Application of carbon cloth loaded non-metallic COF material EN-COF electrode in electrochemical synthesis of urea

Abstract

The application belongs to the technical field of electrocatalysis, and particularly relates to application of a carbon cloth loaded nonmetallic COF material EN-COF electrode in electrochemical synthesis of urea. The application takes an enaminone structure as a connecting unit, and synthesizes a porous organic material EN-COF catalyst from TDOEB and TAPT as raw materials. The catalyst is prepared into ink, and is applied on carbon cloth to prepare the carbon cloth loaded nonmetallic COF material EN-COF electrode. The electrode is used for electrocatalytic urea production, and reaches a Faraday efficiency of 38.69% at-0.5V vs.RHE, and the current density is stabilized at 0.6mA cm ‑2 for 11h. The material has a high Faraday efficiency without participation of metal and in a case of taking CO2 and NO3 ‑ solution as carbon source and nitrogen source respectively, exhibits good electrocatalytic activity and stability, and has a wide application prospect in the field of electrochemical C-N coupling synthesis of urea.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrocatalysis, and particularly relates to application of a carbon cloth loaded nonmetallic COF material EN-COF electrode in electrochemical synthesis of urea. BACKGROUND

[0002] As a new synthesis technology, electrochemical synthesis of urea has several significant advantages compared to the traditional Haber-Bosch method. First, electrochemical synthesis of urea can be carried out at lower temperatures and pressures, which not only reduces the dependence on energy, but also reduces energy consumption and equipment costs during production. Second, since the electrochemical process can be carried out at room temperature and pressure, it provides the possibility of using renewable energy sources such as solar or wind energy, which helps to reduce dependence on fossil fuels and in turn reduce greenhouse gas emissions. In addition, the electrochemical synthesis of urea produces fewer by-products, reducing the complexity and cost of waste disposal. At the same time, the process flow of electrochemical synthesis of urea is more flexible, and the urea output can be adjusted according to actual needs, which provides convenience for small-scale or distributed production. Finally, the development of electrochemical synthesis of urea technology also helps to promote technological innovation in related fields such as the research and development of electrocatalyst materials, opening up new paths for the sustainable development of the chemical industry. The electrocatalytic C-N coupling of nitrogen-containing waste (nitrate, nitrile, nitrogen oxide) and CO2 to produce urea is a new method of urea synthesis that has received much attention in recent years. In a liquid rich in NO3 - , CO2 is introduced and an appropriate overpotential is applied to synthesize urea in one step under the action of an electrocatalyst. Compared to traditional industrial methods, this method has the advantages of low energy consumption, simple operation, and environmental friendliness. The key to achieving high urea output is to develop electrocatalysts with high catalytic activity, good selectivity, and long service life. Covalent organic framework materials (COF) are a new type of functional material that has received much attention in the field of electrochemical synthesis of urea. SUMMARY

[0003] The purpose of the present application is to provide a preparation method of a carbon cloth loaded nonmetallic COF material EN-COF electrode with simple raw materials, convenient synthesis, stable performance, and good selectivity, and application thereof in electrochemical synthesis of urea.

[0004] The technical scheme adopted by the present application is as follows:

[0005] Application of a carbon cloth loaded nonmetallic COF material EN-COF electrode in electrochemical synthesis of urea.

[0006] Further, the application above, the method is as follows: the carbon cloth loaded non-metallic COF material EN-COF electrode is used as the working electrode, the counter electrode is a platinum sheet electrode, the reference electrode is an Ag / AgCl electrode, the cathode electrolyte uses 0.1M KNO3 solution and 0.1M KHCO3 solution each 35mL, the anode electrolyte uses 0.1M KHCO3 solution 70mL, under-0.3~-0.7V vs.RHE potential, Ar or CO2 is introduced into the cathode electrolyte, electrolysis 2h, and the cathode electrolyte product is collected.

[0007] Preferably, under-0.5V vs.RHE potential, CO2 is introduced into the cathode electrolyte.

