A size-controllable carbon-supported PtZn intermetallic compound electrocatalyst, a preparation method and application thereof

Abstract

The application discloses a size-controllable carbon-supported PtZn intermetallic compound electrocatalyst and a preparation method and application thereof, and belongs to the technical field of nanometer catalysts and preparation thereof.The electrocatalyst is a long-range ordered face-centered tetragonal structure PtZn intermetallic compound, Pt and Zn are arranged alternately in atomic layers, and the atomic ratio of Pt to Zn is close to 1:1; the long-range ordered structure not only makes the regulation of transition metals fully play, but also makes the chemical bond formed by Pt atoms more stable transition metal atoms, so that the transition metal atoms are not easy to be dissolved under acidic conditions, and the catalytic activity and stability are further improved. In the application, the size-controllable carbon-supported PtZn intermetallic compound electrocatalyst can be obtained without introducing a surfactant and a protective agent, and the preparation method has the advantages of simplicity and easy implementation.

Description

Technical Field

[0001] This invention belongs to the field of nanocatalysts and their preparation technology, specifically relating to the synthesis of a size-controllable carbon-supported PtZn intermetallic compound and its application in proton exchange membrane fuel cells, high-temperature phosphoric acid fuel cells and other oxygen reduction reactions under acidic environments. Background Technology

[0002] Proton exchange membrane fuel cells (PEMFCs), as electrochemical power generation devices, do not involve a heat engine process and are therefore not limited by the Carnot cycle, exhibiting high energy conversion efficiency (40%–60%). They are also environmentally friendly, emitting almost no nitrogen oxides or sulfur oxides. Currently, Pt-based electrocatalysts remain the preferred choice for commercial PEMFCs. Compared to non-precious metal electrocatalysts, they possess excellent activity and durability in acidic media, thus improving the ORR rate. However, due to the rarity of Pt metal, Pt-based electrocatalysts account for approximately 40–50% of the cost. Therefore, developing platinum-based electrocatalysts with higher oxygen reduction activity and greater stability remains crucial.

[0003] To reduce the amount of Pt metal used and improve the activity of Pt / C electrocatalysts, researchers have conducted extensive work, including alloying Pt-based electrocatalysts, reducing the proportion of alloy components in Pt-based electrocatalysts, optimizing particle size and crystal facets, and adopting ordered intermetallic compound structures. However, the preparation of intermetallic compound electrocatalysts currently mostly requires the addition of surfactants and protective agents (such as hexadecyltrimethylammonium bromide, tri-n-octylphosphine oxide, SiO2, MgO, etc.) to the reaction system, which limits the growth of alloy particles under high-temperature heat treatment, thus obtaining small-particle intermetallic compound electrocatalysts. This not only increases the difficulty and complexity of preparation but also introduces additional impurities into the original system, affecting the intrinsic activity and electrochemical active area of ​​the electrocatalyst. Summary of the Invention

[0004] Therefore, the present invention aims to provide a size-controllable carbon-supported PtZn intermetallic compound electrocatalyst, its preparation method, and its applications. This preparation method can obtain highly ordered carbon-supported PtZn intermetallic compound electrocatalysts with different particle sizes without introducing additional surfactants or protecting agents. The method is simple and easy to implement, has the potential for large-scale preparation, and its activity and stability are superior to commercial platinum-carbon electrocatalysts.

[0005] To achieve the above objectives, the present invention employs the following technical solution:

[0006] A size-controllable carbon-supported PtZn intermetallic compound electrocatalyst, wherein the electrocatalyst is a long-range ordered face-centered tetragonal structure, the PtZn alloy is highly ordered, Pt and Zn are arranged in alternating atomic layers, and the Pt to Zn atomic ratio is close to 1:1.

[0007] Furthermore, the diameter of the size-controllable carbon-supported PtZn intermetallic compound electrocatalyst is 5–10 nm.

[0008] Another aspect of the present invention provides a method for preparing the above-mentioned carbon-supported PtZn intermetallic compound electrocatalyst, which mainly includes the following steps:

[0009] (1) Take a quantitative amount of platinum ion / organic solvent precursor solution and zinc ion / organic solvent precursor solution into the reaction vessel, then add alkaline solution dissolved in organic solvent, control pH>13, ultrasonically disperse evenly, add amorphous carbon powder dispersion dispersed in organic solvent, continue ultrasonically disperse evenly, and obtain a uniformly dispersed slurry.

