Preparation method and application of boron nitride confined platinum single atom-platinum cluster double-site catalyst

Abstract

The invention discloses a preparation method and application of a boron nitride confined platinum single atom-platinum cluster double-site catalyst. The preparation method comprises the following steps: mixing urea, boric acid and carbon nanotubes, and grinding; the ground mixture is placed in an ammonia-argon mixed atmosphere environment for first pyrolysis, and powder is obtained; adding the powder into a boric acid solution, heating and stirring to obtain a defect-rich boron nitride carrier; and washing and drying the carrier, immersing the carrier in a platinum salt aqueous solution, carrying out ultrasonic dispersion, carrying out a vacuum freeze drying method, and finally carrying out second pyrolysis on the dried sample in an ammonia-argon mixed atmosphere to obtain the platinum single atom-platinum cluster composite structure (PtSA-C (at) eBN-CNT) material. The material can efficiently and synergistically catalyze an electrochemical hydrogen evolution reaction (HER) under an alkaline condition (1M KOH), can be applied to a membrane electrode electrochemical cell as a cathode catalyst, shows excellent catalytic activity and stability under working conditions, and has good industrial application potential.

Description

Technical Field

[0001] The present invention mainly relates to the preparation process of catalysts, and particularly relates to a preparation method and application of a boron nitride-confined platinum single atom-platinum cluster dual-site catalyst. Background Art

[0002] Platinum (Pt) has high potential in the field of energy catalysis due to its unique chemical properties and electronic structure. However, as a noble metal, the application of platinum in actual industrial production is often limited by its high cost. Developing platinum-based single-atom catalysts can significantly reduce the amount of platinum used and greatly improve its atomic utilization rate. Nevertheless, most energy conversion reactions often involve multiple electron / proton transfer processes and various reaction intermediates, and the single active site of platinum-based single-atom catalysts is difficult to fully meet the requirements of efficient and sustainable catalysis of these reactions in different media. Constructing a composite of single atoms and ultrafine nanoclusters is a potential solution to the above problems. While maintaining the low-cost advantage, it can achieve efficient energy conversion through the synergistic effect of platinum single atom-platinum cluster dual sites.

[0003] Single-atom-cluster composite catalysts can generally be prepared by stepwise loading, but the operation steps are relatively cumbersome and the cost is high. Therefore, scientists and technicians have developed a "one-pot" preparation technology to achieve the coexistence of single atoms and clusters by regulating the nucleation and growth kinetics of metal components, but still face the challenge of precise control of the structure and spatial distribution of surface metal species. Rational design of the support is the key strategy to break through the above bottleneck. Traditional carbon-based supports usually need to introduce heteroatoms (N, P, S, etc.) to anchor metal components, but the micro-region localization of heteroatoms in the support is limited by the thermodynamic randomness during the synthesis process, which is not conducive to the uniform spatial distribution of metal species and the directional regulation of their microstructures. Boron nitride with intrinsic coordination atoms can directly anchor metal ions / precursors after introducing vacancy defects, thus avoiding the disordered evolution of active sites caused by heteroatoms. In addition, boron nitride is composed of periodically distributed nitrogen with high electronegativity and boron with low electronegativity, providing a multi-dimensional rational design space for the construction of composite sites and the regulation of the electronic structure of metal centers. Summary of the Invention

[0004] The object of the present invention is to provide a preparation method of a boron nitride-confined platinum single atom-platinum cluster dual-site catalyst, comprising the following steps: mixing urea, boric acid and carbon nanotubes and performing grinding treatment; subjecting the ground mixture to a first pyrolysis in a mixed ammonia-argon atmosphere environment to obtain a powder; adding the powder to a boric acid solution, heating and stirring to obtain a defective boron nitride support; washing and drying the support, immersing it in an aqueous solution of platinum salt and dispersing it by ultrasonic treatment, then performing a drying treatment by vacuum freeze-drying method, and finally subjecting the dried sample to a second pyrolysis in a mixed ammonia-argon atmosphere.

