Preparation method of Pd-based catalyst rich in large-scale strain defect structure and application of Pd-based catalyst in electrochemical oxygen reduction reaction

Abstract

The invention particularly relates to a preparation method of a Pd-based catalyst rich in a large-scale strain defect structure and an application of the Pd-based catalyst in an electrochemical oxygen reduction reaction, and the preparation method comprises the following steps: S1, dropwise adding oleylamine into a mixture of ferric acetylacetonate and palladium acetylacetonate, and performing ultrasonic treatment to form a uniform solution; 1.1-1.5 g of ferric acetylacetonate and 0.4-0.8 g of palladium acetylacetonate are added into each liter of oleylamine; and S2, reacting the solution at 150-250 DEG C for 20-28 hours, cooling, washing, and freeze-drying. The Pd catalyst surface dislocation can be synthesized in one step, the surface free energy in the Pd metal core growth process is changed through the stress-strain effect between Pd metal core particles and the Fe3O4 skin, a large-scale strain defect structure is induced, and the good catalytic performance is achieved in the electrochemical oxygen reduction reaction.

Description

Technical Field

[0001] The present invention relates to the technical field of electrocatalysts, and in particular to a method for preparing a Pd-based catalyst rich in large-scale strain defect structures and an application thereof in an electrochemical oxygen reduction reaction. Background Art

[0002] Palladium (Pd), as an element of the same group as platinum (Pt), is abundant in reserves and much cheaper than Pt. It has good oxygen reduction catalytic potential. Many researchers have improved the ORR activity of Pd materials by structural modification and size adjustment. Constructing defect structures on the surface of Pd-based nanomaterials is an effective strategy to regulate the local atomic structure and environment, expose more catalytic active sites, and promote the ORR catalytic process.

[0003] However, traditional methods for synthesizing metal surface strain / dislocation defect structures often require complex equipment and strict reaction conditions, such as high temperature and high pressure processing, chemical vapor deposition, hydrogen peroxide etching, etc. These harsh preparation conditions and procedural complexity greatly limit the practical application of these methods. Therefore, it is crucial to develop a simple and effective synthesis method to directly adjust the surface free energy during the metal formation process to construct large-scale strain defects. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art and to provide a method for preparing a Pd-based catalyst that can synthesize surface dislocations of a Pd catalyst in one step, change the surface free energy during the growth of the Pd metal core through the stress-strain effect between the Pd metal core particles and the Fe3O4 skin, and induce a large-scale strain defect structure, and its application in the electrochemical oxygen reduction reaction.

[0005] The technical solution adopted by the present invention is as follows: The first aspect of the present invention provides a method for preparing a Pd-based catalyst rich in large-scale strain defect structures, which comprises the following steps: S1. Add oleylamine dropwise into a mixture of ferric acetylacetonate and palladium acetylacetonate, and form a uniform solution by ultrasonication. Add 1.1-1.5 g ferric acetylacetonate and 0.4-0.8 g palladium acetylacetonate per liter of oleylamine. S2. The solution is reacted at 150-250°C for 20-28 h, then cooled, washed and freeze-dried.

[0006] A second aspect of the present invention provides an application of a Pd-based catalyst rich in large-scale strain defect structures in an electrochemical oxygen reduction reaction.

[0007] Preferably, (A) Pd@Fe3O4 catalyst is made into a working electrode: Pd@Fe3O4 catalyst and acetylene black are dispersed in a mixed solvent comprising ethanol, ultrapure water and Nafion solution, ultrasonically treated, and the catalyst ink after ultrasonic treatment is dropped onto a rotating disk electrode, and dried to obtain a working electrode; (B) The working electrode and the reference electrode are inserted into the electrolyte, wherein the reference electrode is a mercury oxide electrode and a graphite rod.

[0008] Preferably, in step (A), 0.5-1.5 g of Pd@Fe3O4 catalyst and 0.5-1.5 g of acetylene black are added to each liter of mixed solvent.

[0009] Preferably, in step (A), the volume ratio of C2H5OH, ultrapure water and Nafion solution in the mixed solvent is 10:9:1, and the concentration of the Nafion solution is 5 wt%.

[0010] The beneficial effects of the present invention are as follows: The present invention provides a preparation method of a metal catalyst rich in large-scale strain defect structure and its application in oxygen reduction reaction. First, iron (III) acetylacetonate and palladium (II) acetylacetonate are used as precursors, oleylamine is selected as a solvent, and then the solution is placed in a reactor for heating reaction, and washed and freeze-dried to obtain a Pd@Fe3O4 oxygen reduction catalyst with strain / dislocation defects. The traditional synthesis methods of metal surface strain / dislocation defect structures before this require relatively complex equipment and reaction conditions, and are also highly dependent on equipment and special chemicals, which limits the practical application and economic benefits of these methods.

