Electrocatalytic water treatment electrode and laser direct writing preparation method and application thereof

Abstract

The invention discloses an electrocatalytic water treatment electrode and a laser direct writing preparation method and application thereof, an alloy catalyst precursor solution is dropped on a conductive substrate, and then a laser direct writing method is adopted to prepare an alloy catalyst on the surface of the conductive substrate; the alloy catalyst precursor solution comprises palladium salt, copper salt, a solvent and organic amine. A laser direct writing strategy is used, a series of electro-catalysis devices are prepared, and the preparation method is simple and easy to operate. Compared with the existing research, the PdCu alloy electrode prepared in the invention has the advantages of good nitrate conversion rate, excellent ammonia selectivity and extremely low nitrite generation. The prepared PdCu alloy catalyst has excellent cycling stability, and the preparation method of the electrode of the PdCu alloy catalyst is simple, easy to operate and convenient for practical application.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalytic materials, relates to the preparation technology of electrocatalytic catalysts, and particularly relates to an alloy catalyst prepared by laser direct writing and its application in electrocatalytic water treatment. Background Art

[0002] Nitrate is a common groundwater pollutant. Nitrate can be reduced to nitrite through microbial action in nature, and nitrite can cause cancer, posing a threat to human health. In addition, ammonia is mainly synthesized industrially by the Haber-Bosch method under high temperature and high pressure conditions. The synthesis of ammonia directly promotes the global food production and plays a crucial role in aspects such as human production and life. However, the annual average energy consumption of Haber-Bosch accounts for 1-2% of the total world energy consumption, and its annual CO2 emissions account for about 1.5% of the total greenhouse gases. Therefore, there is an urgent need to find a new catalyst material that can not only convert nitrate pollutants into utilizable ammonia but also meet the requirements of low consumption and no pollution emissions.

[0003] In recent years, with the gradual development of electrocatalytic reduction of nitrate, some achievements have also been made in nitrate reduction to ammonia. Zhao et al. prepared Cu single atoms by high-temperature thermal reduction reaction to achieve electrocatalytic nitrate reduction to ammonia at low concentrations [See: X. Zhao, Q. Geng, F. Dong, K. Zhao, S. Chen, H. Yu, X. Quan, Chem. Eng.J., 2023, 466.]. Gong et al. successfully modified the Co4N substrate with Cu element through a doping strategy to achieve efficient NO3RR [See: Z. Gong, X. Xiang, W. Zhong, C. Jia, P. Chen, N. Zhang, S. Zhao, W. Liu, Y. Chen, Z. Lin, Angewandte Chemie International Edition, 2023, 62.]. Akhil Paliwal et al. prepared a binary alloy based on Cu using an electrodeposition strategy and carried out performance tests and discussions on the NO3RR process [See: A. Paliwal, C. D. Bandas, E. S. Thornburg, R. T. Haasch, A. A. Gewirth, ACS Catalysis, 2023, 13, 6754-6762.]. However, the catalysts prepared by the above several traditional methods cannot be directly used as electrodes, and the prepared catalysts still need to be adhered to the substrate of the working electrode such as carbon cloth through an adhesive to achieve NO3RR. Due to the use of the adhesive, the catalyst is prone to falling off during the working process, reducing the working life of the electrode. In order to improve the efficiency and life of the electrode for electrocatalytic reduction of nitrate to ammonia, a new electrode preparation strategy needs to be developed. In recent years, laser processing, as a binder-free and scalable technology, has highlighted its advantages in in-situ surface modification and has thus received extensive attention from researchers.For example, Huang et al. found that laser-induced amorphous graphene consists of disordered four-membered, five-membered, six-membered, seven-membered, and eight-membered ring structures. Studies have shown that this metal-free material also exhibits excellent nitrate reduction reaction (NO3RR) performance [see: L. Huang, L. Cheng, T. Ma, J. J. Zhang, H. Wu, J. Su, Y. Song, H. Zhu, Q. Liu, M. Zhu, Z. Zeng, Q. He, M. K. Tse, D. T. Yang, B. I. Yakobson, B. Z. Tang, Y. Ren, R. Ye, Adv. Mater., 35 (2023) e2211856.]. However, since the process of electrocatalytic reduction of nitrate to ammonia involves complex 8-electron and 9-proton transfer processes, high requirements are imposed on the catalyst electrode during the electrocatalytic process. To date, there have been few reports on the application of electrodes prepared by laser direct writing technology in the field of electrocatalytic reduction of nitrate. Therefore, developing and utilizing laser direct writing technology to prepare electrodes for electrocatalytic reduction of nitrate to ammonia poses a great challenge. Summary of the Invention

