A nickel-iron bimetallic organic polymer, a preparation method thereof and application thereof in urea electro-synthesis

Abstract

The present application relates to a kind of nickel-iron bimetallic organic polymer catalyst and its preparation method and application in urea electro-synthesis.The nickel-iron bimetallic organic polymer is prepared by using Ni (NO3) 2·6H2O, Fe (NO3) 3·9H2O and pyromellitic dianhydride PMDA as raw materials, Ni (NO3) 3·6H2O and Fe (NO3) 3·9H2O provide metal atom, PMDA as acid anhydride ligand, tetrahydrofuran THF and anhydrous ethanol as solvent to obtain Ni-PMDA@Fe.The present application obtains a kind of bimetallic organic polymer powder with convenient synthesis and stable performance.Under-0.5V v.s.RHE, the highest 409.57h ‑1 ·g ‑1 Urea yield is 41.06%, and the byproduct NH3 is generated with good inhibition effect, the material has higher faradaic efficiency and yield, has wide application prospect in the field of electrochemical C-N coupling synthesis of urea.

Description

Technical Field

[0001] This invention patent belongs to the field of electrocatalysis, and relates to a nickel-iron bimetallic organic polymer, its preparation method, and its application in urea electrosynthesis. Background Technology

[0002] Urea is a small-molecule compound that plays a vital role in the national economy. It is an important agricultural fertilizer and industrial raw material, crucial to national food security and the progress of human industrialization. Traditional urea synthesis relies on syngas reforming, heavily depending on the energy-intensive HaberBosch ammonia synthesis industry (accounting for >2% of global energy supply). In my country, urea production generally uses coal-to-urea processes, generating large amounts of waste (waste liquid, waste gas, and solid waste), severely polluting the environment and producing significant amounts of greenhouse gases. Addressing the drawbacks of traditional industrial methods, electrosynthesis has become a research hotspot in recent years. Utilizing a one-step CN-coupling electrochemical reaction to produce urea not only utilizes CO2 and nitrogen oxide waste to synthesize industrial products but also provides a feasible solution to the greenhouse effect and nitrogen-containing waste pollution. The key to electrosynthesis is finding high-performance and economically available electrocatalysts. Compared to traditional precious metal catalysts, transition metal catalysts have abundant raw material reserves and are economically viable for preparation, offering significant advantages for industrial applications. Compared to single-atom catalysts, bimetallic catalyst systems can provide multiple active sites, exert synergistic effects, and alter the coordination environment. Bimetallic systems of nickel and iron are widely studied dual transition metal systems. Polymer catalysts formed from metals and organic ligands are frequently used to catalyze electrochemical reactions; pyromellitic dianhydride (PMDA) is an excellent tetracarboxylic acid organic ligand. The theory of bimetallic catalysts and coordination polymers provides theoretical feasibility for the electrosynthesis of urea. Summary of the Invention

[0003] The purpose of this invention is to provide a method for preparing a nickel-iron bimetallic organopolymer catalyst Ni-PMDA@Fe that uses readily available raw materials, has a simple preparation method, high catalytic efficiency, and good selectivity, and its application in urea electrosynthesis.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a nickel-iron bimetallic organic polymer, using Ni(NO3)2·6H2O, Fe(NO3)3·9H2O and pyromellitic dianhydride PMDA as raw materials, wherein Ni(NO3)3·6H2O and Fe(NO3)3·9H2O provide metal atoms, PMDA serves as an anhydride ligand, and tetrahydrofuran (THF) and anhydrous ethanol are used as solvents.

[0005] The aforementioned nickel-iron bimetallic organic polymer uses phthalic acid (BDC) instead of pyromellitic dianhydride (PMDA).

[0006] The preparation method of the above-mentioned nickel-iron bimetallic organic polymer is as follows:

[0007] 1) Take Ni(NO3)2·6H2O solid and PMDA solid, dissolve them in THF respectively to obtain metal salt solution and PMDA dispersion. Add PMDA dispersion dropwise to metal salt solution. Disperse the mixture by ultrasound, transfer it to Teflon high-pressure reactor, place it in a forced-air drying oven to react for a specific time and cool to room temperature. Filter the reaction solution and dry and grind the obtained solid to obtain Ni-PMDA precursor.

[0008] 2) Take Ni-PMDA precursor and Fe(NO3)3·9H2O solid, add anhydrous ethanol, stir for 12 h to form a polymer between iron and Ni-PMDA precursor, transfer the stirred liquid to a centrifuge tube for centrifugation, repeat centrifugation several times and wash, transfer to vacuum drying to obtain Ni-PMDA@Fe solid.

