Chlorine evolution electrode, its preparation method and application

Abstract

The application relates to a chlorine evolution electrode and a preparation method and application thereof, the preparation method of the chlorine evolution electrode comprises the following steps: (1) carrying out an electrodeposition reaction on a titanium substrate and an electrolyte to form a cobalt hydroxide nanosheet array coating on the titanium substrate, so as to obtain a first electrode; the electrolyte comprises a cobalt salt and an ammonium salt; (2) first carrying out first calcination on the first electrode, then carrying out second calcination on the product obtained through the first calcination, so as to form a cobalt monoxide coating on the titanium substrate, and obtain a chlorine evolution electrode. The preparation method provided by the application is prepared through specific electrodeposition reaction and twice calcination processes, and a chlorine evolution electrode with high selectivity and high activity under the conditions of wide pH and low chloride ion concentration is prepared.

Description

Technical Field

[0001] This invention relates to the fields of water treatment technology and environmental functional materials technology, and in particular to a chlorine-electrode electrode, its preparation method and application. Background Technology

[0002] In ion-adsorption rare earth deposits, most rare earth elements are adsorbed in the clay minerals in the form of cations and are easily extracted by electrolyte leaching and desorption. The development of ion-adsorption rare earth resources usually involves injecting ammonium sulfate into the deposit as a leaching agent for chemical leaching and enrichment. In the leaching and extraction of rare earths, after most of the injected ammonium sulfate leaching agent is recovered with the rare earth mother liquor, a large amount still remains in the deposit soil.

[0003] Currently, rare earth wastewater treatment methods are mainly divided into three categories: biological methods, physical methods, and chemical methods. Biological methods are primarily used to remove ammonia nitrogen and small amounts of organic matter from wastewater. Common processes include nitrification-denitrification and anaerobic ammonia oxidation. These methods utilize the metabolic activity of microorganisms to convert pollutants into harmless substances. The advantages of biological methods are low energy consumption, low cost, high efficiency, and ease of operation. However, their disadvantages include long treatment cycles, high water quality requirements, and the need for continuous replenishment of organic carbon sources, increasing treatment costs. Physical methods transfer pollutants from water to other media through coagulation, adsorption, filtration, flotation, and centrifugation. These methods typically require subsequent treatment to completely remove pollutants. Common physical methods include adsorption, membrane separation, and ion exchange. However, these methods suffer from secondary pollution problems such as adsorbent regeneration, membrane fouling, and treatment of regenerated ion exchange resins. Chemical methods eliminate pollutants through chemical reactions, exhibiting high removal rates and strong environmental adaptability. These methods mainly include photocatalysis and electrochemical methods. In particular, electrocatalytic oxidation can use catalytic electrodes to generate strong oxidants to remove pollutants. It has the advantages of simple operation, strong environmental adaptability, and no secondary pollution, making it a promising green wastewater treatment technology.

[0004] The electrochemical chlorine evolution reaction (CER) is an important electrochemical reaction widely used in chlor-alkali electrolysis to generate ClO. - Cl2-mediated electrosynthesis. The indirect oxidation process of activated chlorine depends on the hypochlorous acid generated by the reaction involving chloride ions. Rare earth ammonia nitrogen wastewater usually contains salts, therefore, the activated chlorine-mediated ammonia nitrogen removal process has good application prospects.

[0005] Commercially used chlorine evolution electrodes (DSA anodes) are composed of mixed oxides of noble metals Ru and Ir, exhibiting high electrochemical chlorine evolution reaction (CER) activity. For example, prior art CN119287445A discloses a ruthenium-iridium composite electrode prepared by an electrochemical co-deposition method, its preparation method, and its application. The preparation of the ruthenium-iridium composite electrode includes: 1) using a titanium sheet as the anode and a platinum electrode or graphite as the cathode, placed in an atmosphere containing F... -The process involves: 1) anodizing the sample in an aqueous solution; 2) heat-treating the anodized sample in a tube furnace under argon or nitrogen atmosphere to obtain anatase TiO2 nanotubes; 3) using the TiO2 nanotubes as the cathode, co-depositing Ru and Ir nanocrystals in an aqueous solution containing Ru salt, Ir salt, NaNO3, and a small amount of SbCl3 under controlled current; and 4) fully oxidizing the sample with deposited Ru and Ir nanocrystals at a certain temperature to obtain a ruthenium-iridium composite metal oxide electrode. The ruthenium-iridium composite metal oxide electrode prepared by this prior art exhibits high electrocatalytic activity for chlorine evolution and a long service life.

[0006] However, while noble metal catalysts exhibit high CER activity, they also possess high oxygen evolution reaction (OER) activity and low CER selectivity in electrolytes with low chloride ion concentrations. To achieve high CER selectivity, CER typically proceeds at low pH levels. Researchers have also developed chloride evolution electrodes constructed with non-noble metal catalysts; however, these electrodes suffer from low reactivity, requiring higher potentials to drive CER. The reactivity and selectivity of catalytic electrodes limit the development of electrochemical degradation of ammonia nitrogen.

