Preparation method of chlorine-coordinated phosphomolybdic polyacid-based two-dimensional copper complex and application of chlorine-coordinated phosphomolybdic polyacid-based two-dimensional copper complex in electro-catalytic ammonia preparation

Abstract

The invention relates to a preparation method of a chlorine-coordinated phosphomolybdic polyacid-based two-dimensional copper complex and application of the chlorine-coordinated phosphomolybdic polyacid-based two-dimensional copper complex in electro-catalysis ammonia production. The complex has a clear chemical formula {[Cu (C10H8N6) 3O] Cl [Cu (H2O) 7] (PMo12Cl2O40)]}, marked as Cu-PMo12Cl2-C10, and the core of the complex is that a stable two-dimensional layered structure is constructed and formed through bridging of copper ions with an organic ligand 1, 4-di (4H-1, 2, 4-triazole-4-yl) benzene (with a molecular formula of C10H8N6), and the complex has the advantages of high stability, high selectivity, high selectivity and high selectivity. Therefore, the technical problems of poor stability and limited catalytic activity of the traditional polyacid-based metal-organic complex in electro-catalysis application are solved. The preparation method comprises the following steps: by taking copper chloride, phosphomolybdic acid, ammonium metavanadate and the organic ligand as raw materials, carrying out hydrothermal reaction and one-step synthesis. The material is used for electrocatalytic reduction of nitrate radicals, and the maximum ammonia production rate of 18.79 mg h <-1 > mg cat <-1 > and the Faraday efficiency of 80.8% are achieved in a neutral electrolyte of 0.1 M of KNO3 and 0.1 M of K2SO4 under the voltage of-1.1 V vs.RHE. The process is simple, and a high-performance electrocatalyst is provided for ammonia production through nitrate radical reduction.

Description

Technical Field

[0001] This invention relates to the field of catalyst materials for electrocatalytic nitrate reduction to ammonia synthesis, specifically to a method for preparing a chlorine-coordinated phosphomolybdate polyacid-based two-dimensional copper complex and its application in electrocatalytic ammonia production, belonging to the interdisciplinary field of functional inorganic-organic hybrid materials and electrocatalytic energy conversion. Background Technology

[0002] Since the early 20th century, the Haber-Bosch process has been the dominant technology for industrial ammonia synthesis. This process enables large-scale and stable production of ammonia, but it requires operation under high temperature and pressure conditions (typically 300-500℃, 150-300 atm), resulting in extremely high energy consumption per unit of ammonia production. Furthermore, the production of 1 ton of ammonia is accompanied by approximately 1.8 tons of carbon dioxide emissions, severely exacerbating the energy crisis and environmental pressure.

[0003] Electrocatalytic reduction of nitrate to ammonia (e-NO3RR), as an electrochemical process that can be carried out at ambient temperature and pressure, has advantages such as mild reaction conditions, high energy efficiency, and good environmental compatibility, and is considered a promising green synthesis route to replace the traditional Haber-Bosch process. However, existing e-NO3RR systems still face several key challenges in practical applications, such as insufficient catalytic activity, high energy barriers for nitrate adsorption and activation; limited selectivity for ammonia formation, with easy occurrence of side reactions producing nitrogen gas, nitrite, and other products; and poor catalyst stability, with active sites easily agglomerating and leaching, leading to excessively rapid decline in the ammonia production rate, which seriously restricts its industrial application.

[0004] The structure and composition of electrocatalysts are core factors determining the efficiency of the e-NO3RR reaction. Developing catalytic materials with high activity, high selectivity, high stability, and low cost has become a research hotspot in this field. Polyoxometalates (POMs) are a class of polynuclear metal-oxygen cluster compounds based on high oxidation-state transition metals such as tungsten, molybdenum, and vanadium. These compounds possess both reversible redox properties and highly tunable composition and structure, exhibiting excellent functional diversity. Therefore, they show broad application prospects in many cutting-edge fields such as catalytic chemistry, energy conversion technology, functional materials development, and biomedicine. Among them, Keggin-type polyoxometalates [PMo]... 12 O 40 ] 3- (abbreviated as {PMo) 12 The structure consists of a central PO4 tetrahedron and twelve MoO6 octahedra tightly connected by shared oxygen atoms, forming a highly symmetrical cage-like structure. Its high electron density and tunable redox potential make it an ideal building block for constructing functional hybrid materials.

