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Iridium-Tantalum Coated Titanium Anodes

Iridium-Tantalum Coated Titanium Anodes

The best electrodes for oxygen evolution in electrolysis applications are mixed oxides of iridium oxide (IrO₂) and tantalum oxide (Ta₂O₅). The iridium-tantalum-coated titanium electrodes developed by Longsheng Company include options such as plate electrodes, tubular electrodes, mesh electrodes, rod electrodes, and wire electrodes for customer selection. The iridium-tantalum-coated titanium anodes are classified as insoluble, with a strong bond between the platinum-iridium coating and the titanium substrate. Compared to conventional coated electrodes, they enhance resistance to crevice corrosion and significantly improve the durability of the contact area between the titanium substrate and the coating.

Applications of Iridium-Tantalum Coated Titanium Anodes

The IrO₂ and Ta₂O₅ coated titanium anodes exhibit excellent electrocatalytic activity and electrochemical stability, making them widely used in the electrolysis industry, particularly in environments with highly corrosive electrolytic media, harsh working conditions, and extremely high current densities. They are currently recognized as outstanding oxygen evolution electrodes.

  1. Copper Foil Production
    Producing electrolytic copper foil begins with the oxidation of copper to create a copper sulfate solution. This is followed by electrolysis in a foil machine to generate raw foil, which undergoes further processing including acid washing, roughening, curing, and yellow brass plating to yield the finished product. This process involves both electrolysis and electroplating. For example, one copper foil production company’s operational conditions are a sulfuric acid concentration of 120 g/L, a current density of 7-9 kA/m², and an anode-cathode gap of 12 mm. The use of IrTa anodes meets production requirements and addresses the challenges posed by extremely high current densities. The process involves a metal roller, partially immersed in the copper sulfate solution and continuously rotating, serving as the cathode for the electrolysis that produces foil. Electrolytic copper foil is utilized as a conductive material in single-sided printed circuit boards, with increasing usage and decreasing thickness, ranging from 0.15 mm, 0.105 mm, 0.07 mm, 0.05 mm, to 0.035 mm. Electrolytic copper foil is categorized by thickness into several types: 105 um, 70 um, 18 um, 12 um, 9 um, and 5 um, with thicknesses of 12 um and below generally referred to as ultra-thin copper foil. According to surface treatment processes, copper foil can be classified into several types: pink foil (copper-plated surface), gray foil (zinc-plated surface), and yellow foil (yellow brass-plated surface). The IPC standard classifies electrolytic copper foil based on performance into categories such as standard foil (STD—E class), high elongation foil (HD—E class), high temperature and high elongation foil (THE—E class), annealed electrolytic copper foil (ANN—E class), low-temperature annealed electrolytic copper foil (LTA—E class), and annealable electrolytic copper foil (A—E class). In Japan, copper foil for printed circuit boards is produced through electrolysis of copper sulfate solution, with copper plated onto titanium rotary cylinders with diameters of 1-2 meters and heights of 2-3 meters. The copper foil is stripped from one end of the rotating cylinder. The titanium-coated anode used for printed circuit copper foil has a height of approximately 1.3 meters, a surface length of about 2.4 meters, and a plate thickness of around 25 mm. With titanium-based coated anodes, the anode gap does not require adjustment, and the oxygen bubbles generated by the anode vigorously agitate the electrolyte, accelerating the movement of copper ions toward the cathode surface. Thus, the operating current density can be increased to 50 A/dm², significantly enhancing the production rate of the electrolytic cell. The IRO₂ coating applied via thermal decomposition on the titanium substrate performs well under these medium conditions. After setting a very thin platinum intermediate layer, titanium substrate oxidation can be prevented, extending the anode’s lifespan to at least 2.5 years.
  2. Electrolytic Oxidation of Aluminum Foil
    The electrolyte consists of a 10%-15% solution of ammonium dibasic acid, with a current density of 400-1000 A/m². IrTa-coated anodes can be employed for the anodization of aluminum foil, addressing issues related to high organic content.
  3. Zinc Coating of Steel Sheets
    In the electrolytic industry, particularly in zinc plating lines for steel sheets, using dimensionally stable anodes (DSA) with low overpotentials, such as IrO₂ and Ta₂O₅, offers a significant reduction in energy consumption. IrO₂·Ta₂O₅ coated anodes can be utilized on zinc plating lines as a replacement for lead alloy electrodes. Among these anode materials, IrO₂-based anodes exhibit excellent electrode performance, with low oxygen evolution overpotential, reduced consumption of the electrocatalytic active layer, and minimal contamination of the electrolyte. IrO₂·Ta₂O₅ anodes demonstrate long service life under high current densities, such as 10 kA/m², during the electroplating of zinc.
  4. Thick Copper Plating of Circuit Boards
    The anode-cathode distance is 10 mm, and the sulfuric acid concentration is 2 mol/L. IrO₂·Ta₂O₅ coated titanium anodes can be used to address the issue of extremely high acidity.
  5. Chrome Plating
    In the manufacturing of television and computer glass screens, a television glass casing company faces issues with corrosion of the steel mold surfaces due to high temperatures and weakly alkaline molten glass materials. To achieve a smooth surface on the glass screen, the steel mold surface must be plated with hexavalent chromium. IrTa-coated anodes can replace previously used lead electrodes.
  6. Rhodium Plating
