Indium-based oxide heterojunction material and application thereof in electro-catalysis C-N coupling

Abstract

The invention belongs to the technical field of electro-catalysis, and discloses an indium-based oxide heterojunction material and application thereof in electro-catalysis C-N coupling. The heterojunction material is formed by compounding two phases of In2O3 and InNbO4, an atomic-scale close contact heterogeneous interface is formed between the two phases, in an electro-catalysis CN coupling reaction, a niobium element is used for specifically activating CO2 and stabilizing a carbon-containing intermediate, an indium element is used for directionally anchoring NO3 <-> and a reduction product thereof, a hydrogen evolution side reaction is inhibited through the synergistic effect of double active sites, a C-N coupling energy barrier is reduced, and the CN coupling reaction efficiency is improved. Urea synthesis is realized, and high yield and Faraday efficiency are achieved.

Description

Technical Field

[0001] This invention relates to the fields of materials science and electrocatalysis, specifically to an indium-based oxide heterojunction material and its application in electrocatalytic CN coupling. Background Technology

[0002] Urea, an essential fertilizer in agriculture and a crucial chemical raw material in industry, has a huge global demand. Traditional industrial urea synthesis primarily relies on the Bosch-Meiser process, which requires the reaction of ammonia with carbon dioxide under high temperature and pressure conditions. This process is not only energy-intensive but also involves significant fossil fuel consumption and carbon emissions. To address this environmental and energy challenge, electrocatalytic CN-coupling technology driven by renewable electricity has emerged. This technology can convert greenhouse gas CO2 and widely present nitrate / nitrite pollutants into high-value-added urea under mild conditions, achieving "waste-to-treasure" transformation and a carbon-nitrogen dual cycle.

[0003] Despite the significant advantages of electrocatalytic CN-coupling technology, the reaction process involves complex CN-bond formation steps and currently faces two major challenges: first, the reaction kinetics are slow, making it difficult for CO2 reduction intermediates and nitrogen reduction intermediates to effectively match and couple on the catalyst surface; second, the intense competition of reactions (such as the hydrogen evolution reaction HER) leads to low urea selectivity (Faraday efficiency) and yield. Therefore, designing efficient catalysts to precisely control the adsorption behavior of carbon- and nitrogen-containing intermediates and reduce the CN-coupling energy barrier has become a critical technical challenge that urgently needs to be overcome in the field of electrocatalysis.

[0004] At the catalyst design level, constructing dual active sites is the core solution to the aforementioned problems. Niobium-based materials, due to the high valence state of niobium atoms, exhibit extremely strong Lewis acidity. This acidic environment can strongly polarize the CO bonds in the CO2 molecule, thereby effectively activating chemically inert CO2 and stabilizing key carbon-containing intermediates. Indium oxide, as a p-block metal oxide, exhibits excellent specific affinity for nitrogen-containing species due to its unique orbital hybridization characteristics at its surface In sites, enabling directional anchoring and enrichment of nitrogen sources. If these two can be effectively combined to construct a mixed oxide system with rich interfaces, it is expected that the synergistic effect of the interfaces can be utilized. On the one hand, niobium species can capture and activate carbon sources; on the other hand, In2O3 sites can adsorb nitrogen sources, thereby reducing the distance between reaction intermediates at the microscale and significantly promoting the formation of CN bonds. Therefore, developing a structurally stable indium-based oxide heterojunction material with dual-site synergistic effects is of great significance for achieving efficient electrosynthesis of urea. Summary of the Invention

