Electrode material and preparation method thereof

Abstract

The present invention provides an electrode material and a preparation method thereof, which belongs to the field of electrolytic cell electrode technology. The preparation method includes the following steps: S1, pre-treating a stainless steel substrate to obtain a pre-treated substrate; S2, sequentially adding chromium chloride, sodium phosphate and sodium molybdate to water and stirring until completely dissolved, then adjusting the pH value to 2.5-3.0 with a hydrochloric acid solution having a mass concentration of 3.2-3.8% to obtain an electroplating solution; S3, using the pre-treated substrate obtained by S1 as a cathode and graphite as an anode, the electroplating solution obtained by S2 is placed and electroplated to obtain composite-coated stainless steel; S4, cleaning and drying the composite-coated stainless steel obtained by S3, to obtain an electrode material. The present invention can effectively improve the cathode's pitting resistance and thereby increase the cathode's service life.

Description

Technical Field

[0001] The invention belongs to the technical field of electrolytic cell electrodes, and particularly relates to an electrode material and a preparation method thereof. Background Art

[0002] In the electrolytic preparation of sodium perchlorate, the cathode material is stainless steel with a chromium oxide coating on the surface, and there is a large amount of ClO3 in the electrolyte. - In order to enhance the conductivity, hydrochloric acid solution is generally added to make the electrolyte acidic.

[0003] In acidic electrolyte, ClO3 - With H + The generated HClO3 acts as a strong oxidant, causing oxidative corrosion of the coating. Due to the micropores, grain boundary defects, and low density of the chromium oxide coating, oxidative corrosion in the micropores of the chromium oxide coating is exacerbated, leading to pitting corrosion. As a result, corrosion products accumulate and induce stress, causing localized damage to the chromium oxide coating, leading to localized warping or flaking of the coating, shortening the cathode's service life. Summary of the Invention

[0004] In order to solve the problems existing in the background technology, the present invention provides an electrode material and a preparation method thereof, which can effectively improve the pitting corrosion resistance of the prepared electrode material (cathode) and thereby increase the service life of the cathode.

[0005] In order to achieve the above objectives, in a first aspect, the present invention provides a method for preparing an electrode material, comprising the following steps:

[0006] S1. Pre-treating a stainless steel substrate to obtain a pre-treated substrate;

[0007] S2. Chromium chloride, sodium phosphate, and sodium molybdate are sequentially added to water and stirred until completely dissolved, and then the pH value is adjusted to 2.5-3.0 with a hydrochloric acid solution having a mass concentration of 3.2-3.8% to obtain an electroplating solution;

[0008] S3, using the pretreated substrate obtained in S1 as a cathode and graphite as an anode, and placing them in the electroplating solution obtained in S2 for electroplating to obtain composite-coated stainless steel;

[0009] S4. Clean and dry the composite-coated stainless steel obtained in S3 to obtain the electrode material.

[0010] Furthermore, in S1, the specific operation of the pretreatment is: firstly, the stainless steel substrate is alkaline-washed with an alkaline solution to remove oil stains on the surface of the stainless steel substrate; and then, the stainless steel substrate is pickled with a mixed acid solution to obtain the pretreated substrate.

[0011] Furthermore, the temperature of alkali washing is 55-62°C, and the temperature of acid washing is 23-26°C.

[0012] Furthermore, the alkali solution is a sodium hydroxide aqueous solution with a concentration of 50±5 g / L.

[0013] Furthermore, in the mixed acid solution, the volume concentration of nitric acid is 10±1%, and the volume concentration of hydrofluoric acid is 2±0.2%.

[0014] Furthermore, in the electroplating solution, the concentration of chromium chloride is 80-85 g / L, the concentration of sodium molybdate is 15-18 g / L, and the concentration of sodium phosphate is 30-35 g / L.

[0015] Furthermore, in S3, the current density is 4-6A / dm 2 , temperature is 45-48℃, and electroplating time is 25-30min.

[0016] Furthermore, in S4, the specific operations of cleaning and drying are: cleaning the composite-coated stainless steel with deionized water for multiple times, and then drying it at a temperature of 50-55° C. for 60-80 minutes.

