In the field of electrochemical industry, titanium anodes, combining the strong corrosion resistance of titanium substrates with the high catalytic activity of precious metal coatings, have become core key materials in industries such as chlor-alkali production, water electrolysis for hydrogen production, electroplating, and wastewater treatment. These electrodes, which possess both structural stability and high catalytic performance, are also known as Dimensionally Stable Anodes (DSA). For purchasers, the operational efficiency of titanium anodes directly determines production energy consumption, while service life is related to maintenance costs. Both core indicators are closely linked to the key parameters of the surface precious metal coatings.
Among them, precious metal coating systems centered on ruthenium (Ru) and iridium (Ir) are currently the most widely used. There is a common understanding in the industry: the higher the iridium content, the higher the catalytic efficiency tends to be. In addition, the coverage area of precious metal coatings and their influencing factors indirectly affect the performance and service life of titanium anodes by changing the state of the reaction interface.
Starting from basic principles, this article uses a combination of “professional terminology + popular analogies” to dissect the internal logic between ruthenium-iridium coatings and catalytic efficiency, analyze the mechanism by which precious metal coverage area affects efficiency and service life, and explain the changes in the effects of these influencing factors based on the differences in operating conditions across various application industries. It aims to provide purchasers with a scientifically sound and practical reference.
I. Basic Understanding: The “Synergistic Coexistence” Between Titanium Anodes and Precious Metal Coatings
To understand the relationship between precious metal coatings, efficiency, and service life, it is first necessary to clarify a core premise: the performance advantages of titanium anodes stem from the complementary synergy between the “titanium substrate” and the “precious metal coating” – neither can be separated from the other.
1.1 Titanium Substrate: The “Tough Framework” Bearing the Coating
As a substrate material, titanium has four core advantages: first, extremely strong corrosion resistance, making it resistant to erosion in harsh electrochemical environments such as strong acids, strong alkalis, and high temperatures; second, excellent mechanical properties, allowing it to be processed into various forms such as meshes, plates, and tubes to meet the equipment needs of different industries; third, significant environmental advantages – compared to corrosion-resistant materials like lead, titanium has no heavy metal pollution risks and complies with modern industrial environmental requirements; fourth, prominent cost advantages – compared to materials like tantalum that can be processed into various specifications, titanium has lower procurement costs and moderate processing difficulty, enabling effective control of electrode manufacturing costs. It is important to note that while other materials may have partial similar characteristics, they have obvious shortcomings: lead is corrosion-resistant but not environmentally friendly, and long-term use is prone to causing environmental pollution; tantalum can be processed into various shapes and specifications, but its high cost and relatively high processing difficulty make large-scale application impractical.
1.2 Precious Metal Coating: The “Catalytic Heart” Driving Reactions
Oxides of platinum-group precious metals such as ruthenium and iridium are the core solution to the defects of pure titanium. The thickness of such coatings is usually only 5-50μm (approximately 1/2 to 1/10 the diameter of a human hair), yet they can fulfill core functions:
● Reducing reaction activation energy: The electronic orbital structure of precious metals endows them with excellent electron transfer capabilities, allowing them to act as “active sites” for electrocatalytic reactions and significantly lowering the energy threshold required for electrolytic reactions. For example, in the oxygen evolution reaction, the activation energy of pure titanium is as high as 1.2 eV, while an iridium coating can reduce it to 0.4-0.6 eV, significantly improving the reaction rate [Principles and Applications of Electrochemistry, 2023, Chemical Industry Press];
● A dense precious metal coating can completely isolate the electrolyte from the titanium substrate, preventing titanium from being dissolved or passivated. At the same time, its thermal expansion coefficient is close to that of titanium, making it less prone to cracking and peeling due to temperature changes, thus ensuring the long-term stable operation of the electrode.
In simple terms, the titanium substrate is the “tough framework” responsible for bearing the coating and resisting corrosion; the precious metal coating is the “efficient heart” responsible for driving electrolytic reactions. The synergistic cooperation between the two endows titanium anodes with the core advantages of “high efficiency, long service life, and energy saving.”
II. Core Analysis: The Internal Relationship Between Ruthenium-Iridium Combinations, Catalytic Efficiency, And Service Life
In ruthenium-iridium coating systems, the content ratio of ruthenium and iridium is the core variable determining catalytic efficiency, and it also indirectly affects service life by influencing coating stability. To understand this relationship, we need to start with the differences in characteristics between the two precious metals and then analyze the synergistic effects of their ratios.