[0008] The application of any one of the above, the preparation method of the carbon cloth loaded non-metallic COF material EN-COF electrode includes the following steps: TDOEB solid and TAPT solid are loaded into a pyrex tube, dissolved in a mixed solvent, frozen and air is evacuated, then the tube is flame sealed; then put into an oven to heat reaction, cool the tube to room temperature, centrifugal separation and washed with tetrahydrofuran, vacuum drying to collect yellow solid, the solid is ground to obtain catalyst powder; the obtained catalyst powder is mixed with film solution, 2-alkyne black, isopropyl alcohol, ultrapure water to prepare ink, ultrasonic, using a pipette to drop the ink on the carbon cloth to obtain the carbon cloth loaded non-metallic COF material EN-COF electrode.

[0009] Further, the preparation method of the carbon cloth loaded non-metallic COF material EN-COF electrode above, the amount of TDOEB is 0.03mmol, the amount of TAPT is 0.03mmol.

[0010] Further, the preparation method of the carbon cloth loaded non-metallic COF material EN-COF electrode above, the mixed solvent is: 2mL dioxane, 8mL mesitylene and 0.8mL 6M acetic acid solution.

[0011] Further, the preparation method of the carbon cloth loaded non-metallic COF material EN-COF electrode above, the freezing is under 77K liquid nitrogen.

[0012] Further, the preparation method of the carbon cloth loaded non-metallic COF material EN-COF electrode above, the heating reaction temperature is 393K, and the reaction time is 72h.

[0013] Further, the preparation method of the carbon cloth loaded non-metallic COF material EN-COF electrode above, the amount of catalyst powder is 3mg, the amount of 2-alkyne black is 3mg, the amount of film solution is 30μL, the amount of isopropyl alcohol is 170μL, and the amount of ultrapure water is 200μL; the ultrasonic time is 1h.

[0014] Further, the preparation method of the carbon cloth loaded non-metallic COF material EN-COF electrode described above, the pretreatment method of the carbon cloth is: cutting the carbon cloth into a rectangle with a size of 1cm*2cm, sequentially immersing in acetone, anhydrous ethanol, concentrated nitric acid, anhydrous ethanol, acetone, each time ultrasonic oscillation for 30min, and repeatedly washing with ultrapure water, vacuum drying the treated carbon cloth for standby.

[0015] The beneficial effects of the present application are:

[0016] 1. The present application uses a solvothermal strategy to synthesize catalyst powder and prepare ink, uses carbon cloth to load catalyst, and the raw materials are simple and easy to obtain, and the synthesis operation is low in difficulty.

[0017] 2. The catalyst synthesized by the present application is used for electrochemical synthesis of urea, and reaches a highest Faraday efficiency of 38.69% at-0.5V vs.RHE, and exhibits good electrocatalytic activity and stability, and the EN-COF catalyst obtained by the present application has good application prospect in the field of electrocatalytic urea synthesis.

[0018] 3. The catalyst synthesized by the present application is continuously electrolyzed at-0.5V vs.RHE for 11h, and the current density is stably kept at 0.6mAcm -2 , and exhibits good electrocatalytic activity and stability, and the EN-COF catalyst obtained by the present application has good application prospect in the field of electrocatalytic urea synthesis. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is the SEM diagram of the EN-COF catalyst prepared in Example 1.

[0020] Figure 2 is the FT-IR spectrum diagram of the EN-COF catalyst prepared in Example 1.

[0021] Figure 3 is the XRD spectrum diagram of the EN-COF catalyst prepared in Example 1.

[0022] Figure 4 is the N2 adsorption-desorption isotherm diagram of the carbon cloth loaded EN-COF electrode in Example 1.

[0023] Figure 5 is the experimental device diagram of the electrochemical synthesis of urea by the carbon cloth loaded EN-COF electrode in Example 2.

[0024] Figure 6 is the LSV curve comparison diagram of the carbon cloth loaded EN-COF electrode in Ar and CO2 gas in Example 2.

[0025] Figure 7is the UV-vis absorption spectrum and urea standard curve for testing urea yield and Faraday efficiency of diacetyl monooxime method in Example 2.

[0026] Figure 8 is the urea Faraday efficiency graph of carbon cloth loaded EN-COF electrode in Example 2.