[0005] In existing technologies, polyacid-based catalytic materials are mostly prepared through simple composite metal ions or organic ligands, which suffers from poor structural order, insufficient exposure of active sites, and unsatisfactory stability. Especially in the area of ​​polyacid molecular modification, research on halogen atom coordination modification is limited, and no studies have been found on the coordination modification of {PMo} via chlorine atoms and molybdenum sites. 12 Reports have documented the construction of two-dimensional ordered structures from polyacids in synergy with copper ions and organic ligands. Two-dimensional structures maximize the exposure of active sites and accelerate electron transport. Chlorine coordination modification can regulate the electronic structure and catalytic activity of polyacids, while the introduction of copper ions and specific organic ligands can stabilize the structure and optimize reaction selectivity. The synergistic effect of these three factors is expected to overcome the performance bottlenecks of existing polyacid-based catalysts. Based on this, this invention designs and prepares chlorine-coordinated phosphomolybdate polyacid-based two-dimensional copper-organic complexes, providing a new strategy for the development of highly efficient e-NO3RR catalysts. Summary of the Invention

[0006] I. Purpose of the Invention

[0007] To address the shortcomings of existing polyacid-based electrocatalysts in the electrocatalytic reduction of nitrate to ammonia, such as insufficient activity, limited selectivity, and poor stability, as well as the low accuracy of structural control in existing polyacid modification methods, this invention provides a method for preparing chlorine-coordinated phosphomolybdic polyacid-based two-dimensional copper complexes and their applications. This invention utilizes the coordination modification of chlorine atoms with the molybdenum sites in phosphomolybdic dodecanoic acid, combined with the interaction of copper ions with 1,4-bis(4H-1,2,4-triazol-4-yl)benzene (abbreviated as C...). 10 The synergistic assembly of H8N6 organic ligands constructs a two-dimensional ordered hybrid structure, which significantly improves the electrocatalytic activity, ammonia selectivity and cycle stability of the catalyst, and realizes efficient electrocatalytic reduction of nitrate to ammonia at room temperature and pressure.

[0008] II. Technical Solution

[0009] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0010] 1. Raw material mixing and pH adjustment: Weigh copper chloride, phosphomolybdic acid, ammonium metavanadate, and C. 10 Place H8N6 in a beaker, add deionized water, and stir magnetically until a uniform suspension is formed. Adjust the pH of the suspension to 1.0~2.5.

[0011] The molar ratio of copper chloride and phosphomolybdic acid in step 1 is 6:1;

[0012] The copper chloride and C mentioned in step 1 10 The molar ratio of H8N6 is 4:1;

[0013] The mass ratio of copper chloride to water in step 1 is 1 mmol: 5~10 mL;

[0014] The pH adjustment of the suspension to 1.0-2.5 described in step 1 is achieved using a 1 mol / L hydrochloric acid solution and a 1 mol / L sodium hydroxide solution.

[0015] 2. Preparation of the target complex: The reaction solution prepared in step 1 with pH adjusted to 1.0~2.5 was transferred to a 25mL polytetrafluoroethylene reaction vessel and reacted at a constant temperature of 160~180℃ for 3~5 days. After the reaction was completed, the mixture was naturally cooled to room temperature and washed with deionized water and anhydrous ethanol 3~4 times each (20~25mL each time, ultrasonic-assisted washing for 5~8 minutes). After filtration, the mixture was vacuum dried at 50~60℃ for 4~6 hours to obtain black crystals, which is a chlorinated phosphomolybdic polyacid-based two-dimensional copper complex.

[0016] The chemical formula of the chlorine-coordinated phosphomolybdate polyacid-based two-dimensional copper complex described in step 2 is {[Cu(C 10 H8N6)3O]Cl[Cu(H2O)7](PMo 12 Cl2O 40 (abbreviated as Cu-PMo) 12 Cl2-C 10 ), where C 10 H8N6 is 1,4-bis(4H-1,2,4-triazol-4-yl)benzene; its crystal system is triclinic, and its space group is P. The unit cell parameters are a = 10.6479(6) Å, b = 16.8386(10) Å, c = 19.8642(10) Å, α = 89.844(2)°, β = 77.806(2)°, γ = 79.315(2)°, and V = 3418.4(3) Å. 3 .

