Membrane electrode and preparation method and application thereof

Abstract

The invention relates to the technical field of membrane electrodes, in particular to a membrane electrode and a preparation method and application thereof. According to the technical scheme, the method comprises the following steps: carrying out high-temperature pretreatment on a commercial carbon nanotube at 300-800 DEG C for 10-60 minutes to obtain a carbon nanotube with an open structure, adding the obtained carbon nanotube into an oxymetallate aqueous solution which is stirred at a high speed, and carrying out packaging reaction at 25-80 DEG C and at the stirring speed of 10-1000 r / min to obtain the carbon nanotube with the open structure. Preparing a compound in which the oxometallate is encapsulated in the carbon nano tube; and mixing the compound with a Nafion ionomer, ethanol and a commercial platinum carbon catalyst. According to the invention, the optimal balance among the comprehensive performance, the long-acting durability and the manufacturing cost of the membrane electrode is successfully realized, and a key technical support is provided for the development of a high-performance fuel cell.

Description

Technical Field

[0001] This invention relates to the field of membrane electrode technology, and in particular to a membrane electrode, its preparation method, and its application. Background Technology

[0002] Proton exchange membrane fuel cells (PEMFCs), as highly efficient devices that directly convert hydrogen oxidative energy into electrical energy, have become one of the most promising energy conversion devices in the new energy field due to their excellent power density, superior energy conversion efficiency, and zero-emission environmental characteristics. With the advancement of large-scale production of fuel cell stacks, the costs of components such as bipolar plates, proton exchange membranes, and gas diffusion layers have decreased significantly. However, the cost of membrane electrode assemblies remains high, with insufficient utilization of platinum catalysts being a key factor restricting cost optimization.

[0003] Traditional membrane electrode assemblies employ a densely packed structure of commercial platinum-carbon catalysts in their catalyst layers, which presents significant technical bottlenecks: First, the disordered and dense catalyst arrangement easily forms reaction dead zones, causing a large number of platinum active sites to be unable to effectively participate in electrochemical reactions due to the obstruction of reactant diffusion; Second, the dense structure severely restricts mass transfer efficiency, hindering the effective transport of reactants to the three-phase reaction interface and leading to water management imbalance, which significantly affects the long-term operational stability of fuel cells.

[0004] To address the aforementioned issues, researchers have made significant progress by controlling the composition and structure of catalysts. For example, based on the design of a cathode electrode using a vertically oriented carbon nanotube array, an ordered catalytic layer structure perpendicular to the proton exchange membrane was constructed. This structure, through a continuous three-dimensional porous network, highly dispersed support materials, and optimized catalyst-microporous layer interface contact, achieved improved mass transfer performance (Journal of The Electrochemical Society, 2013, 160, 522). Another example is the hierarchical proton transport system using Nafion nanofiber composite ionomers, which increased the power density of H2 / O2 fuel cells by 32.3% compared to traditional structures under conditions of 70℃ and 100% relative humidity, verifying the effect of proton-conducting nanofibers on improving fuel cell performance (Journal of Power Sources, 2014, 253, 104-113). However, during long-term operation, Nafion nanowires also face structural corrosion and collapse issues.

[0005] Based on the above research, there is an urgent need to develop a new method for preparing membrane electrode assemblies (MEAs) to achieve a dual improvement in the utilization rate and durability of the platinum catalyst layer, providing a new technical path for the development of high-performance fuel cells. Therefore, this application proposes a MEA, its preparation method, and its application. Summary of the Invention

[0006] The purpose of this invention is to address the problems of densely packed catalytic layers in traditional membrane electrodes, which result in catalyst reaction dead zones and low mass transfer performance, by proposing a membrane electrode, its preparation method, and its applications.

[0007] In a first aspect, the present invention provides a method for preparing a membrane electrode, characterized by comprising the following steps:

[0008] S1. Commercial carbon nanotubes are pretreated at 300-800℃ for 10-60 min to obtain carbon nanotubes with open structures.

[0009] S2. The carbon nanotubes obtained in step S1 are added to a high-speed stirred aqueous solution of metal oxoate, and an encapsulation reaction is carried out at 25-80℃ and 10-1000r / min to obtain a composite material in which metal oxoate is encapsulated inside carbon nanotubes.

[0010] S3. The composite is mixed with Nafion ionomer, ethanol and commercial platinum-carbon catalyst, and after ultrasonic dispersion treatment, it is sprayed onto the surface of proton exchange membrane to form a cathode catalyst layer.

[0011] The metal oxophosphate is phosphotungstic acid, silicomolybdic acid, molybdic acid, or tungstic acid;

[0012] The Pt loading in the cathode catalyst layer is 0.03-0.4 mg / cm2, and the mass ratio of the composite to Nafion is 1:(0-5).

