Peculiarities of surface layer formation at galvanic displacement of lead by platinum. Activity of Pt-0(Pb) composites in FAOR

Galvanic displacement (GD) of lead (e.d. Pb/GC) by platinum in 10(-3) M K-2 PtCl4 + 0.1 M HClO4 solution is carried out. The formation of Pt-0 in the course of GD at E < 0.0 V (vs. RHE) is found to induce dissolution of a considerable part of Pb by the reaction Pb + 2H(+) -> Pb2+ + H-2. The deposit formed at GD (Pt-0(Pb)(in)) is modified by potential cycling in the E interval of 0.05-1.45 V (1-20 cycles). All the samples are characterized by SEM, EDX, XPS, AES-1CP, and CVA methods. It is shown that no dense Pt shell is formed in the synthesis of Pt-0(Pb)(in). This is explained by the fact that at the stationary potential E-st established at GD, Pb-ad fails to desorb completely from the Pt-0 surface. A scheme of partial incorporation of Pb-ad into the surface layer of Pt-0(Pb)(in), is put forward. After 20 potential cycles, the Pb content in the first atomic layer on the Pt-0(Pb)(20c) surface becomes insignificant. Nonstationary (CVA) and stationary polarization measurements in the 0.5 M HCOOH + 0.1 M HClO4 solution demonstrate the very high activity of Pt-0(Pb) composites in FAOR. Thus, in the low E range (0.2-0.3 V), which is the region most interesting for practice, the specific stationary currents on Pt(Pb)(in), composites exceeds the analogous currents on e.d. Pt by two orders of magnitude. However, the activity of Pt-0(Pb)(20c) turns out to be only similar to 3 times higher than the activity of e.d. Pt. The possible reasons for the observed high activity of Pt-0(Pb) composites in FAOR and instability of their characteristics are discussed.