A method for preparing an ultra-low noble metal alloy supported M-N-C hybrid catalyst by separate vapor deposition and application

Abstract

The application discloses a kind of preparation ultra-low noble metal alloy supported M-N-C hybrid catalyst separation type vapor deposition method.First, N-C is synthesized as nitrogen-doped carbon carrier (specific surface area is greater than 800 m2g-1, particle size is about 90 nm) with 1, 10-phenanthroline monohydrate coated ZIF-8 composite precursor, low sublimation point temperature noble metal salt (such as platinum acetylacetone, rhodium acetylacetone, palladium acetylacetone and the like) is separated from transition metal salt (such as ferrous chloride, ferric chloride, ferrocene, iron acetylacetone, cobalt acetylacetone and the like) at different gasification temperatures to construct M-N-C supported noble metal alloy nanoparticle hybrid catalyst, which simplifies the steps of synthesizing composite catalyst, and successfully synthesizes ultra-low noble metal supported M-N-C hybrid catalyst.

Description

Technical Field

[0001] This invention belongs to the field of nanocatalytic materials technology, specifically relating to a separate vapor deposition method and application for preparing ultra-low noble metal alloy supported MNC hybrid catalysts. Background Technology

[0002] Despite significant progress in oxygen reduction (ORR) electrocatalysts, further performance enhancement remains a challenging task. Besides alloying and morphology control, the support material plays a crucial role in improving activity. Carbon materials such as carbon black, graphene, and carbon nanotubes are widely used as supports for platinum (Pt) catalysts due to their excellent electronic conductivity, chemical stability, and high specific surface area. However, traditional carbon supports are electrocatalytically inactive. Transition metal / nitrogen-doped carbon structures, such as Fe-NC, exhibit catalytic activity for ORR and can provide more active sites in fuel cells compared to traditional carbon supports. Furthermore, studies have revealed that the synergistic effect between Pt-based alloy nanoparticles and Co-NC active sites can promote catalytic performance.

[0003] However, these preparation methods involve acid etching, and the synthesis process often involves multiple washing and filtration steps, which is quite cumbersome. Furthermore, the thermal treatment of hydrogen at 600℃-900℃ also poses significant safety risks during the synthesis process. Developing an environmentally friendly hybrid catalyst preparation process is of great importance to the development of ORR catalysts. In addition, due to the price and resource constraints of Pt, improving Pt utilization and reducing Pt dosage has always been a key focus of Pt-based catalyst research and development.

[0004] This chapter describes a one-step thermal evaporation method in an inert gas atmosphere. Using Zn-ZIF encapsulated with 1,10-phenanthroline monohydrate as a precursor, NC was synthesized as the carbon support. Iron and platinum salts were then thermally evaporated at different temperatures to construct Fe-NC-supported PtFe alloy catalysts. This method simplifies the synthesis of hybrid catalysts and successfully synthesizes low-Pt electrocatalysts. Furthermore, due to the electronic modulation effect of the bimetallic compounds, the catalysts exhibit excellent activity and stability. Summary of the Invention

[0005] The main objective of this invention is to provide a method for preparing ultra-low precious metal alloy supported MNC hybrid catalysts by separate vapor deposition.

[0006] The technical solution adopted by this invention to solve its technical problem is:

[0007] A separate vapor deposition method for preparing ultra-low noble metal alloy supported MNC hybrid catalysts includes the following steps:

[0008] Step (1): Prepare Zn-ZIF rhombic dodecahedrons;

[0009] Step (2): Disperse Zn-ZIF rhombic dodecahedrons and 1,10-phenanthroline monohydrate in an ethanol / water mixed solution at a certain mass ratio (10:1 to 10:5) to form Zn-ZIF@Phen complex;

[0010] Step (3): Transfer the Zn-ZIF@Phen composite to a ceramic boat and calcine it at 700-1000℃ for 60-120 min in an inert gas environment (preferably argon or nitrogen). After cooling, grind it thoroughly to prepare the NC carrier.

[0011] Step (4): Prepare a quartz magnetic boat with three independent spaces, and label them as upstream space, midstream space and downstream space according to the direction of gas flow. Then, place the transition metal salt, noble metal salt and NC support in the upstream space, midstream space and downstream space of the quartz ceramic boat in sequence. Heat treat in an inert atmosphere (preferably argon or nitrogen) at 100℃-300℃ for 1h-3h. During this stage, the vaporization temperature of the noble metal salt is lower than that of the transition metal salt, so it preferentially vaporizes and deposits on the NC support. Then continue to heat treat at 500℃-800℃ for 1h-3h. During this stage, the transition metal salt vaporizes and deposits on the NC support. Then cool down with the furnace to finally obtain the MNC hybrid catalyst supported by noble metal alloy nanoparticles.