[0027] Figure 9 is the catalytic stability test graph of carbon cloth loaded EN-COF electrode in Example 2. DETAILED DESCRIPTION

[0028] Preparation of carbon cloth loaded non-metallic COF material EN-COF electrode in Example 1

[0029] (I) Preparation method is as follows:

[0030] 1) Pretreatment of carbon cloth: cut the carbon cloth into a rectangle of 1 cm x 2 cm size, and sequentially immerse it in acetone, anhydrous ethanol, concentrated nitric acid, anhydrous ethanol, acetone, each time with ultrasonic oscillation for 30 min, and repeatedly wash with ultrapure water, and vacuum dry the treated carbon cloth for standby.

[0031] 2) Preparation of non-metallic COF material: take 0.03 mmol of powder TDOEB and TAPT each, grind together and transfer to a pyrex tube, then add 2 mL of dioxane, 8 mL of mesitylene, and add 0.8 mL of 6M acetic acid solution as catalyst, freeze at 77K (liquid nitrogen) and evacuate air, then flame seal the tube. Then heat the reaction in an oven at 393K for 3 days, cool the tube to room temperature, centrifuge and wash with tetrahydrofuran (THF) several times, and collect the yellow solid after vacuum drying, and grind the solid thoroughly to obtain catalyst powder EN-COF.

[0032] 3) Preparation of carbon cloth loaded catalyst electrode: mix 3 mg of catalyst powder, 3 mg of 2-alkyne black, 30 μL of Dupont film solution, 170 μL of isopropyl alcohol, 200 μL of ultrapure water to make catalyst ink, and ultrasonically disperse the ink for 60 min. Use a pipette to drop the ink on the pretreated carbon cloth, drop amount 10-12 drops, and weigh after drying, and calculate the catalyst loading according to the mass of the carbon cloth before and after dropping.

[0033] (II) Test results

[0034] Figure 1 is the SEM graph of EN-COF of EN-COF catalyst powder prepared in Example 1, from Figure 1 It can be seen that the material has a three-dimensional network structure composed of a variety of micropores. Figure 2 is the FT-IR spectrum of EN-COF catalyst powder prepared in Example 1, from Figure 2It can be seen that the N-H stretch (3450 cm -1 ) of the primary amine and the N-CH3 stretch (1438 cm -1 ) of the TDOEB have disappeared, proving that the TAPT and TDOEB reaction is complete and the reaction proceeds according to the experimental design. Figure 3 is the XRD spectrum of the EN-COF catalyst powder prepared in Example 1, compared with the spectra of the raw materials TAPT and TDOEB. In the newly synthesized EN-COF catalyst powder, the peaks of the raw materials completely disappear, and a COF-specific peak appears at a small angle of 3.5°, proving the generation of the new substance EN-COF. Figure 4 is the N2 adsorption-desorption isotherm graph of the carbon cloth loaded EN-COF electrode in Example 1. From the graph, it can be seen that the material has a significant gas absorption phenomenon, indicating that the material has a significant microporous structure, which is consistent with the SEM structure of Figure 1 .

[0035] Application of the carbon cloth loaded EN-COF electrode in Example 2 in the electrocatalytic synthesis of urea

[0036] Test method: The carbon cloth loaded EN-COF electrode prepared is used as the working electrode.

[0037] The experimental device is shown in Figure 5 . The experimental electrolytic cell is an H-type electrolytic cell from Tianjin Aida, and the proton exchange membrane is a Nafion 117 membrane. The carbon cloth loaded EN-COF electrode prepared in Example 1 is placed on the cathode electrode clamp as the working electrode, the reference electrode uses an Ag / AgCl electrode, and the counter electrode uses a platinum sheet electrode. The cathode electrolyte is 35 mL of a 0.1M KNO3 solution and 35 mL of a 0.1M KHCO3 solution, and the anode electrolyte is 70 mL of a 0.1M KHCO3 solution. The experimental potential is set to -0.3 to -0.7V vs. RHE, Ar or CO2 is introduced into the cathode electrolyte, the electrolysis time is 2h, and the diacetyl monoxime method is used to detect the urea concentration in the cathode electrolyte.

