Composites Pt-n(0) Au are synthesized in PtCl42- solutions by galvanic displacement of Cu-ad monolayers (MLCuad) from polycrystalline (pc) Au (to afford (Pt1Au)-Au-0), and also from (Pt1Au)-Au-0 ((Pt2Au)-Au-0) and (Pt2Au)-Au-0 ((Pt3Au)-Au-0). The data of open-circuit potential transients, CVA, SEM, and XPS studies indicate that the displacement of MLCuad proceeds not layer-by-layer but to form Pt clusters. The degree of blocking of the Au surface by Pt is approximately (%): 65 ((Pt1Au)-Au-0), 80 ((Pt2Au)-Au-0), and 90 ((Pt3Au)-Au-0). These (PtnAu)-Au-0 deposits simulate the gradual transition of Pt coatings close to monolayer to those formed by small Pt particles. The specific rates of methanol oxidation reaction (MOR) (per cm(2) of EASA(Pt)) increase in the row: (Pt1Au)-Au-0 < (Pt2Au)-Au-0 < (Pt3Au)-Au-0 < pc Pt. For the formic acid oxidation (FAOR), the inverse dependence is observed: pc Pt < (Pt3Au)-Au-0 < (Pt2Au)-Au-0 < (Pt1Au)-Au-0. The difference is explained by the fact that the chemisorption of CH3OH requires a larger area (>= 3 Pt surface atoms), whereas its single-site adsorption results in formic acid oxidation by the direct path. It is assumed that the Pt/Au interface of particles plays the important role in the formation of active sites ("ensembles") for FAOR The high specific mass activities (mA/mg Pt) of (PtnAu)-Au-0 composites are observed not only in FAOR, but also in MOR, which is associated with the high degree of dispersion of these Pt deposits (similar to 90-170 m(2) EASA/g Pt). (C) 2015 Elsevier B.V. All rights reserved.