[0017] In a second aspect, the present invention provides an electrode material prepared by the above-mentioned preparation method.

[0018] This application has the following beneficial effects:

[0019] The present invention adopts an electroplating solution comprising chromium chloride, sodium phosphate and sodium molybdate. On the one hand, the phosphate radical (PO4 3- ) by selectively adsorbing on the cathode surface active sites (such as Cr 3+ enriched area), preferentially occupying the grain boundary growth site, inhibiting the disordered accumulation of chromium oxide crystals, thereby reducing the formation of grain boundary cracks and micropores, and the coating has good density, blocking ClO 3- diffusion channels, thereby improving the cathode's anti-pitting corrosion performance.

[0020] On the other hand, the phosphate radical (PO4 3- ) and the molybdate ion of sodium molybdate (MoO4 2- ) are co-deposited in the coating to form a dense oxide film with a doped Mo-PO composite structure, which significantly reduces the porosity of the coating and synergistically improves the cathode's pitting resistance, thereby achieving the effect of synergistically improving the cathode's service life. DETAILED DESCRIPTION

[0021] The present application is further described in detail below with reference to the embodiments.

[0022] Unless otherwise specified, the raw materials used in the examples and comparative examples of the present application are all commercially available.

[0023] Example 1: This example provides a method for preparing an electrode material, comprising the following steps:

[0024] S1. Pretreat the stainless steel substrate. The specific steps are as follows: first, alkaline wash the stainless steel substrate with alkali solution; then, pickle it with a mixed acid solution to obtain a pretreated substrate. The alkaline solution is a sodium hydroxide aqueous solution with a concentration of 50g / L. The alkaline wash temperature is 60°C, and the stainless steel substrate is soaked in a constant temperature water bath for 30 minutes to remove oil stains from the surface. After the alkaline wash, ultrasonically clean the substrate with 60°C deionized water (20kHz) three times, each for 5 minutes. The mixed acid solution contains 10% nitric acid and 2% hydrofluoric acid by volume, with the remainder being deionized water. The pickle wash temperature is 25°C, and the substrate is soaked in a constant temperature water bath for 15 minutes. After pickling, ultrasonically clean the substrate with 25°C deionized water (20kHz) until neutral (pH test paper), and blow dry with nitrogen.

[0025] S2. Add chromium chloride to deionized water and mechanically stir at 300 rpm for 30 minutes; then add sodium phosphate and mechanically stir at 300 rpm for 20 minutes; then add sodium molybdate and mechanically stir at 300 rpm for 15 minutes until completely dissolved. Then, under continuous stirring, slowly add 3.5% hydrochloric acid solution to adjust the pH to approximately 2.8 to prevent precipitation, thereby obtaining an electroplating solution. The electroplating solution has a chromium chloride concentration of 82 g / L, a sodium molybdate concentration of 16 g / L, and a sodium phosphate concentration of 32 g / L.

[0026] S3, the pretreated substrate obtained in S1 was used as a cathode (size 50×50×1mm, effective area 0.5dm 2 ), a high-purity graphite plate as the anode (purity ≥ 99.9%, size 60×60×5mm), was placed in the electroplating solution obtained from S2 for electroplating treatment, with an electrode spacing of 50mm (fixed by a polytetrafluoroethylene fixture), to obtain a composite coated stainless steel. Specific process parameters: current density 5.0A / dm 2 The plating solution was stirred magnetically at 200 rpm (rotor size Φ15×50 mm).

[0027] S4. Clean and dry the composite-coated stainless steel obtained in S3. Specifically, the composite-coated stainless steel is cleaned three times with deionized water, and then dried in a hot air circulation drying oven at a constant temperature of approximately 52°C for 70 minutes at a wind speed of 1.5 m / s to obtain the electrode material. The specific cleaning procedure is a three-stage countercurrent cleaning: first, primary deionized water (25°C), then secondary deionized water (40°C), and finally, tertiary deionized water (25°C). Each cleaning time is 5 minutes, and the water flow rate is 2 L / min.

