Super-hydrophilic boron-doped graphite electrode for electrolysis process and preparation method thereof

Abstract

This invention belongs to the fields of novel graphite materials in the core electronics industry and air pollution control technology in the advanced environmental protection industry. Specifically, it relates to a superhydrophilic boron-doped graphite electrode for electrolysis processes and its preparation method. The electrode includes a graphite substrate and the following functional layers sequentially constructed on the surface of the substrate: a solid-solution boron-doped layer and a surface superhydrophilic oxygen-containing functional group layer. In the solid-solution boron-doped layer, boron atoms are embedded in the graphite lattice, and the surface superhydrophilic oxygen-containing functional group layer is composed of oxygen-containing functional groups introduced by electrochemical oxidation, resulting in a hydrophilic contact angle of less than 10° on the electrode surface. The method includes steps such as mixing graphite powder with a boron source and pressing it into a green body; high-temperature solid-solution boron doping of the green body; crushing, sieving, and secondary shaping; and electrolytic treatment of the electrode for superhydrophilic modification. This invention achieves the reduction of heavy metal pollution through heavy metal anode substitution and the reduction of particulate matter pollution through bubble behavior regulation. It can reduce oxygen evolution overpotential, improve bubble desorption performance, and inhibit graphite oxidation and shedding.

Description

Technical Field

[0001] This invention belongs to the fields of novel graphite materials in the core electronics industry and air pollution control technology in the advanced environmental protection industry. Specifically, it relates to a superhydrophilic boron-doped graphite electrode for electrolysis and its preparation method. Background Technology

[0002] Electrolysis is a key process in many fields, including hydrometallurgy (such as the electrowinning of metals like zinc, copper, nickel, and cobalt), electrochemical synthesis, water electrolysis for hydrogen production, and the chlor-alkali industry. In these processes, factors such as the overpotential of the oxygen evolution reaction (OER), the adhesion and desorption behavior of bubbles on the electrode surface, the long-term stability of the electrode, and whether heavy metal pollution is introduced directly determine the energy efficiency, product quality, production cost, and environmental friendliness of the entire electrolysis process.

[0003] Taking metal electrowinning in hydrometallurgy as an example (such as zinc electrowinning, copper electrowinning, nickel electrowinning, etc.), the principle is to electrolyze a leached and purified metal salt solution to deposit high-purity metal on the cathode. The electricity consumption of this process accounts for 15%–25% of the total smelting cost, making it a key factor determining the company's economic benefits and energy conservation level. Similarly, in the process of producing hydrogen through water electrolysis, the high oxygen evolution overpotential at the anode leads to persistently high energy consumption for hydrogen production; in the chlor-alkali industry, the selectivity of the chlorine evolution reaction at the anode and the stability of the electrode directly affect production efficiency and safe operation. Therefore, reducing the electricity consumption of various electrolysis processes and improving current efficiency have become urgent needs for the industry's green transformation. However, in the aforementioned electrolysis processes, problems such as high oxygen evolution overpotential at the anode, severe bubble adhesion, easy electrode passivation or corrosion, and the risk of heavy metal pollution are common, seriously restricting the improvement of overall energy efficiency and the level of clean production.

[0004] Traditional electrolysis processes (especially hydrometallurgy) widely use lead-based alloy electrodes (such as Pb-Ag, Pb-Ca-Sn, etc.). These electrodes have several inherent drawbacks: First, the oxygen evolution overpotential is as high as 0.8–1.0 V, resulting in persistently high DC power consumption (for example, zinc electrowinning consumes 3000–3400 kWh per ton of zinc), leading to high energy costs. Second, a poorly conductive PbO2 passivation layer easily forms on the surface during operation, causing the cell voltage to gradually increase. Simultaneously, the slow dissolution of the lead electrode results in excessive lead content in the cathode product, leading to decreased product quality and the risk of heavy metal contamination. Third, lead is soft and easily deformable, and its hydrophobic surface makes it difficult to remove bubbles generated by oxygen evolution, further increasing interfacial resistance and reducing current efficiency. In water electrolysis for hydrogen production and the chlor-alkali industry, although titanium electrodes coated with noble metal oxides are commonly used, they are costly, have complex manufacturing processes, and are prone to deactivation under high current density or reverse current conditions. For carbon-based electrodes, unmodified graphite is prone to oxidation and shedding in strongly acidic, high-potential electrolysis environments, and its hydrophobic surface leads to severe bubble adhesion, which limits its direct application.

[0005] To address these issues, researchers have explored various improvement schemes, such as aluminum-lead composite electrodes, graded functional inert electrodes, and coated titanium electrodes. However, these schemes generally suffer from high costs, complex fabrication processes, or insufficient long-term stability, making large-scale industrial applications difficult. For carbon-based electrodes, unmodified graphite is prone to oxidation and shedding in strongly acidic, high-potential electrolytic environments, and its hydrophobic surface leads to severe bubble adhesion, limiting its direct application.

