Preparation method and application of cathode electrode for electrocatalytic reduction of chlorate

Abstract

The invention aims to provide a preparation method and application of a cathode electrode for electrocatalytic reduction of chlorate, belongs to the technical field of chlorate treatment, and realizes electrocatalytic reduction of chlorate by means of non-noble metal through excellent oxidation-reduction capacity of transition metal elements. According to the system, molybdenum foil is used as a substrate material and loaded with Pd / C, and electro-catalytic reduction of chlorate is effectively achieved through the hydrogenation activation effect of Pd and the excellent oxidation-reduction performance of multivalent Mo species. According to the catalytic system disclosed by the invention, the generation of hydrogen evolution side reaction is reduced, selective reduction of chlorate is realized, and the stability and high efficiency of catalytic reduction are ensured.

Description

Technical Field

[0001] The invention belongs to the technical field of chlorate treatment, and in particular relates to a preparation method of a cathode electrode for electrocatalytic reduction of chlorate and application thereof. Background Art

[0002] Chlorate is a byproduct of industrial production processes such as chlor-alkali and electrochemical preparation of disinfectants. It is extremely stubborn in the water environment and difficult to degrade naturally. Traditional chlorate reduction methods include chemical reduction, biological reduction and electrochemical reduction.

[0003] Chemical reduction: using a reducing agent such as sulfite (SO 3 2- ), sulfide (S 2- ) or iron (Fe 2+ ) etc., to reduce chlorate to chloride ions. In the reduction process, it is often necessary to add excessive reducing agents, resulting in reduction by-products such as sulfates and sulfides. In addition, some reducing agents themselves are toxic or corrosive, and improper handling may cause harm to the environment.

[0004] Bioreduction method: using specific microorganisms to reduce chlorate to chloride ions under anaerobic conditions. However, since the metabolism and reproduction of microorganisms require time, the reaction rate of the bioreduction method is usually slow, and microorganisms are sensitive to environmental conditions, so the reaction conditions must be strictly controlled. It has the disadvantages of long reaction time and large reactor footprint.

[0005] Electrochemical reduction method: Chlorate is reduced to chloride ions on the electrode surface by applying an external voltage. The conditions of this method are controllable, but the existence of the hydrogen evolution side reaction leads to increased energy consumption.

[0006] In recent years, catalytic reduction of chlorate has attracted people's attention. A Plá-Hernández, F Rey, AEPalomares. Pt-zeolites as active catalysts for the removal of chlorate inwater by hydrogenation reactions[J]. Catalysis Today, 2024, 429: 114461, using the synergistic effect of numerous acidic sites in zeolites and platinum to achieve simultaneous reduction of chlorate and bromate; Sikora E, Karacs G, Kocserha BVL, et al. Hydrogenation of chlorate ions by commercial carbon supported palladium catalysts-a comparative study[J]. Reactionkinetics, mechanisms and catalysis, 2020, 131(1):129-137, pointing out that under acidic conditions, Pd, Ru, and Rh are combined with activated carbon supports as potential catalysts for the reduction of chlorate and perchlorate; Gao J, Xie S, Liu F. Preparation and Synergy of Supported Ru~0 and Pd~0 for Rapid Chlorate Reduction at pH 7[J]. Environmental Science&Technology: ES&T, 2023, 100 mM chlorate was reduced using Ru-Pd / C catalyst under 1 atmosphere of hydrogen and 20°C. However, hydrogenation-based chlorate reduction usually requires noble metals as active sites and reacts in a hydrogen environment.

