Temperature dependence of impedance spectra of Prussian Blue films deposited on ITO electrodes

The dependence of the charge-transport rates on the redox state of the PB film has been studied. The temperature dependence of the impedance spectra of Prussian Blue firms has been studied at several stabilization potentials between the totally reduced form, Everitt's Salt, and the mixed-valence form, Prussian Blue. An increase in the apparent diffusion coefficient is obtained for films in the blue form, while at intermediate potentials, when the faradaic processes are taking place, the film resistance, evaluated from the impedance spectra, does not vary in an important way. However, at these potentials, a more amorphous him shows a clear increase in the resistance of the film with the temperature. This increase is explained considering an electron-hopping conduction through the film which needs the fixing of positive ions (perhaps hydrogen ions) on the appropriate centres to allow the electron transfer between neighbouring iron sites. (C) 1997 Elsevier Science Ltd.