2.1 Core Characteristic Differences Between Ruthenium and Iridium: The “Division of Labor” Between Activity and Stability
Ruthenium and iridium are both platinum-group precious metals, but they have distinct differences in electrochemical performance. These differences determine their different “divisions of labor” in the coating:
| Performance Dimension | Ruthenium (Ru) and Its Oxides | Iridium (Ir) and Its Oxides |
| Catalytic Activity (Chlorine/Oxygen Evolution) | Relatively high, with basic catalytic activity; electrolytic reactions can be achieved without iridium, especially effective in low-demand chlorine evolution scenarios | High, with significantly improved catalytic efficiency in both oxygen and chlorine evolution reactions; increased content can further optimize reaction rate and reduce energy consumption |
| Chemical Stability | Moderate; prone to pitting corrosion in strong oxidizing and high-temperature environments, with average long-term stability | Excellent; extremely high chemical inertness, resistant to corrosion by strong acids, strong alkalis, and strong oxidants, with a melting point as high as 2443℃ |
| Cost | Relatively low, with obvious cost-performance advantages | Extremely high; global annual output is less than 3 tons, with strong scarcity and much higher cost than ruthenium [U.S. Geological Survey (USGS) Mineral Commodity Summaries 2025] |
| Core Function | Provides basic catalytic capacity to ensure the initiation of electrolytic reactions, suitable for low-demand operating conditions | Core function of improving catalytic efficiency, optimizing reaction kinetics, while enhancing coating stability and extending service life |
From the characteristic differences, a core conclusion can be drawn directly: the core value of ruthenium lies in “basic catalysis + cost control,” while the core value of iridium lies in “high-efficiency catalysis + stable long service life.” This conclusion provides the core logic for subsequent ratio design – the selection of ratios under different operating conditions is essentially a balance between “efficiency requirements, service life requirements, and cost budget.”
2.2 Increased Iridium Content: The “Core Driving” Mechanism for Catalytic Efficiency
The industry understanding that “the higher the iridium content, the higher the catalytic efficiency of ruthenium-iridium coatings” stems from the “dominant active role” and “synergistic stabilization role” of iridium in catalytic reactions. The specific mechanism can be analyzed from two aspects:
First, “increase in high-activity site density.” The essence of catalytic reactions is the electron transfer process between ions in the electrolyte and “active sites” on the coating surface. The greater the number of high-activity sites per unit area, the faster the reaction rate and the higher the catalytic efficiency. Iridium oxides (such as IrO₂) are typical high-activity catalytic components, and the electron transfer capacity of their active sites is far superior to that of ruthenium oxides. When iridium content increases, the density of high-activity sites per unit area also increases, equivalent to “increasing the number of high-efficiency production lines in a reaction factory,” directly improving the electrolytic reaction rate. It should be clarified that pure ruthenium coatings are not without active sites; their active sites simply have lower reaction efficiency and can still meet basic electrolytic needs.
Second, “reduced electron transfer resistance + enhanced lattice stability.” The resistivity of iridium is lower than that of ruthenium. As iridium content increases, the electron conduction channels inside the coating become more unobstructed, reducing the resistance to electron transfer from the coating surface to the titanium substrate and minimizing energy loss caused by “electron congestion.” At the same time, iridium oxides have a stable face-centered cubic lattice structure. When iridium atoms are incorporated into the ruthenium lattice, a “stable mixed lattice” is formed, preventing the loss of ruthenium active sites during reactions and maintaining high catalytic efficiency over the long term. For example, in the electroplating industry, when the molar ratio of iridium in ruthenium-iridium coatings increases from 30% to 60%, the cell voltage can be reduced by 0.15-0.35 V. For an electroplating line with an annual output of 1,000 tons, the annual energy savings can reach 120,000-280,000 kWh [Electroplating & Pollution Control, 2024, 44(3): 45-48].
It is particularly important to clarify that the rule “higher iridium content leads to higher efficiency” holds “on the premise that ruthenium content meets basic activity requirements” and is not unlimited. If iridium content is too high (e.g., exceeding 80%), although catalytic efficiency remains at a high level, it will lead to a sharp increase in costs and increased coating brittleness, making it prone to cracking under mechanical vibration conditions. While pure ruthenium coatings have lower efficiency than ruthenium-iridium mixed coatings, they possess basic catalytic capabilities and still have practical value in low-demand scenarios.
2.3 Feasibility of Pure Ruthenium Coatings: Not “Ineffective,” but “Scenario-Limited”
Many purchasers may wonder: “Since iridium can significantly improve efficiency, can pure ruthenium coatings be used without iridium?” The answer is “yes, but only for specific scenarios.” Pure ruthenium coatings are not without catalytic efficiency; they have basic chlorine evolution activity and can achieve basic electrolytic reactions. However, their efficiency is lower than that of ruthenium-iridium mixed coatings, and due to insufficient stability, their application scenarios are strictly limited to “mild operating conditions.”
