A method for preparing tungsten carbide-doped carbon-supported platinum Pt / C catalyst and its application

Abstract

This invention discloses a method for preparing a tungsten carbide-doped carbon-supported platinum (Pt / C) catalyst and its application. The method involves mixing tungsten oxide and a carbon support in an organic solvent via a hydrothermal process to obtain a precursor powder. The precursor powder is then heat-treated at high temperature and cooled to obtain W-C powder, which is mechanically mixed with conductive carbon powder in an organic solvent to obtain a W-C / C composite support. This support is dispersed in a solvent, and a platinum source is added for reduction. The resulting product is washed and dried to obtain the Pt / W-C / C catalyst. The catalyst is then slurried and coated onto both sides of a proton exchange membrane to form a three-in-one membrane electrode. This invention provides a relatively simple and highly controllable preparation method. By combining hydrothermal synthesis with high-temperature carbonization, the uniform formation and high stability of the W-C framework are ensured. Furthermore, through optimized platinum loading and ionic liquid doping processes, the controllable preparation of a high-performance, high-durability membrane electrode is achieved.

Description

Technical Field

[0001] This invention relates to the field of catalysts for fuel cells, and in particular to a method for preparing a tungsten carbide-doped carbon-supported platinum Pt / C catalyst, and a membrane electrode assembly (CCM) containing the catalyst. Background Technology

[0002] Currently, conventional Pt / C catalysts face multiple challenges during operation. First, hydrogen peroxide (H2O2) and its derived hydroxyl radicals (·OH) are generated during battery operation. These highly oxidizing substances attack the carbon support and proton exchange membrane, leading to catalyst loss and chemical degradation of the membrane module. Second, Pt nanoparticles are prone to dissolution, migration, and Ostwald ripening under potential cycling, resulting in a decrease in active surface area. Furthermore, under low humidity operation, the proton conductivity of the catalyst layer deteriorates sharply, and the catalyst's sensitivity to poisoning by impurities such as carbon monoxide (CO) increases, all of which severely limit the battery's lifespan and reliability.

[0003] To address the aforementioned issues, existing research has attempted to introduce auxiliary components to enhance catalyst stability. Among these, tungsten carbide (WC) has attracted attention due to its high melting point, excellent chemical stability, and unique noble metal-like catalytic properties. WC exhibits structural stability in acidic environments, effectively capturing H₂O₂ and ·OH radicals, mitigating their damage to the catalyst and membrane, and also demonstrating some resistance to CO poisoning. However, single-material modification often has limited effects. Therefore, a novel catalytic layer structure is urgently needed that can synergize with Pt catalysts and provide multiple layers of protection. This structure would physically form a protective layer, inhibiting the ripening and migration of Pt particles while maintaining proton conduction under low humidity conditions. This would synergistically improve the overall durability of the membrane electrode under harsh operating conditions from multiple dimensions, including inhibiting catalyst decay, maintaining proton conduction, and resisting chemical corrosion. Summary of the Invention

[0004] The main technical problem solved by this invention is to provide a method for preparing a tungsten carbide-doped platinum-supported Pt / C catalyst and a membrane electrode containing the catalyst. This method can comprehensively solve the shortcomings of existing Pt / C catalysts in terms of durability, low humidity operation and anti-attenuation performance by constructing a membrane electrode in which platinum is supported by a tungsten carbide-doped composite support and forms a synergistic protection system with the ionic liquid in the catalyst layer.

[0005] To solve the above-mentioned technical problems, one technical solution adopted by the present invention is: to provide a method for preparing a tungsten carbide-doped carbon-supported platinum Pt / C catalyst, comprising the following steps:

[0006] (1) Tungsten oxide and carbon support are dispersed in an organic solvent at a mass ratio of (3-4):(7-6), and mixed by hydrothermal method to lay the foundation for the subsequent formation of a uniform WC framework. After the reaction, the mixture is filtered and dried to obtain the precursor powder.

[0007] (2) The precursor powder obtained in step (1) is heat-treated at a temperature of 1500-2000℃ under an inert atmosphere to react tungsten oxide with carbon to form a tungsten carbide WC framework. After cooling, WC powder is obtained.

[0008] (3) The WC powder obtained in step (2) is mechanically mixed with conductive carbon powder in an organic solvent, filtered and dried to obtain a WC / C composite carrier that combines the chemical protection function of WC with the excellent conductivity of carbon materials.

