Two-dimensional Pd nanosheet electrocatalyst rich in grain boundary and preparation method thereof

Abstract

The invention discloses a two-dimensional Pd nanosheet electrocatalyst rich in grain boundary and a preparation method of the two-dimensional Pd nanosheet electrocatalyst, and belongs to the technical field of electrochemical catalysis. The method comprises the following steps: by taking palladium acetylacetonate as a precursor, ascorbic acid and carbon monoxide as reducing agents and oleylamine as a solvent, carrying out heating reaction in a high-temperature reaction kettle; after the reaction is completed, the obtained mixture is cleaned and dried, and finally the ultrathin two-dimensional Pd nanosheet rich in the grain boundary is prepared. According to the preparation method, the active sites of the basal plane can be greatly increased, the electronic structure of the catalyst can be optimized, the catalytic performance and the quality activity can be effectively improved, and the synthesized two-dimensional Pd nanosheet rich in the grain boundary can be used for a fuel cell, a metal-air battery and an efficient electrocatalyst in the electrochemical oxygen reduction process.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrocatalytic chemistry, and specifically relates to a two-dimensional Pd nanosheet electrocatalyst rich in grain boundaries and a preparation method thereof. Background Art

[0002] For a long time, the large-scale use of fossil fuels as the main energy source has led to a large amount of carbon dioxide emissions, which has triggered great concerns about climate change and environmental problems globally. The conversion and storage technologies of renewable energy are widely regarded as potential alternatives to traditional fossil fuels. However, in practical applications, especially in fuel cells and metal-air batteries, the low efficiency of the cathode oxygen reduction reaction (ORR) has become the main bottleneck restricting their performance. To improve the efficiency of sustainable energy conversion devices and promote their practical applications, the development of highly active and durable ORR electrocatalysts has become a key research direction.

[0003] Platinum group metals (PGMs) can effectively regulate the interaction between the catalyst surface and oxygen-containing intermediates due to their unique chemical properties and electronic structures, thus achieving excellent ORR catalytic performance. However, due to the high cost, scarce reserves, and poor environmental tolerance of PGMs, their large-scale application is restricted. Although the ORR activity of PGM catalysts has been significantly improved under acidic conditions through strategies such as morphology engineering, alloying, and defect engineering, how to further improve their ORR performance in an alkaline environment remains an urgent challenge to be solved.

[0004] Palladium (Pd), as a substitute metal for platinum, has similar electronic structures and chemical properties. Similarly, an ideal ORR catalyst needs to maintain an appropriate binding ability with oxygen molecules to balance the processes of oxygen adsorption, activation, and desorption of oxygen-containing substances. In recent years, optimizing catalytic activity by regulating material morphology and introducing structural defects has become a common method. Two-dimensional Pd nanosheets have attracted much attention due to their large specific surface area and special electronic structures. However, limited by the electrocatalytic inertness of basal plane atoms, their performance still does not meet the requirements of industrial applications. Grain boundary engineering, as a type of defect engineering, has attracted much attention due to its significant performance improvement effect. Grain boundaries are the junctions of regions with different orientations in a single-phase material, with undercoordinated atoms, and strain is induced at the interface, forming a high-energy surface. These characteristics not only provide an ideal environment for the adsorption and activation of reactants or intermediates but also significantly enhance the electrocatalytic performance. However, the two-dimensional nanosheets prepared by existing grain boundary engineering still have problems such as low grain boundary content and low nanosheet purity. Summary of the Invention

[0005] The present invention overcomes the shortcomings of the prior art and proposes a two-dimensional Pd nanosheet electrocatalyst rich in grain boundaries and a preparation method thereof, which solves the problems of low grain boundary content and low purity of the existing two-dimensional Pd nanosheets and can be used as a cathode catalyst for fuel cells.

