POTENTIAL-DEPENDENCE OF THE REDUCTION OF DIOXYGEN AS CATALYZED BY TETRARUTHENATED COBALT TETRAPYRIDYLPORPHYRIN

The electroreduction of O-2 at rotated graphite disk electrodes coated with cobalt tetra-pyridylporphyrin was examined at potentials on the rising portion of the current-potential curve, both before and after f our Ru(NH3)(5)(2+) groups were co-ordinated to the pendant pyridine li gands. The unruthenated porphyrin provides a two-electron reduction of O-2 with a Tafel slope near 120 mV per decade. The ruthenated porphyr in provides a primarily four-electron reduction with a Tafel slope nea r 90mV per decade. Some mechanistic implications of the results are di scussed including the likelihood that an array of partially reduced an d partially oxidized ruthenated porphyrins participates in the catalys is of the reduction of O-2 via a set of parallel reactions.