[0028] Example 2: This example differs from Example 1 in that: This example provides a method for preparing an electrode material, comprising the following steps:

[0029] S1. Pre-treat the stainless steel substrate by first alkaline-washing the substrate with an alkaline solution to remove surface oil and contamination. Then, pickle the substrate with a mixed acid solution to obtain a pre-treated substrate. The alkaline solution is a sodium hydroxide aqueous solution with a concentration of 45 g / L. The alkaline-washing temperature is 55°C. The mixed acid solution contains 9% nitric acid and 1.8% hydrofluoric acid by volume. The pickling temperature is 23°C.

[0030] S2. Chromium chloride, sodium phosphate, and sodium molybdate are sequentially added to water and stirred until completely dissolved. The pH value is then adjusted to 2.5 with a 3.2% hydrochloric acid solution to obtain an electroplating solution. The electroplating solution has a chromium chloride concentration of 80 g / L, a sodium molybdate concentration of 15 g / L, and a sodium phosphate concentration of 30 g / L.

[0031] S3, the pre-treated substrate obtained in S1 is used as cathode and graphite is used as anode, and is placed in the electroplating solution obtained in S2 for electroplating to obtain composite coated stainless steel. The current density is 5.0A / dm 2 , temperature is 45℃, and electroplating time is 25min.

[0032] S4. Cleaning and drying the composite-coated stainless steel obtained in S3. Specifically, the composite-coated stainless steel is cleaned three times with deionized water, and then dried at 50° C. for 80 minutes to obtain the electrode material.

[0033] Example 3: This example differs from Example 1 in that: This example provides a method for preparing an electrode material, comprising the following steps:

[0034] S1. Pre-treat the stainless steel substrate by first alkaline-washing the substrate with an alkaline solution to remove surface oil and contamination. Then, pickle the substrate with a mixed acid solution to obtain a pre-treated substrate. The alkaline solution is a sodium hydroxide aqueous solution with a concentration of 55 g / L. The alkaline-washing temperature is 62°C. The mixed acid solution contains 11% nitric acid and 2.2% hydrofluoric acid by volume. The pickling temperature is 26°C.

[0035] S2. Chromium chloride, sodium phosphate, and sodium molybdate are sequentially added to water and stirred until completely dissolved. The pH value is then adjusted to 3.0 with a 3.8% hydrochloric acid solution to obtain an electroplating solution. The electroplating solution has a chromium chloride concentration of 85 g / L, a sodium molybdate concentration of 18 g / L, and a sodium phosphate concentration of 35 g / L.

[0036] S3, the pre-treated substrate obtained in S1 is used as cathode and graphite is used as anode, and is placed in the electroplating solution obtained in S2 for electroplating to obtain composite coated stainless steel. The current density is 5.0A / dm 2 , temperature is 48℃, and electroplating time is 30min.

[0037] S4. Cleaning and drying the composite-coated stainless steel obtained in S3. Specifically, the composite-coated stainless steel is cleaned three times with deionized water, and then dried at 55° C. for 60 minutes to obtain the electrode material.

[0038] Example 4: This example differs from Example 1 in that: This example provides a method for preparing an electrode material, comprising the following steps:

[0039] S1. Pre-treat the stainless steel substrate. Specifically, wash the stainless steel substrate with an alkaline solution to remove surface oil and contamination. Then, pickle it with a mixed acid solution to obtain a pre-treated substrate. The alkaline solution is a sodium hydroxide aqueous solution with a concentration of 53 g / L. The alkaline wash temperature is 58°C. The mixed acid solution contains a nitric acid concentration of 10.5% by volume and a hydrofluoric acid concentration of 2% by volume. The pickling temperature is 25°C.

[0040] S2. Chromium chloride, sodium phosphate, and sodium molybdate are sequentially added to water and stirred until completely dissolved. The pH is then adjusted to 2.8 with a 3.5% hydrochloric acid solution to obtain an electroplating solution. The electroplating solution has a chromium chloride concentration of 84 g / L, a sodium molybdate concentration of 16 g / L, and a sodium phosphate concentration of 34 g / L.

[0041] S3, the pre-treated substrate obtained in S1 is used as cathode and graphite is used as anode, and is placed in the electroplating solution obtained in S2 for electroplating to obtain composite coated stainless steel. The current density is 5.0A / dm 2 , temperature is 46℃, and electroplating time is 28min.