Scenarios suitable for pure ruthenium coatings must meet three conditions: first, the electrolyte has low corrosiveness with no strong oxidants present; second, the operating temperature is relatively low (usually below 60℃); third, the current density is small (below 1,000 A/m²). For example, simple copper or nickel plating processes in small electroplating workshops, or the treatment of low-concentration organic wastewater. In such scenarios, pure ruthenium coatings can achieve a service life of 2-3 years, with much lower costs than ruthenium-iridium mixed coatings, offering extremely high cost performance.
However, in harsh scenarios such as chlor-alkali industry (saturated brine, 70℃, high current density) and water electrolysis for hydrogen production (strong acid environment, high potential), pure ruthenium coatings will quickly suffer from pitting corrosion and peeling, with a service life of only a few months or even weeks. This will instead lead to a sharp increase in maintenance costs due to frequent electrode replacement, so pure ruthenium coatings are absolutely not suitable for such scenarios.
2.4 The Role of Iridium: The “Core Driver” of Catalytic Efficiency and the “Stabilizer” of Stability
The core role of iridium in the coating is to “improve catalytic efficiency,” while also functioning to “stabilize the coating structure” – an appropriate amount of iridium can enable the stable exertion of ruthenium’s basic activity through “lattice stabilization,” and further achieve efficiency leaps through its own high-activity sites, ultimately achieving a balance between “efficiency, service life, and cost.”
From a microstructural perspective, the lattice structure of ruthenium oxides is relatively loose, making it prone to lattice distortion during electrolytic reactions, leading to the loss of active sites. In contrast, iridium oxides (such as IrO₂) have a stable face-centered cubic lattice structure. When iridium atoms are incorporated into the ruthenium lattice, a “stable mixed lattice” is formed, which not only provides a “support framework” for ruthenium’s basic active sites to prevent their peeling or dissolution but also improves overall catalytic efficiency through iridium’s own high-activity sites.
In addition, the active sites of iridium and ruthenium can form a “synergistic catalytic effect,” further optimizing the electron transfer process. For example, in the oxygen evolution reaction of water electrolysis for hydrogen production, the activation energy of pure ruthenium coatings is 0.7-0.8 eV, while adding a certain proportion of iridium can reduce the activation energy to 0.4-0.5 eV, significantly improving catalytic efficiency and greatly enhancing stability.
Regarding the fact that “iridium is more expensive and generally not used alone,” the core reason is the “mismatch between cost and value.” Pure iridium coatings have extremely strong stability and can achieve a service life of 8-10 years in the chlor-alkali industry. However, due to the high cost of iridium (each square meter of coating requires 15-20 grams of high-purity iridium powder, and based on current market prices, the raw material cost of iridium alone exceeds 10,000 yuan) [Handbook of Titanium Electrode Preparation and Application Technology, 2023, Metallurgical Industry Press], the electrode procurement cost will increase sharply, far exceeding the maintenance cost savings brought by its long service life. Therefore, except for a few extremely harsh special scenarios (such as nuclear industry wastewater treatment), pure iridium coatings are rarely used in the industry. Instead, a ratio of “a small amount of iridium + an appropriate amount of ruthenium” is adopted to achieve a balance between “cost, efficiency, and service life.”
2.5 Performance Of Different Ruthenium-Iridium Ratios: Scenario-Adapted Cases
Based on the above analysis, coatings with different ruthenium-iridium ratios are suitable for different scenarios, and their efficiency and service life performance vary significantly. The following are common ratio types in the industry and their corresponding performance characteristics:
| Ruthenium-Iridium Molar Ratio (Ru:Ir) | Catalytic Efficiency (Relative Value) | Service Life (Typical Operating Conditions) | Suitable Scenarios | Core Advantages |
| 10:0 (Pure Ruthenium) | 85%, with basic catalytic efficiency to meet low-demand electrolytic needs | Mild conditions: 2-3 years; Harsh conditions: 3-6 months | Small-scale electroplating, low-concentration wastewater treatment | Lowest cost, meets basic catalytic needs, suitable for low-demand operating conditions |
| 7:3 | 90%-93%, efficiency significantly higher than pure ruthenium, balanced cost-performance | Moderate conditions: 3-5 years; Harsh conditions: 1-2 years | Conventional electroplating, seawater desalination (medium-low temperature) | Optimal cost-performance, balanced efficiency and cost, suitable for most conventional operating conditions |
| 5:5 | 95%-97%, high-efficiency catalysis, significantly reducing energy consumption | Moderate conditions: 5-8 years; Harsh conditions: 3-5 years | Chlor-alkali industry (small-medium scale), water electrolysis for hydrogen production (small-medium capacity) | High efficiency and energy saving, excellent stability, suitable for mid-to-high-end operating conditions |
| 3:7 | 98%-99%, catalytic efficiency close to peak, optimal energy consumption | Harsh conditions: 5-8 years; Extreme conditions: 3-5 years | Large-scale chlor-alkali plants, high-temperature wastewater treatment | Optimal energy consumption, long service life, suitable for high-demand continuous production |
| 0:10 (Pure Iridium) | 100%, peak catalytic efficiency, lowest energy consumption | Extreme conditions: 8-10 years | Nuclear industry wastewater, ultra-high temperature electrolysis scenarios | Ultimate catalytic efficiency, strongest stability, suitable for extremely harsh operating conditions |
| Data source: Compiled based on comprehensive industry application cases and Handbook of Titanium Electrode Preparation and Application Technology (2023, Metallurgical Industry Press) | ||||
It can be clearly seen from the table that as iridium content increases, the catalytic efficiency of the coating gradually increases, and stability and service life also improve simultaneously, but the cost rises sharply. When making a selection, purchasers need to consider their own efficiency requirements, production continuity needs, and cost budgets, rather than blindly pursuing “high iridium for efficiency” or “pure ruthenium for cost control.”