[0007] Electrocatalytic reduction is a feasible alternative. Wei H, Yancai Y, Lizhi Z. Advances in Electrochemical Reductive Removal of Oxyanions in Water[J]. Acta Chimica Sinica, 2023, 81(8): 979 pointed out that in acidic media, under the influence of external current, metal ions have higher hydrogen evolution activity at the cathode, which helps the reduction of oxygen-containing compounds at the cathode. Bibo Xu, Yunbo Zhai, Wei Chen, et al.Perchlorate catalysis reduction by benzalkonium chloride immobilized biomasscarbon supported Re-Pd bimetallic cluster particle electrode[J]. Chemical Engineering Journal, 2018, by fixing Re-Pd bimetallic cluster particles on biomass carbon to achieve catalytic reduction of perchlorate; Yao F, Zhong Y, Yang Q, et al. Effective adsorption / electrocatalytic degradation of perchlorate using Pd / Pt supported on N-dopedactivated carbon fiber cathode[J]. Journal of hazardous materials, 2016, 323(B), using Pd / Pt supported on nitrogen-doped activated carbon fiber cathode to achieve effective adsorption / electrocatalytic degradation of perchlorate. However, in the process of indirect reduction of pollutants on the electrode surface by highly reducing atomic H (H*) generated by precious metal ions, energy consumption increases, and a large amount of by-products are produced, which reduces the efficiency of electron utilization. Therefore, efficient use of H* and direct catalytic reduction on the electrode surface are the key to improving reaction efficiency and reducing energy consumption. Summary of the invention

[0008] In view of the above problems, the present invention provides a method for preparing a cathode electrode for electrocatalytic reduction of chlorate and its application, which realizes electrocatalytic reduction of chlorate by using transition metal elements with excellent redox ability and non-precious metals. The system uses molybdenum foil as a substrate material and loads Pd / C, and effectively realizes electrocatalytic reduction of chlorate by hydrogenation activation of Pd and excellent redox performance of multivalent Mo species.

[0009] The present invention adopts the following technical solution: A method for preparing a cathode electrode for electrocatalytic reduction of chlorate comprises the following steps: S1. Cut the high-purity molybdenum foil into sheets of 50 mm × 25 mm × 0.2 mm, put them into anhydrous ethanol for ultrasonication for 10 min, and then put them into ultrapure water for ultrasonication for 10 min to remove surface organic matter and impurities; S2. Prepare a 1 mol / L phosphoric acid solution in a 250 mL volumetric flask, weigh 0.4625 g of ammonium fluoride, add the above phosphoric acid solution and stir until uniform, and use it as the electrolyte for this experiment; S3, take 200 mL of electrolyte, pour it into the electrolytic cell, use high-purity molybdenum foil as the working electrode, and Pt sheet as the counter electrode, make the distance between the two electrodes 1.5 cm and fully contact with the electrolyte at the same time, use a constant voltage power supply to apply 0.3 V voltage for 15 minutes; S4. After the reaction, the anode was taken out, washed with ethanol, and dried in vacuum at 45°C for 12 h to obtain MoO grown on the molybdenum foil. X Oxide layer, denoted as MoO X / MF; S5, 10 mg 10% Pd / C was dispersed in 950 μl isopropanol, 50 μl Nafion solution was added, ultrasonicated for 20 min to form black ink, and then evenly dropped on MoO X / MF and dried under vacuum at 45 °C for 12 h to obtain Pd / C-MoO X / MF electrode.

[0010] A cathode electrode is used for electrocatalytic reduction of chlorate.

[0011] A method for electrocatalytic reduction of chlorate using a cathode electrode comprises the following steps: S1. In a split-tank electrochemical reactor, a proton exchange membrane is used to separate the cathode tank and the anode tank, wherein the cathode tank is 400 mL and the anode tank is 200 mL; S2, the anode is iridium tantalum / titanium electrode, the cathode is Pd / C-MoO X / MF electrode, the effective area of ​​the anode and cathode is 10cm 2 , the geometric surface area is 10cm 2 , the distance between anode and cathode is 20 mm; S3, add 170 mL of ultrapure water to the anode tank, add 340 mL of 1 mM chlorate solution to the cathode tank, and then add 1M H 2 SO 4 The solution pH was adjusted to below 2 and stirred with a magnetic stirrer for uniform distribution. The experiment was carried out under an external constant voltage of 3-6 V.