[0009] In the above-mentioned method for preparing a nickel-iron bimetallic organic polymer, in step 1), the molar ratio of Ni(NO3)2·6H2O solid to PMDA is 5:2.

[0010] In the above-mentioned method for preparing a nickel-iron bimetallic organic polymer, step 1) involves a reaction temperature of 120 °C, a reaction time of 48 h, and natural cooling to room temperature.

[0011] In the above-mentioned method for preparing a nickel-iron bimetallic organic polymer, in step 3), the mass ratio of Ni-PMDA precursor to Fe(NO3)3·9H2O is 1:1.

[0012] A nickel-iron bimetallic organic polymer catalytic electrode is prepared by mixing the above-mentioned nickel-iron bimetallic organic polymer with acetylene black, DuPont membrane solution, isopropanol and ultrapure water to form an ink, and then using a syringe to drop the ink onto carbon cloth to obtain the catalytic electrode.

[0013] The above-mentioned nickel-iron bimetallic organic polymer catalytic electrode comprises: nickel-iron bimetallic organic polymer: acetylene black: DuPont membrane solution: isopropanol: ultrapure water = 3 mg: 3 mg: 30 ul: 170 ul: 200 ul.

[0014] The above-mentioned nickel-iron bimetallic organic polymer catalytic electrode is used in the electrochemical synthesis of urea.

[0015] In the above application, the nickel-iron bimetallic organic polymer catalytic electrode is used as the working electrode, the counter electrode is a platinum sheet electrode, the reference electrode is an Ag / AgCl reference electrode, the cathode electrolyte is 35 ml each of 0.1 M KNO3 solution and 0.1 M KHCO3 solution, the anode electrolyte is 70 ml of 0.1 M KHCO3 solution, the electrolysis time is 2 h at a single potential, and the cathode electrolyte product is collected.

[0016] The beneficial effects of this invention are as follows:

[0017] This invention uses Ni(NO3)2·6H2O and Fe(NO3)3·9H2O as reaction raw materials, and synthesizes bimetallic polymers using a solvothermal strategy and a stirring diffusion method. The reaction substrates are economical and readily available, the reaction conditions are mild and controllable, and the synthesis strategy is easy to operate.

[0018] Using the catalytic electrode synthesized in this invention, the electrosynthesis of urea reached a maximum of 409.57 mg·h at -0.5 V vs. RHE. -1 ·g -1 The urea yield and Faraday efficiency of 41.06% are superior to those of the previously prepared Ni-BDC catalyst and Ni-PMDA precursor catalyst, indicating the excellent catalytic activity of the bimetallic catalyst.

[0019] The catalyst in this invention exhibits good inhibition of the main byproduct, ammonia nitrogen. The ammonia nitrogen concentration measured at -0.3 V vs. RHE to -0.05 V vs. RHE was consistently below 53 mg·h⁻¹. -1 ·g -1 This demonstrates the excellent electrocatalytic selectivity of the catalyst of the present invention. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the synthesis of the carbon cloth-supported nickel-iron bimetallic organic polymer catalyst Ni-PMDA@Fe prepared in Example 1.

[0021] Figure 2 This is the Fourier transform infrared (FT-IR) spectrum of the carbon cloth-supported nickel-iron bimetallic organic polymer catalyst Ni-PMDA@Fe prepared in Example 1.

[0022] Figure 3 This is a scanning electron microscope (SEM) image of Ni-PMDA@Fe, a carbon cloth-supported nickel-iron bimetallic organic polymer catalyst prepared in Example 1.

[0023] Figure 4 This is the powder X-ray diffraction (XRD) pattern of the carbon cloth-supported nickel-iron bimetallic organic polymer catalyst Ni-PMDA@Fe prepared in Example 1.

[0024] Figure 5 This is a diagram of the electrochemical experimental setup for the carbon cloth-supported Ni-PMDA@Fe catalytic electrode in Example 2.

[0025] Figure 6 The left image shows the linear voltammetry (LSV) curves of the carbon cloth-supported Ni-PMDA@Fe catalytic electrode in Ar and CO2 atmospheres, and the right image shows a comparison of the LSV curves of the three catalysts Ni-PMDA@Fe, Ni-PMDA, and Ni-BDC.

[0026] Figure 7 The graph shows the urea yield of the carbon cloth-supported Ni-PMDA@Fe catalytic electrode in Example 2 (left) and a comparison graph of the yields of Ni-PMDA@Fe, Ni-PMDA, Ni-BDC and empty carbon cloth (right).

