A method for preparing a platinum-based metal catalyst with compressed (111) interplanar spacing and applications thereof

Abstract

The application discloses a preparation method of a (111) crystal face spacing compressed platinum-based metal catalyst, and defects of carbon nanotubes are improved by nitrogen atom doping modification, and then uniform dispersion of a Pt active component on a carbon nanotube carrier surface is improved; a Pt-N bond is formed between N atoms and the Pt component, which is beneficial to improving Pt loading and can effectively improve stability of the Pt active component; the N atoms can also serve as active sites, a (111) crystal face compression effect of a Pt-based electrocatalyst is realized, oxygen reduction intermediate binding energy is weakened, H2O is more easily desorbed on the catalyst surface, and therefore, the electrocatalytic activity of the catalyst is improved; and the prepared (111) crystal face spacing compressed platinum-based metal catalyst is used as a PEMFC cathode catalyst, an energy barrier in an oxygen reduction reaction is reduced, oxygen reduction intermediate binding energy is weakened, and the desorption rate of H2O on the catalyst surface is accelerated, and therefore, the overall efficiency of the PEMFC is improved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of hydrogen energy materials, in particular to a preparation method of a (111) crystal face spacing compressed platinum-based metal catalyst and application thereof. BACKGROUND

[0002] Hydrogen fuel cells have been considered as the next generation engine for automobiles, stationary power sources, portable power sources and other power sources, but due to the fact that the cathode oxygen reduction reaction (ORR) involves multi-step electron transfer and mass transfer efficiency is low, the kinetic speed is slow, and a large amount of noble metal catalyst, mainly platinum (Pt), is required. For decades, Pt-based materials have been considered as the most effective catalyst on the cathode of a fuel cell, especially in a proton exchange membrane fuel cell (PEMFC) in an acidic medium. So far, the wide application of PEMFC is still hindered by the high cost and scarcity of Pt metal, prompting people to seek innovative methods to improve the Pt catalytic efficiency and reduce the Pt utilization rate.

[0003] The Pt (111) crystal face is the most effective lattice for adsorbing oxygen and oxygen reduction intermediates due to its close-packed atomic structure, thereby promoting the intrinsic oxygen reduction activity of the catalyst. However, the Pt (111) surface interface will be significantly affected by structural modification, changing the electronic and geometric properties of the catalyst, and then affecting the adsorption / desorption and reaction rate of the oxygen reduction reaction intermediates on the surface interface of the catalyst. Strain engineering is a technology that introduces lattice distortion or deformation into the catalyst material, and has become a powerful tool for adjusting the catalytic performance of Pt-based electrodes. Strain effect can be caused by various means, such as synthesis method or introduction of support materials. Among them, the introduction of support materials is of great significance because various supports are often used for battery electrode catalysts to better disperse active sites and minimize the use of noble metal Pt. SUMMARY

[0004] The purpose of the present application is to provide a preparation method of a (111) crystal face spacing compressed platinum-based metal catalyst and application thereof.

[0005] The present application is realized by the following technical solutions:

[0006] A preparation method of a (111) crystal face spacing compressed platinum-based metal catalyst, the method comprising the following steps:

[0007] (1) mixing carbon nanotubes and nitrogen-based materials in a mass ratio of 1:6 to 1:12, preferably 1:10, in an aqueous solution, heating to reflux at 60-65 DEG C for 6-8 h, cooling to room temperature and filtering;

[0008] (2) calcining the filtered solid obtained in step (1) at a high temperature of 500-700 DEG C under a nitrogen atmosphere, and cooling to room temperature to obtain nitrogen-doped carbon nanotubes;

[0009] (3) forming a mixed solution of the nitrogen-doped carbon nanotubes obtained in step (2) and a platinum metal precursor, and drying the mixed solution in a vacuum at 50-70℃;

[0010] (4) grinding the mixture obtained in step (3) in a ball mill, washing and drying the mixture in a vacuum at 50-70℃;

[0011] (5) reducing the powder obtained in step (4) at a high temperature of 500-700℃ in a reducing atmosphere to obtain the crystal face compressed Pt-based metal electrocatalyst.

[0012] Preferably, the nitrogen-based material in step (1) is one or more of hydrazine hydrate, urea and melamine, the heating reflux temperature is 60℃, and the reflux time is 8h.

[0013] Preferably, the calcination temperature in step (2) is 700℃, and the calcination time is 2h.

[0014] Preferably, the platinum metal precursor in step (3) is an alcohol-soluble platinum group metal precursor, including one or more of chloroplatinic acid hydrate, chloroplatinic acid salt and platinum acetylacetone.

