The adsorption of OOH, the main product of the first step in the O-2 reduction on Pt(111) surfaces, is studied on Pt-based bimetallic three-atom clusters. Cr, Co, and Ni are better adsorption sites for OOH than Pt, but the strong adsorption might not favor the dissociation of OOH. However, the presence of Cr, Co, or Ni in the vicinity of a Pt atom increases its electron density, enhancing the Pt ability to transfer electrons to oxygenated species. Thus, Cr, Co, or Ni in the subsurface, rather than on the exposed surface, may contribute favorably to catalyze the O-2 reduction. (c) 2005 Elsevier B.V. All rights reserved.