[0011] We found that iron (III) acetylacetonate played a key role in the synthesis process. Without iron (III) acetylacetonate, the synthesized Pd catalyst surface had almost no dislocation defects and tensile strain. The method we invented can simply and efficiently synthesize Pd@Fe3O4 oxygen reduction catalysts with large-scale dislocation defects in one step, which can provide a synthetic idea for designing surface defects of nanomaterials. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, without paying creative labor, other drawings obtained based on these drawings still belong to the scope of the present invention.

[0013] Figure 1 It is the XRD (X-ray diffraction) spectrum of Pd@Fe3O4 in Example 1; Figure 2 It is the HAADF (High angle annular dark field) image of Pd@Fe3O4 in Example 1; Figure 3 This is the EDS (Energy Dispersive Spectrometer) mapping diagram of Pd@Fe3O4 in Example 1; Figure 4 HRTEM (High-Resolution Transition Electron Microscopy) image of Pd@Fe3O4 in Example 1; Figure 5 This is a low-magnification morphology image of Pd@Fe3O4 in Example 1; Figure 6 This is a low-magnification morphology image of Pd in ​​Example 2; Figure 7 HRTEM image of Pd in ​​Example 2; Figure 8 CV (Cyclic Voltammetry) diagram of Pd@Fe3O4 and Pt / C in Example 2; Fig. 9 The LSV (Linear Sweep Voltammetry) diagram of Pd@Fe3O4 and Pt / C in Example 2; Fig.10 CV diagrams of Pd and Pd@Fe3O4 in Comparative Example 2; Fig.11 LSV diagram of Pd and Pd@Fe3O4 in Comparative Example 2; Fig.12 LSV diagram of Pd@Fe3O4 samples prepared at 80℃ and 200℃ in Comparative Example 3. DETAILED DESCRIPTION

[0014] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings.

[0015] Example 1 The method for preparing a Pd@Fe3O4 catalyst having dislocation defects comprises the following specific steps: 15 ml of oleylamine was dropped into a mixture of 20 mg of acetylacetonate iron (III) and 10 mg of acetylacetonate palladium (II), and ultrasonicated for 30 minutes to form a uniform solution; the solution was then reacted at 200°C for 24 hours and cooled to room temperature; the solution was mixed with ethanol in a centrifuge tube, ultrasonicated for 5 minutes, the centrifuge was set to 5 minutes, the speed was 12000, washed with ethanol three times, and then washed once with cyclohexane and ethanol according to the above steps, and finally washed with ultrapure water, leaving about 2 ml of ultrapure water at the bottom of the test tube; freeze-dried for 24 hours to obtain the sample (i.e. Pd@Fe3O4).

[0016] The above Pd@Fe3O4 sample was made into a working electrode, and the specific steps were as follows: All electrochemical tests were performed in a CHI 760E electrochemical workstation at room temperature (25°C) in a three-electrode cell with 0.1 M KOH as the electrolyte. The reference electrode was a mercuric oxide (Hg / HgO) electrode and a graphite rod. 1 mg Pd@Fe3O4 catalyst and 1 mg acetylene black were dispersed in a mixture of 500 µL C2H5OH, 450 µL ultrapure water and 50 µL Nafion solution (5 wt%) and ultrasonically treated for 30 min. 10 µL of the ultrasonically treated catalyst ink was dropped onto a rotating disk electrode and dried to obtain a working electrode.

[0017] Comparative Example 1 The only difference from Example 1 is that in step (1), 20 mg of iron (III) acetylacetonate is not added to prepare a Pd catalyst sample, and the method of Example 1 is used to prepare the Pd catalyst sample prepared above into a working electrode.

[0018] Comparative Example 2 The only difference from Example 1 is that the solution is reacted at 80°C for 24 hours to prepare a Pd@Fe3O4 catalyst sample, and the method of Example 1 is used to make the Pd@Fe3O4 catalyst sample prepared above into a working electrode.

[0019] Morphological characterization The Pd@Fe3O4 catalyst prepared in Example 1 was tested. Figure 1 As shown in the figure, the XRD pattern matches well with Pd-PDF#46-104, proving that the synthesized sample has good crystallinity. At the same time, no Fe phase is seen in the figure, indicating that the Fe content is low and is not reflected in the XRD. Figure 2 is the HAADF image of Pd@Fe3O4, Figure 3The EDS mapping diagram of the corresponding area (surface scan obtained by the energy spectrometer) shows that Pd and Fe elements do exist in the product, and the scanning patterns of Pd and Fe elements are highly similar, and the distribution range of Fe element is relatively wide, indicating that the ultra-thin "Fe skin" can basically completely cover the "Pd core". Figure 4 This is a high-resolution transmission electron microscopy (HRTEM) image of Pd@Fe3O4. The interplanar spacing of Pd(111) in Pd@Fe3O4 is 8-10% larger than that of pure metal Pd (d(111) = 2.25 Å). This result also indicates that the tensile strain effect of the Pd surface lattice in the Pd@Fe3O4 sample will lead to the formation of edge dislocations. In addition, Figure 5 The TEM image in also shows more dislocation / strain regions in the Pd@Fe3O4 sample prepared in Example 1.

