Cu-ni4n composite catalyst, preparation method and application thereof

Abstract

The present application relates to the technical field of electrocatalytic ammonia oxidation reaction, and particularly relates to a Cu-Ni4N composite catalyst and a preparation method and application thereof. Pure Ni4N as an electrocatalyst for ammonia oxidation reaction has poor catalytic effect. In view of the above problem, the present application provides a Cu-Ni4N composite catalyst, which regulates the electronic structure of the nitrogenated four nickel by introducing copper elements, utilizes the synergistic effect between copper and nickel, and effectively optimizes the adsorption behavior of the catalyst surface to the intermediate of the ammonia oxidation reaction. The peroxidation potential of the ammonia oxidation can be obviously reduced, the reaction current density can be improved, and the poisoning effect of the intermediate on the active sites can be reduced, so that the activity and long-term operation stability of the electrocatalytic ammonia oxidation reaction can be significantly improved. Compared with the pure Ni4N catalyst, the Cu-Ni4N composite catalyst has substantial improvement in the ammonia oxidation performance.

Description

Technical Field

[0001] This invention relates to the field of electrocatalytic ammonia oxidation reaction technology, specifically to a Cu-Ni4N composite catalyst, its preparation method, and its application. Background Technology

[0002] Ammonia, as a carbon-free fuel and a highly efficient hydrogen storage medium, demonstrates unique advantages in solving the challenges of hydrogen energy storage and transportation. Ammonia possesses high energy density, is easily liquefied, and its production, storage, and transportation supply chain is already quite mature, effectively avoiding the high utilization costs associated with pure hydrogen fuel. Direct ammonia fuel cells, powered by the direct oxidation of ammonia, are a novel clean energy conversion technology. Because they avoid the use of carbon-based fuels, this technology does not produce carbon dioxide emissions, and has therefore attracted widespread attention.

[0003] In direct ammonia fuel cells, the ammonia oxidation reaction at the anode is a crucial step determining cell performance. However, the ammonia oxidation reaction currently faces three main limitations: high peroxidation potential, low current density, and the tendency of reaction intermediates to poison the catalyst surface. Therefore, developing high-performance electrocatalysts for the ammonia oxidation reaction is essential for promoting the practical application of direct ammonia fuel cells.

[0004] Transition metal nitrides have shown promising applications in electrocatalysis in recent years. Among them, nickel tetranitride (Ni4N) possesses excellent metallic conductivity, high chemical stability, and abundant nickel active sites. Compared with traditional nickel-based oxides or hydroxides, the introduction of nitrogen atoms into Ni4N can modulate the electronic structure of nickel atoms, thereby improving the catalyst's adsorption behavior for reaction intermediates and enhancing electrocatalytic activity. On the other hand, copper possesses good conductivity and electronic modulation capabilities. Introducing copper into the Ni4N system is expected to further optimize the catalyst's electronic structure through the synergistic effect between copper and nickel components, improve the utilization rate of active sites, and promote charge transport and reaction kinetics in the ammonia oxidation process.

[0005] Currently, reports on the application of copper-nickel tetranitride (Cu-Ni4N) composite catalysts in electrochemical ammonia oxidation reactions are still limited. In particular, research on constructing Cu-Ni4N composite catalysts using a combination of co-precipitation, calcination, and nitriding treatments, and their application in ammonia oxidation reactions, is insufficient. Therefore, this invention provides a Cu-Ni4N composite catalyst and its preparation method. This catalyst is prepared by co-precipitating water-soluble divalent copper salt and nickel salt under alkaline conditions, followed by calcination and urea-involved nitriding treatment, which can effectively improve the catalytic performance of electrochemical ammonia oxidation reactions. Summary of the Invention

[0006] A problem with existing technologies is that pure Ni4N exhibits poor catalytic performance as an electrocatalyst for ammonia oxidation. To address this issue, this invention provides a Cu-Ni4N composite catalyst, the preparation method of which includes the following steps: (1) Under alkaline conditions, water-soluble divalent inorganic copper salt and water-soluble inorganic nickel salt undergo a co-precipitation reaction in deionized water. After the reaction is completed, the mixture is allowed to stand for at least 12 hours. Then, the precipitate is collected by solid-liquid separation, washing, and drying to obtain the precursor powder. (2) The precursor powder was placed in a muffle furnace and calcined in air to obtain the calcined product; (3) The calcined product and urea were ground and mixed evenly at a mass ratio of 1:5. Then, the mixture was calcined at high temperature under nitrogen protection and then naturally cooled to room temperature to obtain Cu-Ni4N composite catalyst.