[0005] To address the shortcomings of existing catalytic systems in electrocatalytic urea synthesis, such as difficulties in CN coupling, low yields, and severe side reactions, this invention provides an indium-based oxide heterojunction material and its application in electrocatalytic CN coupling. The aim is to construct an indium-based oxide heterojunction structure through a solvothermal process combined with high-temperature calcination, enabling the catalyst to possess dual active centers for the specific adsorption of carbon and nitrogen sources, thereby effectively reducing the energy barrier and achieving highly active and selective urea electrosynthesis.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: This invention first discloses a method for preparing indium-based oxide heterojunction materials for electrocatalytic CN coupling, characterized by: firstly, mixing indium salt and niobium salt to prepare an indium-based oxide heterojunction precursor using a solvothermal method, and then obtaining the indium-based oxide heterojunction material through high-temperature calcination. Specifically, the method includes the following steps: Step 1: Weigh 1-3 mmol of indium salt, 0.5-2 mmol of niobium salt, and 4-6 mmol of hexamethylenetetramine, dissolve them in a mixed solvent of 50-100 mL of water and 1-methyl-2-pyrrolidone, and carry out a solvothermal reaction at 150-250 °C for 10-30 h. After the reaction is completed, centrifuge, wash, and dry the product to collect the powder product and obtain the indium-based oxide heterojunction precursor. Step 2: Place the indium-based oxide precursor in a tube furnace and calcine it at high temperature under argon protection. The calcine temperature is 600~900℃, the holding time is 60~300 min, and the heating rate is 0.5~10℃ / min. After calcine, allow it to cool naturally to room temperature to obtain the indium-based oxide heterojunction material.

[0007] Furthermore, the indium salt is In(NO3)3, InCl3, or In2(SO4)3, and the niobium salt is NbCl5 or niobium oxalate.

[0008] Further, in step 1, the volume ratio of water to 1-methyl-2-pyrrolidone in the mixed solvent is 1~3:1.

[0009] The indium-based oxide heterojunction material prepared in this invention is composed of two phases, In₂O₃ and InNbO₄, forming an atomically close heterojunction interface. This interface can construct a built-in electric field to promote electron transfer. By controlling the molar ratio of indium salt to niobium salt within the range of 1 to 3:1, the content ratio of the In₂O₃ phase to the InNbO₄ phase can be precisely controlled, thereby optimizing the ratio of dual active sites.

[0010] This invention also discloses the application of the prepared indium-based oxide heterojunction material in the electrocatalytic CN-CN coupling to produce urea. Specifically, the indium-based oxide heterojunction material is used as the working electrode catalyst in an electrolyte system containing carbon dioxide and nitrate, where a coupling reaction between a carbon dioxide reduction intermediate and a nitrate reduction intermediate is catalyzed under applied voltage to generate urea. In the indium-based oxide heterojunction material: niobium exists in the +5 oxidation state, forming Lewis acidic active sites for specifically activating CO2 and stabilizing carbon-containing intermediates; indium forms specific adsorption sites for nitrogen-containing species through special orbital hybridization, for directional anchoring of NO3. - The dual active sites work synergistically to suppress hydrogen evolution side reactions and lower the CN coupling energy barrier, thus achieving highly selective and high-yield synthesis of urea.

[0011] Further, a specific application method can be as follows: the indium-based oxide heterojunction material is dispersed in a mixture of ethanol, water, and naphthol solution to prepare a slurry; the slurry is then sprayed onto carbon paper to obtain the indium-based oxide heterojunction catalyst. In an H-type electrolytic cell or a flow electrolytic cell system, using the catalyst as the cathode, a platinum sheet as the anode, and Ag / AgCl as the reference electrode, a CO2 saturated solution containing nitrates (such as potassium nitrate) is used as the electrolyte, and a certain potential is applied to carry out the reaction, thereby achieving CN-coupling to prepare urea.

[0012] Compared with the prior art, the beneficial effects of the present invention are reflected in: 1. This invention presents an indium-based oxide heterojunction material for electrocatalytic CN coupling prepared by a two-step process combining solvothermal treatment and high-temperature calcination. The process is simple and reproducible. High-temperature phase separation successfully constructed a heterojunction interface with close contact between In₂O₃ and InNbO₄, exhibiting high structural stability.

