Spectroelectrochemistry of new prussian blue films prepared by a cast method

New Prussian Blue (PB) films were prepared by being cast from colloidal PB dispersions in an organic solvent containing cationic surfactants. The electrochromic behaviors of the cast PB films are similar to those of electrodeposited PB films. However, the cyclic voltammetries of both the PB films were quite different from each other. To make the difference clear, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and X-ray photospectroscopy (XPS) were used in measurements of these films grown on Pt and indium tin oxide electrodes. The EDX results for fresh PB films indicated that cast films contain K⁺ ions, suggesting a soluble-form PB, KFe[Fe(CN)₆], while electrodeposited films do not, suggesting an insoluble-form PB, Fe₄[Fe(CN)₆]₃. The transient spectral observations indicated the participation of a unique electrochemically active iron(III) site in the reductive cycles of a cast film, although the participation of a plural electrochemically active iron(III) sites was proposed for an electrodeposited film. After a repeated cyclic scan a cast PB film maintained its unique active site, while an electrodeposited film had plural sites comprising both a soluble and an insoluble form of PB.