Mixed metal oxide electrode

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Mixed metal oxide (MMO) electrodes are devices with useful properties for use as anodes in electrochemical electrolysis reaction. The term refers to electrodes in which the surface contains several kinds of metal oxides. One kind, usually RuO2, IrO2, or PtO2, is the electrocatalyst which conducts electricity and catalyzes the desired reaction such as production of chlorine gas. The other metal oxide is typically titanium dioxide which does not conduct or catalyze the reaction, but is cheaper and prevents corrosion of the interior. The substrate of the electrode is typically a titanium plate or expanded titanium mesh.

The loading or amount of precious metal on the substrate (that is, other than the titanium) can be in the order of around 10 to 12 grams per square metre.[1]

Applications include use as anodes in electrolytic cells for producing free chlorine from saltwater in swimming pools, in electrowinning of metals, in printed circuit board manufacture, electrotinning and zinc electro-galvanising of steel, as anodes for cathodic protection of buried or submerged structures.


Henri Bernard Beer registered his patent on mixed metal oxide electrodes in 1965. The patent named "Beer 65", also known as "Beer I", which Beer claimed the deposition of Ruthenium oxide, and admixing a soluble titanium compound to the paint, to approximately 50% (with molar percentage RuO2:TiO2 50:50). His second patent, Beer II , reduced the Ruthenium oxide content below 50%.[2]


  1. ^ "Reverse electrodialysis: Evaluation of suitable electrode systems", Chapter 4 of the doctoral thesis of Joost Veerman, 2009, p. 70.
  2. ^ H.B. Beer. Journal of Electrochemical Soc. 127, 1980, 303C