[0012] In one embodiment, step (2) involves dispersing Zn-ZIF rhombic dodecahedrons and 1,10-phenanthroline monohydrate in an ethanol / water mixed solution at a certain mass ratio (10:1 to 10:5) to form a Zn-ZIF@Phen complex.

[0013] In one embodiment, step (3) involves transferring the Zn-ZIF@Phen composite into a ceramic boat, calcining it at 700-1000℃ for 60-120 minutes in an inert gas (argon or nitrogen) environment, cooling it down, and then grinding it thoroughly to prepare the NC carrier.

[0014] Preferably, in step (4): the ratio of raw materials in the upstream, midstream, and downstream spaces is 10-100 mg transition metal salt: 1-50 mg precious metal salt: 40-100 mg NC carrier.

[0015] Preferably, the transition metal salt has a vaporization temperature of <800℃, and preferably includes FeCl2, FeCl3, Fe(C5H5)2, and FeC 15 H 21 O6, CoC 10 H14 At least one of the transition metal salts such as O4.

[0016] Preferably, the vaporization temperature of the precious metal salt is <300°C, and it preferably includes C. 10 H 14 O4Pt, C 15 H 21 O6Rh、C 10 H 14 O4Pd, C 15 H 21 At least one of the low vaporization temperature noble metal salts such as O6Ru.

[0017] The MNC hybrid catalyst supported on noble metal alloy nanoparticles prepared in this invention comprises noble metal alloy nanoparticles such as PtM, PdM, RuM, and RhM (where M is a transition metal such as Fe, Co, or Ni), with a noble metal loading of 0.5-2 wt% and a non-noble metal loading of 1-10 wt%, and a specific surface area of ​​600-1000 m². 2 g -1 .

[0018] The beneficial effects of this invention are:

[0019] (1) An NC support with a large external surface area was developed, which makes it easy for vaporized metal to be deposited and anchored on the NC support, so as to ensure uniform dispersion of metal atoms and efficient conversion of subsequent active sites.

[0020] (2) The present invention has a self-made quartz magnetic boat with three independent spaces, which can be used for the preparation of noble metal alloy supported MNC hybrid catalysts by separate vapor deposition.

[0021] (3) This method proposes a stepwise heat treatment, in which the corresponding metals are deposited in steps at the vaporization temperatures of noble metals and transition metals respectively, to prepare noble metal alloy supported MNC hybrid catalysts, and the noble metal loading can be adjusted in a very low range (0.5-2wt%).

[0022] (4) The noble metal alloy-supported MNC hybrid catalyst prepared exhibited excellent performance in the catalytic reaction, with a mass activity of 2.33 A mg. Pt -1 It also exhibits excellent stability, with only a 9.4% decrease in mass activity after 70,000 accelerated cycles. Attached Figure Description

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0024] Figure 1This is a physical image of the quartz magnetic boat with three independent spaces that was self-made in Example 1 of the present invention, and a schematic diagram of the synthesis of the MNC hybrid catalyst supported by noble metal alloy nanoparticles.

[0025] Figure 2 These are SEM images of the carbon support (NC) prepared in Example 1 of this invention, where (a) is an SEM image and (b) is a particle size distribution graph.

[0026] Figure 3 These are TEM images of the MNC hybrid catalyst supported on noble metal alloy nanoparticles prepared in Example 1 of this invention, where (a) is a SEM image and (b) is a particle size distribution graph.

[0027] Figure 4 These are aberration-corrected electron microscopy (SEM) images of the MNC hybrid catalyst supported on noble metal alloy nanoparticles prepared in Example 1 of this invention. (a) is an AC-HADDF-SEM image, and (b) is a higher resolution STEM image.

[0028] Figure 5 The above are the ORR electrocatalytic performance test graphs of the catalyst prepared in Example 1 of this invention, where (a) is the accelerated decay polarization curve after 70,000 cycles, and (b) is the mass activity of the catalyst. Detailed Implementation

[0029] Example 1

[0030] Synthesis of Zn-ZIF rhombic dodecahedron:

[0031] (1) Dissolve 2.97g Zn(NO3)2·6H2O and 6.57g 2-methylimidazole in 100ml of methanol solution respectively, and stir vigorously to form homogeneous solutions A and B.

[0032] (2) At 600 rpm, the solution B from step (1) was quickly poured into the solution A from step (2) to form a white solution. The mixture was stirred and reacted at room temperature for 12 h.

[0033] (3) The material obtained in step (2) is centrifuged at 10,000 rpm, washed three times with methanol solution, and then dried overnight at 70°C to form Zn-ZIF rhombic dodecahedrons.

[0034] Synthesis of Zn-ZIF@Phen complex:

[0035] (1) Disperse 1.0g of Zn-ZIF rhombic dodecahedrons ultrasonically in a solution of 20mL anhydrous ethanol and 10mL ultrapure water for 1h until uniformly dispersed.

