Au@Pt / Pd core-shell material and preparation method and application thereof

Abstract

The present invention provides an Au@Pt / Pd core-shell material and a preparation method and application thereof, belonging to the technical field of nano-functional material preparation. The present invention discloses a method for constructing a microfluidic system, a structural design of a glass microfluidic reaction chip with adjustable mixing, and describes a mechanism for controllable morphology of core-shell materials. A microfluidic reaction chip with a specific number of micro-mixing structures is prepared by a wet etching method, thereby achieving controllable mixing efficiency during the reaction process. Precise control of the core-shell structure is achieved by using controlled mixing efficiency. Compared with existing preparation methods and other traditional methods, the method of the present invention has the advantages of rapidity, strong repeatability, strong controllability, and continuous production.

Description

Technical Field

[0001] The present invention relates to the technical field of nano functional material preparation, and in particular to an Au@Pt / Pd core-shell material and a preparation method and application thereof. Background Art

[0002] Direct ethanol fuel cells (DEFCs) are considered to have great practical application potential and have received widespread attention because of the high energy density (8.1KW·h / kg) of ethanol they use, their low toxicity to the human body, and their renewable green and environmentally friendly energy. The key to DEFC energy conversion efficiency is the catalyst, and the main problem with using ethanol as fuel is that the catalyst has low electrocatalytic activity for ethanol oxidation, and the CC bond is difficult to break, making it difficult to completely oxidize ethanol to CO2 and release 12 electrons. The electrocatalytic oxidation of ethanol on existing catalysts is mainly to produce acetic acid through 4-electron transfer oxidation, which greatly reduces the fuel utilization efficiency. Pt / C is widely used in DEFC anode catalysts because Pt is more active than other metals in CC bond cleavage in EOR. However, due to the low reserves of Pt on the earth and its widespread use in industry, the high cost of Pt has become an obstacle to its commercialization. At the same time, the intermediate products of ethanol oxidation are easily adsorbed on the surface of Pt, occupying the surface active sites of Pt, causing catalyst poisoning and thus losing activity. A promising strategy is to design a core-shell structure material containing a Pt layer on a cheaper metal substrate (Pd, Ag, Au, Ir, Co, etc.), which can efficiently utilize the deposited Pt atoms and improve the catalytic activity and stability of the material through the surface strain effect and electronic effect induced by the substrate.

[0003] The following are the general methods for synthesizing Au@Pt core-shell materials, including chemical deposition, dealloying, electrodeposition, surface segregation, atomic layer deposition, and physical deposition. However, the above methods still face great challenges in continuous production, batch repetition, and precise control of reaction parameters. Microfluidic reactions have many advantages, including enhanced heat and mass transfer, rapid and adjustable mixing of precursor solutions, continuous flow production, and low reagent consumption throughout the optimization process. These characteristics have prompted a large number of researchers to explore the use of continuous flow-based microfluidic devices to synthesize functional nanomaterials with higher uniformity on a large scale. In addition, microfluidic reactors can perform mass diffusion and mixing regulation within a limited volume, and the resulting reaction kinetics are significantly different from traditional bulk solution reactions. By adjusting the flow characteristics of the fluid in the microfluidic, the microfluidic synthesis technology is applied to the precise control of the size, morphology, composition, and structure of nanomaterials, which has important research significance for meeting the current new material needs. Summary of the invention

[0004] The purpose of the present invention is to provide an Au@Pt / Pd core-shell material and a preparation method and application thereof, so as to solve the technical problem that the mixing efficiency in traditional reactions cannot be accurately controlled.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for controllably preparing Au@Pt / Pd core-shell materials using microfluidic technology, comprising the following steps:

[0007] 1) mixing a chloroauric acid solution and a sodium citrate aqueous solution and reacting them to obtain an Au seed solution;

[0008] 2) mixing the Au seed solution and ascorbic acid to obtain an Au precursor solution;

[0009] 3) Adding the Au precursor solution and the Pt / Pd precursor solution into two identical syringes respectively, reacting in a microfluidic reaction chip, and obtaining the product is the Au@Pt / Pd core-shell material;

[0010] The microfluidic reaction chip comprises a mixing unit and a reaction unit, and the mixing unit contains different numbers of S-shaped structures.

