A lead dioxide electrodeposition copper cycle method with built-in auxiliary cathode

Abstract

The application discloses a lead dioxide copper electrodeposition cycle method with an auxiliary cathode, an acid-resistant auxiliary cathode is arranged in an electrodeposition tank, copper ions are precipitated on a graphite cathode preferentially to lead ions during electrodeposition, and lead dendrites are avoided from being generated on the cathode; after a single batch of plated layers is deposited, the polarity of the electrode is switched, a copper-coated graphite plate is used as a copper-dissolving anode, and the built-in auxiliary cathode is paired and powered, so that copper is electrochemically dissolved in situ in the same tank; after the polarity of the electrode is restored, continuous electrodeposition is carried out, and the anode reaction self-generates free nitric acid which can slowly dissolve the copper precipitated on the surface of the auxiliary cathode, so that the closed loop cycle of copper ions in the electrolyte is realized; a stable leveling additive for a nitric acid system is compounded and matched, the auxiliary cathode is made of acid-resistant conductive material, the cathode does not need to be disassembled, no additional copper-dissolving reagent needs to be added, copper salt supplement is reduced, and the continuous production stability and the lead dioxide plating layer deposition quality are improved.

Description

Technical Field

[0001] This invention relates to the field of electrodeposition technology, and in particular to a lead dioxide electrodeposition copper cycling method with an integrated auxiliary cathode. Background Technology

[0002] Lead dioxide coatings possess advantages such as high oxygen evolution potential, resistance to acid and alkali corrosion, dimensional stability, and long service life. Titanium-based electrodes made from lead dioxide are widely used in electrochemical oxidation treatment of industrial wastewater and electrowinning in hydrometallurgical processes. Electrodeposition is the mainstream process for preparing lead dioxide coatings. This process uses an acidic electrolyte containing nitric acid and lead salts, with a graphite plate as the cathode and a pretreated titanium substrate as the anode to complete the coating deposition. During electrodeposition, lead ions are easily reduced at the cathode to form lead dendrites. These dendrites continuously consume the lead components in the electrolyte, and detached particles can easily cause short circuits within the tank, severely affecting production stability and coating deposition quality. The industry-standard solution is to add copper ions to the electrolyte. Utilizing the lower reduction potential of copper ions and their preferential deposition of elemental copper on the graphite cathode surface, when the overall copper ion concentration in the electrolyte is insufficient or local mass transfer is inadequate, the barrier effect of preferential copper ion deposition weakens, and lead ions will directly discharge and be reduced at the cathode surface, regenerating lead dendrites.

[0003] This process has significant drawbacks: throughout the electrodeposition process, copper ions are continuously consumed and converted into elemental copper on the graphite cathode surface, leading to a continuous decrease in the copper ion concentration in the electrolyte. This necessitates the continuous replenishment of copper salt raw materials during production, significantly increasing material costs. Furthermore, the copper deposits on the graphite cathode surface require periodic cleaning, consuming substantial production time and reducing continuous production efficiency. Currently, the industry primarily uses two methods to clean copper deposits on cathodes: physical stripping and offline chemical dissolution. Both methods have inherent and unavoidable drawbacks.

[0004] Both of the existing processes mentioned above only have a single copper ion replenishment pathway. The copper ion decay rate in the electrolyte is fast, requiring frequent manual monitoring, copper salt replenishment, and acidity adjustment, making the process control cumbersome. Furthermore, they cannot utilize the free nitric acid produced by the electrodeposition anode reaction to complete copper dissolution in a coordinated manner. The acidity of the system fluctuates greatly, making it difficult to stably control the copper dissolution rate. This makes it difficult to achieve long-term closed-loop recycling of copper ions in the electrolyte, limiting the cost and efficiency improvement of large-scale continuous production of lead dioxide electrodes. Summary of the Invention

[0005] The main objective of this invention is to provide a copper cyclic method for lead dioxide electrodeposition with a built-in auxiliary cathode. This method achieves in-situ electrochemical dissolution of copper at the graphite cathode by switching polarity, and utilizes self-generated free nitric acid from the electrodeposition process to dissolve the copper deposited at the auxiliary cathode. This completes the closed-loop circulation of copper ions within the tank without disassembling the electrodes or adding external copper dissolving agents, ensuring the stability and quality of continuous lead dioxide plating.