[0004] In view of the above situation, the present invention provides a method for preparing a PdCu alloy catalyst by laser direct writing. This method does not require the use of adhesives and has the advantages of simple operation, low cost, and large-area preparation. Through laser direct writing technology, a uniformly dispersed PdCu alloy catalyst can be directly prepared on the surface of carbon cloth, significantly improving the activity and stability of NO3RR.

[0005] To achieve the above object, the present invention adopts the following technical solutions: An electrocatalytic water treatment electrode, comprising a conductive substrate and an alloy catalyst on its surface; the alloy catalyst is prepared by laser direct writing.

[0006] In the present invention, the alloy catalyst is a PdCu alloy; preferably, the molar ratio of Pd to Cu is (0-1):(1-0) and does not include 0. Preferably, the molar ratio of Pd to Cu is (0.2-0.8):(0.8-0.2). More preferably, the molar ratio of Pd to Cu is (0.5-0.6):(0.4-0.5). In the present invention, the molar ratio of Pd to Cu is calculated based on the feed.

[0007] In the present invention, the conductive substrate includes a carbon material, such as carbon cloth.

[0008] The present invention discloses a method for preparing the above electrocatalytic water treatment electrode, comprising the following steps: using laser direct writing to prepare an alloy catalyst on the surface of a conductive substrate.

[0009] The preparation method of the above-mentioned electrocatalytic water treatment electrode of the present invention comprises the following steps: dropping an alloy catalyst precursor solution onto a conductive substrate, and then preparing an alloy catalyst on the surface of the conductive substrate by laser direct writing.

[0010] In the present invention, the alloy catalyst precursor solution comprises a palladium salt, a copper salt, a solvent and an organic amine. Preferably, the palladium salt comprises palladium acetate, the copper salt comprises copper acetate, the solvent comprises ethanol, and the organic amine comprises dopamine.

[0011] In the present invention, the molar ratio of palladium acetate to copper acetate is (0-1):(1-0) and does not include 0. Preferably, the molar ratio of palladium acetate to copper acetate is (0.2-0.8):(0.8-0.2). More preferably, the molar ratio of palladium acetate to copper acetate is (0.5-0.6):(0.4-0.5).

[0012] The present invention discloses the application of the above-mentioned electrocatalytic water treatment electrode in electrocatalytic reduction of nitrate.

[0013] The present invention discloses a method for electrocatalytic reduction of nitrate, which comprises the following steps: using the above-mentioned electrocatalytic water treatment electrode as a working electrode to carry out electrocatalytic reduction of nitrate.

[0014] The present invention discloses a method for electrocatalytic reduction of nitrate to ammonia, which comprises the following steps: using the above-mentioned electrocatalytic water treatment electrode as a working electrode to carry out electrocatalytic reduction of nitrate to prepare ammonia.

[0015] In the present invention, an electrochemical workstation is used for electrocatalytic reduction of nitrate or electrocatalytic reduction of nitrate to ammonia. The electrochemical workstation is an existing product. The creativity of the present invention lies in using the above-mentioned electrocatalytic water treatment electrode as a working electrode, and the rest is the same as the prior art. The performance test of the prepared PdCu alloy material electrode was carried out by a CorrTest CS310 electrochemical workstation. It can be seen from the linear voltammetry scan results that after adding nitrate ions, the current level increases significantly, indicating that nitrate ions are reduced on the electrode. The conversion rate of nitrate ions is particularly important for the reduction of nitrate ions. The test results show that the catalytic material has the best catalytic performance in a solution with a nitrogen content of 1000 ppm. In addition, the PdCu alloy electrode material also has excellent cyclic stability.