[0017] 3. Preparation of the working electrode: Cu-PMo 12 Cl2-C 10 Place acetylene black and carbon black in an agate mortar at a mass ratio of 1:1 and grind for 15-20 minutes until uniform and fine. Take 3 mg of the mixture and add it to an aqueous solution containing isopropanol and Nafion. Disperse the mixture by ultrasonication to form a uniform slurry. Take 50 μL of the slurry and evenly drop it onto the surface of the activated carbon cloth. Let it stand and dry to obtain a loaded working electrode.

[0018] The mixture mentioned in step 3 is Cu-PMo 12 Cl2-C 10 3mg and acetylene black 3mg;

[0019] The ingredients in step 3 are 1.25 mL of isopropanol, 10 μL of 5% Nafion, and 3.65 mL of water.

[0020] In step 3, the ultrasonic power is 180-200W, the ultrasonic frequency is 40kHz, the ultrasonic time is 2h, and the settling time is 8h.

[0021] The advantages and effects of this invention are as follows:

[0022] I. This invention employs a simple hydrothermal reaction, and for the first time utilizes copper chloride, phosphomolybdic acid, ammonium metavanadate, and C. 10 Using H8N6 as a raw material, chlorine-coordinated {PMo} was prepared. 12 Cl2} polyacid-based two-dimensional copper complex; single-crystal X-ray diffraction results confirmed that the complex prepared in this invention consists of {PMo} 12 Cl2} polyacid anions, copper ions and C 10 H8N6 is constructed through coordination, with two copper ions bridging the Cl atom and the N ligand, forming a complex via C. 10 The triazole group in H8N6, along with the interaction of copper-oxygen hydrogen bonds and electrostatic forces, enables the chlorine-coordinated phosphomolybdic acid-based two-dimensional copper complex to form a stable two-dimensional structure.

[0023] II. The chloro-coordinated phosphomolybdic acid-based two-dimensional copper complex prepared in this embodiment exhibits a Faradaic efficiency of 80.8% and an ammonia production rate of 18.79 mg / h during the electrocatalytic reduction of nitrate to ammonia in a 0.1 M KNO3 + 0.1 M K2SO4 electrolyte at a potential of -1.1 V vs. RHE. –1 mg cat. –1 The performance advantage stems from structural synergy: {PMo 12 The Cl2} motif and two-dimensional layered structure provide high-density active sites, accelerating electron transport; organic ligand C 10 The rigid benzene ring and triazole group of H8N6 stabilize the two-dimensional framework, effectively inhibiting the deactivation of copper active centers during the reaction, significantly improving the cycle stability of the material, and breaking through the bottleneck of activity and stability of traditional catalysts. Attached Figure Description

[0024] Figure 1 is a basic unit structure diagram of a chlorine-coordinated phosphomolybdic acid-based two-dimensional copper complex prepared according to Embodiment 1 of the present invention.

[0025] Figure 2 is a schematic diagram of the stacking arrangement of a chlorine-coordinated phosphomolybdic acid-based two-dimensional copper complex prepared according to Embodiment 1 of the present invention, observed along axes a, b, and c.

[0026] Figure 3 is an infrared spectrum of a chlorine-coordinated phosphomolybdic acid-based two-dimensional copper complex prepared according to Embodiment 1 of the present invention.

[0027] Figure 4 shows the UV-Vis absorption spectra of a chlorine-coordinated phosphomolybdic acid-based two-dimensional copper complex prepared in Embodiment 1 of the present invention after electrocatalytic reaction at different voltages in a 0.1 mol / L KNO3 + 0.1 mol / L K2SO4 solution.

[0028] Figure 5 shows a chlorine-coordinated phosphomolybdic acid-based two-dimensional copper complex prepared in Embodiment 1 of the present invention, with or without NO3. - Linear sweep voltammetry (LSV) curves in electrolyte.