[0006] The present invention is achieved through the following technical solutions: A method for preparing a two-dimensional Pd nanosheet electrocatalyst rich in grain boundaries comprises the following steps: S1. Take palladium acetylacetonate and ascorbic acid in a glass bottle, add oleylamine as a solvent, and fully disperse them to obtain a clear and transparent solution; S2, placing the metal carbonyl in a reaction kettle, adding dimethylformamide as a solvent, fully dispersing it to obtain a clear and transparent solution; S3. Place the glass bottle directly in the reactor to form a double-layer device, and perform heating reaction; after the reaction, the obtained solution is centrifuged and washed several times, and dried to obtain a black powder.

[0007] Preferably, the mass ratio of palladium acetylacetonate to ascorbic acid is 1:0.1 to 1:10.

[0008] Preferably, the molar ratio of the metal carbonyl to dimethylformamide is 1:0.1 to 1:100.

[0009] More preferably, the metal carbonyl is molybdenum hexacarbonyl or tungsten hexacarbonyl.

[0010] Preferably, the reaction temperature of the heating reaction is 50-100° C., and the reaction time is 2-12 hours.

[0011] More preferably, the heating reaction is carried out by placing the glass bottle directly in a polytetrafluoroethylene liner, and then transferring it to a reaction kettle, and carrying out the heating reaction in a constant temperature forced air drying oven.

[0012] Preferably, the sufficient dispersion in steps S1 and S2 is carried out by ultrasonic dispersion at room temperature, wherein step S1 is ultrasonic dispersion at room temperature for 15-30 min, and step S2 is ultrasonic dispersion at room temperature for 30-60 min.

[0013] Preferably, the cleaning liquid used in the washing in step S3 is a mixture of cyclohexane and anhydrous ethanol in a volume ratio of 1:1 to 1:10.

[0014] Preferably, the drying in step S3 is freeze drying or vacuum drying.

[0015] A two-dimensional Pd nanosheet electrocatalyst rich in grain boundaries is prepared by using the method for preparing a two-dimensional Pd nanosheet electrocatalyst rich in grain boundaries.

[0016] The beneficial effects of the present invention compared with the prior art are as follows: 1. In the present invention, palladium acetylacetonate is used as a precursor, ascorbic acid and carbon monoxide are used as reducing agents, and oleylamine is used as a solvent. The heating reaction is carried out in a high-temperature reaction kettle; after the reaction is completed, the obtained mixture is washed and dried, and finally ultrathin two-dimensional Pd nanosheets rich in grain boundaries are prepared. The grain-boundary-rich Pd nanosheets of the present invention have a large specific surface area and excellent charge transport ability. A large number of unsaturated coordinated atoms at the grain boundaries increase the basal plane active sites. Coupled with the significant change in lattice strain near the grain boundaries in the binding affinity for oxygen-containing intermediates, the total potential barrier of the reaction path is effectively regulated, and the electrocatalytic activity is greatly improved. Through electrochemical testing, the prepared grain-boundary-rich ultrathin Pd nanosheet catalyst exhibits excellent electrocatalytic performance for oxygen reduction reaction under alkaline conditions, and has broad application prospects and commercialization potential.

[0017] 2. During the heating process of the reaction in the present invention, metal carbonyl compounds in the inner lining of the reaction kettle decompose first to generate sufficient carbon monoxide. Under the combined action of carbon monoxide and ascorbic acid, palladium acetylacetonate is fully reduced. At the same time, sufficient carbon monoxide is adsorbed on the surface of palladium atoms, promoting its two-dimensional growth, and finally ultrathin palladium nanosheets with rich grain boundaries are obtained. The synthesized two-dimensional Pd nanosheets rich in grain boundaries can be used as highly efficient electrocatalysts in fuel cells, metal-air batteries and electrochemical oxygen reduction processes.

[0018] 3. The preparation method of the present invention is simple in operation and does not require special equipment.

[0019] 4. The synthesized two-dimensional Pd nanosheets rich in grain boundaries of the present invention have a high yield, no interference from impurity elements, and high purity.

