SOME ELECTROCHEMICAL CONSEQUENCES OF POTENTIAL-INDUCED SURFACE RECONSTRUCTION ON AU(100) - DOUBLE-LAYER NONUNIFORMITY AND ELECTRODE-KINETICS

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 voltamme try and differential capacitance measurements. together with in-situ s canning tunneling microscopy (STM). Initially unreconstructed (i.e. (1 X 1)) Au(100) yields capacitance-potential potential (C-E) profiles i n dilute (1 mM) perchloric acid in the vicinity of the potential of ze ro charge E(pzc) which are consistent with the presence of an essentia lly uniform distribution of electronic charge across the surface. Upon electrochemically inducing hexagonal surface reconstruction by holdin g the potential below -0.2 V for periods of up to ca. 20 min. these C- E minima are substantially broadened. The latter observation implicate s the presence of electrostatically distinct surface domains with ''lo cal'' E(pzc) values that are significantly (0.1-0.2 V) lower as well a s higher than that for unreconstructed Au(100), having dimensions at l east comparable with the Debye length of the diffuse layer (ca. 9.5 nm ) in 1 mM HClO4. This finding is consistent with the real-space surfac e morphology as obtained by in-situ STM under these conditions, which shows the common presence of corrugated features, such as edges of rec onstructed strands. in addition to domains featuring quasi-hexagonal a tomic packing. The sharp potential-induced removal of the reconstructi on 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 sig nificantly (1.3 to 1.7-fold) accelerated by Au(100) reconstruction. Th ese effects appear to be due to the involvement of gold atomic sites f eaturing lower coordination numbers which are seen to be formed upon s urface reconstruction.