[0007] Therefore, how to develop a chlorine evolution electrode that still exhibits high selectivity and high activity under wide pH and low chloride ion concentration conditions has become an urgent problem to be solved. Summary of the Invention

[0008] To address the aforementioned technical problems, the present invention aims to provide a chlorine evolution electrode, its preparation method, and its applications. The preparation method provided by the present invention, through a specific electrodeposition reaction and a two-stage calcination process, yields a chlorine evolution electrode that maintains high selectivity and high activity under wide pH and low chloride ion concentration conditions.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a method for preparing a chlorine evolution electrode, the method comprising the following steps:

[0011] (1) A titanium substrate is subjected to an electrodeposition reaction with an electrolyte to form a cobalt hydroxide nanosheet array coating on the titanium substrate, thereby obtaining a first electrode; the electrolyte includes cobalt salt and ammonium salt;

[0012] (2) The first electrode is first calcined, and then the product obtained from the first calcination is calcined a second time to form a cobalt suboxide coating on the titanium substrate to obtain the chlorine-electrode.

[0013] The method for preparing the chlorine evolution electrode provided by this invention employs an electrodeposition reaction to load cobalt hydroxide onto a high-purity titanium substrate. Introducing ammonium salts into the electrolyte of the electrodeposition reaction effectively controls the deposition rate and morphology of cobalt-containing compounds on the titanium substrate, forming a well-morphologically sound and uniformly deposited cobalt hydroxide nanosheet array coating on the titanium substrate surface, and making the coating on the substrate surface more stable and robust. Combined with a two-stage calcination process, in the first calcination, the cobalt hydroxide nanosheet array coating on the titanium substrate surface is converted into a cobalt tetroxide nanosheet array coating. In the second calcination, the cobalt tetroxide nanosheet array coating is further converted into a cobalt suboxide coating, resulting in a chlorine evolution electrode with high active area, good coating morphology, and higher reactivity and chlorine evolution selectivity.

[0014] The preparation method employed in this invention improves the dispersion of the nanoparticles formed on the titanium substrate surface, effectively increasing the active area of ​​the chlorine evolution electrode and promoting the exposure of more reactive sites on the electrode surface. The combined effect of the morphology and the high activity of cobalt oxide itself provides the chlorine evolution electrode with high reactivity and selectivity. Furthermore, the resulting chlorine evolution electrode exhibits superior kinetic performance and low charge migration impedance, achieving high chlorine evolution current efficiency across low chloride ion concentrations and a wide pH range. The raw materials and processes used in this invention are inexpensive, and the preparation process eliminates the use of hazardous gases such as hydrogen, thus improving the safety of the chlorine evolution electrode preparation process.

[0015] Preferably, the titanium substrate is pretreated before the electrodeposition reaction.

[0016] Preferably, the pretreatment of the titanium substrate includes immersing the titanium substrate in an acidic solution to obtain a pretreated titanium substrate.

[0017] This invention uses an acidic solution to pretreat the titanium substrate and etch the surface of the titanium substrate, which is beneficial to form a strong cobalt hydroxide nanosheet coating on the surface of the titanium substrate. This allows for the formation of a highly dispersed and uniform cobalt suboxide coating on the surface of the titanium substrate by combining a two-stage calcination process, effectively increasing the active area of ​​the obtained chlorine evolution electrode and further improving the activity and selectivity of the chlorine evolution electrode.

[0018] Preferably, the acidic solution includes an oxalic acid solution.

[0019] Preferably, the mass concentration of the acidic solution is 1~5wt%, for example 1.0wt%, 1.5wt%, 2.0wt%, 2.5wt%, 3.0wt%, 3.5wt%, 4.0wt%, 4.5wt%, or 5.0wt%.

[0020] Preferably, the soaking temperature is 80~100℃, such as 80℃, 82℃, 84℃, 86℃, 88℃, 90℃, 92℃, 94℃, 96℃, 98℃ or 100℃.

[0021] Preferably, the soaking temperature is 1~3h, for example 1.0h, 1.2h, 1.4h, 1.6h, 1.8h, 2.0h, 2.2h, 2.4h, 2.6h, 2.8h or 3.0h.

[0022] Preferably, after the titanium substrate is soaked in an acidic solution, the treated titanium substrate is washed and dried to obtain a pretreated titanium substrate.

[0023] Preferably, the washing reagent includes deionized water.

[0024] Preferably, during the electrodeposition reaction, the pretreated titanium substrate is used as the cathode and the counter electrode is used as the anode.

[0025] Preferably, the counter electrode comprises either a platinum sheet or a high-purity titanium sheet.

[0026] Preferably, the purity of the high-purity titanium sheet is 99.99% or higher, such as 99.990%, 99.991%, 99.992%, 99.993%, 99.994%, 99.995%, 99.996%, 99.997%, 99.998%, or 99.999%.

[0027] Preferably, the pretreated titanium substrate is used as the cathode, the counter electrode as the anode, and the current density of the electrodeposition reaction is 10~30 mA / cm². 2 For example, 30mA / cm 2 28mA / cm 2 26mA / cm 2 24mA / cm 2 22mA / cm 2 20mA / cm 2 18mA / cm 2 16mA / cm 2 14mA / cm 2 12mA / cm 2 or 10mA / cm 2 wait.