[0006] To achieve the above objectives, the present invention provides a lead dioxide electrodeposition copper cycling method with a built-in auxiliary cathode, comprising the following steps: In an electrolyte containing nitric acid, lead salt and copper ions, a pretreated titanium substrate is used as the anode and a graphite plate as the cathode. An acid-resistant auxiliary cathode is arranged in the electrodeposition tank. A DC power supply is turned on to perform lead dioxide electrodeposition. An oxidation reaction occurs at the anode to generate a lead dioxide coating and continuously generate hydrogen ions. Copper ions in the electrolyte are preferentially reduced and deposited on the surface of the graphite plate cathode to form elemental copper. After a single batch of lead dioxide is deposited to the preset thickness, the deposition power supply is disconnected, and the graphite plate with elemental copper on its surface is reconnected to the positive terminal of the power supply as the copper dissolution anode. The auxiliary cathode is connected to the negative terminal of the power supply, and DC current is applied to perform in-situ electrochemical dissolution of copper on the copper-coated graphite plate. The elemental copper on the surface of the graphite plate is oxidized and converted into copper ions that enter the electrolyte. After the in-situ copper dissolution is completed, the original polarity of the graphite plate and the auxiliary cathode is restored, and the next batch of titanium substrate to be plated is put in as the anode. The lead dioxide electrodeposition is restarted. The copper deposited on the surface of the auxiliary cathode is gradually dissolved by the free nitric acid continuously generated by the anode during the electrodeposition process and returns to the electrolyte in the form of copper ions. After each batch of electrodeposition, the above in-situ copper dissolution operation is repeated to reuse copper ions in the electrolyte in a closed loop.

[0007] Furthermore, the step of reconnecting the graphite plate coated with elemental copper to the positive terminal of the power supply as the copper-dissolving anode, connecting the auxiliary cathode to the negative terminal of the power supply, and applying direct current to perform in-situ electrochemical copper dissolution on the copper-coated graphite plate includes: The current density for in-situ electrochemical copper dissolution is controlled at 2-10 A / dm², and the electrolyte temperature is maintained at 60-70℃. When electricity is applied, the elemental copper on the surface of the graphite plate is completely dissolved, and the graphite plate is restored to a clean surface. During the copper dissolution process, copper ions dissolve into the electrolyte, and at the same time, some metallic copper is deposited on the surface of the auxiliary cathode.

[0008] Furthermore, the step of energizing the graphite plate until the elemental copper on the surface is completely dissolved and the graphite plate regains its clean surface includes: During the in-situ electrochemical copper dissolution process, the color change of the graphite plate surface is monitored. When the surface of the graphite plate changes from copper red to the original graphite color, it is determined that the elemental copper has been completely dissolved, and the power is stopped.

[0009] Furthermore, the step of gradually dissolving the copper deposited on the auxiliary cathode surface by the free nitric acid continuously generated by the anode during the electrodeposition process includes: During the electrodeposition process, an oxidation reaction continuously occurs at the anode to generate hydrogen ions, and the concentration of free nitric acid in the electrolyte increases simultaneously. The free nitric acid produced by the system itself dissolves the copper deposited on the surface of the auxiliary cathode. The copper deposited on the auxiliary cathode surface slowly dissolves and transforms into copper ions, which are then dispersed into the electrolyte, continuously replenishing the copper ions consumed during the electrodeposition process.

[0010] Furthermore, the step of the anode undergoing an oxidation reaction to generate a lead dioxide coating and continuously generating hydrogen ions, and copper ions in the electrolyte preferentially reducing and depositing elemental copper on the graphite cathode surface, includes: During the electrodeposition process, excess hydrogen ions in the system are consumed by adding lead oxide slurry, and the concentration of free nitric acid in the electrolyte is maintained at 2-8 g / L. When the concentration of free nitric acid in the system is low during or after the electrochemical copper dissolution process, a small amount of nitric acid should be added to maintain the acidic environment of the system. During the copper dissolution stage, the concentration of free nitric acid is controlled at 5-8 g / L to enhance the copper dissolution side reaction and reduce the amount of copper deposited on the auxiliary cathode surface. If the initial acidity of the system is too high before copper dissolution, the initial acidity is reduced accordingly to match the acid consumption during the copper dissolution process.

[0011] Furthermore, the step of connecting the DC power supply for lead dioxide electrodeposition includes: The electrodeposition current density was controlled at 100-300 A / m², the electrolyte temperature was maintained at 60-70℃, and the single electrodeposition time was set to 6h. During the electrodeposition process, lead oxide slurry is continuously replenished to stabilize the lead ion concentration in the electrolyte and maintain the copper ion concentration in the system above 1 g / L. A leveling additive is added to the electrolyte. The leveling additive is selected from at least one of dodecyltrimethylammonium bromide, dodecyl dimethylamine hydantoin, and N-butyl-N-methylpiperidine bromide, and the addition amount is 0.05-0.5 g / L.

[0012] Furthermore, the acid-resistant auxiliary cathode is made of any one of the acid-resistant conductive materials selected from graphite plates, graphite rods, or titanium plates.