[0015] Preferably, the vacuum drying temperature in step (4) is 60℃, and the drying time is 24h.

[0016] Preferably, the reducing atmosphere in step (5) is hydrogen / argon mixed gas, and the temperature is 700℃.

[0017] The above preparation method modifies the carbon nanotubes by nitrogen atom doping, enhances the dispersion effect of the carbon nanotubes, uniformly loads Pt-based metal nanoparticles on the surface of the modified carbon nanotubes, forms a chemical bond between the nitrogen atom and the Pt component, compresses the Pt(111) crystal face of the Pt nanoparticles with a particle diameter of 2-8nm, and improves the electrocatalytic performance of the platinum-based metal.

[0018] Therefore, the application also protects the application of the (111) crystal face compressed platinum-based metal catalyst obtained by the above preparation method in hydrogen fuel cells (PEMFC) as a cathode oxygen reduction catalyst of PEMFC.

[0019] The application has the following beneficial effects:

[0020] (1) The application realizes the (111) crystal face compression effect of the Pt-based electrocatalyst by nitrogen atom doping modification, and expands the crystal face spacing compressed Pt-based metal catalyst carrier from a metal oxide to a carbon nanotube carrier.

[0021] (2) The present application applies compression strain to the Pt(111) surface by nitrogen atom doping modification, weakens the oxygen reduction intermediate binding energy, makes H2O more easily desorb on the catalyst surface, and thus improves the electrocatalytic activity of the catalyst.

[0022] (3) The present application reduces Pt component loss and improves the Pt component loading in the catalyst by low-temperature heating reflux, high-temperature calcination and grinding treatment.

[0023] (4) The adoption of N atom doping modification on the carbon nanotube can improve the defect sites of the carbon nanotube, and thus improve the uniform dispersion of the Pt active component on the surface of the carbon nanotube carrier.

[0024] (5) The formation of Pt-N bond between the N atom and the Pt component not only helps to improve the Pt loading, but also effectively improves the stability of the Pt active component; and the N atom itself can also serve as an active site to improve the oxygen reduction activity of the catalyst.

[0025] In summary, the present application improves the defect sites of the carbon nanotube by nitrogen atom doping modification, and thus improves the uniform dispersion of the Pt active component on the surface of the carbon nanotube carrier. Moreover, the formation of Pt-N bond between the N atom and the Pt component not only helps to improve the Pt loading, but also effectively improves the stability of the Pt active component; and the N atom itself can also serve as an active site to realize the compression effect of the (111) crystal surface of the Pt-based electrocatalyst, weaken the oxygen reduction intermediate binding energy, make H2O more easily desorb on the catalyst surface, and thus improve the electrocatalytic activity of the catalyst. The prepared (111) crystal surface compression Pt-based metal catalyst as the cathode catalyst of PEMFC can reduce the energy barrier in the oxygen reduction reaction, weaken the oxygen reduction intermediate binding energy, accelerate the desorption rate of H2O on the catalyst surface, and thus improve the overall efficiency of the PEMFC. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The TEM photos of the prepared crystal surface compression Pt-based metal electrocatalyst (labeled as Pt / N-CNT) in Example 1 are shown in Figures a-c, and the C, Pt and N element distribution maps (EDS) are shown in Figures d-f. It can be seen that the N element is uniformly doped into the CNT, and the Pt element is uniformly distributed on the surface of the N-CNT carrier.

[0027] Figure 2 The TEM photo of the prepared undoped carbon nanotube supported Pt-based catalyst (labeled as Pt / CNT) in Comparative Example 1 is shown in Figure. It can be seen that, compared with the catalyst Pt / N-CNT in Example 1, the Pt particles in the Pt / CNT catalyst in Comparative Example 1 are not uniformly dispersed, and have agglomeration phenomenon.

[0028] Figure 3The spectra of the catalysts of Example 1 and Comparative Example 1. Among them, a is the N1S spectrum of the catalyst Pt / N-CNT in Example 1, there is a Pt-N chemical bond at 399.4 eV, indicating that there is a strong metal-support interaction between Pt / N-CNT; b is the Pt 4f spectrum of the catalysts of Example 1 and Comparative Example 1, compared with the Pt / CNT catalyst of Comparative Example 1, the Pt 4f spectrum of the Pt / N-CNT catalyst in Example 1 shifts to low binding energy, indicating that the doped N in the N-CNT support provides more electrons for the Pt active component, which is consistent with the presence of oxidized N in the N1s spectrum.