[0016] Compared with the existing technology, the present invention using the above technical solution has the following advantages: (1) The present invention uses a laser direct writing strategy, explores its performance in the electrocatalytic field, and prepares a series of electrocatalytic devices. The preparation method is simple and easy to operate.

[0017] (2)Compared with existing research, the PdCu alloy electrode prepared in the present invention has good nitrate conversion rate, excellent ammonia selectivity, and extremely low nitrite generation.

[0018] (3)The PdCu alloy catalyst used in the present invention has excellent cyclic stability, and the preparation method of its electrode is simple, easy to operate, and convenient for practical application. Description of the Drawings

[0019] Figure 1 It is a TEM image of the PdCu alloy catalyst.

[0020] Figure 2 It is a HRTEM image of the PdCu alloy catalyst.

[0021] Figure 3 It is a diagram for screening the optimal working voltage of the PdCu alloy catalyst.

[0022] Figure 4 It is a comparative X-ray photoelectron spectroscopy (XPS) diagram of Pd, Cu, and PdCu alloy catalysts.

[0023] Figure 5 It is a comparative linear voltammetry scan diagram of the PdCu alloy catalyst electrode device before and after adding nitrate.

[0024] Figure 6 It is a kinetic curve of nitrate conversion and ammonia generation of the PdCu alloy catalyst electrode.

[0025] Figure 7 It is a comparative selectivity diagram of the PdCu alloy catalyst electrode for ammonia and nitrite at different concentrations.

[0026] Figure 8 It is a comparative performance diagram of different catalysts.

[0027] Figure 9 It is a cyclic stability performance diagram of the PdCu alloy catalyst electrode.

[0028] Figure 10 It is a comparative performance and stability diagram of the PdCu alloy catalyst and other reported literatures. Detailed Embodiments

[0029] The preparation method of the electrocatalytic water treatment electrode of the present invention comprises the following steps: Palladium acetate, copper acetate, ethanol and dopamine are mixed and stirred in a certain proportion to obtain alloy catalyst precursor solutions with different molar ratios of palladium and copper. Then, the precursor solution is drop-coated on carbon cloth by a drop-coating method, and then laser direct writing treatment is carried out to prepare a catalytic electrode device. Preferably, copper acetate and palladium acetate powders with different molar ratios are weighed by an analytical balance and poured into a bottle containing ethanol and dopamine, and a uniformly dispersed mixed solution of palladium acetate and copper acetate is obtained by ultrasonic treatment. Then, the mixed solution is dropped on the carbon cloth under the irradiation of an infrared lamp by a micro syringe, and laser treatment is carried out to obtain a PdCu alloy electrode for catalytic reduction of nitrate to ammonia. Further preferably, during ultrasonic treatment, the temperature is 20-30 °C and the time is 10-30 minutes.

[0030] The electrocatalytic water treatment electrode of the present invention is composed of carbon cloth (substrate), Pd and Cu2O bimetallic alloy.

[0031] As an example, the preparation method of the palladium acetate and copper acetate dispersion precursor (alloy catalyst precursor solution) is as follows: Dopamine powder and ethanol are weighed into a bottle, and then copper acetate and palladium acetate powders with different molar ratios are weighed and poured into the sample bottle. Then, the sample bottle is shaken and ultrasonic treatment is carried out to obtain a uniformly dispersed palladium and copper precursor solution.

[0032] In the above technical solution, palladium acetate and copper acetate are fed according to the molar ratio of Pd and Cu, that is, the molar ratio of Pd and Cu is (0-1):(1-0), such as 0:1, 0.2:0.8, 0.55:0.45, 0.8:0.2, 1:0 respectively, and single palladium or copper is used as a comparison.