[0013] The present invention also provides a titanium-based lead dioxide electrode prepared by the above-described method, wherein the electrode is based on a pretreated titanium substrate and has a lead dioxide coating deposited on its surface.

[0014] Furthermore, a tin-antimony oxide intermediate layer is provided between the titanium substrate and the lead dioxide coating, and the lead dioxide coating is a cerium-doped lead dioxide active layer.

[0015] This invention also provides an application of a titanium-based lead dioxide electrode, which is used as an oxygen evolution anode in water treatment or hydrometallurgical fields.

[0016] The lead dioxide electrodeposition copper cycling method with an integrated auxiliary cathode provided in the above embodiments has the following beneficial effects: The structure uses a pre-installed auxiliary cathode in the tank, and copper can be electrochemically dissolved in situ simply by switching the electrode polarity. There is no need to disassemble the graphite cathode or add a separate copper dissolution tank. It is compatible with fixed integrated electrodeposition tanks, reducing equipment and labor costs. A dual copper ion replenishment pathway is constructed: copper is dissolved by anodic oxidation of graphite plates, and copper is slowly dissolved by nitric acid produced by electrodeposition in the auxiliary cathode. Copper ions are recycled in a closed loop for a long time, which greatly reduces the amount of copper salt replenishment. When the concentration of free nitric acid in the system is low during or after the electrochemical copper dissolution process, a small amount of nitric acid should be added to maintain the acidic environment of the system, so as to avoid residual oxidant from damaging the density of the lead dioxide coating and improve the coating deposition quality. The copper dissolution process shares the same electrolyte system as the electrodeposition process, eliminating the need to stop the machine to clean the cathode separately, ensuring continuous operation of the production line and improving equipment utilization. The dynamic balance between the hydrogen ions generated by electrodeposition and the acid consumed by copper dissolution ensures the self-stabilization of the system's acidity. Combined with a special stabilizing and leveling additive, it can continuously suppress lead dendrites, ensuring the deposition quality of lead dioxide coatings and simplifying the daily management of electrolytes. Attached Figure Description

[0017] Figure 1 This is a flowchart of a lead dioxide electrodeposition copper cycling method with a built-in auxiliary cathode provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the in-situ copper melting process in a single-cell chamber with an embedded auxiliary cathode in this invention. Figure 3 This is a comparison curve of the changes in copper nitrate concentration in each group of electrolytes in this invention; Figure 4 These are images of the graphite cathodes after electrodeposition in various examples of this invention. The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0019] Reference Figure 1 This is a schematic diagram of a lead dioxide electrodeposition copper cycling method with a built-in auxiliary cathode proposed in this invention, including the following steps: S1, in an electrolyte containing nitric acid, lead salt and copper ions, a pretreated titanium substrate is used as the anode and a graphite plate as the cathode. An acid-resistant auxiliary cathode is arranged in the electrodeposition tank. A DC power supply is turned on to perform lead dioxide electrodeposition. An oxidation reaction occurs at the anode to generate a lead dioxide coating and continuously generate hydrogen ions. Copper ions in the electrolyte are preferentially reduced and deposited on the surface of the graphite plate cathode to form elemental copper. S2. After a single batch of lead dioxide is deposited to the preset thickness, the deposition power supply is disconnected. The graphite plate with elemental copper on its surface is reconnected to the positive terminal of the power supply as the copper dissolution anode, and the auxiliary cathode is connected to the negative terminal of the power supply. Direct current is applied to the copper-coated graphite plate to perform in-situ electrochemical copper dissolution. The elemental copper on the surface of the graphite plate is oxidized and converted into copper ions that enter the electrolyte. S3. After the in-situ copper dissolution is completed, the original polarity of the graphite plate and the auxiliary cathode is restored. The next batch of titanium substrate to be plated is put in as the anode, and lead dioxide electrodeposition is started again. The copper deposited on the surface of the auxiliary cathode is gradually dissolved by the free nitric acid continuously generated by the anode during the electrodeposition process and returns to the electrolyte in the form of copper ions. S4. After each batch of electrodeposition, repeat the above in-situ copper dissolution operation to reuse copper ions in the electrolyte in a closed loop.

