A flower-shaped PtAl nanocrystalline catalyst and its preparation method and application

Abstract

The present invention discloses a flower-shaped PtAl nanocrystalline catalyst and its preparation method and application, which belongs to the field of electrocatalysis technology. The catalyst particle size is 20 to 200 nm and is composed of two elements, Pt and Al. Al accounts for 2 to 30% of the mass of the flower-shaped PtAl nanocrystalline catalyst. Al is doped in the Pt nanocrystal in the form of atoms. Ethylenediamine molecules are used as a complexing agent. SO3 2‑ The flower-shaped PtAl nanocrystals are produced in a reactor by co-reduction using ethylene glycol as a reducing agent, using a directional adsorbent to regulate the growth rate of the crystal face. The invention also discloses the application of these PtAl nanocrystals in oxygen reduction reactions. Due to the presence of stress and electronic effects, as well as the high stability of Pt and Al in acidic electrolytes, the flower-shaped PtAl nanocrystal catalysts provided by the invention exhibit high catalytic activity and stability in oxygen reduction reactions.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrocatalysis, and in particular relates to a flower-shaped PtAl nanocrystalline catalyst and a preparation method and application thereof. Background Art

[0002] As a high-energy-density, zero-carbon, renewable energy carrier, hydrogen will play an increasingly important role in the adjustment of energy structure. It is estimated that by 2050, 20% of the world's CO2 emission reduction will be achieved through hydrogen substitution. By then, hydrogen consumption will account for 18% of the world's energy market. Compared with hydrogen energy utilization methods such as hydrogen-fueled steam turbines, hydrogen fuel cells are more efficient energy conversion devices. They can directly convert the chemical energy stored in hydrogen fuel and oxidant into electrical energy through electrochemical reactions at lower temperatures (<100°C). They are green and environmentally friendly, have high energy conversion efficiency (40%-60%), high specific energy, and highly stable operation. They are considered to be the core technology in the hydrogen energy application system. However, in the large-scale application of hydrogen fuel cells, the high cost, low activity and poor stability of catalysts have always been the core problems that have plagued their development, mainly manifested in the following aspects:

[0003] 1. Currently, the commercial cathode catalyst for fuel cells is a carbon-supported platinum catalyst, which has high production costs. The oxygen reduction reaction activity of non-platinum catalysts is low, which greatly reduces the output power of the fuel cell. Improving the utilization rate of metal platinum is the key to reducing the cost of fuel cells.

[0004] 2. Other metals, such as Ni, Co, and Fe atoms, doped into Pt nanocrystals can regulate the activity of Pt catalysts through stress effects and electronic effects, but Ni, Co, and Fe atoms are easily precipitated in acidic electrolytes, resulting in poor catalyst stability.

[0005] 3. Some catalysts with regular morphologies, such as nanoflower-like catalysts, exhibit higher catalytic performance due to their selective exposure of highly active crystal faces and highly active sites such as edges and corners. However, in the preparation process of nanocrystals with regular morphologies, organic macromolecular templates (CTAB, PVP, etc.) and strongly coordinating organic solvents (oleylamine, etc.) are often used to control the morphology and size of the nanocrystals. These templates and organic solvents have extremely strong adsorption capacity and occupy the active sites of the catalyst, which is difficult to remove and seriously affects the adsorption of the reaction molecules on the active sites. Removing these surface adsorbents requires a series of complex post-processing processes, which not only increases the preparation cost of the catalyst, but may also cause structural damage to the catalyst and increase the particle size, thereby reducing its activity.

[0006] Therefore, it is of great significance to promote the large-scale application of fuel cells to synthesize a nanocrystalline catalyst with regular morphology and good stability by using small molecule complexation and directional adsorption. Summary of the Invention

[0007] In order to solve the problems of high cost, low activity and poor stability of existing oxygen reduction reaction catalysts, the present invention proposes a flower-shaped PtAl nanocrystalline catalyst and its preparation method and application.

[0008] To achieve the above objectives, the present invention provides a flower-shaped PtAl nanocrystal catalyst. The flower-shaped PtAl nanocrystal catalyst has a particle size of 20 to 200 nm and is composed of two elements, Pt and Al. Al accounts for 2 to 30% of the mass of the flower-shaped PtAl nanocrystal catalyst, and Al is doped in the Pt nanocrystal in atomic form.

