Electrochemical and Electrogravimetric Investigations of Prussian Blue on the Gold Electrode in the Presence of Tallium(I) Ions

Electrode processes of Prussian Blue (PB), deposited on the gold electrode, have been investigated in potassium and thallium salts solutions, using electrogravimetric and cyclic voltammetric methods. It is shown, that both electrode processes of PB (reduction of PB to Everitt's salt and its oxidation to Berlin Yellow) undergo changes, when potassium ions are replaced by thallium(I) ones. In the presence of thallium, the formation of new redox system is observed, and Tl(I) acts as a counter-ion. The equilibrium constant of the reaction: K(I)PB + Tl(I) = Tl(I)PB + K(I) was estimated to be equal to K = (1.7_0.6)×104. At the same time almost 50% of the PB layer looses its electrochemical activity, whereas the remaining PB phase is electrochemically active. After transfer of the electrode to KNO3 solution, majority of inactivated layer recovers its previous activity. These findings are tentatively interpreted as a result of formation of two phases of PB with Tl(I): electrochemically active and inactive. Both phases are in equilibrium, and thallium ions could be replaced by potassium one. In the case of the Fe(CN) /63 4 electrode process (at more positive potentials), in the presence of Tl(I) irreversible deactivation occurs, since in KNO3 solution, no reactivation of the electrode process is observed.