Method for preparing PtPd nanosheet through gas-solid phase reaction

Abstract

The invention relates to a method for preparing a PtPd nanosheet through a gas-solid phase reaction. The growth speed of crystal faces is changed by utilizing selective adsorption of reducing mixed gases H2, CO and NH3 on Pt and Pd crystal faces, so that the morphology of nanoparticles is regulated and controlled, and the PtPd nanosheet without a surfactant is synthesized. According to the method, no surfactant or end-capping reagent is needed in the synthesis process, the PtPd nanosheet can be obtained through simple gas-solid phase reduction, large-scale production of the catalyst can be achieved, and the prepared catalyst is used for efficiently catalyzing the acid oxygen reduction reaction.

Description

Technical Field

[0001] The invention relates to a method for preparing PtPd nanosheets by gas-solid phase reaction, belonging to the technical field of two-dimensional nano material preparation. Background Art

[0002] As a renewable energy source, hydrogen energy has the advantages of good combustion performance, high calorific value, and environmental friendliness. It is one of the most promising clean energy sources. However, due to the ultra-high overpotential associated with the oxygen reduction reaction (ORR), the energy conversion efficiency of hydrogen in fuel cells is low. Therefore, there is an urgent need for an efficient ORR catalyst to improve the working efficiency of fuel cells. In the ORR electrocatalytic process, the Pt surface has good adsorption characteristics for small molecules and is considered to be an efficient ORR catalyst. In order to further improve the ORR activity, researchers have conducted extensive explorations on Pt-based catalysts, mainly in three aspects: metal doping, component regulation, and morphology control. Introducing metal elements such as Ni, Ru, and Pd into Pt and regulating the composition and morphology of the alloy can optimize the electronic structure of the catalyst, introduce lattice effects and synergistic effects, and thus improve the ORR activity.

[0003] At present, precious metal catalysts are booming in the field of ORR catalysis, and many efficient Pt-based catalysts have been explored, including PtNi octahedron, PtRu nanosheets and PtPb nanosheets. Two-dimensional nanosheets have large specific surface area and internal strain, which are conducive to the exposure of active sites and the transmission of ions, and therefore have excellent electrocatalytic performance. However, the design of precious metal nanosheet catalysts still has problems and shortcomings that cannot be ignored. The low scale-up capacity of traditional wet synthesis methods limits the large-scale production of precious metal nanosheet catalysts. In addition, in the design of precious metal nanosheet catalysts, some organic matter is usually introduced as surfactants and capping agents, which can not only regulate the morphology of nanoparticles, but also contaminate the catalyst, and the cleaning process is very cumbersome. The low scale-up capacity and complex synthesis process increase the production cost of the catalyst, limiting the large-scale promotion of these technologies. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a new method for synthesizing PtPd nanosheet electrocatalysts in a simple and efficient manner. Due to the adoption of a solid-state chemical synthesis method without a liquid phase, it has the advantages of scalability, easy operation, low cost, etc., and can be used for large-scale production of PtPd nanosheets. According to the adsorption characteristics of different reducing gases on Pt and Pd crystal surfaces, the growth rate of the crystal surface is regulated by changing the components of the reducing gas, and PtPd nanosheets without surfactant are synthesized. Due to the synergistic effect of metal doping and two-dimensional nanosheet structure, PtPd nanosheets show high catalytic activity and have high application value in the field of acidic ORR electrocatalysis.

[0005] The implementation process of the present invention is as follows: A method for preparing PtPd nanosheets comprises the following steps: (1) loading a soluble platinum salt and a soluble palladium salt onto a carrier carbon black or activated carbon, wherein the molar ratio of the soluble platinum salt to the soluble palladium salt is 1-10:1, wherein the platinum loading is 15-30 wt% and the palladium loading is 1-10 wt%; (2) The carrier loaded with soluble platinum salt and soluble palladium salt is reduced at 150-300 °C, using Ar as carrier gas, and the reducing gas is a mixture of H2, CO and NH3, the volume ratio of Ar, H2, CO and NH3 is 10-30:60-80:1-10:1-10, and the heating rate is 1-20 °C·min -1 .