[0013] 2. The material obtained by this invention integrates the advantages of two metal oxides: the niobate phase fully utilizes the strong Lewis acid sites of Nb to effectively activate CO2 and stabilize carbon-containing intermediates; the indium oxide phase utilizes the specific adsorption of In sites to stabilize NO3. - And its reduction products. This two-site mechanism effectively inhibits HER side reactions and significantly increases local reactant concentrations.

[0014] 3. The material described in this invention utilizes the built-in electric field at the heterojunction interface to promote electron transfer and lower the thermodynamic energy barrier of the CN coupling step. Under optimal conditions, this material exhibits excellent performance in the electrocatalytic co-reduction of CO2 and nitrate, with a urea yield significantly higher than that of single-component indium oxide or indium niobate, and also demonstrates good long-term operational stability.

[0015] 4. The preparation method of the indium-based oxide heterojunction material of the present invention is simple, the reaction conditions are controllable and easy to scale up, and the catalyst obtained has both high efficiency and stability, making it suitable for large-scale electrocatalytic urea synthesis and showing good industrial application prospects. Attached Figure Description

[0016] Figure 1 This is a TEM image of the InNbO4 material obtained in Example 1.

[0017] Figure 2 This is the XRD pattern of the InNbO4 material obtained in Example 1.

[0018] Figure 3 This is a TEM image of the indium-based oxide heterojunction material obtained in Example 2.

[0019] Figure 4 This is the XRD pattern of the indium-based oxide heterojunction material obtained in Example 2.

[0020] Figure 5 This is a TEM image of the indium-based oxide heterojunction material obtained in Example 3.

[0021] Figure 6 This is the XRD pattern of the indium-based oxide heterojunction material obtained in Example 3.

[0022] Figure 7 This is a TEM image of the In2O3 material obtained in Example 4.

[0023] Figure 8 This is the XRD pattern of the In2O3 material obtained in Example 4.

[0024] Figure 9 This is a Faraday efficiency diagram of the electrocatalytic CN coupling of the materials obtained in Examples 1-4.

[0025] Figure 10 This is a diagram showing the urea yield of the materials obtained in Examples 1-4 via electrocatalytic CN coupling. Detailed Implementation

[0026] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to examples. The following content is merely an example and illustration of the concept of the present invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, as long as they do not depart from the inventive concept or exceed the scope defined by the claims, all of which should fall within the protection scope of the present invention.

[0027] Example 1 In this embodiment, pure-phase InNbO4 material was prepared according to the following steps: Step 1: Add 1.8 mmol of In(NO3)3 and 1.8 mmol of NbCl5 to 22.5 mL of 1-methyl-2-pyrrolidone solvent and stir until homogeneous to form suspension a. Add 5 mmol of hexamethylenetetramine to 50 mL of deionized water and stir until completely dissolved to obtain solution b. Quickly pour solution b into suspension a, stir until homogeneous, and transfer to a Teflon-lined stainless steel reactor. Seal the reactor and allow it to stand at 200°C for 12 hours. After the reaction is complete, allow the reaction solution to cool naturally at room temperature. The resulting precipitate is separated by centrifugation, washed three times successively with deionized water and ethanol, and dried overnight at 60°C to obtain the precursor powder.

[0028] Step 2: Place the precursor powder in a tube furnace and heat it to 700°C at a rate of 5°C / min under an argon atmosphere. Hold the temperature for 2 hours and then cool it to room temperature to obtain the pure phase of InNbO4.

[0029] Figure 1 The TEM image of InNbO4 obtained in this embodiment shows that the material is a flower-like aggregated nanostructure with a size of 200-300 nm. Figure 2 The image shows the XRD pattern of InNbO4 obtained in this embodiment. After the precursor was calcined at high temperature, a pure phase of InNbO4 with high crystallinity was obtained.

