Current oscillations in the reduction or oxidation of some anions involving convection mass transfer

We have discovered a new kind of current oscillation during the reduction or oxidation of some anions, which appeared over the limiting reduction or oxidation current of the anions and was loaded on the current of hydrogen or oxygen evolution. The overlap of a positive feedback (convection mass transfer of the anions induced by hydrogen or oxygen evolution, and the increase of the potential difference in the cell when the current is smaller) and a negative feedback (depletion of the surface concentration of the anions by reduction or oxidation, and the decrease of the potential difference in the cell when the current is larger) between the bistable states accounts for the oscillations, and a 'hidden' negative impedance in the second ascending branch of the polarization curve was observed for the first time. Our model has also shed some light on the other systems reported in the literature, in which convection mass transfer also plays an important role in the current oscillations. In addition, the potential oscillations during the oxidation of Fe(CN)(6)(4-) are reported here for the first time, and are similar to the potential oscillations during the reduction of Fe(CN)(6)(3-) reported in our previous paper [Z. Li, J. Cai, S. Zhou, J. Electroanal. Chem., in press]. (C) 1997 Elsevier Science S.A.