Innovative Combination of Three Alternating Current Relaxation Techniques: Electrical Charge, Mass, and Color Impedance Spectroscopy. Part II: Prussian Blue ⇆ Everitt's Salt Process

The simultaneous recording, of three impedance functions (electrochemical impedance, color, and mass impedance) allows the role of different species to be distinguished easily during electrochemical processes in conducting and electrochromic films. Herein, this technique has been applied to the study of the Prussian blue films at several potentials between the blue form (Prussian blue) and the colorless form (Everitt's salt). At these potentials, these electrochemical reactions take place by means of exchange of different ions. Thus, the exchange of potassium cations is related to the changes of absorbance at 690 nm, whereas the exchange of protons does not introduce color changes at this wavelength. There is also another site for potassium insertion that does not produce any color change at this wavelength. The analysis of experimental results obtained from this technique has allowed these contributions to be distinguished. Besides, the fitting of the different impedance signals has allowed independent information on the kinetics of electron motion, ion exchange, and color changes to be obtained.