PtPdRuCuNi alloy aerogel and application of PtPdRuCuNi alloy aerogel modified by PTFE as catalyst layer in DMFC

Abstract

The invention discloses PtPdRuCuNi alloy aerogel and application of the PtPdRuCuNi alloy aerogel modified by PTFE to a DMFC as a catalyst layer, the PtPdRuCuNi alloy aerogel is prepared through the following steps: step 1, taking aqueous solutions of a Pt metal salt precursor, a Pd metal salt precursor, a Ru metal salt precursor, a Cu metal salt precursor and a Ni metal salt precursor, and uniformly mixing to obtain a mixed solution; step 2, adding a NaBH4 aqueous solution into the mixed solution obtained in the step 1, uniformly stirring, and standing for full reaction to obtain a solution containing PtPdRuCuNi pentabasic alloy aerogel; and step 3, removing the PtPdRuCuNi quinary alloy aerogel in the step 2, taking out the PtPdRuCuNi quinary alloy aerogel from the solution, and washing and drying the PtPdRuCuNi quinary alloy aerogel to obtain the PtPdRuCuNi alloy aerogel. And a hydrophobic agent PTFE is further introduced, so that a water transmission channel of the cathode catalyst layer of the direct methanol fuel cell is optimized, the oxygen transmission resistance is reduced, and the oxygen transmission efficiency and the power density of the membrane electrode are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cell alloy aerogel nanomaterials, and particularly to a PtPdRuCuNi alloy aerogel and its application as a catalytic layer in DMFC after being modified by PTFE. Background Art

[0002] In order to solve the increasingly growing global energy consumption and environmental pollution caused by the use of fossil fuel energy, the development of new sustainable clean energy is particularly important for solving current environmental pollution and energy shortage problems. Direct methanol fuel cells (DMFCs) have attracted much attention due to their advantages such as high energy density, high energy conversion efficiency, rapid start-up at low temperature, environmental friendliness, and simple battery structure. As a new energy conversion method, they are widely used in various fields.

[0003] At present, Pt-based catalysts, as one of the key components for catalyzing methanol electrochemical reactions, still have problems such as high cost, low activity, and poor stability. An excellent electrocatalyst must have excellent catalytic activity, the ability to resist poisoning by intermediates (such as CO), electrical conductivity, and stability. The influence of synthesis methods on catalytic performance is also crucial. Among them, aerogels have attracted great interest due to their unique structural characteristics (including large specific surface area, self-supporting structure, and three-dimensional porous structure). Due to the unique physical and chemical properties of nanostructured noble metals, three-dimensional aerogels have abundant catalytic active sites, rich pore distributions, fast mass / electron transfer channels, and excellent structural stability, showing broad application prospects in the field of catalysis. Especially in electrocatalysis, they exhibit good activity superior to commercial noble metal catalysts.

[0004] Currently, the carbon-supported Pt metal catalyst used in fuel cells has the following problems: the cost of Pt is high; the presence of ionomers will hinder the transport of electrons and oxygen; the corrosion of carbon reduces the battery life, while the Pt-based alloy aerogel catalyst has the characteristics of a porous self-supporting carbon-free carrier and has no such problems as carbon corrosion. The advantages of aerogels are that their electronic conductivity is better than the conduction between particles, the large specific surface area can expose more active sites, the large porosity promotes the transport of water, gas, and protons, and the interconnected structure reduces Ostwald ripening and aggregation. Therefore, it is necessary to develop highly active electrocatalysts to promote the further development of electrocatalysts in the field of fuel cells.