[0009] (4) The WC / C composite support obtained in step (3) is dispersed in a solvent, a platinum source is added, and then a reducing agent is added at a pH of 8-12 to carry out a reduction reaction to form platinum nanoparticles with uniform particle size. After the reaction, the particles are washed and dried to obtain the Pt / WC / C catalyst. This catalyst combines the free radical scavenging ability of WC with the catalytic activity of highly dispersed Pt, thus improving the overall durability of the catalyst.

[0010] In a preferred embodiment of the present invention, in step (1), the tungsten oxide is either tungsten trioxide (WO3) or tungsten dioxide (WO2) to provide an effective tungsten source.

[0011] In a preferred embodiment of the present invention, in step (1), the carbon support is either XC-72 or acetylene black ECP300 to provide an initial support with a high specific surface area.

[0012] In a preferred embodiment of the present invention, in step (1), the temperature of the hydrothermal reaction is 100-200°C and the time is 2-3 h, so that the tungsten oxide and the carbon support are fully and uniformly mixed.

[0013] In a preferred embodiment of the present invention, in steps (1) and (3), the organic solvent is one or a mixture of several of N-methylpyrrolidone, tetrahydrofuran or n-butanol, used to achieve effective dispersion and mixing of the raw materials.

[0014] In a preferred embodiment of the present invention, in step (3), the mass ratio of WC powder to conductive carbon powder is (1-4):(9-6); the mechanical mixing time is 2-4 h, which precisely balances the free radical capture function and electronic conduction ability of the composite carrier, and avoids the decrease in conductivity due to excessive WC content, or the weakening of the protective effect due to excessively low WC content.

[0015] In a preferred embodiment of the present invention, in step (4), the platinum source is chloroplatinic acid; the reducing agent is one of sodium borohydride or sodium citrate, used to achieve efficient and uniform reduction of the platinum precursor.

[0016] Another technical solution adopted by the present invention is to provide a membrane electrode comprising a Pt / WC / C catalyst prepared by any of the methods described above. The membrane electrode preparation method includes: mixing the Pt / WC / C catalyst, an ionic liquid, and an isopropanol solution to form a catalyst slurry; coating the slurry onto both sides of a proton exchange membrane to form a cathode catalyst layer and an anode catalyst layer; and assembling the slurry with the proton exchange membrane to form a three-in-one membrane electrode. The mass ratio of the ionic liquid to the Pt / WC / C catalyst is (0.5-1.5):1. Through the synergistic effect of the ionic liquid and WC, proton conduction is maintained and platinum particle ripening is inhibited under low humidity.

[0017] In a preferred embodiment of the present invention, the ionic liquid is preferably an imidazole ionic liquid, including one or more of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ([C2mim][NTf2]), 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ([C4mim][NTf2]), and 1-butyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide salt ([C4dmim][NTf2]), to provide a stable microenvironment with high proton conduction capability.

[0018] In a preferred embodiment of the present invention, the platinum loading in the cathode catalyst layer is 0.2 to 0.4 mg / cm², and the platinum loading in the anode catalyst layer is 0.05 to 0.15 mg / cm².

[0019] In a preferred embodiment of the present invention, the proton exchange membrane is a composite membrane reinforced with expanded polytetrafluoroethylene with a thickness of 8μm to 15μm, which improves the overall performance and durability of the battery.

[0020] In a preferred embodiment of the present invention, a gas diffusion layer is provided on the outer side of the anode catalyst layer and the cathode catalyst layer. The gas diffusion layer is Toray TGP-H-60, TGP-H-090, or TGP-H-120 carbon paper or other carbon cloth, forming a five-layer membrane electrode assembly (MEA).

[0021] The beneficial effects of this invention are: This invention provides a relatively simple and highly controllable preparation method. By combining hydrothermal synthesis with high-temperature carbonization, the uniform formation and high stability of the WC framework are ensured. Furthermore, through optimized platinum loading and ionic liquid doping processes, the controllable preparation of high-performance and high-durability membrane electrodes is achieved. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0023] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set" and "connection" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0024] In this invention, unless otherwise expressly specified and limited, "above or below" a first feature may include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on" the first feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the first feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0025] This invention includes:

[0026] Example 1: A method for preparing a tungsten carbide-doped carbon-supported platinum Pt / C catalyst, comprising the following steps:

[0027] (1) Weigh 4.0 g of WO3 and 6.0 g of Vulcan XC-72 carbon powder and place them in a 500 mL three-necked flask. Add 100 mL of NMP as an organic solvent and stir thoroughly for 2 hours in an 80 °C water bath to ensure uniform dispersion of the mixture. Then transfer the mixed suspension to a 500 mL stainless steel reactor and carry out a hydrothermal reaction at 200 °C for 2 hours to achieve preliminary molecular-level composite of the tungsten source and the carbon support. After the reaction is completed, allow it to cool naturally to room temperature, filter and dry to obtain the precursor powder.

