Electrochemical impedance study of self-assembled layer-by-layer iron–silicotungstate/poly(ethylenimine) modified electrodes

Electrochemical impedance spectroscopy (EIS) has been used to study multilayer films containing anionic iron-substituted silicotungstate [SiW11FeIII(H2O)O39]5− (SiW11Fe) and positively charged poly(ethylenimine) self-assembled by the layer-by-layer method on glassy carbon and indium tin oxide electrodes. The effect of the charge of the outermost layer of the multilayer assembly on the electron transfer of soluble species was studied using the redox probes [Fe(CN)6]3− and [Ru(NH3)6]3+; cyclic voltammetry indicating that the surface charge has a significant effect on the process. EIS demonstrated that the electrostatic attraction or repulsion between the surface and the redox probes plays a significant role. Analysis of the impedance spectra showed that the charge transfer resistance increases with an increasing number of bilayers for both redox probes and that the porosity of the multilayer film, which varies with the electrode substrate, also has a significant effect on the electrochemical response.