Structure and inhibition effects of anion adlayers during the course of O 2 reduction

Abstract

Structures of Br adlayers were determined on the Ag(100), Au(100) and Pt(111) electrode surfaces during the course of O 2 reduction by using synchrotron surface X-ray scattering techniques and correlated with the O 2 reduction activity obtained from rotating disk electrode measurements. On Ag(100), the c(2×2) Br adlayer, precludes the O 2 adsorption in ‘bridge’ configuration, and the O 2 reduction current resulting solely from adsorption in the ‘end-on’ configuration through the four-fold symmetry holes in the c(2×2) Br lattice is observed at large overpotentials. On Au(100), O 2 reduction is completely inhibited by the c(√2×2√2)R45° phase. The reaction takes place only at potentials negative of the low potential limit of the existence of that phase. O 2 reduction is also completely blocked by the commensurate (3×3) Br adlayer on Pt(111) at high potentials. Below 0.5 V, the ordered phase vanishes and O 2 reduction takes place. Adsorbed disordered Br adions change the mechanism of O 2 reduction on Pt(111) into a 2e-reaction. O 2 affects the stability of ordered Br adlayer on Pt(111), but not on Ag(100) and Au(100).