Effects of hydration on the resistances and electrochemical responses of Nafion(R) coatings on electrodes

Procedures are described for coating electrodes with films of Nafion(R) that are saturated with Os(bpy)(3)(2+) and exist in one of two limiting states: fully hydrated or dehydrated. The anodic electrochemical responses from Os(bpy)(3)(2+)-saturated, dehydrated coatings include unusual spiked features that are the result of the initially high ionic resistance of such coatings. Electro-oxidation of such coatings leads to immediate decreases in resistance as one-third of the Os(bpy)(3)(2+) counterions are ejected and large quantities of H2O molecules are incorporated by the coatings. On the basis of quartz crystal microgravimetric, a.c. impedance, and voltammetric measurements, a model is proposed for the internal structures of Nafion(R) coatings which accounts for their observed behavior.