[0006] Therefore, developing a cost-effective, low oxygen evolution overpotential, stable, and environmentally friendly superhydrophilic graphite electrode material, while simultaneously achieving heavy metal anode replacement to reduce heavy metal pollution and bubble behavior regulation to reduce particulate matter pollution, is of great significance for reducing electrolysis energy consumption, improving product quality, and promoting cleaner production in the electronics industry and electrochemical industry. Summary of the Invention

[0007] This invention discloses a superhydrophilic boron-doped graphite electrode for electrolysis processes and its preparation method, aiming to overcome the shortcomings of existing electrode technologies for electrolysis, particularly addressing the technical bottlenecks of traditional lead-based alloy electrodes and existing modified graphite electrodes in terms of oxygen evolution overpotential, bubble desorption performance, product purity, and electrode stability. Specifically, it solves the following key problems: 1. Reduce the oxygen evolution overpotential of the electrode and decrease electrolysis energy consumption. Traditional lead-based electrodes have an oxygen evolution overpotential as high as 0.8-1.0V, resulting in high energy consumption per ton of zinc. Simultaneously, bubbles adhering to the electrode surface cover active sites, hindering electrochemical reactions and further increasing electrolysis energy consumption. This invention significantly improves the conductivity and electrocatalytic activity of the graphite electrode through solid solution boron doping, reducing the oxygen evolution overpotential; and through superhydrophilic modification, it enables rapid bubble desorption, preventing active sites from being covered by bubbles, thereby synergistically reducing electrolysis energy consumption.

[0008] 2. Achieving a controllable transformation of the electrode surface from hydrophobic to superhydrophilic, improving bubble desorption performance, and regulating bubble behavior to reduce particulate matter pollution. Traditional electrode surfaces are hydrophobic, making it easy for numerous bubbles generated by oxygen evolution to adhere and difficult to desorb, increasing interfacial resistance and reducing current efficiency. Simultaneously, the bubbles entrain particulate matter, exacerbating pollution. This invention, through electrolytic superhydrophilic modification of the electrode surface, transforms it from hydrophobic to superhydrophilic, significantly improving bubble desorption behavior on the electrode surface, promoting rapid bubble release, reducing particulate matter adhesion, and further reducing interfacial resistance and particulate matter pollution.

[0009] 3. Increase product purity: Traditional lead-based electrodes continuously dissolve during use, releasing Pb. 2+Lead ions, which co-deposit at the cathode, cause excessive lead content in the cathode, reducing product grade. This invention uses a lead-free graphite-based electrode, eliminating the leaching of heavy metal ions during electrolysis and removing lead contamination at the cathode, significantly improving product purity.

[0010] 4. Reduce heavy metal pollution and achieve heavy metal anode replacement to mitigate heavy metal pollution. By using lead-free graphite-based electrodes to replace traditional lead-based alloy anodes, no lead or other heavy metal ions are dissolved during electrolysis, avoiding heavy metal contamination of the electrolyte and cathode products, truly achieving heavy metal anode replacement and reducing heavy metal pollution at the source.

[0011] 5. Prevents the formation of a surface passivation layer, improving the long-term operational stability of the electrode. Traditional lead-based electrodes are prone to forming a poorly conductive PbO2 passivation layer during long-term operation, leading to a continuous increase in cell voltage. This invention uses boron-doped graphite as the electrode material, which has good chemical inertness and structural stability in acidic electrolytes, preventing the formation of a passivation layer and ensuring long-term stability of the cell voltage.

[0012] 6. Extending the service life of graphite anodes. In highly acidic, high-potential electrolytic environments, the surface carbon atoms of unmodified graphite electrodes are easily oxidized to CO or CO2, leading to graphite layer peeling, a loose structure, and gradual electrode thinning or even failure. This invention, through solid solution boron doping, enhances the oxidation resistance of the carbon skeleton by embedding boron atoms into the graphite lattice. Simultaneously, the oxygen-containing functional group layer formed by the electrolytic superhydrophilic modification of the electrode can, to a certain extent, block the deep erosion of active oxygen, thereby significantly inhibiting the oxidation and peeling of the graphite electrode and extending its service life.

[0013] 7. Simplify the preparation process, reduce production costs, and meet the requirements of industrial applications. Existing improvement schemes often suffer from complex processes and high costs.

[0014] To achieve the above objectives, the technical solution of the present invention is as follows: A method for preparing a superhydrophilic boron-doped graphite electrode for electrolysis processes includes the following steps: Step 1: Pre-treat graphite powder and mix it with a boron source to obtain a mixed powder; Step 2: Press the mixed powder obtained in Step 1 into a green body; Step 3: The green body obtained in Step 2 is subjected to high-temperature solid solution boron doping treatment to obtain boron-doped graphite bulk material; Step 4: The boron-doped graphite bulk material obtained in Step 3 is crushed, sieved, and then formed into a boron-doped graphite electrode green blank. Step 5: The boron-doped graphite electrode green blank obtained in Step 4 is used as the electrode and placed in an electrolytic cell for electrode electrolysis treatment to perform superhydrophilic modification. Step 6: Take out the electrode processed in Step 5 and perform post-processing to obtain a superhydrophilic boron-doped graphite electrode for zinc electrolysis.

