Structure sensitivity of CO oxidation on gold single crystal surfaces in alkaline solution: Surface X-ray scattering and rotating disk measurements

A combination of in situ surface X-ray scattering (SXS) and cyclic voltammetry (CV) measurements have been performed to determine the effect that the surface atomic structure of the low-index faces of Au single crystals has on carbon monoxide (CO) oxidation in alkaline solution. For the (1 1 1), (1 0 0) and (1 1 0) surface orientations, potentiodynamic measurements of the scattered X-ray intensity at key reciprocal lattice points have been employed to determine the potential window of stability for the reconstructed surfaces. By saturation of the electrolyte with CO, the effect that adsorbed CO has on the stability of the reconstructed surfaces has been investigated. The presence of CO acts to stabilize the surface reconstructions over a wider potential range, causing a positive shift in the potential for the lifting of the Au(1 1 1) surface reconstruction of ∼200 mV. In the case of the (1 0 0) and (1 1 0) orientations, the adsorption of CO stabilizes the reconstruction over the entire potential range studied. The oxidation of dissolved CO was found to be structure-sensitive, with the activity decreasing in the order Au(1 1 0)-(1 × 2) > Au(1 0 0)-“hex” > Au(1 1 1)-(23 × √3). The structure-sensitivity is correlated with the surface density of low coordinated sites.