[0005] Factors affecting the performance of direct methanol fuel cells, such as the loading of the anode catalyst layer, the doping of the ionic polymer Nafion, methanol permeation through the anode, and cathode flooding, etc., will all affect the catalytic performance and stability. The anode reaction is the methanol oxidation reaction, which requires a sufficiently efficient catalyst to catalyze the decomposition of methanol to produce protons. Therefore, a highly efficient or high-loading catalyst is needed at the anode; at high current densities, pure catalysts may become unstable and fall off, and Nafion can also act as a binder to fix the catalyst layer and conduct protons at the same time; fuel cells must operate at high current densities, and at high current densities, cathode flooding may occur. In this case, the generated water cannot be discharged in time, oxygen diffusion is inhibited, and the oxygen reduction reaction is limited, which has a greater impact on the performance of fuel cells. Therefore, strengthening water management is one of the key factors to improve battery performance. Summary of the Invention

[0006] The object of the present invention is to provide a PtPdRuCuNi alloy aerogel in view of the technical defects existing in the prior art.

[0007] Another object of the present invention is to provide the application of the PtPdRuCuNi alloy aerogel as a catalyst modified by PTFE in the cathode of a direct methanol fuel cell.

[0008] The technical solution adopted to achieve the object of the present invention is as follows:

[0009] A PtPdRuCuNi alloy aerogel is prepared by the following steps:

[0010] Step 1, an aqueous solution of a Pt metal salt precursor, a Pd metal salt precursor, a Ru metal salt precursor, a Cu metal salt precursor, and a Ni metal salt precursor is added to deionized water and mixed evenly to obtain a mixed solution;

[0011] Step 2, an aqueous solution of NaBH4 is added to the mixed solution obtained in Step 1, stirred evenly, and then allowed to stand for sufficient reaction to obtain a system containing a PtPdRuCuNi quinary alloy aerogel;

[0012] Step 3, the PtPdRuCuNi quinary alloy aerogel is taken out from the system obtained in Step 2, washed and dried to obtain a PtPdRuCuNi alloy aerogel.

[0013] In the above technical solution, in the mixed solution of Step 1, the molar ratio of Pt, Pd, Ru, Cu, and Ni in the Pt metal salt precursor, Pd metal salt precursor, Ru metal salt precursor, Cu metal salt precursor, and Ni metal salt precursor is 10:2:3:3:2.

[0014] In the above technical solution, in step 2, the concentration of the NaBH4 aqueous solution is 0.5 - 1 mol / L.

[0015] In the above technical solution, the reaction time in step 2 is 2 - 3 minutes, and the reaction temperature is 20 °C.

[0016] In the above technical solution, in step 3, during washing and drying, deionized water is used for washing, and vacuum freeze-drying is used.

[0017] On the other hand, the present invention also includes the application of the PtPdRuCuNi alloy aerogel as a catalyst after PTFE modification in the cathode of a direct methanol fuel cell.

[0018] On the other hand, the present invention also includes a gas diffusion electrode, which includes a gas diffusion layer and a catalyst layer supported on the gas diffusion layer. The catalyst layer is prepared by the following steps: dispersing the PtPdRuCuNi alloy aerogel, PTFE, and Nafion in a solvent to obtain a uniformly mixed catalyst slurry, coating the catalyst slurry on the gas diffusion layer, and drying to obtain the gas diffusion electrode.

[0019] In the above technical solution, the mass ratio of the PtPdRuCuNi alloy aerogel, PTFE, and Nafion is (7 - 9):(0.5 - 1.5):(0.5 - 1.5). More preferably, the mass ratio of the PtPdRuCuNi alloy aerogel, PTFE, and Nafion is 8:1:1.

[0020] On the other hand, the present invention also includes a membrane electrode, which includes a cathode gas diffusion electrode, a proton exchange membrane, and an anode gas diffusion electrode pressed together in sequence. The cathode gas diffusion electrode is the above-mentioned gas diffusion electrode. Preferably, the anode gas diffusion electrode is a gas diffusion electrode based on a PtRu / C catalyst.