[0020] 5. The present invention can not only greatly increase the basal plane active sites, but also help to optimize the electronic structure of the catalyst, effectively improve the catalytic performance and mass activity, providing an important research direction and application prospect for the development of highly efficient ORR electrocatalysts. Description of the Drawings

[0021] Figure 1 Scanning electron microscope image of the two-dimensional Pd nanosheets rich in grain boundaries prepared in Example 1; Figure 2 High-magnification transmission electron microscope image of the two-dimensional Pd nanosheets rich in grain boundaries prepared in Example 1; Figure 3 Selected area diffraction pattern of the two-dimensional Pd nanosheets rich in grain boundaries prepared in Example 1; Figure 4 X-ray diffraction pattern of the two-dimensional Pd nanosheets rich in grain boundaries prepared in Example 1; Figure 5LSV curves of the grain-boundary-rich two-dimensional Pd nanosheets prepared in Example 1 and commercial platinum-carbon catalyst in 0.1 M KOH (rotation speed: 1600 rpm).

[0022] Figure 6 Schematic diagram of the synthesis for preparing the grain-boundary-rich two-dimensional Pd nanosheets in the present invention. Detailed implementation manners

[0023] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer and more understandable, the present invention will be further described in detail in combination with examples and drawings. It should be understood that the specific examples described herein are only used to explain the present invention and are not used to limit the present invention. The technical solutions of the present invention will be described in detail below in combination with examples and drawings, but the protection scope is not limited by this.

[0024] Example 1 This example proposes a preparation method of a grain-boundary-rich two-dimensional Pd nanosheet electrocatalyst: S1. First, weigh 20 mg of palladium acetylacetonate and 10 mg of ascorbic acid into a 20 ml glass bottle, and at the same time add 5 ml of oleylamine, and ultrasonically disperse for 30 min at room temperature to obtain a clear and transparent solution; S2. Then weigh 60 mg of molybdenum hexacarbonyl into a 50 ml polytetrafluoroethylene liner, and at the same time add 4 ml of dimethylformamide, and ultrasonically disperse for 60 min at room temperature to obtain a clear and transparent solution.

[0025] S3. Place the 20 ml glass bottle directly into the 50 ml polytetrafluoroethylene liner to form a double-layer device, and then transfer the double-layer device to a high-pressure reaction kettle, heat at 80 °C for 12 h in a constant-temperature blast drying oven, add ethanol to the obtained product for centrifugation, and then wash it 4-5 times with a cyclohexane / ethanol mixed solution with a volume ratio of 1:1, and dry it in a vacuum oven at 60 °C to obtain the grain-boundary-rich two-dimensional Pd nanosheets.

[0026] Figure 1 Scanning electron microscope image of the grain-boundary-rich two-dimensional Pd nanosheets prepared in Example 1. It can be seen from the figure that the morphology of the sample prepared in Example 1 is nanosheets.

[0027] Figure 2 High-resolution transmission electron microscope image of the grain-boundary-rich two-dimensional Pd nanosheets prepared in Example 1. It can be seen from the figure that the obtained nanosheets have rich grain boundaries on the surface.

[0028] Figure 3 Selected area diffraction pattern of the grain-boundary-rich two-dimensional Pd nanosheets prepared in Example 1. It can be seen from the figure that the obtained palladium nanosheets are polycrystalline structures.

[0029] Figure 4 X-ray diffraction pattern of the grain boundary-rich two-dimensional Pd nanosheets prepared in Example 1. It can be seen from the figure that the diffraction peak positions in the experimental spectrum coincide with those in the standard card, proving that the structures of the two are the same and the purity of the prepared sample is good; Figure 5 LSV curves (rotation speed: 1600 rpm) of the grain boundary-rich two-dimensional Pd nanosheets prepared in Example 1 and commercial Pt / C catalyst in 0.1 M KOH. It can be seen from the figure that the half-wave potential of the obtained palladium nanosheets is 0.94 V, and the performance far exceeds that of the commercial Pt / C catalyst, which is 0.86 V.