[0029] Figure 6 shows the ammonia production and Faraday efficiency of a chlorine-coordinated phosphomolybdic acid-based two-dimensional copper complex prepared in Embodiment 1 of the present invention at different voltages in a 0.1 mol / L KNO3 + 0.1 mol / L K2SO4 solution. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to implementation, comparative cases, and accompanying drawings, but the embodiments of the present invention are not limited thereto. Any modifications or equivalent substitutions to the technical solutions of the present invention that do not depart from the spirit and scope of the technical solutions of the present invention should be covered within the protection scope of the present invention.

[0031] Specific Implementation Method 1: This implementation method describes a method for preparing a chlorine-coordinated phosphomolybdic polyacid-based two-dimensional copper complex and its electrocatalytic application in ammonia production. The molecular formula of the complex is {[Cu(C]} 10 H8N6)3O]Cl[Cu(H2O)7](PMo 12 Cl2O 40 (abbreviated as Cu-PMo) 12 Cl2-C 10 Its basic structural unit contains two copper ions, three 1,4-bis(4H-1,2,4-triazol-4-yl)benzene organic ligands, and one {PMo 12 Cl2} type polyacid anion and seven water molecules. Cu in the complex provides the same chemical environment, and Cu binds the organic ligand C. 10 In H8N6, the N atom is bonded to the Cl atom, forming a two-dimensional organometallic complex with phosphomolybdic acid as the matrix.

[0032] Specific Implementation Method 2: The preparation method of a chlorine-coordinated phosphomolybdic acid-based two-dimensional copper complex of this embodiment is completed according to the following steps.

[0033] 1. Raw material mixing and pH adjustment: Weigh copper chloride, phosphomolybdic acid, ammonium metavanadate, and C. 10 Place H8N6 in a beaker, add deionized water, and stir magnetically until a uniform suspension is formed. Adjust the pH of the suspension to 1.0~2.5.

[0034] The molar ratio of copper chloride and phosphomolybdic acid in step 1 is 6:1;

[0035] The copper chloride and C mentioned in step 1 10 The molar ratio of H8N6 is 4:1;

[0036] The mass ratio of copper chloride to water in step 1 is 1 mmol: 5~10 mL;

[0037] The pH adjustment of the suspension to 1.0-2.5 described in step 1 is achieved using a 1 mol / L hydrochloric acid solution and a 1 mol / L sodium hydroxide solution.

[0038] 2. Preparation of the target complex: The reaction solution prepared in step 1 with pH adjusted to 1.0~2.5 was transferred to a 25mL polytetrafluoroethylene reaction vessel and reacted at a constant temperature of 160~180℃ for 3~5 days. After the reaction was completed, the mixture was naturally cooled to room temperature and washed with deionized water and anhydrous ethanol 3~4 times each (20~25mL each time, ultrasonic-assisted washing for 5~8 minutes). After filtration, the mixture was vacuum dried at 50~60℃ for 4~6 hours to obtain black crystals, which is a chlorinated phosphomolybdic polyacid-based two-dimensional copper complex.

[0039] The chemical formula of the chlorine-coordinated phosphomolybdate polyacid-based two-dimensional copper complex described in step 2 is {[Cu(C 10 H8N6)3O]Cl[Cu(H2O)7](PMo 12 Cl2O 40 (abbreviated as Cu-PMo) 12 Cl2-C 10 ), where C 10 H8N6 is 1,4-bis(4H-1,2,4-triazol-4-yl)benzene; its crystal system is triclinic, and its space group is P. The unit cell parameters are a = 10.6479(6) Å, b = 16.8386(10) Å, c = 19.8642(10) Å, α = 89.844(2)°, β = 77.806(2)°, γ = 79.315(2)°, and V = 3418.4(3) Å. 3 .

[0040] 3. Preparation of the working electrode: Cu-PMo 12 Cl2-C 10Place acetylene black and carbon black in an agate mortar at a mass ratio of 1:1 and grind for 15-20 minutes until uniform and fine. Take 3 mg of the mixture and add it to an aqueous solution containing isopropanol and Nafion. Disperse the mixture by ultrasonication to form a uniform slurry. Take 50 μL of the slurry and evenly drop it onto the surface of the activated carbon cloth. Let it stand and dry to obtain a loaded working electrode.

