THE INFLUENCE OF WATER ON THE OXIDATION OF PROPYLENE CARBONATE ON PLATINUM - AN ELECTROCHEMICAL, INSITU FT-IR AND ONLINE MS STUDY

Electro-oxidation of 0.5 M LiClO4/propylene carbonate (PC) electrolyte containing less-than-or-equal-to 0.006 M, 0.056 M and 0.56 M H2O was investigated on platinum applying cyclic voltammetry, in situ FT-ir and on-line mass spectroscopy measurements. Using these techniques we show that the bulk oxidation of PC in the presence of trace water begins at 4.0 V vs Li/Li+. The potential dependence of the oxidation rate is investigated by monitoring the CO2 signals (mass intensity at m/e = 44 and ir absorption at wavenumber k = 2342 cm-1) parallel to the anodic current. An increased water content in the electrolyte results in both an increased oxidation current density and an enhanced CO2 formation rate. Evidence was found for a film formation on the electrode at 2.0 V and for a further oxidation of this film at 2.6 V. The nature of this film is discussed.