Surface processes and electrocatalysis on the Pt(hkl )/Bi-solution interface

In this article we review the most important findings for Bi modified Pt single crystal electrodes. The main focus is on results obtained on Pt(111)–Biir but also some data for Pt(100)–Biir are provided. Our own data are discussed in the light of previous data from the literature. By making use of in situ surface X-ray scattering in combination with ex situ X-ray photoelectron spectroscopy and cyclic voltammetry it is possible to establish a link between surface atomic structures and electrochemical surface processes. In short, Biir was found to remain in its zero-valent state over the whole potential range. Besides a physical site blocking effect, Biir alters the adsorption properties of Hupd, OHad, and anions from the supporting electrolyte due to electronic modifications of the platinum surface atoms. Rotating (ring-)disk electrode measurements were carried out to study the kinetics of H2, CO or HCOOH electrooxidation on Pt(111)–Biir or the oxygen reduction reaction on Pt(100)–Biir, respectively. The kinetics of CO oxidation (both CO stripping and continuous CO oxidation) is accelerated initially on the Biir modified Pt(111) surface compared to pure Pt(111) electrodes. The same effect was observed during the oxidation of formic acid. The oxygen reduction activity on Pt(100)–Biir is reduced s. pure Pt(100) due to the reduced number of active Pt sites for the reaction (site blocking). At negative potentials, however, the formation of peroxide is enhanced on the Biir modified electrode. Hence, the selectivity of oxygen reduction to H2O2 (2-electron reduction) s. the reduction to H2O (4-electron reduction) is enhanced.