Abstract: The mechanism of electrochemical oxidation of hypophosphite on a polycrystalline platinum electrode was studied by SNIFTIRS (i.e. Subtractively Normalized Interfacial FTIR Spectroscopy) as well as by cyclic voltammetry.The in-situ IR reflectance spectra were analyzed as a function of the Pt electrode potentials in 0.5 mol/L H₂SO₄+0.1 mol/L NaH₂PO₂solution.The in-situ IRband characteristics are those near 2100, 1250 and 1110cm^-1, assigned as the presence of adsorbed hydrogen atom on Pt and non-adsorbed H₃PO₄molecule or phosphate species, respectively.It was concluded that both hydrogen atoms and H₂PO₂are the adsorbed species on Pt in the potential range where the oxidation occurs, and the final oxidation product was H₃PO₄rather than phosphate, different from the oxidation of hypophosphite on Ni electrode.Accordingly, a new mechanism was proposed for the hypophosphite oxidation on Pt electrodes in acidic media, i.e. in the potential range lower than 0.8 V(vs.SCE) the adsorbed H₂PO₂was directly oxidized to phosphate via phosphite, and in the potential range higher than 0.8 V the oxygen-adsorbed species on Pt participates in the oxidation of H₂PO₂into phosphate.

Key words: Hypophosphite, Electrooxidation, Chemical plating, Platinum electrode, SNIFTIRS