[0020] As described in step S1 above, an acidic electrolyte system containing lead nitrate and copper nitrate is prepared. The electrolyte contains a stabilizing and leveling component adapted to the nitric acid environment, ensuring the overall electrolyte environment inhibits the crystal growth of elemental lead at the cathode. The titanium substrate undergoes polishing, acid washing, and activation treatment, and a tin-antimony oxide intermediate layer is formed on the surface through thermal decomposition. Cerium is introduced during the plating preparation stage to improve the corrosion resistance of the lead dioxide electrode. An acid-resistant conductive auxiliary cathode is fixedly arranged inside the electrodeposition tank. The auxiliary cathode can be made of graphite plates, titanium plates, or a combination of multiple graphite rods or strips. The area ratio of the auxiliary cathode to the working graphite cathode can be adjusted to 1:1 to 3:1, with both submerged below the electrolyte surface in separate sections. Increasing the overall area of ​​the auxiliary cathode reduces the thickness of the deposited copper layer and increases the solid-liquid contact area, accelerating the copper dissolution rate using self-produced nitric acid in the subsequent steps. The copper dissolution process can be flexibly controlled by adjusting the size and overall shape of the auxiliary cathode. After the DC power is turned on, the electrodeposition reaction continues. Lead ions in the anode region undergo oxidation to gradually form a lead dioxide coating. This oxidation reaction simultaneously and continuously releases hydrogen ions, and the free nitric acid content inside the electrolyte accumulates and increases with deposition time. Copper ions in the electrolyte have a lower reduction potential and preferentially migrate to the graphite cathode surface, forming a uniform copper coating. This copper layer isolates lead ions from direct contact with the graphite substrate, eliminating the risk of short circuits caused by continuous lead dendrite precipitation and detachment. During the electrodeposition process, lead oxide slurry is continuously added to the system to maintain a stable lead ion content. The copper component in the electrolyte remains within its effective range for a long period. The entire reaction system relies on its own anodic reaction to accumulate acidity, requiring no external addition of acidic agents. Simultaneously, the titanium substrate coating is formed and uniform copper deposition occurs on the graphite working cathode surface within the tank, providing the raw material reserves needed for copper ion recycling in the single-tank in-situ copper dissolution process.

[0021] As described in step S2 above, after the lead dioxide coating in a single batch reaches the preset thickness, the DC power supply circuit is cut off, and the electrode wiring method inside the electrodeposition tank is adjusted. The graphite plate with a copper layer on its surface is connected to the positive terminal of the power supply to act as the copper-dissolving anode, and the acid-resistant auxiliary cathode pre-installed in the tank is connected to the negative terminal of the power supply. The entire electrode structure remains immersed in the original electrolyte, and no electrode components need to be removed from the tank. After the copper-dissolving DC power is turned on, the elemental copper on the surface of the graphite plate undergoes an oxidation reaction and dissociates into the liquid phase system. The copper ion content inside the electrolyte increases simultaneously, and the dissolved copper ions are evenly dispersed throughout the electrolyte. During the copper-dissolving energized operation, the electrolyte maintains the same operating temperature range as the electrodeposition stage. The newly dissolved copper ions in the electrolyte continuously migrate to the surface of the energized auxiliary cathode and are reduced and deposited, so that a thin copper layer gradually forms on the surface of the auxiliary cathode. Under the electrodeposition condition, the auxiliary cathode has no external power supply and no copper deposition occurs. The appearance of the graphite plate surface is continuously monitored. When the copper-red color completely fades, revealing the original graphite color, the copper dissolving power supply is cut off, indicating that the elemental copper on the graphite plate surface has been completely dissolved. The entire copper dissolving process is completed within the same electrodeposition tank without the need for an additional independent copper dissolving container or the transfer and disassembly of the cathode. The copper ions generated during copper dissolution are directly retained in the electrolyte, providing a copper recycling source for the next round of electrodeposition processes. The copper layer deposited on the cathode surface also provides a circulating medium for the self-produced nitric acid copper dissolution process.

[0022] As described in step S3 above, after the copper dissolution process is completed, the electrode wiring is adjusted, the graphite plate and the built-in auxiliary cathode are restored to their initial polarity, and a new pretreated titanium substrate is placed in the tank to serve as the anode for the next round of electrodeposition. The entire electrode assembly remains immersed in the original electrolyte system without needing to drain or replace the tank solution. The DC power supply is then connected to restart the lead dioxide deposition reaction. Oxidation continues in the anode area to generate a lead dioxide coating, and the reaction simultaneously releases hydrogen ions, continuously increasing the free nitric acid content in the electrolyte. Copper ions in the electrolyte still preferentially migrate and deposit towards the graphite cathode. The thin copper layer remaining on the surface of the auxiliary cathode is the result of precipitation during the previous in-situ electrochemical copper dissolution process. The gradually accumulating free nitric acid in the electrolyte continues to react with the copper deposited on the surface of the auxiliary cathode, slowly converting the surface copper into copper ions that diffuse evenly into the liquid phase system, continuously replenishing the copper components consumed during the electrodeposition process. The two copper ion replenishment pathways complement each other. The graphite plate copper dissolution process provides a phased increase in copper ions, while the auxiliary cathode's self-produced acid dissolution continuously and slowly releases copper ions during the continuous electrodeposition stage, stabilizing the copper component content within the electrolyte. This significantly reduces the amount and frequency of copper salt replenishment. Only a small amount of copper salt needs to be added during long-term continuous production when excessive copper component loss occurs, which is sufficient to maintain stable system operation. The entire process relies on the same electrolyte circulation. The anode's self-produced nitric acid directly completes the dissolution and conversion of copper deposited on the auxiliary cathode, without introducing external copper dissolving agents. The system's acidity and copper ion content rely on their own dynamic equilibrium through reaction, supporting multiple batches of uninterrupted continuous deposition of lead dioxide coatings.