[0013] Optionally, the mass ratio of carbon nanotubes, metal oxometalates and water in step S2 is 1:(0.1-10):(100-1000).

[0014] Optionally, the ultrasonic dispersion in step S3 has a power of 10-150W, a temperature of 25-80℃, and a time of 10-2000min.

[0015] In a second aspect, the present invention provides a membrane electrode prepared by the method described in the first aspect, wherein the cathode catalyst layer of the membrane electrode contains a composite of metal oxophosphates encapsulated inside carbon nanotubes, and the catalyst layer has a locally ordered structure guided by the one-dimensional structure of carbon nanotubes.

[0016] Optionally, the catalytic layer achieves efficient material transport through a proton-electron dual-channel synergistic transport mechanism.

[0017] Thirdly, the present invention provides a fuel cell including the membrane electrode described in the second aspect.

[0018] Compared with the prior art, this application includes at least one of the following beneficial technical effects:

[0019] This invention constructs a "proton-electron dual-channel" mechanism to synergistically enhance catalytic activity and mass transfer efficiency, achieving high catalytic performance with low platinum loading.

[0020] The present invention features a stable encapsulation structure that effectively quenches free radicals. Combined with an ordered catalytic layer, it significantly improves chemical stability and physical durability. It also greatly increases platinum atom utilization, effectively reducing the manufacturing cost of the membrane electrode.

[0021] The preparation process parameters of this invention are clear and highly controllable, and the raw materials used are readily available, thus possessing good prospects for large-scale production.

[0022] This invention successfully achieves the optimal balance between overall performance, long-term durability and manufacturing cost of membrane electrode assembly, providing key technical support for the development of high-performance fuel cells. Attached Figure Description

[0023] Figure 1 This is a scanning electron microscope image of the cathode catalyst layer obtained in Example 1 of the present invention;

[0024] Figure 2 These are the mass activity diagrams obtained in Examples 1 and 2, respectively.

[0025] Figure 3 These are electrochemical active area diagrams obtained in Examples 1 and 2, respectively.

[0026] Figure 4 These are the half-wave potential diagrams obtained in Examples 1 and 2, respectively.

[0027] Figure 5 These are the mass activity diagrams obtained in Examples 2 and 3, respectively.

[0028] Figure 6 These are electrochemical active area diagrams obtained in Examples 2 and 3, respectively.

[0029] Figure 7 These are the half-wave potential diagrams obtained in Examples 2 and 3, respectively.

[0030] Figure 8 This is a comparison chart of current density and power density obtained in Embodiments 4 and 5 of the present invention. Detailed Implementation

[0031] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, unless otherwise specified, the following embodiments and features described therein can be combined with each other.

[0032] Example 1

[0033] This embodiment provides a catalyst slurry preparation, comprising encapsulated metal oxometalate carbon nanotubes, Nafion, ethanol, and a commercial platinum-carbon catalyst, wherein the loading of Pt particles in the catalyst is 0.4 mg / cm³. 2 The mass ratio of Nafion to carbon nanotubes encapsulating metal oxophosphates is 1:0.3.

[0034] This embodiment also provides a method for preparing the above-mentioned cathode catalyst layer, which specifically includes the following steps:

[0035] (I) A typical synthesis of carbon nanotube composites encapsulating metal oxoates involves heating carbon nanotubes (20 mg) at 600 °C for 30 minutes to remove the tips of the carbon nanotubes, thereby allowing molecules to enter the carbon nanotube lumen, and to remove adsorbates such as water and oxygen.

[0036] (II) Take the black solid obtained in step (I) and add it to a solution of 200 mg of metal oxometalate in 3 mL of water under rapid stirring. Then sonicate the suspension for 2 minutes, followed by stirring at room temperature for 2 days. Then filter the suspension to obtain the black solid.

[0037] (III) Mix 2 mg of carbon nanotubes with 1 ml of ethanol and use an ultrasonic cleaner to sonicate for 120 min to obtain a homogeneous mixture.

[0038] (IV) Take 160 μl of the mixture obtained in step (III), 0.96 mg of 5 wt% Nafion, 2 mg of 40% commercial platinum-carbon catalyst, 375 μl of ethanol and 270 μl of other components and mix them. Use an ultrasonic cleaner to ultrasonically mix for 120 min to obtain a uniform mixture.

[0039] Take 10 μl of the mixture from step (Ⅳ) and measure the ORR polarization curve on a rotating disk electrode. Set the rotation speed to 1600 r / min and the scan rate to 50 mV / S.