[0021] On the other hand, the present invention also includes a direct methanol fuel cell, which includes an end plate, a current collector plate, a bipolar plate, a gasket, and the above-mentioned membrane electrode.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] 1. The present invention uses sodium borohydride as a reducing agent to prepare a PtPdRuCuNi quinary alloy aerogel catalyst by a one-step reduction method. The carbon-free supported three-dimensional porous self-supporting aerogel structure has a large number of surface active sites, a large specific surface area, and high stability.

[0024] 2. This catalyst can be used as the cathode catalyst for the oxygen reduction reaction in direct methanol fuel cells. By introducing the hydrophobic agent PTFE, the water transport channels in the cathode catalyst layer of direct methanol fuel cells are optimized, the oxygen transport resistance is reduced, the oxygen transport efficiency and the membrane electrode power density are improved, and the preparation method is simple and the conditions are mild. The addition of multiple elements provides new ideas for the preparation of other multi-component alloy electrocatalysts. Description of the Drawings

[0025] Figure 1 It is an optical picture of the preparation process of the PtPdRuCuNi quinary alloy aerogel.

[0026] Figure 2 It is a transmission electron microscope photograph (TEM) of the PtPdRuCuNi quinary alloy aerogel.

[0027] Figure 3 In it, a is the EDS element spectrum of the PtPdRuCuNi quinary alloy aerogel, and b is the XRD spectrum of the PtPdRuCuNi quinary alloy aerogel.

[0028] Figure 4 In it, a is the SEM image of the PtPdRuCuNi alloy aerogel, b is the SEM image of PtPdRuCuNi-10% Nafion, and c, d are the SEM images of PtPdRuCuNi-10% PTFE 10% Nafion.

[0029] Figure 5 It is a schematic structural diagram of the DMFC battery.

[0030] Figure 6 It is a comparison of the polarization curves of PtPdRuCuNi-10% Nafion, PtPdRuCuNi-5% PTFE 5% Nafion, PtPdRuCuNi-10% PTFE 10% Nafion and PtPdRuCuNi-15% PTFE 15% Nafion as cathode catalysts in the DMFC single cell (the test conditions are the same).

[0031] Figure 7 It is the polarization curve of the cathode catalyst layer membrane electrode of PtPdRuCuNi-10% PTFE 10% Nafion varying with the oxygen partial pressure under the back pressures of 50 kPa, 100 kPa, 150 kPa and 200 kPa (the test conditions are the same).

[0032] Figure 8The polarization curves of the PtPdRuCuNi-10% Nafion cathode catalyst layer membrane electrode with the change of oxygen partial pressure under the back pressures (back pressures) of 50 kPa, 100 kPa, 150 kPa, and 200 kPa (the test conditions are the same).

[0033] Figure 9 In it, a is the linear relationship diagram of the limiting current density of the PtPdRuCuNi-10% PTFE 10% Nafion membrane electrode and the oxygen partial pressure; b is the curve diagram of the oxygen transport resistance and the limiting current density of the PtPdRuCuNi-10% PTFE 10% Nafion membrane electrode; c is the linear relationship diagram of the limiting current density of the PtPdRuCuNi-10% Nafion membrane electrode and the oxygen partial pressure; d is the curve diagram of the oxygen transport resistance and the limiting current density of the PtPdRuCuNi-10% Nafion membrane electrode.

[0034] Figure 10 It is the comparison of the linear relationship between the total oxygen transport resistance and the back pressure of the membrane electrodes with PtPdRuCuNi-10% PTFE 10% Nafion and PtPdRuCuNi-10% Nafion as the cathode catalyst layer. Specific implementation mode

[0035] The following further elaborates on the present invention in combination with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0036] Example 1

[0037] A PtPdRuCuNi quinary alloy aerogel is prepared through the following steps:

[0038] Step 1, Take 200 μl of 97 mmol / L H2PtCl6 aqueous solution, 40 μl of 97 mmol / L PdCl2 aqueous solution, 60 μl of 97 mmol / L RuCl3 aqueous solution, 60 μl of 97 mmol / L CuCl2 aqueous solution, and 40 μl of 97 mmol / L NiCl2 aqueous solution and add them to a conical flask containing 100 ml of ultrapure water. Under the temperature condition of 20 °C, stir with a magnetic stirrer (rotation speed 1000 RPM) for 0.5 hour to make them mix evenly.