[0023] As described in step S4 above, after all electrodeposition processes are completed, the power is cut off again, and the operation of switching the polarity of the graphite plate and the built-in auxiliary cathode is repeated to carry out in-situ electrochemical copper dissolution treatment again. The entire process uses the same electrolyte system, and there is no need to drain or replace the liquid in the tank. The two copper ion replenishment paths, graphite plate anode copper dissolution and auxiliary cathode acid copper dissolution, continuously cycle and play their roles. The graphite plate copper dissolution process releases copper ions to replenish the electrolyte consumption, while the copper deposited on the surface of the auxiliary cathode is slowly dissolved by the system's self-produced nitric acid during the electrodeposition stage, continuously releasing copper components. The two replenishment methods operate alternately, allowing the copper composition of the electrolyte to remain within a stable range for a long time. The anodic reaction continuously generates hydrogen ions, while the copper dissolution reaction continuously consumes hydrogen ions. The acidity of the system relies on its own dynamic equilibrium. During the electrodeposition stage, excess hydrogen ions are consumed by adding lead oxide slurry, and free nitric acid is stably controlled at 2-8 g / L. During the copper dissolution stage, the acidity is maintained at 5-8 g / L to adjust the amount of copper deposited at the auxiliary cathode. If the acidity is insufficient, a small amount of nitric acid is added, significantly reducing the frequency of artificial acid adjustment. The stabilizing and leveling components in the electrolyte continue to play a role, inhibiting the formation of lead dendrites at the cathode in the long term. In the continuous preparation process of multiple batches, there is no need to continuously add copper salt raw materials. Copper elements repeatedly transform between the ionic form in the electrolyte and the elemental form at the cathode, realizing the closed-loop recycling of copper resources in the tank. The entire process is compatible with integrated electrodeposition tanks where the electrodes cannot be disassembled. During continuous production, the lead dioxide coating deposited on the anode surface and the tin-antimony oxide intermediate layer are well bonded, and the adhesion and corrosion resistance of the cerium-doped active coating remain stable throughout.

[0024] The present invention will be specifically described below through examples and comparative examples.

[0025] Example 1 In this embodiment, a 5cm × 6cm industrial pure titanium substrate was selected. The substrate was then sanded and acid-washed with dilute nitric acid to remove surface oxide scale and oil. A tin-antimony oxide intermediate layer was then prepared on the titanium substrate surface using a thermal decomposition process to obtain Ti@Sb-SnO. x Composite substrate. The tin-antimony oxide interlayer isolates the titanium substrate from direct corrosion by the nitric acid electrolyte, while simultaneously enhancing the bonding strength between the lead dioxide coating and the titanium substrate, preventing coating detachment and failure.

[0026] Lead oxide slurry was prepared and dissolved in 34% dilute nitric acid by stirring, maintaining the pH of the system at 1.5. Copper nitrate was added to the solution to supply copper ions, and cerium nitrate was added to modify the lead dioxide coating. Dodecyltrimethylammonium bromide was then added as a stabilizing and leveling additive for the nitric acid system. The working electrolyte was prepared by adding pure water to the final volume. Copper ions preferentially deposit at the cathode, isolating lead ions and inhibiting lead dendrite formation at its source. Cerium nitrate doping into the lead dioxide coating improves the oxygen evolution catalytic performance and corrosion resistance of the electrode. The selected leveling additive is not easily decomposed under strong nitric acid oxidation, continuously optimizing the smoothness of the copper deposition at the cathode. The total electrolyte volume was controlled at 2 L, and the electrolyte temperature was maintained at 60–70 °C throughout the process.

[0027] Figure 2 This is a schematic diagram of the electrodeposition tank structure used in this embodiment. Figure 2 The left side shows a schematic diagram of the electrode arrangement under electrodeposition conditions. Figure 2 The diagram on the right shows the electrode arrangement for in-situ electrochemical copper dissolution. The electrodeposition tank is an integrated, non-removable structure. An acid-resistant graphite auxiliary cathode is fixedly installed inside the tank. The Ti@Sb-SnOx substrate to be plated serves as the working anode, and the graphite plate acts as the deposition cathode. All three types of electrodes are submerged below the electrolyte surface. The entire electrode assembly does not require disassembly; simply switching the electrode wiring polarity allows switching between the deposition and copper dissolution processes. No separate copper dissolution tank is needed, making it suitable for large-scale fixed electrodeposition tank production scenarios.