[0029] Figure 4 The high-resolution transmission electron microscopy (HR-TEM) pictures of the catalysts of Example 1 and Comparative Example 1. Among them, a is the local high-resolution TEM picture of the Pt / N-CNT catalyst, b is the fine picture at the box in figure a, c is the schematic diagram of the (111) crystal plane compression of the Pt / N-CNT catalyst; correspondingly, d is the local high-resolution TEM picture of the Pt / CNT catalyst, e is the fine picture at the box in d, c is the schematic diagram of the (111) crystal plane compression of the Pt / CNT catalyst; through the fine structure analysis of the HR-TEM picture, the U axis and the V axis of the (111) plane of the Pt / N-CNT catalyst particle in Example 1 are and The lattice spacing is The included angle is 126°; while the U axis and the V axis of the (111) plane of the Pt / CNT catalyst particle in Comparative Example 1 are and The lattice spacing is The included angle is 122.5°. Therefore, compared with the Pt / CNT catalyst of Comparative Example 1, the compression strain of the Pt / N-CNT catalyst in Example 1 in the two-dimensional plane is 6.3% (2D plane compression), which proves that the N atom doping can produce compression strain of the Pt (111) crystal plane.

[0030] Figure 5 The electrochemical performance test of the catalysts of Example 1 and Comparative Example 1 by linear sweep voltammetry (LSV). Compared with the catalyst Pt / CNT of Comparative Example 1, the polarization curve of the catalyst Pt / N-CNT in Example 1 is positively shifted, and the half-wave potential is 21 mV, as shown in a of Figure 4 The Tafel curve is shown in b of Figure 3 The Tafel slope of the catalyst Pt / N-CNT in Example 1 is 47.8 mV / dec, which is smaller than 65.4 mV / dec of the catalyst Pt / CNT of Comparative Example 1, indicating that the crystal plane compressed Pt / N-CNT catalyst has better oxygen reduction activity.

[0031] Figure 6XRD patterns and parameters of catalysts of Example 1, Comparative Example 1 and Comparative Example 2, wherein a is the XRD pattern of the catalysts of Example 1, Comparative Example 1 and the standard Pt(111) pattern (PDF #70-2431) of Comparative Example 2, and b is the Pt(111) interplanar spacing parameter of Comparative Example 2.

[0032] Figure 7 TEM picture and structure analysis of Comparative Example 3, wherein a is the picture of the catalyst of Comparative Example 3, b is the HR-TME picture, and c is the local fine structure analysis of b. As can be seen from c, the interplanar spacing of Comparative Example 3 is The interplanar spacing is basically consistent with the interplanar spacing parameters of the catalysts in the reference patent CN 114068967A. DETAILED DESCRIPTION

[0033] The following is a further description of the present application, but not a limitation of the present application.

[0034] Example 1

[0035] This example is to prepare an interplanar spacing compressed Pt-based metal catalyst under preferred conditions.

[0036] First, 100 mL of 30% hydrazine hydrate is mixed with 100 mL of deionized water, and 500 mg of carbon nanotubes (CNT, mass ratio of carbon nanotubes to hydrazine hydrate 1:10) is added under stirring. The mixed solution is heated to reflux at 60°C for 8 h, cooled to room temperature and then filtered. The filtered solid is calcined at 700°C under N2atmosphere for 2 h, and then cooled to room temperature to obtain nitrogen-doped carbon nanotubes (N-CNT).

[0037] A Pt / N-CNT catalyst is synthesized by a combination of grinding and calcination. Chloroplatinic acid hydrate (H2PtCl6·6H2O, Pt≥37.5%) is dissolved in ethanol, and the above N-CNT is added to the Pt precursor solution under stirring. The mixture is vacuum dried at 60°C for 24 h, and then the solid mixture is ground into powder by a ball mill. The powder is rinsed with deionized water for several times, and then dried at 60°C under vacuum for 24 h. Finally, the powder is calcined at 700°C under H2reducing atmosphere for 5 h to obtain the Pt / N-CNT catalyst.

[0038] Secondly, the interplanar spacing compressed Pt-based metal electrocatalyst in this example is equipped with catalyst ink, and a linear sweep voltammetry curve (LSV) is tested by a three-electrode system. The test conditions are as follows: O2saturated H2SO4solution, concentration 0.5 M; rotating disc electrode diameter 5 mm, rotation speed 1600 rpm; scanning voltage range 0-1.2 V (vs. RHE), scanning rate 10 mV s-1. The results are shown in Figure 5 ​

[0039] Comparative Example 1

[0040] The Pt / CNT catalyst was synthesized under the same conditions as in Reference Example 1 by using the same method, except that the nitrogen-doped carbon nanotube N-CNT carrier was replaced by a carbon nanotube CNT, and other conditions were the same. The morphology and element characterization are shown in Figure 2 , Figure 3 and Figure 4 ; and the obtained electrochemical performance curves are shown in Figure 5 .

