Structure of Au(111) and Au(100) Single-Crystal Electrode Surfaces at Various Potentials in Sulfuric Acid Solution Determined by In Situ Surface X-ray Scattering

Abstract

Potential-dependent surface structures of Au (111) and Au(100) single-crystal electrodes in a 50 mM H 2 SO 4 solution were investigated at an atomic level using in situ surface X-ray scattering (SXS) techniques. It was confirmed that both the Au(111) and Au(100) surfaces were reconstructed with an attached submonolayer of an oxygen species, most probably water, at 0 V (vs Ag/AgCl). Results at +0.95 V supported a previously suggested model for both the Au(111) and the Au(100) electrodes that, based on infrared and scanning tunneling microscopy measurements, the surfaces were a (1 × 1) structure with the coadsorbed sulfate anion and hydronium cation (H 3 O + ). At +1.05 V, where a small amount of an anodic current flowed, adsorption of a monolayer of oxygen species was observed on both surfaces. When the single-crystal gold electrodes were electrochemically oxidized at +1.40 V, the expansion of the gold surface by about one monolayer of Au atoms was observed, suggesting the penetration of oxygen into the surface gold layers (i.e., the formation of two layers of surface oxide). When the surface oxide was reduced at +0.65 V, the surface structure returned back to the structure observed at +0.95 V before the oxide formation (i.e., a (1 × 1) structure with coadsorbed sulfate anion and H 3 O + ). When the potential was reduced to 0 V, the surfaces were reconstructed again but with slightly more random structures than those before the potential cycle.

Step-by-step Investigation of Atomically Flattening Processes of Au(111) Single Crystal Surfaces

“…7(b)]. In addition, the sharp oxidation and reduction peaks, which were as exactly same as one measured at the typical Au(111) electrode, 10 were observed [ Fig. 7(c)], indicating that the (111) atomic arrangement on the most of all area of the Au(111) disk surface was obtained.…”

“…The Au(111) surface was cleaned and flattened by several methods such as i) keeping in concentrated H 2 SO 4 for a night, ii) 10 …”

“…Therefore, the surface should be mechanically polished and used in a meniscus mode for the electrochemical measurements. Single crystals can be commercially available and there are some reports using the commercially available Au(111) single crystal disks as electrodes, [9][10][11][12] or as a substrate for the SAMs during the electrochemical measurements. 13,14 However, there are few detailed reports about the fundamental preparation methods of atomically flat Au(111) single crystal surfaces.…”

Surface X-ray Scattering of Pd(110) and Pd(311) in Electrochemical Environments

“…4). Calculations using density functional theory (DFT) predict the expansion of interlayer spacings due to the adsorbed oxygen on Pd, 36 Au 37 and Ru. 38 The value of d 12 is smaller than that of the bulk on Pt(311) electrode in Ar saturated solution.…”

Self-Assembly Process of Flatly Adsorbed Porphyrin Self-Assembled Monolayer on a Au(111) Surface Studied by ex situ Scanning Tunneling Microscopy and Electrochemical Reductive Desorption Measurements

“…[51][52][53] The roughness factor of the surface was estimated from the charge for the reduction of gold oxide to be less than 1.2. 52 The surface modifications of the Au(111) disk substrates were carried out by immersing the substrates in a benzene solution containing 50 µM (M = mol dm ¹3 ) TMMPP, which is a relatively low concentration, at RT for 1 min-90 h.…”