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

Abstract

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)–Bi_ir but also some data for Pt(100)–Bi_ir 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, Bi_ir was found to remain in its zero-valent state over the whole potential range. Besides a physical site blocking effect, Bi_ir alters the adsorption properties of H_upd, OH_ad, 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)–Bi_ir or the oxygen reduction reaction on Pt(100)–Bi_ir, respectively. The kinetics of CO oxidation (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 oxygen reduction activity on Pt(100)–Bi_ir 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 Bi_ir modified electrode. Hence, the selectivity of oxygen reduction to H₂O₂ (2-electron reduction) s. the reduction to H₂O (4-electron reduction) is enhanced.