[0033] In the above technical solution, after the palladium and copper precursor dispersion is drop-coated on the carbon cloth, laser treatment is carried out to prepare an electrode on the carbon cloth. Preferably, after obtaining the carbon cloth loaded with copper acetate and palladium acetate, laser processing is carried out with a carbon dioxide cutting machine to obtain a PdCu alloy catalytic electrode as the electrocatalytic water treatment electrode.

[0034] In the present invention, the electrode substrate used is mainly carbon cloth, and the carbon cloth is surface-treated before use. Plasma surface treatment is preferably used, such as treating with oxygen plasma for 15 min; preferably, the size of the carbon cloth substrate is 1×1 cm 2 。

[0035] The technical solution of the present invention will be further described below in conjunction with the drawings and specific examples. Unless otherwise specified, the reagents, materials and instruments used in the following examples can be obtained by commercial means. The carbon cloth is treated with oxygen plasma for 15 min before use; preferably, the size of the carbon cloth substrate is 1×1 cm 2 。

[0036] Example 1 Preparation of Palladium Acetate and Copper Acetate Precursor Solutions At room temperature, first, add 2 mg of dopamine powder and 10 mL of ethanol solution into a sample bottle containing 10 mL; then weigh palladium acetate and copper acetate powders with a molar ratio of Pd to Cu of 1:9 (palladium acetate: 24.51 mg, copper acetate: 163.49 mg), add them into the above sample bottle, and ultrasonicate for 20 minutes at 28 °C to obtain a uniformly dispersed palladium acetate and copper acetate precursor solution for standby.

[0037] Referring to the above method, change the feeding amounts of copper acetate and palladium acetate to obtain precursor solutions with different Pd and Cu molar ratios.

[0038] Example 2 Preparation of PdCu Alloy Material Electrode Devices The PdCu alloy material electrode devices are prepared by laser processing. First, under the irradiation of an infrared lamp, use a micro syringe to drop the palladium acetate and copper acetate precursor solution onto a carbon cloth (substrate) treated with oxygen plasma at a rate of 100 μL / min; secondly, use a carbon dioxide laser cutting machine to process the 1×1 cm 2 carbon cloth with parameters of a power of 4 W, a scanning rate of 10 mm / s, and a scanning interval of 0.05 mm to obtain a PdCu alloy catalyst loaded on the carbon cloth. 2 The TEM, HRTEM, XRD, and XPS spectra of the catalytic electrode materials alloyed with different ratios of copper acetate and palladium acetate were characterized respectively. The TEM test results show that palladium metal and copper ions are well distributed on the carbon cloth (

[0039] ); the HRTEM ( Figure 1 )) test results show that the lattice of palladium crystals expands, allowing copper to embed into the palladium crystals; the XRD ( Figure 2 )) results show that a PdCu alloy is formed after laser treatment; the XPS ( Figure 3 )) results show that Cu Figure 4 is reduced to Cu 2+ on the carbon cloth through electron transfer, and at the same time Pd + is also reduced to Pd 2+ 0 . All these results indicate the successful preparation of the PdCu alloy material.

[0040] Example 3 Performance Testing of PdCu Alloy Electrodes ​The PdCu alloy material electrode device is mainly tested by an electrochemical workstation (model CorrTest CS310). Before the test, the working electrode is connected to the carbon cloth (i.e., the PdCu alloy material electrode), the counter electrode is connected to the platinum sheet, and the saturated calomel electrode is used as the reference electrode. After assembly, it is placed in a 0.5 M sodium sulfate solution, and the linear voltammetric sweep curve is mainly tested, with the sweep potential range of 0.0~-1.8 V, and the constant voltage sweep curve, with the voltage range of -0.8~-1.8 V. Then, under the same conditions, the assembled electrode is placed in a solution containing 0.5 M sodium sulfate and 1000 ppm potassium nitrate in nitrogen content, and the above tests are repeated.