[0039] Step 2, Prepare 3.88 ml of a clear aqueous solution of 1 mol / L sodium borohydride (NaBH4), quickly add it to the conical flask, keep stirring with a magnetic stirrer (rotation speed 1000 RPM) under the temperature condition of 20 °C to make the reaction uniform. The stirring time (rotation speed 1000 RPM) is 2 minutes, then take out the magnetic stirrer, transfer the conical flask to a water bath at 20 °C and keep it at a constant temperature for 6 hours to make the reaction sufficient, and let it stand for precipitation to form Pt41.33 Pd 5.92 Ru 31.8 Cu 15.55 Ni 5.41 Five - element alloy aerogel.

[0040] Step 3: Take out the PtPdRuCuNi five - element alloy aerogel prepared in Step 2, wash it 4 times with ultrapure water, quickly freeze it with liquid nitrogen, and then put it into a vacuum freeze - dryer for freeze - drying for 8 hours to obtain a black powder - like PtPdRuCuNi five - element alloy aerogel.

[0041] As Figure 1 shown, before adding the sodium borohydride aqueous solution, it is an orange - yellow and well - mixed solution. After adding the sodium borohydride aqueous solution and maintaining for 6 hours, the PtPdRuCuNi five - element alloy aerogel precipitates to form a film at the bottom of the conical flask, and the material polycondenses after slight shaking.

[0042] As Figure 2 in a, the scale is 200 nm, Figure 2 in b, the scale is 50 nm. It can be seen that the PtPdRuCuNi five - element alloy aerogel is a three - dimensional porous self - supporting aerogel structure with abundant pores. Figure 2 In c, it is the ligament size distribution diagram, and its average ligament size is 5 - 6 nm.

[0043] Figure 3 In a, it is the EDS elemental spectrum of the PtPdRuCuNi five - element alloy aerogel. The inset is the corresponding elemental atomic ratio. The atomic ratio of Pt / Pd / Ru / Cu / Ni is 41.33 / 5.92 / 31.8 / 15.55 / 5.41; Figure 3 In b, it is the comparison of the XRD spectra of the PtPdRuCuNi five - element alloy aerogel with the standard PDF cards of pure Pt (Pt - 04 - 0802), pure Pd (Pd - 46 - 1043), pure Ru (Ru - 06 - 0633), pure Cu (Cu - 04 - 0836), and pure Ni (Ni - 04 - 0850). The XRD spectrum of PtPdRuCuNi shows typical X - ray diffraction peaks of (111), (200), (220), and (311) at the peak positions of 40.7°, 47°, 69°, and 83°. It belongs to the FCC face - centered cubic crystal phase. The peak positions of its diffraction peaks in the XRD pattern shift in the direction of increasing 2θ angle relative to pure Pt, indicating that the addition of elements such as Pd, Ru, Cu, and Ni causes lattice distortion, and the lattice constant decreases relative to pure Pt, and the material forms a five - element alloy.

[0044] Example 2

[0045] In this example, the PtPdRuCuNi quinary alloy aerogel prepared in Example 1 is used as a catalyst, and ultra-low molecular weight PTFE is introduced to alleviate the battery performance degradation caused by cathode flooding.

[0046] Prepare the catalyst slurry: Disperse the PtPdRuCuNi quinary alloy aerogel prepared in Example 1 in an isopropanol solvent, and then divide it into four samples. In the four samples, add 10% Nafion, 5% PTFE and 5% Nafion, 10% PTFE and 10% Nafion, 15% PTFE and 15% Nafion respectively to prepare the catalyst slurry.

