Structure of Active Phases during the Course of Electrocatalytic Reactions

Abstract

Structures of ordered adsorbates have been determined during the course of the electrocatalytic reduction of oxygen by using synchrotron surface X-ray scattering techniques. The origin of the catalytic action of Tl adlayers on O2 reduction on Au has been determined, and a possibility of measuring the adsorption configuration-specific activity in O2 reduction has been demonstrated in the reaction on Ag(100) with Br adlayer. On the Au(111) electrode surface, the oxidation/redeposition of Tl in catalyzing the four-electron oxygen reduction is revealed from the analysis of X-ray diffraction intensity as a function of the O2 reduction current for the (3 × )-2TlBr adlayer. This indicates that the redox property of the metal adsorbates is responsible for the catalytic effect. On Ag(100) with the c(2 × 2) Br adlayer, the O2 reduction current resulting solely from adsorption in the “end-on” configuration through the 4-fold symmetry holes in the c(2 × 2) Br lattice is observed, showing that the “bridge” adsorption may not be necessary for the four-electron O2 reduction on Ag at large overpotentials.