[0028] Preferably, the cobalt salt includes any one or a combination of at least two of cobalt nitrate, cobalt sulfate, cobalt chloride, or cobalt bromide.

[0029] Preferably, the ammonium salt includes any one or a combination of at least two of ammonium chloride, ammonium fluoride, or ammonium sulfate.

[0030] Preferably, in the electrolyte, the concentration of cobalt ions in the cobalt salt is 0.001~0.500 mol / L, for example, 0.001 mol / L, 0.010 mol / L, 0.050 mol / L, 0.100 mol / L, 0.150 mol / L, 0.200 mol / L, 0.250 mol / L, 0.300 mol / L, 0.350 mol / L, 0.400 mol / L, 0.450 mol / L, or 0.500 mol / L.

[0031] Preferably, in the electrolyte, the concentration of ammonium ions in the ammonium salt is 0.10~0.50 mol / L, for example, 0.10 mol / L, 0.15 mol / L, 0.20 mol / L, 0.25 mol / L, 0.30 mol / L, 0.35 mol / L, 0.40 mol / L, 0.45 mol / L, or 0.50 mol / L.

[0032] Preferably, the temperature of the electrodeposition reaction is 20~40℃, such as 20℃, 22℃, 24℃, 26℃, 28℃, 30℃, 32℃, 34℃, 36℃, 38℃ or 40℃.

[0033] Preferably, the electrodeposition reaction time is 200~400s, such as 200s, 220s, 240s, 260s, 280s, 300s, 320s, 340s, 360s, 380s or 400s.

[0034] Preferably, after the electrodeposition reaction, the electrode obtained by the electrodeposition reaction is dried.

[0035] Preferably, the drying temperature is 30~100℃, such as 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, 90℃ or 100℃.

[0036] Preferably, the drying time is 1 to 10 hours, such as 1 hour, 2 hours, 4 hours, 6 hours, 8 hours, or 10 hours.

[0037] Preferably, the first electrode is subjected to a first calcination to form a cobalt tetroxide nanosheet array coating on the titanium substrate.

[0038] Preferably, the temperature of the first calcination is 300~400℃, such as 300℃, 320℃, 340℃, 360℃, 380℃, 400℃, 420℃, 420℃, 440℃, 460℃, 480℃ or 500℃.

[0039] Preferably, the heating rate of the first calcination is 3~5℃ / min, for example 3℃ / min, 4℃ / min or 5℃ / min.

[0040] Preferably, the first calcination time is 1 to 3 hours, such as 1.0 hour, 1.5 hours, 2.0 hours, 2.5 hours or 3 hours.

[0041] Preferably, the atmosphere for the first calcination is an air atmosphere.

[0042] Preferably, the second calcination temperature is 500~800℃, for example 500℃, 550℃, 600℃, 650℃, 700℃, 750℃ or 800℃.

[0043] Preferably, the heating rate of the second calcination is 3~5℃ / min, for example 3℃ / min, 4℃ / min or 5℃ / min.

[0044] Preferably, the second calcination time is 1 to 2 hours, such as 1.0 hour, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours, or 2.0 hours.

[0045] Preferably, the atmosphere for the second calcination is an argon atmosphere.

[0046] Preferably, the purity of the argon atmosphere is 99.99% or higher, such as 99.99%, 99.999%, or 99.9999%.

[0047] As a preferred technical method of the present invention, the preparation method of the chlorine evolution electrode includes the following steps:

[0048] S1. Immerse the titanium substrate in an acidic solution with a mass concentration of 1~5wt% and soak it at a temperature of 80~100℃ for 1~3 hours. After washing the treated titanium substrate, it is then dried to obtain a pretreated titanium substrate.

[0049] S2. Using the pretreated titanium substrate as the cathode and the counter electrode as the anode, an electrodeposition reaction is carried out in an electrolyte. The current density of the electrodeposition reaction is 10~30 mA / cm². 2 The electrode is subjected to a second drying process at a temperature of 20-40°C for 200-400 seconds. The electrode obtained after the electrodeposition reaction is then subjected to a second drying process at a temperature of 30-100°C for 1-10 hours. This process forms a cobalt hydroxide nanosheet array coating on the titanium substrate, resulting in the first electrode. The electrolyte comprises cobalt salt and ammonium salt. In the electrolyte, the concentration of cobalt ions in the cobalt salt is 0.001-0.500 mol / L, and the concentration of ammonium ions in the ammonium salt is 0.1-0.5 mol / L.

[0050] S3. The first electrode is placed in an air atmosphere and calcined at 300~400℃ for 1~3h. The heating rate of the first calcination is 3~5℃ / min. A cobalt tetroxide nanosheet array coating is formed on the titanium substrate to obtain the second electrode.

[0051] S4. The second electrode is placed in an argon atmosphere and subjected to a second calcination at 500~800℃ for 1~2h. The heating rate of the second calcination is 3~5℃ / min, and a cobalt suboxide coating is formed on the titanium substrate to obtain the chlorine evolution electrode.

[0052] In a second aspect, the present invention provides a chlorine evolution electrode, which is prepared by the preparation method described in the first aspect; the chlorine evolution electrode includes a titanium substrate and a cobalt suboxide coating on the surface of the titanium substrate.