[0041] Under the condition of -1.6 V, the performance results of different Pd:Cu molar ratios show that under the condition of a molar ratio of 0.55:0.45, the ammonia production rate of the catalyst reaches 30.55 mg h -1 cm -2 ( Figure 5 ); Further, change the power of Example 2 to 3 W or 5 W, and the rest remains the same. The ammonia production of the Pd 0.55 Cu 0.45 alloy catalyst is less than 16 mg h -1 cm -2 .

[0042] The test results under different voltage conditions show that the ammonia selectivity of the Pd 0.55 Cu 0.45 alloy catalyst is the highest under the condition of -1.6 V. Therefore, -1.6 V is the optimal working voltage ( Figure 6 ).

[0043] The performance test of the prepared PdCu alloy material electrode was carried out by a CorrTest CS310 electrochemical workstation. From the results of linear voltammetric sweep ( Figure 7 ), it can be seen that after adding nitrate, the current level increases significantly, indicating that nitrate is reduced on the electrode. The conversion rate of nitrate is particularly important for the reduction of nitrate. Figure 8 The test results show that the catalytic material has the best catalytic performance in a solution with a nitrogen content of 1000 ppm. In addition, the stability performance of the catalyst is tested by a flow electrolytic cell experiment through a peristaltic pump. The experiment shows that the PdCu alloy electrode material electrode also has excellent cycle stability ( Figure 9 ). Finally, compared with most alloy catalysts synthesized by related PdCu alloy catalysts and other strategies in the past two years, the catalysts prepared in this experiment have superior performance and stability ( Figure 10 ).

[0044] In summary, the present invention discloses a PdCu alloy material electrode. The prepared electrode has excellent ammonia production performance, up to 30.55 mg h -1 cm -2 -2, and excellent stability, up to 1500 hours. These excellent properties not only prove that the laser addition strategy can enhance the reduction performance of materials for nitrate, but also solve the problem of the degradation of nitrate pollutants, generating reusable ammonia, which provides extremely useful reference for the future recycling of energy. In the future, this method of electrochemically reducing nitrate to ammonia will become the main method for nitrate degradation.

Claims

1. An electrocatalytic water treatment electrode, comprising a conductive substrate and an alloy catalyst on its surface, characterized in that: The alloy catalyst is prepared by laser direct writing method.

2. The electrocatalytic water treatment electrode according to claim 1, characterized in that: The alloy catalyst is PdCu alloy.

3. The electrocatalytic water treatment electrode according to claim 1, characterized in that: The molar ratio of Pd to Cu is (0-1):(1-0) and does not include 0.

4. The method for preparing the electrocatalytic water treatment electrode according to claim 1, characterized in that: The method comprises the following steps: preparing an alloy catalyst on the surface of a conductive substrate by a laser direct writing method to obtain an electrocatalytic water treatment electrode.

5. The method for preparing the electrocatalytic water treatment electrode according to claim 4, characterized in that: The alloy catalyst precursor solution is dropped onto a conductive substrate, and then the alloy catalyst is prepared on the surface of the conductive substrate by a laser direct writing method; the alloy catalyst precursor solution comprises palladium salt, copper salt, solvent and organic amine.

6. The method for preparing the electrocatalytic water treatment electrode according to claim 5, characterized in that: The palladium salt includes palladium acetate, the copper salt includes copper acetate, the solvent includes ethanol, and the organic amine includes dopamine.

7. The method for preparing the electrocatalytic water treatment electrode according to claim 6, characterized in that: The molar ratio of palladium acetate to copper acetate is (0-1):(1-0) and does not include 0.

8. Use of the electrocatalytic water treatment electrode according to claim 1 in electrocatalytic reduction of nitrate.

9. A method for electrocatalytic reduction of nitrates, characterized in that: The method comprises the following steps: using the electrocatalytic water treatment electrode according to claim 1 as a working electrode to perform electrocatalytic reduction of nitrate.

10. A method for producing ammonia by electrocatalytic reduction of nitrates, characterized in that: The method comprises the following steps: using the electrocatalytic water treatment electrode according to claim 1 as a working electrode to electrocatalytically reduce nitrate to prepare ammonia.

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