[0005] Preferably, the mass ratio of boric acid is 10-15%, the mass ratio of urea is 60-75%, and the carbon nanotubes are 10-30%.

[0006] Preferably, the temperature of the first pyrolysis is 700-1100 °C, and the heat preservation time is 2-5 hours.

[0007] Preferably, the heating temperature is 75-95 °C, and the stirring time is 25-45 minutes.

[0008] Preferably, the duration of ultrasonic dispersion is 4-5 hours, and the solution temperature during ultrasonic treatment is 20-30 °C.

[0009] Preferably, the platinum salt aqueous solution contains chloroplatinic acid, platinum nitrate, and platinum sulfate.

[0010] Preferably, the vacuum freeze-drying method is freeze-drying using a vacuum freezer, and the freeze-drying time is 30-45 hours.

[0011] Preferably, the sample after drying treatment is placed in a tubular furnace. The temperature of the second pyrolysis is 650-850 °C, and the pyrolysis time is 3-5 hours. Then a PtSA-C@eBN-CNT catalyst with rich-defect boron nitride confinement and uniform distribution of platinum single atoms and platinum clusters can be obtained. The platinum single atoms of this catalyst are uniformly distributed, and the cluster particle size is 1.0-1.9 nm.

[0012] Another object of the present invention is to provide the application of a boron nitride-confined platinum single atom-platinum cluster dual-site catalyst prepared by the above method; including applications in electrocatalytic water splitting, hydrogen reduction reaction (HOR), oxygen reduction reaction (ORR), carbon dioxide reduction reaction (CO 2 RR), air batteries, membrane electrodes and other energy devices.

[0013] We carried out acid etching treatment on it to obtain rich-defect boron nitride, and then through fine adjustment of conditions such as the dosage of platinum salt, reaction temperature, and reaction duration, the precise spatial arrangement of platinum single atoms and platinum clusters was achieved under mild conditions. The present invention provides a new scheme for the synthesis of low-loading single atom-cluster composite platinum-based catalysts, and also provides important support for its popularization in the industrial field. Future research can further optimize the preparation process, explore the influence of different carriers and reaction conditions on the catalyst performance, so as to realize the large-scale preparation and wider application of this composite catalyst.

[0014] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention synthesizes a platinum single atom-platinum cluster dual-site catalyst on high-defect boron nitride for the first time; (2) The boron nitride layer prepared by the present invention is coated around the carbon nanotubes, with a thickness of about 1.2 nm; (3) The platinum metal atoms prepared by the present invention are uniformly distributed in the form of single atoms and clusters; (4) The preparation method used in the present invention is simple, the materials are easy to obtain, and large-scale preparation can be carried out; (5) The boron nitride-confined platinum single atom-platinum cluster dual-site catalyst PtSA-C@eBN-CNT prepared by the present invention exhibits excellent HER catalytic performance. The proposed catalyst has an overpotential of 25 mV at a current density of 10 mA·cm -2 in an alkaline medium. At an extremely low metal loading (only 4 μg Pt ·cm -2 ), the turnover frequency (TOF) of the catalyst is 18.9 s -1 (overpotential 0.15 V).

[0015] (6) The boron nitride-confined platinum single atom-platinum cluster dual-site catalyst PtSA-C@eBN-CNT prepared by the present invention is a good cathode material for alkaline anion exchange membrane electrodes; the membrane electrode device achieved a current density of 1.0 A·cm -2 at a cell voltage of 1.93 V, and the energy efficiency reached 76%, which is significantly better than the electrolyzer using commercial Pt / C as the cathode catalyst.

[0016] (7) The boron nitride-confined platinum single atom-platinum cluster dual-site catalyst prepared by the present invention has wide applications in the field of energy catalysis and can be used in other reactions such as ORR, HOR, and CO 2 RR. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is the aberration-corrected transmission electron microscopy image of PtSA-C@eBN-CNT of the present invention.