[0028] The titanium substrate was connected to the positive terminal of the power supply, and the graphite plate to the negative terminal. Electrodeposition was initiated by connecting the DC power supply and continued for 6 hours. During the electrodeposition process, lead oxide slurry was intermittently added to stabilize the lead ion content in the system. The electrochemical reactions occurring in this stage are as follows: Anode reaction: + + +2

[0029] Lead ions in the electrolyte migrate to the surface of the titanium substrate anode and undergo an oxidation reaction to form a dense lead dioxide coating. For every 1 mol of lead dioxide generated, 4 mol of hydrogen ions are released simultaneously. The continuous accumulation of hydrogen ions increases the concentration of free nitric acid in the electrolyte, thus reserving an acidic medium for the autolysis reaction that assists in the deposition of copper at the cathode.

[0030] Cathode main reaction:

[0031] Copper ions have a lower reduction potential than lead ions, and are preferentially reduced on the surface of the graphite cathode to form a uniform copper layer, thus preventing lead ions from precipitating dendrites at the cathode. Cathode side reaction: +2 = ↑ A small amount of hydrogen ions undergo a hydrogen evolution side reaction at the cathode, which does not interfere with the main deposition process.

[0032] After electrodeposition, the titanium substrate is removed, washed with water and dried to obtain a cerium-doped titanium-based lead dioxide electrode. At this point, the surface of the graphite plate is completely covered with a layer of copper-red elemental copper.

[0033] Disconnect the deposition power supply, adjust the electrode polarity, connect the copper-clad graphite plate to the positive terminal of the power supply as the copper-dissolving anode, connect the built-in graphite auxiliary cathode to the negative terminal of the power supply, and apply direct current to carry out in-situ copper dissolution treatment. Maintain the electrolyte temperature at 60–70°C. The electrochemical reactions in this stage are as follows: Copper dissolution anodic reaction (graphite plate surface):

[0034] The elemental copper on the surface of the graphite plate loses electrons and oxidizes into copper ions, which diffuse evenly into the electrolyte, thus recovering the copper element. The copper color on the plate is continuously observed; once the copper-red color completely fades, revealing the original graphite color, the copper dissolution is considered complete. The entire copper dissolution process is completed within the same electrodeposition tank, without transferring or disassembling any electrodes, and without adding any external copper-dissolving agents such as nitric acid or hydrogen peroxide. Copper re-dissolution is achieved solely through electrochemical oxidation.

[0035] After the copper dissolution process is completed, the original electrode polarity is restored, and a brand-new pretreated titanium substrate is used as the anode. Lead dioxide electrodeposition is then restarted. The anode continues to undergo oxidation, generating hydrogen ions, and the concentration of free nitric acid in the electrolyte continues to increase. This facilitates a chemical reaction between the copper deposited on the cathode surface and the self-generated nitric acid. 3 + +2 = 3 +2 ↑+

[0036] The system's own free nitric acid slowly dissolves the elemental copper on the surface of the auxiliary cathode, converting the copper back into copper ions and dispersing them into the electrolyte, continuously replenishing the copper components consumed in electrodeposition. This process forms two synergistic copper supply pathways: the graphite plate dissolves copper in situ to release copper ions, while the auxiliary cathode's self-generated acid dissolves copper to continuously and slowly release copper ions, stabilizing the copper ion content in the electrolyte.

[0037] In this multi-batch continuous electrodeposition process, no additional copper nitrate raw material is required. After production, electrolyte samples are taken for testing, and the copper ion concentration is 1.8 g / L, which is higher than the critical concentration required to suppress lead dendrites. There is no lead dendrite shedding or short circuit inside the electrodeposition tank, and the lead dioxide coating deposited on the anode surface is smooth and dense, without defects such as bubbles or pinholes. Compared with conventional processes without auxiliary cathodes or copper circulation, this embodiment significantly reduces the amount of copper salt raw material added. The entire process does not require shutdown to disassemble the cathode, and the integrated electrodeposition tank can achieve uninterrupted continuous production of multiple batches.

