providing a catalyst matrix; Coating a modified layer on the outer surface of the catalyst matrix to obtain the modified catalyst.

9. The preparation method of the modified catalyst according to claim 8, characterized in that, The preparation method includes: Step S1: Taking the catalyst matrix and performing first dispersion in a first solvent to obtain a catalyst matrix dispersion liquid; Step S2: Taking a modifier and performing second dispersion in a second solvent, and then adding the catalyst matrix dispersion liquid for heat treatment to obtain the modified catalyst.

10. The preparation method of the modified catalyst according to claim 8 or 9, characterized in that, The modifier is a silane containing a mercapto functional group; and / or The modifier is 3-mercaptopropyltriethoxysilane.

11. The preparation method of the modified catalyst according to any one of claims 8 to 10, characterized in that, By weight percentage, the weight ratio of the catalyst matrix to the modifier is (3 to 15):1; and / or The molar concentration of the modifier is 0.05 to 0.2 mmol.

12. The preparation method of the modified catalyst according to any one of claims 8 to 11, characterized in that, In step S2, after the heat treatment, ammonia water also needs to be added to the heated material to adjust the pH value to 9 to 11; and / or After adding ammonia water, hydrolysis, centrifugation, washing and drying treatments also need to be carried out in sequence.

13. The preparation method of the modified catalyst according to any one of claims 8 to 12, characterized in that, The first solvent is a mixed solution of ethanol and water, wherein the mass ratio of ethanol to water is (0.2 to 1.2):

1.

14. The preparation method of the modified catalyst according to any one of claims 8 to 13, characterized in that, The first dispersion is carried out in an ultrasonic instrument, the ultrasonic frequency is 20 to 100 kHz, the ultrasonic temperature is 0 to 25 °C, and the ultrasonic time is 1 to 4 h.

15. The preparation method of the modified catalyst according to any one of claims 8 to 14, characterized in that, The second solvent is selected from one or more of ethanol, isopropanol, n-propanol or water.

16. The preparation method of the modified catalyst according to any one of claims 8 to 15, characterized in that, The second dispersion is carried out in a stirrer, the stirring speed is 100 to 2000 rpm, the stirring temperature is 50 to 80 °C, and the stirring time is 0.5 to 6 h.

17. The preparation method of the modified catalyst according to any one of claims 8 to 16, characterized in that, The heating temperature is 60 to 70 °C, and the heating time is 0.5 to 6.0 h.

18. A membrane electrode, characterized in that, The membrane electrode includes the modified catalyst according to any one of claims 1 to 7, or the modified catalyst obtained by the preparation method of the modified catalyst according to any one of claims 8 to 17.

19. A fuel cell, comprising a membrane electrode, characterized in that, The membrane electrode is the membrane electrode according to claim 18.

20. An application of the fuel cell according to claim 19 in the fields of transportation, ship, distributed energy and standby power supply.

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