[0010] (2) Stir and keep warm at 110-130℃ for 2-5 hours, cool to 60-80℃, add an appropriate amount of deionized water, continue stirring and keeping warm for 2-5 hours, then wash with water, filter, dry, grind to obtain solid powder.

[0011] (3) The solid powder obtained in step (2) is heat-treated at 500-700°C for 1-4 hours under a hydrogen / inert gas atmosphere to obtain a carbon-supported PtZn intermetallic compound electrocatalyst, or after heat treatment and acid washing, a carbon-supported PtZn intermetallic compound electrocatalyst is obtained.

[0012] Furthermore, the organic solvent mentioned in step (1) includes ethylene glycol.

[0013] Furthermore, in step (1), the source of platinum ions is selected from platinum chlorate, potassium chloroplatinate, and potassium chloroplatinate; the source of zinc ions is selected from zinc nitrate, zinc chloride, and zinc sulfate.

[0014] Furthermore, the alkaline component in the alkaline solution in step (1) is NaOH or KOH.

[0015] Further, in step (1), the molar ratio of zinc ions to platinum ions is 2:1 to 20:1, the ultrasonic time is 30 min to 3 h, the pH value of the slurry is controlled at 13 to 14, and the final concentration of platinum ions is 0.1 to 20 mM.

[0016] Furthermore, in step (1), the total mass ratio of zinc ions and platinum ions to the mass ratio of amorphous carbon powder is 1:100 to 1:2.

[0017] Furthermore, after the stirring and heat preservation in step (2) is completed, the pH value of the slurry is controlled at 7 to 9.

[0018] Furthermore, the specific process of water washing in step (2) is to wash with ultrapure water until the XRF detection shows no chloride ions in the filtrate.

[0019] Furthermore, the drying in step (2) is specifically vacuum drying at a temperature of 40–90°C.

[0020] Furthermore, in step (3), the heat treatment is carried out in a tube furnace, with the heating rate controlled at 1 to 5 °C / min and the cooling rate controlled at 1 to 2 °C / min; the pickling time is determined according to the amount of Zn in the solid powder after high-temperature heat treatment.

[0021] Furthermore, the inert gas in step (3) includes nitrogen, argon, helium and neon.

[0022] Further, the specific process of heat treatment in step (3) is as follows: under a reducing atmosphere with a hydrogen / argon volume ratio of 10:90, the solid powder obtained in step (2) is heated to 500-700℃ at 5℃ / min and held for 1-4 hours; then it is naturally cooled to room temperature.

[0023] Furthermore, in step (3), the heat treatment temperature is 600℃ and the time is 1 to 2 hours.

[0024] Furthermore, the specific process of acid washing in step (3) is to acid wash it in 0.1M HClO4 for 4 to 12 hours.

[0025] The present invention also provides the application of the above-mentioned carbon-supported PtZn intermetallic compound electrocatalyst in redox reactions under acidic conditions.

[0026] Furthermore, the applications include those in proton exchange membrane fuel cells and high-temperature phosphoric acid fuel cells.

[0027] Compared with existing technologies, the size-controllable carbon-supported PtZn intermetallic compound electrocatalyst of the present invention has the following advantages:

[0028] 1. The preparation method of the present invention does not introduce additional surfactants and protective agents, the synthesis system is simple, the synthesis method is convenient and effective, and it has the potential for large-scale production;

[0029] 2. Compared with a single Pt / C catalyst, the electrocatalyst of the present invention improves catalytic performance and reduces the cost of the electrocatalyst through alloying;

[0030] 3. This invention further enhances the oxygen reduction activity and stability of the electrocatalyst through an ordered alloy catalyst preparation method;

[0031] 4. The particle size of the carbon-supported PtZn intermetallic compound prepared by this invention is controllable;

[0032] 5. This catalyst has a wide range of applications and can be used as an oxygen reduction electrocatalyst in proton exchange membrane fuel cells, high-temperature phosphoric acid electrolyte fuel cells, and other acidic environments. Attached Figure Description

[0033] To more clearly illustrate the embodiments of the present invention, the accompanying drawings involved in the embodiments will be briefly described below.

[0034] Figure 1 X-ray diffraction (XRD) patterns of carbon-supported PtZn electrocatalysts with different particle sizes prepared in Examples 1-5.