III. Key Extension: The Impact of Precious Metal Coverage Area on Efficiency and Service Life
In addition to the precious metal content ratio, “coverage area” is also a core parameter affecting the performance of titanium anodes. Here, “coverage area” does not simply refer to the macroscopic surface area of the electrode, but rather the proportion of the titanium substrate effectively covered by the precious metal coating and the microscopic active area on the coating surface – both jointly determine the size of the “effective reaction area” at the reaction interface, thereby affecting efficiency and service life.
3.1 Dual Dimensions of Coverage Area: Macroscopic Coverage and Microscopic Activity
Many purchasers easily equate “electrode size” with “coverage area,” which is a common misunderstanding. In fact, precious metal coverage area includes two key dimensions:
First, “macroscopic coverage integrity”: refers to the proportion of the titanium substrate covered by the precious metal coating, which should ideally reach 100%. If the macroscopic coverage is incomplete (e.g., due to coating missing, pinholes, or other defects), the uncovered titanium substrate will directly come into contact with the electrolyte during electrolysis, quickly forming an oxide film and corroding. This not only reduces overall catalytic efficiency but may also cause the coating to peel off from the defect, significantly shortening service life. For example, if the coating has a 5% missing area, the service life of the electrode may be reduced by 30%-50% [Electrochemical Engineering Materials, 2022, Chemical Industry Press].
Second, “microscopic active area”: refers to the actual reaction area formed by the microscopic structure (such as cracks and pores) on the coating surface. This area is usually much larger than the macroscopic surface area of the electrode. For example, a ruthenium-iridium coating treated with special processes can have a microscopic active area 3-5 times the macroscopic surface area, equivalent to “building more production lines in the same factory space,” which can significantly improve catalytic efficiency.
In simple terms, macroscopic coverage integrity determines the “basic service life threshold” of the electrode, while microscopic active area determines the “efficiency ceiling” of the electrode. Together, they constitute the core value of “precious metal coverage area.”
3.2 Mechanism Of Coverage Area’s Impact On Efficiency And Service Life
3.2.1 Impact On Catalytic Efficiency: The Direct Determinant Of The “Effective Reaction Area”
Catalytic efficiency is positively correlated with the total reaction volume per unit time, which depends on the size of the “effective reaction area.” When macroscopic coverage is complete and the microscopic active area is large, ions in the electrolyte can come into contact with more precious metal active sites, the electron transfer process is more sufficient, the reaction rate is faster, and the catalytic efficiency is higher.
For example, in the scenario of water electrolysis for hydrogen production, a titanium substrate pretreated by micro-arc oxidation (which can form 20-50 nm honeycomb micro-pores to increase the microscopic active area) can achieve an electrolytic efficiency of 95.2% with a ruthenium-iridium coating, while the efficiency of an ordinary coating without pretreatment is only 89% [Materials Surface Engineering, 2023, 36(5): 78-83]. Conversely, if there are defects in macroscopic coverage, the oxide film formed on the uncovered titanium substrate will increase overall resistance, leading to higher cell voltage and energy consumption. At the same time, the increase in unreacted ions will further reduce efficiency.
3.2.2 Impact on Service Life: The Integrity Guarantee of the “Corrosion Protection Barrier”
The core protective effect of the precious metal coating relies on its complete coverage of the titanium substrate. When macroscopic coverage is incomplete, the electrolyte will penetrate through the defects, directly corroding the titanium substrate. At the same time, the gases or products generated by corrosion will further damage the surrounding coating, forming “corrosion diffusion,” leading to large-area peeling of the coating and ultimately causing electrode failure.
The rationality of the microscopic structure also affects service life: if the microscopic porosity is too high (exceeding 25%), although it can increase the active area, it will cause the electrolyte to penetrate to the substrate through the pores, accelerating coating peeling; if the porosity is too low, the active area will be insufficient, leading to reduced efficiency, and the stress inside the coating cannot be released, making it prone to cracking defects. The ideal microscopic structure is “moderate porosity + dense grain boundaries,” which can not only ensure the active area but also block electrolyte penetration.
