Spatial bifurcations in the generic N-NDR electrochemical oscillator with negative global coupling: Theory and surface plasmon experiments

Pattern formation during the oscillatory reduction of IO ₄ ^- at a rectangular gold film electrode was investigated by means of surface plasmon microscopy. Several one-dimensional spatial symmetry breakings were observed when a negative global coupling (NGC) was imposed by partially compensating the electrolyte resistance, using a negative impedance device. Respective theoretical investigations of the prototype electrochemical oscillator with an N-shaped current-potential characteristic (N-NDR), corresponding to the IO ₄ ^- reduction, are presented. A complete picture of the spatial bifurcations reproducing the symmetry breakings at a fixed NGC strength is given. The agreement between experiment and model is further emphasized by numerical simulations that revealed a state with double broken symmetry, which we termed asymmetric standing wave. Furthermore, the theoretical studies allow for identification of patterns that arise, owing to a complex interplay of the nonlinear kinetics and unavoidable nonuniformities in the experimental setup. Due to the general nature of the oscillator studied, the observed effects are expected to be representative for N-NDR oscillators under NGC.