[0009] The flower-shaped PtAl nanocrystal catalyst provided by the present invention has a particle size of 20 to 200 nm. Al is doped in the Pt nanocrystal in atomic form. Due to the large difference in atomic radius between Pt and Al, the Al doping can increase the surface stress of the Pt nanocrystal. At the same time, the electronic effect between Al and Pt can further adjust the electronic structure of Pt, promoting the desorption of oxygen-containing intermediates during the oxygen reduction reaction. Al is not easily precipitated from PtAl in an acidic electrolyte, thereby increasing the stability of the catalyst.

[0010] A method for preparing the flower-shaped PtAl nanocrystalline catalyst comprises the following steps:

[0011] Step 1: a platinum metal precursor, an aluminum metal precursor, and a solvent are mixed, stirred, and then ethylenediamine and sulfite are added. After stirring and ultrasonication, a reducing agent is added to obtain a mixed solution A;

[0012] Step 2: heating the mixed solution A and filtering to obtain solid powder B;

[0013] Step 3: heating and calcining the solid powder B in a reducing atmosphere to obtain a flower-shaped PtAl nanocrystalline catalyst.

[0014] Furthermore, in step 1, the platinum metal precursor is one of chloroplatinic acid, platinum acetylacetonate, ammonium chloroplatinate and potassium chloroplatinate;

[0015] The aluminum metal precursor is one of aluminum chloride, aluminum nitrate and aluminum tribromide;

[0016] The solvent is one of deionized water, anhydrous ethanol and isopropanol;

[0017] The sulfite is one of sodium sulfite (Na2SO3), potassium sulfite (K2SO3) and ammonium sulfite ((NH4)2SO3);

[0018] The reducing agent is ethylene glycol.

[0019] Furthermore, in step 1, the mass ratio of the platinum metal precursor to the aluminum metal precursor is 30:1 to 3:1;

[0020] The volume ratio of ethylenediamine to solvent is 0.01:1 to 0.1:1;

[0021] The volume ratio of the reducing agent to the solvent is 0.2:1 to 5:1;

[0022] After sulfite is added, its mass concentration is 0.1% to 5%.

[0023] Furthermore, in step 2, the heating temperature is 80 to 240° C. and the heating time is 0.2 to 12 hours. The heating reaction in step 2 is preferably carried out in a reactor.

[0024] Furthermore, in step 3, the reducing atmosphere is a mixture of hydrogen and nitrogen or hydrogen and argon, wherein the volume ratio of hydrogen is 2% to 50%.

[0025] Furthermore, in step 3, the heating and calcining temperature is 200-600° C. and the heating and calcining time is 0.2-12 hours. The heating and calcining reaction in step 3 is preferably carried out in a tube furnace, first transferring the solid powder B to a quartz boat, and then placing it in the tube furnace for heating and calcining.

[0026] The present invention utilizes ethylenediamine molecules as complexing agents, SO3 2- A flower-shaped PtAl nanocrystalline catalyst is prepared in a reactor through nucleation-oriented growth using a co-reduction method with ethylene glycol as a reducing agent to regulate the growth rate of the crystal face. The flower-shaped PtAl nanocrystalline catalyst is used in an oxygen reduction reaction. Due to the presence of stress effects, electronic effects, and the high stability of Pt and Al in acidic electrolytes, the flower-shaped PtAl nanocrystalline catalyst has high catalytic activity and stability for the oxygen reduction reaction.

[0027] Application of the flower-shaped PtAl nanocrystalline catalyst in oxygen reduction reaction.

[0028] Application of the flower-shaped PtAl nanocrystalline catalyst in hydrogen fuel cells.

[0029] Compared with the prior art, the present invention has the following advantages and technical effects:

[0030] (1) The method of the present invention does not use organic macromolecular templates and strong coordination organic solvents, but uses ethylenediamine molecules as complexing agents, SO3 2- It is a directional adsorbent to regulate the growth rate of the crystal surface.

[0031] (2) The catalyst prepared by the method of the present invention is composed of two elements, Pt and Al, and has a flower-like regular morphology and a size of 20 to 200 nm.

[0032] (3) Due to the large difference in atomic radius between Pt and Al, Al doping can increase the surface stress of Pt nanocrystals.

[0033] (4) The electronic effect between Al and Pt can further regulate the electronic structure of Pt and promote the desorption of oxygen-containing intermediates during the oxygen reduction reaction.

[0034] (5) Al is stable in acidic electrolyte and is not easily precipitated from PtAl, which increases the stability of the catalyst.