[0030] Figure 6 Schematic diagram of the synthesis of the grain boundary-rich two-dimensional Pd nanosheets prepared in Example 1.

[0031] Example 2 This example proposes a preparation method for a grain boundary-rich two-dimensional Pd nanosheet electrocatalyst: S1. First, weigh 10 mg of palladium acetylacetonate and 5 mg of ascorbic acid into a 10-ml glass bottle, and simultaneously add 5 ml of oleylamine. Ultrasonically disperse for 15 min at room temperature to obtain a clear and transparent solution; S2. Then, weigh 40 mg of molybdenum hexacarbonyl into a 25-ml polytetrafluoroethylene liner, and simultaneously add 3 ml of dimethylformamide. Ultrasonically disperse for 60 min at room temperature to obtain a clear and transparent solution; S3. Place the 10-ml glass bottle directly into the 25-ml polytetrafluoroethylene liner, transfer it to a high-pressure reaction kettle, heat it at 80 °C for 12 h in a constant-temperature forced-air drying oven. Add ethanol to the obtained product for centrifugation, and then wash it 4-5 times with a cyclohexane / ethanol mixed solution with a volume ratio of 1:3. Dry it in a vacuum oven at 60 °C to obtain grain boundary-rich ultrathin palladium nanosheets.

[0032] Example 3 This example proposes a preparation method for a grain boundary-rich two-dimensional Pd nanosheet electrocatalyst: S1. First, weigh 100 mg of palladium acetylacetonate and 50 mg of ascorbic acid into a 50-ml glass bottle, and simultaneously add 20 ml of oleylamine. Ultrasonically disperse for 30 min at room temperature to obtain a clear and transparent solution; S2. Then, weigh 300 mg of molybdenum hexacarbonyl into a 100-ml polytetrafluoroethylene liner, and simultaneously add 20 ml of dimethylformamide. Ultrasonically disperse for 60 min at room temperature to obtain a clear and transparent solution; S3. Place a 50-ml glass bottle directly into a 100-ml polytetrafluoroethylene liner, transfer it to a high-pressure reactor, heat it at 80 °C for 12 h in a constant-temperature forced-air drying oven, add the obtained product to ethanol for centrifugation, and then wash it 4 - 5 times with a cyclohexane / ethanol mixed solution. Dry it in a vacuum oven at 60 °C to obtain two-dimensional Pd nanosheets rich in grain boundaries.

[0033] Example 4 This example presents a method for preparing a two-dimensional Pd nanosheet electrocatalyst rich in grain boundaries: S1. First, weigh 20 mg of palladium acetylacetonate and 10 mg of ascorbic acid into a 50-ml glass bottle, add 15 ml of oleylamine at the same time, and ultrasonically disperse for 15 min at room temperature to obtain a clear and transparent solution. S2. Then, weigh 60 mg of molybdenum hexacarbonyl into a 50-ml polytetrafluoroethylene liner, add 4 ml of dimethylformamide at the same time, and ultrasonically disperse for 30 min at room temperature to obtain a clear and transparent solution.

[0034] S3. Place a 20-ml glass bottle directly into a 50-ml polytetrafluoroethylene liner to form a double-layer device, then transfer the double-layer device to a high-pressure reactor, heat it at 100 °C for 6 h in a constant-temperature forced-air drying oven, add the obtained product to ethanol for centrifugation, and then wash it 4 - 5 times with a cyclohexane / ethanol mixed solution with a volume ratio of 1:1. Dry it in a vacuum oven at 60 °C to obtain two-dimensional Pd nanosheets rich in grain boundaries.

[0035] Example 5 This example presents a method for preparing a two-dimensional Pd nanosheet electrocatalyst rich in grain boundaries: S1. First, weigh 20 mg of palladium acetylacetonate and 10 mg of ascorbic acid into a 50-ml glass bottle, add 15 ml of oleylamine at the same time, and ultrasonically disperse for 20 min at room temperature to obtain a clear and transparent solution. S2. Then, weigh 60 mg of molybdenum hexacarbonyl into a 50-ml polytetrafluoroethylene liner, add 4 ml of dimethylformamide at the same time, and ultrasonically disperse for 30 min at room temperature to obtain a clear and transparent solution.