[0012] The beneficial effects of the present invention are as follows: First, the use of non-precious metals greatly reduces costs and improves the economy of the technology; second, it avoids the dangerous operation of adding hydrogen during the precious metal hydrogenation process, and significantly improves safety; thirdly, the new catalytic system reduces the occurrence of hydrogen evolution side reactions and achieves the selective reduction of chlorate, ensuring the stability and efficiency of the catalytic reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 A flow chart for preparing the cathode electrode of the present invention; Figure 2 Schematic diagram of a device for electrocatalytic reduction of chlorate using the cathode electrode of the present invention; Figure 3 It is the reduction rate curve of chlorate under different reduction voltages; Figure 4 The reduction rate curve of chlorate under different pH conditions; Figure 5 is the reduction rate curve of chlorate at different chlorate solution concentrations; Figure 6 is the reduction curve of chlorate under the conditions of pH 2.0, reduction voltage 3 V, and reduction current 12 mA; Figure 7 Pd / C-MoO X / MF pair Selective reduction curve diagram of Among them: 1- molybdenum foil; 2- electrolytic cell; 3- magnetic stirrer; 4- electrochemical workstation; 5- pipette; 6- vacuum drying oven. DETAILED DESCRIPTION

[0014] In order to make the purpose, technical scheme and advantages of the present invention more clear, the specific embodiments of the present invention are described in detail, but are not limited thereto. The raw materials used in the embodiments are all common commercial products unless otherwise specified; the methods used are all commonly used methods in the art unless otherwise specified.

[0015] A method for preparing a cathode electrode for electrocatalytic reduction of chlorate comprises the following steps: S1. Cut the high-purity molybdenum foil into sheets of 50 mm × 25 mm × 0.2 mm, put them into anhydrous ethanol for ultrasonication for 10 min, and then put them into ultrapure water for ultrasonication for 10 min to remove surface organic matter and impurities; S2. Prepare a 1 mol / L phosphoric acid solution in a 250 mL volumetric flask, weigh 0.4625 g of ammonium fluoride, add the above phosphoric acid solution and stir until uniform, and use it as the electrolyte for this experiment; S3, take 200 mL of electrolyte, pour it into the electrolytic cell, use high-purity molybdenum foil as the working electrode, and Pt sheet as the counter electrode, make the distance between the two electrodes 1.5 cm and fully contact with the electrolyte at the same time, use a constant voltage power supply to apply 0.3 V voltage for 15 minutes; S4. After the reaction, the anode was taken out, washed with ethanol, and dried in vacuum at 45°C for 12 h to obtain MoO grown on the molybdenum foil. X Oxide layer, denoted as MoO X / MF; S5, 10 mg 10% Pd / C was dispersed in 950 μl isopropanol, 50 μl Nafion solution was added, ultrasonicated for 20 min to form black ink, and then evenly dropped on MoO X / MF and dried under vacuum at 45 °C for 12 h to obtain Pd / C-MoO X / MF electrode.

[0016] Example 1 A method for electrocatalytic reduction of chlorate using a cathode electrode is carried out under different reduction voltage conditions, wherein 2V, 3V, 4V, 5V, 6V and 8V are selected as the reduction voltages respectively, and a 36h split-tank reduction experiment is carried out under the conditions of an initial molar concentration of chlorate of 1mM and an initial pH of 2. Figure 3 The relationship between different voltages and reduction rates is shown in Figure 2. The results show that when Pd / C-MoO X When the reduction voltage of the / MF electrode was reduced from 8 V to 3 V, the chlorate reduction efficiency increased from 78.71% to 98.24%; when the voltage was further reduced to 2 V, the reduction efficiency dropped to 87.16%.

[0017] Example 2 A method for electrocatalytic reduction of chlorate using a cathode electrode was conducted under different chlorate solution pH conditions. A 36h split-cell reduction experiment was conducted under the conditions of an initial chlorate molar concentration of 1mM, a pH of 1-4, and a reduction voltage of 3V. The results are shown in FIG. Figure 4 As shown, when the pH is 2, the chlorate reduction rate is as high as 98.24%, when the pH is 1, the reduction rate decreases to 91.04%, and when the pH increases to 4, the reduction rate is only 3.95%.