[0015] Preferably, step one includes the following specific steps: selecting high-purity graphite powder and boron source, placing the graphite powder and boron source in a ball mill jar, adding zirconia grinding balls, and ball milling at a speed of 100-400 rpm for 2-12 hours under an inert atmosphere or a closed dry process, so that the boron source is uniformly coated on the surface of the graphite powder or mixed with the graphite powder.

[0016] The core function of this step is to achieve uniform mixing of boron source and graphite powder at the micron scale through mechanical ball milling, providing a uniform material basis for subsequent high-temperature solid solution doping.

[0017] Preferably, in step one, the boron source is selected from one or more of boric acid (H3BO3), borax (Na2B4O7·10H2O), boron oxide (B2O3), or elemental boron powder.

[0018] Preferably, step two specifically involves: loading the mixed powder obtained in step one into a metal mold, using uniaxial dry pressing to form a green blank after demolding.

[0019] Preferably, step three specifically involves: placing the green blank obtained in step two in a boron-doped furnace, heating it to 1100-1800℃ under an inert atmosphere (argon or nitrogen), and holding it for 2-8 hours. During this process, boron is released from the boron source and diffuses into the graphite lattice, replacing some carbon atoms to form boron-doped graphite bulk material.

[0020] The core function of this step is that boron atoms replace some carbon atoms in the graphite lattice, introducing hole carriers and significantly improving the electronic conductivity and electrocatalytic activity of graphite, thereby effectively reducing the overpotential of the oxygen evolution reaction. Simultaneously, boron doping enhances the bonding strength of the graphite lattice and improves the oxidation resistance of the carbon framework.

[0021] Preferably, step four includes: pressing the uniform boron-doped graphite powder obtained after sieving into shape again according to the method in step two to obtain a boron-doped graphite electrode green blank with the final required shape and size.

[0022] Preferably, step five includes: the electrolyte for electrode electrolysis is a neutral salt solution.

[0023] Preferably, in step five, the neutral salt solution is an aqueous solution of sodium sulfate (Na₂SO₄) with a concentration of 1-100 mmol / L.

[0024] The core function of this step is that, under electrode polarization conditions, a mild electrochemical oxidation occurs on the surface of boron-doped graphite, introducing oxygen-containing functional groups (such as C=O, C-OH, COOH, etc.), transforming the surface from a hydrophobic state to a superhydrophilic state (contact angle <10°). This superhydrophilic surface significantly reduces the adhesion between bubbles and the electrode, promoting the rapid desorption of oxygen-evolving bubbles at a small size and high frequency. This allows for the regulation of bubble behavior, reducing particulate contamination, lowering interfacial resistance, and further improving current efficiency.

[0025] Preferably, in step six, the post-processing step includes: washing the removed electrode with deionized water and drying it at 80-100°C for 2-4 hours.

[0026] Based on the above technical solutions, the present invention provides a superhydrophilic boron-doped graphite electrode for electrolysis processes. The electrode includes a graphite substrate and the following functional layers sequentially constructed on the surface of the substrate: a solid solution boron-doped layer and a surface superhydrophilic oxygen-containing functional group layer. In the solid solution boron-doped layer, boron atoms are embedded in the graphite lattice, and the surface superhydrophilic oxygen-containing functional group layer is composed of oxygen-containing functional groups introduced by electrochemical oxidation, so that the hydrophilic contact angle of the electrode surface is less than 10°.

[0027] The beneficial effects of the superhydrophilic boron-doped graphite electrode for electrolysis processes and its preparation method of the present invention are as follows: 1. Significantly reduces oxygen evolution overpotential, achieving energy saving and consumption reduction. Through solid solution boron doping treatment, the conductivity and electrocatalytic activity of graphite electrodes are greatly improved. The oxygen evolution overpotential is reduced by 0.3-0.5 V compared with traditional lead-based electrodes, and the DC power consumption per ton of zinc can be reduced by 8%-12%, resulting in good economic benefits.

[0028] 2. Superhydrophilic surface modification significantly improves bubble desorption performance, enabling bubble behavior control and reducing particulate matter contamination. Through electrode electrolysis, oxygen-containing functional groups are introduced into the surface of boron-doped graphite, achieving a controllable transition from hydrophobic to superhydrophilic. Bubbles on the superhydrophilic surface are more likely to desorb rapidly at a smaller size, reducing bubble aggregation and interfacial resistance. Simultaneously, it effectively reduces contamination caused by particulate matter entrained in bubbles, improving current efficiency and cleanliness.

[0029] 3. Avoids passivation layer formation, ensuring good long-term operational stability. Boron-doped graphite exhibits excellent chemical inertness and structural stability in acidic zinc electrolytes, preventing the formation of a poorly conductive passivation layer and ensuring long-term stable cell voltage.