3.3 Core Factors Influencing Precious Metal Coverage Area
Precious metal coverage area is not determined by a single factor but is affected by multiple links such as “substrate pretreatment, coating process, and coating formulation.” Specifically, it can be summarized into four categories of core factors:
● Quality of titanium substrate pretreatment: This is the foundation for ensuring coverage integrity. The surface of the titanium substrate needs to undergo pretreatment such as sandblasting, pickling, or micro-arc oxidation to form a uniformly rough surface (with a roughness Ra of 2-3 μm being optimal) [Titanium and Titanium Alloy Surface Treatment Technology, 2024, China Machine Press]. This can enhance the bonding force between the coating and the substrate, avoiding problems such as missing coating and sagging during the coating process. If the pretreatment is incomplete, and there is oil, oxide film, or impurities on the substrate surface, the bonding between the coating and the substrate will be insufficient, making it prone to peeling during subsequent use and indirectly damaging coverage integrity;
● Coating process parameters: The coating process (such as brushing, spraying, physical vapor deposition, etc.) and its parameters (such as coating solution concentration, drying temperature, sintering temperature) directly affect the coverage effect. For example, when using the “brushing-drying-sintering” cycle process, the first 5 cycles require thick coating to fill the substrate pores, and subsequent precise coating to control the thickness. If the coating solution concentration is too high, it will cause cracking on the coating surface; if the sintering temperature is insufficient (below 450℃), the coating crystallinity will be low, the grain boundaries will be loose, and pores will be prone to excessive size; if the temperature is too high (exceeding 600℃), it will cause the decomposition of precious metal oxides, reducing coating activity and bonding force;
● Coating formulation design: The ratio of thickeners and thinners in the coating formulation, as well as the concentration of precious metal salts, will affect the fluidity and film-forming properties of the coating solution. If the binder ratio is too high, the coating will be dense but the active area will be insufficient; if there is too much thinner, the coating solution will be too dilute, making it prone to missing coating and excessively thin coatings. In addition, adding a small amount of rare earth elements or transition metals can optimize the microscopic structure of the coating and improve the uniformity and stability of coverage;
● Electrode structure design: The macroscopic structure of the electrode (such as mesh, plate, tube) also affects the coverage area. For example, the surface area of a mesh electrode is much larger than that of a plate electrode of the same volume, and the electrolyte fluidity is better, which can increase the microscopic active area; if a plate electrode is designed in an arc shape, it can optimize current distribution, avoid excessive local current leading to rapid coating loss, and indirectly ensure coverage integrity.
3.4 The Impact Of Different Titanium Anode Shapes On Efficiency And Service Life
The macroscopic shape of titanium anodes directly determines their surface area utilization rate, electrolyte flow efficiency, and current distribution uniformity, thereby significantly affecting catalytic efficiency and service life. Anodes of different shapes adapt to the needs of different operating conditions by changing the size and distribution of the “effective reaction area” and the mechanical stability of their own structures. Common titanium anode shapes on the market mainly include mesh, plate, tube, and filament, with distinct differences in performance.
From the perspective of core impact logic: on the one hand, the shape determines the contact area between the anode and the electrolyte (i.e., macroscopic reaction area) and the electrolyte flow rate. The larger the contact area and the smoother the flow, the more sufficient the ion diffusion and electron transfer, and the higher the catalytic efficiency; on the other hand, the shape affects the mechanical strength and stress distribution of the anode. The more stable the structure and the more uniform the stress, the less prone it is to deformation, coating peeling, and other problems under long-term electrolysis or fluid impact, and the longer the service life.
3.4.1 Common Titanium Anode Shapes and Their Performance Characteristics
The following are four widely used titanium anode shapes on the market, with an analysis of their specific impacts on efficiency and service life based on their structural design:
Mesh titanium anodes
The core structure is a mesh woven from titanium wires, with mesh sizes customizable according to operating conditions (common mesh sizes are 1-5 mm). Its greatest advantage is its large specific surface area, which can significantly increase the contact probability between the microscopic active area and the electrolyte. At the same time, the mesh structure does not hinder electrolyte flow, which can reduce ion diffusion resistance and greatly improve catalytic efficiency. However, due to the relatively small diameter of titanium wires (usually 0.5-2 mm), the mechanical strength is relatively low, making it prone to deformation and fracture under strong fluid impact or frequent disassembly and assembly, which in turn leads to coating peeling and shortened service life.
Plate titanium anodes
Flat plate structure with a thickness of usually 2-5 mm; the surface can be sandblasted, grooved, or otherwise treated to increase roughness. It has strong structural stability and high mechanical strength, and can withstand high temperatures, high pressures, and strong fluid impact. The coating bonds more firmly with the substrate, resulting in a longer service life. However, the flat plate structure has a small specific surface area and average electrolyte fluidity, and the ion diffusion efficiency is lower than that of mesh anodes, so the catalytic efficiency is relatively low; if the current distribution is uneven, local excessive coating loss may also occur.