[0030] Example 2 In this embodiment, indium-based oxide heterojunction materials are prepared according to the following steps: Step 1: Add 2.4 mmol of In(NO3)3 and 1.2 mmol of NbCl5 to 22.5 mL of 1-methyl-2-pyrrolidone solvent and stir until homogeneous to form suspension a. Add 5 mmol of hexamethylenetetramine to 50 mL of deionized water and stir until completely dissolved to obtain solution b. Quickly pour solution b into suspension a, stir until homogeneous, and transfer to a Teflon-lined stainless steel reactor. After sealing, allow the reaction to stand at 200°C for 12 hours. After the reaction is complete, allow the reaction solution to cool naturally at room temperature. The resulting precipitate is separated by centrifugation, washed three times successively with deionized water and ethanol, and dried overnight at 60°C to obtain the precursor powder.

[0031] Step 2: Place the precursor powder in a tube furnace, heat it to 700°C at a rate of 5°C / min under an argon atmosphere, hold it at that temperature for 2 hours, and then cool it to room temperature to obtain an indium-based oxide heterojunction material.

[0032] Figure 3 The image shows a TEM image of the indium oxide heterojunction material obtained in this embodiment. It can be seen that the material is a flower-like aggregated nanostructure with a size of 200-300 nm. Figure 4The image shows the XRD pattern of the indium-based oxide heterojunction material obtained in this embodiment. After high-temperature calcination, the precursor yielded a mixed phase of In2O3 and InNbO4 with high crystallinity.

[0033] Example 3 In this embodiment, indium-based oxide heterojunction materials are prepared according to the following steps: Step 1: Add 2.7 mmol of In(NO3)3 and 0.9 mmol of NbCl5 to 22.5 mL of 1-methyl-2-pyrrolidone solvent and stir until homogeneous to form suspension a. Add 5 mmol of hexamethylenetetramine to 50 mL of deionized water and stir until completely dissolved to obtain solution b. Quickly pour solution b into suspension a, stir until homogeneous, and transfer to a Teflon-lined stainless steel reactor. Seal the reactor and allow it to stand at 200°C for 12 hours. After the reaction is complete, allow the reaction solution to cool naturally at room temperature. The resulting precipitate is separated by centrifugation, washed three times successively with deionized water and ethanol, and dried overnight at 60°C to obtain the precursor powder.

[0034] Step 2: Place the precursor powder in a tube furnace, heat it to 700°C at a rate of 5°C / min under an argon atmosphere, hold it at that temperature for 2 hours, and then cool it to room temperature to obtain an indium-based oxide heterojunction material.

[0035] Figure 5 The image shows a TEM image of the indium oxide heterojunction material obtained in this embodiment. It can be seen that the material is a flower-like aggregated nanostructure with a size of 200-300 nm. Figure 6 The image shows the XRD pattern of the indium-based oxide heterojunction material obtained in this embodiment. After high-temperature calcination, the precursor yielded a mixed phase of In2O3 and InNbO4 with high crystallinity.

[0036] Example 4 In this embodiment, In2O3 material is prepared according to the following steps: Step 1: Add 3.6 mmol of In(NO3)3 to 22.5 mL of 1-methyl-2-pyrrolidone solvent and stir until homogeneous to form suspension a. Add 5 mmol of hexamethylenetetramine to 50 mL of deionized water and stir until completely dissolved to obtain solution b. Quickly pour solution b into suspension a, stir until homogeneous, and transfer to a Teflon-lined stainless steel reactor. Seal the reactor and allow it to stand at 200°C for 12 hours. After the reaction is complete, allow the reaction solution to cool naturally at room temperature. The resulting precipitate is separated by centrifugation, washed three times successively with deionized water and ethanol, and dried overnight at 60°C to obtain the precursor powder.

[0037] Step 2: Place the precursor powder in a tube furnace, heat it to 700°C at a rate of 5°C / min under an argon atmosphere, hold it at that temperature for 2 hours, and then cool it to room temperature to obtain In2O3 material.

[0038] Figure 7 The image shows a TEM image of the In2O3 material obtained in this embodiment. It can be seen that the material consists of irregular nanoparticles with a size of 100-200 nm. Figure 8 The image shows the XRD pattern of the In2O3 material obtained in this embodiment. After the precursor was calcined at high temperature, a highly crystalline In2O3 phase was obtained.

