On the origin of the selectivity of oxygen reduction of ruthenium-containing electrocatalysts in methanol-containing electrolyte

The reactivity with water and methanol of oxygen-reducing (Ru1-x,MoxSeOz) and oxygen (from water)-evolving eletrocatalysts (RuS2, RuO2), which permit electron transfer via ruthenium d-states, was studied using electrochemical techniques and differential electrochemical mass spectroscopy (DEMS). In contrast to platinum, which is depolarised by methanol, ruthenium compounds show a high reactivity with water species and an extremely low reactivity with methanol. We conclude that the ruthenium-centred coordination chemical reactivity with water channels electrochemical currents, thus producing kinetic selectivity. The reason for the higher reactivity with water of Ru d-states as compared to platinum is seen in the higher density of d-states near the Fermi level as shown by this comparative study. (C) 2000 Academic Press.