[0036] (2) Add 250 mg of 1,10-phenanthroline monohydrate, disperse by ultrasonication for 1 h, and stir at 600 rpm for 12 h. (3) Stir and evaporate the solvent at 80 °C, place in a vacuum drying oven at 70 °C to dry thoroughly, scrape off the sample with a scraper, grind, and obtain Zn-ZIF@Phen complex.

[0037] Synthesis of NC vectors:

[0038] (1) 500 mg of Zn-ZIF@Phen complex was thoroughly ground and then transferred to a ceramic boat.

[0039] (2) The NC carrier was calcined in an argon atmosphere at 1000℃ for 60 min (heating rate of 10℃ / min), and then cooled to room temperature in the furnace. The carrier was collected to obtain the NC carrier.

[0040] Synthesis of MNC hybrid catalysts supported on noble metal alloy nanoparticles:

[0041] (1) Sequentially add 70mg FeCl2·4H2O, 15mg C 10 H 14 O4Pt and 80mg NC carrier were placed at three locations on the ceramic boat: upstream, midstream, and downstream.

[0042] (2) Heat treatment is carried out in an inert atmosphere (argon or nitrogen) at 100℃-300℃ for 1h-3h. During this stage, the vaporization temperature of the noble metal salt is lower than that of the transition metal salt, so it preferentially vaporizes and deposits on the NC support. Then, the temperature is raised to 500℃-800℃ for 1h-3h. During this stage, the transition metal salt vaporizes and deposits on the NC support. Then, the temperature is lowered with the furnace to finally obtain the MNC hybrid catalyst supported by noble metal alloy nanoparticles.

[0043] Example 2

[0044] Similar to Example 1, except that C 10 H 14 Replace O4Pt with C 15 H 21 O6Rh

[0045] Example 3

[0046] Similar to Example 1, except that C 10 H 14 Replace O4Pt with C 10 H 14 O4Pd

[0047] Example 4

[0048] Similar to Example 1, except that C10 H 14 Replace O4Pt with C 15 H 21 O6Ru

[0049] Example 5

[0050] Similar to Example 1, except that FeCl2 is replaced with CoC 10 H 14 O4

[0051] Example 6

[0052] Similar to Example 1, except that FeCl2 is replaced with CoC 10 H 14 O4, C 10 H 14 Replace O4Pt with C 15 H 21 O6Rh

[0053] Example 7

[0054] Similar to Example 6, C 10 H 14 Replace O4Rh with C 10 H 14 O4Pd

[0055] Example 8

[0056] Similar to Example 6, except that C 10 H 14 Replace O4Rh with C 10 H 14 O4Ru

[0057] Electrocatalytic testing:

[0058] The MNC hybrid catalyst supported on noble metal alloy nanoparticles prepared in Example 1 was used.

[0059] In this work, all electrochemical measurements were performed on a CHI760e electrochemical workstation with a standard three-electrode system. The reference electrode was a saturated calomel electrode (SCE). A graphite rod was used as the counter electrode. A ring-disk electrode (RRDE, 0.2475 cm⁻¹) was used. 2 This electrode was used as the working electrode. Before electrochemical testing, it was successively polished 200 times with Al2O3 grinding powder with particle sizes of 5μm, 1μm, and 0.3μm, using a figure-eight polishing method to ensure even force distribution and a smooth surface. After polishing with each particle size, the electrode was ultrasonically cleaned 3-5 times with ultrapure water to remove the grinding powder. Ethanol can be used during the cleaning process to remove adsorbed organic matter from the electrode surface.

[0060] Before electrode preparation, the catalyst needs to be formulated into ink and sonicated for at least one hour. The catalyst ink was prepared by ultrasonically dispersing 4 mg of catalyst in 1 mL of a solution containing 600 μL isopropanol, 390 μL ultrapure water, and 10 μL 5% Nafion solution. Then, 16.8 μL of the catalyst ink was coated onto a rotating disk electrode (RRDE, disk area: 0.2475 cm²). 2 The area of ​​the Pt ring is 0.1866 cm². 2 The catalyst was then dried. Finally, the catalyst loading was approximately 0.4 mg / cm³. -2 By using the transformation equation E RHE =E SCE +0.2415+0.059pH, the potential in this work is called the reversible hydrogen electrode (RHE) potential.

