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

In this article we review the most important findings for Bi modified Pt si ngle crystal electrodes. The main focus is on results obtained on Pt(111)-B i-ir but also some data for Pt(100)-Bi-ir are provided. Our own data are di scussed 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 photoel ectron spectroscopy and cyclic voltammetry it is possible to establish a li nk between surface atomic structures and electrochemical surface processes. In short, Bi-ir was found to remain in its zero-valent state over the whol e potential range. Besides a physical site blocking effect, Bi-ir alters th e adsorption properties of H-upd, OHad, and anions from the supporting elec trolyte due to electronic modifications of the platinum surface atoms. Rota ting (ring-)disk electrode measurements were carried out to study the kinet ics of H-2, CO or HCOOH electrooxidation on Pt(111)-Bi-ir or the oxygen red uction reaction on Pt(100)-Bi-ir, respectively. The kinetics of CO oxidatio n (both CO stripping and continuous CO oxidation) is accelerated initially on the Bi-ir modified Pt(111) surface compared to pure Pt(111) electrodes. The same effect was observed during the oxidation of formic acid. The oxyge n reduction activity on Pt(100)-Bi-ir is reduced vs. pure Pt(100) due to th e reduced number of active Pt sites for the reaction (site blocking). At ne gative potentials, however, the formation of peroxide is enhanced on the Bi -ir modified electrode. Hence, the selectivity of oxygen reduction to H2O2 (2-electron reduction) es. the reduction to H2O (4-electron reduction) is e nhanced.