[0053] The chlorine evolution electrode provided by this invention is prepared by a specific preparation method. The cobalt oxide coating in the chlorine evolution electrode has good dispersion and high uniformity on the titanium substrate surface and the coating is firmly attached to the substrate surface. The coating on the surface of the chlorine evolution electrode is more uniform and has a high active area, which can expose more reactive sites on the electrode surface. In addition, it has excellent kinetic performance and low charge migration impedance, thus maintaining high selectivity and high activity under wide pH and low chloride ion concentration conditions.

[0054] Thirdly, the present invention provides an application of the chlorine-electrode as described in the second aspect, wherein the chlorine-electrode is applied to the degradation of ammonia nitrogen in rare earth wastewater.

[0055] The highly selective and highly active chlorine-electrode provided by this invention has excellent application effects in the ammonia nitrogen degradation process of rare earth wastewater, and can effectively shorten the ammonia nitrogen degradation time and improve the ammonia nitrogen degradation efficiency.

[0056] Compared with the prior art, the present invention has at least the following beneficial effects:

[0057] (1) The preparation method provided by this invention employs an electrodeposition reaction combined with a two-stage calcination process, which can improve the dispersion of the microstructure of nanoparticles formed on the titanium substrate surface, effectively increase the active area of ​​the chlorine evolution electrode, and promote the exposure of more reactive sites on the surface of the chlorine evolution electrode. Under the combined effect of morphology and the high activity of cobalt oxide itself, the chlorine evolution electrode is provided with high reactivity and selectivity. Furthermore, the obtained chlorine evolution electrode also has excellent kinetic performance and low charge migration impedance, and can obtain high chlorine evolution current efficiency in both low chloride ion concentration and wide pH range. The raw materials and processes used in this invention are inexpensive, and the use of dangerous gases such as hydrogen is omitted during the preparation process, thus improving the safety of the chlorine evolution electrode preparation process.

[0058] (2) The chlorine evolution electrode provided by the present invention is prepared by a specific preparation method. The cobalt oxide coating in the chlorine evolution electrode has good dispersion and high uniformity on the titanium substrate surface and the coating is firmly attached to the substrate surface. The coating on the surface of the chlorine evolution electrode is more uniform and has a high active area, which can expose more reactive sites on the electrode surface. In addition, it has excellent kinetic performance and low charge migration impedance, so it still has high selectivity and high activity under wide pH and low chloride ion concentration conditions.

[0059] (3) The highly selective and highly active chlorine-electrode provided by the present invention has excellent application effects in the ammonia nitrogen degradation process of rare earth wastewater, and can effectively shorten the ammonia nitrogen degradation time of rare earth wastewater and improve the efficiency of ammonia nitrogen degradation. Attached Figure Description

[0060] Figure 1 These are X-ray diffraction patterns of the coating in the second electrode and the coating in the chlorine evolution electrode obtained by the preparation method provided in Embodiment 1 of the present invention.

[0061] Figure 2 This is a scanning electron microscope image of the chlorine-electron electrode obtained by the preparation method provided in Example 1 of this invention.

[0062] Figure 3 The chlorine evolution electrode prepared by the preparation method provided in Example 1 of this invention is used in a 5 mol / L NaCl electrolyte and at a 10 mA / cm² temperature. 2 Voltage-time curves under current density conditions.

[0063] Figure 4 The linear sweep voltammetric curves are those of the chlorine evolution electrode obtained in Example 1 of the present invention, the chlorine evolution electrode obtained in Comparative Example 2, and the commercial DSA electrode provided in Comparative Example 4. Detailed Implementation

[0064] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0065] The titanium plates used in the following examples and comparative examples have a purity of 99.99% and a thickness of 0.5 mm, and the platinum sheets have a purity of 99.99%.

[0066] The argon atmosphere used in the following examples has a purity of 99.99%.

[0067] Example 1

[0068] This embodiment provides a method for preparing a chlorine evolution electrode, including the following steps:

[0069] S1. Immerse the titanium plate in a 5wt% oxalic acid solution at 95℃ for 2 hours. Wash the treated titanium plate with deionized water and then perform a first drying to obtain a pretreated titanium plate.

[0070] S2. Using the pretreated titanium plate obtained in step S1 as the cathode and a platinum sheet as the anode, an electrodeposition reaction is carried out in an electrolyte. The current density of the electrodeposition reaction is 20 mA / cm². 2 The temperature was set at 30℃ for 300s; then, the electrode obtained after the electrodeposition reaction was dried at 60℃ for 2h to form a cobalt hydroxide nanosheet array coating on the titanium plate, thus obtaining the first electrode; the electrolyte used in the electrodeposition reaction was a mixed solution composed of cobalt nitrate and ammonium chloride, in which the concentration of cobalt ions in cobalt nitrate was 0.05mol / L and the concentration of ammonium ions in ammonium chloride was 0.31mol / L.

[0071] S3. The first electrode obtained in step S2 is placed in an air atmosphere and calcined at 350°C for 2 hours. The heating rate of the first calcination is 5°C / min. A cobalt tetroxide nanosheet array coating is formed on the titanium plate to obtain the second electrode.

