Potential oscillations during the reduction of Fe(CN)(6)(3-) ions with convection feedback

Potential oscillations, which were observed during Fe(CN)(6)(3-) reduction under galvanostatic conditions in 1 mol dm(-3) NaOH solution on a platinum electrode, are described. The bifurcation boundaries were measured in the parameter plane of applied current vs. Fe(CN)(6)(3-) concentration. A broad limiting current plateau (zero slope) occurring in the current-potential curve in combination with a negative real impedance is a typical characteristic for this kind of oscillation, and the oscillation amplitudes are within that region. The bistability, i.e., Fe(CN)(6)(3-) reduction and hydrogen evolution at different potentials, coupled with convection feedback induced by hydrogen evolution, accounts for the oscillations. The sequence of chaotic-quasiperiodic-periodic-quasiperiodic oscillations, which appeared when the applied current was increased monotonously, was characterized by time series, power spectra, phase portraits and one-dimensional maps. (C) 1997 Elsevier Science S.A.