Spatio-temporal pattern formation during the reduction of peroxodisulfate in the bistable and oscillatory regime: A surface plasmon microscopy study

Using surface plasmon microscopy we demonstrate that oscillations as well as transitions in the bistable regime during the reduction of S₂O^2-₈ at Ag electrodes are accompanied by wave phenomena. Typical velocities of the waves range from some centimeters per second to meters per second, depending on the conductivity of the electrolyte. The characteristic length of the patterns is determined by the temporal dynamics of the potential drop across the double layer at high mass transport and by the dynamics of the concentration of S₂O^2-₈ at the electrode at low mass transport. The first gives rise to potential fronts with front widths between 0.1 and 0.5 mm; the second leads to smooth structures on the order of centimeters. Further, the influence of the electrode boundary on the pattern formation in electrochemical systems is discussed, as well as the generality of the above-mentioned characteristic times and lengths.