[0041] The mixture mentioned in step 3 is Cu-PMo 12 Cl2-C 10 3mg and acetylene black 3mg;

[0042] The ingredients in step 3 are 1.25 mL of isopropanol, 10 μL of 5% Nafion, and 3.65 mL of water.

[0043] In step 3, the ultrasonic power is 180-200W, the ultrasonic frequency is 40kHz, the ultrasonic time is 2h, and the settling time is 8h.

[0044] The structure of a chlorine-coordinated phosphomolybdic acid-based two-dimensional copper complex prepared in Example 2 was determined:

[0045] Conclusion ① X-ray crystallographic parameters: see Table 1

[0046] Table 1. Crystallographic parameters of materials

[0047]

[0048]

[0049] a R1 = ∑║F o │─│F c ║ / ∑│F o │. b wR2= {∑[w(F o 2 —F c 2 ) 2 ] / ∑[w(F o 2 ) 2 ]} 1 / 2

[0050] The chemical formula of a chlorine-coordinated phosphomolybdic acid-based two-dimensional copper complex is {[Cu(C 10 H8N6)3O]Cl[Cu(H2O)7](PMo 12 Cl2O 40 (abbreviated as Cu-PMo) 12 Cl2-C 10 ), where C 10H8N6 is 1,4-bis(4H-1,2,4-triazol-4-yl)benzene; its crystal system is triclinic, and its space group is P. The unit cell parameters are a = 10.6479(6) Å, b = 16.8386(10) Å, c = 19.8642(10) Å, α = 89.844(2)°, β = 77.806(2)°, γ = 79.315(2)°, and V = 3418.4(3) Å. 3 .

[0051] The invention will be further described below with reference to the accompanying drawings:

[0052] Figure 1 is a schematic diagram of the structure of a chlorine-coordinated phosphomolybdic acid-based two-dimensional copper complex prepared according to Embodiment 2 of the present invention, which is a schematic diagram of the basic structural unit.

[0053] Figure 2 shows the packing arrangement of a chlorine-coordinated phosphomolybdic acid-based two-dimensional copper complex prepared according to Embodiment 2 of the present invention, observed along axes a, b, and c, visually presenting the spatial packing characteristics of the two-dimensional structure.

[0054] Figure 3 shows the infrared spectrum of a chlorine-coordinated phosphomolybdic acid-based two-dimensional copper complex prepared according to Embodiment 2 of the present invention. Figure 3 As shown, the infrared spectrum is at 1639 cm⁻¹ -1 1258 cm -1 1113 cm -1 1056 cm -1 1012 cm -1 922cm -1 640cm -1 The spectral bands were assigned to {PMo} in the complex. 12 The characteristic peak of Cl2 stretching vibration; the vibration peak is at 1000 cm⁻¹. -1 ~1600cm -1 The presence of organic ligands within the range confirms the successful synthesis of the complex.

[0055] Figure 4 shows the UV-Vis absorption spectra of a chlorinated phosphomolybdic acid-based two-dimensional copper complex prepared in Embodiment 2 of the present invention at different voltages in a neutral electrolyte of 0.1 mol / L K₂SO₄ + 0.1 mol / L KNO₃. Using a three-electrode system, time-current curves (it) were measured at different voltages in the neutral electrolyte. After one hour of measurement, 10 mL of electrolyte from the cathode electrolytic cell was collected, and then colorimetric analysis was performed. The UV-Vis absorption spectra were obtained using a UV spectrophotometer. Figure 4 It can be seen that as the applied voltage increases, the absorbance of the electrolyte that underwent color development after electrocatalysis also gradually increases in the absorbance test.

[0056] Figure 5 shows the chlorine-coordinated phosphomolybdic acid-based two-dimensional copper complex prepared in Embodiment 1 of the present invention, with or without NO3. - Linear sweep voltammetry (LSV) curves in the electrolyte. As shown in the figure, within the voltage range of -0.8 V to -1.2 V vs. RHE, the reduction current density of the chloro-coordinated phosphomolybdic acid-based two-dimensional copper complex in the electrolyte containing nitrate ions is significantly higher than that in the electrolyte without nitrate ions, indicating the electrocatalytic reduction ability of the chloro-coordinated phosphomolybdic acid-based two-dimensional copper complex for nitrate reduction.