[0007] Preferably, in step (1), the molar percentage of water-soluble divalent copper salt to water-soluble nickel salt is 50:50.

[0008] Preferably, the water-soluble divalent inorganic copper salt in step (1) is at least one of copper nitrate trihydrate, copper chloride dihydrate, and copper sulfate pentahydrate.

[0009] Preferably, the water-soluble inorganic nickel salt in step (1) includes at least one of nickel nitrate hexahydrate, nickel chloride hexahydrate, and nickel sulfate hexahydrate.

[0010] Preferably, the calcination temperature in step (2) is 400℃ and the calcination time is 2h.

[0011] Preferably, the calcination temperature in step (3) is 500°C and the calcination time is 4 hours.

[0012] An electrocatalytic ammonia oxidation reaction is described above, which uses the Cu-Ni4N composite catalyst as its electrocatalyst.

[0013] Beneficial effects: (1) The Cu-Ni4N composite catalyst provided by this invention modulates the electronic structure of nickel tetranitride by introducing copper, and effectively optimizes the adsorption behavior of intermediates in the ammonia oxidation reaction on the catalyst surface by utilizing the synergistic effect between copper and nickel. Experiments show that this composite catalyst can significantly reduce the peroxidation potential of ammonia oxidation, increase the reaction current density, and reduce the poisoning effect of intermediates on active sites, thereby significantly improving the activity and long-term operational stability of the electrocatalytic ammonia oxidation reaction. Compared with the pure Ni4N catalyst, the Cu-Ni4N composite catalyst has a substantial improvement in ammonia oxidation performance.

[0014] (2) The Cu-Ni4N composite catalyst prepared in this invention can be directly used as the anode electrocatalyst for direct ammonia fuel cells, exhibiting excellent catalytic efficiency for ammonia oxidation in alkaline electrolytes. The application of this catalyst helps promote the development of direct ammonia fuel cells and provides an efficient and stable catalytic material option for achieving carbon-free clean energy conversion. Attached Figure Description

[0015] Figure 1 : This is the X-ray diffraction (XRD) pattern of 50Cu-50Ni4N obtained in Example 1 of this invention.

[0016] Figure 2 : This is a comparison chart showing the performance of the catalysts obtained in Example 1 and Comparative Examples 1-4 of the present invention in the electrocatalytic ammonia oxidation reaction.

[0017] Figure 3 The double-layer capacitance (C) of the catalysts obtained in Example 1 and Comparative Examples 1-4 of this invention in an electrolyte composed of 1M KOH aqueous solution and 0.5M NH4Cl aqueous solution at a volume ratio of 2:1 is given. dl )picture.

[0018] Figure 4 The image shows the steady-state test (it) of the 50Cu-50Ni4N obtained in Example 1 of this invention in an electrolyte composed of 1M KOH aqueous solution and 0.5M NH4Cl aqueous solution at a volume ratio of 2:1 under a voltage of 0.65 (V vs. Ag / AgCl). Detailed Implementation

[0019] The present invention will be described in detail below with reference to embodiments. However, it should be understood that the following embodiments are merely illustrative examples of implementation of the present invention and are not intended to limit the scope of the present invention.

[0020] Example 1 A method for preparing a Cu-Ni4N composite catalyst is as follows: (1) Weigh 2.908g of nickel nitrate hexahydrate and 2.416g of copper nitrate trihydrate (molar percentage of 50:50, total molar mass of 0.02mol) and add them to 200 mL of deionized water. Stir well to obtain mixture A. (2) Add 1 mol / L sodium hydroxide solution dropwise to mixture A at 600 rpm to adjust the pH of mixture A to 10 so that nickel ions and copper ions co-precipitate. Continue stirring for 2 hours and let stand for 12 hours to obtain mixture B. (3) Centrifuge the mixture B and wash the resulting precipitate three times with deionized water and anhydrous ethanol, respectively. (4) The washed product was placed in an oven at 80°C and dried for 12 h to obtain precursor powder; (5) The precursor powder was placed in a muffle furnace and calcined at 400°C for 2 h to obtain the calcined product; (6) The calcined product and urea are mixed and ground at a mass ratio of 1:5, and then placed in a tube furnace and calcined at 500°C for 4 h under nitrogen protection. After the reaction is completed, the mixture is cooled to room temperature to obtain a black powder, namely Cu-Ni4N composite catalyst, which is denoted as 50Cu-50Ni4N composite catalyst.