[0047] As Figure 4 shown, the micro-morphology of the material is analyzed by high-resolution scanning electron microscopy. Figure 4 In [a], the SEM image of the PtPdRuCuNi alloy aerogel under a 500 nm scale can be seen. It can be seen that the PtPdRuCuNi alloy aerogel has a network structure with abundant pores. The high porosity facilitates mass transfer and provides more reaction sites at the same time. Figure 4 In [b], the SEM image of PtPdRuCuNi-10% Nafion (the dry weight mass ratio of PtPdRuCuNi to Nafion is 9:1) under a 500 nm scale can be seen. It can be seen that the catalyst still maintains a porous network structure, and at the same time, Nafion exists on the surface, making the alloy aerogel maintain high stability. Figure 4 In [c] and [d], the SEM images of PtPdRuCuNi-10% PTFE 10% Nafion (the dry weight mass ratio of PtPdRuCuNi, PTFE, and Nafion is 8:1:1) under 2 μm and 500 nm scales are shown. There are no obvious cracks on the surface. While Nafion exists on the surface of the catalyst, PTFE exists in the pore structure of the catalyst. The presence of PTFE increases the hydrophobicity and optimizes the transport channels of water and oxygen.

[0048] Coat the uniformly mixed catalyst slurry on the GDL (Gas diffusion layer, GDL, the gas diffusion layer is composed of carbon paper and microporous layer). After drying in an oven, a gas diffusion electrode (Gas diffusion electrode, GDE) loaded with a catalyst layer is obtained. The gas diffusion electrode is composed of a gas diffusion layer and a catalyst layer.

[0049] In this embodiment, three GDEs are prepared. The catalyst layers in the three GDEs are PtPdRuCuNi-10% PTFE 10% Nafion (PtPdRuCuNi quinary alloy aerogel, the mass ratio of Nafion to PTFE is 8:1:1), PtPdRuCuNi-15% PTFE 15% Nafion (PtPdRuCuNi quinary alloy aerogel, the mass ratio of Nafion to PTFE is 7:1.5:1.5), and PtPdRuCuNi-5% PTFE 5% Nafion (PtPdRuCuNi quinary alloy aerogel, the mass ratio of Nafion to PTFE is 9:0.5:0.5).

[0050] Comparative Example 1

[0051] In this comparative example, one GDE is prepared. The preparation method is the same as that in Example 2, except that PTFE is not added in this comparative example. The catalyst in the GDE of this comparative example is PtPdRuCuNi-10% Nafion (the mass ratio of PtPdRuCuNi to Nafion is 9:1).

[0052] Example 3

[0053] Take the three GDEs prepared in Example 2 as the cathode GDEs, and use a hot press to press the cathode GDEs, N115 proton exchange membrane (purchased from Suzhou Shengnuoke Technology Co., Ltd.) and the anode GDEs into an MEA with a sandwich structure at a pressure of 3 MPa for 3 minutes. The anode catalyst in the anode GDE is a commercial PtRu / C catalyst (GDE, the PtRu loading is 2 mg cm -2 , purchased from Shanghai Hesen Electric Co., Ltd.) at a temperature of 130 °C, and then assemble three proton exchange membrane fuel cell single cell test devices based on the MEA as Figure 5 shown. It mainly consists of components such as end plates, current collector plates, bipolar plates, gaskets and membrane electrodes. The membrane electrode assembly (MEA) is an important and complex component in proton exchange membrane fuel cells, and is composed of an anode gas diffusion layer, an anode catalyst layer, a proton exchange membrane, a cathode catalyst layer and a cathode gas diffusion layer.

[0054] Comparative Example 2

[0055] In this comparative example, take the GDE prepared in Comparative Example 1 as the cathode GDE, and use the same method as in Example 3 to prepare a proton exchange membrane fuel cell single cell test device.