[0020] The Pd catalyst prepared in Comparative Example 1 was tested. Figure 6 As shown, no dislocation / strain phenomena were observed in the low-magnification morphology of Pd, indicating that iron(III) acetylacetonate plays a key role in directly regulating the surface free energy during the formation of the metal catalyst to construct large-scale strain defects. Figure 7 This is a high-resolution transmission electron microscope (HRTEM) image of Pd. The interplanar spacing of Pd(111) in the sample is 2.27 Å, which has no significant difference compared with pure metallic Pd (d(111) = 2.25 Å), indicating that the surface of the sample prepared without adding iron(III) acetylacetonate has neither dislocations nor obvious lattice tensile strain.

[0021] Electrochemical performance characterization The working electrode prepared in Example 2 was subjected to electrochemical testing. Figure 8 , Fig. 9 The performance advantages of Pd@Fe3O4 compared with commercial Pt / C are shown, such as Figure 8 As shown in the cyclic voltammogram, in the oxygen-saturated 0.1 M KOH solution, the oxygen reduction cathode peaks of the samples are all around 0.7V ~ 0.85 V, indicating that they have high catalytic activity. Among them, the reduction peak potential and current density of the Pd@Fe3O4 sample are higher, indicating that its oxygen reduction catalytic performance is better. At 1600 rpm, the ORR activity of the catalyst is compared with that of Pt / C ( Fig. 9 ), the initial potential (E0) of Pd@Fe3O4 is 0.962 V, which is higher than that of Pt / C catalyst (0.945 V). 1 / 2 =0.847V) and Pd@Fe3O4 catalyst (E 1 / 2 =0.865 V), Pd@Fe3O4 also exhibits a higher half-wave potential.

[0022] The working electrode prepared in Comparative Example 2 was subjected to electrochemical testing. Fig.10 (CV) Fig.11 (LSV) shows the performance gap between Pd catalyst and Pd@Fe3O4 catalyst.

[0023] The working electrode prepared in Comparative Example 2 was subjected to electrochemical testing. Fig.12 (LSV) shows the performance gap between Pd@Fe3O4 samples prepared at 70-90℃ and Pd@Fe3O4 prepared at 150-250℃.

[0024] The above disclosure is only the preferred embodiment of the present invention, which certainly cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for preparing a Pd-based catalyst rich in large-scale strain defect structures, It is characterized in that It includes the following steps: S1. Add oleylamine dropwise into a mixture of ferric acetylacetonate and palladium acetylacetonate, and form a uniform solution by ultrasonication. Add 1.1-1.5 g ferric acetylacetonate and 0.4-0.8 g palladium acetylacetonate per liter of oleylamine. S2. The solution was reacted at 150-250°C for 20-28 h, then cooled, washed, and freeze-dried to obtain Pd@Fe 3 O 4 catalyst.

2. Use of a Pd-based catalyst rich in large-scale strain defect structure prepared as claimed in claim 1 in an electrochemical oxygen reduction reaction.

3. Use of the Pd-based catalyst rich in large-scale strain defect structure according to claim 2 in an electrochemical oxygen reduction reaction, Features: (A) Put Pd@Fe 3 O 4 Catalyst made into working electrode: Pd@Fe 3 O 4 The catalyst and acetylene black are dispersed in a mixed solvent including ethanol, ultrapure water and Nafion solution, and ultrasonic treatment is performed. The catalyst ink after ultrasonic treatment is dropped onto a rotating disk electrode, and the working electrode is prepared after drying. (B) The working electrode and the reference electrode are inserted into the electrolyte, wherein the reference electrode is a mercury oxide electrode and a graphite rod.

4. Use of the Pd-based catalyst rich in large-scale strain defect structure according to claim 3 in an electrochemical oxygen reduction reaction, Features: In step (A), 0.5-1.5 g Pd@Fe was added per liter of mixed solvent. 3 O 4 Catalyst and 0.5-1.5g acetylene black.

5. Use of the Pd-based catalyst rich in large-scale strain defect structure according to claim 3 in an electrochemical oxygen reduction reaction, Features: In step (A), C 2 H 5 The volume ratio of OH, ultrapure water, and Nafion solution is 10:9:1, and the concentration of Nafion solution is 5 wt%.

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