Ultra-small ordered noble metal-zinc intermetallic compound catalyst embedded in mesoporous carbon and preparation method of ultra-small ordered noble metal-zinc intermetallic compound catalyst

Abstract

The invention discloses an ultra-small ordered noble metal-zinc intermetallic compound catalyst embedded in mesoporous carbon and a preparation method thereof, and belongs to the technical field of nano material electro-catalysis. The catalyst comprises a mesoporous carbon carrier and an ultra-small ordered noble metal-zinc intermetallic compound embedded into the mesoporous carbon carrier, and the preparation process mainly comprises the following steps: adsorbing a noble metal precursor into a pore channel of the mesoporous carbon carrier by using an impregnation method, and then reacting with noble metal at high temperature by using zinc vapor to obtain the ultra-small ordered noble metal-zinc intermetallic compound. And generating the ultra-small ordered noble metal-zinc intermetallic compound embedded in the mesoporous carbon in situ. The preparation method is simple to operate and high in universality, and has the potential of large-scale production. The synthesized ultra-small ordered noble metal-zinc intermetallic compound has high intrinsic catalytic activity and stability, is embedded into the mesoporous carbon carrier, can avoid direct contact with an ionic polymer and weaken poisoning of sulfonate radicals to the catalyst, and is an electrocatalyst with a good application prospect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nanomaterial electrocatalysis, and particularly relates to an ultra-small ordered noble metal-zinc intermetallic compound catalyst embedded in mesoporous carbon and a preparation method thereof. BACKGROUND

[0002] Noble metal catalysts have high intrinsic catalytic reaction activity and play an irreplaceable role in energy conversion devices such as fuel cells and water electrolysis. However, during electrochemical reactions, noble metal elements are easily dissolved, resulting in poor electrochemical stability and rapid activity decay. By controlling the reaction conditions, noble metals are alloyed with transition metals to form intermetallic compounds with ordered atomic arrangement, which can increase the dissolution energy barrier of noble metal elements, optimize the adsorption of reaction intermediates on the surface of noble metal catalysts, and thus significantly improve the activity and stability of noble metal-based catalysts.

[0003] Currently, the preparation of noble metal-based intermetallic catalysts is usually carried out at high temperatures. During the ordering process, intermetallic compounds are prone to particle migration, resulting in the Oswald ripening effect, which causes grain sintering and size increase, and reduces the atomic utilization rate of noble metals. Developing a controllable synthesis method to control the particle size of the catalyst while constructing highly ordered noble metal-based intermetallic catalysts is the key to designing efficient catalysts.

[0004] In addition, the binding mode of intermetallic compounds with the carrier is very important for their performance expression. Currently reported intermetallic compounds are usually adsorbed on the surface of carbon carriers, and the interaction between them is weak, which can easily lead to detachment and dissolution during chemical reactions. During the preparation of electrodes, it is inevitable to add ionic polymers as binders, which directly coat the surface of intermetallic catalysts. The toxic effect between sulfonate in ionic polymer and noble metal will inhibit the expression of active sites and reduce the activity and stability of the catalyst. In addition, the uneven distribution of ionic polymers during device preparation will also cause serious mass transfer resistance, which will further affect the performance expression of the catalyst in the device. Although some studies have shown that optimizing the adsorption properties of ionic polymers through coordination strategies and structural isolation can significantly reduce gas transfer resistance, there are very limited reports on advanced noble metal-based intermetallic compound catalysts. By optimizing the synthesis, in-situ synthesis of noble metal-based intermetallic compounds with small particle size and high order degree inside the porous carbon carrier can reduce their direct contact with ionic polymers and improve their catalytic activity and stability, which is of great significance for the further development and application of noble metal-based catalysts. SUMMARY

[0005] To solve the above problems of the prior art, the present application intends to provide an ultra-small ordered noble metal-zinc intermetallic compound electrocatalyst embedded in mesoporous carbon and a preparation method thereof, so as to realize the improvement of the reaction activity and stability of the intermetallic catalyst and the excellent mass transfer characteristics.

[0006] In one aspect, the present application provides an ultra-small ordered noble metal-zinc intermetallic compound catalyst embedded in mesoporous carbon, which comprises a porous carbon carrier and an ultra-small ordered noble metal-zinc intermetallic compound embedded in the interior of the porous carbon carrier, the porous carbon carrier is a mesoporous carbon material with a pore size of 2-50 nm, and the noble metal-zinc intermetallic compound contains zinc and at least one noble metal M, wherein the ultra-small ordered noble metal-zinc intermetallic compound is a nanoparticle with an average particle size of not more than 5 nm.