[0056] Since the catalyst layer without Nafion is unstable and the performance decays, no comparative example of a membrane electrode without Nafion is carried out in this application.

[0057] Test Example

[0058] Test process of the membrane electrode of a direct methanol fuel cell:

[0059] Install the single-cell test device of the proton exchange membrane fuel cell obtained in Example 3 and Comparative Example 2 onto the single-cell test fixture for testing. Use an electronic load (IT8511A + ) to conduct performance tests on the single-cell membrane electrode. Before the test, first introduce deionized water to activate the membrane electrode for 3 hours. After activation, the anode electrolyte for the direct methanol fuel cell membrane electrode test is an aqueous methanol solution with a concentration of 1 M and a flow rate of 2 ml min -1 ; humidified O2 is introduced on the cathode side at a flow rate of 200 standard cubic centimeters per minute (SCCM). Record the voltage and power density data of the membrane electrode varying with the current density through the electronic load, and the battery temperature is 65°C.

[0060] The test results are as follows:

[0061] As Figure 6The polarization curves and power density curves of the membrane electrode tests of direct methanol fuel cells with a battery temperature of 65 °C, a commercial PtRu / C anode GDE, and four GDEs prepared above as the cathode GDE are shown. The open-circuit voltage of the catalyst layer without PTFE is 0.715 V, which is higher than that of the membrane electrode based on 10% PTFE and 10% Nafion (0.709 V), the membrane electrode based on 5% PTFE and 5% Nafion (0.706 V), and the membrane electrode based on 15% PTFE and 15% Nafion (0.683 V). And the voltage drop trend in the battery activation polarization region at lower current densities is lower than that of the membrane electrode containing PTFE because the conductivity of PTFE is poor and the total resistance of the membrane electrode is higher; the battery performance of the membrane electrode based on 15% PTFE and 15% Nafion is the lowest, probably because the content of PTFE and Nafion is too high and the mass transfer is poor. The battery performance of the membrane electrode based on 5% PTFE and 5% Nafion is relatively low, probably because the content of Nafion is too small and the catalyst layer is unstable and falls off, and its performance decays in the subsequent tests; in the ohmic region, especially the mass transfer region, at higher current densities, the advantages of the catalyst layer based on 10% PTFE and 10% Nafion are highlighted. The hydrophobicity of PTFE optimizes the water transport in the cathode catalyst layer, reduces the influence of water on the oxygen transport, and enables the oxygen reduction reaction to proceed smoothly. At the same time, sufficient Nafion makes the catalyst layer more stable and promotes the proton transport rate. Therefore, the membrane electrode based on 10% PTFE and 10% Nafion shows higher battery performance. At a current density of 240 mA cm -2 The maximum mass specific power density is about 74.4 mW mg Pt -1 , while the highest power density of the membrane electrode without PTFE is 57.7 mW mg Pt -1 , and after 180 mA cm -2 , the mass specific power density decays with the increase of the current density, indicating the potential of the PtPdRuCuNi alloy aerogel as a catalyst for the cathode oxygen reduction reaction and the feasibility and effectiveness of improving the cathode water management by introducing the hydrophobic agent PTFE.

[0062] Testing and data analysis of oxygen transport resistance: First, pass N2 through the membrane electrode to expel air and water in the membrane electrode at a flow rate of 300 SCCM. Wait until the open circuit voltage drops below 0.1 V. Then, pass H2 (300 SCCM) through the anode and O2 (300 SCCM) through the cathode. Test and activate the membrane electrode at 65 °C to make the membrane electrode reach the normal state. Then, pass O2 and N2 (total gas flow rate is 500 SCCM) through the cathode. Polarization curve data of the current density of the membrane electrode varying with voltage at different oxygen partial pressures (2%, 3%, 4%, 5%) under different back pressures (50 kPa, 100 kPa, 150 kPa, 200 kPa) were tested. The voltage was set from 0.8 V to 0.1 V, and each voltage was maintained for 30 s. The test interval under different oxygen partial pressure states was 10 min.

