Mixed Metal Oxide (MMO) electrodes, also known as Dimensionally Stable Anodes (DSA), are composite electrodes manufactured by applying a thermally decomposed layer of electrocatalytically active mixed metal oxides onto a valve metal substrate (primarily titanium).
Core Structure
Substrate: Typically titanium (Ti), chosen for its ability to form a dense passivation layer (TiO₂) that provides exceptional corrosion resistance under anodic polarization.
Catalytic Coating: A thin layer (usually several micrometers to tens of micrometers thick) composed of two or more metal oxides. This coating serves as the "soul" of the electrode, enabling electrical conductivity and catalytic reactions.
Working Principle: While the titanium substrate itself is non-conductive, the MMO coating acts as both an excellent electronic conductor and a highly efficient electrocatalyst. It significantly reduces the overpotential of target reactions, enabling more efficient conversion of electrical energy into chemical energy while protecting the underlying titanium substrate from corrosion.
Key Features of MMO Electrodes
►Exceptional Electrocatalytic Activity
The MMO coating is engineered to exhibit high intrinsic activity for specific reactions (e.g., Chlorine Evolution Reaction, CER), dramatically reducing the overpotential required. This leads to significantly lower cell voltage and energy consumption (achieving 15%-30% energy savings compared to traditional graphite electrodes).
►Outstanding Dimensional Stability
The coating firmly adheres to the titanium substrate, preventing consumption and deformation during electrolysis-unlike graphite electrodes. The geometric dimensions of the electrode remain virtually unchanged throughout its lifespan, hence the name "Dimensionally Stable Anode." This ensures operational stability and uniform current distribution in electrolytic cells.
►Exceptionally Long Service Life
Thanks to the superior corrosion resistance of both the coating and the titanium substrate, MMO electrodes can last for years or even over a decade, far exceeding the lifespan of traditional graphite electrodes (months) or lead-based anodes (1-2 years). This drastically reduces maintenance costs and downtime associated with electrode replacement.
►Excellent Environmental Compatibility and Product Purity
The electrode itself does not participate in reactions, avoiding contamination of electrolytic products and electrolytes caused by corrosion (a common issue with graphite anodes). It also eliminates the risk of heavy metal pollution associated with lead-based anodes.
►Customizable Catalytic Selectivity
By varying the types and ratios of metal oxides in the coating, the electrode's performance can be "tailored" to exhibit high selectivity for specific reactions. For example, ruthenium-based coatings prioritize the Chlorine Evolution Reaction (CER), while iridium-based coatings favor the Oxygen Evolution Reaction (OER).
Primary Application Fields
Chlor-Alkali Industry
Application: Electrolysis of brine to produce chlorine (Cl₂), sodium hydroxide (NaOH), and hydrogen (H₂). This is the earliest and most critical application of MMO electrodes, serving as the foundation of their development.
Antifouling via Seawater Electrolysis
Application: Onboard or coastal facilities electrolyze seawater to generate sodium hypochlorite (NaClO), used to eradicate microorganisms and prevent biofouling in pipelines and condensers.
Industrial Wastewater Treatment
Application: Direct electrochemical oxidation of toxic organic compounds (e.g., phenols, cyanides) in wastewater, or indirect generation of strong oxidants (e.g., hypochlorite, ozone) for disinfection and decolorization.
Cathodic Protection
Application: Used as impressed current anodes to protect metallic structures such as port facilities, ships, and buried pipelines from electrochemical corrosion. MMO anodes are the preferred choice due to their longevity and high efficiency.
Electrometallurgy
Application: Employed in the electrowinning and refining of metals (e.g., copper, zinc, cobalt).
Other Emerging Fields
Green Hydrogen Production: Serving as oxygen evolution anodes (OER) in water electrolysis.
Organic Electrosynthesis: Synthesizing high-value-added chemicals.
Ozone Generators: Enabling efficient ozone production.
