Electrochemical formation of ternary oxide films - an EQCM approach to galvanostatic deposition of alkali earth metal tungstates and molybdates

Galvanostatic deposition of barium and strontium tungstates and molybdates on tungsten and molybdenum electrodes in alkaline media (pH≅12) was studied by means of Electrochemical Quartz Crystal Microbalance (EQCM). Formation of surface ternary oxide layers proceeds via dissolution and precipitation mechanism when the initial electrochemical formation of tungsten/molybdenum oxides is followed by the oxide dissolution and tungstate/molybdate precipitation. Mass change signals were used to comprehend different regimes of the tungstate/molybdate deposition with respect to deposition efficiency. While the formation of molybdates is restricted by dissolution process, the tungstates formation is limited by transport of film forming cations to the electrode.