Study of growth and the electrochemical behavior of Prussian blue films using electrochemical quartz crystal microbalance

Using cyclic voltammetry sind chronoamperometry combined with electrochemical quartz crystal microbalance, the deposition of Prussian blue (PB) on a gold electrode from solutions containing Fe3+ and Fe(CN)(0)(3-) ions was studied. The change of mass in cyclic voltammetry experiments in the first cycles points to fast deposition of PB. In longer cycling the exit and entrance of cations (K+, NH4+) is observed in the anodic and cathodic run, respectively. In potentiostatic deposition four types of behaviors of the mass (and charge) change in time as, functions of potential were found. The results point to the electrodeposition of a mixture of the "insoluble" and "soluble" form of PB in the range 0.55-0.25 V. Energy-dispersive X-ray (EDX) analysis indicates that at 0.35 V both soluble and insoluble PB is formed. Prolonged cycling of such electrodes in KCl solutions does not change the K:Fe ratio. At 0.10 V K2Fe[Fe(CN)(6)] is obtained. The solubility products of KFe[Fe(CN)(6)] and Fe-4[Fe(CN)(6)](3) were estimated based on the potentiostatic deposition experiments. The process of the dissolution of the PB deposits under potentiostatic conditions at positive potentials was also studied and the rate of dissolution was calculated. When the PB layers on the electrode are very thin, the change of mass shows that, as a net result, nonhydrated potassium ions exit or enter the layer in the redox reactions. Similar behavior is observed far ammonium ions. Smaller values of apparent molar mass are found when thicker PB layers are used. (C) 1999 The Electrochemical Society, S0013-4651(98)03-108-5. All rights reserved.