Ring-disk study of thin mercury films on platinum

The interactions of Pt and Hg have been studied using a Pt ring-disk electrode. Depending upon the amount of mercury plated different surface species were found. The surface species Pt₂Hg and Pt-Hg exist for less than one monolayer coverage. PtHg₂ is formed on the electrode surface as the second monolayer of mercury is deposited. At least one other Pt-Hg species forms and penetrates beneath the Pt-solution interface as the next few monolayers of mercury are deposited. Bulk mercury exists in comparable amounts to that of subsurface Hg only after about 50 monolayers of Hg have been deposited on Pt. This bulk mercury is converted to the subsurface compound at a finite rate. The oxidation of the surface and subsurface Pt-Hg compounds produces Hg(II), while the oxidation of bulk Hg forms mainly Hg(I). The deposition and oxidation of thick films of mercury from Pt results in the platinization of the electrode surface, with a well-adhering film of Pt black.