Iridium/Ruthenium-based Titanium-based Metal Oxide Anodes (MMO/DSA Anodes)

Commonly known as titanium-based noble metal oxide coated anodes, the substrate is industrial pure titanium (TA1/TA2), and the surface is deposited with a platinum group metal mixed oxide catalyst layer through thermal decomposition. The full name is Size Stabilized Anode (DSA). The two main systems in the industry are: Ruthenium-based (Ru-based, chlorine-evolving) and Iridium-based (Ir-based, oxygen-evolving).

Basic Structure and Preparation

1. Substrate: Titanium plate/titanium mesh/titanium tube; titanium easily forms a passivated TiO₂ barrier layer under anodic polarization, isolating the electrolyte and ensuring a conductive substrate.

2. Pretreatment: Degreasing → Sandblasting → Oxalic acid etching (to increase adhesion).

3. Coating Preparation: Noble metal precursor coating/ultrasonic spraying → segmented high-temperature thermal oxidation sintering to form rutile phase oxides (RuO₂, IrO₂). 4. Core Differentiation Logic

> Ruthenium-based: Excellent at Chlorine Evolution Reaction (CER); Iridium-based: Excellent at Oxygen Evolution Reaction (OER)

Ruthenium-based Titanium-based Anodes (Ru-based, often RuO₂-IrO₂ composite coating)

Typical Formulation: RuO₂-IrO₂-TiO₂ ternary coating (industrial standard ruthenium-iridium anode)

Performance Characteristics: Extremely low chlorine evolution overpotential, high chlorine production efficiency, low energy consumption. Excellent stability in neutral/weakly alkaline chlorine-containing systems, lower cost than pure iridium systems.

Fatal Weakness: Prone to failure under strong oxygen evolution conditions. Under high anode potential, RuO₂ is oxidized to volatile RuO₄, leading to continuous loss of precious metals and rapid coating deactivation; unsuitable for acidic systems or systems primarily involving oxygen evolution.

Applicable Scenarios (Chlorine Evolution Dominant):

– Chlor-alkali industry, electrolytic production of sodium hypochlorite and sodium chlorate

– Seawater electrolysis, pool salt and chlorination disinfection, circulating water electrolysis for algae removal and sterilization. Chlorine-containing wastewater, cathodic protection (seawater, soil environments)

Incompatible environments: Sulfuric acid systems, pure water electrolysis, high-potential continuous oxygen evolution conditions; high fluoride ion environments will rapidly corrode titanium substrates.

Iridium-based Titanium Anodes (Ir series, mainstream: IrO₂-Ta₂O₅ iridium-tantalum coating)

Typical Formulation: IrO₂-Ta₂O₅ (molar ratio typically 7:3, classic formulation for acidic oxygen evolution)

Performance Characteristics: Excellent oxygen evolution catalytic activity, long-term stability in strongly acidic media
Resistant to oxidation at high anodic potentials; IrO₂ does not easily form volatile oxides; Ta₂O₅ acts as an inert framework, inhibiting coating cracking and extending lifespan
Tolerant of high current density and high-temperature acidic electrolytes

Iridium is expensive, resulting in higher initial procurement costs; chlorine evolution activity is weaker than ruthenium-based anodes

Applicable Scenarios (Oxygen Evolution Dominant):

– Copper/aluminum foil electrolysis, PCB VCP electroplating, hydrometallurgical metal electrowinning

– Advanced oxidation treatment of acidic organic wastewater

– PEM water electrolysis for hydrogen production anodes, pure water/dilute acid electrolysis

– Sulfuric acid medium electrolysis system

Core Selection Criteria (Directly Applicable to Engineering Applications)

1. High chloride ion content in electrolyte, target chlorine/hypochlorous acid production → Ruthenium-iridium anode (Ru-based)

2. Electrolyte primarily sulfuric acid, almost no chlorine production, continuous oxygen evolution → Iridium-tantalum anode (Ir-based)

3. Mixed systems (containing both Cl⁻ and significant oxygen evolution)

– Mild operating conditions: High iridium ratio Ruthenium-iridium coating

– Strong acid + high potential: Iridium-tantalum preferred, Ruthenium-based is not recommended

4. Absolutely avoid pitfalls: Do not use Ruthenium-based anodes in continuously oxygen-evolving acidic baths, as their lifespan may be shortened several times.

Common Extended Knowledge Points

1. Coating loading: Industrial standard 8–35 g/m²; higher current density requires higher precious metal loading.

2. Fluoride ion hazards: Regardless of whether it’s iridium or ruthenium-based, electrolytes containing F⁻ will damage the passivation film on the titanium substrate, causing rapid electrode failure. 3. New manufacturing process: Ultrasonic spraying can achieve a more uniform and dense coating, improving electrode life and reducing the amount of precious metals used compared to manual brushing (a mainstream application area for Cheersonic Ultrasonic).

4. Failure assessment: A continuous increase in tank voltage and a decrease in gas production are mostly due to active coating loss or titanium substrate passivation.

About Cheersonic

Cheersonic is the leading developer and manufacturer of ultrasonic coating systems for applying precise, thin film coatings to protect, strengthen or smooth surfaces on parts and components for the microelectronics/electronics, alternative energy, medical and industrial markets, including specialized glass applications in construction and automotive.

Our coating solutions are environmentally-friendly, efficient and highly reliable, and enable dramatic reductions in overspray, savings in raw material, water and energy usage and provide improved process repeatability, transfer efficiency, high uniformity and reduced emissions.

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