[0030] 4. Significantly inhibits the oxidation and shedding of graphite electrodes, extending their service life. Solid solution boron doping enhances the oxidation resistance of the graphite lattice. Combined with the barrier effect of the oxygen-containing functional group surface layer formed by electrode electrolysis on active oxygen, it effectively reduces the oxidation loss of carbon atoms on the graphite surface (CO / CO2 generation) during electrolysis. The electrode structure remains intact, and the service life is extended by more than 50% compared with unmodified graphite electrodes.

[0031] 5. Significantly improves the purity of zinc products, avoids heavy metal pollution, and achieves heavy metal anode replacement to reduce heavy metal pollution. This invention uses a lead-free graphite-based electrode, and no heavy metal ions such as Pb2+ are dissolved during electrolysis, eliminating pollution of the cathode zinc from the source. Tests show that the lead content in the cathode zinc produced using the electrode of this invention is less than 0.0015 wt%, far lower than that of traditional lead electrode systems (lead content is usually 0.005-0.01 wt%), meeting the quality requirements of high-purity zinc and extra-high-grade zinc, truly achieving heavy metal anode replacement to reduce heavy metal pollution.

[0032] 6. The preparation process is simple, the cost is controllable, and it is easy to promote industrialization. This invention only requires two core processing steps: solid solution boron doping and electrode electrolysis. The process is short, the equipment requirements are low, and the raw materials are widely available, making it suitable for large-scale production and possessing extremely high industrial application value.

[0033] 7. Environmentally friendly, with no risk of heavy metal pollution. The graphite matrix itself does not contain toxic heavy metals such as lead, and no heavy metals are leached during use, avoiding the harm to the environment and operators caused by traditional lead electrodes, and meeting the requirements of green and clean production. Attached Figure Description

[0034] Figure 1 Comparison of cell voltage during electrolysis between the modified boron-doped graphite electrode of this invention, a traditional lead-based anode, and a graphite anode; Figure 2 Comparison of oxygen evolution efficiency during electrolysis between the modified boron-doped graphite electrode of this invention, a traditional lead-based anode, and a graphite anode; Figure 3 A comparison of electrolysis energy consumption during electrolysis between traditional lead-based anodes and graphite anodes and the modified boron-doped graphite electrode of this invention; Figure 4 Comparison of the average bubble detachment diameter during electrolysis between traditional lead-based anodes and graphite anodes and the modified boron-doped graphite electrode of this invention; Figure 5 Comparison of oxygen-containing functional groups between graphite anode and graphite electrode after electrolysis during the electrolysis process. Detailed Implementation

[0035] The following description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0036] The following embodiments can be understood as illustrating a part of the structure or method of the present invention individually, or as combining the embodiments to explain the broader structure or method of the present invention.

[0037] This invention provides the following technical solution: a method for preparing a superhydrophilic boron-doped graphite electrode for electrolysis processes, specifically comprising the following steps: Step 1: Pretreatment of graphite powder and mixing with boron source: High-purity artificial graphite powder is selected, with a purity ≥99.9%, particle size ≤45 μm (325 mesh), ash content ≤0.05%, and tap density of 0.60–0.80 g / cm³. The boron source is selected from one or more of boric acid (purity ≥99.5%), borax (purity ≥99.0%), boron oxide (purity ≥98.0%), or elemental boron powder (purity ≥95%). The boron element is weighed at a mass ratio of 1.0%–5.0% (preferably 2.0%–4.0%) of the graphite powder mass. The weighed graphite powder and boron source are placed in a zirconium oxide or agate ball mill jar, and zirconium oxide grinding balls with a diameter of 5–10 mm are added, with a ball-to-powder mass ratio of 10:1–20:1. High-purity argon gas (flow rate 0.5–1 L / min) is introduced into the container for protection, or the container is directly sealed for dry ball milling. The ball milling speed is 100–400 rpm, and the milling time is 2–12 hours, so that the boron source is uniformly coated on the surface of the graphite powder or mixed with the graphite powder. If the green body is prone to cracking during subsequent pressing, 1%–3% of a polyvinyl alcohol aqueous solution (concentration 5 wt%) can be added as a binder after ball milling, and ball milling can continue for 10–20 minutes. Then, the mixed powder is passed through an 80-mesh sieve and placed in a vacuum drying oven to dry at 60–80℃ for 2–4 hours.

[0038] Step 2: Pressing and shaping: The dried mixed powder is uniformly loaded into a cemented carbide or stainless steel mold (internal surface roughness ≤ 0.8 μm), and uniaxial dry pressing is used for molding. The pressing pressure is 100–200 MPa (preferably 120–180 MPa), and the holding time is 1–3 minutes (preferably 2 minutes). After slowly releasing the pressure, the mold is demolded to obtain a green body. The density of the green body should reach 70%–85% of the theoretical density (approximately 1.3–1.6 g / cm³), and the thickness is typically 5–15 mm.

