A gold-silver / silver-platinum nanocatalyst, its preparation method and application

Abstract

The present invention discloses a gold-silver / silver-platinum nanocatalyst, a preparation method thereof and an application thereof. In the present invention, a one-dimensional silver-gold-silver heterogeneous nanomaterial solution, a wrapping agent and deionized water are mixed to obtain a mixed solution 1; an ascorbic acid solution and a platinum precursor solution are added dropwise to the mixed solution 1 to obtain a mixed solution 3; the mixed solution 3 is stirred at room temperature and allowed to stand for aging for reaction; centrifugal separation and washing are carried out to obtain the gold-silver / silver-platinum nanocatalyst. Based on the one-dimensional silver-gold-silver heterogeneous nanomaterial as the reaction basis and based on the metal activity relationship existing among silver, platinum and gold, a gold-silver / silver-platinum nanocatalyst with continuously variable morphology is obtained by controlling the molar ratio of metal silver in the added one-dimensional silver-gold-silver heterogeneous nanomaterial to metal platinum in the platinum precursor. The catalyst has excellent electrocatalytic methanol oxidation performance. When the added silver:platinum molar ratio is 1:1, its peak current can reach 1582.9 mA / mg Pt .

Description

Technical Field

[0001] The present invention belongs to the field of new energy functional nanomaterials, and particularly relates to a gold-silver / silver-platinum nanocatalyst, a preparation method thereof and an application thereof. Background Art

[0002] Due to its advantages of cleanness and high efficiency, direct methanol fuel cells have become an optimal solution for alleviating environmental pollution and energy crisis in recent years and have attracted the attention of researchers from all walks of life. Among them, platinum-based nanocatalysts, as materials with excellent catalytic performance, have been widely used in the field of fuel cells, especially direct methanol fuel cells. However, problems such as the relatively scarce platinum resources, high price, instability during the catalytic process and easy poisoning by intermediates have seriously hindered the commercial application of platinum-based nanocatalytic materials. Therefore, reducing the platinum content in the catalyst and improving the platinum-based nanocatalyst have become important research directions.

[0003] Alloying and hollowing are common ideas for improving platinum-based nanocatalysts. The introduction of noble metals such as gold and silver can achieve the purposes of reducing the platinum content, improving the catalytic performance of the material and enhancing the anti-poisoning ability. At present, methods for preparing materials containing gold, silver and platinum include chemical reduction method, replacement method, etc. Among them, in the chemical reduction method, various precursor solutions are mixed and then an appropriate amount of reducing agent is added to directly form alloyed nanocatalysts through co-reduction. The products obtained by this method are mostly core-shell structured nanoflowers, and usually only the thickness of the alloy shell layer can be adjusted by changing the concentration of the precursor solution, or with gold / silver nanostructures as the substrate, granular or needle-shaped platinum or silver-platinum nanocrystals are deposited on their surfaces to form a core-shell structure. For example, Luo et al. deposited needle-shaped platinum nanocrystals on the surface of silver nanowires to form a core-shell structured silver@platinum nanowire for the electrocatalytic oxidation of methanol. However, this method cannot continuously and controllably change its morphology in various types (Luo B, Zhao Q, Zhang Y, et al. Core-shell Ag nanowires@Pt nanorods catalyst: Synthesis and application in direct methanol fuel cells. Materials Letters, 2018, 233: 138-141.); for the replacement method, due to the difference in the metal activity order of silver, platinum and gold, nanocatalysts can be simply and effectively prepared on gold-silver nanomaterials through replacement reactions. At the same time, the morphology and composition can be changed by adjusting the shape of the gold-silver nanomaterials and various reaction parameters. The method based on the replacement reaction is easy to operate, the products are easy to control and the experimental reproducibility is strong, which is a very promising method. Summary of the Invention

[0004] Aiming at the deficiencies of the above-mentioned existing technologies, the purpose of the present invention is to provide a gold-silver / silver-platinum nanocatalyst for electrocatalytic methanol oxidation, its preparation method and application.

[0005] Based on the one-dimensional silver-gold-silver heterogeneous nanomaterial as the reaction basis and the metal activity relationship among silver, platinum, and gold, a gold-silver / silver-platinum nanocatalyst with continuously variable morphology is obtained by controlling the molar ratio of metallic silver in the added one-dimensional silver-gold-silver heterogeneous nanomaterial to metallic platinum in the platinum precursor; this catalyst has excellent electrocatalytic methanol oxidation performance.

[0006] The purpose of the present invention is achieved through the following technical solutions.

