MMO Titanium Anodes for Electrodialysis

In an electrodialysis system, the MMO titanium anode is the core component providing the DC electric field. Its main functions are: to initiate oxidation reactions, primarily the oxygen evolution reaction (2H₂O – 4e⁻ → O₂↑ + 4H⁺) or the chlorine evolution reaction (2Cl⁻ – 2e⁻ → Cl₂↑).

To provide a stable DC electric field, driving the directional migration of ions in the solution.

To ensure the long-term stable operation of the electrodialysis system and reduce maintenance costs.

The performance of the anode affects the desalination rate, energy consumption, water recovery rate, and service life of the electrodialysis system.

There are four main types of coating systems for MMO titanium anodes used in electrodialysis:

Ruthenium-based coatings (RuO₂-based): including ruthenium-titanium, ruthenium-iridium-titanium, and ruthenium-iridium-tin coatings, suitable for chloride evolution reaction environments with high chloride ion concentrations (>1000 mg/L).

Iridium-based coatings (IrO₂-based): including iridium-tantalum, iridium-tantalum-titanium, and high-iridium coatings, suitable for oxygen evolution reaction environments with low chloride ion concentrations (<500 mg/L).

Platinum-based coatings (Pt-based): including pure platinum coatings and platinum-iridium alloy coatings, suitable for applications requiring extremely high purity and long-term stability.

Multi-layer gradient coatings: Wstitanium’s exclusive technology, combining the advantages of multiple coatings for superior performance and longer service life.

The choice of coating system depends on factors such as the chloride ion concentration in the solution, pH value, main electrochemical reactions, and operating current density. Generally, ruthenium-based coatings are chosen for high-chlorine environments, iridium-based coatings for low-chlorine environments, and platinum-based coatings for extremely high purity requirements.

The lifespan of an MMO titanium anode depends on several factors. Under standard operating conditions (pH=7, temperature = 25°C, current density = 1000A/m², chloride ion concentration = 1000mg/L, continuous operation), the designed lifespans of different coating systems are as follows:

Ruthenium-iridium titanium coating: 3-5 years
Iridium-tantalum coating: 5-8 years
High-iridium coating: 8-12 years
Pure platinum coating: 10-15 years

The main factors affecting the lifespan of an MMO titanium anode are:

Coating quality: Including coating composition, thickness, uniformity, and adhesion, this is the most critical factor affecting lifespan.

Operating conditions: Including pH value, temperature, current density, chloride ion concentration, and impurity content. The harsher the conditions, the shorter the lifespan.

Operating methods: Frequent electrode reversal, current fluctuations, and improper shutdown protection will all shorten the anode’s lifespan.

Maintenance: Regular cleaning, voltage monitoring, and other maintenance measures can extend the anode’s lifespan.

Frequent polarity reversal electrodialysis (EDR) is an improved technology developed from conventional electrodialysis. It reverses the polarity of the positive and negative electrodes every certain period (usually 15-20 minutes), simultaneously switching the inlet and outlet valves of the concentrate and desalination chambers accordingly.

The advantages of EDR technology are automatic cleaning of fouling formed on the ion exchange membrane and electrode surfaces, preventing scaling and contamination, and improving system operational stability and water recovery rate.

Wstitanium’s multi-layer gradient ruthenium-iridium and pure platinum coated MMO titanium anodes are well-suited for frequent polarity reversal operation. These coatings have excellent adhesion and stability, will not crack or peel off during repeated polarity reversals, and possess self-cleaning capabilities, effectively removing deposits from the electrode surface.

Yes, MMO titanium anodes are ideally suited for use in bipolar membrane electrodialysis (BPED) systems. BPED is an electrodialysis technology that converts salts into corresponding acids and bases. Its anode chamber is typically a strongly acidic environment, where the oxygen evolution reaction (OER) is the primary reaction occurring at the anode.

Wstitanium recommends using high-iridium coated (High Ir) MMO titanium anodes in BPED systems. The high-iridium coating exhibits extremely high OER catalytic activity and strong corrosion resistance, ensuring long-term stable operation under strongly acidic conditions and high current densities.

Yes, MMO titanium anodes are the standard anode material for EDI systems. EDI is a pure water production technology that combines electrodialysis and ion exchange. Its feed water is reverse osmosis permeate with a very low chloride ion concentration, and the anode primarily undergoes the oxygen evolution reaction (OER).

Wstitanium recommends using iridium-tantalum (Ir-Ta) or pure platinum (Pt) coated MMO titanium anodes in EDI systems. Both coatings do not leach any harmful substances, ensuring the purity of the product water, while also exhibiting excellent OER catalytic activity and stability.

The failure of an MMO titanium anode mainly manifests as coating degradation and passivation of the titanium substrate. This can be determined through the following phenomena:

Increased cell voltage: At the same current density, the cell voltage increases by more than 0.3V compared to the initial value. This is the most obvious sign of anode failure.

Decreased current efficiency: The desalination rate decreases, and energy consumption increases.

White spots appear on the electrode surface: This is the TiO₂ insulating layer formed by passivation of the titanium substrate.

Coating peeling: Obvious coating peeling occurs on the electrode surface.

Electrolyte discoloration: If the electrolyte turns yellow or black, it may be due to the dissolution of noble metal oxides in the coating or corrosion of the titanium substrate.

When any of the above phenomena occur, it indicates that the anode has failed or is about to fail and needs to be replaced promptly.

Wstitanium provides complete quality certification documents for each batch of products, including:

Material certification: Material analysis report of the titanium substrate, conforming to ASTM B265 standard.

Coating test report: Including test data such as coating composition, thickness, loading capacity, and adhesion.

Electrochemical performance test report: Including test data such as oxygen evolution/chlorine evolution potential and current efficiency.

Dimensional inspection report: Dimensional and tolerance inspection data of the product.

Appearance inspection report: Results of appearance quality inspection of the product.

RoHS/REACH compliance certification: The product complies with EU RoHS and REACH environmental standards.

In addition, we can provide test reports from authoritative third-party institutions upon customer request.

The lifespan of an MMO titanium anode is generally 3-15 years, with a maximum of 30 years, depending on operating conditions and coating quality. The main factors affecting the lifespan of an MMO titanium anode are:

Coating quality: The composition, thickness, uniformity, and adhesion of the coating affect the anode’s lifespan.

Electrolyte composition: Strong acids, strong alkalis, high salinity, and the presence of corrosive ions such as fluoride ions accelerate coating aging and failure.

Operating current density: Higher current density leads to faster anode consumption and shorter lifespan.

Operating temperature: Increased temperature accelerates coating dissolution and aging; the consumption rate doubles for every 10°C increase in temperature.

Polarity reversal: Frequent polarity reversals accelerate coating reduction and peeling, shortening lifespan.

Mechanical damage: Mechanical scratches and impacts during installation and maintenance can damage the coating, leading to localized corrosion.