Deposition of platinum monolayers on gold

Deposition of small amount of Pt is reported onto polycrystalline Au from H2PtCl6-containing solutions. Spontaneous deposition, yielding about 5% of a full-packed monolayer, has been found at the steady-state open circuit potential. Formation of a somewhat more dense, but still a partial monolayer could be observed at potentials between the steady-state open circuit potential and that of the onset of bulk deposition. A specific difference of monolayer and bulk deposition is that Pt surface area levels off with time and keeps increasing for the former and latter types of deposition, respectively. Pt monolayers with quite high coverages can be formed in a rather narrow, 20-30 mV potential region only. The surface areas of Pt and of the Pt-free Au have been simultaneously measured as cyclic voltammetry peak charges. From these measurements, the site requirement of the Pt atoms was determined to be around four; that is, each Pt atom blocks the oxidation of about four underlying/neighbouring Au atoms, implying their distant positions. Based on the results, Au surfaces coated with monoatomic Pt layers of quite high coverages can be prepared.