[0007] A preparation method of a gold-silver / silver-platinum nanocatalyst, comprising the following steps:

[0008] (1) Mix a one-dimensional silver-gold-silver heterogeneous nanomaterial solution, a wrapping agent, and deionized water, and stir evenly at room temperature to obtain a mixed solution 1;

[0009] (2) Under stirring at room temperature, add an ascorbic acid solution dropwise to the mixed solution 1 in step (1) to obtain a mixed solution 2;

[0010] (3) Under stirring at room temperature, add a platinum precursor solution dropwise to the mixed solution 2 in step (2) to obtain a mixed solution 3;

[0011] (4) Stir the mixed solution 3 in step (3) at room temperature, let it stand for aging to react; after the reaction ends, centrifuge, separate, and wash to obtain the gold-silver / silver-platinum nanocatalyst.

[0012] Preferably, the silver concentration in the one-dimensional silver-gold-silver heterogeneous nanomaterial solution in step (1) is 0.1 - 1.5 mM;

[0013] Preferably, the wrapping agent in step (1) is one or more of cetyltrimethylammonium chloride, polyvinylpyrrolidone, and cetyltrimethylammonium bromide.

[0014] Preferably, the concentration of the ascorbic acid solution in step (2) is 5 - 10 mM.

[0015] Preferably, the platinum precursor in step (3) is one or more of chloroplatinic acid, platinum chloride, sodium chloroplatinate, and potassium chloroplatinate;

[0016] Preferably, the concentration of the platinum precursor solution is 1 - 5 mM.

[0017] Preferably, the molar ratio of ascorbic acid in step (2) to platinum in the platinum precursor solution in step (3) is 1:0.1 - 1.0;

[0018] Preferably, the concentration of the encapsulating agent in the mixed solution 3 in step (3) is 1-10 mg / mL.

[0019] Preferably, the molar ratio of silver in the one-dimensional silver-gold-silver heterogeneous nanomaterial solution in step (1) to platinum in the platinum precursor solution in step (3) is 0.2-10:1;

[0020] Preferably, the concentration of platinum in the mixed solution 3 in step (3) is 0.15-4.5 mM.

[0021] Preferably, when the molar ratio of silver in the one-dimensional silver-gold-silver heterogeneous nanomaterial solution in step (1) to platinum in the platinum precursor solution in step (3) is 0.5:1, the morphology of the obtained gold-silver / silver-platinum nanocatalyst is a coated structure;

[0022] Preferably, when the molar ratio of silver in the one-dimensional silver-gold-silver heterogeneous nanomaterial solution in step (1) to platinum in the platinum precursor solution in step (3) is 1:1, the morphology of the obtained gold-silver / silver-platinum nanocatalyst is a dumbbell-like structure composed of hollow nanorods connecting two nanoflowers;

[0023] Preferably, when the molar ratio of silver in the one-dimensional silver-gold-silver heterogeneous nanomaterial solution in step (1) to platinum in the platinum precursor solution in step (3) is 2-5:1, the morphology of the obtained gold-silver / silver-platinum nanocatalyst is a partially hollow rod-like structure;

[0024] Preferably, when the molar ratio of silver in the one-dimensional silver-gold-silver heterogeneous nanomaterial solution in step (1) to platinum in the platinum precursor solution in step (3) is 10:1, the morphology of the obtained gold-silver / silver-platinum nanocatalyst is a solid rod-like structure with slightly alloyed surface.

[0025] Preferably, the time for stirring at room temperature in step (4) is 3-10 min; the time for static aging is 4-8 h.

[0026] Preferably, the preparation method of the one-dimensional silver-gold-silver heterogeneous nanomaterial solution includes the following steps:

[0027] (a) Dissolve a gold source, a silver source, an encapsulating agent, and a reducing agent in water to obtain a mixed solution;

[0028] (b) Perform a hydrothermal reaction on the mixed solution obtained in step (a), control the initial pressure at 0.6-1.2 MPa, the reaction temperature at 180-230 °C, and the reaction time at 16-24 h;

[0029] (c) After the reaction in step (b) ends, cool it to room temperature, and after centrifugal washing, disperse it in water to obtain a one-dimensional silver-gold-silver heterogeneous nanomaterial solution.

[0030] The Au-Ag / AgPt nanocatalyst prepared by the above-mentioned preparation method.

[0031] The application of the above-mentioned Au-Ag / AgPt nanocatalyst in electrocatalytic methanol oxidation.

