Chemisorption and Electrochemical Activity of Thiophenols at Well-Defined Pd(111) Surfaces: Studies by LEED, AES, HREELS, and Electrochemistry

Abstract

The chemisorption and electrochemical activity of 2,5-dihydroxythiophenol (DHT) and 2-(8mercaptooctyl)-1,4-benzenediol (DHOT) on well-defined Pd(111) surfaces were studied by Auger electron spectroscopy (AES), low energy electron diffraction (LEED), high resolution electron energyloss spectroscopy (HREELS), and electrochemistry (EC). Results confirm that DHT is chemisorbed in two discrete orientations such that at low concentrations, DHT is oxidatively bound to the surface through the diphenol and mercapto groups as quinonoid and S moieties, respectively, whereas at high concentrations, the molecule is coordinated oxidatively through the-SH group in a vertical S-η 1 orientation. When DHT is chemisorbed in a vertical orientation, the diphenol group is pendant and thus exhibits reversible quinone/diphenol redox activity. However, when the compound acts as a bidentate ligand (at low concentrations), the ring loses its redox activity. Iodine was then found to displace the coordinated quinone ring causing it to regain its electrochemical activity. Electrochemical results also show that by comparing the redox behavior of chemisorbed DHT and DHOT, interactions between DHT molecules on the Pd(111) surface are indeed found to be mediated by the surface.

Density Functional Theory and Experimental Surface Science as Complementary Methods for Interfacial-Structure Elucidation and CO2-Reduction Studies

“…As an example, the surface geometry, configuration and position of quinone-based, aromatic and simple molecules such as hydroquinone [1], hydroquinone sulfonate [2,3], benzene [4], 2,3-dimethylhydroquinone [5], sulfuric acid [6] and atomic hydrogen [7] adsorbed on bulk Pd and Pd thin-film surfaces have successfully been identified utilizing this technique. This scheme is extremely essential especially in ascertaining structure-composition-function relationships of surface-modified materials and in establishing methods for surface-structure elucidation for surface-reaction mechanistic studies.…”