[0011] Furthermore, the mixing unit consists of 0, 5, 10, 20 or 50 S-shaped structures.

[0012] Furthermore, the total length of the S-shaped structure is 3.89 mm, and one S-shaped structure is composed of two semicircular arcs, wherein the radius of the inner arc is 50 μm, and the radius of the outer arc is 450 μm.

[0013] Further, the reaction unit is a spiral structure with a total length of 1 to 80 cm;

[0014] The microfluidic reaction chip is 6 to 15 cm long and 3 to 10 cm wide.

[0015] Furthermore, the mass concentration of the chloroauric acid solution is 0.8-1.2wt%, and the mass concentration of the sodium citrate aqueous solution is 0.8-1.2wt%;

[0016] The volume ratio of the chloroauric acid solution to the sodium citrate aqueous solution is 1:8-11.

[0017] Furthermore, in the step 1), the reaction temperature is 70-90° C., and the reaction time is 20-40 min.

[0018] Furthermore, the volume mass ratio of the Au seed solution to ascorbic acid is 8-12 mL: 4-6 mg.

[0019] Further, the flow rates of the Au precursor solution and the Pt / Pd precursor solution in the syringe are independently 10 to 500 μL / min, the Pt / Pd precursor solution comprises an ethanol solution of chloroplatinic acid or an ethanol solution of potassium tetrachloropalladate, and the mass concentration of the ethanol solution of chloroplatinic acid or the ethanol solution of potassium tetrachloropalladate is 0.8 to 1.2 wt%;

[0020] In the step 3), the reaction temperature is 50-70°C.

[0021] The invention provides an Au@Pt / Pd core-shell material.

[0022] The invention provides an application of Au@Pt / Pd core-shell material in electrocatalytic ethanol.

[0023] Beneficial effects of the present invention:

[0024] 1) The preparation method adopted by the present invention is relatively simple, has precise condition control, high repeatability and is easy to operate;

[0025] 2) The nucleation of the Au@Pt core-shell material prepared by the present invention can be regulated by the designed chip structure;

[0026] 3) The Au@Pt and Au@Pd core-shell materials prepared in the present invention have high ethanol oxidation activity and good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a schematic diagram of the microfluidic system of the present invention;

[0028] Figure 2 The microfluidic reaction chip design and physical diagram of the present invention;

[0029] Figure 3 TEM image (A) of the Au seed solution prepared in Example 1 of the present invention and the particle size distribution diagram of Au particles (B);

[0030] Figure 4 TEM image of the Au@Pt core-shell material prepared in Example 1 of the present invention;

[0031] Figure 5 It is a fluid simulation diagram in a straight channel structure and an S-shaped structure in the chip structure of the present invention;

[0032] Figure 6 This is an optical microscope image of the Au@Pd core-shell material synthesized in Example 3 of the present invention;

[0033] Figure 7 These are performance test diagrams of the Au@Pt and Au@Pd core-shell materials prepared in Examples 1 and 3 of the present invention. DETAILED DESCRIPTION

[0034] The present invention provides a method for controllably preparing Au@Pt / Pd core-shell materials using microfluidic technology, comprising the following steps:

[0035] 1) mixing a chloroauric acid solution and a sodium citrate aqueous solution and reacting them to obtain an Au seed solution;

[0036] 2) mixing the Au seed solution and ascorbic acid to obtain an Au precursor solution;

[0037] 3) Adding the Au precursor solution and the Pt / Pd precursor solution into two identical syringes respectively, reacting in a microfluidic reaction chip, and obtaining the product is the Au@Pt / Pd core-shell material;

[0038] The microfluidic reaction chip comprises a mixing unit and a reaction unit, and the mixing unit contains different numbers of S-shaped structures.