[0032] The present invention uses alloying and hollowing strategies to prepare an Au-Ag / AgPt nanocatalyst for electrocatalytic methanol oxidation, and the morphology of the prepared nanocatalyst can be regulated by controlling the molar ratio of silver in the one-dimensional silver-gold-silver heteronanomaterial solution to platinum in the platinum precursor solution (Ag:Pt). As the Ag:Pt molar ratio increases continuously, nanomaterials with core-shell structure, dumbbell structure, hollow rod structure, and solid rod structure can be prepared in sequence.

[0033] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0034] (1) Based on the one-dimensional silver-gold-silver heteronanomaterial as the reaction basis, the introduction of gold and silver metals is beneficial to maintaining the stability of the platinum-based nanocatalyst and improving the anti-poisoning ability of platinum. In addition, the heterostructure is conducive to the construction and transformation of nanocatalysts with various morphologies.

[0035] (2) The operation of the present invention is simple and has good repeatability. By changing the Ag:Pt molar ratio, continuous and controllable changes in the morphology of the prepared nanocatalyst can be achieved.

[0036] (3) The Au-Ag / AgPt nanocatalyst prepared by the present invention has excellent electrocatalytic methanol oxidation performance. When the added Ag:Pt molar ratio is 1:1, its peak current can reach 1582.9 mA / mg. Pt . Description of the Drawings

[0037] Figure 1 It is a transmission electron microscope image of the Au-Ag / AgPt nanocatalyst prepared in Example 1 of the present invention when the added Ag:Pt molar ratio is 0.5:1.

[0038] Figure 2 It is a transmission electron microscope image of the Au-Ag / AgPt nanocatalyst prepared in Example 2 of the present invention when the added Ag:Pt molar ratio is 1:1.

[0039] Figure 3 It is a transmission electron microscope image of the Au-Ag / AgPt nanocatalyst prepared in Example 3 of the present invention when the added Ag:Pt molar ratio is 5:1.

[0040] Figure 4 It is a transmission electron microscope image of the Au-Ag / AgPt nanocatalyst prepared in Example 4 of the present invention when the added Ag:Pt molar ratio is 10:1.

[0041] Figure 5UV-Vis absorption spectra of the Au-Ag / AgPt nanocatalysts prepared in Examples 1, 2, 5, and 6 of the present invention.

[0042] Figure 6 Cyclic voltammograms of the Au-Ag / AgPt nanocatalysts prepared in Examples 1, 2, 5, and 6 of the present invention and platinum black under alkaline conditions (0.5 M KOH). Detailed implementation manners

[0043] The following further illustrates the specific implementation of the present invention in conjunction with the drawings and examples, but the implementation and protection of the present invention are not limited thereto. It should be noted that for the processes not specifically described in detail below, those skilled in the art can implement or understand them with reference to the prior art. For reagents or instruments without indicating the manufacturer, they are regarded as conventional products that can be obtained through commercial purchase.

[0044] Preparation method of one-dimensional Ag-Au-Ag heterogeneous nanomaterials:

[0045] (1) In a 20 mL polytetrafluoroethylene inner liner, 100 mg of polyvinylpyrrolidone, 600 mg of cetyltrimethylammonium chloride, 420 μL of 48.56 mM chloroauric acid solution, and 800 μL of 102 mM silver nitrate solution were mixed, and ultrapure water was added to a total volume of 10 mL. The mixture was stirred evenly at room temperature to obtain a mixed solution.

[0046] (2) The inner liner was transferred to a reaction kettle and sealed. Nitrogen was filled until the initial pressure was 1.2 MPa. The reaction kettle was transferred to an oil bath at 230 °C and reacted for 24 h under stirring.

[0047] (3) After the reaction, the reaction kettle was naturally cooled to room temperature, the reaction solution was taken out, centrifugally washed 3 times with ultrapure water, dispersed in ultrapure water, and fixed to 5 mL. At this time, the silver content in the one-dimensional Ag-Au-Ag heterogeneous nanomaterial solution was about 0.48 mM.

[0048] Example 1

[0049] All glassware used was soaked in freshly prepared aqua regia for 1 h, washed with ultrapure water, and dried for later use.

[0050] Preparation method of Au-Ag / AgPt nanocatalyst:

[0051] (1) Weigh 10 mg of cetyltrimethylammonium chloride and add it to 414 μL of deionized water. After stirring evenly, add 300 μL of the one-dimensional Ag-Au-Ag heterogeneous nanomaterial solution with a silver content of 0.48 mM, and stir evenly at room temperature to obtain a mixed solution.

[0052] (2) Pipette 143 μL of 10 mM ascorbic acid solution and add it dropwise to the mixed solution in step (1), and stir evenly at room temperature to obtain a mixed solution.