[0006] In the above step (1), the soluble platinum salt is selected from chloroplatinic acid and platinum acetylacetonate.

[0007] In the above step (1), the soluble palladium salt is selected from chloropalladic acid and palladium acetylacetonate.

[0008] In the above step (2), the volume ratio of Ar, H2, CO and NH3 is 20~30:65~75:1~5:1~5.

[0009] In the above step (2), the heating rate is 2~15 °C·min -1 .

[0010] Application of the PtPd nanosheets prepared by the above preparation method in electrocatalytic fuel cells.

[0011] The PtPd nanosheets prepared by the above method showed excellent catalytic activity in acidic ORR with a half-wave potential of 0.921 V.

[0012] Beneficial effects of the present invention: The present invention prepares PtPd nanosheets by gas-solid phase synthesis method, which is easy to operate and has strong scalability. The PtPd nanosheets are synthesized by using the adsorption characteristics of the unique ratio of reducing mixed gas H2, CO and NH3 on the surface of Pt and Pd, which provides a new method and new idea for designing efficient Pt-based catalysts. The prepared PtPd nanosheets show excellent catalytic performance in acidic ORR, with a half-wave potential of up to 0.921 V. The present invention provides a simpler and more efficient preparation scheme for PtPd nanosheets, which has potential application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 is a TEM image of PtPd@CB obtained by calcining in a reducing gas in Example 1; Figure 2 is the XRD spectra of PtPd@CB, Pt@CB and Pd@CB in Example 1; Figure 3 is a TEM image of PtPd@CB obtained by calcining in a single reducing gas in Example 2; Figure 4 is a TEM image of PtPd@CB calcined in two reducing gases in Example 3; Figure 5 is a TEM image of PtPd@CB calcined in a reducing gas in Example 4, with gas flow rates of Ar, H2, CO, and NH3 being 20, 70, 2, and 8 sccm, respectively; Figure 6 is a TEM image of PtPd@CB calcined in a reducing gas in Example 5, with gas flow rates of Ar, H2, CO, and NH3 being 20, 70, 8, and 2 sccm, respectively; Figure 7 is a TEM image of PtPd@CB calcined in a reducing gas in Example 6, with gas flow rates of Ar, H2, CO, and NH3 being 10, 70, 10, and 10 sccm, respectively; Figure 8 TEM images of PtPd@CB obtained by calcination in reducing gas in Example 7, with reaction temperatures of 150 ºC, 250 ºC, and 300 ºC, respectively; Fig. 9 TEM images of PtPd@CB calcined in reducing gas in Example 8 at heating rates of 1, 10, and 20 ºC·min -1 ; Fig.10 is the electrochemical performance diagram of the catalyst prepared in Example 1 and commercial Pt / C; Fig.11 is the electrochemical performance diagram of PtPd@CB obtained by calcining in a single reducing gas in Example 2; Fig.12 This is the electrochemical performance diagram of PtPd@CB obtained by calcining in two reducing gases in Example 3. DETAILED DESCRIPTION

[0014] The technical solution of the present invention is further described below with reference to specific embodiments, but the protection scope of the present invention is not limited thereto.

[0015] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the art can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be purchased commercially. Example 1

[0016] A method for preparing PtPd nanosheets by gas-solid phase synthesis method comprises the following steps: 0.53 g of platinum acetylacetonate, 0.26 g of palladium acetylacetonate and 1 g of carbon black are weighed and dissolved in a mixed solution of acetone (100 ml) and deionized water (200 ml). The suspension is ultrasonicated for 30 minutes to obtain a uniform solution, and then the mixed solution is transferred to an eggplant-shaped bottle for rotary evaporation drying at a speed of 125 rpm and a temperature of 60 ºC. After the water is completely evaporated, it is placed in a vacuum drying oven for 12 hours at a drying temperature of 60 ºC. After complete drying, it is ground and the ground PtPd precursor powder is collected in a glass bottle for standby use.