[0035] Figure 2 X-ray diffraction patterns of the carbon-supported PtZn intermetallic compound electrocatalysts prepared in Examples 1 and 8, and the carbon-supported Pt electrocatalyst prepared in Comparative Example 2.

[0036] Figure 3 Transmission electron microscopy (TEM) images of the carbon-supported PtZn electrocatalysts prepared in Example 1(A) and Example 7(B) before heat treatment and the carbon-supported Pt electrocatalysts prepared in Comparative Example 2(C) before heat treatment.

[0037] Figure 4 Oxygen reduction polarization curves of the carbon-supported PtZn intermetallic compound electrocatalyst prepared in Example 1 and the commercial carbon-supported Pt electrocatalyst of Comparative Example 1 in oxygen-saturated 0.1M perchloric acid electrolyte.

[0038] Figure 5 Cyclic voltammetry scans of the carbon-supported PtZn intermetallic compound electrocatalyst prepared in Example 1 and the commercial carbon-supported Pt electrocatalyst of Comparative Example 1 in nitrogen-saturated 0.1M perchloric acid electrolyte. Detailed implementation method:

[0039] The present invention will be further described below with reference to specific embodiments, which will enable those skilled in the art to better understand the invention. However, the present invention is not limited to these specific embodiments.

[0040] Example 1:

[0041] A method for preparing a size-controllable carbon-supported PtZn intermetallic compound electrocatalyst includes the following steps:

[0042] (1) Prepare a 3.7 mg / mL chloroplatinic acid / ethylene glycol solution and a 10 mg / mL zinc nitrate / ethylene glycol solution. Transfer 5.390 mL of platinum salt solution and 1.337 mL of zinc salt solution into round-bottom flasks, respectively.

[0043] (2) Weigh 98 mg NaOH and dissolve it in 20 mL of ethylene glycol solution, then transfer it to the round-bottom flask mentioned above and sonicate for 30 minutes to make the solution evenly mixed; weigh 80 mg amorphous carbon powder and disperse it in 30 mL of ethylene glycol, then transfer it to the round-bottom flask in the same way and sonicate for 3 hours to obtain a uniformly dispersed slurry.

[0044] (3) Place the above round-bottom flask in an oil bath and heat it at 130°C for 3 hours with magnetic stirring. Then lower the temperature to 60°C, add 50 mL of ultrapure water, and continue stirring at 60°C for 3 hours. Then wash and filter with ultrapure water, dry under vacuum at 80°C, collect the sample and grind it to obtain solid powder.

[0045] (4) Place the above solid powder in a tube furnace and heat it to 600°C at a heating rate of 5°C / min under a 10% H2 / Ar atmosphere. Maintain the temperature for 2 hours and then allow it to cool naturally to room temperature to obtain the target product.

[0046] XRD analysis confirmed the product's crystal structure to be L10-PtZn. The catalyst particle size was 6.3 nm, and the catalyst order was 82%.

[0047] Catalyst grain size calculation:

[0048]

[0049] Where d is the grain size (nm), representing the average thickness of the grain in the direction perpendicular to the (hk1) crystal plane. λ is the wavelength of the incident X-rays (here taken as 1.54056). θ is the incident angle of the X-rays on the crystal plane. B is the measured half-width at half-maximum (FWHM) of the diffraction peak in the sample, which, after double-line correction and instrument factor correction, needs to be converted to radians (rad) during the calculation.

[0050] Catalyst order calculation:

[0051]

[0052] I 110 I is the diffraction peak intensity of the (110) crystal plane. 111 The intensity of the diffraction peak of the (111) crystal plane.

[0053] Example 2:

[0054] The preparation method is the same as that in Example 1, except that the heating time in step (4) is 1 hour.

[0055] XRD analysis confirmed the product's crystal structure to be L10-PtZn. The catalyst grain size was 5.5 nm, with an order degree of 66%.

[0056] Example 3:

[0057] The preparation method is the same as that in Example 1, except that the heating temperature in step (4) is 500°C.

[0058] XRD analysis confirmed the product's crystal structure to be L10-PtZn. The catalyst grain size was 5.4 nm, with an order degree of 64%.

[0059] Example 4:

[0060] The preparation method is the same as that in Example 1, except that the heating temperature in step (4) is 500°C and the heating time is 1 hour.

[0061] XRD analysis confirmed the product's crystal structure to be L10-PtZn. The catalyst grain size was 4.8 nm, with an order degree of 54%.