[0072] S4. The second electrode obtained in step S3 is placed in an argon atmosphere and calcined at 550°C for 2 hours. The heating rate of the second calcination is 5°C / min. A cobalt suboxide coating is formed on the titanium plate to obtain the chlorine-electrode.

[0073] Example 2

[0074] This embodiment provides a method for preparing a chlorine evolution electrode, including the following steps:

[0075] S1. Immerse the titanium plate in a 1 wt% oxalic acid solution at 80°C for 3 hours. Wash the treated titanium plate with deionized water and then perform a first drying process to obtain a pretreated titanium plate.

[0076] S2. Using the pretreated titanium plate obtained in step S1 as the cathode and a platinum sheet as the anode, an electrodeposition reaction is carried out in an electrolyte. The current density of the electrodeposition reaction is 30 mA / cm². 2 The temperature was set at 20℃ for 200s; then, the electrode obtained after the electrodeposition reaction was dried at 100℃ for 1h to form a cobalt hydroxide nanosheet array coating on the titanium plate, thus obtaining the first electrode; the electrolyte used in the electrodeposition reaction was a mixed solution composed of cobalt nitrate and ammonium chloride. In the electrolyte, the concentration of cobalt ions in cobalt nitrate was 0.001mol / L, and the concentration of ammonium ions in ammonium chloride was 0.1mol / L.

[0077] S3. The first electrode obtained in step S2 is placed in an air atmosphere and calcined at 300°C for 3 hours. The heating rate of the first calcination is 3°C / min. A cobalt tetroxide nanosheet array coating is formed on the titanium plate to obtain the second electrode.

[0078] S4. The second electrode obtained in step S3 is placed in an argon atmosphere and calcined at 500°C for 2 hours. The heating rate of the second calcination is 3°C / min. A cobalt suboxide coating is formed on the titanium plate to obtain a chlorine-electrode electrode, which includes a titanium plate and a cobalt suboxide coating on the surface of the titanium plate.

[0079] Example 3

[0080] This embodiment provides a method for preparing a chlorine evolution electrode, including the following steps:

[0081] S1. Immerse the titanium plate in a 3wt% oxalic acid solution at 100℃ for 1 hour. Wash the treated titanium plate with deionized water and then perform a first drying to obtain a pretreated titanium plate.

[0082] S2. Using the pretreated titanium plate obtained in step S1 as the cathode and a platinum sheet as the anode, an electrodeposition reaction is carried out in an electrolyte. The current density of the electrodeposition reaction is 10 mA / cm². 2 The temperature was set at 40℃ for 400s. Then, the electrode obtained after the electrodeposition reaction was dried at 50℃ for 10h to form a cobalt hydroxide nanosheet array coating on the titanium plate, thus obtaining the first electrode. The electrolyte used in the electrodeposition reaction was a mixed solution composed of cobalt nitrate and ammonium chloride. In the electrolyte, the concentration of cobalt ions in cobalt nitrate was 0.5mol / L, and the concentration of ammonium ions in ammonium chloride was 0.5mol / L.

[0083] S3. The first electrode obtained in step S2 is placed in an air atmosphere and calcined at 400°C for 1 hour. The heating rate of the first calcination is 5°C / min. A cobalt tetroxide nanosheet array coating is formed on the titanium plate to obtain the second electrode.

[0084] S4. The second electrode obtained in step S3 is placed in an argon atmosphere and calcined at 800°C for 1 hour. The heating rate of the second calcination is 5°C / min. A cobalt suboxide coating is formed on the titanium plate to obtain the chlorine-electrode.

[0085] Example 4

[0086] The only difference between this embodiment and Embodiment 1 is that the second calcination temperature in step S4 is 450°C. All other aspects are the same as in Embodiment 1.

[0087] Example 5

[0088] The only difference between this embodiment and Embodiment 1 is that the second calcination temperature in step S4 is 850°C. All other aspects are the same as in Embodiment 1.

[0089] Example 6

[0090] The only difference between this embodiment and Embodiment 1 is that the pretreatment process of the titanium plate with oxalic acid solution in step S1 is omitted. All other contents are the same as in Embodiment 1.

[0091] Example 7

[0092] The only difference between this embodiment and Embodiment 1 is that the current density of the electrodeposition reaction in step S2 is 5 mA / cm². 2 The rest of the content is the same as in Example 1.

[0093] Example 8

[0094] The only difference between this embodiment and Embodiment 1 is that the current density of the electrodeposition reaction in step S2 is 35 mA / cm². 2 The rest of the content is the same as in Example 1.

[0095] Example 9

[0096] The only difference between this embodiment and Example 1 is that the concentration of cobalt ions in cobalt nitrate in the electrolyte used for the electrodeposition reaction in step S2 is 1 mol / L. All other aspects are the same as in Example 1.

[0097] Example 10

[0098] The only difference between this embodiment and Example 1 is that the concentration of ammonium ions in the ammonium chloride electrolyte used in the electrodeposition reaction of step S2 is 0.05 mol / L. All other aspects are the same as in Example 1.

[0099] Example 11

[0100] The only difference between this embodiment and Example 1 is that the concentration of ammonium ions in the ammonium chloride electrolyte used in the electrodeposition reaction of step S2 is 1 mol / L. All other aspects are the same as in Example 1.