[0039] In the present invention, the material of the microfluidic reaction chip is glass, and the channel thereof is a circular channel.

[0040] In the present invention, the mixing unit is composed of 0, 5, 10, 20 or 50 S-shaped structures, preferably 50 S-shaped structures.

[0041] In the present invention, the total length of the S-shaped structure is 3.89 mm, and one S-shaped structure is composed of two semicircular arcs, wherein the radius of the inner arc is 50 μm, and the radius of the outer arc is 450 μm.

[0042] In the present invention, the reaction unit is a spiral structure with a total length of 1 to 80 cm, preferably 5 to 70 cm, and more preferably 10 to 60 cm; the length of the microfluidic reaction chip is 6 to 15 cm, preferably 7 to 14 cm, and more preferably 9 to 11 cm; the chip width is 3 to 10 cm, preferably 4 to 9 cm, and more preferably 5 to 8 cm.

[0043] In the present invention, by using microfluidic reaction chips with different structures, the mixing efficiency of the reactants is precisely controlled to achieve controllable preparation of Au@Pt / Pd core-shell materials, and it can also be extended to the preparation of other core-shell materials. The microfluidic reaction chip structure consists of two injection channels, a mixing unit that can control the number of S-shaped, a spiral reaction unit and a sample collection channel.

[0044] In the present invention, AutoCAD software is used for chip design, and the mixing module is composed of different numbers of S-shaped structures. The S-shaped micro-mixing structure is the key to controlling nucleation dynamics, and the inner arc radius of the structure is 50 μm, and the channel size is a circular channel of 100 to 400 μm. The injection pump, the microfluidic reaction chip, and the product collection device are connected by a fused silica capillary, the syringe is connected to the quartz capillary channel Luer joint, and the microfluidic reaction chip is connected to the quartz capillary by epoxy resin glue. The length and inner diameter of the fused silica capillary can be adjusted as needed.

[0045] In the present invention, when the micro-mixed structure mixing unit is composed of 0 S-type structures, an Au@Pt core-shell structure is obtained, in which the Pt element is uniformly distributed on the surface of the Au seed. As the number of S-type structures increases, granular Pt simple substance and branched core-shell mixed products appear. When the number of S-type structures is greater than 20, a pure branched Au@Pt core-shell product is obtained.

[0046] In the present invention, the mass concentration of the chloroauric acid solution is 0.8-1.2 wt %, preferably 0.9-1.1 wt %, and more preferably 1.0 wt %.

[0047] In the present invention, the mass concentration of the sodium citrate aqueous solution is 0.8-1.2 wt %, preferably 0.9-1.1 wt %, and more preferably 1.0 wt %.

[0048] In the present invention, the volume ratio of the chloroauric acid solution to the sodium citrate aqueous solution is 1:8-11, preferably 1:9-11, and more preferably 1:10.

[0049] In the present invention, in the step 1), the reaction temperature is 70-90°C, preferably 75-855°C, and more preferably 80°C; the reaction time is 20-40 min, preferably 25-35 min, and more preferably 30 min.

[0050] In the present invention, the volume mass ratio of the Au seed solution to ascorbic acid is 8-12 mL: 4-6 mg, preferably 9-11 mL: 4.5-5.5 mg, and more preferably 10 mL: 5.0 mg.

[0051] In the present invention, the flow rates of the Au precursor solution and the Pt / Pd precursor solution in the syringe are independently 10 to 500 μL / min, preferably 50 to 400 μL / min, and more preferably 100 to 300 μL / min.

[0052] In the present invention, the Pt / Pd precursor solution comprises an ethanol solution of chloroplatinic acid or an ethanol solution of potassium tetrachloropalladate, preferably an ethanol solution of chloroplatinic acid; the mass concentration of the ethanol solution of chloroplatinic acid or the ethanol solution of potassium tetrachloropalladate is 0.8-1.2wt%, preferably 0.9-1.1wt%, and more preferably 1.0wt%.