[0042] S4. Cleaning and drying the composite-coated stainless steel obtained in S3. Specifically, the composite-coated stainless steel is cleaned three times with deionized water, and then dried at 55° C. for 70 minutes to obtain the electrode material.

[0043] Comparative Example 1: This comparative example differs from Example 1 only in that sodium molybdate and sodium phosphate are omitted from the electroplating solution, that is, the electroplating solution contains only chromium chloride.

[0044] Specifically, this example provides a method for preparing an electrode material, comprising the following steps:

[0045] S1. Pretreat the stainless steel substrate. The specific steps are as follows: first, alkaline wash the stainless steel substrate with alkali solution; then, pickle it with a mixed acid solution to obtain a pretreated substrate. The alkaline solution is a sodium hydroxide aqueous solution with a concentration of 50g / L. The alkaline wash temperature is 60°C, and the stainless steel substrate is soaked in a constant temperature water bath for 30 minutes to remove oil stains from the surface. After the alkaline wash, ultrasonically clean the substrate with 60°C deionized water (20kHz) three times, each for 5 minutes. The mixed acid solution contains 10% nitric acid and 2% hydrofluoric acid by volume, with the remainder being deionized water. The pickle wash temperature is 25°C, and the substrate is soaked in a constant temperature water bath for 15 minutes. After pickling, ultrasonically clean the substrate with 25°C deionized water (20kHz) until neutral (pH test paper), and blow dry with nitrogen.

[0046] S2. Chromium chloride was added to deionized water and mechanically stirred at 300 rpm for 30 minutes until completely dissolved. The pH was then adjusted to 2.8 with 3.5% hydrochloric acid solution to obtain an electroplating solution. The concentration of chromium chloride in the electroplating solution was 82 g / L.

[0047] S3, the pretreated substrate obtained in S1 was used as a cathode (size 50×50×1mm, effective area 0.5dm 2 ), a high-purity graphite plate as the anode (purity ≥ 99.9%, size 60×60×5mm), was placed in the electroplating solution obtained from S2 for electroplating treatment, with an electrode spacing of 50mm (fixed by a polytetrafluoroethylene fixture), to obtain a composite coated stainless steel. Specific process parameters: current density 5.0A / dm 2 The plating solution was stirred magnetically at 200 rpm (rotor size Φ15×50 mm).

[0048] S4. Clean and dry the composite-coated stainless steel obtained in S3. Specifically, the composite-coated stainless steel is cleaned three times with deionized water, and then dried in a hot air circulation drying oven at a constant temperature of approximately 52°C for 70 minutes at a wind speed of 1.5 m / s to obtain the electrode material. The specific cleaning procedure is a three-stage countercurrent cleaning: first, primary deionized water (25°C), then secondary deionized water (40°C), and finally, tertiary deionized water (25°C). Each cleaning time is 5 minutes, and the water flow rate is 2 L / min.

[0049] Comparative Example 2: This comparative example differs from Example 1 only in that sodium phosphate is deleted from the electroplating solution. That is, the electroplating solution contains chromium chloride and sodium molybdate.

[0050] Comparative Example 3: This comparative example differs from Example 1 only in that sodium molybdate is deleted from the electroplating solution. That is, the electroplating solution contains chromium chloride and sodium phosphate.

[0051] Test example: Test object: Electrode material samples were prepared according to Examples 1 to 4 and Comparative Examples 1 to 3.

[0052] Test Method: The corrosion resistance of the coating is tested using a salt spray test. An acidic salt spray test solution (containing 5% NaCl) with a pH of approximately 3.2 is prepared and sprayed continuously on each sample for 72 hours. The test temperature is set at 25±2°C. After the test, the surface is examined with a 10x magnifying glass to determine the pitting area and grade it. The grading reference standard is shown in Table 1.

[0053] Test results: See Table 2.

[0054] Table 1. Grading reference standards

[0055]

[0056] Table 2. Test results of test examples

[0057]

[0058] Result analysis: By analyzing Examples 1 to 4 in combination with the data in Table 1, it can be seen that the electrode materials (cathode) prepared in the present invention (Examples 1 to 4) have excellent pitting corrosion resistance.