[0017] 20 mg of PtPd precursor powder was weighed and placed in a quartz boat. After being placed in a tube furnace, it was purged with Ar for 30 minutes, and then a reducing gas was introduced for calcination. The gas flow rates of Ar, H2, CO, and NH3 were 26, 70, 2, and 2 sccm, respectively. The temperature was 200 ºC, and the heating rate was 5 ºC·min -1 , the insulation time is 2 h.

[0018] Figure 1 This is the TEM image of PtPd@CB obtained by calcining in a reducing gas. The results show that the PtPd@CB catalyst prepared by the gas-solid phase synthesis method has a two-dimensional nanosheet structure with a lateral size range of 6~8 nm.

[0019] Figure 2 The XRD spectra of PtPd@CB, Pt@CB and Pd@CB are the same as those of PtPd@CB. The crystal structure is explained by XRD spectra. The characteristic peaks of PtPd@CB at 40.12°, 46.52°, 67.91° and 81.86° are well attributed to the (111), (200), (220) and (311) crystal planes of fcc PtPd alloy, respectively. There are no other diffraction peaks of single Pt or Pd in ​​the XRD spectrum, and the characteristic peak of PtPd@CB is between Pt@CB and Pd@CB, indicating that high-purity PtPd alloy can be synthesized by gas-solid phase synthesis. In addition, compared with the standard PDF cards of Pt@CB and Pt, the characteristic peaks of PtPd@CB shift to high angles, indicating that the introduction of Pd causes compressive strain in the Pt-Pt bond. XRD analysis results show that the gas-solid phase synthesis method successfully introduced Pd into Pt and generated internal strain.

[0020] Example 2

[0021] This embodiment provides a method for preparing PtPd nanosheets by gas-solid phase synthesis, and the specific steps are as follows: Weigh 20 mg of PtPd precursor powder and place it in a quartz boat. Place it in a tube furnace and purge it with Ar for 30 minutes. Then, introduce a single reducing gas for calcination. The flow rate of H2 is 100 sccm, the temperature is 200 ºC, and the heating rate is 5 ºC·min -1 , the insulation time is 2 h.

[0022] Figure 3 The TEM image of PtPd@CB obtained by calcination with a single reducing gas. Irregularly shaped PtPd nanoparticles were obtained by reduction in H2, indicating that H2 has a weak ability to regulate the morphology of PtPd nanoparticles. In CO and NH3, the number of PtPd nanoparticles decreased, indicating that CO and NH3 have a weak ability to reduce PtPd precursors. The inventors also tried to use CO or NH3 as a single reducing gas, but failed to obtain the morphology of PtPd nanosheets.

[0023] Example 3 This embodiment provides a method for preparing PtPd nanosheets by gas-solid phase synthesis, and the specific steps are as follows: 20 mg of PtPd precursor powder was weighed and placed in a quartz boat. After being placed in a tube furnace, it was purged with Ar for 30 minutes. Then, two reducing gases and Ar were introduced for calcination. The gas flow rates of Ar, H2, and CO were 28, 70, and 2 sccm, respectively. The temperature was 200 ºC and the heating rate was 5 ºC·min. -1 , the insulation time is 2 h.

[0024] Figure 4 TEM images of PtPd@CB obtained by calcination in two reducing gases. Irregularly shaped PtPd nanoparticles were obtained in two reducing gases H2 and CO with different compositions, indicating that PtPd nanosheets cannot be obtained by calcination in two reducing gases H2 and CO. Similarly, the inventors failed to obtain PtPd nanosheets using CO and NH3, H2 and NH3 combinations.

[0025] Example 4 This embodiment provides a method for preparing PtPd nanosheets by gas-solid phase synthesis, and the specific steps are as follows: 20 mg of PtPd precursor powder was weighed and placed in a quartz boat. After being placed in a tube furnace, it was purged with Ar for 30 minutes, and then a reducing gas was introduced for calcination. The gas flow rates of Ar, H2, CO, and NH3 were 20, 70, 2, and 8 sccm, respectively. The temperature was 200 ºC, and the heating rate was 5 ºC·min -1 , the insulation time is 2 h.