[0053] In the present invention, in the step 3), the reaction temperature is 50-70°C, preferably 55-65°C, and more preferably 60°C.

[0054] In the present invention, the microfluidic technology of the present invention can be extended to the preparation of other non-platinum core-shell structures.

[0055] The invention provides an Au@Pt / Pd core-shell material.

[0056] The invention provides an application of Au@Pt / Pd core-shell material in electrocatalytic ethanol.

[0057] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0058] Example 1

[0059] Preparation of Au@Pt core-shell material:

[0060] Prepare the precursor solution: add 0.166mL HAuCl4 aqueous solution (1.0wt%) to 10mL ultrapure water. Heat the mixture to 80℃ in a thermal shaker and shake at 900 rpm. After 2 minutes, add 1.66mL sodium citrate aqueous solution (1.0wt%) and continue shaking for 30 minutes. As the mixture changes from colorless to gray and finally to wine red, the Au seed solution is obtained. Figure 3 The TEM image of the synthesized Au seed solution (A) and the size distribution of the Au particles (B) are shown in Figure 1. Figure 3 It can be seen that the synthesized Au particles are uniform in size, with an average particle size of 15.6±1.3nm and a narrow size distribution range, which meets the requirements of subsequent experiments.

[0061] 5 mg of ascorbic acid was dissolved in the AuNPs seed solution obtained above to obtain an Au precursor solution; 0.429 mL of H2PtCl6 ethanol solution (1.0 wt%) was added to 10 mL of ultrapure water and ultrasonicated for 10 minutes to obtain a Pt precursor solution.

[0062] The Au precursor solution and Pt precursor solution are sucked into a glass syringe, and the needle is held against a clean paper with the needle facing upwards, and the air in the syringe is pushed out until the paper becomes wet. Remove the needle from the glass syringe and connect it to the capillary of the connected chip through the PMMA microfluidic reaction chip connector. Place the microfluidic reaction chip on a heating plate and heat it to 60°C, and introduce the capillary at the tail end of the chip into the collection tube. Use a syringe pump to inject the two solutions into the two corresponding inlets of the microfluidic reaction chip, push the sample into the microfluidic reaction chip at a flow rate of 50 μL / min, and collect the corresponding products at the outlet.

[0063] The above-mentioned microfluidic reaction chip uses AutoCAD software for chip design. The designed chip channel width is 400μm, and the entire chip consists of a mixing unit and a reaction unit. The mixing unit is used to mix the fluid in the channel and has a variety of structures, such as 0, 5, 10, 20, and 50 S-shaped structures. The total length of a single S-shaped structure is 3.89mm, and an S-shaped structure consists of two semicircular arcs, with an inner arc radius of 50μm and an outer arc of 450μm. The reaction module is a spiral structure with a total length of 1 to 80cm, a chip length of 6 to 15cm, and a chip width of 3 to 10cm.

[0064] Figure 4 This is a TEM image of the material synthesized in the 50-mixing unit microfluidic reaction chip structure. From the line scan and surface scan results in the figure, it can be seen that the synthesized material is an Au@Pt core-shell material with Au as the core and Pt as the outer layer; Figure 5 The following are TEM images of materials synthesized in microfluidic reaction chip structures with 0 mixing units (straight channel), 5 mixing units, 10 mixing units, and 20 mixing units. It can be seen from the figures that the materials synthesized in chips with different mixing unit structures are significantly different. The nucleation process of Au@Pt core-shell materials can be regulated by the design of microfluidic reaction chip structure.

[0065] Example 2

[0066] Preparation of an Au@Pt core-shell material:

[0067] Preparation of precursor solution: 0.166 mL of HAuCl4 aqueous solution (1.0 wt%) was added to 10 mL of ultrapure water. The mixture was heated to 70°C in a thermal shaker and shaken at 900 rpm. After 2 minutes, 1.66 mL of sodium citrate aqueous solution (1.0 wt%) was added and continued to shake for 30 minutes. As the mixture changed from colorless to gray and finally to wine red, the AuNPs seed solution was obtained.