[0039] Step 3: High-temperature solution doping with boron: Place the green sample in a graphite crucible or corundum boat and put it into the isothermal zone of a high-temperature tube furnace, box furnace, or dedicated boron-doped furnace (maximum operating temperature ≥1800℃, temperature control accuracy ±5℃). First, evacuate to ≤10 Pa, then introduce high-purity argon (≥99.999%) or high-purity nitrogen (≥99.999%) at a flow rate of 100–200 mL / min. Repeat this replacement process three times to ensure the oxygen content in the furnace is ≤10 ppm. Increase the temperature to 1200–1800℃ (preferably 1400–1600℃) at a heating rate of 5–10℃ / min and hold for 2–8 hours (preferably 4–6 hours). After holding, turn off the heating power, keep the inert gas circulating, and allow it to cool naturally to room temperature. Stop the gas flow and remove the sample only when the furnace temperature drops below 200℃. During this process, boron is released from the boron source and diffuses into the graphite lattice, replacing some carbon atoms to form boron-doped graphite materials, whose resistivity is reduced by 20% to 40% compared to undoped graphite.

[0040] Step 4: Crushing, Screening and Secondary Molding The boron-doped bulk material (which may be slightly sintered) is lightly crushed using an agate mortar or a light ball mill (zirconia jar) to avoid over-grinding and damaging the crystal lattice. After crushing, it is passed through a 100-200 mesh standard sieve to obtain uniform boron-doped graphite powder. This powder is then subjected to a secondary molding process using the pressing method described above. To obtain higher density, the pressing pressure can be increased to 150-200 MPa, and the holding time can be 2-3 minutes. Optionally, the secondary-molded green body is placed in a sintering furnace and heated to 800-1000℃ at a rate of 5℃ / min under an inert atmosphere (argon or nitrogen, flow rate 100 mL / min), held for 1-2 hours, and then cooled with the furnace to further improve the mechanical strength and conductivity of the electrode.

[0041] Step 5: Electrolytic superhydrophilic modification of electrodes: Prepare a sodium sulfate (Na₂SO₄) aqueous solution with a concentration of 1–100 mmol / L using deionized water (resistivity ≥18 MΩ·cm). Use a boron-doped graphite electrode that has undergone secondary molding (and optionally sintering) as the working electrode, connected by copper wire, with the non-working surface insulated with epoxy resin. The counter electrode is a platinum sheet (area ≥2 cm²) or a high-purity graphite plate, and the reference electrode is a saturated calomel electrode (SCE) or an Ag / AgCl electrode. The electrolytic cell is made of glass or polypropylene and has a volume of 500–1000 mL. When using constant potential mode, the electrode potential is set to +2.0–+2.5 V (vs. SCE), preferably +2.2 V; when using constant current mode, the current density is set to 30–80 mA / cm², preferably 40–60 mA / cm². The processing time is 10–60 minutes, and the electrolyte temperature is controlled at 25–60 °C. During electrolysis, the surface is gently stirred with a magnetic stirrer (100–200 rpm) to promote bubble desorption and maintain uniform concentration. Immediately after treatment, the working electrode is removed and rinsed 3–5 times with deionized water to remove residual electrolyte. This step induces mild electrochemical oxidation of the boron-doped graphite surface under electrode polarization conditions, introducing oxygen-containing functional groups (such as C=O, C-OH, COOH, etc.) to transform the surface from a hydrophobic state (contact angle >100°) to a superhydrophilic state (contact angle <10°). This significantly reduces bubble adhesion and promotes rapid desorption of oxygen-evolving bubbles with small sizes (average diameter <0.3 mm), thereby controlling bubble behavior and mitigating particulate matter pollution.

[0042] Step Six: Post-processing: The cleaned electrodes are placed in a forced-air drying oven and dried at 80–100℃ for 2–4 hours to obtain a high-efficiency, energy-saving, superhydrophilic boron-doped graphite electrode for zinc electrolysis. It is recommended to perform quality inspection on the finished product: resistivity should be measured using the four-probe method, and should be 20%–40% lower than that of undoped graphite; the surface contact angle should be measured using the seat-drop method (deionized water), and should be less than 10° (superhydrophilic); in a simulated zinc electrolyte (Zn… 2+ The oxygen evolution overpotential (OEC) determined by linear sweep voltammetry in a solution of 50 g / L H₂SO₄ and 150 g / L H₂SO₄ at 40℃) should be less than 0.5 V (vs. SCE); the bulk density determined by Archimedes' water displacement method should be no less than 1.75 g / cm³. 3 .

[0043] Example 1: Step 1: Pretreatment of graphite powder and mixing with boron source: 100 g of high-purity graphite powder (99.9% purity, 325 mesh particle size, and a bulk density (tapered) of approximately 0.65 g / cm³) was selected. 8.9 g of boric acid (H₃BO₃) was weighed (boron content is approximately 3.0% of the graphite powder mass). The graphite powder and boric acid were placed together in a zirconia ball mill jar, and 2000 g of zirconia milling balls were added (ball-to-powder ratio 20:1). The ball mill jar was sealed, and argon gas was introduced for protection. The mixture was ball-milled at 250 rpm for 6 hours.

[0044] Step 2: Pressing and shaping: Take out the mixed powder obtained in step one, add 2% (5 wt%) of PVA aqueous solution as a binder, and mix thoroughly. Then, put it into a circular stainless steel mold with an inner diameter of 50 mm, and press it uniaxially under a pressure of 150 MPa for 2 minutes. After demolding, a green body with a diameter of about 50 mm and a thickness of about 8 mm is obtained.