[0018] Figure 2 is the X-ray powder diffraction pattern of PtSA-C@eBN-CNT of the present invention.

[0019] Figure 3 is the linear sweep voltammetry curve of HER of PtSA-C@eBN-CNT of the present invention on a glassy carbon electrode.

[0020] Figure 4 is the turnover frequency (TOF) of PtSA-C@eBN-CNT of the present invention.

[0021] Figure 5 is the cyclic voltammetry (CV) stability test of PtSA-C@eBN-CNT of the present invention on a glassy carbon electrode.

[0022] Figure 6 This is the galvanostatic stability test of PtSA-C@eBN-CNT of the present invention.

[0023] Figure 7 This is the linear sweep voltammetry curve and stability test of the membrane electrode electrolyzer of PtSA-C@eBN-CNT of the present invention.

[0024] Figure 8 This is a photo of the actual application scenario of the membrane electrode electrolyzer assembled with PtSA-C@eBN-CNT of the present invention. Detailed implementation mode

[0025] Example 1 Preparation of PtSA-C@eBN-CNT catalyst; Boric acid, urea, and amino-functionalized multi-walled carbon nanotubes (CNTs) were mixed evenly according to a mass ratio of 13:60:27 and then thoroughly ground in a mortar. Under an ammonia-argon mixed atmosphere, the temperature was gradually raised to 1050 °C at a rate of 15 °C per minute and maintained for 2 hours to synthesize a black powder sample labeled BN@CNT. BN@CNT was added to a 0.5 M boric acid solution and stirred in an oil bath at 90 °C for 40 minutes. Subsequently, it was washed and dried to obtain eBN@CNT. eBN@CNT was added to 5 mL of H 2 O, and then the mixture was ultrasonically treated for 5 minutes to achieve uniform dispersion. Subsequently, H 2 PtCl 6 ·6H 2 O solution was added dropwise to the mixture. The resulting suspension was then ultrasonically treated at a constant temperature of 20 - 30 °C for 4 hours. The ultrasonically treated suspension was placed in a vacuum freezer and freeze-dried for 35 hours; finally, the dried sample was heated to 800 °C at a rate of 15 °C per minute in a tube furnace and maintained at this temperature for 3 - 5 hours in an ammonia-argon mixed atmosphere for thermal decomposition, thereby obtaining a black powder sample PtSA-C@eBN-CNT. The aberration-corrected transmission electron microscopy image of the product prepared in this example is shown in Figure 1 ; The X-ray diffraction pattern is shown in Figure 2 ; The X-ray absorption near-edge structure spectrum is shown in Figure 3 .

[0026] Example 2 Electrochemical catalytic alkaline HER activity test of PtSA-C@eBN-CNT obtained in Example 1; PtSA-C@eBN-CNT obtained in Example 1 was used as the HER catalyst. All electrochemical tests were carried out on a CHI760E electrochemical workstation (produced by Shanghai Chenhua Co., Ltd.). In a 1.0 M KOH aqueous solution, a traditional three-electrode system was adopted. The working electrode was a glassy carbon electrode coated with the catalyst, the counter electrode was a carbon rod, and the reference electrode was a Hg / HgO electrode. To prepare a uniform ink, 5 mg of the catalyst powder was dispersed in 20 μL of Nafion solution, 180 μL of isopropanol, and 130 μL of deionized water. Subsequently, 10 μL of the ink was drop-coated on a glassy carbon electrode (GCE) and allowed to dry naturally. Figure 3 The linear sweep voltammetry curve shown was obtained at a scan rate of 5.0 mV / s, and the overpotential at a current density of 10 mA‧cm -2 was 25.2 mV. Figure 4 It shows that at an extremely low metal loading (only 4 μg Pt ·cm -2 ), the turnover frequency (TOF) of the catalyst was 18.9 s -1 (overpotential 0.15 V). Figure 5 For the linear sweep voltammetry curves of PtSA-C@eBN-CNT before and after 40,000 cycles of CV scanning, the curves of linear sweep voltammetry before and after CV scanning almost coincided. Figure 6 It shows that the catalyst can operate at a current density of 100 mA·cm -2 for at least 120 hours, indicating its good catalytic stability.