[0068] 6 mg of ascorbic acid was dissolved in the AuNPs seed solution obtained above to obtain an Au precursor solution; 0.429 mL of H2PtCl6 ethanol solution (1.0 wt%) was added to 10 mL of ultrapure water and ultrasonicated for 10 minutes to obtain a Pt precursor solution.

[0069] The other steps are the same as those in Example 1, and the morphological characteristics of the obtained Au@Pt core-shell material are consistent with those in Example 1.

[0070] Example 3

[0071] Preparation of an Au@Pd core-shell material:

[0072] Prepare the precursor solution: add 0.27 mL of K2PdCl4 ethanol solution (1.0 wt%) into 10 mL of ultrapure water, and ultrasonicate for 10 minutes to obtain a Pd precursor solution. Other steps are the same as in Example 1.

[0073] like Figure 6 A and B are TEM images of the materials synthesized in the 0-mixing unit microfluidic reaction chip structure. It can be seen from the figure that Pd exists in irregular small particles. Figure 6 C and D are TEM images of the materials synthesized in the 50-mixing unit microfluidic reaction chip structure. It can be seen from the figures that Pd grows on the surface of Au to form Au@Pd core-shell material.

[0074] Example 4

[0075] Preparation of an Au@Pd core-shell material:

[0076] Preparation of precursor solution: 0.166 mL of HAuCl4 aqueous solution (1.0 wt%) was added to 10 mL of ultrapure water. The mixture was heated to 70°C in a thermal shaker and shaken at 900 rpm. After 2 minutes, 1.66 mL of sodium citrate aqueous solution (1.0 wt%) was added and continued to shake for 30 minutes. As the mixture changed from colorless to gray and finally to wine red, the AuNPs seed solution was obtained.

[0077] 6 mg of ascorbic acid was dissolved in the AuNPs seed solution obtained above to obtain an Au precursor solution; 0.27 mL of K2PdCl4 ethanol solution (1.0 wt%) was added to 10 mL of ultrapure water and ultrasonicated for 10 minutes to obtain a Pd precursor solution.

[0078] The other steps are the same as those in Example 3, and the morphological characteristics of the obtained Au@Pt core-shell material are consistent with those in Example 3.

[0079] Application Examples

[0080] The electrochemical performance test of the core-shell materials obtained in Example 1 (50 mixed units) and Example 3 (50 mixed units) was carried out:

[0081] The electrochemical test was carried out on a CHI1030c electrochemical workstation of Shanghai Chenhua Company, using a conventional standard three-electrode system at room temperature. A glassy carbon electrode (GCE, diameter 4.0 mm) was selected as the working electrode. A mercury-mercury oxide electrode (Hg / HgO, MMO) and a platinum sheet electrode were used as the reference electrode and the counter electrode, respectively. 10 μL of dendritic Au@Pt core-shell material (50 mixed units obtained from a microfluidic reaction chip) aqueous dispersion (Pt element content was 7.8 μg / mL, tested by ICP) or commercial Pt / C (1 mg / mL) ethanol suspension was transferred to the surface of the glassy carbon rotating disk electrode, and then 5 μL of perfluorosulfonic acid 117 (0.05 wt%) was used to treat the electrode surface and dried in dry air at room temperature for 3 h. Before the test, the electrode was heated to 1.0 mol·L -1 In KOH solution, 200 mV·s -1 The working electrode was electrochemically cleaned at a voltage of 0.0 to 1.2 V (vs. RHE) for 30 cycles. -1 Ethanol + 1.0 mol·L -1 In the mixed solution of KOH, the scan rate was 50 mV·s -1 The enhanced oil recovery activity of the material was measured in the range of 0.0 to 1.2 V (vs. RHE). -1 KOH+1.0mol·L -1 The durability was measured by chronoamperometry (CA) in an ethanol solution at a voltage of 0.75 V for 3600 seconds. Figure 7 The performance test results show that at a potential of 0.75 V, the peak current densities of Au@Pt and Au@Pd are 4530 mA·mg -1 and 5800mA·mg -1 , is a commercial Pt / C (540mAmg -1 ) are 8.4 and 10.7 times that of commercial Pt / C, and their ethanol oxidation activity is significantly higher than that of commercial Pt / C. The prepared Au@Pt and Au@Pd core-shell materials have good catalytic performance and stability for the electrocatalytic oxidation of ethanol.

