Peculiarities in the electrocatalytic behavior of ultralow platinum deposits on gold synthesized by galvanic displacement

• Ptn0Au composites (n = 1÷3) were obtained by the successive displacement of three MLCuad in the PtCl42 − solution.
• The displacement of MLCuad proceeded to afford Pt clusters rather than layer-by-layer.
• Pt10Au – Pt20Au – Pt30Au – pc Pt, the specific surface activity of Pt increased as regards MOR and decreased as regards FAOR.
• The possible reasons for the different behavior of Ptn0Au activity with the increase in n in FAOR and MOR are discussed.
• Composites Ptn0Au demonstrated the high degree of Pt utilization not only in FAOR but also in MOR.

Composites Ptn0Au are synthesized in PtCl42 − solutions by galvanic displacement of Cuad monolayers (MLCuad) from polycrystalline (pc) Au (to afford Pt10Au), and also from Pt10Au (Pt20Au) and Pt20Au (Pt30Au). 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 (Pt10Au), 80 (Pt20Au), and 90 (Pt30Au). These Ptn0Au 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 cm2 of EASAPt) increase in the row: Pt10Au < Pt20Au < Pt30Au < pc Pt. For the formic acid oxidation (FAOR), the inverse dependence is observed: pc Pt < Pt30Au < Pt20Au < Pt10Au. The difference is explained by the fact that the chemisorption of СН3ОН 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 Ptn0Au composites are observed not only in FAOR, but also in MOR, which is associated with the high degree of dispersion of these Pt deposits (~ 90–170 m2 EASA/g Pt).