A two-dimensional Pd nanosheet electrocatalyst rich in grain boundaries and a preparation method thereof

Abstract

The application discloses a kind of two-dimensional Pd nanosheet electrocatalysts rich in grain boundary and a preparation method thereof, and belongs to the technical field of electrochemical catalysis;The application is with acetylacetone palladium as precursor, ascorbic acid and carbon monoxide as reducing agent, oleylamine as solvent, heating reaction in high temperature reaction kettle;After reaction is completed, the obtained mixture is washed and dried, and finally the ultra-thin two-dimensional Pd nanosheet rich in grain boundary is prepared;The application not only can greatly increase basal plane active site, but also helps to optimize the electronic structure of catalyst, effectively improves catalytic performance and mass activity, and the synthesized two-dimensional Pd nanosheet rich in grain boundary can be used for fuel cell, metal air battery and efficient electrocatalyst in electrochemical oxygen reduction process.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrochemical catalysis, and particularly relates to a two-dimensional Pd nanosheet electrocatalyst rich in grain boundaries and a preparation method thereof. BACKGROUND

[0002] The conversion and storage technology of renewable energy is widely considered as a potential alternative 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) becomes the main bottleneck limiting its performance. In order to improve the efficiency of sustainable energy conversion devices and promote their practical application, the development of high-activity and durable ORR electrocatalysts has become a key research direction.

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

[0004] Palladium (Pd) as a substitute metal for platinum has similar electronic structure and chemical properties. Similarly, an ideal ORR catalyst needs to have a moderate binding ability with oxygen molecules to balance the adsorption, activation and desorption process of oxygen-containing substances. In recent years, adjusting the material morphology combined with introducing structural defects to optimize catalytic activity has become a common method. Two-dimensional Pd nanosheets have attracted much attention due to their large specific surface area and special electronic structure, but due to the electrocatalytic inertness of basal plane atoms, their performance does not meet the needs of industrial application. As a kind of defect engineering, grain boundary engineering has attracted much attention due to its significant performance improvement. Grain boundaries are the junctions of different oriented regions in single-phase materials, have under-coordinated atoms, and induce strain at the interface to form high-energy surfaces. 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 the problems of low grain boundary content and low nanosheet purity. SUMMARY

[0005] The present application overcomes the shortcomings of the prior art, and provides 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 nanosheet purity of existing two-dimensional Pd nanosheets, and can be used as a fuel cell cathode catalyst.

[0006] The present application is realized by the following technical solutions:

[0007] A preparation method of a two-dimensional Pd nanosheet electrocatalyst rich in grain boundaries, comprising the following steps:

[0008] S1, taking palladium acetylacetonate and ascorbic acid in a glass bottle, adding oleylamine as a solvent, dispersing sufficiently to obtain a clear transparent solution;

[0009] S2, taking a metal carbonyl compound in a reaction kettle, adding dimethylformamide as a solvent, dispersing sufficiently to obtain a clear transparent solution;

[0010] S3, placing the glass bottle directly in the reaction kettle to form a double-layer device, and performing a heating reaction; centrifuging and washing the obtained solution several times, and drying to obtain a black powder.

[0011] Preferably, the mass ratio of palladium acetylacetonate and ascorbic acid is 1:0.1-1:10.

[0012] Preferably, the molar ratio of the metal carbonyl compound to dimethylformamide is 1:0.1-1:100.

[0013] More preferably, the metal carbonyl compound is molybdenum hexacarbonyl or tungsten hexacarbonyl.

[0014] Preferably, the reaction temperature of the heating reaction is 50-100 DEG C, and the reaction time is 2-12 h.

[0015] More preferably, the heating reaction is that the glass bottle is directly placed in a polytetrafluoroethylene lining, and then transferred to the reaction kettle, and the heating reaction is performed in a constant-temperature air drying oven.

[0016] Preferably, the sufficient dispersion in steps S1 and S2 is ultrasonic dispersion under room temperature conditions. In step S1, ultrasonic dispersion is performed under room temperature conditions for 15-30 min, and in step S2, ultrasonic dispersion is performed under room temperature conditions for 30-60 min.

[0017] Preferably, the washing liquid used in step S3 is a cyclohexane and anhydrous ethanol mixed liquid, and the volume ratio is 1:1-1:10.

[0018] Preferably, the drying in step S3 is freeze-drying or vacuum drying.

[0019] A two-dimensional Pd nanosheet electrocatalyst rich in grain boundaries is prepared by using the preparation method of the two-dimensional Pd nanosheet electrocatalyst rich in grain boundaries.