[0082] It can be seen from the above embodiments that the present invention provides an Au@Pt / Pd core-shell material and a preparation method and application thereof. The microfluidic reaction chip structure designed by the present invention can control the nucleation process of Au@Pt or Au@Pd core-shell materials, and the prepared Au@Pt and Au@Pd core-shell materials have good catalytic activity and stability for ethanol electrocatalytic oxidation.

[0083] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing Au@Pt / Pd core-shell materials using microfluidic technology, characterized in that: The following steps are involved: 1) mixing the chloroauric acid solution and the sodium citrate aqueous solution and reacting them to obtain an Au seed solution; 2) mixing the Au seed solution and ascorbic acid to obtain an Au precursor solution; 3) The Au precursor solution and the Pt / Pd precursor solution are added into two identical syringes respectively, and reacted in a microfluidic reaction chip to obtain the Au@Pt / Pd core-shell material; The microfluidic reaction chip comprises a mixing unit and a reaction unit, wherein the mixing unit comprises different numbers of S-shaped structures; In the step 3), the reaction temperature is 60°C; The mixing unit consists of 0, 5, 10, 20 or 50 S-shaped structures; The total length of the S-shaped structure is 3.89 mm, and one S-shaped structure is composed of two semicircular arcs, wherein the inner arc radius is 50 μm and the outer arc radius is 450 μm; The nucleation process of the core-shell material is controlled by the S-type structure. When the micro-mixed structure mixing unit is composed of 0 S-type structures, the Au@Pt / Pd core-shell structure is obtained, in which the Pt / Pd elements are uniformly distributed on the surface of the Au seed. As the number of S-type structures increases, granular Pt / Pd elements and branched core-shell mixed products appear. When the number of S-type structures is greater than 20, a pure branched Au@Pt / Pd core-shell product is obtained.

2. The method for controllably preparing Au@Pt / Pd core-shell material using microfluidic technology according to claim 1, characterized in that: The reaction unit is a spiral structure with a total length of 1 to 80 cm; The microfluidic reaction chip is 6-15 cm long and 3-10 cm wide.

3. The method for controllably preparing Au@Pt / Pd core-shell material using microfluidic technology according to claim 1 or 2, characterized in that: The mass concentration of the chloroauric acid solution is 0.8-1.2wt%, and the mass concentration of the sodium citrate aqueous solution is 0.8-1.2wt%; The volume ratio of the chloroauric acid solution to the sodium citrate aqueous solution is 1:8-11.

4. The method for controllably preparing Au@Pt / Pd core-shell material using microfluidic technology according to claim 3, characterized in that: In the step 1), the reaction temperature is 70-90° C. and the reaction time is 20-40 min.

5. The method for controllably preparing Au@Pt / Pd core-shell material using microfluidic technology according to claim 1 or 4, characterized in that: The volume mass ratio of the Au seed solution to ascorbic acid is 8-12 mL: 4-6 mg.

6. The method for controllably preparing Au@Pt / Pd core-shell material using microfluidic technology according to claim 5, characterized in that: The flow rates of the Au precursor solution and the Pt / Pd precursor solution in the syringe are independently 10-500 μL / min, and the Pt / Pd precursor solution comprises an ethanol solution of chloroplatinic acid or an ethanol solution of potassium tetrachloropalladate, and the mass concentration of the ethanol solution of chloroplatinic acid or the ethanol solution of potassium tetrachloropalladate is 0.8-1.2 wt%.

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