[0027] Figure 8 The graph shows the urea Faradaic efficiency of the carbon cloth-supported Ni-PMDA@Fe catalytic electrode in Example 2 (left) and the selectivity comparison graph of Ni-PMDA@Fe, Ni-PMDA, and Ni-BDC (right).

[0028] Figure 9 This is a comparison diagram of the double-layer capacitance of the Ni-PMDA@Fe catalyst of the present invention with that of Ni-PMDA, Ni-BDC, and hollow carbon cloth in Example 2. Detailed Implementation

[0029] Example 1: Preparation of a carbon cloth-supported nickel-iron bimetallic organic polymer Ni-PMDA@Fe electrode

[0030] (I) Preparation method

[0031] 1) Preparation of Ni-PMDA polymer precursor: 1.5 mmol of reactant Ni(NO3)2·6H2O and 0.6 mmol of PMDA ligand were accurately weighed using a precision electronic balance. Ni(NO3)2·6H2O and PMDA were dissolved in 30 ml and 15 ml of THF, respectively, and stirred for 30 min to form a homogeneous metal salt solution and PMDA dispersion. The PMDA dispersion was then added dropwise to the metal salt solution using a dropper, with continuous stirring using a magnetic stirrer. The mixed solution was ultrasonically dispersed and transferred to a 100 ml Teflon autoclave. The reaction was carried out at 120 °C for 2880 min in a forced-air drying oven. After natural cooling to room temperature, the liquid in the reactor was removed and filtered using a sand filter. The solid particles on the filter paper layer were transferred to a vacuum drying oven and vacuum dried for 12 h to obtain the Ni-PMDA precursor.

[0032] 2) Synthesis of Ni-PMDA@Fe polymer: 50 mg of Ni-PMDA precursor and 50 mg of Fe(NO3)3·9H2O solid were accurately weighed using a precision electronic balance, and 50 ml of anhydrous ethanol was added. The mixture was stirred with a magnetic stirrer for 12 h to allow the iron to form a polymer with the precursor. The stirred liquid was transferred to a centrifuge tube and centrifuged at 12000 rpm for 10 min. The centrifugation was repeated three times and the mixture was washed three times with anhydrous ethanol. The solid in the centrifuge tube was transferred to a vacuum dryer and dried for 12 h to obtain Ni-PMDA@Fe solid.

[0033] 3) Pretreatment of carbon cloth: Cut the conductive carbon cloth into regular rectangles of 1 cm × 2 cm in size, and soak them in acetone, anhydrous ethanol, concentrated nitric acid, anhydrous ethanol and acetone in sequence for pretreatment. Each soaking is ultrasonically vibrated for 30 min, and then washed repeatedly with ultrapure water. The pretreated carbon cloth is then placed in a vacuum drying oven to dry for later use.

[0034] 4) Preparation of Ni-PMDA@Fe polymer catalytic electrode: Accurately weigh 3 mg of Ni-PMDA@Fe catalyst powder and 3 mg of acetylene black using an electronic balance. Accurately pipette 30 μL of DuPont membrane solution, 170 μL of isopropanol, and 200 μL of ultrapure water. Mix and ultrasonically disperse for 30 min to prepare the ink. Use a syringe to evenly drop the catalyst ink onto the treated carbon cloth, 10-12 drops per piece. After drying, weigh the carbon cloth and calculate the catalyst loading based on the mass of the carbon cloth before and after the addition.

[0035] (II) Test Results

[0036] Figure 1 The preparation route of the carbon cloth-supported nickel-iron bimetallic organic polymer Ni-PMDA@Fe electrode in Example 1 can be divided into three parts: synthesis of Ni-PMDA precursor, synthesis of Ni-PMDA@Fe polymer, and preparation of catalyst electrode. Figure 2 The Fourier transform infrared (FT-IR) spectra of the polymer Ni-PMDA@Fe and PMND ligands are shown. The PMND spectrum exhibits distinct conjugated anhydride characteristics, including at 1770 cm⁻¹. -1 The strong absorption peak at C=O and at 1200 cm⁻¹ -1 ~1310 cm -1 The cyclic anhydride CO stretching vibration at 3400 cm⁻¹ resulted in the synthesized Ni-PMDA@Fe polymer exhibiting this effect. -1 The broad and strong peak appearing at 1400 cm⁻¹ is produced by the stretching vibration of the -OH groups of exposed carboxylic acids in the polymer. -1 and 1550 cm -1 The two consecutive strong peaks appearing at the point coincide with the characteristic peaks of the carbonyl group in the carboxylate, indicating that the metal and PMDA ligand have successfully coordinated and polymerized. Figure 3 The image shows a scanning electron microscope (SEM) image of the polymer Ni-PMDA@Fe. The polymer powder appears as a micron-sized, irregularly shaped blocky solid with a rough surface morphology and some cracks and defects. Figure 4 This is the powder X-ray diffraction (XRD) spectrum of the polymer Ni-PMDA@Fe. The Ni-PMDA precursor has similar peak positions to the previously reported Co-PMDA and is considered to be a homologue. Ni-PMDA@Fe shows a large carbon bulge peak and low crystallinity, exhibiting typical characteristics of low-crystallinity polymers.

