AN FTIR STUDY OF ADSORBED SULFATE SPECIES ON POLYCRYSTALLINE PLATINUM WITH APPLICATION OF GROUP-THEORY TO THE PROBLEM OF BAND ASSIGNMENT FOR ADSORBED SPECIES

The adsorption of sulfate and bisulfate ions on polycrystalline platinum electrodes in the pH range between 0.2 and 3 is studied using a fluoride supporting electrolyte. The spectra exhibit band splitting for degenerate modes which are interpreted as being caused by the adsorption. Group theory and the surface selection rule are used to assign the observed modes and to establish the coordination of the ions to the metal surface. Adsorbed sulfate and bisulfate are found to be doubly and triply coordinated respectively. The acid-base properties at the surface are affected by the applied electric field, as indicated by the surface [HSO4-]/[SO42-] ratio. The potential dependence of the band position is analyzed for the two strongest modes of both ions.