Tube titanium anodes
Hollow tube structure with a common inner diameter of 10-50 mm and a tube wall thickness of 2-4 mm, which can be used individually or combined into tube bundles. The advantage of the tube structure is that the electrolyte can flow inside or outside the tube, resulting in high mass transfer efficiency, especially suitable for continuous flow operating conditions; at the same time, the stress distribution of the tube structure is uniform, and the mechanical stability is between that of mesh and plate anodes. Its efficiency is slightly lower than that of mesh anodes but higher than that of plate anodes; the service life is greatly affected by the tube wall thickness – the thicker the wall, the stronger the corrosion resistance and mechanical damage resistance, and the longer the service life.
Filament Titanium Anodes
Made of titanium wires with a diameter of 0.1-1 mm, usually used individually or in multiple combinations. Its greatest feature is its small size and high flexibility, which can be adapted to electrolytic equipment in narrow spaces (such as small laboratory reactors and precision electroplating equipment). Due to the extremely small wire diameter, the specific surface area is large, and the short-term catalytic efficiency is high. However, the mechanical strength is extremely low, making it prone to breakage under external force. In addition, the coating coverage area is limited, and the coating is prone to peeling from the filament during long-term use, resulting in the shortest service life.
To more intuitively compare the performance differences of titanium anodes of different shapes, the following table summarizes the core parameters, efficiency impact, service life impact, and suitable scenarios of each shape:
| Anode Shape | Core Structural Parameters | Impact on Catalytic Efficiency (Relative Value) | Impact on Service Life (Typical Operating Conditions) | Suitable Scenarios |
| Mesh | Mesh size: 1-5 mm, wire diameter: 0.5-2 mm | 95%-100%, high specific surface area + excellent fluidity, optimal efficiency | 3-5 years, moderate mechanical strength, prone to deformation under impact | Chlor-alkali industry, electroplating, seawater desalination |
| Plate | Thickness: 2-5 mm, surface can be grooved/sandblasted | 85%-90%, small specific surface area, moderate efficiency | 5-8 years, stable structure, strong impact resistance, long service life | Small-scale wastewater treatment, laboratory electrolysis, low-flow operating conditions |
| Tube | Inner diameter: 10-50 mm, wall thickness: 2-4 mm, can be combined into tube bundles | 90%-95%, high mass transfer efficiency, higher efficiency than plate anodes | 4-6 years, uniform stress, moderate corrosion resistance | Water electrolysis for hydrogen production, continuous flow wastewater treatment, fluid electrolytic equipment |
| Filament | Diameter: 0.1-1 mm, single/multiple combinations | 92%-96%, large specific surface area, high short-term efficiency | 1-2 years, extremely low mechanical strength, prone to coating peeling | Precision electroplating, small closed reactors, special space electrolysis |
| Data source: Compiled based on comprehensive industry application cases and Handbook of Titanium Electrode Preparation and Application Technology (2023, Metallurgical Industry Press) | ||||
In summary, the differences in efficiency and service life of titanium anodes of different shapes are essentially a balance between “specific surface area, flow efficiency” and “mechanical stability.” When selecting a type, purchasers need to choose an anode of appropriate shape based on their own equipment structure, electrolyte flow rate, spatial size, and other operating conditions to maximize its performance advantages.
IV. Industry Differences: Changes in Impact Effects Under Different Application Scenarios
The “relationship between ruthenium-iridium ratio, coverage area, efficiency, and service life” analyzed earlier is not consistent across all industries. Differences in operating conditions among different application industries (such as electrolyte composition, temperature, current density, production continuity requirements, etc.) will lead to significant changes in the effects of these influencing factors. The following analyzes the difference characteristics of four core application industries one by one:
4.1 Chlor-Alkali Industry: Stability First, Iridium Content and Coverage Integrity Are Key
The core operating conditions of the chlor-alkali industry are “saturated brine + 70℃ high temperature + high current density (1500-3000 A/m²) + long-term continuous operation,” which are typical harsh operating conditions [Chlor-Alkali Industry Technology Handbook, 2023, Chemical Industry Press]. The core demand for titanium anodes in this industry is “long service life and low maintenance costs,” with efficiency being a secondary consideration.
In this industry, the impact of iridium content is far greater than that of ruthenium content: if the iridium content is insufficient (e.g., Ru:Ir > 7:3), the coating will quickly suffer from pitting corrosion in strong oxidizing and high-temperature environments, with a service life of less than 2 years, which cannot meet the needs of continuous production. Therefore, the industry generally adopts a ratio of Ru:Ir = 5:5 or 3:7, which can achieve a service life of 3-8 years [Chlor-Alkali Industry Technology Handbook, 2023, Chemical Industry Press].