[0063] The total oxygen transport resistance R of the membrane electrode under different working conditions was calculated by the following formula total ,

[0064]

[0065] I lim is the limiting current density of the membrane electrode, with the unit of A m -2 ; P O2 is the oxygen partial pressure, with the unit of Pa; F is the Faraday constant, which is 96485 C mol -1 ; R is the molar gas constant, which is 8.31 J(mol K) -1 ; T is the thermodynamic temperature of the cathode inlet gas, with the unit of K; the oxygen transport resistance R total , with the unit of s m -1 .

[0066] It can be seen from Figures 7-8 that the oxygen partial pressures are 2%, 3%, 4% and 5% of the total back pressure respectively, the battery temperature is 65 °C, and the gas humidity is 100%. It can be seen that as the back pressure and oxygen partial pressure increase, the current density gradually increases, and the performance of the membrane electrode gradually increases. However, compared with the polarization curve of the PtPdRuCuNi membrane electrode containing PTFE, the current density of the PtPdRuCuNi-10% Nafion membrane electrode is smaller and the catalytic performance is lower at the same voltage.

[0067] As Figure 9 shown, by linearly fitting the relationship between the limiting current density and the oxygen partial pressure of the two membrane electrodes under different back pressures to obtain different slopes, calculating the total oxygen transport resistance through the formula, plotting the relationship curve between the total oxygen transport resistance and the limiting current density under different back pressures, and calculating the relationship between the total oxygen transport resistance and the limiting current of different membrane electrodes under different back pressures through the formula, Figure 7In a, b are the relationship curves of the limiting current density with the oxygen partial pressure and the total oxygen transport resistance with the limiting current under different back pressures for the PtPdRuCuNi cathode catalyst layer membrane electrode containing PTFE, Figure 7 In c, d are the relationship curves of the limiting current density with the oxygen partial pressure and the total oxygen transport resistance with the limiting current under different back pressures for the PtPdRuCuNi membrane electrode without PTFE. It can be seen from the figure that at the same back pressure, the limiting current density increases more with the increase of the oxygen partial pressure, and at the same time the total oxygen transport resistance also increases. With the increase of the back pressure, the limiting current density and the total oxygen transport resistance increase. With the increase of the oxygen partial pressure, the oxygen reduction reaction rate of the cathode accelerates, indicating the improvement of the membrane electrode performance; but under the same conditions, the limiting current density of the membrane electrode containing PTFE is higher than that of the membrane electrode without PTFE, and at the same time the total oxygen transport resistance is lower than that of the membrane electrode without PTFE, indicating that the presence of PTFE optimizes the water transport in the catalyst layer and reduces the oxygen transport resistance.

[0068] As Figure 10 shown, by analyzing and fitting the total oxygen transport resistance of the two membrane electrodes under different back pressures, the linear relationship between the total oxygen transport resistance (R total ) and the total back pressure (P) is obtained, as shown by the solid line part in the figure. The slopes corresponding to PtPdRuCuNi - 10% PTFE 10% Nafion and PtPdRuCuNi - 10% Nafion are k respectively. The larger the slope, the faster the rate of increase of the oxygen transport resistance with the increase of the back pressure, corresponding to more difficult oxygen transport in the catalyst layer and slower oxygen reduction reaction rate; by extending the straight line to the back pressure value of 0, as shown by the intercept of the dotted line part and the Y-axis in the figure, the oxygen transport resistance of the membrane electrode when the back pressure is 0 can be obtained, and the pressure-independent resistance (R NP ) can be distinguished, which is related to the oxygen transport resistance in the microporous layer and catalyst layer of the gas diffusion layer, and the pressure-dependent resistance (R P ), which is related to the oxygen transport resistance in the plate flow field and the matrix layer of the gas diffusion layer. R NP is the intercept, and R P is the difference between R total and R NP . When there is no pressure, the oxygen transport mechanism in the catalyst layer follows Knudsen diffusion. The calculated R NP of the PtPdRuCuNi - PTFE and PtPdRuCuNi membrane electrodes are about 9 s m -1 and 32 s m -1 respectively, and R CLis the difference in oxygen transport resistance between the two catalytic layers, indicating that the oxygen transport resistance of the membrane electrode with the cathode catalytic layer of PtPdRuCuNi containing PTFE is 23 s m lower than that of the membrane electrode with the cathode catalytic layer of PtPdRuCuNi without PTFE -1 , R CL is 23 s m -1 , indicating that the catalytic layer containing the hydrophobic agent exhibits excellent performance in optimizing water management and effectively reduces the oxygen transport resistance in the membrane electrode.