[0026] Figure 5 TEM images of PtPd@CB calcined at gas flow rates of 20, 70, 2, and 8 sccm for Ar, H2, CO, and NH3, respectively. The results show that the number of nanosheets synthesized under this condition is small and the lateral size of the particles is large, indicating that a high partial pressure of NH3 (>5 sccm) may promote the anisotropic growth of nanoparticles, but is not conducive to the formation of nanosheets.

[0027] Example 5 This embodiment provides a method for preparing PtPd nanosheets by gas-solid phase synthesis, and the specific steps are as follows: 20 mg of PtPd precursor powder was weighed and placed in a quartz boat. After being placed in a tube furnace, it was purged with Ar for 30 minutes, and then a reducing gas was introduced for calcination. The gas flow rates of Ar, H2, CO, and NH3 were 20, 70, 8, and 2 sccm, respectively. The temperature was 200 ºC, and the heating rate was 5 ºC·min -1 , the insulation time is 2 h.

[0028] Figure 6 TEM images of PtPd@CB calcined at gas flow rates of 20, 70, 8, and 2 sccm for Ar, H2, CO, and NH3, respectively, show that it contains fewer nanosheets, so a higher partial pressure of CO (>5 sccm) is not conducive to the formation of nanosheets.

[0029] Example 6 This embodiment provides a method for preparing PtPd nanosheets by gas-solid phase synthesis, and the specific steps are as follows: 20 mg of PtPd precursor powder was weighed and placed in a quartz boat. After being placed in a tube furnace, it was purged with Ar for 30 minutes, and then a reducing gas was introduced for calcination. The gas flow rates of Ar, H2, CO, and NH3 were 20, 70, 10, and 10 sccm, respectively. The temperature was 200 ºC, and the heating rate was 5 ºC·min -1 , the insulation time is 2 h.

[0030] Figure 7 TEM images of PtPd@CB calcined at gas flow rates of 10, 70, 10, and 10 sccm for Ar, H2, CO, and NH3, respectively. The results show that the shape of PtPd@CB is irregular, which indicates that the formation of nanosheets is not conducive when the partial pressures of CO and NH3 are high (>5 sccm).

[0031] Example 7 This embodiment provides a method for preparing PtPd nanosheets by gas-solid phase synthesis, and the specific steps are as follows: 20 mg of PtPd precursor powder was weighed and placed in a quartz boat. After being placed in a tube furnace, it was purged with Ar for 30 minutes, and then a reducing gas was introduced for calcination. The gas flow rates of Ar, H2, CO, and NH3 were 26, 70, 2, and 2 sccm, respectively. The temperature was 300°C, and the heating rate was 5°C min. -1 , the insulation time is 2 h.

[0032] Figure 8 The following are TEM images of PtPd@CB calcined in a reducing atmosphere at 150 ºC, 250 ºC, and 300 ºC. The TEM images show that calcination at 150 ºC may result in insufficient metal reduction, while calcination at 300 ºC may cause agglomeration of nanoparticles.

[0033] Example 8 This embodiment provides a method for preparing PtPd nanosheets by gas-solid phase synthesis, and the specific steps are as follows: 20 mg of PtPd precursor powder was weighed and placed in a quartz boat. After being placed in a tube furnace, it was purged with Ar for 30 minutes, and then a reducing gas was introduced for calcination. The gas flow rates of Ar, H2, CO, and NH3 were 26, 70, 2, and 2 sccm, respectively. The temperature was 200 ºC, and the heating rate was 10 ºC min. -1 , the insulation time is 2 h.

[0034] Fig. 9 TEM images of PtPd@CB calcined in reducing gas at heating rates of 1, 10, and 20 ºC·min -1 When the heating rate is 1 ºC·min -1 When the heating rate is 20 ºC·min, the metal nucleation rate is reduced, thus forming larger nanoparticles. -1 Smaller nanoparticles are formed.

