The Adsorption of Sulfate on Gold(111) in Acidic Aqueous Media: Adlayer Structural Inferences from Infrared Spectroscopy and Scanning Tunneling Microscopy
Abstract
The potential-dependent adsorption of sulfate on ordered Au(111) from acidic aqueous electrolytes has been examined in-situ by means of infrared reflection-absorption spectroscopy (IRAS) and by atomic-resolution scanning microscopy (STM) in order to explore further the nature of the adsorbate bonding and the structural changes attending the formation of the ordered adlayer at high potentials, as observed recently by using STM (ref. 8). Solution conditions that encompassed aqueous sulfuric acid, sulfuric acid/sulfate electrolytes of varying pH, and dilute sulfate in excess perchloric acid were selected in order to facilitate comparisons with recent adsorbate compositional data extracted from chronocoulometric and radiotracer measurements which utilized the last type of electrolyte (ref. 9). Essentially the same ordered adlayer structures were deduced by STM to form at suitably high potentials (> 0.8 V vs. SCE) in both sulfuric acid and the mixed sulfate/excess perchloric acid media. The adlayer, which exhibits a (sq. rt.3 x sq. rt.7) symmetry, involves a fractional sulfate coverage of 0.2, in accordance with chronocoulometic and radiotracer data (ref. 9). The possibility that the ordered sulfate adlayer incorporates coadsorbed hydronium cations is discussed; such coadsorption is suggested by the presence of additional tunneling maxima in the STM images. The IRAS data display a prominent S-0 stretching band (,vso) at 1155-1220 cm-l, the potential-dependent intensity of which correlates with the sulfate surface concentrations reported in ref. 9. The appearance of this vso feature is also insensitive to the electrolyte conditions, including pH, consistent with its assignment to adsorbed sulfate, rather than to bisulfate.
Document Details
- Document Type
- Technical Report
- Publication Date
- Feb 01, 1994
- Accession Number
- ADA276643
Entities
People
- Gregory J. Edens
- Michael J. Weaver
- Xiaoping Gao
Organizations
- Purdue University