[0039] The electrocatalytic CN-coupling performance of the indium oxide heterojunction materials prepared in the above embodiments was tested in an H-cell: The materials obtained in each embodiment were dispersed in a mixture of ethanol, water, and 5 wt% naphthol solution (volume ratio 4:1:0.005), and ultrasonically formed into a uniform slurry. The slurry was then sprayed onto carbon paper to prepare the catalyst. In the H-cell, the catalyst was used as the cathode, Ag / AgCl as the reference electrode, and a CO2 saturated solution containing 0.1 mol / L KNO3 as the cathode electrolyte. Different cathode potentials were applied to carry out the reaction. The electrolyte after the reaction was collected, and the urea concentration was determined by UV-Vis spectrophotometry. The Faraday efficiency and yield diagrams of the electrocatalytic CN-coupling of the materials obtained in Examples 1-4 are shown below. Figure 9 and Figure 10 As shown in the figure, Example 2 achieved the highest urea yield at the optimal potential, and its Faraday efficiency was significantly better than that of Example 3, far exceeding that of the pure phase material. This demonstrates that by constructing a dual-site synergistic mechanism of Nb-activated carbon source and In-anchored nitrogen source, the performance of electrocatalytic CN-coupled urea production can be significantly improved.

[0040] The above description is merely an example and illustration of the concept of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the concept of the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. An indium-based oxide heterojunction material for electrocatalytic CN coupling, characterized in that: The indium-based oxide heterojunction material is composed of two phases, In2O3 and InNbO4, with an atomically close heterojunction interface between the two phases.

2. A method for preparing the indium-based oxide heterojunction material according to claim 1, characterized in that: First, indium salt and niobium salt are mixed and an indium-based oxide heterojunction precursor is prepared by a solvothermal method. Then, the indium-based oxide heterojunction material is obtained by high-temperature calcination.

3. The preparation method according to claim 2, characterized in that, Includes the following steps: Step 1: Weigh 1-3 mmol of indium salt, 0.5-2 mmol of niobium salt, and 4-6 mmol of hexamethylenetetramine, dissolve them in a mixed solvent of 50-100 mL of water and 1-methyl-2-pyrrolidone, and carry out a solvothermal reaction at 150-250 °C for 10-30 h. After the reaction is completed, centrifuge, wash, and dry the product to collect the powder product and obtain the indium-based oxide heterojunction precursor. Step 2: Place the indium-based oxide precursor in a tube furnace and calcine it at high temperature under argon protection. The calcine temperature is 600~900℃, the holding time is 60~300 min, and the heating rate is 0.5~10℃ / min. After calcine, allow it to cool naturally to room temperature to obtain the indium-based oxide heterojunction material.

4. The preparation method according to claim 3, characterized in that: The indium salt is In(NO3)3, InCl3, or In2(SO4)3.

5. The preparation method according to claim 3, characterized in that: The niobium salt is NbCl5 or niobium oxalate.

6. The preparation method according to claim 3, characterized in that: The volume ratio of water to 1-methyl-2-pyrrolidone in the mixed solvent described in step 1 is 1~3:

1.

7. The application of the indium-based oxide heterojunction material according to claim 1 or the indium-based oxide heterojunction material prepared by any one of claims 2 to 6 in electrocatalytic CN coupling.

8. The application according to claim 7, characterized in that: The application is the electrocatalytic co-reduction of carbon dioxide and nitrate to synthesize urea, using the indium-based oxide heterojunction material as the working electrode catalyst.

9. The application according to claim 7 or 8, characterized in that, In the indium-based oxide heterojunction material: niobium exists in the +5 valence state, forming Lewis acidic active sites for specifically activating CO2 and stabilizing carbon-containing intermediates; indium forms specific adsorption sites for nitrogen-containing species through special orbital hybridization, for directional anchoring of NO3. - and its reduction products; The synergistic effect of dual active sites inhibits the hydrogen evolution side reaction and lowers the CN coupling energy barrier, thereby enabling urea synthesis.

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