[0040] Figure 1 This is a transmission electron microscope image of the cathode catalyst layer obtained in this embodiment. As can be seen from the image, the carbon nanotube structure encapsulating the metal oxophosphate is intact.

[0041] Example 2

[0042] The only difference between this embodiment and Embodiment 1 is that the mass ratio of the ionomer to the carbon nanotubes encapsulating the metal oxophosphate provided in this embodiment is 1:0.

[0043] Example 3

[0044] The only difference between this embodiment and Embodiment 1 is that the mass ratio of the ionomer to the carbon nanotubes encapsulating the metal oxophosphate provided in this embodiment is 1:0.5.

[0045] like Figures 2-4 It can be seen that the addition of carbon nanotubes encapsulated with metal oxometalates improves the catalyst utilization rate, and the catalyst utilization rate is highest when the ratio of ionomer to carbon nanotubes is 0.3.

[0046] like Figures 5-7 It can be seen that the addition of carbon nanotubes encapsulated with metal oxometalates improves the catalyst utilization rate, and the catalyst utilization rate is highest when the ratio of ionomer to carbon nanotubes is 0.5.

[0047] Example 4

[0048] This embodiment provides a method for preparing a membrane electrode, comprising encapsulating carbon nanotubes containing metal oxophosphates, Nafion, ethanol, and a commercial platinum-carbon catalyst, wherein the loading of Pt particles in the cathode catalyst layer is 0.12 mg / cm³. 2 The mass ratio of ionomer to encapsulated metal oxophosphate carbon nanotubes was 1:0, and the mass ratio of ionomer to carbon was 0.8; the loading of Pt particles in the anode catalyst layer was 0.08 mg / cm³. 2 The mass ratio of ionomer to carbon nanotubes is 1:0, and the mass ratio of ionomer to carbon is 0.8.

[0049] A commercial platinum-carbon catalyst was sprayed onto one side of the proton exchange membrane, located on the anode side of the fuel cell, and the resulting catalyst layer was the anode catalyst layer. A catalyst containing mixed encapsulated metal oxophosphate carbon nanotubes was sprayed onto the other side of the proton exchange membrane, located on the cathode side of the fuel cell, and the resulting catalyst layer was the cathode catalyst layer.

[0050] The performance of the battery was tested using a fuel cell testing system, measuring the current density and power density at 80℃ and 100RH.

[0051] Example 5

[0052] The only difference between this embodiment and embodiment 4 is that the mass ratio of the ionomer to the carbon nanotubes encapsulating the metal oxophosphate provided in this embodiment is 1:0.3.

[0053] Figure 8 The graphs show a comparison of current density and power density obtained in Examples 4 and 5. As can be seen from the graphs, the addition of carbon nanotubes encapsulated with metal oxometalates increases the current density and power density.

[0054] This invention introduces carbon nanotubes encapsulating metal oxophosphates into the catalyst layer, constructing an "electron-proton" coupled transport system: carbon nanotubes act as an electron transport framework, optimizing the electron conduction network of the catalyst layer; metal oxophosphates enhance the mass activity and electrochemical active area of ​​the catalyst layer by accelerating proton dissociation and transfer on the catalyst surface. The two synergistically drive a positive shift in the oxygen reduction half-wave potential, ensuring high catalytic efficiency while reducing platinum loading, effectively solving the problem of insufficient platinum utilization in traditional membrane electrodes and reducing membrane electrode costs.

[0055] Carbon nanotubes with a specific aspect ratio and encapsulating metal oxometalates enable a locally ordered structure in the catalyst layer. This regulates the proton transport microenvironment on the catalyst surface, significantly reducing mass transport resistance and maintaining stable performance output at high current densities. This overcomes the bottleneck of low mass transfer efficiency inherent in traditional densely packed structures. Polyoxometalates possess excellent free radical quenching capabilities, effectively suppressing free radical damage to the proton exchange membrane and catalyst layer during fuel cell operation, significantly improving the long-term operational stability of the membrane electrode assembly (MEA). Simultaneously, the locally ordered catalyst layer structure reduces reaction dead zones, preventing catalyst failure due to localized stress concentration or material accumulation, further extending the MEA's lifespan.

[0056] The preparation steps of this invention (carbon nanotube pretreatment, metal oxophosphate encapsulation catalyst layer preparation, etc.) all employ controllable process parameters (such as high-temperature treatment temperature, stirring speed, ultrasonic power, etc.). By adjusting these parameters, the structure and performance of the catalyst layer can be stably controlled, meeting the consistency requirements of large-scale production. Furthermore, the raw materials used (commercial carbon nanotubes, platinum-carbon catalysts, etc.) are readily available and require no special equipment, lowering the barrier to industrial application. In summary, this invention, through structural innovation and process optimization, achieves comprehensive improvements in catalytic efficiency, mass transfer performance, durability, and cost control of the membrane electrode assembly, providing a practical and feasible technical path for the development of high-performance, low-cost fuel cells.