[0035] (6) The catalyst of the present invention has high platinum utilization rate, low cost, easy synthesis and the like, can be produced on a large scale, and can be used in electrocatalytic oxygen reduction reactions. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0037] Figure 1 This is a scanning electron microscope photograph of the flower-shaped PtAl nanocrystalline catalyst obtained in Example 1;

[0038] Figure 2 This is a transmission electron microscope photograph of the flower-shaped PtAl nanocrystalline catalyst obtained in Example 1;

[0039] Figure 3 This is a high-magnification transmission electron microscope photograph of the flower-shaped PtAl nanocrystalline catalyst obtained in Example 1;

[0040] Figure 4 This is the XPS spectrum of the flower-shaped PtAl nanocrystal catalyst obtained in Example 1;

[0041] Figure 5 The oxygen reduction reaction activities of the flower-shaped PtAl nanocrystal catalyst obtained in Example 1 and commercial Pt / C;

[0042] Figure 6 Figure 1 is a stability test diagram of the flower-shaped PtAl nanocrystal catalyst and commercial Pt / C obtained in Example 1;

[0043] Figure 7 This is a scanning electron microscope photograph of the spherical PtAl nanocrystalline catalyst obtained in Comparative Example 1;

[0044] Figure 8 This is a scanning electron microscope photograph of the cubic PtAl nanocrystalline catalyst obtained in Comparative Example 2. DETAILED DESCRIPTION

[0045] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0046] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0047] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0048] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be illustrative only.

[0049] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0050] The commercial Pt / C in the examples of the present invention was purchased from Alfa Aesar (China) Chemical Co., Ltd.

[0051] Example 1

[0052] Preparation of Flower-like PtAl Nanocrystalline Catalysts

[0053] Dissolve 0.03 g of chloroplatinic acid and 0.005 g of aluminum chloride in 20 mL of deionized water, add 0.5 mL of ethylenediamine and 0.5 g of Na2SO3, stir thoroughly, and ultrasonicate, then add 20 mL of reducing agent ethylene glycol to obtain a mixed solution A;

[0054] The mixed solution A was transferred to a 50 mL reactor, maintained at 120°C for 5 h, and then filtered to obtain solid powder B;

[0055] The solid powder B was transferred to a quartz boat, placed in a tube furnace, heated to 300° C. in a 5% hydrogen-nitrogen mixed gas (hydrogen volume ratio 5%) atmosphere, and maintained at this temperature for 3 hours to obtain a flower-shaped PtAl nanocrystalline catalyst.

[0056] The scanning electron microscope photo of the flower-shaped PtAl nanocrystalline catalyst obtained in this example is shown in Figure 1 ,from Figure 1 It can be seen that the PtAl nanocrystals are flower-shaped and have a size of 100 nm.

[0057] The transmission electron microscope photo of the flower-shaped PtAl nanocrystalline catalyst obtained in this example is shown in Figure 2 ,from Figure 2 The flower-like structure of PtAl nanocrystals was confirmed in

[16] .

[0058] The high-magnification transmission electron microscope photo of the flower-shaped PtAl nanocrystalline catalyst obtained in this example is shown in Figure 3 ,from Figure 3 It can be seen that Al atoms are doped in Pt nanocrystals.

[0059] X-ray photoelectron spectroscopy (XPS)

[0060] The XPS spectrum of the flower-shaped PtAl nanocrystalline catalyst obtained in this example is as follows Figure 4 As shown in the figure, compared with Pt / C, the binding energy of Pt element in PtAl nanocrystals is negatively shifted by 0.4 eV, indicating that there is a strong electronic interaction between Pt and Al elements.

[0061] Catalytic performance of flower-like PtAl nanocrystals for oxygen reduction reaction

[0062] A three-electrode system was used, with flower-shaped PtAl nanocrystalline catalyst and commercial Pt / C as working electrodes, Ag / AgCl electrode as reference electrode, Pt wire as auxiliary electrode, and 0.1 mol / L perchloric acid aqueous solution saturated with oxygen as electrolyte solution. Linear sweep polarization curves were recorded on an electrochemical workstation (CHI660d, Shanghai Chenhua Instrument Co., Ltd.). The rotation speed of the rotating electrode was 1600 rpm, the scanning range was 0.9-0.1 V (relative to standard hydrogen electrode), and the scanning speed was 20 mV / s. The oxygen reduction reaction activity of the flower-shaped PtAl nanocrystalline catalyst and the commercial Pt / C in Example 1 is shown in FIG. Figure 5 ,Depend on Figure 5 It can be seen that the half-wave potential of the PtAl nanocrystalline catalyst is 0.89 V, which is 10 mV more positive than that of commercial Pt / C, indicating that the PtAl nanocrystalline catalyst has high oxygen reduction reaction activity.