In terms of coverage area, the impact of macroscopic coverage integrity is particularly prominent: the electrolyte in the chlor-alkali industry is extremely corrosive, and even minor coating defects can quickly cause substrate corrosion and electrode failure. Therefore, the industry has an almost zero tolerance for coating missing rate, and at the same time, the microscopic porosity needs to be controlled between 15%-20%, which not only ensures a certain active area but also avoids electrolyte penetration. In addition, the chlor-alkali industry mostly uses mesh anodes, which can improve efficiency by increasing the macroscopic surface area, while optimizing electrolyte fluidity and reducing coating loss caused by local overheating.
4.2 Water Electrolysis For Hydrogen Production: Balancing Efficiency And Stability, Ruthenium-Iridium Synergy And Microscopic Activity Are Core
The operating conditions of water electrolysis for hydrogen production (especially proton exchange membrane water electrolysis) are “strong acid environment + high potential + medium-high temperature (80-100℃).” The core demand is “high efficiency and energy saving + long service life” – efficiency directly determines hydrogen production costs, while service life is related to the equipment investment return cycle.
In this industry, the synergistic effect of ruthenium and iridium is crucial: pure ruthenium coatings have insufficient stability, while pure iridium coatings have low efficiency and high costs. Therefore, the industry mostly adopts a ratio of Ru:Ir = 6:1-7:3, which not only ensures high catalytic efficiency (reducing hydrogen production power consumption) but also achieves stable operation for more than 1500 hours through the lattice stabilization effect of a small amount of iridium. For example, a study shows that a catalyst with an iridium-ruthenium atomic ratio of only 1:6 still maintains excellent stability after continuous operation for 1500 hours at a current density of 2 A/cm², and the iridium loading is reduced by 80% [Journal of Hydrogen Energy, 2024, 29(2): 112-119], significantly controlling costs.
In terms of coverage area, the impact of microscopic active area is more significant: water electrolysis for hydrogen production has extremely high requirements for efficiency. Increasing the microscopic active area through micro-arc oxidation pretreatment or rare earth doping technology can increase the electrolytic efficiency to over 95%, reducing the power consumption per cubic meter of hydrogen by 1-2 kWh. At the same time, due to the high potential in the operating conditions, macroscopic coverage integrity also needs to be strictly guaranteed; otherwise, local high current density is likely to occur at defects, accelerating coating loss.
4.3 Electroplating Industry: Efficiency First, Ruthenium Content and Microscopic Activity Are Key
The operating conditions of the electroplating industry vary greatly: conventional electroplating (such as copper plating and nickel plating) has mild operating conditions (room temperature, low current density, weakly acidic electrolyte), while high-end electroplating (such as chrome plating of auto parts) has relatively harsh operating conditions (medium-high temperature, high current density). The core demand of this industry is “high catalytic efficiency + uniform current distribution” to ensure coating quality, and the service life demand varies according to production scale.
In conventional electroplating scenarios, pure ruthenium coatings or high-ruthenium ratios (Ru:Ir = 10:0 or 7:3) can meet the requirements: the high catalytic efficiency of pure ruthenium coatings can reduce cell voltage and save energy, while the cost is low, and a service life of 2-3 years can match the maintenance cycle of small and medium-sized electroplating workshops; high-end electroplating scenarios require a ratio of Ru:Ir = 5:5 to balance efficiency and service life, avoiding production delays due to frequent electrode replacement.
In terms of coverage area, the core factors are microscopic active area and current distribution uniformity: the larger the microscopic active area, the more uniform the current distribution, and the denser the coating, which can avoid pinholes, nodular defects, and increase the coating qualification rate from 82% to 97% [Electroplating Process and Quality Control, 2023, China Machine Press]. Therefore, the electroplating industry mostly uses mesh or arc-shaped electrodes, which not only increase the microscopic active area but also optimize current distribution; at the same time, high requirements are placed on substrate pretreatment to ensure firm bonding between the coating and the substrate, avoiding coating peeling caused by current impact.
4.4 Wastewater Treatment Industry: Complex Operating Conditions, Adaptive Design Is Core
The operating conditions of the wastewater treatment industry are the most complex. Different wastewaters vary greatly in composition (such as phenol-containing, chlorine-containing, heavy metal-containing), concentration, pH value, and temperature. The core demand is “efficient degradation of pollutants + strong corrosion resistance,” and the service life demand depends on the corrosiveness of the wastewater.