[0027] Example 3 Performance test of the membrane electrode electrolyzer of PtSA-C@eBN-CNT obtained in Example 1; Using PtSA-C@eBN-CNT obtained in Example 1 as the cathode catalyst and NiFe LDH as the anode catalyst, an electrolyzer based on an anion exchange membrane (AEM) was constructed. Figure 7 It shows that the device achieved a current density of 1.0 A·cm -2 at a cell voltage of 1.89 V, significantly superior to the electrolyzer using commercial Pt / C as the cathode catalyst. Photos of the actual application scenario of the assembled membrane electrode electrolyzer are shown in Figure 8 .

[0028] In this invention, for the first time, a platinum-based single atom-cluster composite catalyst was synthesized on highly defective boron nitride. This catalyst exhibits excellent alkaline HER performance, with an overpotential as low as 25 mV at a current density of 10 mA·cm -2 , and at the same time has a high TOF of up to 18.9 s -1 at an overpotential of 0.15 V. bulkThe value is about 27 times that of commercial 20 wt% Pt / C. The present invention provides a new paradigm for the preparation of catalysts with low platinum loading and also lays a theoretical and experimental foundation for its application in actual industrial production.

Claims

1. A method for preparing a boron nitride confined platinum single atom-platinum cluster dual-site catalyst, characterized in that: The method comprises the following steps: mixing urea, boric acid and carbon nanotubes, and grinding the mixture; placing the ground mixture in an ammonia-argon mixed atmosphere for a first pyrolysis to obtain powder; adding the powder into a boric acid solution, heating and stirring to obtain a defect-rich boron nitride carrier; washing and drying the carrier, immersing the carrier in a platinum salt aqueous solution, and dispersing the carrier by ultrasound, followed by drying by vacuum freeze drying, and finally subjecting the dried sample to a second pyrolysis in an ammonia-argon mixed atmosphere.

2. The method according to claim 1, characterized in that: The mass ratio of the boric acid is 10-15%, the mass ratio of the urea is 60-75%, and the mass ratio of the carbon nanotubes is 10-30%.

3. The method according to claim 1, characterized in that The temperature of the first pyrolysis is 700-1100° C., and the insulation time is 2-5 hours.

4. The method according to claim 1, characterized in that: The heating temperature is 75-95° C., and the stirring time is 25-45 minutes.

5. The method according to claim 1, characterized in that The duration of the ultrasonic dispersion is 4-5 hours, and the solution temperature during the ultrasonic dispersion is 20-30°C.

6. The method according to claim 1, characterized in that The platinum salt aqueous solution comprises chloroplatinic acid, platinum nitrate and platinum sulfate.

7. The method according to claim 1, characterized in that The vacuum freeze drying method is to use a vacuum freezer for freeze drying, and the freeze drying time is 30-45 hours.

8. The method according to claim 1, characterized in that: The dried sample is placed in a tubular furnace, the second pyrolysis temperature is 650-850° C., and the pyrolysis time is 3-5 hours.

9. The boron nitride confined platinum single atom-platinum cluster dual-site catalyst prepared according to any one of claims 1 to 8, characterized in that: The platinum single atoms of the catalyst are evenly distributed, and the cluster particle size is 1.0-1.9 nm.

10. The use of a boron nitride confined platinum single atom-platinum cluster dual-site catalyst according to claim 9, characterized in that: The catalyst is used in electrocatalytic water decomposition, hydrogen oxidation reaction, oxygen reduction reaction, carbon dioxide reduction reaction, air batteries and membrane electrode energy devices.

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