[0018] Example 3 A method for electrocatalytic reduction of chlorate using a cathode electrode is carried out under different chlorate solution concentration conditions, wherein the concentration of the chlorate solution is 0.5-50 mM, the pH is 2, and the reduction voltage is 3 V. Figure 5 As shown, during the 36 h electrolysis process, the absolute removal efficiencies of 0.5, 1, 10, and 50 mM chlorate solutions were 99.19%, 98.24%, 83.94%, and 55.31%, respectively.

[0019] Example 4 like Figure 6 As shown in Figure 2, under the conditions of pH 2.0, reduction voltage 3 V, chlorate concentration 1 mM, and reduction current 12 mA, chlorate can be reduced on Pd / C-MoO X / MF electrode and completely converted into chloride ions, with a reduction rate of up to 98.24%.

[0020] Example 5 like Figure 7 As shown in the figure, under the conditions of a reduction voltage of 3 V, an initial solution pH of 2, and a reduction voltage of 3 V, bromide ions reduced the reduction rate to 91.32%, chloride ions reduced the reduction rate to 88.89%, and when NO 3 - The reduction rate was only 81.38% when ClO 3 - The competition for active sites leads to NO 3 - There is almost no reduction itself, which shows that Pd / C-MoO X / MF to ClO 3 - Selective reduction.

[0021] The technical features of the above embodiments can be combined arbitrarily. In order to make the description concise, all possible combinations of the technical features in the above embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification. The above embodiments only express several implementation methods of the present application, and their descriptions are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present application, several deformations and improvements can be made, which all belong to the protection scope of the present application. Therefore, the protection scope of the patent of this application shall be based on the attached claims.

Claims

1. A method for preparing a cathode electrode for electrocatalytic reduction of chlorate, characterized in that: The steps include: S1. Cut the high-purity molybdenum foil into sheets of 50 mm × 25 mm × 0.2 mm, put them into anhydrous ethanol for ultrasonication for 10 min, and then put them into ultrapure water for ultrasonication for 10 min to remove surface organic matter and impurities; S2. Prepare a 1 mol / L phosphoric acid solution in a 250 mL volumetric flask, weigh 0.4625 g of ammonium fluoride, add the above phosphoric acid solution and stir until uniform, and use it as the electrolyte for this experiment; S3, take 200 mL of electrolyte, pour it into the electrolytic cell, use high-purity molybdenum foil as the working electrode, and Pt sheet as the counter electrode, make the distance between the two electrodes 1.5 cm and fully contact with the electrolyte at the same time, use a constant voltage power supply to apply 0.3 V voltage for 15 minutes; S4. After the reaction, the anode was taken out, washed with ethanol, and dried in vacuum at 45°C for 12 h to obtain MoO grown on the molybdenum foil. X Oxide layer, denoted as MoO X / MF; S5, 10 mg 10% Pd / C was dispersed in 950 μl isopropanol, 50 μl Nafion solution was added, ultrasonicated for 20 min to form black ink, and then evenly dropped on MoO X / MF and dried under vacuum at 45 °C for 12 h to obtain Pd / C-MoO X / MF electrode.

2. A cathode electrode prepared by the preparation method as claimed in claim 1 for electrocatalytic reduction of chlorate.

3. A cathode electrode for electrocatalytic reduction of chlorate according to claim 2, characterized in that: The steps include: S1. In a split-tank electrochemical reactor, a proton exchange membrane is used to separate the cathode tank and the anode tank, wherein the cathode tank is 400 mL and the anode tank is 200 mL; S2, the anode is iridium tantalum / titanium electrode, the cathode is Pd / C-MoO X / MF electrode, the effective area of ​​the anode and cathode is 10cm 2 , the geometric surface area is 10cm 2 , the distance between anode and cathode is 20 mm; S3. Add 170 mL of ultrapure water to the anode tank and 340 mL of 1 mM chlorate solution to the cathode tank, then add 1 M H2SO4 dropwise to adjust the pH of the solution to below 2, stir with a magnetic stirrer to ensure uniform distribution, and conduct the experiment under an external constant voltage of 3-6 V.

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