[0020] The beneficial effects of the present application relative to the prior art are:

[0021] 1. The application uses acetylacetone palladium as a precursor, ascorbic acid and carbon monoxide as a reducing agent, and oleylamine as a solvent to carry out heating reaction in a high-temperature reaction kettle; after the reaction is completed, the obtained mixture is washed and dried, and finally the ultra-thin two-dimensional Pd nanosheet rich in grain boundaries is prepared. The Pd nanosheet rich in grain boundaries has a large specific surface area and excellent charge transport capacity, a large number of unsaturated coordinated atoms at the grain boundaries increase the basal plane active sites, and the lattice strain near the grain boundaries significantly changes the binding affinity to oxygen-containing intermediates, thereby effectively regulating the total barrier of the reaction path and greatly improving the electrocatalytic activity. Through electrochemical testing, the prepared ultra-thin Pd nanosheet catalyst rich in grain boundaries exhibits excellent oxygen reduction reaction electrocatalytic performance in alkaline conditions, and has wide application prospect and commercialization potential.

[0022] 2. In the reaction heating process, the metal carbonyl in the reaction kettle lining decomposes to generate sufficient carbon monoxide, and under the joint action of carbon monoxide and ascorbic acid, acetylacetone palladium is fully reduced, at the same time, sufficient carbon monoxide is adsorbed on the surface of palladium atoms, promoting two-dimensional growth, and finally obtaining ultra-thin palladium nanosheet with rich grain boundaries. The synthesized two-dimensional Pd nanosheet rich in grain boundaries can be used as an efficient electrocatalyst in fuel cells, metal-air batteries and electrochemical oxygen reduction processes.

[0023] 3. The preparation method of the application is simple to operate and does not require special equipment.

[0024] 4. The two-dimensional Pd nanosheet rich in grain boundaries synthesized by the application has high yield, no impurity element interference and high purity.

[0025] 5. The application not only can greatly increase the basal plane active sites, but also helps to optimize the electronic structure of the catalyst, effectively improve the catalytic performance and mass activity, and provides an important research direction and application prospect for the development of efficient ORR electrocatalysts. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The scanning electron microscope image of the two-dimensional Pd nanosheet rich in grain boundaries prepared in Example 1;

[0027] Figure 2 The high-magnification transmission electron microscope image of the two-dimensional Pd nanosheet rich in grain boundaries prepared in Example 1;

[0028] Figure 3 The selected area diffraction pattern of the two-dimensional Pd nanosheet rich in grain boundaries prepared in Example 1;

[0029] Figure 4 The X-ray diffraction pattern of the two-dimensional Pd nanosheet rich in grain boundaries prepared in Example 1;

[0030] Figure 5LSV curves of the grain boundary-rich two-dimensional Pd nanosheets prepared in Example 1 and a commercial platinum carbon catalyst in 0.1 M KOH (rotation speed: 1600 rpm).

[0031] Figure 6 Synthetic scheme for preparing grain boundary-rich two-dimensional Pd nanosheets in the present application. DETAILED DESCRIPTION

[0032] In order to make the technical problems to be solved by the present application, technical solutions and beneficial effects clearer, the present application is further described in conjunction with the embodiments and drawings. It should be understood that the specific embodiments described herein are only used to explain the present application and not used to limit the present application. The technical solutions of the present application are described in detail below in conjunction with the embodiments and drawings, but the protection scope is not limited thereto.

[0033] Example 1

[0034] The present embodiment proposes a method for preparing a grain boundary-rich two-dimensional Pd nanosheet electrocatalyst:

[0035] S1, first weigh 20 mg of palladium acetylacetone and 10 mg of ascorbic acid in a 20 ml glass bottle, and add 5 ml of oleylamine, ultrasonically disperse at room temperature for 30 min, and obtain a clear transparent solution;

[0036] S2, weigh 60 mg of molybdenum hexacarbonyl in a 50 ml polytetrafluoroethylene liner, and add 4 ml of dimethylformamide, ultrasonically disperse at room temperature for 60 min, and obtain a clear transparent solution.

[0037] S3, place the 20 ml glass bottle directly in 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 in a constant-temperature air drying oven at 80℃ for 12 h, add the obtained product to ethanol, centrifuge, and then wash with a cyclohexane / ethanol mixture in a volume ratio of 1:1 for 4-5 times, and dry in a 60℃ vacuum oven, to obtain the grain boundary-rich two-dimensional Pd nanosheets.