[0036] S3. Place a 20-ml glass bottle directly into a 50-ml polytetrafluoroethylene liner to form a double-layer device, then transfer the double-layer device to a high-pressure reactor, heat it at 50 °C for 10 h in a constant-temperature forced-air drying oven, add the obtained product to ethanol for centrifugation, and then wash it 4 - 5 times with a cyclohexane / ethanol mixed solution with a volume ratio of 1:10. Dry it in a vacuum oven at 60 °C to obtain two-dimensional Pd nanosheets rich in grain boundaries.

[0037] The above content is a further detailed description of the present invention in combination with specific preferred embodiments. It cannot be determined that the specific embodiments of the present invention are limited thereto. For those of ordinary skill in the technical field to which the present invention pertains, without departing from the present invention, several simple deductions or substitutions can still be made, and all should be regarded as belonging to the scope of patent protection determined by the claims submitted for the present invention.

Claims

1. A method for preparing a two-dimensional Pd nanosheet electrocatalyst rich in grain boundaries, characterized in that: The following steps are involved: S1. Take palladium acetylacetonate and ascorbic acid in a glass bottle, add oleylamine as a solvent, and fully disperse them to obtain a clear and transparent solution; S2, placing the metal carbonyl in a reaction kettle, adding dimethylformamide as a solvent, fully dispersing it to obtain a clear and transparent solution; S3. Place the glass bottle directly in the reactor to form a double-layer device, and perform heating reaction; after the reaction, the obtained solution is centrifuged and washed several times, and dried to obtain a black powder.

2. The method for preparing a two-dimensional Pd nanosheet electrocatalyst rich in grain boundaries according to claim 1, characterized in that: The mass ratio of palladium acetylacetonate to ascorbic acid is 1:0.1~1:

10.

3. The method for preparing a two-dimensional Pd nanosheet electrocatalyst rich in grain boundaries according to claim 1, characterized in that: The molar ratio of the metal carbonyl to dimethylformamide is 1:0.1~1:

100.

4. The method for preparing a two-dimensional Pd nanosheet electrocatalyst rich in grain boundaries according to claim 3, characterized in that: The metal carbonyl is molybdenum hexacarbonyl or tungsten hexacarbonyl.

5. The method for preparing a two-dimensional Pd nanosheet electrocatalyst rich in grain boundaries according to claim 1, characterized in that: The reaction temperature of the heating reaction is 50-100° C., and the reaction time is 2-12 hours.

6. The method for preparing a two-dimensional Pd nanosheet electrocatalyst rich in grain boundaries according to claim 5, characterized in that: The heating reaction is to place the glass bottle directly in the polytetrafluoroethylene liner, then transfer it to the reaction kettle, and carry out the heating reaction in a constant temperature blast drying oven.

7. The method for preparing a two-dimensional Pd nanosheet electrocatalyst rich in grain boundaries according to claim 1, characterized in that: The sufficient dispersion in steps S1 and S2 is carried out by ultrasonic dispersion at room temperature.

8. The method for preparing a two-dimensional Pd nanosheet electrocatalyst rich in grain boundaries according to claim 1, characterized in that: The cleaning liquid used for washing in step S3 is a mixture of cyclohexane and anhydrous ethanol in a volume ratio of 1:1 to 1:

10.

9. The method for preparing a two-dimensional Pd nanosheet electrocatalyst rich in grain boundaries according to claim 1, characterized in that: The drying in step S3 is freeze drying or vacuum drying.

10. A two-dimensional Pd nanosheet electrocatalyst rich in grain boundaries, characterized in that: The electrocatalyst is prepared by the method for preparing a two-dimensional Pd nanosheet electrocatalyst rich in grain boundaries as described in any one of claims 1 to 9.

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