[0028] (2) The precursor powder was placed in a tube furnace and heated to 1800°C at a rate of 5°C / min under an argon protective atmosphere. The temperature was then maintained at this temperature for 2 hours for high-temperature carbonization treatment, so that WO3 reacted fully with carbon to form a stable tungsten carbide (WC) framework. After cooling to room temperature in the furnace, the product was removed and weighed to obtain 8.5 g of black WC powder.

[0029] (3) Take 5.0 g of the prepared WC powder and 5.0 g of XC-72 carbon powder and add them together to 100 mL of NMP solvent. Stir at 300 rpm for 2 hours using a mechanical fan stirrer to ensure that the WC powder and conductive carbon powder are fully and uniformly mixed. After mixing, filter and dry to obtain the WC / C composite carrier.

[0030] (4) Weigh 1.0 g of the WC / C composite carrier obtained in step (2) and disperse it in 100 mL of anhydrous ethanol. Then, add 0.6 g of chloroplatinic acid (H2PtCl6·6H2O) as a platinum precursor and stir continuously. While stirring, add dropwise 0.5 mol / L sodium borohydride (NaBH4) aqueous solution as a reducing agent to adjust and maintain the pH of the entire reaction system at 12.

[0031] The reaction was continued with stirring in a 50°C water bath for 4 hours to ensure complete reduction of platinum. After the reaction, the mixture was filtered and washed with ethanol until the filtrate was neutral to remove impurities such as chloride ions. The resulting solid was dried in a vacuum drying oven at 80°C to obtain a Pt / WC / C catalyst with a platinum loading of approximately 60%.

[0032] (5) The preparation method of the membrane electrode CCM includes: weighing 0.2 g of the 60% Pt / WC / C catalyst prepared above, 0.2 g of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ([C2mim][NTf2]) ionic liquid, 50 mL of isopropanol and 0.2 g of deionized water (as a dispersing agent), and placing them together in a ball mill jar. Mixing is performed using a ball mill at a speed of 200 rpm for 1.5 hours to form a uniform and stable catalyst slurry.

[0033] Using ultrasonic spraying equipment, the above slurry was precisely sprayed onto both sides of the Gore Select® 12 μm enhanced proton exchange membrane. The spraying process was controlled to ensure that the platinum loading on the cathode side was 0.3 mg / cm² and the platinum loading on the anode side was 0.1 mg / cm², forming a CCM.

[0034] Subsequently, the CCM and the hydrophobically treated Toray TGP-H-60 carbon paper (as a gas diffusion layer) are hot-pressed in a hot press for 90 seconds to assemble a complete membrane electrode assembly (MEA).

[0035] Example 2: A method for preparing a tungsten carbide-doped carbon-supported platinum Pt / C catalyst, comprising the following steps:

[0036] (1) Weigh 3.0 g of WO2 and 7.0 g of acetylene black ECP300J carbon powder and place them in a 500 mL three-necked flask. Add 100 mL of tetrahydrofuran as an organic solvent and stir thoroughly in a water bath at 75 °C for 12 hours to ensure uniform dispersion of the mixture. Then transfer the mixed suspension to a 500 mL reaction vessel and carry out a hydrothermal reaction at 200 °C for 3 hours to achieve preliminary molecular-level composite of the tungsten source and the carbon support. After the reaction is completed, allow it to cool naturally to room temperature, filter and dry to obtain the precursor powder.

[0037] (2) The precursor powder was placed in a tube furnace and heated to 1600°C at a rate of 5°C / min under an argon protective atmosphere. The temperature was then maintained at this temperature for 2 hours for high-temperature carbonization treatment, so that WO2 reacted fully with carbon to form a stable tungsten carbide (WC) framework. After cooling to room temperature in the furnace, the product was removed and weighed to obtain 7.5 g of black WC powder.

[0038] (3) Take 6.0 g of the prepared WC powder and 4.0 g of ECP300J carbon powder (i.e., the mass ratio of WC to C is 6:4) and add them together to 100 mL of tetrahydrofuran solvent. Stir at 300 rpm for 2 hours using a mechanical fan stirrer to ensure that the WC powder and conductive carbon powder are fully and uniformly mixed. After mixing, filter and dry to obtain the WC / C composite carrier.

