Some electrochemical consequences of potential-induced surface reconstruction on Au(100): Double-layer nonuniformity and electrode kinetics

Abstract

Some consequences of potential-induced surface reconstruction upon the double-layer structure and electrocatalytic properties of Au(100) in aqueous perchloric acid have been explored by means of cyclic voltammetry and differential capacitance measurements, together with in-situ scanning tunneling microscopy (STM). Initially unreconstructed (i.e. (1 × 1)) Au(100) yields capacitance-potential ( C-E) profiles in dilute (1 mM) perchloric acid in the vicinity of the potential of zero charge E pzc which are consistent with the presence of an essentially uniform distribution of electronic charge across the surface. Upon electrochemically inducing hexagonal surface reconstruction by holding the potential below −0.2 V for periods of up to ca. 20 min, these C-E minima are substantially broadened. The latter observation implicates the presence of electrostatically distinct surface domains with “local” E pzc values that are significantly (0.1–0.2 V) lower as well as higher than that for unreconstructed Au(100), having dimensions at least comparable with the Debye length of the diffuse layer (ca. 9.5 mn) in 1 mM HClO 4. This finding is consistent with the real-space surface morphology as obtained by in-situ STM under these conditions, which shows the common presence of corrugated features, such as edges of reconstructed strands, in addition to domains featuring quasi-hexagonal atomic packing. The sharp potential-induced removal of the reconstruction inferred from the appearance of a voltammetric feature at 0.6 V/SCE in perchloric acid is confirmed by STM data acquired during potential sweeps, which also show that the 24% excess gold atoms released form arrays of metal clusters. The rates of proton electroreduction are significantly (1.3 to 1.7-fold) accelerated by Au(100) reconstruction. These effects appear to be due to the involvement of gold atomic sites featuring lower coordination numbers which are seen to be formed upon surface reconstruction.