Oxygen reduction catalysts have been prepared by modifying Ru/C catalysts (either commercial or self-made) using iron phenanthroline complexes adsorbed at the surface of the catalysts and heat treated at elevated temperatures. This new type of catalyst shows an oxygen reduction activity which is 3-5 times higher than the activity of an unmodified Ru/C catalyst. Furthermore, it is higher than that of catalysts based on Ru/C modified with Se, however, the activity of Pt/C is still not yet matched. Structural characterisation indicates that the catalysts consist of ruthenium nanoparticles. These nanoparticles most likely are covered by centres of type FeNxCy also found in carbon supported iron catalyst for oxygen reduction prepared by pyrolysis of iron, nitrogen and carbon via heat treatment steps. (c) 2005 Elsevier B.V. All rights reserved.