[0061] Before measuring ORR, the catalyst on the working electrode must be electrochemically cleaned using cyclic voltammetry. First, in a 0.1 M HClO4 solution saturated with N2, at 100 mV s... -1 The scan rate was maintained between 0.03V and 1.30V (vs. RHE) until the CV curves completely overlapped to ensure catalyst cleanliness. Then, a scan rate of 50 mV s was applied. -1 CV curves were acquired at a scan rate of 0.03V–1.05V (vs. RHE). The electrochemical active area of ​​Pt on the working electrode was determined by calculating the area of ​​the hydrogen region in the CV curve. Then, the gas was converted to O2, and O2 was continuously introduced for at least 20 minutes to ensure oxygen saturation in the electrolyte. The rotator was set to an appropriate speed and turned on, typically 1600 rpm or 900 rpm, followed by a scan rate of 10 mV / s. -1 LSV curves were acquired at a scan rate in the potential range of 0.3V–1.1V (vs. RHE). The half-wave potential of the oxygen reduction reaction could be obtained from the LSV curves, and the kinetic current and mass activity of the catalyst were calculated using the Koutecky-Levich (KL) equation. All electrode potential data were 80% IR compensated.

[0062] The results showed that the MNC hybrid catalyst supported on noble metal alloy nanoparticles exhibited excellent oxygen reduction reaction (ORR) activity and superior stability in acidic media. The mass activity reached 2.33 A mg. Pt -1 It also exhibits excellent stability, with only a 9.4% decrease in mass activity after 70,000 accelerated cycles.

[0063] The above description is merely a preferred embodiment of the present invention, and therefore should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made in accordance with the scope of the patent and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A separate vapor deposition method for preparing ultra-low noble metal alloy supported MNC hybrid catalysts, comprising the following steps: Step (1): Prepare Zn-ZIF rhombic dodecahedrons; Step (2): Disperse Zn-ZIF rhombic dodecahedrons and 1,10-phenanthroline monohydrate in an ethanol / water mixed solution at a mass ratio of 10:1 to 10:5 to form Zn-ZIF@Phen complex; Step (3): The Zn-ZIF@Phen composite was transferred to a ceramic boat and calcined at 700-1000℃ for 60 min-120 min in an inert gas environment. After cooling, it was thoroughly ground to prepare the NC support. Step (4): Prepare a quartz magnetic boat with three independent spaces, and label them as upstream space, midstream space and downstream space according to the direction of gas flow. Then, place the transition metal salt, noble metal salt and NC support into the upstream space, midstream space and downstream space of the quartz ceramic boat in sequence. In an inert atmosphere, heat treat at 100 ℃ - 300 ℃ for 1 h - 3 h, then continue to heat treat at 500 ℃ - 800 ℃ for 1 h - 3 h, and then cool down with the furnace to finally obtain the MNC hybrid catalyst supported by noble metal alloy nanoparticles.

2. The method according to claim 1, characterized in that, Step (1) includes the following steps: 2.97 g Zn(NO3)2·6H2O and 6.57 g 2-methylimidazole are dissolved in 100 ml of methanol solution respectively and stirred vigorously to form a homogeneous solution; then, the two homogeneous solutions are mixed and stirred for 12 h - 24 h; finally, Zn-ZIF rhombic dodecahedrons with a size of 80 nm – 150 nm are obtained by centrifugation.

3. The method according to claim 1, characterized in that, In step (2), 0.5 g – 5 g of Zn-ZIF rhombic dodecahedrons were uniformly dispersed in a mixed solution of 20 mL of anhydrous ethanol and 10 mL of ultrapure water, and 100 mg – 1 g of 1,10-phenanthroline monohydrate was added. The mixture was stirred for 5 h – 20 h. The solvent was then evaporated at 80 ºC and thoroughly dried in a vacuum drying oven at 70 ºC. The sample was scraped off with a scraper and ground.

4. The method according to claim 1, characterized in that, In step (4), the ratio of raw materials in the upstream, midstream and downstream spaces is 10-100 mg transition metal salt: 1-50 mg precious metal salt: 40-100 mg NC carrier.

5. The method according to claim 1, characterized in that... In step (4), the transition metal salt is a transition metal salt with a vaporization temperature below 800 °C.

6. The method according to claim 5, characterized in that... The transition metal salts with temperatures below 800 °C include FeCl2, FeCl3, Fe(C5H5)2, and FeC. 15 H 21 O6, CoC 10 H 14 At least one of O4.

7. The method according to claim 1, characterized in that, In step (4), the precious metal salt is a precious metal salt with a low vaporization temperature of less than 300°C.

8. The method according to any one of claims 1-7 prepares a noble metal alloy nanoparticle-supported MNC hybrid catalyst.

9. The MNC hybrid catalyst supported on noble metal alloy nanoparticles according to claim 8, characterized in that: The noble metal alloy nanoparticles are PtM, PdM, RuM, and RhM, where M is at least one of the transition metals Fe, Co, and Ni. The noble metal loading is 0.5-2 wt%, the non-noble metal loading is 1-10 wt%, and the specific surface area is 600-1000 m². 2 g -1 .

10. The application of the MNC hybrid catalyst supported on noble metal alloy nanoparticles according to claim 8 in electrocatalytic oxygen reduction and proton exchange membrane fuel cells.

Images