[0053] (3) Pipette 143 μL of 2 mM chloroplatinic acid solution into the mixed solution obtained in step (2), stir evenly at room temperature to obtain a mixed solution. At this time, the total volume of the mixed solution is 1 mL, and the molar ratio of silver to platinum added is 0.5:1.

[0054] (4) Stir the mixed solution in step (3) at room temperature for 5 min and then let it stand for aging for 5 h.

[0055] (5) Collect the reaction solution, then carry out centrifugal separation and washing to obtain the Au - Ag / AgPt nanocatalyst prepared with a silver:platinum molar ratio of 0.5:1.

[0056] The transmission electron microscope photograph of the nanocatalytic material prepared in this example is as Figure 1 shown, presenting a uniform coating structure with a gold icosahedron in the center and a silver - platinum alloy on the outside.

[0057] Example 2

[0058] Preparation method of Au - Ag / AgPt nanocatalyst:

[0059] The difference from Example 1 is that the deionized water is 486 μL, the chloroplatinic acid is 71 μL, and the molar ratio of silver to platinum added is 1:1.

[0060] The transmission electron microscope photograph of the nanocatalytic material prepared in this example is as Figure 2 shown, presenting a dumbbell - like structure with well - dispersed hollow nanorods connecting two nanoflowers. The center of the hollow nanorod is a gold icosahedron, and the outer shell and nanoflowers are silver - platinum alloys.

[0061] Example 3

[0062] Preparation method of Au - Ag / AgPt nanocatalyst:

[0063] The difference from Example 1 is that the deionized water is 542.8 μL, the chloroplatinic acid is 14.2 μL, and the molar ratio of silver to platinum added is 5:1.

[0064] The transmission electron microscope photograph of the nanocatalytic material prepared in this example is as Figure 3 shown, presenting a uniform partially hollow nanorod structure with a gold icosahedron in the center and silver - platinum alloy distributed in the hollow part and on the surface of the nanorod.

[0065] Example 4

[0066] Preparation method of Au - Ag / AgPt nanocatalyst:

[0067] The difference from Example 1 is that the deionized water is 549.9 μL, chloroplatinic acid is 7.1 μL, and the molar ratio of added silver to platinum is 10:1.

[0068] The transmission electron microscope photograph of the nano-catalytic material prepared in this example is as Figure 4 shown, presenting a solid nano-rod structure with slightly alloyed surface. The center is a gold icosahedron, and the silver-platinum alloy is distributed on the surface of the solid nano-rod.

[0069] Example 5

[0070] Preparation method of gold-silver / silver-platinum nano-catalyst:

[0071] The difference from Example 1 is that the deionized water is 521.5 μL, chloroplatinic acid is 35.5 μL, and the molar ratio of added silver to platinum is 2:1.

[0072] Example 6

[0073] Preparation method of gold-silver / silver-platinum nano-catalyst:

[0074] The difference from Example 1 is that the deionized water is 533.3 μL, chloroplatinic acid is 23.7 μL, and the molar ratio of added silver to platinum is 3:1.

[0075] The nano-catalytic materials prepared in Examples 5 and 6 have a similar structure to the material prepared in Example 3, presenting a uniform partially hollow nano-rod structure. The center is a gold icosahedron, and the silver-platinum alloy is distributed in the hollow part and on the surface of the nano-rod.

[0076] Figure 5 UV-visible absorption spectra of the gold-silver / silver-platinum nano-catalysts prepared in Examples 1, 2, 5, and 6 and the one-dimensional silver-gold-silver hetero-nanomaterials. It can be seen that as the ratio of added silver to platinum decreases, the typical double-peak feature of the nano-rod structure gradually weakens, and the characteristic single peak of the gold particles at a wavelength of 580 nm gradually becomes prominent. Combining Figures 1-4 , it can be explained that the reduction reaction between the added ascorbic acid and the platinum precursor and the displacement reaction between the platinum precursor and the silver atoms in the one-dimensional silver-gold-silver hetero-nanorods form a competitive relationship, thus reducing the reduction rate of the platinum precursor by silver atoms and the deposition growth rate on the one-dimensional nanorods. When the added platinum precursor is less, that is, the silver:platinum is larger, fewer platinum atoms are displaced by silver atoms, and the reaction rate is slower. Therefore, a dumbbell-like structure connecting two nano-flowers with hollow nano-rods ( Figure 2 ), a partially hollow nano-rod structure ( Figure 3 ), and a solid nano-rod structure with slightly etched surface ( Figure 4), and when the amount of the platinum precursor added increases, the reduction reaction between ascorbic acid and the platinum precursor can no longer strongly balance the reaction of silver atoms replacing platinum atoms, and the replacement reaction rate is relatively fast. Therefore, the rod-like structure collapses and a structure similar to coating is formed. Figure 1 ) It shows that the continuous controllable change of the morphology of the prepared nanocatalyst can be achieved by changing the molar ratio of silver:platinum added in the present invention.

