Preparation method of anti-scaling electrode with automatic scale shedding

Abstract

The present invention belongs to the technical field of electrode preparation, and discloses a preparation method of an anti-scaling electrode with automatic scale shedding, and the steps are as follows: pretreatment of the substrate, construction of active sites, coating of an inert surface, and strengthening of active sites. Different from the traditional method of cleaning the cathode after scaling, the present invention takes a new approach and constructs a highly dispersed nano-tip active site on the inert surface to achieve the positioning and directional growth of scale on the electrode. The hydrogen bubbles generated by electrolysis on the active sites will transfer along the inert surface and coalesce into a bubble layer and large bubbles, thereby preventing the surface from undergoing the electrolysis and scale nucleation processes. Therefore, only the top of the nano-tip serves as the reaction site for electrolyzing water and the landing point for scale crystals. As the scale grows, the nano-scale foothold is difficult to support, and finally it spontaneously falls off under the vibration generated by the bubble rupture. The present invention opens a window for solving the problem of cathode scaling and has scientific value and practicality for the application of electrochemical technology in actual water bodies.

Description

Technical Field

[0001] The invention belongs to the technical field of electrode preparation, and in particular relates to a method for preparing an anti-scaling electrode with automatic scale shedding. Background Art

[0002] Electrochemical technology has been widely studied in the production of hydrogen or extraction of uranium from seawater, extraction of lithium from salt lakes, degradation of pollutants in industrial wastewater, softening of circulating cooling water, etc. However, in actual water, Ca 2+ Mg 2+ (Hardness) and HCO3 - (Alkalinity) may react with OH produced by water electrolysis - Reactions occur to form insulating Mg(OH)2 and CaCO3 scale layers. Once the cathode is covered with a continuous scale layer, the electrochemical reaction is hindered. Currently, mechanical descaling, acid cleaning, and electrode polarity reversal are used to remove the scale layer on the cathode, but these methods increase operating costs, shorten electrode life, and often interrupt the reaction. Therefore, the inherent scaling phenomenon is plaguing the application of electrochemical technology in actual water.

[0003] Obviously, to fundamentally solve this problem, a new type of cathode with anti-scaling function must be developed. To this end, the scale crystal nucleation on the cathode surface must be analyzed. As one of the necessary conditions for scale crystal nucleation, the OH produced by electrolysis of water on the cathode - Ions diffuse into the solution under the influence of the electric field and concentration gradient. - The H produced by electrolysis of water at the anode + Obviously, the OH near the cathode - The concentration is higher than OH in the solution - Other necessary conditions for scale crystal nucleation are Ca 2+ Mg 2+ and HCO3 - As long as these ions migrate from the solution to the cathode and encounter OH - , scale crystals will nucleate near the cathode surface. In addition, the solid surface can reduce the nucleation barrier and increase the nucleation rate. Therefore, most of the crystal nuclei are precipitated on the cathode surface.

[0004] Therefore, the current methods for removing scale layers essentially involve removing the scale that has already covered the electrode surface through secondary treatment, and the electrodes do not have the ability to remove scale by themselves. The reference High-performance Ti / IrO2-RhOx-Ta2O5 electrodes for polarity reversal applications removes scale from the electrode by reversing the polarity of the electrode. The Chinese patent with the patent number 200620032114.5 also discloses an electro-chemical reactor that operates with reversed polarity. Additionally, the references Analysis of mechanical descaling: and modelling approach experimental, the Chinese invention patent with the patent number 202110581157.8, a rotary electro-chemical continuous hardening removal device, and the Chinese invention patent with the patent number 202110715978.6, an electro-chemical water treatment device with a scale removal function, all use mechanical methods to remove the scale deposited on the electrode. However, the above methods inevitably damage the electrode and block the reaction, which also makes the use process of electro-chemical technology cumbersome, increases the additional treatment cost, and limits the application of electro-chemical technology. Summary of the Invention

[0005] The present invention aims to provide a preparation method and mechanism of action for an anti-scaling electrode with automatic scale shedding. For the first time, a new idea of establishing an anti-scaling cathode by dispersing nano-scale active sites on an inert surface is proposed. The electrolysis of water and the growth of scale crystals are controlled by nano-scale active sites, and the nano-scale footholds generate unstable adhesion. The inert surface can adjust the movement path of H2 bubbles, induce the rupture and vibration of large bubbles near the top of the nano-tips, and promote the spontaneous detachment of chain-like scale crystals. Thus, the purpose of automatic scale shedding from the electrode surface is achieved.

