Efforts were made to simplify the structure of Ru-based catalysts, and to tailor industrially practicable methanol insensitive oxygen reduction catalysts both by thermolysis of Ru-carbonyls in organic solvents and by modified preparation techniques of Ru colloids. Selective catalysis was found to be essentially independent of the chalcogene (Se) used which, however, is a crucial factor for facilitating efficient electron transfer. All preparations contained Ru-metal particles of nm size, the surfaces of which were modified by carbonyl and carbido-carbonyl complexes or carbon compounds. The role of carbon as ligand to Ru clusters stabilizing the Ru interface against oxidation and in promoting catalytic electron exchange via nonbonding Ru d-states is theoretically analysed in a model calculation. An analogy is drawn to a biological Fe - only hydrogenase centre in order to discuss projected key experiments for optimizing reduction catalysis: the stabilization of small, inherently unstable catalytic metal clusters by CO or CN and their linking via electron bridges such as S and Se to electron reservoirs (metal colloids).