Abstract
The oxygen reduction reaction (ORR) in alkaline media has been investigated on chalcogen-modified ruthenium nanoparticles (Ru/C, Se/Ru/C, Se/RuMo/C, S/Ru/C, S/RuMo/C) synthesized in-house via aqueous routes. In acidic medium, it is well known that modification by a chalcogen prevents the oxidation of the underlying transition-metal (Ru) surface, thereby promoting direct molecular O2 adsorption on the Ru metal. On an unmodified Ru catalyst in alkaline media, the surface oxides on Ru mediate the 2e– reduction of molecular O2 to a stable peroxide anion (HO2–) intermediate via an outer-sphere electron-transfer mechanism. This increases the activity of HO2– near the electrode surface and decreases the overpotential for ORR by effectively carrying out the reduction of HO2– to OH– at the oxide-free ruthenium metal site. An increase in ORR activity of Ru is observed by modification with a chalcogen; however, the increase is not as significant as observed in acidic media. Ternary additives, such as Mo, were found...
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