Structure of Active Adlayers on Bimetallic Surfaces: Oxygen Reduction on Au(111) with Bi Adlayers

Abstract

The structure of Bi adlayers on the Au(111) electrode surface during the course of O2 reduction has been investigated by in situ surface X-ray scattering. Under oxygen reduction conditions, both the low-coverage (2 × 2)-Bi and the close-packed (p × √3)-2Bi adlayer structures are stable. We developed an electrochemical drop cell that provides a more uniform potential distribution during high current conditions compared with commonly used thin-layer cells. Our results clearly indicate distinctly different catalytic properties for the two ordered bismuth adlayer phases. In the potential region corresponding to the (2 × 2)-Bi phase, O2 reduction is promoted to a four-electron reaction, albeit with relatively slow kinetics. The close-packed (p × √3)-2Bi phase, formed at more negative potentials, appears to have a limited number of sites available for four-electron reduction, but the reaction kinetics on this adlayer is enhanced by an increased overpotential.