[0039] (4) Weigh 1.0 g of the WC / C composite carrier obtained in step (2) and disperse it in 100 mL of anhydrous ethanol. Then add 0.7 g of chloroplatinic acid (H2PtCl6·6H2O) as a platinum precursor and continue stirring. While stirring, add dropwise 0.3 mol / L sodium citrate aqueous solution as a reducing agent to adjust and maintain the pH of the entire reaction system at 10.

[0040] The reaction was refluxed and stirred in an 80°C water bath for 6 hours to ensure complete reduction of platinum. After the reaction, the mixture was filtered and washed with anhydrous ethanol until the filtrate was neutral to remove impurity ions. The resulting solid was dried in a vacuum drying oven at 80°C to obtain a Pt / WC / C catalyst with a platinum loading of approximately 50%.

[0041] (5) The preparation method of the membrane electrode CCM includes: weighing 0.2 g of the 50% Pt / WC / C catalyst prepared above, 0.25 g of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ([C4mim][NTf2]) ionic liquid, and 50 mL of isopropanol as a dispersant, and placing them together in a ball mill jar. The mixture is then mixed at 200 rpm for 1.5 hours using a ball mill to form a uniform and stable catalyst slurry.

[0042] Using ultrasonic spraying equipment, the above slurry was precisely sprayed onto both sides of the Gore Select® 8 μm enhanced proton exchange membrane. The spraying process was controlled to ensure that the platinum loading on the cathode side was 0.3 mg / cm² and the platinum loading on the anode side was 0.1 mg / cm², forming a CCM.

[0043] Subsequently, the CCM and the hydrophobically treated Toray TGP-H-080 carbon paper (as a gas diffusion layer) are hot-pressed in a hot press for 90 seconds to assemble a complete membrane electrode assembly (MEA).

[0044] Comparative Example 1: The preparation method includes:

[0045] (1) Cut a Gore 12 micrometer membrane as a proton exchange membrane, weigh 0.2 g of 60% Pt / C catalyst, 0.2 g of DuPont 520 solution, 50 mL of ethylene glycol, and 0.2 g of deionized water, and mix them for 15 minutes at 10000 rpm using a high-speed shear emulsifier to prepare a catalyst slurry.

[0046] (2) Using the same spraying process, the slurry was sprayed onto both sides of the Gore 12µm membrane, and the platinum loading of the anode and cathode was controlled to be exactly the same as in Example 1 (cathode 0.3 mg / cm², anode 0.1 mg / cm²) to form the membrane electrode CCM. TGP-H-60 carbon paper was used as the gas diffusion layer, and the membrane electrode assembly (MEA) was hot-pressed and assembled under the same conditions.

[0047] The membrane electrode assembly (MEA) prepared according to the methods of Examples 1, 2 and Comparative Example 1 was loaded into a single-cell test fixture and its performance was evaluated on a fuel cell test system.

[0048] Durability test conditions: battery temperature 80℃; anode (hydrogen) inlet humidity 100% RH, cathode (air) inlet humidity 100% RH; back pressure of both hydrogen and air 200 kPa; anode metering ratio 1.2, cathode metering ratio 2.5.

[0049] An accelerated stress testing protocol was adopted: under a nitrogen atmosphere, a potential cycle was applied to the cathode, with a potential range of 1.0 V–1.5 V (relative to the reversible hydrogen electrode), and a scan rate of 500 mV / s. Polarization curves were recorded at the initial state (0 cycles), after 2000 cycles, and after 5000 cycles.

[0050] Different humidity test conditions: Battery temperature 80℃, back pressure 200 kPa, fixed voltage point (e.g. 0.8 V), the current density was tested at anode and cathode inlet humidity of 40% RH, 80% RH, and 100% RH to evaluate low humidity performance.

[0051] To quantify the effectiveness of the invention, the current density of Examples 1, 2, and Comparative Example 1 at different aging stages (0 cycles, 2000 cycles, and 5000 cycles) at 0.65 V was recorded to evaluate the corrosion resistance durability of the carbon support (results are shown in Table a). Simultaneously, the current density at 0.8 V under different relative humidities (40%, 80%, and 100%) was recorded to evaluate the low-humidity performance of the membrane electrode (results are shown in Table b).

[0052] Table a. Comparison of carbon support durability data between Examples 1 & 2 and Comparative Example 1:

[0053]

[0054] Table b: Comparison of low humidity performance data between the examples and the comparative examples:

[0055]

[0056] As can be seen from the data in Table a, after 5000 cycles of intense potential cycling aging, the current density attenuation of the membrane electrodes of Examples 1 and 2 of the present invention at 0.65 V decreased by approximately 15.5% and 24.5%, respectively, which is significantly less than the approximately 30% decrease in Comparative Example 1.

[0057] This indicates that the WC / C composite support prepared in this invention has excellent resistance to carbon corrosion. This is mainly attributed to the fact that the WC framework can effectively remove free radicals such as ·OH generated during fuel cell operation, avoid Pt agglomeration, reduce its oxidative corrosion on the carbon support, and thus better maintain the structural stability of the catalyst.

[0058] As can be clearly seen from the data in Table b, under different humidity conditions, especially under low humidity (40% RH) conditions, the current density of Examples 1 and 2 of the present invention is significantly higher than that of Comparative Example 1.

[0059] This fully demonstrates that the imidazole ionic liquid introduced into the catalyst layer has a synergistic effect with the WC support. The ionic liquid provides an effective proton conduction pathway under low humidity, which significantly improves the water management capability and low humidity adaptability of the membrane electrode.

[0060] The test results of the above embodiments and comparative examples fully demonstrate that the tungsten carbide-doped carbon-supported platinum catalyst and its membrane electrode preparation method provided by the present invention, by constructing a WC composite support and introducing ionic liquid, successfully and synergistically improves the durability (especially the resistance to carbon corrosion) and low humidity operation performance of fuel cells. The technical effect is significant and superior to traditional Pt / C catalysts.

[0061] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a tungsten carbide-doped carbon-supported platinum Pt / C catalyst, characterized in that, Includes the following steps: (1) Tungsten oxide and carbon support are mixed in an organic solvent by hydrothermal method, and after reaction, the mixture is filtered and dried to obtain precursor powder; (2) The precursor powder obtained in step (1) is heat-treated at a temperature of 1500-2000℃ under an inert atmosphere to react tungsten oxide with carbon to form a tungsten carbide WC framework. After cooling, WC powder is obtained. (3) The WC powder obtained in step (2) and conductive carbon powder are mechanically mixed in an organic solvent at a mass ratio of (1-4):(9-6) for 2-4 h. After filtration and drying, the WC / C composite carrier is obtained. (4) Disperse the WC / C composite support obtained in step (3) in a solvent, add a platinum source, and then add a reducing agent under the condition of pH 8-12 to carry out a reduction reaction. After the reaction, wash and dry to obtain the Pt / WC / C catalyst.

2. The method for preparing the tungsten carbide-doped carbon-supported platinum Pt / C catalyst according to claim 1, characterized in that, In step (1), the tungsten oxide is either tungsten trioxide (WO3) or tungsten dioxide (WO2).

3. The method for preparing the tungsten carbide-doped carbon-supported platinum Pt / C catalyst according to claim 1, characterized in that, In step (1), the carbon support is either XC-72 or acetylene black ECP300.

4. The method for preparing the tungsten carbide-doped carbon-supported platinum Pt / C catalyst according to claim 1, characterized in that, In step (1), the hydrothermal reaction temperature is 100-200℃ and the time is 2-3 h.

5. The method for preparing the tungsten carbide-doped carbon-supported platinum Pt / C catalyst according to claim 1, characterized in that, In steps (1) and (3), the organic solvent is one or a mixture of several of N-methylpyrrolidone, tetrahydrofuran, or n-butanol.

6. The method for preparing the tungsten carbide-doped carbon-supported platinum Pt / C catalyst according to claim 1, characterized in that, In step (4), the platinum source is chloroplatinic acid; the reducing agent is either sodium borohydride or sodium citrate.

7. A membrane electrode, characterized in that, The method for preparing a membrane electrode, including the Pt / WC / C catalyst prepared by any one of claims 1 to 6, comprises: mixing the Pt / WC / C catalyst, an ionic liquid, and an isopropanol solution to form a catalyst slurry, coating the slurry onto both sides of a proton exchange membrane to form a cathode catalyst layer and an anode catalyst layer, and assembling the slurry with the proton exchange membrane to form a three-in-one membrane electrode.

8. The membrane electrode according to claim 7, characterized in that, The ionic liquid is an imidazole ionic liquid, including one or more of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, or 1-butyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide salt.

9. The membrane electrode according to claim 7, characterized in that, The platinum loading in the cathode catalyst layer is 0.2–0.4 mg / cm², and the platinum loading in the anode catalyst layer is 0.05–0.15 mg / cm².

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