[0006] The technical solution of the present invention:

[0007] A preparation method for an anti-scaling electrode with automatic scale shedding, the steps are as follows:

[0008] (1) Pretreatment of the substrate: Immerse the metal substrate in a mixed acid solution for 20 minutes for impurity removal and etching, then immerse it in an oxalic acid solution with a mass fraction of 1-5% for 1-48 hours and take it out, and then perform acid-base neutralization treatment with a 1 g / L sodium hydroxide aqueous solution and wash it clean with water, and store it in an absolute ethanol solution for later use;

[0009] (2) Construction of active sites: Under a constant temperature condition of 15-60 °C, use an aqueous solution mixed with an alkaline reagent, a dispersant, and an aggregating agent as the electrolyte, and at a current density of 2.5-25 mA / cm 2React for 5 - 35 minutes under the conditions to complete the preparation of uniformly dispersed conical active sites on the electrode; then rinse the electrode thoroughly and store it in absolute ethanol for later use;

[0010] (3) Coating of inert surface: Immerse the electrode with conical active sites in an ethanol solution mixed with an inert reagent and a dispersing reagent for 1 - 30 minutes, and let it dry naturally for later use;

[0011] (4) Strengthening of active sites: Under the conditions of 0 - 30 °C, use an aqueous potassium hydroxide solution with a concentration of 0.1 - 5.5 mol / L as the electrolyte for the electrode after inert treatment, and react at a current density of 0.2 - 2.0 mA / cm 2 for 0.5 - 10 minutes to obtain an anti - scaling electrode with automatically shedding scale.

[0012] The metal substrate is stainless steel, iron, copper, titanium, etc.

[0013] The mixed acid solution is composed of hydrochloric acid with a concentration of 38 wt.%, concentrated sulfuric acid, hydrofluoric acid, and high - purity water, and their volume ratio is 1:2:0.1:6.9.

[0014] The alkaline reagent includes but is not limited to sodium hydroxide, potassium hydroxide, calcium hydroxide, etc.

[0015] The dispersant includes but is not limited to sodium tripolyphosphate, polyacrylamide, methyl pentanol, sodium polyacrylate salt, etc.

[0016] The aggregating agent includes but is not limited to sodium polyacrylonitrile, hydroxylated vinyl acetate, ammonium acetate, etc.

[0017] The mass ratio of the alkaline reagent, dispersant, and aggregating agent is 1 - 15:0.01 - 0.3:0.01 - 2.5.

[0018] The inert agent includes but is not limited to dodecyl mercaptan, polytetrafluoroethylene, polysilane, fluorocarbon polymer, etc.

[0019] The mass ratio of the inert agent and the dispersant is 0.1 - 5:0.01 - 0.5.

[0020] The beneficial effects of the present invention:

[0021] (1) The prepared anti - scaling electrode with automatically shedding scale can control the positioning and directional growth of scale crystals on the electrode surface, and then automatically shed under the dual action of its own gravity and bubble vibration, realizing the self - cleaning function of scale, avoiding the secondary damage caused by traditional descaling methods to the electrode treatment process, and completely solving the problem of electrode scaling.

[0022] (2) The effective combination of the active sites and the inert surface on the anti-scaling electrode makes the active sites the main positions for the nucleation of scale crystals. Therefore, the stability of the inert surface is improved, and the existence of the inert surface also increases the stability of the active sites. Finally, the anti-scaling electrode exhibits satisfactory stability. Description of the Drawings

[0023] Figure 1 It is a diagram of the preparation method and action mechanism of an anti-scaling electrode with automatic scale shedding according to the present invention.

[0024] Figure 2 It is a scanning electron microscope image of the anti-scaling electrode.

[0025] Figure 3 It is the growth state of scale crystals on the electrode.

[0026] Figure 4 It is the growth state of scale crystals on the electrode. Detailed Embodiments

[0027] In order to further illustrate the present invention, the present invention will be described in detail below in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0028] Embodiment 1

[0029] A preparation method of an anti-scaling electrode with automatic scale shedding is as follows:

[0030] (1) Pretreatment of the substrate: Immerse the metal copper mesh in a mixed acid solution composed of concentrated hydrochloric acid, concentrated sulfuric acid, hydrofluoric acid and high-purity water with a concentration of 38 wt.% for 20 minutes for impurity removal and etching. The volume ratio of the four liquids is 1:2:0.1:6.9. Then immerse it in an oxalic acid solution with a mass fraction of 1.5% for 6 hours and take it out. After neutralizing the residual acidic liquid with a 1 g / L sodium hydroxide aqueous solution, wash it clean with high-purity water and store it in an absolute ethanol solution for use;