[0062] Example 5:

[0063] The preparation method is the same as that in Example 1, except that the heating temperature in step (4) is 700°C and the heating time is 1 hour.

[0064] XRD analysis confirmed the product's crystal structure to be L10-PtZn. The catalyst grain size was 9.1 nm, with an order degree of 72%.

[0065] Example 6:

[0066] The preparation method is the same as that in Example 1, except that 8.085 mL of platinum salt and 2.005 mL of zinc salt are removed in step (1).

[0067] XRD analysis confirmed the product's crystal structure to be L10-PtZn. The catalyst grain size was 6.8 nm, with an order degree of 74%.

[0068] Example 7:

[0069] (1) Prepare a 3.7 mg / mL chloroplatinic acid / ethylene glycol solution and a 10 mg / mL zinc nitrate / ethylene glycol solution. Transfer 5.390 mL of platinum salt solution and 13.370 mL of zinc salt solution into round-bottom flasks, respectively.

[0070] (2) Weigh 97 mg NaOH and dissolve it in 20 mL of ethylene glycol solution, then transfer it to the round-bottom flask mentioned above and sonicate for 30 minutes to mix the solution evenly; weigh 80 mg amorphous carbon powder and disperse it in 30 mL of ethylene glycol, then transfer it to the round-bottom flask in the same way and sonicate for 3 hours to obtain a uniformly dispersed slurry.

[0071] (3) Place the above round-bottom flask in an oil bath and heat it at 130°C for 3 hours with magnetic stirring. Then lower the temperature to 60°C, add 50 mL of ultrapure water, and continue stirring at 60°C for 3 hours. Then wash and filter with ultrapure water, dry under vacuum at 80°C, collect the sample and grind it to obtain solid powder.

[0072] (4) The above solid powder is placed in a tube furnace and heated to 600°C at a heating rate of 5°C / min under a 10% H2 / Ar atmosphere. The temperature is maintained for 2 hours and then cooled naturally to room temperature to obtain solid powder.

[0073] (5) Place the above powder in 100 mL of 0.1 M perchloric acid solution, stir at room temperature for 6 hours, filter, and vacuum dry at 80 °C to obtain the target product.

[0074] Example 8:

[0075] The preparation method is the same as in Example 3, except that 26.740 mL of zinc salt is removed in step (1).

[0076] XRD analysis confirmed the product's crystal structure to be L10-PtZn. The catalyst grain size was 4.6 nm, with an order degree of 68%.

[0077] Comparative Example 1:

[0078] The carbon-supported platinum catalyst was a commercially available Pt / C catalyst (20 wt% platinum) from Johnson Mattey, UK.

[0079] Comparative Example 2:

[0080] The preparation method is the same as in Example 1, except that zinc salt was not added in step (1) to prepare a platinum-carbon catalyst. XRD confirmed that the product was a face-centered cubic carbon-supported platinum catalyst, and the obtained material had low oxygen reduction activity.

[0081] Example 9:

[0082] Electrochemical performance testing methods

[0083] 3 mg of the catalysts prepared in the examples and comparative examples were added to a mixed solution of 2.9 mL anhydrous ethanol and 0.1 mL Nafion (5 wt%). After ultrasonic dispersion for at least 30 minutes, a uniformly mixed ink was obtained. 10 μL of the prepared ink was evenly coated onto a glassy carbon rotating disk electrode using a pipette, and then allowed to evaporate completely. This was used as the working electrode, with a platinum wire as the counter electrode and a saturated calomel electrode as the reference electrode. The catalyst was first activated by scanning the potential range of 0.05–1.2 V (relative to the reversible hydrogen electrode) for 20 cycles in a 0.1 M perchloric acid solution saturated with nitrogen at a scan rate of 50 mV / s. Cyclic voltammetry curves of different catalysts were recorded at the 20th cycle. Subsequently, linear scanning voltammetry curves of different catalysts were obtained by scanning the potential range of 0–1.2 V in an oxygen-saturated 0.1 M perchloric acid solution at a scan rate of 10 mV / s and a rotation speed of 1600 rpm within the potential range of 0–1.2 V.

[0084] from Figure 1 As can be seen, the alloy particles of the carbon-supported PtZn intermetallic compound electrocatalyst prepared by this invention have a consistent structure, all being L10-PtZn intermetallic compounds, and the particle size gradually increases with the increase of heat treatment temperature.