[0045] Step 3: High-temperature solution doping with boron: The green body obtained in step two was placed in a graphite crucible and then placed in a high-temperature tube furnace. High-purity argon gas (flow rate 150 mL / min) was introduced, and the temperature was increased to 1500°C at a rate of 8°C / min, and held at that temperature for 5 hours. After the treatment, the green body was allowed to cool naturally to room temperature, while maintaining an argon atmosphere below 200°C.

[0046] Step 4: Crushing, Screening and Secondary Molding The boron-doped block obtained in step three was removed, lightly crushed using an agate mortar, and then passed through a 150-mesh sieve to obtain uniform boron-doped graphite powder. This powder was then pressed into shape again under 150 MPa pressure, following the method in step two, to obtain the final electrode green body. Subsequently, it was sintered at 900℃ for 1 hour under an argon atmosphere and then cooled in the furnace.

[0047] Step 5: Electrolytic superhydrophilic modification of electrodes: The sintered electrode obtained in step four was used as the electrode and placed in an electrolytic cell. The electrolyte was a 20 mmol / L Na₂SO₄ aqueous solution. A constant current mode was used with a current density of 50 mA / cm², a treatment time of 30 minutes, and the electrolyte temperature was controlled at 40℃.

[0048] Step Six: Post-processing: The electrode processed in step five is taken out, washed three times with deionized water, and dried at 90°C for 3 hours to obtain a high-efficiency and energy-saving superhydrophilic boron-doped graphite electrode.

[0049] Performance testing: Under simulated zinc electrolysis conditions (Zn 2+The electrode was tested under the following conditions: 50 g / L H₂SO₄, 160 g / L H₂SO₄, current density 500 A / m², temperature 40℃. Results showed that the oxygen evolution overpotential of this electrode was 0.35 V (vs. SCE); the surface contact angle decreased from 112° (hydrophobic) to 8° (superhydrophilic); the resistivity decreased by 32% compared to undoped graphite; the DC power consumption per ton of zinc was 2866 kWh; the oxygen evolution efficiency (based on the theoretical oxygen evolution potential of 1.23 V, the energy efficiency corresponding to the actual oxygen evolution overpotential) increased to 98.7%; the average bubble detachment diameter decreased from 50 μm to 9 μm, and the bubble behavior regulation significantly reduced particulate matter pollution; after 500 hours of continuous operation, the electrode mass loss rate was only 2.3%, while the mass loss rate of the unmodified graphite electrode under the same conditions was 8.5%; the lead content in the cathode zinc produced using this electrode was <0.001 wt%, far lower than the 0.008 wt% of the traditional lead electrode system, fully realizing the replacement of heavy metal anodes to reduce heavy metal pollution.

[0050] Example 2: Step 1: Pretreatment of graphite powder and mixing with boron source: 100 g of the same high-purity graphite powder as in Example 1 was selected. 6.4 g of boron oxide (B₂O₃) was weighed (the boron content is approximately 2.0% of the graphite powder mass). The graphite powder and boron oxide were placed together in a zirconia ball mill jar, and 1500 g of zirconia milling balls were added (ball-to-powder ratio 15:1). The mill jar was sealed, and argon gas was introduced for protection. The mixture was milled at 280 rpm for 5 hours.

[0051] Step 2: Pressing and shaping: Same as in Example 1, but the pressing pressure was adjusted to 180 MPa and held for 2 minutes.

[0052] Step 3: High-temperature solution doping with boron: The green body obtained in step two was placed in a high-temperature tube furnace, and high-purity nitrogen gas (flow rate 120 mL / min) was introduced. The temperature was increased to 1600°C at a rate of 10°C / min, and held for 4 hours. The cooling method was the same as in Example 1.

[0053] Step 4: Crushing, Screening and Secondary Molding Similar to Example 1, after sieving, it was pressed again under a pressure of 180 MPa and sintered at 850°C for 1.5 hours under an argon atmosphere.

[0054] Step 5: Electrolytic superhydrophilic modification of electrodes: The electrolyte was a 10 mmol / L Na₂SO₄ aqueous solution. A constant potential mode was used, with the electrode potential set at +2.2 V (vs. SCE), the treatment time at 40 minutes, and the electrolyte temperature controlled at 35℃.

[0055] Step Six: Post-processing: Same as Example 1.

[0056] Performance testing: Under the same simulated zinc electrolysis conditions, the oxygen evolution overpotential of this electrode was 0.36 V (vs. SCE), the surface contact angle was 9° (superhydrophilic), the average bubble detachment diameter was reduced to 11 μm, the resistivity was reduced by 28% compared to undoped graphite, the DC power consumption per ton of zinc was 2820 kWh, which is 12% lower than that of traditional electrodes; the anode energy consumption (per ton of zinc) was 2876 kWh / t; the oxygen evolution efficiency was improved to 96.2%; after 500 hours of operation, the electrode mass loss rate was 2.9%, and the lead content in the cathode zinc was <0.0015wt%, thus achieving the pollution reduction targets of heavy metal anode replacement and bubble behavior regulation.