[0038] Figure 1 The scanning electron microscope image of the grain boundary-rich two-dimensional Pd nanosheets prepared in Example 1, from which it can be seen that the sample prepared in Example 1 has a nanosheet morphology.

[0039] Figure 2 The high-resolution transmission electron microscope image of the grain boundary-rich two-dimensional Pd nanosheets prepared in Example 1, from which it can be seen that the obtained nanosheets have abundant grain boundaries on the surface.

[0040] Figure 3The selected area diffraction pattern of the two-dimensional Pd nanosheet rich in grain boundaries prepared in Example 1, from which it can be seen that the obtained Pd nanosheet is a polycrystalline structure.

[0041] Figure 4 The X-ray diffraction pattern of the two-dimensional Pd nanosheet rich in grain boundaries prepared in Example 1, from which it can be seen that the obtained spectrum and the diffraction peak position in the standard card are consistent, proving that the structures are consistent, and the prepared sample has good purity.

[0042] Figure 5 The LSV curve (rotating speed is 1600 rpm) of the two-dimensional Pd nanosheet rich in grain boundaries prepared in Example 1 in 0.1 M KOH with a commercial platinum carbon catalyst, from which it can be seen that the half-wave potential of the obtained Pd nanosheet is 0.94 V, which is much higher than that of the commercial platinum carbon catalyst, 0.86 V.

[0043] Figure 6 The synthesis schematic diagram of the two-dimensional Pd nanosheet rich in grain boundaries prepared in Example 1.

[0044] Example 2

[0045] This example proposes a preparation method of a two-dimensional Pd nanosheet electrocatalyst rich in grain boundaries:

[0046] S1, first weigh 10 mg of palladium acetylacetonate and 5 mg of ascorbic acid in a 10 ml glass bottle, and add 5 ml of oleylamine, and ultrasonically disperse for 15 min at room temperature to obtain a clear transparent solution;

[0047] S2, weigh 40 mg of molybdenum hexacarbonyl in a 25 ml polytetrafluoroethylene liner, and add 3 ml of dimethylformamide, and ultrasonically disperse for 60 min at room temperature to obtain a clear transparent solution;

[0048] S3, directly place the 10 ml glass bottle in the 25 ml polytetrafluoroethylene liner, and transfer it to a high-pressure reaction kettle, and heat it in a constant-temperature air drying oven at 80℃ for 12 h, then add the obtained product to ethanol, centrifuge, and wash it with a cyclohexane / ethanol mixture in a volume ratio of 1:3 for 4-5 times, and dry it in a 60℃ vacuum oven, to obtain the ultra-thin Pd nanosheet rich in grain boundaries.

[0049] Example 3

[0050] This example proposes a preparation method of a two-dimensional Pd nanosheet electrocatalyst rich in grain boundaries:

[0051] S1, first weigh 100 mg of palladium acetylacetonate and 50 mg of ascorbic acid in a 50 ml glass bottle, and add 20 ml of oleylamine, and ultrasonically disperse for 30 min at room temperature to obtain a clear transparent solution;

[0052] S2, 300 mg of molybdenum hexacarbonyl was weighed in a 100 ml Teflon liner, 20 ml of dimethylformamide was added, and ultrasonic dispersion was performed at room temperature for 60 min to obtain a clear and transparent solution;

[0053] S3, a 50 ml glass bottle was directly placed in a 100 ml Teflon liner, and then transferred to a high-pressure reaction kettle, heated in a constant-temperature air drying oven at 80°C for 12 h, the obtained product was added to ethanol and centrifuged, and then washed with a cyclohexane / ethanol mixture for 4-5 times, and dried in a vacuum oven at 60°C to obtain the two-dimensional Pd nanosheet rich in grain boundaries.

[0054] Example 4

[0055] The present embodiment provides a method for preparing a two-dimensional Pd nanosheet electrocatalyst rich in grain boundaries:

[0056] S1, first, 20 mg of palladium acetylacetone and 10 mg of ascorbic acid were weighed in a 50 ml glass bottle, 15 ml of oleylamine was added, and ultrasonic dispersion was performed at room temperature for 15 min to obtain a clear and transparent solution;

[0057] S2, 60 mg of molybdenum hexacarbonyl was weighed in a 50 ml Teflon liner, 4 ml of dimethylformamide was added, and ultrasonic dispersion was performed at room temperature for 30 min to obtain a clear and transparent solution.

