Bistable/oscillatory system based on the electroreduction of thiocyanate complexes of nickel(II) at a streaming mercury electrode. Experiment and simulation

Oscillatory electroreduction of the thiocyanate complexes of nickel(II) at stationary mercury electrodes is complicated by the formation and accumulation of the heterogeneous Ni amalgam and a surface active NiS adsorbate. Consequently, dynamic instabilities observed at such electrodes always have a transient character. To overcome these difficulties, following our previous studies of the Ni(II)-SCN- oscillator, we describe the new experimental approach, based on the application of the streaming mercury electrode to the studies of nonlinear dynamic instabilities of this system. A special experimental setup was assembled. We found that in the presence of an appropriate serial ohmic resistance in the electric circuit. not only the sustained oscillations, but also the bistable behavior in the current-voltage characteristics occurred, which was not reported for this process so far. The experimental diagram of regions or the bistability, monostability and oscillations in the U-R-s parameter space is constructed. For the explanation of the bistability, the numerical models were elaborated which quantitatively confirmed the observed phenomena as originating from the coupling of the negative differential polarization resistance with ohmic potential drops.