[0085] from Figure 2 As can be seen, with the increase of Zn salt content in the feed, the particle size of carbon-supported PtZn intermetallic compound electrocatalyst decreases; at the same time, with the introduction of Zn element, the lattice constant changes significantly.

[0086] from Figure 3 As can be seen from the above, the alloy particles of the carbon-supported PtZn intermetallic compound electrocatalyst prepared by this invention are uniformly distributed and show no obvious agglomeration.

[0087] from Figure 4 As can be seen, the electrocatalyst prepared by this invention introduces the alloying element Zn, which significantly improves the catalytic activity of the electrocatalyst, and its mass-specific activity is superior to that of commercial Pt / C catalysts.

[0088] from Figure 5 As can be seen, the electrocatalyst prepared by this invention has a significantly better area-to-area activity than commercial Pt / C catalysts, and has potential application value.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A size-controllable carbon-supported PtZn intermetallic compound electrocatalyst, characterized in that, The electrocatalyst has a face-centered tetragonal structure, and the PtZn alloy is highly ordered, with Pt and Zn arranged alternately in atomic layers; The preparation method of the carbon-supported PtZn intermetallic compound electrocatalyst includes the following steps: (1) Take a quantitative amount of platinum ion / organic solvent precursor solution and zinc ion / organic solvent precursor solution into the reaction vessel, then add alkaline solution dissolved in organic solvent, control pH>13, disperse evenly, add amorphous carbon powder dispersion dispersed in organic solvent, continue to disperse evenly, and obtain slurry; (2) Stir and keep the slurry obtained in step (1) at 110~130℃ for 2~5h, cool it to 60~80℃, add an appropriate amount of deionized water, continue stirring and keeping it warm for 2~5h, then wash with water, filter, dry, grind to obtain solid powder. (3) The solid powder obtained in step (2) is heat-treated at 500~700℃ for 1~4h under a hydrogen / inert gas atmosphere to obtain a carbon-supported PtZn intermetallic compound electrocatalyst, or after heat treatment and acid washing, a carbon-supported PtZn intermetallic compound electrocatalyst is obtained.

2. The carbon-supported PtZn intermetallic compound electrocatalyst as described in claim 1, characterized in that, The atomic ratio of Pt to Zn in the electrocatalyst is 1:

1.

3. The carbon-supported PtZn intermetallic compound electrocatalyst as described in claim 1, characterized in that, The organic solvent mentioned in step (1) includes ethylene glycol; the source of platinum ions is selected from one or more combinations of platinum chlorate, potassium chloroplatinate, and potassium chloroplatinate; the source of zinc ions is selected from one or more combinations of zinc nitrate, zinc chloride, and zinc sulfate; the alkaline component in the alkaline solution is NaOH or KOH.

4. The carbon-supported PtZn intermetallic compound electrocatalyst as described in claim 1, characterized in that, In step (1), the molar ratio of zinc ions to platinum ions is 2:1 to 20:1; the pH value of the slurry is controlled at 13 to 14, the final concentration of platinum ions is 0.1 to 20 mM; and the mass ratio of the total mass of zinc ions and platinum ions to the mass of amorphous toner is 1:100 to 1:

2.

5. The carbon-supported PtZn intermetallic compound electrocatalyst as described in claim 1, characterized in that, After the stirring and heat preservation in step (2) is completed, the pH value of the slurry is controlled at 7~9.

6. The carbon-supported PtZn intermetallic compound electrocatalyst as described in claim 1, characterized in that, In step (3), the heat treatment is carried out in a tube furnace, with the heating rate controlled at 1~5℃ / min and the cooling rate controlled at 1~2℃ / min; the inert gases include nitrogen, argon, helium and neon.

7. The carbon-supported PtZn intermetallic compound electrocatalyst as described in claim 1, characterized in that, The specific process of heat treatment in step (3) is as follows: under a reducing atmosphere with a hydrogen / argon volume ratio of 10:90, the solid powder obtained in step (2) is heated to 500~700℃ at 5℃ / min, held for 1~4 hours, and then naturally cooled to room temperature.

8. The application of the carbon-supported PtZn intermetallic compound electrocatalyst according to claim 1 or 2 in redox reactions under acidic conditions.

9. The application as described in claim 8, characterized in that, The applications include those in proton exchange membrane fuel cells and high-temperature phosphoric acid fuel cells.

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