[0063] Stability testing of flower-like PtAl nanocrystal catalysts and commercial Pt / C

[0064] The current-time curve of the catalyst (flower-shaped PtAl nanocrystal catalyst and Pt / C catalyst in Example 1) was tested under the same catalytic performance three-electrode system test conditions at a constant potential of 0.7 V. The stability test diagram is shown in FIG. Figure 6 ,Depend on Figure 6 It can be seen that after 12 hours, the PtAl nanocrystalline catalyst did not show significant attenuation, which was significantly better than the commercial Pt / C catalyst (attenuated by 20%).

[0065] from Figure 5 and Figure 6 It can be seen from the performance diagram that the activity and stability of the flower-like PtAl nanocrystal catalyst are much higher than those of commercial Pt / C.

[0066] Example 2

[0067] Preparation of Flower-like PtAl Nanocrystalline Catalysts

[0068] Dissolve 0.05 g of platinum acetylacetonate and 0.01 g of aluminum nitrate in 30 mL of anhydrous ethanol, add 3 mL of ethylenediamine and 0.6 g of K2SO3, stir thoroughly, and ultrasonicate, then add 150 mL of reducing agent ethylene glycol to obtain a mixed solution A;

[0069] The mixed solution A was transferred to a 200 mL reactor, maintained at 80°C for 12 h, and then filtered to obtain solid powder B;

[0070] The solid powder B was transferred to a quartz boat and placed in a tube furnace. The mixture was heated to 600°C in a 5% hydrogen-argon mixture (5% hydrogen by volume) and maintained at this temperature for 0.2 hours to produce flower-shaped PtAl nanocrystal catalysts. Scanning electron microscopy images show the catalyst's flower-like shape, measuring 80 nm in size, with Al atoms doped within the Pt nanocrystals.

[0071] Using the same test conditions as Example 1, the test results confirmed that the flower-shaped PtAl nanocrystalline catalyst has better catalytic activity and stability than commercial Pt / C.

[0072] Example 3

[0073] Preparation of Flower-like PtAl Nanocrystalline Catalysts

[0074] Dissolve 0.08 g of ammonium chloroplatinate and 0.02 g of aluminum tribromide in 20 mL of isopropanol, add 0.2 mL of ethylenediamine and 0.5 g of (NH4)2SO3, stir thoroughly, and sonicate, then add 4 mL of reducing agent ethylene glycol to obtain a mixed solution A;

[0075] The mixed solution A was transferred to a 50 mL reactor, maintained at 240°C for 0.2 h, and then filtered to obtain solid powder B;

[0076] The solid powder B was transferred to a quartz boat and placed in a tube furnace. The mixture was heated to 400°C in a 5% hydrogen-argon mixture (5% hydrogen by volume) and maintained at this temperature for 5 hours to produce flower-shaped PtAl nanocrystal catalysts. Scanning electron microscopy images show the catalyst's flower-like shape, measuring 80 nm in size, with Al atoms doped within the Pt nanocrystals.

[0077] Using the same test conditions as Example 1, the test results confirmed that the flower-shaped PtAl nanocrystalline catalyst has better catalytic activity and stability than commercial Pt / C.

[0078] Example 4

[0079] Preparation of Flower-like PtAl Nanocrystalline Catalysts

[0080] Dissolve 0.09 g of potassium chloroplatinate and 0.03 g of aluminum tribromide in 20 mL of anhydrous ethanol, add 1 mL of ethylenediamine and 0.5 g of K2SO3, stir thoroughly, and ultrasonicate, then add 20 mL of reducing agent ethylene glycol to obtain a mixed solution A;

[0081] The mixed solution A was transferred to a 50 mL reactor, maintained at 200 °C for 5 h, and then filtered to obtain solid powder B;

[0082] The solid powder B was transferred to a quartz boat and placed in a tube furnace. The mixture was heated to 300°C in a 5% hydrogen-argon mixture (5% hydrogen by volume) and maintained at this temperature for 10 hours to produce flower-shaped PtAl nanocrystal catalysts. Scanning electron microscopy images show the catalyst's flower-like shape, measuring 120 nm in size, with Al atoms doped within the Pt nanocrystals.

[0083] Using the same test conditions as Example 1, the test results confirmed that the flower-shaped PtAl nanocrystalline catalyst has better catalytic activity and stability than commercial Pt / C.