[0101] Example 12

[0102] The only difference between this embodiment and Embodiment 1 is that the first calcination temperature in step S3 is 250°C. All other aspects are the same as in Embodiment 1.

[0103] Example 13

[0104] The only difference between this embodiment and Embodiment 1 is that the first calcination temperature in step S3 is 450°C. All other aspects are the same as in Embodiment 1.

[0105] Comparative Example 1

[0106] The only difference between this comparative example and Example 1 is that in the electrodeposition reaction of step S2, the addition of ammonium chloride is omitted, and only cobalt nitrate with a cobalt ion concentration of 0.05 mol / L is used as the electrolyte. All other contents are the same as in Example 1.

[0107] Comparative Example 2

[0108] The only difference between this comparative example and Example 1 is that the preparation method of the chlorine evolution electrode provided in this comparative example omits all processes in step S4, and directly uses the titanium plate obtained in step S3 and the second electrode with the cobalt tetroxide nanosheet coating on the titanium plate as the chlorine evolution electrode. All other contents are the same as in Example 1.

[0109] Comparative Example 3

[0110] The only difference between this comparative example and Example 1 is that the preparation method of the chlorine evolution electrode provided in this comparative example omits all the processes in step S3, and directly places the first electrode obtained in step S2 in an argon atmosphere for calcination at 550°C for 2 hours. All other contents are the same as in Example 1.

[0111] Comparative Example 4

[0112] The only difference between this comparative example and Example 1 is that the chlorine-evolving electrode provided in this comparative example is a commercial DSA anode, specifically composed of a titanium plate and a coating disposed on the titanium plate. The coating specifically comprises oxides of ruthenium and iridium, with a molar ratio of ruthenium to iridium of 15:5. Correspondingly, the commercial DSA anode was purchased from Suzhou Shuertai Industrial Technology Co., Ltd. All other contents are the same as in Example 1.

[0113] The chlorine evolution electrodes prepared by the methods provided in Examples 1-13 and Comparative Examples 1-4 were placed in a 5 mol / L NaCl electrolyte and energized at different current densities for 30 min. The chlorine evolution Faraday efficiency was then tested. The pH of the electrolyte before the reaction was 6, and the pH after the reaction was 9.5. The test results are shown in Table 1.

[0114] Table 1

[0115]

[0116] The chlorine evolution electrodes prepared by the methods provided in Examples 1-13 and Comparative Examples 1-4 were placed in NaCl electrolytes of different concentrations at 10 mA / cm². 2 After energizing for 30 minutes, the chlorine evolution Faraday efficiency was tested. The pH of the NaCl electrolyte before the reaction was 6, and the pH after the reaction was 9.5. The test results are shown in Table 2.

[0117] Table 2

[0118]

[0119] The oxygen evolution electrodes prepared by the methods provided in Examples 1-13 and Comparative Examples 1-4 were subjected to 60 mL of different ammonia nitrogen simulation solutions (0.05 mol / L NaCl + 50 mg NH4). + -N and 0.5 mol / L NaCl + 50 mg NH4 + -N) with 10mA / cm 2 When ammonia nitrogen was degraded using current density, the time required for complete removal of ammonia nitrogen from the solution (i.e., the ammonia nitrogen concentration in the ammonia nitrogen simulation solution was below 0.5 ppb) was recorded. The test results are shown in Table 3.

[0120] Table 3

[0121]

[0122] The chlorine evolution electrodes prepared by the methods provided in Examples 1-13 and Comparative Examples 1-4 were subjected to electrochemical impedance spectroscopy and double-layer capacitance tests in 5 mol / L NaCl, where the double-layer capacitance was used to evaluate the reactive surface area. The test results are shown in Table 4 (where Rs is the solution resistance, Rct is the charge migration impedance, and C...). dl (This is a double-layer capacitor).

[0123] Table 4

[0124]

[0125] The test results show that:

[0126] (1) As can be seen from Examples 1 to 3, the preparation method provided by the present invention prepares a chlorine evolution electrode that still has high selectivity and high activity under wide pH and low chloride ion concentration conditions through a specific electrodeposition reaction and a two-stage calcination process.

[0127] Figure 1 X-ray diffraction patterns of the coating in the second electrode and the coating in the chlorine evolution electrode obtained by the preparation method provided in Example 1 are given. As can be seen from the figure, the preparation method provided in Example 1 successfully prepared the cobalt tetroxide nanosheet array coating on the titanium plate in step S3, and in step S4, the cobalt tetroxide nanosheet array coating on the titanium plate was completely converted into a cobalt suboxide coating.

[0128] Figure 2 Scanning electron microscope images of the chlorine evolution electrode obtained by the preparation method provided in Example 1 are given. As can be seen from the figure, the cobalt oxide in the chlorine evolution electrode prepared in Example 1 has good dispersion and high uniformity, and excellent morphology, which is dispersed nanoparticles.

[0129] Figure 3 The chlorine-evolving anode prepared by the method provided in Example 1 has a performance of 10 mA / cm. 2 The voltage-time curves under current density conditions show that the chlorine evolution electrode prepared by the method provided in Example 1 performs well in 5 mol / L NaCl electrolyte and at 10 mA / cm². 2 Under current density conditions, it can operate stably for 564 hours.