[0058] S3, a 20 ml glass bottle was directly placed in a 50 ml Teflon liner to form a double-layer device, and then the double-layer device was transferred to a high-pressure reaction kettle, heated in a constant-temperature air drying oven at 100°C for 6 h, the obtained product was added to ethanol and centrifuged, and then washed with a cyclohexane / ethanol mixture with a volume ratio of 1:1 for 4-5 times, and dried in a vacuum oven at 60°C to obtain the two-dimensional Pd nanosheet rich in grain boundaries.

[0059] Example 5

[0060] The present embodiment provides a method for preparing a two-dimensional Pd nanosheet electrocatalyst rich in grain boundaries:

[0061] S1, first, 20 mg of palladium acetylacetone and 10 mg of ascorbic acid were weighed in a 50 ml glass bottle, 15 ml of oleylamine was added, and ultrasonic dispersion was performed at room temperature for 20 min to obtain a clear and transparent solution;

[0062] S2, 60 mg of molybdenum hexacarbonyl was weighed in a 50 ml Teflon liner, 4 ml of dimethylformamide was added, and ultrasonic dispersion was performed at room temperature for 30 min to obtain a clear and transparent solution.

[0063] S3, 20ml glass bottle is directly placed in 50ml polytetrafluoroethylene lining to constitute a double-layer device, and then the double-layer device is transferred to a high-pressure reaction kettle, heated in a constant-temperature air drying oven at 50℃ for 10h, the obtained product is added into ethanol, centrifuged, washed 4-5 times with a cyclohexane / ethanol mixture with a volume ratio of 1:10, and dried in a vacuum oven at 60℃ to obtain two-dimensional Pd nanosheets rich in grain boundaries.

[0064] The above is a further detailed description of the present application in combination with specific preferred embodiments, and it cannot be considered that the specific embodiments of the present application are limited to this. For ordinary skilled persons in the art to which the present application belongs, a number of simple deductions or substitutions can be made without departing from the present application, and all of them shall be considered to belong to the scope of patent protection determined by the submitted claims.

Claims

1. A method for preparing a two-dimensional Pd nanosheet electrocatalyst rich in grain boundaries, characterized in that, The method comprises the following steps: S1, taking palladium acetylacetonate and ascorbic acid in a glass bottle, and adding oleylamine as a solvent, and fully dispersing to obtain a clear and transparent solution; S2, taking metal carbonyl in a reactor liner, and adding dimethylformamide as a solvent, and fully dispersing to obtain a clear and transparent solution; S3, placing the glass bottle directly in the reactor liner to form a double-layer device, and performing a heating reaction; the solution obtained after the reaction is centrifuged and washed several times, and dried to obtain a black powder; the reaction temperature of the heating reaction is 50-100 DEG C, and the reaction time is 2-12 h; in the heating reaction, the metal carbonyl in the reactor liner is first decomposed to generate sufficient carbon monoxide, and under the joint action of carbon monoxide and ascorbic acid, the palladium acetylacetonate is fully reduced, and at the same time, sufficient carbon monoxide is adsorbed on the surface of the palladium atom to promote two-dimensional growth, and finally, an ultra-thin palladium nanosheet with rich grain boundaries is obtained.

2. The method of claim 1, wherein the method is characterized by, The mass ratio of palladium acetylacetonate to ascorbic acid is 1:0.1-1:

10.

3. The method of claim 1, wherein the method is characterized by, The molar ratio of metal carbonyl to dimethylformamide is 1:0.1-1:

100.

4. The method of claim 3, wherein the method is characterized by, The metal carbonyl is molybdenum hexacarbonyl or tungsten hexacarbonyl.

5. The method of claim 1, wherein the method is characterized by, The heating reaction is to place the glass bottle directly in a polytetrafluoroethylene liner, and then transfer it to a reactor, and perform a heating reaction in a constant-temperature air drying oven.

6. The method of claim 1, wherein the method is characterized by, The fully dispersing in steps S1 and S2 is ultrasonic dispersion under room temperature conditions.

7. The method of claim 1, wherein the method is characterized by, The washing liquid used in step S3 is a mixed liquid of cyclohexane and anhydrous ethanol, and the volume ratio is 1:1-1:

10.

8. The method of claim 1, wherein the method is characterized by, The drying in step S3 is freeze-drying or vacuum drying.

9. A two-dimensional Pd nanosheet electrocatalyst enriched with grain boundaries, characterized in that, The method is used to prepare a two-dimensional Pd nanosheet electrocatalyst rich in grain boundaries.

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