UNIDIRECTIONAL CURRENT FLOW OF REVERSIBLE REDOX COUPLES ON A MOO3 FILM-MODIFIED MICROELECTRODE

In this paper, we have investigated the reactivity of the molybdenum o xide film toward some standard redox systems (e.g., ferrocene (Fc) and its derivatives) and observed a few interesting phenomena. The result s demonstrate that the electrochemical behaviour of Fc and its derivat ives at the oxide-modified carbon fiber (CF) microelectrode differs fr om that at a bare CF microelectrode, The conductivity of the molybdenu m oxide film is seriously affected by the range and the direction of t he potential scan, which influences the electrochemical behaviour of t hese redox systems at the film electrode. If the cycling potential is more positive than the reduction potential of the molybdenum oxide fil m, the reduction and oxidation peak currents of Fc and its derivatives could not be observed. The result indicates that the molybdenum oxide film on a microelectrode surface cannot transfer electrons between th e surface of the electrode and Fc or its derivatives due to the existe nce of a high resistance between the interface in these potential rang es. On the other hand, if the lower limit of the scan potential was ex tended to a potential more negative than the reduction peak potential of the film, the oxidation peak of Fc or its derivatives appeared at a bout the potential relative to E-0 of Fc or its derivatives on the bar e electrode, and the peak current is proportional to the concentration of these couples in the electrolyte. To our surprise, the peak height on the modified electrode is much larger than that on the bare CF mic roelectrode under the same conditions in the range of low concentratio n of these couples, and the oxidation peak potential of these couples is more negative than that on the bare CF microelectrode. On the basis of the experimental observation, we propose that these redox couples may undergo an interaction with the reduction state of the molybdenum oxide film. The new phenomena that we observed have been explained by using this interaction. (C) 1997 Elsevier Science S.A.