[0069] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A PtPdRuCuNi alloy aerogel, characterized in that, Prepared by the following steps: Step 1: An aqueous solution of a Pt metal salt precursor, a Pd metal salt precursor, a Ru metal salt precursor, a Cu metal salt precursor, and a Ni metal salt precursor is added to deionized water and mixed evenly to obtain a mixed solution; Step 2: An aqueous solution of NaBH4 is added to the mixed solution obtained in Step 1. After stirring evenly, it is left standing to react sufficiently to obtain a system containing a PtPdRuCuNi quinary alloy aerogel; Step 3: The PtPdRuCuNi quinary alloy aerogel is taken out from the system obtained in Step 2, washed and dried to obtain a PtPdRuCuNi alloy aerogel.

2. The PtPdRuCuNi alloy aerogel according to claim 1, characterized in that, In the mixed solution of Step 1, the molar ratio of Pt, Pd, Ru, Cu, and Ni in the Pt metal salt precursor, Pd metal salt precursor, Ru metal salt precursor, Cu metal salt precursor, and Ni metal salt precursor is 10:2:3:3:

2.

3. The PtPdRuCuNi alloy aerogel according to claim 1, wherein In Step 2, the concentration of the aqueous solution of NaBH4 is 0.5 - 1 mol / L.

4. The PtPdRuCuNi alloy aerogel according to claim 1, characterized in that, In Step 2, the reaction time is 2 - 3 minutes and the reaction temperature is 20 °C.

5. The PtPdRuCuNi alloy aerogel according to claim 1, characterized in that, In Step 3, during washing and drying, it is washed with deionized water and vacuum freeze-dried.

6. The application of the PtPdRuCuNi alloy aerogel as described in any one of claims 1 - 5 in the cathode of a direct methanol fuel cell after being modified by PTFE.

7. A gas diffusion electrode, characterized in that, It includes a gas diffusion layer and a catalyst layer supported on the gas diffusion layer. The catalyst layer is prepared by the following steps: The PtPdRuCuNi alloy aerogel, PTFE, and Nafion are dispersed in a solvent to obtain a uniformly mixed catalyst slurry. The catalyst slurry is coated on the gas diffusion layer and dried to obtain the gas diffusion electrode.

8. The gas diffusion electrode according to claim 7, wherein The mass ratio of the PtPdRuCuNi alloy aerogel, PTFE, and Nafion is (7 - 9):(0.5 - 1.5):(0.5 - 1.5). More preferably, the mass ratio of the PtPdRuCuNi alloy aerogel, PTFE, and Nafion is 8:1:

1.

9. A membrane electrode, characterized in that, It includes a cathode gas diffusion electrode, a proton exchange membrane, and an anode gas diffusion electrode pressed together in sequence. The cathode gas diffusion electrode is the gas diffusion electrode as described in claim 7 or 8. Preferably, the anode gas diffusion electrode is a gas diffusion electrode based on a PtRu / C catalyst.

10. A direct methanol fuel cell, characterized in that, It includes an end plate, a current collector plate, a bipolar plate, a gasket, and a membrane electrode as described in claim 9.

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