[0059] Combining the data in Table 1, we analyze Example 1 and Comparative Examples 1 to 3. By comparing Comparative Example 1 with Comparative Example 2, we can see that adding sodium molybdate to the electroplating solution containing chromium chloride will cause the pitting corrosion resistance of the electrode material (cathode) to decrease instead of increase. This is because when there is only chromium chloride in the electroplating solution, the chromium oxide coating formed by the chromium chloride has a passivating effect, but the microstructure has grain boundary defects and pores, which are easily absorbed by ClO3 - Penetrates through defects and causes local corrosion. Sodium molybdate is added to the electrolyte alone, and the MoO4 introduced by sodium molybdate 2- , forming MoO2 or MoO3 film, which has poor compatibility with chromium-based coatings, resulting in increased stress in the coating and increased porosity, ClO3 - The corrosion is intensified by diffusion through the pores to the substrate surface.

[0060] By comparing Comparative Example 1 with Comparative Example 3, it can be seen that adding sodium phosphate to the electroplating solution containing chromium chloride can improve the pitting corrosion resistance of the electrode material (cathode). This is because the phosphate radical (PO4 3- ) by selectively adsorbing on the cathode surface active sites (such as Cr 3+ enriched area), preferentially occupying the grain boundary growth site, inhibiting the disordered accumulation of chromium oxide crystals, thereby reducing the formation of grain boundary cracks and micropores, and the coating has good density, blocking ClO 3-diffusion channels, thereby improving the cathode's anti-pitting corrosion performance.

[0061] By comparing with Example 1, it can be seen that the addition of sodium molybdate and sodium phosphate to the electroplating solution containing chromium chloride can produce a synergistic effect and synergistically improve the pitting corrosion resistance of the prepared electrode material (cathode). This is because the phosphate radical (PO4 3- ) and the molybdate ion of sodium molybdate (MoO4 2- ) is co-deposited in the coating to form a composite oxide film doped with Mo-PO structure. The Mo-PO complex fills the grain boundary gap and reduces the porosity. The chemical stability of the composite film is better than that of a single oxide, inhibiting ClO3 - penetration and pitting expansion, thereby synergistically improving the cathodic anti-pitting performance.

[0062] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0063] In addition, the various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for preparing an electrode material, characterized in that: The following steps are involved: S1. Pretreating the stainless steel substrate, specifically, performing the following steps: first, alkali-washing the stainless steel substrate with an alkali solution, wherein the alkali solution is a sodium hydroxide aqueous solution with a concentration of 50±5 g / L and a temperature of 55-62° C.; then, pickling the stainless steel substrate with a mixed acid solution, wherein the volume concentration of nitric acid is 10±1%, the volume concentration of hydrofluoric acid is 2±0.2%, and the temperature of the pickling is 23-26° C.; then, ultrasonically cleaning the stainless steel substrate with deionized water until neutral, and drying with nitrogen gas, to obtain a pretreated substrate; S2, chromium chloride, sodium phosphate and sodium molybdate are added to water in sequence, and stirred until completely dissolved, and then the pH value is adjusted to 2.5-3.0 with a hydrochloric acid solution having a mass concentration of 3.2-3.8%, to obtain an electroplating solution; in the electroplating solution, the concentration of chromium chloride is 80-85g / L, the concentration of sodium molybdate is 15-18g / L, and the concentration of sodium phosphate is 30-35g / L; S3: The pretreated substrate obtained in S1 is used as the cathode and the high-purity graphite plate with a purity of ≥99.9% is used as the anode. The substrate is placed in the electroplating solution obtained in S2 for electroplating. The electroplating solution is magnetically stirred at 200 rpm and the current density is 4-6 A / dm 2 , the temperature is 45-48°C, the electroplating time is 25-30min, and a composite coated stainless steel is obtained; S4. Clean and dry the composite-coated stainless steel obtained in S3 to obtain the electrode material.

2. The method for preparing the electrode material according to claim 1, wherein: In S4, the specific operations of cleaning and drying are: cleaning the composite-coated stainless steel with deionized water for multiple times, and then drying at a temperature of 50-55° C. for 60-80 minutes.

3. An electrode material, characterized in that The method according to claim 1 or 2 is used to prepare the product.

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