A preparation method of a PtZn / CNTs catalyst for ammonia oxidation

Abstract

The application discloses a preparation method of an ammonia oxidation PtZn / CNTs catalyst. The preparation method of the catalyst comprises the following steps: firstly, 31 mg of K2PtCl4, 16 mg of Zn(CH3COO)2 and 60 mg of CNTs are added into 60 mL of DMF, and after ultrasonic dispersion for 20 min, vacuum drying is carried out at 100 DEG C for 7 h. After the obtained powder is ground, heat treatment is carried out at 900 DEG C for 2 h under a nitrogen atmosphere, and after natural cooling, a PtZn / CNTs catalyst is obtained. The catalyst has the electronic structure regulation effect of the PtZn alloy and the high-conductivity and high-stable carrier advantages of the CNTs, can optimize the adsorption behavior of an ammonia oxidation reaction intermediate, improve the AOR catalytic activity and long-term stability of the catalyst, and reduce the amount of the noble metal Pt, and is suitable for direct ammonia fuel cell anode catalytic materials. The method is simple and efficient, does not need a reducing agent, and is suitable for large-scale production and commercial application.

Description

Technical Field

[0001] This invention relates to a method for preparing a PtZn / CNTs catalyst for ammonia oxidation, belonging to the field of novel functional nanomaterials and catalytic energy conversion technology. Background Technology

[0002] Ammonia, as a carbon-free energy carrier with high hydrogen content, easy storage and transportation, holds significant application potential in direct ammonia fuel cells and electrochemical energy conversion. The ammonia oxidation reaction (AOR), a key reaction at the anode of direct ammonia fuel cells, directly impacts the cell's output performance due to its catalytic efficiency and stability. However, this reaction involves multiple electron transfers and has slow reaction kinetics, leading to catalytic activity degradation. Therefore, developing AOR catalysts with high catalytic activity and good stability is a pressing technical challenge in this field.

[0003] Currently, platinum (Pt)-based catalysts are considered highly effective catalytic materials for ammonia resorption and oxidation (AOR) due to their excellent adsorption and activation capabilities for ammonia molecules. However, single Pt catalysts suffer from drawbacks such as high noble metal content, insufficient surface electronic structure regulation, and limited reaction kinetics, making their catalytic activity and stability insufficient for practical applications. Introducing zinc (Zn) to form a PtZn alloy allows for the regulation of Pt's electronic structure through intermetallic electronic interactions, resulting in a more suitable d-band center structure. This optimizes the adsorption / desorption free energy of intermediates in the AOR process, promotes AOR kinetics, and reduces the amount of Pt required. However, PtZn alloy particles are prone to agglomeration during preparation, leading to insufficient exposure of effective active sites, limited electron transport, and poor long-term stability. Carbon nanotubes (CNTs), with their high specific surface area, good electrical conductivity, and excellent chemical stability, can serve as supports for PtZn alloy nanoparticles, improving the dispersion of metal particles and enhancing the catalyst's electron transport capability. Therefore, developing a PtZn alloy-supported CNT catalyst is of great significance for improving the catalytic activity and stability of AOR.

[0004] Although PtZn alloy catalysts have potential advantages in regulating the electronic structure of Pt and reducing the amount of precious metals used, current PtZn alloy-supported CNT catalysts still suffer from problems such as insufficient flexibility in controlling the alloy composition, easy agglomeration of metal particles, and difficulty in effectively adjusting the Zn content. Therefore, there is a need to develop a simple and compositionally tunable preparation method for PtZn / CNT catalysts with high-efficiency AOR catalytic performance. Summary of the Invention

[0005] To avoid the shortcomings of the prior art, the present invention provides a method for preparing a catalyst for the ammonia oxidation of PtZn / CNTs.

[0006] One of the objectives of this invention is to provide a novel method for preparing a PtZn / CNTs catalyst for ammonia oxidation.

[0007] The second objective of this invention is to provide a simple and easy-to-implement one-step thermal reduction method for a tubular furnace.

[0008] The third objective of this invention is to provide a catalyst with significantly high AOR catalytic activity.

[0009] The PtZn / CNTs catalyst prepared in this invention is made from potassium chloroplatinate (K2PtCl4), zinc acetate (Zn(CH3COO)2), carbon nanotubes (CNTs), and N,N-dimethylformamide (DMF) through a series of steps including ultrasonic dispersion, vacuum drying, and tube furnace heating. The preparation process includes the following specific steps: 1. First, weigh 25-35 mg of K2PtCl4, 10-20 mg of Zn(CH3COO)2 and 60 mg of CNTs, and add them to 60 mL of DMF to dissolve them completely to obtain a black solution; then place the black solution in an ultrasonic bath for 20 min of ultrasonic dispersion treatment to obtain a uniformly dispersed black suspension. 2. Transfer the black suspension obtained in step 1 to a vacuum drying oven and dry it at 100 °C for 7 hours to obtain a black powder; 3. Take out the black powder obtained in step 2 and grind it thoroughly. Then, put it into a quartz boat and place it in the center of a tube furnace. Keep it at 400-1000 ℃ for 2 h under a nitrogen atmosphere. After the reaction is completed, take it out and let it cool naturally to finally obtain the black PtZn / CNTs catalyst.

