ON THE ADSORPTION OF H2PO4- AND H3PO4 ON PLATINUM - AN INSITU FT-IR STUDY

The adsorption of H2PO4- and H3PO4 on platinum is studied in the presence of a fluoride supporting-electrolyte at different pH. At potentials below 900 mV the H2PO4- ion is doubly coordinated to the surface, presenting a C2v symmetry. The adsorption geometry changes in the oxide region to a single coordinated form with a C(s) symmetry. At low potentials the undissociated phosphoric acid is coordinated to the platinum surface through one oxygen atom presenting a C3v symmetry and dissociates to HPO4(2)- at positive potentials. The onset of dissociation depends on the pH. The potential dependence of the observed bands is discussed in terms of the band assignment.