ELECTROCHEMICAL DEPOSITION OF PRUSSIAN BLUE FROM A SINGLE FERRICYANIDE SOLUTION

A method of reparation of prussian blue (PB) from a single ferricyanid e solution and the mechanism of its formation are discussed: In a weak acidic medium (pH 3.6) of KH2PO4 (0.1 M)-HCl, a thin film of PB is de posited on a gold electrode surface by using cyclic voltammetry betwee n -0.2 and + 0.6 V. It is confirmed that the coincident effect of the solution acidity on the PB preparation is exhibited by using either ca thodical polarization or cyclic voltammetry. The UV-vis absorption spe ctra from the various acidic solutions indicate that the absorption cu rve of pH at 3.6 is different from those of other pH values. Under the same conditions, PB cannot be deposited on a gold electrode surface f rom the ferrocyanide solution by using cyclic voltammetry and cathodic al polarization. in addition, a kind of blue precipitate is gradually produced in the ferricyanide solution during standing after one day, a nd this is verified to be PB by the two pairs of its characteristic re dox peaks at about +0.2 and +0.8 V vs. Ag/AgCl, which are obtained by immobilizing the blue precipitate mechanically on a gold electrode sur face and recording the cyclic voltammogram while no similar precipitat e occurs in the ferrocyanide solution during its standing course. Furt hermore the Fe2+ cannot be oxidized to Fe3+ on a gold electrode even w hen the positive potential reaches to +1.0 V, while Fe3+ can be easily reduced to Fe2+ at -0.2 V. It is concluded that the PB formation from the ferricyanide solution lies in the dissociation of ferricyanide io ns.