[0041] Comparative Example 2

[0042] In order to better understand the compression effect of carbon nanotubes and heteroatom-doped carbon nanotubes on the Pt(111) crystal plane, according to the XRD characterization results of Example 1 and Comparative Example 1, the Pt(111) crystal plane of the XRD standard card was used as Comparative Example 2, and the lengths of the U axis and the V axis of the standard Pt(111) crystal plane were calculated by the Bragg X-ray diffraction equation The interplanar spacing was and the included angle was 120°, and the results are shown in Figure 6 .

[0043] Comparative Example 3

[0044] Reference Example 1, except that the nitrogen-doped carbon nanotube was replaced by N-doped porous carbon, and the preparation method of the N-doped porous carbon was referred to Example 1 in CN 114068967 A, and the obtained catalyst was recorded as Pt / N-C. The TEM picture and structure analysis are shown in Figure 7 . It can be seen from the c in Figure 7 that the interplanar spacing of Comparative Example 3 was which was basically consistent with the interplanar spacing parameters of the catalyst in the reference patent CN 114068967 A. Comparison between Example 1 and Comparative Example 3 showed that the nitrogen-doped carbon nanotube could improve the crystal plane compression effect compared with the N-doped porous carbon.

[0045] Compared with Comparative Example 2, the Pt(111) crystal plane compression effect of the Pt / CNT catalyst in Comparative Example 1 was 8.8%, and the Pt(111) crystal plane compression effect of the Pt / N-CNT catalyst in Example 1 was 14.6%. Further, it was illustrated that the Pt-based catalyst prepared by the carbon nanotube of the method was beneficial to the crystal plane compression, and the heteroatom-doped carbon nanotube could further improve the crystal plane compression effect.

[0046] Finally, it should be noted that the above is only the preferred embodiment of the present application, and for those skilled in the art, the technical solutions described in the foregoing embodiments can still be modified, or some technical features therein can be replaced by equivalents, or some operation steps can be improved. Any modification, replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a (111) interplanar spacing compressed platinum group metal catalyst, characterized by, The method comprises the following steps: (1) mixing carbon nanotubes and nitrogen-based materials in an aqueous solution at a mass ratio of 1:6-1:12, heating and refluxing at 60-65 ℃ for 6-8 h, cooling to room temperature and filtering; the nitrogen-based materials are one or more of hydrazine hydrate, urea and melamine; (2) calcining the filtered solid obtained in step (1) at a high temperature of 500-700 ℃ under a nitrogen atmosphere, cooling to room temperature to obtain nitrogen-doped carbon nanotubes; (3) forming a mixed solution of the nitrogen-doped carbon nanotubes obtained in step (2) and a platinum metal precursor, and drying in a vacuum at 50-70 ℃; (4) grinding the mixture obtained in step (3) with a ball mill, washing and drying in a vacuum at 50-70 ℃; (5) reducing the powder obtained in step (4) at a high temperature of 500-700 ℃ under a reducing atmosphere to obtain the (111) crystal face compressed Pt-based metal catalyst, and the crystal face compression effect of the (111) crystal face compressed Pt-based metal catalyst is 14.6%.

2. The production method according to claim 1, characterized by, The heating and refluxing temperature in step (1) is 60 ℃, and the refluxing time is 8 h.

3. The preparation method according to claim 1, characterized in that, The carbon nanotubes and the nitrogen-based materials are mixed in an aqueous solution at a mass ratio of 1:

10.

4. The method of claim 1, wherein, The calcination temperature in step (2) is 700 ℃, and the calcination time is 2 h.

5. The preparation method according to claim 1, characterized in that, The platinum metal precursor in step (3) is an alcohol-soluble platinum group metal precursor, including one or more of chloroplatinic acid hydrate, chloroplatinic acid salt and platinum acetylacetone.

6. The method of claim 1, wherein, The vacuum drying temperature in step (4) is 60 ℃, and the drying time is 24 h.

7. The preparation method according to claim 1, characterized in that, The reducing atmosphere in step (5) is hydrogen / argon mixed gas, and the temperature is 700 ℃.

8. Application of the (111) crystal face compressed Pt-based metal catalyst prepared by the preparation method of claim 1 in a hydrogen fuel cell as a cathode oxygen reduction catalyst.

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