[0010] The beneficial effects of this invention are: 1. This invention provides a method for preparing a PtZn / CNTs catalyst for ammonia oxidation, characterized by using K2PtCl4, Zn(CH3COO)2, CNTs, and DMF as raw materials, and sequentially performing ultrasonic dispersion, vacuum drying, and tube furnace heating treatment to complete the catalyst synthesis. This preparation process requires no complex equipment, is simple to operate, has a short reaction time, and is suitable for implementation under normal laboratory conditions; 2. The PtZn / CNTs catalyst prepared in this invention achieves uniform distribution and stable loading of PtZn alloy particles under the synergistic effect of the high specific surface area and excellent conductivity of CNTs, which significantly improves the charge transfer rate and reaction interface stability, and is beneficial to improving the AOR catalytic efficiency. 3. The prepared catalyst exhibits excellent AOR electrocatalytic activity and operational stability under alkaline electrolyte conditions, with high peak current density and low onset potential. Its overall electrocatalytic performance is significantly better than that of commercial Pt / C catalysts and other comparative samples. 4. The drugs used in this invention are safe and controllable under standardized operation, and the preparation is simple and quick. After preparation, no complicated and tedious steps are required, making it particularly suitable for batch preparation and industrial-scale production and commercial application. Attached Figure Description

[0011] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings will be briefly introduced in the description of the embodiments or the prior art below. However, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0012] Figure 1 Transmission electron microscope image of the PtZn / CNTs catalyst prepared in this invention.

[0013] Figure 2 High-angle annular dark-field transmission electron microscope image and corresponding elemental analysis diagram of the PtZn / CNTs catalyst prepared for this invention.

[0014] Figure 3 The image shows the X-ray photoelectron spectrum of the PtZn / CNTs catalyst prepared in this invention.

[0015] Figure 4 The AOR performance test graphs are for the PtZn / CNTs catalyst prepared in this invention and the commercial Pt / C catalyst.

[0016] Figure 5 The stability test results are shown for the PtZn / CNTs catalyst prepared in this invention and the commercial Pt / C catalyst. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0018] Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention.

[0019] Unless otherwise specified, the experimental methods described in the following embodiments are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0020] Example 1: First, 31 mg of K₂PtCl₄, 16 mg of Zn(CH₃COO)₂, and 60 mg of CNTs were weighed and dissolved thoroughly in 60 mL of DMF to form a black solution. The resulting black solution was then ultrasonically dispersed in an ultrasonic bath for 20 min to obtain a uniformly dispersed black suspension. This black suspension was transferred to a vacuum drying oven and dried at 100 °C for 7 h to obtain a black powder. The black powder was then removed, thoroughly ground, placed in a quartz boat, and positioned in the center of a tube furnace. The furnace was heated at 900 °C for 2 h under a nitrogen atmosphere. After the reaction was complete, the powder was removed and allowed to cool naturally to obtain the final black PtZn / CNT catalyst.

[0021] Example 2: First, 35 mg of K₂PtCl₄, 18 mg of Zn(CH₃COO)₂, and 60 mg of CNTs were weighed and dissolved thoroughly in 60 mL of DMF to form a black solution. The resulting black solution was then ultrasonically dispersed in an ultrasonic bath for 20 min to obtain a uniformly dispersed black suspension. This black suspension was transferred to a vacuum drying oven and dried at 100 °C for 7 h to obtain a black powder. The black powder was then removed, thoroughly ground, placed in a quartz boat, and positioned in the center of a tube furnace. The furnace was heated at 1000 °C for 2 h under a nitrogen atmosphere. After the reaction was complete, the powder was removed and allowed to cool naturally to obtain the final black PtZn / CNT catalyst.

[0022] Example 3: First, 28 mg of K₂PtCl₄, 14 mg of Zn(CH₃COO)₂, and 60 mg of CNTs were weighed and dissolved thoroughly in 60 mL of DMF to form a black solution. The resulting black solution was then ultrasonically dispersed in an ultrasonic bath for 20 min to obtain a uniformly dispersed black suspension. This black suspension was transferred to a vacuum drying oven and dried at 100 °C for 7 h to obtain a black powder. The black powder was then removed, thoroughly ground, placed in a quartz boat, and positioned in the center of a tube furnace. The furnace was heated at 800 °C for 2 h under a nitrogen atmosphere. After the reaction was complete, the powder was removed and allowed to cool naturally to obtain the final black PtZn / CNT catalyst.