[0037] Comparative Example 1: Ni-BDC Catalyst

[0038] Preparation of Ni-BDC catalyst: 1.5 mmol of reactant Ni(NO3)2·6H2O and 0.6 mmol of terephthalic acid BDC ligand were accurately weighed using a precision electronic balance. Ni(NO3)2·6H2O and BDC were dissolved in 30 ml and 15 ml of THF, respectively, and stirred for 30 min to form a homogeneous metal salt solution and BDC dispersion. The BDC dispersion was then added dropwise to the metal salt solution using a dropper, with continuous stirring using a magnetic stirrer. The mixed solution was ultrasonically dispersed and transferred to a 100 ml Teflon autoclave. The reaction was carried out at 120 °C for 2880 min in a forced-air drying oven. After natural cooling to room temperature, the liquid in the reactor was removed and filtered using a sand core filter. The solid particles on the filter paper were transferred to a vacuum drying oven and vacuum dried for 12 h to obtain the Ni-BDC catalyst.

[0039] Example 2: Application of Ni-PMDA@Fe electrode in electrocatalytic urea synthesis

[0040] (a) Testing methods

[0041] The experimental setup for this experiment is as follows: Figure 5The experimental electrolytic cell used was an H-type electrolytic cell from Tianjin Aida, with a single cell volume of 100 ml. The proton exchange membrane was a DuPont Nafion 117 membrane. The Ni-PMDA@Fe catalytic electrode prepared in Example 1 was fixed to the cathode electrode clamp as the working electrode. The reference electrode was an Ag / AgCl electrode, and the counter electrode was a platinum electrode. The cathode electrolyte was a mixture of 35 ml of 0.1 M KNO3 solution and 35 ml of 0.1 M KHCO3 solution, and the anolyte was 70 ml of 0.1 M KHCO3 solution. Before testing, the electrodes underwent CV activation pretreatment for 2000 s, followed by LSV linear voltammetry, constant voltage electrolysis (it) testing, and electrochemical active surface area (ECSA) testing. The it potential was set to -0.3 ~ 0.5 V vs RHE, and the electrolysis time was set to 2 h. The electrolyte composition was determined using spectrophotometry. The external standard method and the diacetyl monooxime method were used to determine the urea concentration in the electrolyte, and the indophenol blue method was used to determine the ammonia nitrogen concentration in the electrolyte.

[0042] (II) Test Results

[0043] Using Ni-PMDA@Fe electrode as the working electrode, linear voltammetry tests were performed under CO2 and Ar atmospheres, and the corresponding linear voltammetry curves (LSV) were plotted. Figure 6 The LSV curves obtained from the experiment show that the current density of the Ni-PMDA@Fe catalyst under CO2 atmosphere is higher than that under Ar atmosphere, indicating that the catalyst has CN coupling catalytic activity. In addition, the LSV of Ni-PMDA@Fe was compared with that of the precursors Ni-PMDA and Ni-BDC catalysts. Among them, the Ni-PMDA@Fe catalyst has the highest current density in the range above -0.3 V vs. RHE, which shows the activity advantage of the catalyst of the present invention. Figure 7 To determine the yield of the target product urea using the diacetyl monooxime method and to compare the yields of the Ni-PMDA@Fe catalyst with those of Ni-PMDA catalyst, Ni-BDC catalyst, and blank carbon cloth urea, the catalyst of this invention achieved a maximum yield of 409.57 mg·h⁻¹ at -0.5 V vs. RHE. -1 ·g -1 The yield was higher than that of blank carbon cloth (CP), Ni-PMDA precursor and Ni-BDC catalyst. Figure 8 To experimentally determine the urea and ammonia nitrogen Faradaic efficiencies of the Ni-PMDA@Fe catalyst and compare the urea selectivity of several catalysts, the catalyst of this invention achieved the highest urea Faradaic efficiency of 41.06% at -0.5 V vs. RHE, and effectively suppressed the formation of the byproduct ammonia nitrogen. The urea selectivity of the catalyst of this invention is significantly higher than that of the Ni-PMDA precursor and Ni-BDC catalyst. Figure 9 The double-layer capacitance of various catalysts was measured using an electrochemical CV method, representing the size of the electrochemical active surface area (ECSA) of each catalyst. Among them, the Ni-PMDA@Fe catalyst obtained the highest double-layer capacitance, indicating the advantage of the catalyst of the present invention in terms of catalytic kinetics.