[0031] (2) Construction of active sites: React in a constant temperature water bath at 50 °C. Weigh 1 g, 0.2 g and 2 g of potassium hydroxide, polyacrylamide and hydroxyethyl vinyl acetate and dissolve them in 100 mL of high-purity water as the electrolyte. React at a current density of 5 mA / cm 2 for 17 minutes to prepare uniformly dispersed conical active sites on the electrode. After rinsing clean, store it in absolute ethanol for use;

[0032] (3) Coating of the inert surface: Dissolve 0.2 g and 0.4 g of polytetrafluoroethylene and sodium tripolyphosphate in 100 mL of ethanol solution, and then immerse the material containing active sites in it for 30 minutes and air dry it for use;

[0033] (4) Strengthening of the active site: The inert-treated material was reacted for 2 minutes at 0 °C with 5 mol / L aqueous potassium hydroxide solution as the electrolyte at a current density of 0.3 mA / cm 2 to obtain an anti-scaling electrode with automatic scale shedding. The morphology of the prepared anti-scaling electrode is shown in Figure 2 .

[0034] The ordinary electrode is a metal copper mesh only treated by step 1.

[0035] The electrode anti-scaling experiment was carried out in an electrochemical reaction tank. The anode and cathode used RuO2-IrO2-TiO2 / Ti mesh and the anti-scaling electrode respectively. A solution with a hardness of 300 mg / L was prepared as the simulated water for the water softening performance test. The anti-scaling electrode with an electrode area of 100 cm 2 was horizontally placed with the anode in the reactor containing the simulated water. A constant current density of 1 mA / cm 2 was applied. After reacting for 60 min, the residual calcium ion concentration in the simulated water was measured. And the used electrode was placed in an oven at 60 °C to dry and then weighed. The electrode weight gain data was obtained according to the mass difference of the electrode before and after the reaction. The experimental processes of the ordinary electrode and the anti-scaling electrode were the same. The experimental results are shown in Table 1:

[0036] Table 1. Hardness removal and anti-scaling performance of ordinary electrodes and anti-scaling electrodes

[0037]

[0038] According to Table 1, it can be seen that the weight gain of the anti-scaling electrode after the reaction is less than 1 mg, far lower than that of the ordinary electrode. And through calculation, the anti-scaling rate of the anti-scaling electrode exceeds 98%, and the anti-scaling performance is significantly improved. In addition, after observing the microscopic morphology of the anti-scaling electrode at the end of the experiment, scale crystals in a chain-like structure were found on the electrode surface ( Figure 3 , 4 ), and this structure was only found on the anti-scaling electrode and detected in the corresponding treated solution. Therefore, it is proved that the crystals can only form at the tips of the anti-scaling electrode and automatically fall off after growing into a chain-like structure and fall into the solution automatically, thus realizing the anti-scaling performance of the electrode.

[0039] Example 2

[0040] Comparing the performance of the anti-scaling electrode and the ordinary electrode in removing metal ions from seawater and the electrode stability:

[0041] A preparation method of an anti-scaling electrode with automatic scale shedding, the preparation steps are the same as those in Example 1, and the ordinary electrode is a metal copper mesh only treated by step 1.

[0042] Using seawater directly as the liquid to be treated, calcium and magnesium ions in it are removed. The concentration of calcium ions in seawater is 253 mg / L, and the concentration of magnesium ions is 1300 mg / L. With an area of 100 cm 2 The anti-scaling electrode and the ordinary electrode are placed as reaction cathodes in the electrochemical reaction tank containing seawater, and a constant current density of 1 mA / cm 2 is applied for metal ion removal and stability testing. The experimental results are shown in Table 2:

[0043] Table 2. Metal ion removal and anti-scaling performance of ordinary electrodes and anti-scaling electrodes

[0044]

[0045] As can be seen from Table 2, after treatment, the magnesium ions in seawater have been significantly removed. However, due to the insufficient alkalinity in seawater, only about half of the calcium ion concentration can be degraded. However, it can be seen that the metal ion removal ability of the anti-scaling electrode is significantly better than that of the ordinary electrode, which is directly related to the active sites of the anti-scaling electrode. Because the active sites can accelerate the decomposition of water to produce OH - , thereby promoting the reaction with Mg 2+ , HCO3 - and Ca 2+ in seawater. In addition, by weighing the electrodes before and after the reaction, the electrode weight gain of the anti-scaling electrode is the least, and the electrode anti-scaling rate exceeds 90%. It can be seen that the anti-scaling electrode still has good anti-scaling performance in actual seawater.