[0038] Comparative Example 1 The lead dioxide electrodeposition working solution was prepared according to the same formula as in Example 1, with the electrolyte composition and concentration remaining consistent. The pH of the solution was controlled at approximately 1.5. The deposition tank remained the same, but without an auxiliary cathode. A titanium-based antimony-tin oxide substrate was used as the anode, and a parallel graphite plate was immersed in the electrolyte as the cathode. The plating solution temperature was maintained at 60-70°C, and the electrolyte volume was maintained at 2L. After connecting the DC power supply, the current density was controlled at 100-300 A / m², and deposition continued for 6 hours. During the first batch of electrodeposition, lead oxide slurry and copper nitrate were periodically added to maintain the copper nitrate concentration in the plating solution above 1 g / L and the nitric acid concentration below 8 g / L. After the first batch was completed, the deposited lead dioxide electrode was removed, copper nitrate was added to the initial concentration of 5 g / L, a new titanium-based anode was replaced, and the second batch of deposition was started. The process parameters for this batch were consistent with the first batch, with no additional copper nitrate added throughout the process, only the nitric acid concentration was controlled below 8 g / L. After deposition, the anode electrode was removed, washed with deionized water, and dried to obtain a titanium-based lead dioxide electrode. The concentration of copper nitrate in the second batch of electrolyte was as follows: Figure 3 As shown, with the extension of deposition time, the color of the electrolyte gradually lightens and the concentration of copper ions continues to decrease. After 6 hours of deposition, the concentration of copper ions in the electrolyte is about 0.7 g / L. The decrease in concentration is significantly higher than that of Example 1 which uses a recycling process. The appearance of the deposited lead dioxide coating in this batch is normal, but the copper ion consumption rate in the plating solution is fast. Copper salt needs to be added frequently and in large quantities to maintain continuous production. The material cost and maintenance cost of long-term operation are relatively high.

[0039] To verify the influence of the auxiliary cathode copper dissolution process, the changes in copper nitrate concentration in the electrolyte of Example 1 and Comparative Example 1 were monitored throughout the second batch of electrodeposition tests. The results are as follows: Figure 3 As shown, the specific analysis is as follows: The initial copper nitrate concentration was set at 5 g / L for both experimental groups. During electrodeposition, copper ions were continuously reduced and deposited at the cathode, and the copper nitrate concentration in both electrolytes gradually decreased with increasing reaction time. The rate of decrease in copper ion concentration directly characterizes the copper recycling capacity of the system; the slower the decrease, the better the copper ion replenishment effect and the higher the process stability.

[0040] Comparative Example 1 had no copper recycling measures; copper ions were consumed without replenishment, resulting in the fastest concentration decrease. After 2 hours of deposition, the concentration dropped to approximately 2.5 g / L; after 4 hours, it approached the critical concentration of 1 g / L for lead dendrite inhibition; and after 6 hours of deposition, the final value was approximately 0.7 g / L, falling below the effective inhibition threshold, making it impossible to stably avoid risks such as lead dendrite growth and plating solution contamination in the long term. Figure 4 As shown in the right figure, dendrites have formed on the surface of the graphite cathode after deposition. In contrast, the copper layer of the graphite cathode in Example 1 is relatively smooth and has no dendrites.

[0041] Example 1 employs an independent dissolution tank circulation process. Through a single-tank in-situ copper dissolution process with an internal auxiliary cathode, copper is dissolved on the graphite plate surface by polarity switching. Copper ion replenishment is achieved by dissolving copper deposited on the auxiliary cathode using self-produced nitric acid via electrodeposition. This process demonstrates excellent copper ion replenishment and the slowest rate of concentration decrease. The concentration is approximately 3.6 g / L after 2 hours of deposition, approximately 2.5 g / L after 4 hours, and approximately 1.8 g / L after 6 hours, with a copper ion concentration retention rate approaching 36%. The system exhibits optimal concentration stability.

[0042] In summary, this invention establishes an anode-cathode system by arranging an auxiliary cathode and a copper-plated graphite electrode in the electrodeposition tank. The process utilizes the electrode reaction to dissolve elemental copper on the surface of the graphite electrode, and leverages the self-generated acidity of electrodeposition to dissolve copper deposits on the auxiliary cathode. No additional copper-dissolving agents are required, achieving a closed-loop circulation of copper ions within the system. This process eliminates the need for prolonged downtime to clean copper deposits on the cathode and does not require disassembly of the cathode plate, significantly improving equipment utilization and production continuity. The copper dissolution process consumes excess nitric acid in the system, preventing the introduction of external strong oxidizing impurities and effectively ensuring the quality of the lead dioxide coating. Furthermore, combined with the acid-consuming effect of lead source replenishment, the system's acidity can dynamically stabilize, reducing manual control, lowering material and maintenance costs, and meeting the requirements for large-scale continuous production of lead dioxide electrodes.

[0043] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, apparatus, article, or method that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, apparatus, article, or method. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, apparatus, article, or method that includes that element.

