Effect of pH, Fluorination, and Number of Layers on the Inhibition ofElectrochemical Reactions by Grafted, Hyperbranched Poly(acrylic acid) Films

摘要

We report the electrode-passivation properties of both fluorinated and unmodifiedhyperbranched poly(acrylic acid) (PAA) films as a function of pH and the number of PAA layers. Both cyclic voltammetry and ac-impedance spectroscopy show that the extent of blocking increases with the number of layers regardless of the solution pH. However, passivation resulting from unfluorinated PAA films decreases with increasing pH while passivation due to fluorinated films increases with increasing pH. Three-layer fluorinated films can increase the charge transfer resistance of the electrode by up to a factor of 6 X 10(exp 4). Although Randles equivalent circuit can be used to model the electrochemistry of electrodes covered with unfluorinated PAA, fluorinated PAA-coated electrodes often require additional circuit elements due to the high resistance of these hydrophobic films.