In this industry, the ruthenium-iridium ratio needs to be customized according to the type of wastewater: when treating chlorine-containing wastewater, the catalytic activity of ruthenium can improve chlorine evolution efficiency and degrade organic pollutants, so a ratio of Ru:Ir = 7:3 can be adopted; when treating refractory organic wastewater such as phenol-containing wastewater, operation under strong oxidizing conditions is required, so the iridium content needs to be increased (Ru:Ir = 5:5) to enhance coating stability; when treating high-concentration strong acid wastewater, a high-iridium ratio of Ru:Ir = 3:7 is required to ensure service life.
In terms of coverage area, the balance between macroscopic coverage integrity and microscopic porosity is particularly important: wastewater containing pollutants is highly corrosive, and incomplete macroscopic coverage will quickly lead to electrode failure; at the same time, the high concentration of pollutants in wastewater requires a sufficient microscopic active area to improve degradation efficiency. Therefore, the industry mostly adopts a “gradient coating + moderate porosity” design: the bottom layer is a dense layer to ensure coverage integrity, and the surface layer is a porous layer to increase the active area, which can achieve a COD removal rate of 98% and reduce the cost per ton of wastewater treatment by 40% [Electrochemical Wastewater Treatment Technology, 2024, China Environmental Science Press].
V. Purchasing Guide: Selection Logic Based on Core Needs
Through the systematic analysis above, purchasers can clarify that the core of titanium anode selection is the precise matching between “operating condition requirements” and “coating parameters.” The following are core suggestions for the purchasing process to help purchasers avoid misunderstandings and achieve the optimal balance between “cost, efficiency, and service life”:
5.1 First Clarify Core Needs: Efficiency Priority or Service Life Priority?
Before purchasing, it is necessary to sort out core needs: if the production scale is small, the operating conditions are mild (such as small electroplating workshops), and cost sensitivity is high, priority can be given to high-ruthenium ratios or pure ruthenium coatings to pursue high cost performance; if the production continuity is high, the operating conditions are harsh (such as large-scale chlor-alkali plants, water electrolysis for hydrogen production projects), and the maintenance cost is high, priority should be given to medium-high iridium ratios to ensure long service life; if it is between the two (such as conventional electroplating, small-medium scale wastewater treatment), a balanced ratio of Ru:Ir = 7:3 or 5:5 can be selected to balance efficiency and service life.
5.2 Pay Attention to Process Details Related to Coverage Area
When purchasing, attention should not only be paid to the precious metal content but also to the manufacturer’s process guarantee measures for “coverage area.” For example: Is the titanium substrate pretreated by micro-arc oxidation? How many cycles of “brushing-drying-sintering” are used in the coating process? What are the control standards for coating missing rate and porosity? These details directly determine the actual performance and service life of the electrode.
5.3 Reject “Blind Content Obsession” and Emphasize the Synergy of Formula and Process
Some purchasers fall into the misunderstanding of “the higher the precious metal content, the better.” In fact, high-quality titanium anodes rely on the synergy of “reasonable formula + precise process” rather than simple content accumulation. For example, through nanostructure design or rare earth doping technology, higher efficiency and longer service life can be achieved while reducing the precious metal content – a certain technology can reduce the iridium loading from 1.5 mg/cm² to 0.5 mg/cm², reducing costs by 60% while maintaining the same service life [Application of Nanocatalytic Materials in Electrochemistry, 2024, Science Press]. Therefore, when purchasing, emphasis should be placed on the manufacturer’s technical strength rather than just comparing the precious metal content.
5.4 Select Adaptive Structures Based on Industry Characteristics
Different industries have different requirements for electrode structures: the chlor-alkali and electroplating industries are suitable for mesh anodes to increase surface area and current distribution uniformity; the wastewater treatment industry is suitable for plate or tube anodes to adapt to different reactor designs; water electrolysis for hydrogen production is suitable for porous structure anodes to improve mass transfer efficiency. When purchasing, the corresponding electrode structure should be selected according to the own equipment type.
VI. Summary: The Essence of the Core Relationship Is “Balance and Adaptation”
The core relationship between the precious metal content, coverage area, operational efficiency, and service life of titanium anode coatings is essentially the balance and adaptation between “performance requirements, operating conditions, and cost budget”:
From the perspective of content ratio, the core value of ruthenium is “basic catalysis,” and the core value of iridium is “stability.” The selection of the ratio needs to find a balance between efficiency and service life according to the harshness of the operating conditions; from the perspective of coverage area, macroscopic integrity guarantees the service life threshold, and microscopic active area improves the efficiency ceiling, whose effects are affected by multiple links such as pretreatment and coating process; from the perspective of industry differences, the operating conditions of different industries determine the weight of influencing factors, and the key to selection is “adaptability to operating conditions” rather than “absolute optimal parameters.”
For purchasers, understanding this core logic can avoid blind selection and achieve the maximization of cost and benefit under the premise of meeting production needs; for industry development, optimizing formula design, improving process levels, and realizing coating technology with “low precious metal content, high efficiency, and long service life” will be the core development direction of the titanium anode industry in the future.