[0077] Figure 6 The cyclic voltammetry curves of the Au-Ag / AgPt nanocatalysts prepared in Examples 1, 2, 5, and 6 and platinum black under alkaline conditions (0.5 M KOH) are shown. It can be seen that when the added silver:platinum is 1:1, 2:1, and 3:1 respectively, the peak currents are 1582.9 mA / mg Pt , 567.3 mA / mg Pt , 366.9 mA / mg Pt , and their electrocatalytic performance for methanol is better than that of platinum black (the peak current is 277.3 mA / mg Pt ), and the performance is the best when the silver:platinum is 1:1. When the silver:platinum is 1:2, due to the fragmentation of the one-dimensional rod-like structure, its electrocatalytic performance for methanol oxidation is poor.

[0078] The above embodiments are the preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent substitution methods and are all included in the protection scope of the present invention.

Claims

1. A method for preparing a gold-silver / silver-platinum nanocatalyst, characterized in that, It includes the following steps: (1) Mix the one-dimensional silver-gold-silver heterogeneous nanomaterial solution, the encapsulating agent, and deionized water, and stir evenly at room temperature to obtain mixed solution 1; (2) While stirring at room temperature, add ascorbic acid solution dropwise to the mixed solution 1 in step (1) to obtain mixed solution 2; (3) While stirring at room temperature, add platinum precursor solution dropwise to the mixed solution 2 in step (2) to obtain mixed solution 3; (4) Stir the mixed solution 3 in step (3) at room temperature, let it stand for aging to carry out the reaction; after the reaction ends, centrifuge, separate, and wash to obtain the Au-Ag / AgPt nanocatalyst; The encapsulating agent in step (1) is cetyltrimethylammonium chloride; The molar ratio of ascorbic acid in step (2) to platinum in the platinum precursor solution in step (3) is 1:0.1; The molar ratio of silver in the one-dimensional silver-gold-silver heterogeneous nanomaterial solution in step (1) to platinum in the platinum precursor solution in step (3) is 1:1; The morphology of the Au-Ag / AgPt nanocatalyst is a dumbbell-like structure formed by hollow nanorods connecting two nanoflowers.

2. The preparation method according to claim 1, characterized in that, The silver concentration in the one-dimensional silver-gold-silver heterogeneous nanomaterial solution in step (1) is 0.1 - 1.5 mM.

3. The preparation method according to claim 1, characterized in that, The concentration of the ascorbic acid solution in step (2) is 5 - 10 mM; The platinum precursor in step (3) is one or more of chloroplatinic acid, platinum chloride, sodium chloroplatinate, and potassium chloroplatinate; the concentration of the platinum precursor solution is 1 - 5 mM.

4. The preparation method according to claim 1, characterized in that, The concentration of the encapsulating agent in the mixed solution 3 in step (3) is 1 - 10 mg / mL.

5. The preparation method according to claim 1, wherein The concentration of platinum in the mixed solution 3 in step (3) is 0.15 - 4.5 mM.

6. The preparation method according to claim 1, characterized in that, The time for stirring at room temperature in step (4) is 3 - 10 min; the time for standing and aging is 4 - 8 h.

7. The preparation method according to claim 1, characterized in that The preparation method of the one-dimensional silver-gold-silver heterogeneous nanomaterial solution includes the following steps: (a) Dissolve the gold source, silver source, encapsulating agent, and reducing agent in water to obtain a mixed solution; (b) Carry out a hydrothermal reaction on the mixed solution obtained in step (a), control the initial pressure at 0.6 - 1.2 MPa, the reaction temperature at 180 - 230 °C, and the reaction time at 16 - 24 h; (c) After the reaction in step (b) ends, cool it to room temperature, and after centrifuging and washing, disperse it in water to obtain the one-dimensional silver-gold-silver heterogeneous nanomaterial solution.

8. The Au-Ag / AgPt nanocatalyst prepared by the preparation method according to any one of claims 1 - 7.

9. The application of the Au-Ag / AgPt nanocatalyst according to claim 8 in electrocatalytic methanol oxidation.

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