[0057] By encapsulating metal oxometalates within carbon nanotubes and combining them with Nafion ionomers and platinum-carbon catalysts, a highly efficient proton-electron dual-channel synergistic transport mechanism was constructed within the catalytic layer. The carbon nanotubes optimized the electron conduction network, while the encapsulated metal oxometalates significantly enhanced proton transport efficiency. This structure significantly reduced the mass transfer resistance of the oxygen reduction reaction, enabling the membrane electrode to operate even with low platinum loadings (0.03-0.4 mg / cm³). 2Even under certain conditions, it still exhibits high electrochemical active area, high-quality activity, and a positively shifted half-wave potential, achieving a synergistic enhancement of catalytic activity and mass transport capability. The encapsulation structure stably confines the metal oxometalate within the carbon nanotube channels, preventing dissolution and loss, thus sustainably exerting its free radical quenching ability and effectively suppressing the chemical corrosion of the proton exchange membrane and catalyst by free radicals generated during fuel cell operation. Simultaneously, the one-dimensional rigidity of carbon nanotubes helps form a locally ordered catalytic layer structure, reducing reaction dead zones and preventing physical failure of the catalyst due to localized stress concentration or water flooding, thereby significantly improving the long-term operational life and stability of the membrane electrode assembly.

[0058] The unique composite structure constructed in this invention greatly improves the utilization rate of platinum atoms, enabling a significant reduction in the amount of precious metal platinum used (as low as 0.03 mg / cm³). 2 While achieving high current density and power density, this method can still maintain or even improve the battery's output performance. It provides a practical and effective solution to the industry bottleneck of excessively high membrane electrode costs. The raw materials used in this preparation method (such as commercial carbon nanotubes and platinum-carbon catalysts) are readily available, and the key process parameters (such as high-temperature pretreatment temperature, stirring speed, and ultrasonic power) are well-defined and controllable. It requires no special or complex equipment, exhibits good process repeatability and consistency, and lays a solid foundation for the large-scale preparation and commercial application of high-performance membrane electrodes.

[0059] This invention, through synergistic innovation in materials, structure, and process, has successfully achieved comprehensive optimization of membrane electrode assemblies in terms of catalytic efficiency, mass transfer performance, durability, and manufacturing cost, providing a technologically advanced solution with significant competitive advantages for the development of high-performance, long-life, and low-cost fuel cells.

[0060] The above specific embodiments are merely several optional embodiments of the present invention. Based on the technical solutions of the present invention and the relevant teachings of the above embodiments, those skilled in the art can make various alternative improvements and combinations to the above specific embodiments.

Claims

1. A method for preparing a membrane electrode, characterized in that, Includes the following steps: S1. Commercial carbon nanotubes are pretreated at 300-800℃ for 10-60 min to obtain carbon nanotubes with open structures. S2. The carbon nanotubes obtained in step S1 are added to a high-speed stirred aqueous solution of metal oxoate, and an encapsulation reaction is carried out at 25-80℃ and 10-1000r / min to obtain a composite material in which metal oxoate is encapsulated inside carbon nanotubes. S3. The composite is mixed with Nafion ionomer, ethanol and commercial platinum-carbon catalyst, and after ultrasonic dispersion treatment, it is sprayed onto the surface of proton exchange membrane to form a cathode catalyst layer. The metal oxophosphate is phosphotungstic acid, silicomolybdic acid, molybdic acid, or tungstic acid; The Pt loading in the cathode catalyst layer is 0.03-0.4 mg / cm³. 2 The mass ratio of the complex to Nafion is 1:(0-5).

2. The method for preparing a membrane electrode according to claim 1, characterized in that, The mass ratio of carbon nanotubes, metal oxometalates and water in step S2 is 1:(0.1-10):(100-1000).

3. The method for preparing a membrane electrode according to claim 1, characterized in that, The ultrasonic dispersion in step S3 has a power of 10-150W, a temperature of 25-80℃, and a time of 10-2000min.

4. A membrane electrode, characterized in that, Prepared by the method of any one of claims 1-3, the cathode catalyst layer of the membrane electrode contains a composite of metal oxophosphates encapsulated inside carbon nanotubes, and the catalyst layer has a locally ordered structure guided by the one-dimensional structure of carbon nanotubes.

5. The membrane electrode according to claim 4, characterized in that, The catalyst layer achieves efficient material transport through a proton-electron dual-channel synergistic transport mechanism.

6. A fuel cell, characterized in that, Includes the membrane electrode as described in claim 4 or 5.

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