[0057] Comparative Example 1 (Conventional lead-based alloy electrode): A Pb-0.8%Ag alloy electrode was used, and tests were conducted under the same zinc electrolysis conditions. The oxygen evolution overpotential was 0.85 V, the surface contact angle was 99.3° (hydrophobic), the DC power consumption per ton of zinc was 3104 kWh, and the oxygen evolution efficiency was approximately 92.7%. The average bubble detachment diameter was 50 μm, indicating poor bubble behavior control and severe particulate contamination. After 200 hours of operation, a PbO2 passivation layer appeared on the surface, and the cell voltage increased by 15%. The lead content in the cathode zinc was 0.008 wt%, exceeding the high-purity zinc standard requirements, thus failing to achieve heavy metal anode replacement.

[0058] Comparative Example 2 (boron-doped graphite electrode without superhydrophilic modification): Boron-doped graphite electrodes were prepared according to steps one through four of Example 1, but the electrode electrolysis superhydrophilic treatment in step five was omitted. Performance testing: The oxygen evolution overpotential was 0.54 V (low), but the surface contact angle was 108° (still hydrophobic), the average bubble detachment diameter was 28 μm, bubble desorption was slow, the bubble behavior control effect was poor, particulate matter contamination was not effectively reduced, the DC power consumption per ton of zinc was 3049 kWh, and the oxygen evolution efficiency was approximately 89.5%; after 500 hours of operation, the electrode mass loss rate was 5.1%, higher than the 2.3% in Example 1, indicating that the oxygen-containing functional group layer formed by superhydrophilic modification has a synergistic effect on inhibiting oxidation and detachment. The zinc and lead content of the cathode was <0.001 wt%, and although there was no heavy metal contamination, the advantages of superhydrophilicity and bubble control were not fully utilized.

[0059] The above embodiments and comparative examples fully illustrate that this invention, through the powder metallurgy route "starting from graphite powder" combined with the synergistic effect of solid solution boron doping and electrode electrolysis superhydrophilic modification, has successfully developed superhydrophilic graphite electrode materials. This has achieved the reduction of heavy metal pollution through heavy metal anode replacement and the reduction of particulate matter pollution through bubble behavior regulation. Significant effects have been achieved in reducing oxygen evolution overpotential, improving bubble desorption performance, inhibiting graphite oxidation and shedding, and improving the purity of zinc products, thus achieving efficient, clean, and stable operation of the electrolysis process.

Claims

1. A superhydrophilic boron-doped graphite electrode for use in electrolysis processes, characterized in that, The electrode comprises a graphite substrate and the following functional layers sequentially constructed on the surface of the substrate: a solid solution boron-doped layer and a surface superhydrophilic oxygen-containing functional group layer; wherein, in the solid solution boron-doped layer, boron atoms are embedded in the graphite lattice, and the surface superhydrophilic oxygen-containing functional group layer is composed of oxygen-containing functional groups introduced by electrochemical oxidation, so that the hydrophilic contact angle of the electrode surface is less than 10°.

2. The method for preparing a superhydrophilic boron-doped graphite electrode for electrolysis according to claim 1, characterized in that, Includes the following steps: Step 1: Pre-treat graphite powder and mix it with a boron source to obtain a mixed powder; Step 2: Press the mixed powder obtained in Step 1 into a green body; Step 3: The green body obtained in Step 2 is subjected to high-temperature solid solution boron doping treatment to obtain boron-doped graphite bulk material; Step 4: The boron-doped graphite bulk material obtained in Step 3 is crushed, sieved, and then formed into a boron-doped graphite electrode green blank. Step 5: The boron-doped graphite electrode green blank obtained in Step 4 is used as the electrode and placed in an electrolytic cell for electrode electrolysis treatment to perform superhydrophilic modification. Step 6: Take out the electrode processed in Step 5 and perform post-processing to obtain a superhydrophilic boron-doped graphite electrode for zinc electrolysis.

3. The method for preparing a superhydrophilic boron-doped graphite electrode for electrolysis according to claim 2, characterized in that, Step one includes the following specific steps: Select high-purity graphite powder and boron source, place the graphite powder and boron source in a ball mill jar, add zirconia grinding balls, and ball mill at 100-400 rpm for 2-12 hours under an inert atmosphere or a closed dry process, so that the boron source is uniformly coated on the surface of the graphite powder or mixed with the graphite powder; wherein, the mass of boron element accounts for 1.0% to 5.0% of the mass of graphite powder. The second step is specifically as follows: the mixed powder obtained in the first step is loaded into a metal mold, and uniaxial dry pressing is used for molding. After demolding, a green body is obtained; wherein, the pressing pressure is 100-200 MPa, and the holding time is 1-3 minutes. The specific steps of step three are as follows: the green blank obtained in step two is placed in a boron-doped furnace and heated to 1100-1800℃ under an inert atmosphere and held for 2-8 hours. During this process, boron is released from the boron source and diffuses into the graphite lattice, replacing some carbon atoms to form boron-doped graphite bulk material. Step four includes: pressing the uniform boron-doped graphite powder obtained after sieving into shape again according to the method in step two to obtain a boron-doped graphite electrode green body with the final required shape and size. Step five includes: the electrolyte for electrode electrolysis is a neutral salt solution; In step six, the post-processing steps include: washing the removed electrode with deionized water and drying it at 80-100℃ for 2-4 hours.