[0007] Preferably, the noble metal M is selected from at least one of platinum, gold, palladium, iridium and ruthenium, and the noble metal-zinc intermetallic compound is at least a binary zinc-based intermetallic compound.

[0008] The mesoporous carbon material includes but is not limited to ordered mesoporous carbon CMK-3, porous carbon nanofiber, porous carbon nanotube, metal organic framework material derived porous carbon material or commercial porous carbon, etc.

[0009] In another aspect, the present application provides a preparation method for preparing the above-mentioned ultra-small ordered noble metal-zinc intermetallic compound catalyst embedded in mesoporous carbon, which comprises the following steps: S1, adding a noble metal precursor into deionized water, ultrasonicating at room temperature to make it completely dissolved to form a noble metal precursor solution; adding a mesoporous carbon material into the above-mentioned solution, ultrasonicating at room temperature to make the carbon material completely dispersed into the solution; then, placing the mesoporous carbon dispersion adsorbing the noble metal precursor at room temperature, and naturally drying to obtain the mesoporous carbon material adsorbing the noble metal precursor, for standby; S2, adding zinc nitrate into solvent A, stirring to form a zinc nitrate solution; adding 2-methyl imidazole into solvent B, stirring to form a 2-methyl imidazole solution; under stirring, adding the above-mentioned zinc nitrate solution into the 2-methyl imidazole solution, continuing to stir for a period of time, then centrifuging and washing for multiple times, and drying to obtain a zinc-based metal framework material; calcining the obtained zinc-based metal framework material under an argon atmosphere to obtain a carbon-loaded nanometer zinc material, for standby; S3, placing the mesoporous carbon material adsorbed with the noble metal precursor obtained in the step S1 downstream of the gas flow in a tube furnace, placing the carbon-supported nanometer zinc material obtained in the step S2 upstream of the gas flow in the tube furnace, and calcining under a hydrogen / argon mixed gas to cause the nanometer zinc material upstream to form zinc metal vapor at high temperature and react with the noble metal downstream under the driving of the gas flow, so as to obtain the super-small ordered noble metal-zinc intermetallic compound catalyst embedded in the mesoporous carbon.

[0010] The preparation method provided by the application mainly includes two processes of adsorption of noble metal precursors on mesoporous carbon materials and subsequent high-temperature metal vapor reaction. First, the noble metal precursor solution enters the pore channel of the mesoporous carbon material through capillary adsorption, and in the subsequent heating process, the noble metal precursor is pyrolyzed and reduced into small noble metal nanocrystals. As the temperature continues to rise, the nanometer zinc upstream becomes zinc vapor at high temperature, moves to the downstream with the carrier gas flow, contacts the noble metal nanocrystals formed by pyrolysis, and occurs alloying reaction. This process not only inhibits the continuous growth of the noble metal nanocrystals, but also promotes the ordered rearrangement of noble metal atoms and zinc atoms, and finally realizes the in-situ generation of highly ordered noble metal-zinc intermetallic electrocatalyst particles with small and uniform particle size in the mesoporous carbon pores.

[0011] In the step S1, the noble metal precursor can be a noble metal salt, including but not limited to platinum tetrachloride, chloroplatinic acid, chloroauric acid, sodium chloropalladate, iridium trichloride, and ruthenium trichloride.

[0012] Further, in the step S1, the mass ratio of the noble metal precursor to the mesoporous carbon material is 1:2-1:20, preferably 1:5-1:10; in the step S2, the molar ratio of zinc nitrate to 2-methylimidazole is 1:1-1:10, preferably 1:2-1:8; and in the step S3, the mass ratio of the mesoporous carbon material adsorbed with the noble metal precursor to the carbon-supported nanometer zinc material is 1:1-1:20, preferably 1:2-1:5.

[0013] In the step S2, the solvent A and the solvent B used to dissolve the zinc nitrate and the 2-methylimidazole can be the same or different, and are selected from deionized water, methanol, or N,N-dimethylformamide, etc. Different solvent selection will affect the morphology of the zinc-based metal framework material synthesized, but will not affect the content of the carbon-supported nanometer zinc after calcination. The stirring time of the mixture of the zinc nitrate solution and the 2-methylimidazole can be 1-24 hours, preferably 12-24 hours. The calcination temperature of the zinc-based metal framework material is 400-650℃, preferably 550-600℃; the temperature rising speed is 1-10℃ / min, preferably 3-5℃ / min; and the calcination time is 1-10 hours, preferably 2-5 hours.

[0014] Further, the temperature of the calcination treatment in step S3 is 700-1000°C, preferably 800-900°C; the temperature increasing rate is 1-10°C / min, preferably 2-5°C / min; and the time is 1-12 hours, preferably 2-5 hours.

[0015] The loading amount of the noble metal-zinc intermetallic compound obtained in step S3 in the carbon carrier is 2%-50%, preferably 5%-30%.

[0016] The ultra-small ordered noble metal-zinc intermetallic compound catalyst embedded in mesoporous carbon of the present application has high catalytic activity and stability, and has great application prospect as an electrocatalyst in the field of energy conversion devices such as fuel cells and water electrolysis.

[0017] Compared with the prior art, the present application has the following advantages: (1) The noble metal-zinc intermetallic compound catalyst prepared by the present application has uniform particle size and high order degree, with an average particle size below 5 nm and an order degree above 90%, which can provide efficient catalytic sites for catalytic reactions.

[0018] (2) The noble metal-zinc intermetallic compound catalyst prepared by the present application is mostly located in the pores of the mesoporous carbon material, which can reduce direct contact with ionomer and inhibit the poisoning effect of sulfonate, thereby improving the activity and stability of the noble metal-based catalyst.

[0019] (3) In the noble metal-zinc intermetallic compound catalyst prepared by the present application, the spatial distribution between the intermetallic catalyst particles and the carbon carrier can alleviate the serious mass transfer resistance problem caused by uneven distribution of ionomer, and the mass transfer performance of the catalyst prepared by the present application is significantly improved compared with traditional carbon carriers.

[0020] (4) The preparation method of the present application is simple, which can avoid complex subsequent treatment processes such as acid and alkali soaking and washing, and has the potential for scale-up production. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 Figure 1 is a low-magnification transmission electron microscope image of the ultra-small ordered platinum-zinc intermetallic compound (PtZn / NC) electrocatalyst embedded in porous carbon nanofibers prepared in Example 1 of the present application, and the insert is a particle size distribution graph of the platinum-zinc intermetallic compound.

[0022] Figure 2 Figure 2 is a high-magnification transmission electron microscope image of the ultra-small ordered platinum-zinc intermetallic compound electrocatalyst (PtZn / NC) embedded in porous carbon nanofibers prepared in Example 1 of the present application.

[0023] Figure 3The X-ray diffraction pattern is shown for the ultra-small ordered platinum-zinc intermetallic compound electrocatalyst (PtZn / NC) embedded in porous carbon nanofibers prepared in Example 1 of this invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and should not be construed as limiting the invention.

[0025] Example 1 (1) Weigh 0.05 mmol of platinum tetrachloride and add it to 10 mL of deionized water. Sonicate at room temperature for 10 minutes to completely dissolve it. Then add 50 mg of porous carbon nanofibers and continue to sonicate at room temperature for 60 minutes. Then pour the solution into a petri dish and allow it to dry naturally at room temperature to obtain porous carbon nanofibers that adsorb the platinum precursor for later use.

[0026] (2) Weigh 15 mmol of zinc nitrate hexahydrate and add it to 300 mL of methanol. Stir for 20 minutes to form a zinc nitrate solution. Weigh 120 mmol of 2-methylimidazole and add it to 150 mL of methanol. Stir for 20 minutes to form a 2-methylimidazole solution. While stirring, add the zinc nitrate solution to the 2-methylimidazole solution and continue stirring at room temperature for 12 hours. Then centrifuge at 9000 rpm / min for 5 min. Wash the collected product three times with methanol. Place the obtained sample in a vacuum oven and vacuum dry at 80 °C to obtain a zinc-based metal framework material. Place the zinc-based metal framework material obtained above in a tube furnace and heat it to 600 °C at a rate of 5 °C / min under an argon atmosphere. Maintain this temperature for 2 hours to obtain carbon-supported zinc nanomaterials for later use.

[0027] (3) Place the porous carbon nanofibers that adsorbed the platinum precursor obtained in step (1) downstream of the gas flow in the tube furnace, and place the carbon-supported nano-zinc material obtained in step (2) upstream of the gas flow in the tube furnace. Under a hydrogen / argon (5%~10% hydrogen) mixed gas, raise the temperature to 800°C at a heating rate of 5°C / min and maintain it at this temperature for 2 hours. Then, allow it to cool naturally to room temperature to obtain the ultra-small ordered platinum-zinc intermetallic compound electrocatalyst (PtZn / NC) embedded in the porous carbon nanofibers.

[0028] from Figure 1 and Figure 2 It can be seen that the PtZn nanoparticles on the carbon nanofibers have small and uniform particle sizes, with an average particle size of less than 5 nm. Figure 3It can be seen that the sample has two obvious superlattice diffraction peaks near 25° and 31°, indicating that the synthesized PtZn intermetallic compound has a high degree of ordering.

[0029] The catalyst exhibits a half-wave potential higher than 0.92 V in a 0.1 mol / L perchloric acid solution saturated with oxygen, exceeding that of commercial 20% platinum-carbon catalysts, indicating its significant application potential in proton exchange membrane fuel cells.

[0030] Example 2 (1) Weigh 0.05 mmol of chloroplatinic acid and add it to 10 mL of deionized water. Sonicate at room temperature for 10 minutes to completely dissolve it. Then add 50 mg of ordered mesoporous carbon CMK-3 and continue to sonicate at room temperature for 60 minutes. Then pour the solution into a petri dish and let it dry naturally to obtain ordered mesoporous carbon CMK-3 that adsorbs platinum precursors for later use.

[0031] (2) Weigh 9 mmol of zinc nitrate hexahydrate and add it to 120 mL of deionized water. Stir for 20 minutes to form a zinc nitrate solution. Weigh 47.5 mmol of 2-methylimidazole and add it to 120 mL of deionized water. Stir for 20 minutes to form a 2-methylimidazole solution. While stirring, add the zinc nitrate solution to the 2-methylimidazole solution and continue stirring at room temperature for 10 hours. Then centrifuge at 9000 rpm / min for 5 min. Wash the collected product three times with deionized water and once with ethanol. Place the obtained sample in a vacuum oven and vacuum dry at 80 °C to obtain a zinc-based metal framework material. Place the zinc-based metal framework material obtained above in a tube furnace and heat it to 550 °C at a heating rate of 5 °C / min under an argon atmosphere. Maintain this temperature for 5 hours to obtain carbon-supported zinc nanomaterials for later use.

[0032] (3) The ordered mesoporous carbon CMK-3 with adsorbed platinum precursor obtained in step (1) is placed downstream of the gas flow in a tube furnace, and the carbon-supported zinc nanomaterial obtained in step (2) is placed upstream of the gas flow in a tube furnace. Under a hydrogen / argon (5%~10% hydrogen) mixed gas, the temperature is increased to 800℃ at a heating rate of 5℃ / min and maintained at this temperature for 2 hours. Then, it is naturally cooled to room temperature to obtain the ultra-small ordered platinum-zinc intermetallic compound electrocatalyst (PtZn / CMK-3) embedded in the ordered mesoporous carbon CMK-3. The PtZn / CMK-3 particles are uniform in size, with an average size of less than 5 nm, and have obvious superlattice diffraction peaks.

[0033] Example 3 (1) Weigh 0.02 mmol sodium chloropalladium and add it to 10 mL of deionized water. Sonicate at room temperature for 10 minutes to completely dissolve it. Then add 50 mg of porous carbon derived from metal-organic framework material (ZIF-8) and continue to sonicate at room temperature for 60 minutes. Then pour the solution into a petri dish and let it dry naturally to obtain porous carbon derived from metal-organic framework material that adsorbs palladium precursor, for later use.

[0034] (2) Weigh 15 mmol of zinc nitrate hexahydrate and add it to 100 mL of N,N-dimethylformamide. Stir for 20 minutes to form a zinc nitrate solution. Weigh 120 mmol of 2-methylimidazole and add it to 50 mL of N,N-dimethylformamide. Stir for 20 minutes to form a 2-methylimidazole solution. While stirring, add the zinc nitrate solution to the 2-methylimidazole solution and continue stirring at room temperature for 20 hours. Then centrifuge at 9000 rpm / min for 5 min. Wash the collected product three times with methanol. Place the obtained sample in a vacuum oven and vacuum dry at 80 °C to obtain a zinc-based metal framework material. Place the zinc-based metal framework material obtained above in a tube furnace and heat it to 600 °C at a rate of 5 °C / min under an argon atmosphere. Maintain this temperature for 2 hours to obtain carbon-supported zinc nanomaterials for later use.

[0035] (3) The ZIF-8-derived porous carbon with adsorbed palladium precursor obtained in step (1) is placed downstream of the gas flow in a tube furnace, and the carbon-supported zinc nanomaterial obtained in step (2) is placed upstream of the gas flow in the tube furnace. Under a hydrogen / argon (5%–10% hydrogen) mixed gas, the temperature is increased to 750°C at a heating rate of 3°C / min and maintained at this temperature for 2 hours. Then, it is naturally cooled to room temperature to obtain the ultra-small ordered palladium-zinc intermetallic compound electrocatalyst (PdZn / ZIF-C) embedded in the ZIF-8-derived porous carbon. The average particle size of PdZn / ZIF-C is less than 10 nm and has obvious superlattice diffraction peaks.

Claims

1. An intermetallic compound catalyst characterized in that, The catalyst comprises a porous carbon carrier and an ultra-small ordered noble metal-zinc intermetallic compound embedded inside the porous carbon carrier, wherein the porous carbon carrier is a mesoporous carbon material with a pore size of 2-50 nm; the ultra-small ordered noble metal-zinc intermetallic compound comprises zinc and at least one noble metal, and the intermetallic compound is a nanoparticle with an average particle size of not more than 5 nm.

2. The intermetallic compound catalyst according to claim 1, characterized in that, The noble metal is at least one selected from platinum, gold, palladium, iridium and ruthenium.

3. The intermetallic compound catalyst according to claim 1, characterized in that, The loading amount of the ultra-small ordered noble metal-zinc intermetallic compound in the porous carbon carrier is 2%-50%.

4. The intermetallic compound catalyst according to claim 1, characterized in that, The mesoporous carbon material is ordered mesoporous carbon CMK-3, porous carbon nanofiber, porous carbon nanotube, metal organic framework material derived porous carbon material or commercial porous carbon.

5. A preparation method of the intermetallic compound catalyst according to any one of claims 1-4, comprising the following steps: S1, dissolving a noble metal precursor in deionized water to obtain a noble metal precursor solution, then adding mesoporous carbon material, and ultrasonicating at room temperature to make it completely dispersed in the solution; Subsequently, the mesoporous carbon material adsorbed with the noble metal precursor is naturally dried at room temperature to obtain the mesoporous carbon material adsorbed with the noble metal precursor; S2, preparing a zinc nitrate solution and a 2-methyl imidazole solution, adding the zinc nitrate solution to the 2-methyl imidazole solution under stirring, continuing to stir for a period of time, then centrifuging, washing and drying to obtain a zinc-based metal framework material, which is calcined under an argon atmosphere to obtain a carbon-loaded nanometer zinc material; S3, placing the mesoporous carbon material adsorbed with the noble metal precursor obtained in step S1 downstream of the gas flow in a tube furnace, and placing the carbon-loaded nanometer zinc material obtained in step S2 upstream of the gas flow in the tube furnace, and calcining under a hydrogen / argon mixed gas to promote the nanometer zinc material upstream to form zinc metal vapor at high temperature, which is carried by the gas flow to react with the noble metal downstream to obtain the intermetallic compound catalyst.

6. The production method according to claim 5, wherein The noble metal precursor in step S1 is one or more selected from platinum tetrachloride, chloroplatinic acid, chloroauric acid, sodium chloropalladate, iridium trichloride and ruthenium trichloride.

7. The production method according to claim 5, wherein The mass ratio of the noble metal precursor to the mesoporous carbon material in step S1 is 1:2-1:20; the molar ratio of zinc nitrate to 2-methyl imidazole in step S2 is 1:1-1:10; and the mass ratio of the mesoporous carbon material adsorbed with the noble metal precursor to the carbon-loaded nanometer zinc material in step S3 is 1:1-1:

20.

8. The production method according to claim 5, wherein In step S2, the solvent used to dissolve zinc nitrate and 2-methyl imidazole is one or more selected from deionized water, methanol and N,N-dimethylformamide.

9. The production method according to claim 5, wherein In step S2, the calcination temperature of the zinc-based metal framework material is 400-650°C, and the time is 1-10 hours; and in step S3, the calcination temperature is 700-1000°C, and the time is 1-12 hours.

10. Application of the intermetallic compound catalyst according to any one of claims 1-4 as an electrocatalyst in a fuel cell or a water electrolysis device.

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