[0035] Example 9 The electrochemical performance of the PtPd@CB prepared in Examples 1 to 3 was tested in 0.1 M HClO4. The oxygen reduction catalytic performance of the catalyst was measured using an electrochemical workstation equipped with a rotating ring disk electrode device. -1 Cyclic voltammetry (CV) curves were recorded at a scan rate of 1600 rpm and 10 mV·s in an O2-saturated 0.1 M HClO4 solution. -1 The oxygen reduction polarization (LSV) curves were measured at a scan rate of 2.

[0036] Fig.10 The electrochemical performance diagram of PtPd@CB prepared in Example 1 and commercial Pt / C catalyst, Fig.10 (a) and (b) are CV and LSV curves, respectively. The test results show that Pt 1.5 Pd1 nanosheets have the highest acidic ORR activity. As shown in Table 1, Pt 1.5 The half-wave potential of Pd1 nanosheets is 0.921 V, which is about 38 mV higher than that of commercial Pt / C. 1.5 The mass activity and specific activity of Pd1 nanosheets are 1.19 A·mg Pt -1 and 1.96 mA·cm -2 , which are 6.3 and 8.2 times of commercial Pt / C respectively.

[0037] Fig.11 The electrochemical performance diagram of PtPd@CB prepared in Example 2 is shown in FIG. Fig.11 (a) and (b) are CV and LSV curves, respectively. The half-wave potentials of PtPd@CB reduced in pure H2, pure CO and pure NH3 are 0.885, 0.874 and 0.855 V, respectively, which are all lower than PtPd@CB reduced in mixed gas (0.921 V), indicating that the activity of PtPd@CB reduced in a reducing gas is lower than that of PtPd@CB reduced in a mixed gas.

[0038] Fig.12 The electrochemical performance diagram of PtPd@CB prepared in Example 3 is shown in FIG. Fig.12 (a) and (b) are CV and LSV curves, respectively. The half-wave potentials of PtPd@CB reduced in H2 and CO, H2 and NH3, and NH3 and CO are 0.896, 0.890, and 0.868 V, respectively, which are all lower than the PtPd@CB reduced in mixed gas (0.921 V), indicating that the activity of PtPd@CB obtained in the two reducing gases is lower than that of PtPd@CB reduced in mixed gas.

Claims

1. A method for preparing PtPd nanosheets, characterized in that The following steps are involved: (1) loading a soluble platinum salt and a soluble palladium salt onto a carrier carbon black or activated carbon, wherein the molar ratio of the soluble platinum salt to the soluble palladium salt is 1-10:1, wherein the platinum loading is 15-30 wt% and the palladium loading is 1-10 wt%; (2) The carrier loaded with soluble platinum salt and soluble palladium salt is reduced at 150-300 °C, using Ar as carrier gas, and the reducing gas is a mixture of H2, CO and NH3, the volume ratio of Ar, H2, CO and NH3 is 10-30:60-80:1-10:1-10, and the heating rate is 1-20 °C·min -1 .

2. The method for preparing PtPd nanosheets according to claim 1, characterized in that: In step (1), the soluble platinum salt is selected from chloroplatinic acid and platinum acetylacetonate.

3. The method for preparing PtPd nanosheets according to claim 1, characterized in that: In step (1), the soluble palladium salt is selected from chloropalladic acid and palladium acetylacetonate.

4. The method for preparing PtPd nanosheets according to claim 1, characterized in that: In step (2), the volume ratio of Ar, H2, CO and NH3 is 20~30:65~75:1~5:1~5.

5. The method for preparing PtPd nanosheets according to claim 1, characterized in that: In step (2), the heating rate is 2~15 °C·min -1 .

6. The PtPd nanosheets prepared by the preparation method according to claim 1.

7. Use of the PtPd nanosheets according to claim 7 in electrocatalytic fuel cells.

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