VOLTAMMETRY WITH POLY(ETHYLENE OXIDE)-COATED MICROELECTRODES IN CARBON-DIOXIDE

Voltammograms of ferrocene in CO2 were obtained with a microelectrode coated with a film of poly(ethylene oxide) containing LiCF3SO3 (PEO:Li ). In CO2 modified with water or acetonitrile the voltammograms exhibi ted high conductivity due to the plasticization of the film by the pol ar modifiers. Ferrocene voltammograms could also be obtained in unmodi fied CO2, albeit with severe ohmic distortion. Characterization by DSC and SEM of PEO:Li after treatment in CO2 revealed that the amorphous domains of the film become swollen, and hence plasticized, to a suffic ient extent to exhibit some conductivity in unmodified CO2. The conduc tivity of films containing the redox complex Ru(bpy)3(PF6)2 was signif icantly improved in unmodified CO2. This bulky redox complex improved the conductivity of the film by decreasing the T(m) of the polymer, as shown with DSC. Voltammograms of ferrocene in unmodified CO2 obtained with PEO:Li films containing the redox complex also exhibited minimal ohmic distortion. These results show that by appropriate manipulation of the composition and properties of the films, voltammetry can be pe rformed in a broad variety of CO2-based fluids, including unmodified C O2.