[0130] (2) By comparing Example 1 and Examples 4-5, it can be seen that if the second calcination temperature is too low, the electrode catalytic activity will be low; if the second calcination temperature is too high, the coating will peel off, thereby causing the electrode performance to decline.

[0131] (3) By comparing Example 1 and Example 6, it can be seen that if the pretreatment process of titanium plate with oxalic acid solution is omitted in the present invention, the dispersion and uniformity of the cobalt oxide coating formed on the surface of titanium plate will be poor, thereby affecting the activity and selectivity of the chlorine electrode.

[0132] (4) By comparing Example 1 and Example 7-8, it can be seen that if the current density is too low, the coating load will be low; if the current density is too high, the coating will peel off. Both will lead to a decrease in the performance of the obtained chlorine electrolysis.

[0133] (5) A comparison of Examples 1 and 9-11 shows that if the concentration of cobalt salt in the electrolyte is too high, the coating will peel off. If the concentration of ammonium salt in the electrolyte is too low, the coating will peel off; if the concentration of ammonium salt is too high, the coating will be difficult to form. Therefore, it can be seen that if the concentration of cobalt salt or ammonium salt in the electrolyte is too high or too low, the performance of the obtained chlorine-electrode electrode will deteriorate.

[0134] (6) By comparing Example 1 and Example 12-13, it can be seen that if the first calcination temperature is too low, the electrode activity will be low; if the first calcination temperature is too high, the coating will peel off, thereby resulting in poor activity and selectivity of the obtained electrode.

[0135] (7) By comparing Example 1 and Comparative Example 1, it can be seen that if the ammonium salt in the electrolyte used in the electroprecipitation reaction is omitted in this invention, the growth rate of cobalt-containing compounds on the titanium plate will be too fast. In the resulting chlorine-electrode, the dispersion, uniformity and stability of the coating on the titanium plate surface are poor, the coating is not firmly in contact with the titanium plate surface, and the activity and selectivity of the chlorine-electrode will be significantly worse.

[0136] (8) By comparing Example 1 and Comparative Example 2, it can be seen that if all the processes of step S4 are omitted in this invention and the electrode of the cobalt tetroxide nanosheet on the titanium plate is directly used as the chlorine evolution electrode, the activity of the chlorine evolution electrode will be significantly insufficient, so that the chlorine evolution electrode cannot maintain a high chlorine evolution Faraday effect in both low chloride ion concentration and wide pH range, and the degradation rate of ammonia nitrogen solutions of different concentrations will decrease.

[0137] (9) By comparing Example 1 and Comparative Example 3, it can be seen that if the entire process of step S3 is omitted and the first electrode obtained in step S2 is directly calcined at 550°C for 2 hours under an argon atmosphere, the activity of its chlorine evolution electrode will be significantly reduced.

[0138] (10) By comparing Example 1 and Comparative Example 4, it can be seen that, compared with commercial DSA electrodes, the chloride evolution electrode prepared by the preparation method provided by the present invention still has high chloride evolution Faraday efficiency under wide pH and low chloride ion concentration conditions, and has high degradation efficiency in ammonia nitrogen solutions of different concentrations.

[0139] Figure 4 Linear sweep voltammetric curves of the chlorine evolution electrode obtained by the preparation method provided in Example 1, the chlorine evolution electrode obtained in Comparative Example 2, and the commercial DSA electrode provided in Comparative Example 3 are given. As can be seen from the figure, the chlorine evolution activity of the chlorine evolution electrode with a cobalt suboxide coating on a titanium plate obtained by the preparation method provided by the present invention is significantly higher than that of the commercial DSA electrode and the electrode composed of a titanium plate and a cobalt tetroxide nanosheet coating on the titanium plate. The chlorine evolution potential is lower than that of the commercial DSA electrode and the electrode composed of a titanium plate and a cobalt tetroxide nanosheet coating on the titanium plate.

[0140] In summary, the preparation method provided by this invention employs an electrodeposition reaction combined with a two-stage calcination process, which improves the dispersion of the nanoparticles formed on the titanium substrate surface, effectively increasing the active area of ​​the chlorine evolution electrode and promoting the exposure of more reactive sites on the electrode surface. The morphology and the high reactivity of cobalt oxide itself jointly contribute to the reactivity and selectivity of the chlorine evolution electrode. Furthermore, the obtained chlorine evolution electrode exhibits superior kinetic performance and low charge migration impedance, achieving high chlorine evolution current efficiency across low chloride ion concentrations and a wide pH range. The raw materials and processes used in this invention are inexpensive, and the preparation process eliminates the use of hazardous gases such as hydrogen, thus improving the safety of the chlorine evolution electrode preparation process.

[0141] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a chlorine evolution electrode, characterized in that, The method for preparing the chlorine evolution electrode includes the following steps: (1) A titanium substrate is subjected to an electrodeposition reaction with an electrolyte to form a cobalt hydroxide nanosheet array coating on the titanium substrate, thereby obtaining a first electrode; the electrolyte includes cobalt salt and ammonium salt; (2) The first electrode is first calcined, and then the product obtained from the first calcination is calcined a second time to form a cobalt suboxide coating on the titanium substrate to obtain the chlorine evolution electrode; The atmosphere for the first calcination is air; the atmosphere for the second calcination is argon.

