Typically, the anode of a water electrolyser comprises a catalyst for the oxygen evolution reaction (an OER electrocatalyst). Appropriate OER electrocatalysts are known to the skilled person and have been described e.g. by M. Carmo et al., “A comprehensive review on PEM water electrolysis”, International Journal of Hydrogen Energy, Vol. 38, 2013, pp. 4901-4934; and H. Dau et al., “The Mechanism of Water Oxidation: From Electrolysis via Homogeneous to Biological Catalysis”, ChemCatChem, 2010, 2, pp. 724-761.

S. P. Jiang and Y. Cheng, Progress in Natural Science: Materials International, 25 (2015), pp. 545-553, provide a review on electrocatalysts for the oxygen evolution reaction in water electrolysis.

It is known that iridium or ruthenium or oxides thereof are efficient catalysts for the oxygen evolution reaction. As iridium and ruthenium are expensive, it is desirable to have a sufficiently high catalytic activity even a low amounts of iridium and/or ruthenium, and a very low dissolution of these metals into the surrounding electrolyte under the highly corrosive operating conditions of PEM water electrolysers and fuel cells.

Bulk catalysts have a limited surface area for electrochemical activity. For increasing the catalytically active surface area, it is generally known to apply a catalyst on a support.