[0044] In summary, this invention presents a nickel-iron bimetallic organopolymer catalyst, Ni-PMDA@Fe, applied to the field of urea electrosynthesis. It exhibits high urea yield and selectivity, along with kinetic advantages, demonstrating superior overall performance compared to Ni-PMDA precursors and common Ni-BDC catalysts. Therefore, this carbon cloth-supported nickel-iron bimetallic catalyst shows promising development and application prospects in the field of urea electrosynthesis.

Claims

1. A nickel-iron bimetallic organic polymer, characterized in that, The mixture was prepared using Ni(NO3)2·6H2O, Fe(NO3)3·9H2O and pyromellitic dianhydride PMDA as raw materials, wherein Ni(NO3)2·6H2O and Fe(NO3)3·9H2O provided metal atoms, PMDA served as an anhydride ligand, and tetrahydrofuran (THF) and anhydrous ethanol were used as solvents. The preparation method of the nickel-iron bimetallic organic polymer is as follows: 1) Take Ni(NO3)2·6H2O solid and PMDA solid, dissolve them in THF respectively to obtain metal salt solution and PMDA dispersion. Add PMDA dispersion dropwise to metal salt solution. Disperse the mixture by ultrasound, transfer it to Teflon high-pressure reactor, place it in a forced-air drying oven to react for a specific time and cool to room temperature. Filter the reaction solution and dry and grind the obtained solid to obtain Ni-PMDA precursor. 2) Take Ni-PMDA precursor and Fe(NO3)3·9H2O solid, add anhydrous ethanol, stir for 12 h to form a polymer between iron and Ni-PMDA precursor, transfer the stirred liquid to a centrifuge tube for centrifugation, repeat centrifugation several times and wash, transfer to vacuum drying to obtain Ni-PMDA@Fe solid.

2. The nickel-iron bimetallic organic polymer according to claim 1, characterized in that, Use phthalic acid BDC instead of pyromellitic dianhydride PMDA.

3. The nickel-iron bimetallic organic polymer according to claim 1, characterized in that, In step 1), the molar ratio of Ni(NO3)2·6H2O solid to PMDA is 5:

2.

4. The nickel-iron bimetallic organic polymer according to claim 1, characterized in that, In step 1), the reaction temperature is 120 °C, the reaction time is 48 h, and the mixture is allowed to cool naturally to room temperature.

5. The nickel-iron bimetallic organic polymer according to claim 1, characterized in that, In step 3), the mass ratio of Ni-PMDA precursor to Fe(NO3)3·9H2O is 1:

1.

6. A nickel-iron bimetallic organic polymer catalytic electrode, characterized in that, The nickel-iron bimetallic organic polymer of claim 1 is mixed with acetylene black, DuPont membrane solution, isopropanol and ultrapure water to prepare an ink. The ink is then dropped onto carbon cloth using a syringe to obtain a catalytic electrode.

7. The nickel-iron bimetallic organic polymer catalytic electrode according to claim 6, characterized in that, Nickel-iron bimetallic organic polymer: acetylene black: DuPont membrane solution: isopropanol: ultrapure water = 3 mg: 3 mg: 30 ul: 170 ul: 200 ul.

8. The application of the nickel-iron bimetallic organic polymer catalytic electrode according to claim 6 or 7 in electrochemical urea synthesis.

9. The application according to claim 8, characterized in that, Using the nickel-iron bimetallic organic polymer catalytic electrode as described in claim 6 or 7 as the working electrode, the counter electrode as a platinum sheet electrode, and the reference electrode as an Ag / AgCl reference electrode, the cathode electrolyte is 35 ml each of 0.1 M KNO3 solution and 0.1 M KHCO3 solution, and the anolyte is 70 ml of 0.1 M KHCO3 solution. The electrolysis time is 2 h at a single potential, and the cathode electrolyte product is collected.

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