    In recent years, there has been a growing interest in platinum jewelry. The plating of white gold jewelry is, in fact, rhodium plating. Rhodium plating involves the use of a rhodium sulfate plating solution, which is highly acidic and corrosive. IrTa-coated titanium anodes are widely used in the rhodium plating industry.
  7. Electrolysis of Silver Nitrate
    Coarse silver can be refined into fine silver through electrolysis, with the electrolyte containing approximately 80 g/L of silver and 20 g/L of nitric acid. Using insoluble anodes for electrolysis to recover silver, IrTa-coated titanium electrodes are used as anodes, with silver deposited on the cathode. The electrolysis waste solution contains only about 10 g/L of silver, which can be sold at 150 g/L.
  8. Electrolytic Organic Synthesis
    The electrodialysis method can directly electrolyze tetramethylammonium chloride to produce high-purity tetramethylammonium hydroxide, using IrO₂·Ta₂O₅ coated titanium anodes, which have a lifespan many times longer than standard RuSnTi coatings.
  9. Electrometallurgy
    In electrometallurgy, zinc production has traditionally employed lead alloy anodes containing small quantities of silver, antimony, or calcium. Issues arise with lead anodes, including instability in size, high oxygen evolution overpotential (approximately 800 mV), and corrosion during anode polarization. Lead ions dissolve into the electrolyte and deposit on the cathode, contaminating the zinc metal and affecting product quality. Dimensionally stable anodes (DSA) coated with various metal oxides, such as RuO₂, IrO₂, MnO₂, and Ta₂O₅, exhibit low oxygen overpotential and inert characteristics, making them suitable for use as oxygen evolution anode coatings in acidic solutions. Among the coating compositions, an IRO₂ (70% molar fraction)·Ta₂O₅ (30% molar fraction) combination is considered an excellent oxygen evolution anode coating. In this composition, IrO₂ serves as the electrochemically active material for anode polarization, while Ta₂O₅ enhances the chemical stability of IrO₂. The estimated lifespan of Ti/IrO₂·Ta₂O₅ anodes can reach 5 to 10 years.
  10. Electrochemical Purification in Industry
    Although Ti/IrO₂ anodes are relatively expensive, they have recently been employed in electrochemical purification processes. This is due to their successful use as oxygen evolution electrodes in moderately strong acidic or weakly acidic solutions. In contrast, classical Ti/RuO₂ electrodes have a short lifespan when used in low-concentration chloride ion solutions. Ti/IrO₂ anodes can be used to remove cations from wastewater (at the cathode) or to eliminate harmful substances from wastewater through anodic oxidation. Ti/IrO₂·Ta₂O₅ coated electrodes can successfully serve as oxygen evolution electrodes in the treatment of electroflotation wastewater containing dispersed peptides and oils. The stable cathode material used is stainless steel. The anode and cathode current densities are both maintained at 100-200 A/m², and the gas bubbles (H₂ and O₂) generated by the electrochemical method are sized between 50-100 μm, ensuring high efficiency in electroflotation, achieving up to 99.5% removal of harmful substances from wastewater, reducing concentrations from 1-10 g/L to 1-10 mg/L. The wastewater flow rate through the electrolysis cell is 12-16 m³/h, with a voltage of 4-6 V and a current of 300 A. The Ti/IrO₂ anode (with an area of 2 m², an iridium coating of 12.3 g/m², and a composition of 65 mol% IrO₂ and 35 mol% Ta₂O₅) operates in the electrolysis cell for over 4 years.
  11. Electrochemical Activity in Solutions Containing Organic Small Molecules
    Due to the adsorption poisoning of intermediate products like CO, pure platinum (Pt) is not an ideal electrode for the point catalysis of small organic molecules. In recent years, dimensionally stable anodes (DSA) have begun to be applied for the electro-oxidative removal of organic pollutants, with these active anodes effectively oxidizing difficult-to-degrade pollutants into biodegradable intermediate organic products.
  12. High-Speed Tin Plating of Steel Sheets
    Titanium anodes with ruthenium-titanium coatings are widely used in the salt electrolysis industry due to their excellent electrocatalytic activity for chlorine evolution, with over 90% of chlor-alkali companies worldwide employing them, achieving lifespans of up to 10 years. However, they cannot be used in oxygen evolution electrochemical systems, where their lifespan is very short. Iridium-based coated titanium anodes possess excellent electrocatalytic activity for oxygen evolution and maintain high stability in oxygen evolution electrochemical systems. Since 1997, they have been widely used in high-speed zinc plating lines utilizing sulfate plating solutions, with a lifespan of approximately 1 year, replacing the previously used lead alloy anodes. If organic substances are present in the electrolyte, when oxygen is evolved at the anode, the coated anode may experience issues of “rapid loss of the active coating in the presence of organic substances,” resulting in significantly reduced lifespans, sometimes even less than one day. The patterns observed in the “rapid loss of the active coating in the presence of organic substances” phenomenon are as follows: (1) The occurrence of rapid loss of the active coating in the presence of organic substances is always accompanied by a substantial increase in electrode potential, sometimes rising by several hundred millivolts.
    (2) The increase in electrode potential due to the presence of organic substances only occurs during the oxygen evolution reaction at the anode and does not affect the electrode potential during chlorine evolution at the anode or hydrogen evolution at the cathode.
    (3) The increase in electrode potential and the associated rapid loss of the active coating in the presence of organic substances do not occur with other systems such as lead alloys; this phenomenon is unique to platinum group metal and its oxide system electrodes.

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