2. The preparation method according to claim 1, characterized in that, The titanium substrate is pretreated before the electrodeposition reaction.

3. The preparation method according to claim 2, characterized in that, The pretreatment of the titanium substrate includes immersing the titanium substrate in an acidic solution to obtain a pretreated titanium substrate.

4. The preparation method according to claim 3, characterized in that, The acidic solution includes oxalic acid solution.

5. The preparation method according to claim 3, characterized in that, The mass concentration of the acidic solution is 1~5wt%.

6. The preparation method according to claim 3, characterized in that, The soaking temperature is 80~100℃.

7. The preparation method according to claim 3, characterized in that, The soaking time is 1 to 3 hours.

8. The preparation method according to claim 2, characterized in that, During the electrodeposition reaction, the pretreated titanium substrate is used as the cathode and the counter electrode is used as the anode.

9. The preparation method according to claim 8, characterized in that, The counter electrode comprises either a platinum sheet or a high-purity titanium sheet.

10. The preparation method according to claim 8, characterized in that, Using the pretreated titanium substrate as the cathode and the counter electrode as the anode, the current density of the electrodeposition reaction is 10~30 mA / cm². 2 .

11. The preparation method according to claim 1, characterized in that, The cobalt salt includes any one or a combination of at least two of cobalt nitrate, cobalt sulfate, cobalt chloride, or cobalt bromide.

12. The preparation method according to claim 1, characterized in that, The ammonium salt includes any one or a combination of at least two of ammonium chloride, ammonium fluoride, or ammonium sulfate.

13. The preparation method according to claim 1, characterized in that, In the electrolyte, the concentration of cobalt ions in the cobalt salt is 0.001~0.500 mol / L.

14. The preparation method according to claim 1, characterized in that, In the electrolyte, the concentration of ammonium ions in the ammonium salt is 0.1~0.5 mol / L.

15. The preparation method according to claim 1, characterized in that, The electrodeposition reaction is carried out at a temperature of 20~40℃.

16. The preparation method according to claim 1, characterized in that, The electrodeposition reaction takes 200-400 seconds.

17. The preparation method according to claim 1, characterized in that, After the electrodeposition reaction, the electrode obtained by the electrodeposition reaction is dried.

18. The preparation method according to claim 17, characterized in that, The drying temperature is 30~100℃.

19. The preparation method according to claim 17, characterized in that, The drying time is 1 to 10 hours.

20. The preparation method according to claim 1, characterized in that, The first electrode is then subjected to a first calcination to form a cobalt tetroxide nanosheet array coating on the titanium substrate.

21. The preparation method according to claim 1, characterized in that, The first calcination temperature is 300~400℃.

22. The preparation method according to claim 1, characterized in that, The heating rate of the first calcination is 3~5℃ / min.

23. The preparation method according to claim 1, characterized in that, The first calcination time is 1 to 3 hours.

24. The preparation method according to claim 1, characterized in that, The second calcination temperature is 500~800℃.

25. The preparation method according to claim 1, characterized in that, The heating rate for the second calcination is 3~5℃ / min.

26. The preparation method according to claim 1, characterized in that, The second calcination time is 1-2 hours.

27. The preparation method according to claim 1, characterized in that, The preparation method includes the following steps: S1. Immerse the titanium substrate in an acidic solution with a mass concentration of 1~5wt% and soak it at a temperature of 80~100℃ for 1~3h. After washing the treated titanium substrate, it is then dried to obtain a pretreated titanium substrate. S2. Using the pretreated titanium substrate as the cathode and the counter electrode as the anode, an electrodeposition reaction is carried out in an electrolyte. The current density of the electrodeposition reaction is 30~10 mA / cm². 2 The electrode is subjected to a second drying process at a temperature of 20-40°C for 200-400 seconds. The electrode is then dried for 1-10 hours at a temperature of 30-100°C to form a cobalt hydroxide nanosheet array coating on the titanium substrate, thus obtaining the first electrode. The electrolyte comprises cobalt salt and ammonium salt. In the electrolyte, the concentration of cobalt ions in the cobalt salt is 0.001-0.500 mol / L, and the concentration of ammonium ions in the ammonium salt is 0.1-0.5 mol / L. S3. The first electrode is placed in an air atmosphere and calcined at 300~400℃ for 1~3h. The heating rate of the first calcination is 3~5℃ / min. A cobalt tetroxide nanosheet array coating is formed on the titanium substrate to obtain the second electrode. S4. The second electrode is placed in an argon atmosphere and subjected to a second calcination at 500~800℃ for 1~2h. The heating rate of the second calcination is 3~5℃ / min, and a cobalt suboxide coating is formed on the titanium substrate to obtain the chlorine evolution electrode.

28. A chlorine evolution electrode, characterized in that, The chlorine evolution electrode is prepared by the preparation method according to any one of claims 1-27; the chlorine evolution electrode includes a titanium substrate and a cobalt suboxide coating on the surface of the titanium substrate.

29. An application of the chlorine evolution electrode according to claim 28, characterized in that, The chlorine-electrode is used for the degradation of ammonia nitrogen in rare earth wastewater.

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