What Factors Affect the Efficiency of MMO Anodes?

What Factors Affect the Efficiency of MMO Anodes?

Mixed Metal Oxide(MMO) anodes are featured for low electrical resistance, good electrochemical activity, corrosion resistance, and dimensional stability. Low electrical resistance reduces energy consumption in the electrochemical process.  

The MMO anode properties are mainly determined by pretreatment of the base metal before it is coated by electrochemically active oxide layer, heat treatment temperature, amount of metal per deposition cycle, and thickness of the coating layer. These factors impact often more strongly anode’s properties than the chemical composition of the coating.

The good electrochemically active layer structure is often cracked and porous to increase the surface area in contact with electrolytes. Electrochemical activity depends on the number of active sites in the coating that are in contact with electrolytes. Only the rutile-type oxides are considered electrochemically active, for example, RuO2, IrO2, PtO2, MnO2, RhO2, and PbO2. From those oxides RuO2, IrO2 and RhO2 are metallic conductors, and PtO2, MnO2, and PbO2 are semiconductors. Electrochemically active oxides that are used in anodes are commonly RuO2 and IrO2. During operation oxide layer forms on the surface of the noble metal anode that acts as active oxide and protects the noble metal from dissolving. This phenomenon has been noticed for example with platinum whose surface will form a PtO2 layer.