[0021] After preparing the above catalyst into a working electrode and performing electrochemical ammonia oxidation tests, refer to the appendix of the instruction manual. Figure 2 The initial potential is 0.44 (V vs. Ag / AgCl), and the current density at the same voltage is 97.05 mA / cm². 2 .

[0022] Comparative Example 1 is the same as Example 1, except that the amount of nickel nitrate hexahydrate added in Comparative Example 1 is 1.454 g, and the amount of copper nitrate trihydrate added is 3.624 g. The catalyst obtained in Comparative Example 1 is designated as the 75Cu-25Ni4N composite catalyst.

[0023] Comparative Example 2 is the same as Example 1, except that the amount of nickel nitrate hexahydrate added in Comparative Example 2 is 2.036 g, and the amount of copper nitrate trihydrate added is 3.141 g. The catalyst obtained in Comparative Example 2 is designated as the 65Cu-35Ni4N composite catalyst.

[0024] Comparative Example 3 is the same as Example 1, except that the amount of nickel nitrate hexahydrate added in Comparative Example 3 is 3.780 g, and the amount of copper nitrate trihydrate added is 1.691 g. The catalyst obtained in Comparative Example 3 is designated as the 35Cu-65Ni4N composite catalyst.

[0025] Comparative Example 4 is the same as Example 1, except that copper nitrate trihydrate was not added in Comparative Example 4, and the amount of nickel nitrate hexahydrate added was 5.816 g. The catalyst obtained in Comparative Example 4 is designated as Ni4N catalyst.

[0026] Performance testing The performance evaluation of electrocatalytic ammonia oxidation was conducted using an electrochemical workstation. First, weigh 2.5 mg of catalyst and 2.5 mg of activated carbon, add them to 950 μL of anhydrous ethanol and 50 μL of 5 wt% Nafion solution, and sonicate to prepare a catalyst suspension. Then, add the suspension dropwise in small amounts until the surface area reaches 0.1256 cm². 2 The catalyst was naturally air-dried on a glassy carbon electrode to prepare a catalyst with a loading of 0.24 mg / cm³. 2 Working electrode; Secondly, an electrochemical test was conducted using a three-electrode electrolytic cell reactor. The reference electrode was an Ag / AgCl electrode (saturated KCl) (with the final potential corrected to a standard hydrogen electrode), and the counter electrode was a platinum wire connected to an electrochemical workstation. The electrochemical test was performed in an electrolyte solution composed of 1M KOH aqueous solution and 0.5M NH4Cl aqueous solution in a volume ratio of 2:1.

[0027] Cyclic voltammetry (CV): Before testing, the working electrode is activated using a rapid scanning method to increase active sites and generate active groups (such as ∙OH), thereby improving the catalytic performance of the electrode material. The voltage test range is 0–0.8 V. The initial scan rate is 50 mV / s until the curves coincide, then the scan rate is changed to 25 mV / s until the curves coincide again.

[0028] Linear voltammetry (LSV): The oxidation initiation potential and current response value on the surface of the catalytic electrode material during the electrocatalytic oxidation of ammonia were measured at a scan rate of 5 mV / s.

[0029] Electric double layer capacitance (Cdl): proportional to the electrochemically active specific surface area of ​​the catalyst, it refers to the linear fitting curve obtained by performing cyclic voltammetry scans at scan rates of 20 mV / s, 40 mV / s, 60 mV / s, 80 mV / s, and 100 mV / s within the non-Radida reaction range, obtaining the scan rate-current density relationship curve, and calculating it based on the curve.

[0030] The electrocatalytic performance of the catalysts obtained in the embodiments and comparative examples of this invention was tested and evaluated. The test results are shown in Table 1.