4. The method for preparing a superhydrophilic boron-doped graphite electrode for electrolysis according to claim 3, characterized in that, In step five, the neutral salt solution is a 1-100 mmol / L sodium sulfate aqueous solution. Under electrode polarization conditions, the surface of the boron-doped graphite electrode green body undergoes mild electrochemical oxidation, introducing oxygen-containing functional groups and changing the surface from a hydrophobic state to a superhydrophilic state.

5. The method for preparing a superhydrophilic boron-doped graphite electrode for an electrolysis process according to claim 3, characterized in that, In step one, the high-purity graphite powder has a purity ≥99.9%, a particle size ≤45 μm, an ash content ≤0.05%, and a tap density of 0.60–0.80 g / cm³; the boron source is selected from one or more of the following: boric acid with a purity ≥99.5%, borax with a purity ≥99.0%, boron oxide with a purity ≥98.0%, or elemental boron powder with a purity ≥95%; the mass of boron element accounts for 2.0%–4.0% of the mass of graphite powder; the ball milling uses a zirconium oxide or agate ball milling jar, the diameter of the milling balls is 5–10 mm, and the ball-to-material mass ratio is 10:1–20:1; high-purity argon gas with a flow rate of 0.5–1 L / min is introduced for protection during ball milling; the ball milling speed is 200–300 rpm, and the ball milling time is 4–8 hours.

6. The method for preparing a superhydrophilic boron-doped graphite electrode for an electrolysis process according to claim 3, characterized in that, In step two, the pressing and molding process uses a cemented carbide or stainless steel mold with an inner surface roughness of ≤0.8 μm, a pressing pressure of 120–180 MPa, and a holding time of 2 minutes; the green compact density reaches 70%–85% of the theoretical density, and the thickness is 5–15 mm.

7. The method for preparing a superhydrophilic boron-doped graphite electrode for an electrolysis process according to claim 3, characterized in that, In step three, the boron-doping furnace is a high-temperature tubular furnace, a box furnace, or a dedicated boron-doping furnace, with a maximum operating temperature ≥1800℃ and a temperature control accuracy of ±5℃. The green billet is placed in a graphite crucible or corundum boat. First, a vacuum is drawn to ≤10Pa, then high-purity argon or high-purity nitrogen with a purity greater than ≥99.999% is introduced at a flow rate of 100–200 mL / min, and the gas is purged three times to ensure that the oxygen content in the furnace is ≤10 ppm. The heating rate is 5–10℃ / min, the holding temperature is 1400–1600℃, and the holding time is 4–6 hours. After the holding period, the furnace is allowed to cool naturally to room temperature, and inert gas is kept circulating until the furnace temperature is below 200℃.

8. The method for preparing a superhydrophilic boron-doped graphite electrode for an electrolysis process according to claim 3, characterized in that, In step four, crushing is performed using an agate mortar and pestle or a light ball mill; the sieve mesh size is 100-200 mesh; the secondary forming pressing pressure is increased to 150-200 MPa, and the holding time is 2-3 minutes; the green body after secondary forming is placed in a sintering furnace, and under an argon or nitrogen atmosphere with a flow rate of 100 mL / min, the temperature is increased to 800-1000℃ at a rate of 5℃ / min, and the temperature is held for 1-2 hours, followed by furnace cooling.

9. A method for preparing a superhydrophilic boron-doped graphite electrode for an electrolysis process according to claim 4, characterized in that, In step five, the sodium sulfate aqueous solution concentration is 5–50 mmol / L, prepared using deionized water with a resistivity ≥18 MΩ·cm; the electrode electrolysis treatment employs a three-electrode system, with a boron-doped graphite electrode as the working electrode, a platinum sheet or high-purity graphite plate as the counter electrode, and a saturated calomel electrode or Ag / AgCl electrode as the reference electrode; in constant potential mode, the electrode potential is set to +2.0–+2.5 V vs. SCE; in constant current mode, the current density is set to 30–80 mA / cm². 2 The processing time is 10 to 60 minutes, and the electrolyte temperature is controlled at 25 to 60°C. During electrolysis, the electrolyte is gently stirred with a magnetic stirrer at a speed of 100 to 200 rpm.

10. A method for preparing a superhydrophilic boron-doped graphite electrode for an electrolysis process according to claim 9, characterized in that, In step five, when using constant potential mode, the electrode potential is set to +2.2 V vs. SCE; when using constant current mode, the current density is set to 40–60 mA / cm². 2 The superhydrophilic modification is such that the hydrophilic contact angle of the electrode surface is less than 10°; the oxygen-containing functional groups introduced on the surface include C=O, C-OH, and COOH.

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