Site-specific catalytic activity of model platinum surfaces in different electrolytic environments as monitored by the CO oxidation reaction

Abstract

Stepped Pt surfaces having different width (111) terraces interrupted by (110) or (100) monoatomic steps were employed to evaluate the catalytic activity towards CO oxidation at specific sites of these surfaces in HClO4, H2SO4, and H3PO4 solutions, as well as in phosphate buffer and alkaline solution. The catalytic activity at the (111) terraces was sensitive to the nature of the anions derived from the electrolyte dissociation, while no effect on catalytic activity was detected at the monoatomic steps. For the same stepped surface, a change in solution pH, passing from acid to alkaline solutions, had contrasting effects on catalytic activity at the (111) terraces and the step sites, with the catalytic activity of the (111) terraces improving, while catalytic activity at the step sites deteriorated. It was found that the release of CO surface sites occurred preferentially from the (111) terraces of the Pt(s)-[(n-1)(111)×(110)] series, while from Pt(s)-[(n)(111)×(100)] surfaces, (111) terrace and (100) step sites were released simultaneously.

Determination of Specific Electrocatalytic Sites in the Oxidation of Small Molecules on Crystalline Metal Surfaces

“…In electrocatalysis of CO stripping experiments, after COads oxidation at the most active sites, CO molecules do not occupy them again, because the COads behave as an "immobile" species during the process. This is a general characteristic of CO stripping on Pt electrodes in entire pH range [25,51,52].…”

“…If we consider the (111) terraces and steps/defects, the strength of CO adsorption at the specific sites is a parameter which must be considered in the kinetic analysis of the preferential electrocatalytic oxidation of CO, and this preference is directly linked to the local arrangement of atoms at the catalyst surface. In this regard, the influence of (100) steps in improving catalytic activity of (111) terraces is lower in comparison to the catalytic shift in (111) terraces in presence of (110) steps, despite the intrinsic catalytic activity of the (110) and (100) steps are very similar to each other [25].…”

“…In the case of solution pH, the mechanisms by which this parameter affects the catalytic activity are much more complex than previously thought. In this sense, at the surface of a same catalyst (consisting of nonequivalent sites), the change of solution pH passing from acidic toward alkalinity catalytically favored some kind of sites (as highly coordinated Pt atoms, the (111) terrace sites), while the catalytic activity of the sites consisting of low coordination atoms was inhibited [25]. Then, the recognition of the active sites in electrocatalysis involve at least two environment aspects: one intrinsic to the catalyst surface, involving geometric and electronic factors (which include scale or size factors) and the possible influence of the local electrochemical environment (extrinsic to the catalyst surface).…”

“…Data recorded at sweep rate 50 mV s -1 . The data were reproduced and adapted from[49] American Chemical Society with permission and[25] Elsevier with permission.…”

“…It is appropriate to anticipate that this experimental procedure is because the COads adlayer apparently behaves as a typical poison ("immobile") layer during the COads is oxidation. In the last five years, we have conducted a series of experiments in this direction in the entire pH range, and it was found that at stepped Pt surfaces the most active sites consist in (111) terraces[25,51,52]. The intrinsic catalytic activity of step and kink sites is lower compared to the catalytic activity at the (111) terraces of those kinds of surface.…”