Effect of adsorbed layers on the anodic oxidation of simple organic compounds. Part 4.—Ag adsorption on Pt and its effect on HCOOH oxidation

Abstract

The adsorption of Ag on a smooth Pt electrode in 1 M H₂SO₄ at 40°C has been studied from 0.45 to 0.75 V (RHE) in solutions varying from 10^–4 to 10^–6 M. The effect of adsorbed Ag on the oxidation rate of HCOOH has been examined at 0.65 and 0.75 V. A diffusion-limited adsorption process is indicated. Analysis of the oxidation state of the adsorbed layer to θ^Ag_ads= 0.59 yields a value of 0.77 electrons/site. Above this coverage, a value of 1.97 electrons/site is obtained. This suggests, in the former case, a mixed layer composed of Ag singly bonded to a single Pt site with some single bonding to two Pt sites. At the higher coverages, two Ag atoms are apparently attached to a single Pt surface site. The rate of adsorption of Ag⁺ is decreased by the presence of HCOOH. Below θ^Ag_ads∼0.40, the oxidation rate of HCOOH is enhanced compared with that of an electrode partially covered with adsorbed HCOOH intermediates. Above this coverage, the oxidation is inhibited.