[0057] Figure 6 shows the ammonia yield and Faraday efficiency at different voltages in the nitrate reduction to ammonia synthesis reaction of a chlorine-coordinated phosphomolybdic acid polyacid-based two-dimensional copper complex prepared in Embodiment 2 of the present invention, in a 0.1 mol / L K₂SO₄ + 0.1 mol / L KNO₃ solution. Figure 6 It can be seen that at a potential of -1.1 V vs. RHE, the optimal Faraday efficiency is 80.8%, corresponding to an ammonia production of 18.79 mg h⁻¹. –1 mg cat. –1 Therefore, chlorine-coordinated phosphomolybdate polyacid-based two-dimensional copper complexes can serve as highly efficient electrocatalysts for the reduction of nitrates to ammonia.

[0058] In summary: Regarding the two-dimensional copper complex {[Cu(C]} of chlorine-coordinated phosphomolybdic acid group in Implementation Case 2... 10 H8N6)3O]Cl[Cu(H2O)7](PMo 12 Cl2O 40 (abbreviated as Cu-PMo) 12 Cl2-C 10 This invention successfully prepared phosphomolybdic acid (PMo) using a simple hydrothermal synthesis method and successfully applied it to the electrocatalytic reduction of nitrates to synthesize ammonia. 12 Cl2} is used as the basic unit, and catalytically active metal element Cu and organic ligand C are introduced. 10 H8N6 was used to improve electrocatalytic selectivity and stability, resulting in a chlorine-coordinated phosphomolybdate polyacid-based two-dimensional copper complex electrocatalyst. With its excellent redox activity, high conductivity, and stable structure, this material shows promising application prospects in the electrocatalytic reduction of nitrates to ammonia.

Claims

1. A chlorinated phosphomolybdic polyacid-based two-dimensional copper complex, characterized in that, Its chemical formula is {[Cu(C)} 10 H8N6)3O]Cl[Cu(H2O)7](PMo 12 Cl2O 40 )]}, where C 10 H8N6 is 1,4-bis(4H-1,2,4-triazol-4-yl)benzene; the complex has a two-dimensional layered structure formed by the bridging of the dichlorinated phosphomolybdic polyacid anion and copper ions by the organic ligand.

2. The chlorine-coordinated phosphomolybdate polyacid-based two-dimensional copper complex according to claim 1, characterized in that, It belongs to the triclinic crystal system and has the space group P. The unit cell parameters are a = 10.6479(6) Å, b = 16.8386(10) Å, c = 19.8642(10) Å, α = 89.844(2)°, β = 77.806(2)°, γ = 79.315(2)°, and V = 3418.4(3) Å. 3 .

3. A method for preparing the chloro-coordinated phosphomolybdic acid-based two-dimensional copper complex as described in claim 1 or 2, characterized in that, This method is a hydrothermal method, which includes the following steps: Copper chloride, phosphomolybdic acid, ammonium metavanadate, and organic ligand C 10 Dissolve H8N6 in water, stir well, and adjust the pH of the mixture to 1.0-2.5; The resulting reaction mixture was placed in a sealed reactor and crystallized at 160-180℃ for 3-5 days. After the reaction was completed, the chlorine-coordinated phosphomolybdic polyacid-based two-dimensional copper complex was obtained by cooling, washing and drying.

4. The method according to claim 3, characterized in that, The molar ratio of copper chloride to phosphomolybdic acid is 6:

1.

5. The method according to claim 3, characterized in that, The molar ratio of copper chloride to ammonium metavanadate is 2:

1.

6. The method according to claim 3, characterized in that, The copper chloride and organic ligand C 10 The molar ratio of H8N6 is 4:

1.

7. The method according to claim 3, characterized in that, Adjust the pH using a 1 mol / L hydrochloric acid solution and / or a 1 mol / L sodium hydroxide solution.

8. An application of a chloro-coordinated phosphomolybdic acid-based two-dimensional copper complex prepared by the method described in claims 1-7, characterized in that, The chlorine-coordinated phosphomolybdate polyacid-based two-dimensional copper complex was used as an electrode material and applied to the electrocatalytic reduction of nitrate to ammonia synthesis under ambient temperature and pressure.

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