[0023] Example 4: First, 25 mg of K₂PtCl₄, 12 mg of Zn(CH₃COO)₂, and 60 mg of CNTs were weighed and dissolved thoroughly in 60 mL of DMF to form a black solution. The resulting black solution was then ultrasonically dispersed in an ultrasonic bath for 20 min to obtain a uniformly dispersed black suspension. This black suspension was transferred to a vacuum drying oven and dried at 100 °C for 7 h to obtain a black powder. The black powder was then removed, thoroughly ground, placed in a quartz boat, and positioned in the center of a tube furnace. The furnace was heated at 600 °C for 2 h under a nitrogen atmosphere. After the reaction was complete, the powder was removed and allowed to cool naturally to obtain the final black PtZn / CNT catalyst.

[0024] Example 5: First, 22 mg of K₂PtCl₄, 10 mg of Zn(CH₃COO)₂, and 60 mg of CNTs were weighed and dissolved thoroughly in 60 mL of DMF to form a black solution. The resulting black solution was then ultrasonically dispersed in an ultrasonic bath for 20 min to obtain a uniformly dispersed black suspension. This black suspension was transferred to a vacuum drying oven and dried at 100 °C for 7 h to obtain a black powder. The black powder was then removed, thoroughly ground, placed in a quartz boat, and positioned in the center of a tube furnace. The furnace was heated at 400 °C for 2 h under a nitrogen atmosphere. After the reaction was complete, the powder was removed and allowed to cool naturally to obtain the final black PtZn / CNT catalyst.

[0025] Figure 1 Transmission electron microscopy (TEM) image of the PtZn / CNTs catalyst prepared in Example 1. From... Figure 1 It can be seen that the network structure of CNTs provides an excellent supporting framework for the dispersion of PtZn nanoparticles.

[0026] Figure 2 High-angle annular dark-field transmission electron microscope image and corresponding elemental analysis diagram of the PtZn / CNTs catalyst prepared in Example 1. It is noteworthy that, from... Figure 2 It can be seen that C, Pt and Zn elements are distributed in the PtZn / CNTs catalyst.

[0027] Figure 3 X-ray photoelectron spectroscopy (XPS) spectra of the PtZn / CNTs prepared in Example 1 and the commercial Pt / C catalyst. From... Figure 3 It can be seen that the Pt 4f of PtZn / CNTs 7 / 2The peak binding energy is 71.6 eV, lower than the binding energy of commercial Pt / C (71.8 eV). This phenomenon indicates that the introduction of Zn facilitates electron transfer from Zn to Pt, increasing the electron density on the Pt surface. This electronic structure modulation helps optimize the adsorption behavior of AOR intermediates at Pt sites, improves the electron transfer rate, and enhances catalytic activity.

[0028] Figure 4 AOR performance graphs for the PtZn / CNTs catalysts prepared in Examples 1-5 and the commercial Pt / C catalysts are shown. Figure 4 It can be seen that at 10 mV s -1 Under the test conditions, the peak current density of the highly efficient ammonia oxidation electrocatalyst PtZn / CNTs prepared in Example 1 was significantly higher than that of the catalysts prepared in Examples 2, 3, 4, and 5 and the commercial Pt / C catalyst, indicating that the PtZn / CNTs catalyst prepared in Example 1 has excellent AOR performance.

[0029] Figure 5 The graphs show the stability test results of the PtZn / CNTs catalysts prepared in Examples 1-5 and the commercial Pt / C catalyst. Figure 5 It can be seen that, under a constant voltage test condition of 0.7 V, after 500 s, the current density of the PtZn / CNTs catalyst prepared in Example 4 is higher than that of the catalysts prepared in Examples 2, 3, 4, and 5, as well as the commercial Pt / C catalyst. This indicates that the PtZn / CNTs catalyst prepared in Example 1 has excellent stability.

[0030] Obviously, those skilled in the art can make various modifications and variations to the method for preparing a PtZn / CNTs catalyst for ammonia oxidation described in this invention without departing from the spirit and scope of this invention. Therefore, if these modifications and variations of this invention fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing a PtZn / CNTs catalyst for ammonia oxidation, comprising the following steps: First, weigh 22-35 mg of K2PtCl4, 10-18 mg of Zn(CH3COO)2 and 60 mg of CNTs, add them to 60 mL of DMF and dissolve them completely to form a black solution; The resulting black solution was then ultrasonically dispersed in an ultrasonic bath for 20 min to obtain a uniformly dispersed black suspension. The black suspension was transferred to a vacuum drying oven and dried at 100 °C for 7 h to obtain a black powder. The obtained black powder was then removed and thoroughly ground, placed in a quartz boat, and positioned in the center of a tube furnace. The furnace was then heated at 400 °C–1000 °C for 2 h under a nitrogen atmosphere. After the reaction was complete, the powder was removed and allowed to cool naturally, ultimately yielding a black PtZn / CNTs catalyst.

2. The method for preparing the highly efficient PtZn / CNTs electrocatalyst for ammonia oxidation according to claim 1, characterized in that, The dosage of CNTs is 60 mg.

3. The method for preparing the highly efficient PtZn / CNTs electrocatalyst for ammonia oxidation according to claim 1, characterized in that, The amount of DMF used is 60 mL.

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