[0084] Comparative Example 1

[0085] The same as Example 1, except that ethylenediamine was not added, the PtAl nanocrystalline catalyst obtained was spherical, and its scanning electron microscope photo is as shown in FIG. Figure 7 shown.

[0086] From the comparison between Example 1 and Comparative Example 1, it can be seen that the addition of ethylenediamine can control the nucleation rate of PtAl nanocrystals, inhibit the Ostwald ripening of nanocrystals, and contribute to the formation of flower-like structures.

[0087] Using the same test conditions as in Example 1, the test results confirmed that the flower-shaped PtAl nanocrystals can expose more catalytic sites and have higher catalytic activity than the spherical PtAl nanocrystals.

[0088] Comparative Example 2

[0089] The same as Example 1, except that no Na2SO3 was added, the PtAl nanocrystalline catalyst obtained was in the shape of a cube, as shown in the scanning electron microscope photograph. Figure 8 shown.

[0090] Using the same test conditions as in Example 1, the test results confirmed that the flower-shaped PtAl nanocrystals had higher catalytic activity than the cubic PtAl nanocrystals.

[0091] From the comparison between Example 1 and Comparative Example 2, it can be seen that the addition of Na2SO3 is conducive to the directional growth of PtAl nanocrystals and the formation of flower-like structures.

[0092] Comparative Example 3

[0093] The same as Example 1, except that a PtNi catalyst was prepared and 0.005 g of nickel chloride was added when preparing the mixed solution A.

[0094] From the comparison between Example 1 and Comparative Example 3, it can be seen that due to the large difference in atomic radius between Pt and Al, Al doping can increase the surface stress of Pt nanocrystals, and Al is stable in acidic electrolyte and is not easily precipitated from PtAl, thereby increasing the stability of the catalyst.

[0095] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for preparing a flower-shaped PtAl nanocrystalline catalyst, characterized in that: The following steps are involved: Step 1: a platinum metal precursor, an aluminum metal precursor, and a solvent are mixed, stirred, and then ethylenediamine and sulfite are added. After stirring and ultrasonication, a reducing agent is added to obtain a mixed solution A; Step 2: heating the mixed solution A and filtering to obtain solid powder B; Step 3: heating and calcining the solid powder B in a reducing atmosphere to obtain a flower-shaped PtAl nanocrystalline catalyst; The flower-shaped PtAl nanocrystal catalyst has a particle size of 20-200 nm and is composed of two elements, Pt and Al. Al accounts for 2-30% of the mass of the flower-shaped PtAl nanocrystal catalyst and is doped in the Pt nanocrystal in the form of atoms.

2. The method for preparing the flower-shaped PtAl nanocrystalline catalyst according to claim 1, wherein: In step 1, the platinum metal precursor is one of chloroplatinic acid, platinum acetylacetonate, ammonium chloroplatinate and potassium chloroplatinate; The aluminum metal precursor is one of aluminum chloride, aluminum nitrate and aluminum tribromide; The solvent is one of deionized water, anhydrous ethanol and isopropanol; The sulfite is one of sodium sulfite, potassium sulfite and ammonium sulfite; The reducing agent is ethylene glycol.

3. The method for preparing the flower-shaped PtAl nanocrystalline catalyst according to claim 2, wherein: In step 1, the mass ratio of the platinum metal precursor to the aluminum metal precursor is 30:1 to 3:1; The volume ratio of ethylenediamine to solvent is 0.01:1 to 0.1:1; The volume ratio of the reducing agent to the solvent is 0.2:1 to 5:1; After sulfite is added, its mass concentration is 0.1% to 5%.

4. The method for preparing the flower-shaped PtAl nanocrystalline catalyst according to claim 1, wherein: In step 2, the heating temperature is 80 to 240° C., and the heating time is 0.2 to 12 hours.

5. The method for preparing the flower-shaped PtAl nanocrystalline catalyst according to claim 1, wherein: In step 3, the reducing atmosphere is a mixture of hydrogen and nitrogen or hydrogen and argon, wherein the volume ratio of hydrogen is 2% to 50%.

6. The method for preparing the flower-shaped PtAl nanocrystalline catalyst according to claim 1, characterized in that: In step 3, the heating and calcining temperature is 200-600° C., and the heating and calcining time is 0.2-12 hours.

7. Use of the flower-shaped PtAl nanocrystalline catalyst prepared by the method according to any one of claims 1 to 6 in an oxygen reduction reaction.

8. Use of the flower-shaped PtAl nanocrystalline catalyst prepared by the method according to any one of claims 1 to 6 in a hydrogen fuel cell.

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