[0031] Table 1 The XRD pattern of 50Cu-50Ni4N obtained in Example 1 can be found in the appendix of the specification. Figure 1 The images show that the characteristic diffraction peaks of the sample are consistent with the Ni4N standard card (No. JCPDS 36-1300) and the Cu standard card (No. JCPDS 85-1326), indicating that Cu-Ni4N was successfully synthesized.

[0032] A comparison chart of the performance of the catalysts obtained in Example 1 and Comparative Examples 1-4 in the ammonia oxidation reaction is shown in the appendix of the instruction manual. Figure 2 .

[0033] In the ammonia oxidation reaction test, the oxidation onset potential and current response value of the catalytic electrode material surface were tested by cyclic voltammetry (CV). The voltage test range was 0 to 0.8 V. First, the scan rate was 50 mV / s until the curves overlapped, and then the scan rate was changed to 25 mV / s until the curves overlapped.

[0034] In the ammonia oxidation reaction test, the oxidation onset potential and current response value of the catalytic electrode material surface were tested by linear voltammetry (LSV) at a scan rate of 5 mV / s.

[0035] Test results show that, compared with other catalytic materials, the 50Cu-50Ni4N catalyst obtained in Example 1 has a maximum current density of 97.05 mA / cm². 2 With an onset potential as low as 0.44 (V vs. Ag / AgCl), it exhibits the best catalytic activity for ammonia oxidation.

[0036] The double-layer capacitance (C0) of the catalysts obtained in Examples 1 and Comparative Examples 1-4 in a mixed electrolyte solution consisting of 1M KOH aqueous solution and 0.5M NH4Cl aqueous solution at a volume ratio of 2:1 dl (See attached instruction manual for diagram) Figure 3 The image shows that the electric double-layer capacitance of 50Cu-50Ni4N is the largest, at 3.42 mF / cm². 2 It has the best electrochemically active specific surface area and the highest catalytic activity, and its trend is consistent with the activity curve.

[0037] The steady-state test (it) of the 50Cu-50Ni4N obtained in Example 1 in an electrolyte composed of 1M KOH aqueous solution and 0.5M NH4Cl aqueous solution at a volume ratio of 2:1 under a voltage of 0.65 (V vs. Ag / AgCl) is shown in the appendix of the instruction manual. Figure 4 As shown in the figure, the oxidation current density of the catalyst 50Cu-50Ni4N reaches equilibrium after an initial decrease due to concentration polarization.

[0038] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A Cu-Ni4N composite catalyst, characterized in that, The preparation method includes the following steps: (1) Under alkaline conditions, water-soluble divalent inorganic copper salt and water-soluble inorganic nickel salt undergo a co-precipitation reaction in deionized water. After the reaction is completed, the mixture is allowed to stand for at least 12 hours. Then, the precipitate is collected by solid-liquid separation, washing, and drying to obtain the precursor powder. (2) The precursor powder was placed in a muffle furnace and calcined in air to obtain the calcined product; (3) The calcined product and urea were ground and mixed evenly at a mass ratio of 1:

5. Then, the mixture was calcined at high temperature under nitrogen protection and then naturally cooled to room temperature to obtain Cu-Ni4N composite catalyst.

2. The Cu-Ni4N composite catalyst according to claim 1, characterized in that, In step (1), the molar percentage of water-soluble divalent copper salt and water-soluble nickel salt is 50:

50.

3. The Cu-Ni4N composite catalyst according to claim 1, characterized in that, In step (1), the water-soluble divalent inorganic copper salt is at least one of copper nitrate trihydrate, copper chloride dihydrate, and copper sulfate pentahydrate.

4. The Cu-Ni4N composite catalyst according to claim 1, characterized in that, In step (1), the water-soluble inorganic nickel salt includes at least one of nickel nitrate hexahydrate, nickel chloride hexahydrate, and nickel sulfate hexahydrate.

5. The Cu-Ni4N composite catalyst according to claim 1, characterized in that, The calcination temperature in step (2) is 400℃ and the calcination time is 2h.

6. The Cu-Ni4N composite catalyst according to claim 1, characterized in that, The calcination temperature in step (3) is 500℃ and the calcination time is 4h.

7. An electrocatalytic ammonia oxidation reaction, characterized in that, The Cu-Ni4N composite catalyst according to any one of claims 1-6 is used as its electrocatalyst.

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