Masayuki Itagaki, Tatsuo Suzuki and Kunihiro Watanabe
Department of Industrial Chemistry, Faculty of Science and Technology, Science University of Tokyo, Chiba
The kinetics of transpassive dissolution of the Mo electrode has been investigated using electrochemical impedance spectroscopy (EIS). Nyquist plots of impedance responses conrresponding to transpassive dissolution of Mo in aqueous alkaline solutions (pH10~12) show a capacitive loop at -0.4V~-0.1V vs. SSE and an apparent Warburg impedance above 0 V. A theoretical model is proposed that takes into account the electrochemical reaction at the metal/electrolyte interface and the diffusion of dissolved Mo (VI) ions. The comparison of the theoretical electrochemical impedance with experimental data leads to the conclusion that not only electroshemical reaction at the interface but also diffusion process of dissolved species determine the total reaction rate above 0 V. The surface concentration of Mo (VI) ions calculated by the present theoretical model is more than 102 mol/m3, when the diffusion process influences the electrochemical impedance responses and polarization curves.
(Received December 19, 1994)
molybdenum, alkaline solutions, transpassive dissolution, electrochemical impedance spectroscopy, Warburg impedance
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