Potential-Step Chronocoulometric Investigation of the Surface Coverages of Coadsorbed Bi and Hydroxide on Au(111) Electrodes

Bi underpotentially deposited on Au(111) has been studied using potential-step chronocoulometry to determine the actual surface coverage of Bi. In the potential region where this system exhibits catalytic activity for the electroreduction of peroxide to water, the observed coverage is 0.25 monolayer (ML), which agrees well with the coverage of the reported (2 × 2) Bi overlayer observed by scanning probe microscopy in this region. At more cathodic potentials, the coverage increases to 0.67 ML. This coverage agrees with that expected based on the ( p × √3) structure proposed from scanning tunneling microscopy, atomic force microscopy, and SXS measurements in this region. The electrosorption valency calculated based on these coverages is 3, indicating that the Bi is fully discharged on the surface. Potential-step chronocoulometry has been used at various pH values to determine the surface coverage of hydroxide anion in the presence of underpotentially deposited (upd) Bi. The coverage is negligible in the absence of upd Bi and at potentials where the Bi adlayer condenses. It rises to a peak of 0.17 ML in the region where the coverage is 0.25 ML, indicating that OH - is coadsorbed with the Bi.