[0038] The LSV curves of the carbon cloth loaded EN-COF electrode in Ar and CO2 atmospheres are shown in Figure 6 . The current density in the Ar atmosphere is higher than that in the CO2 atmosphere, that is, the hydrogen evolution side reaction in the Ar atmosphere is strong, the hydrogen evolution reaction in the CO2 atmosphere is weakened, which is conducive to the reduction reaction of CO2 and NO3 - and further C-N coupling to synthesize urea.

[0039] The standard curve for urea testing and the urea Faraday efficiency are shown in Figure 7 , Figure 8 . The five standard curve concentrations set in the experiment are 0, 0.5, 1.0, 1.5, and 2.0μg mL -1The R-value of the standard curve was measured experimentally. 2 The value reached 0.99906, indicating high reliability, and it can be used as an external standard curve. Figure 8 For the measurement results, the carbon cloth-loaded EN-COF electrode achieved a maximum Faraday efficiency of 38.69% at -0.5V vs. RHE.

[0040] Catalytic stability test, such as Figure 9 As shown: At the potential where the Faraday efficiency is highest, continuous electrolysis using the chronoamperometry method for 11 hours resulted in a stable current density of 0.6 mA / cm². -1 This demonstrates that the prepared catalyst electrode has high catalytic stability.

[0041] In summary, the carbon cloth-supported non-metallic COF material EN-COF electrode of the present invention has high Faradaic efficiency and good electrocatalytic stability. Therefore, this carbon cloth-supported EN-COF electrode has a promising development prospect in the field of electrocatalytic urea synthesis.

Claims

1. The application of a carbon cloth-supported non-metallic COF material EN-COF electrode in the electrochemical synthesis of urea, characterized in that, The preparation method of the carbon cloth-supported non-metallic COF material EN-COF electrode includes the following steps: TDOEB solid and TAPT solid are loaded into a pyrex tube, dissolved in a mixed solvent, frozen and the air is removed, and the tube is flame-sealed; then it is placed in an oven and heated at 393 K for 72 h, the tube is cooled to room temperature, centrifuged and washed with tetrahydrofuran, vacuum dried and the yellow solid is collected, the solid is thoroughly ground to obtain catalyst powder; the obtained catalyst powder is mixed with membrane solution, 2-acetylenite black, isopropanol and ultrapure water to prepare ink, sonicated, and the ink is dropped onto carbon cloth using a pipette to obtain the carbon cloth-supported non-metallic COF material EN-COF electrode; The mixed solvent is: 2 mL dioxane, 8 mL mesitylene, and 0.8 mL 6 M acetic acid solution.

2. The application according to claim 1, characterized in that, The method is as follows: EN-COF electrode, a carbon cloth-supported non-metallic COF material, is used as the working electrode, a platinum sheet electrode as the counter electrode, and an Ag / AgCl electrode as the reference electrode. The cathode electrolyte consists of 35 mL each of 0.1 M KNO3 solution and 0.1 M KHCO3 solution, and the anolyte consists of 70 mL of 0.1 M KHCO3 solution. Ar or CO2 is introduced into the cathode electrolyte at a potential of -0.3 to -0.7 V vs. RHE, and electrolysis is performed for 2 h. The cathode electrolyte products are then collected.

3. The application according to claim 2, characterized in that, CO2 was introduced into the cathode electrolyte at a potential of -0.5 V vs. RHE.

4. The application according to claim 1, characterized in that, The dosage of TDOEB was 0.03 mmol, and the dosage of TAPT was 0.03 mmol.

5. The application according to claim 1, characterized in that, The freezing was performed at 77 K in liquid nitrogen.

6. The application according to claim 1, characterized in that, The amount of catalyst powder used is 3 mg, the amount of 2-acetylene black used is 3 mg, the amount of membrane solution used is 30 μL, the amount of isopropanol used is 170 μL, and the amount of ultrapure water used is 200 μL; the ultrasonic time is 1 h.

7. The application according to claim 1, characterized in that, The pretreatment method for the carbon cloth is as follows: cut the carbon cloth into rectangles of 1 cm × 2 cm, soak them in acetone, anhydrous ethanol, concentrated nitric acid, anhydrous ethanol and acetone in sequence, ultrasonically vibrate for 30 min each time, and wash them repeatedly with ultrapure water. The treated carbon cloth is then vacuum dried for later use.

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