[0046] The excellent performance of the anti-scaling electrode is not only shown in the metal removal performance in seawater, but also reflected in the voltage change during the reaction. As can be seen from Table 3, during the continuous use of 300 hours, the voltage of the ordinary electrode rises linearly to 7.9 V, while the voltage of the anti-scaling electrode rises slightly to 3.7 V. If the voltage rises too much, it will lead to an increase in energy consumption. The increase in voltage is directly related to the deposition of scale on the electrode. When too many scale crystals are deposited on the electrode, an insulating scale layer will form on the electrode surface, so the voltage will increase. In summary, the anti-scaling electrode has excellent anti-scaling performance and stability.

[0047] Table 3. Voltage change of ordinary electrodes and anti-scaling electrodes during continuous operation for 300 h

[0048]

[0049] Example 3

[0050] Comparison of the performance of anti-scaling electrodes and ordinary electrodes for metal ion removal in seawater (CO2 is introduced):

[0051] A preparation method of an anti-scaling electrode with automatic scale shedding, the preparation steps are the same as those in Example 1, and the ordinary electrode is a metal copper mesh only treated through Step 1.

[0052] Use seawater directly as the liquid to be treated and remove calcium and magnesium ions in it. The seawater contains a calcium ion concentration of 253 mg / L and a magnesium ion concentration of 1300 mg / L. With an area of 100 cm 2 Place the anti-scaling electrode and the ordinary electrode as the reaction cathode in an electrochemical reaction tank containing seawater, and apply a constant current density of 1 mA / cm 2 to remove metal ions. In addition, according to the hint that the calcium ion removal effect in Example 2 is not obvious, extra CO2 is introduced to make up for the shortage of carbon source in seawater. The experimental results are shown in Table 4:

[0053] Table 4. Metal ion removal and anti-scaling performance of ordinary electrodes and anti-scaling electrodes (CO2 is introduced)

[0054]

[0055] As can be seen from Table 4, after the reaction, the magnesium ions in the seawater have been significantly removed, and the concentration of calcium ions has also decreased significantly due to the introduction of CO2. Especially for the anti-scaling electrode, the removal rates of calcium ions and magnesium ions have reached 98.7% and 96.4% respectively, and the electrode weight gain is only 8.9 mg, far lower than that of the ordinary electrode. It can be seen that after introducing CO2, while improving the magnesium ion removal performance, the removal ability of the electrode for calcium ions in seawater is significantly improved, and the anti-scaling performance of the anti-scaling electrode in seawater is further enhanced.

Claims

1. A preparation method of an anti-scaling electrode with automatic scale shedding, characterized in that, The steps are as follows: (1)Pretreatment of the substrate: Immerse the metal substrate in the mixed acid solution for 20 min for impurity removal and etching, then immerse it in the oxalic acid solution with a mass fraction of 1-5% for 1-48 h and take it out. After neutralization treatment with 1 g / L sodium hydroxide aqueous solution, wash it with water and store it in anhydrous ethanol solution for use; (2)Construction of active sites: Under a constant temperature condition of 15 - 60 °C, using an aqueous solution mixed with an alkaline reagent, a dispersant, and an aggregating agent as the electrolyte, reacting for 5 - 35 min under the condition of a current density of 2.5 - 25 mA / cm 2 to complete the preparation of uniformly dispersed conical active sites on the electrode; then rinsing the electrode clean and storing it in absolute ethanol for later use; (3)Coating of the inert surface: Immerse the electrode with conical active sites in the ethanol solution mixed with the inert agent and the dispersant for 1-30 minutes, and let it dry naturally for use; (4)Enhancement of active sites: The electrode treated inertially is reacted under the conditions of 0 - 30 °C, with an aqueous potassium hydroxide solution of 0.1 - 5.5 mol / L as the electrolyte, and at a current density of 0.2 - 2.0 mA / cm 2 for 0.5 - 10 min to obtain an anti-scaling electrode with automatic scale shedding; In step (2), the dispersant is polyacrylamide, and in step (3), the dispersant is sodium tripolyphosphate; The aggregating agent is hydroxylated vinyl acetate; The inert agent is polytetrafluoroethylene.

2. The preparation method according to claim 1, characterized in that, The mixed acid solution is composed of hydrochloric acid with a concentration of 38 wt.%, concentrated sulfuric acid, hydrofluoric acid and high-purity water, and their volume ratio is 1:2:0.1:6.

9.

3. The preparation method according to claim 1, characterized in that, The metal substrate is stainless steel, iron, copper, or titanium.

4. The preparation method according to claim 1, characterized in that, The alkaline reagents include sodium hydroxide, potassium hydroxide, and calcium hydroxide.

5. The preparation method according to claim 1, characterized in that, The mass ratio of the alkaline reagent, the dispersant and the aggregating agent is 1-15: 0.01-0.3: 0.01-2.

5.

6. The preparation method according to claim 1, characterized in that, The mass ratio of the inert agent and the dispersant is 0.1-5: 0.01-0.5.

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