[0044] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for lead dioxide electrodeposition of copper using a built-in auxiliary cathode, characterized in that, Includes the following steps: In an electrolyte containing nitric acid, lead salts, and copper ions, a pretreated titanium substrate is used as the anode and a graphite plate as the cathode. An acid-resistant auxiliary cathode is placed in the electrodeposition tank. A DC power supply is applied for lead dioxide electrodeposition. An oxidation reaction occurs at the anode to generate a lead dioxide coating and continuously generate hydrogen ions. Copper ions in the electrolyte are preferentially reduced and deposited as elemental copper on the surface of the graphite cathode. During the electrodeposition process, excess hydrogen ions in the system are consumed by adding lead oxide slurry, and the concentration of free nitric acid in the electrolyte is maintained at 2-8 g / L. After a single batch of lead dioxide is deposited to the preset thickness, the deposition power supply is disconnected, and the graphite plate with elemental copper on its surface is reconnected to the positive terminal of the power supply as the copper dissolution anode, and the auxiliary cathode is connected to the negative terminal of the power supply. The current density of in-situ electrochemical copper dissolution is controlled at 2-10 A / dm², and the electrolyte temperature is maintained at 60-70℃. Direct current is applied to perform in-situ electrochemical dissolution of copper-clad graphite plates. The elemental copper on the surface of the graphite plate is oxidized and converted into copper ions, which enter the electrolyte. During the dissolution process, copper ions dissolve into the electrolyte, and simultaneously, some metallic copper is deposited on the surface of the auxiliary cathode. During the dissolution stage, the concentration of free nitric acid is controlled at 5-8 g / L to enhance the copper dissolution side reaction and reduce the amount of copper deposited on the surface of the auxiliary cathode. If the initial acidity of the system is too high before copper dissolution, the initial acidity is reduced accordingly to match the acid consumption during the dissolution process. If the concentration of free nitric acid in the system is too low during or after the electrochemical copper dissolution process, a small amount of nitric acid is added to maintain the acidic environment of the system. The current is applied until the elemental copper on the surface of the graphite plate is completely dissolved and the graphite plate has a clean surface. After the in-situ copper dissolution is completed, the original polarity of the graphite plate and the auxiliary cathode is restored, and the next batch of titanium substrate to be plated is put in as the anode. The lead dioxide electrodeposition is restarted. The copper deposited on the surface of the auxiliary cathode is gradually dissolved by the free nitric acid continuously generated by the anode during the electrodeposition process and returns to the electrolyte in the form of copper ions. After each batch of electrodeposition, the above in-situ copper dissolution operation is repeated to reuse copper ions in the electrolyte in a closed loop.

2. The lead dioxide electrodeposition copper cycling method with an integrated auxiliary cathode according to claim 1, characterized in that, The step of applying electricity until the elemental copper on the graphite plate surface is completely dissolved and the graphite plate is restored to a clean surface includes: During the in-situ electrochemical copper dissolution process, the color change of the graphite plate surface is monitored. When the surface of the graphite plate changes from copper red to the original graphite color, it is determined that the elemental copper has been completely dissolved, and the power is stopped.

3. The lead dioxide electrodeposition copper cycling method with an integrated auxiliary cathode according to claim 1, characterized in that, The step of gradually dissolving the copper deposited on the auxiliary cathode surface during electrodeposition by the free nitric acid continuously generated by the anode includes: During the electrodeposition process, an oxidation reaction continuously occurs at the anode to generate hydrogen ions, and the concentration of free nitric acid in the electrolyte increases simultaneously. The free nitric acid produced by the system itself dissolves the copper deposited on the surface of the auxiliary cathode. The copper deposited on the auxiliary cathode surface slowly dissolves and transforms into copper ions, which are then dispersed into the electrolyte, continuously replenishing the copper ions consumed during the electrodeposition process.

4. The lead dioxide electrodeposition copper cycling method with an integrated auxiliary cathode according to claim 1, characterized in that, The step of connecting a DC power supply for lead dioxide electrodeposition includes: The electrodeposition current density was controlled at 100-300 A / m², the electrolyte temperature was maintained at 60-70℃, and the single electrodeposition time was set to 6h. During the electrodeposition process, lead oxide slurry is continuously replenished to stabilize the lead ion concentration in the electrolyte and maintain the copper ion concentration in the system above 1 g / L. A leveling additive is added to the electrolyte. The leveling additive is selected from at least one of dodecyltrimethylammonium bromide, dodecyl dimethylamine hydantoin, and N-butyl-N-methylpiperidine bromide, and the addition amount is 0.05-0.5 g / L.

5. The lead dioxide electrodeposition copper cycling method with an integrated auxiliary cathode according to claim 1, characterized in that, The acid-resistant auxiliary cathode is made of any one of the following acid-resistant conductive materials: graphite plate, graphite rod, or titanium plate.

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