The anodic and cathodic behaviour of polycrystalline Pt in sodium hypophosphite solutions has been investigated by cyclic voltammetry. In acid solutions the voltammograms show that, owing to the presence of the reducing agent, electrooxidation of species related to H₃PO₃ occurs in the potential range 0.6 to 1.4 V with respect to NHE. In alkaline solutins the presence of NaH₂PO₂ partially inhibits the HER and displaces the formation of the oxygen monolayer on platinum to higher potentials. The voltammetric peaks are attributed to the electrooxidation of the products resulting from the chemical decomposition of NaH₂PO₂ in contact with the Pt surface.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas