Oscillatory behavior has been observed for almost all electrochemical reactions in a certain, although sometimes small, range of external parameters. Only in the past ten years has it been possible, however, to find a common explanation for the occurrence of these temporal self-organization phenomena of chemically completely different electrochemical reactions. The breakthrough was achieved because new methods and concepts, which had been developed in nonlinear dynamics to describe the spontaneous formation of order in various disciplines, could be applied. This development in turn was only possible because the underlying laws are universal at a certain abstract level. Oscillations are only one possible manifestation of nonlinear behavior. Examples of other features that are often closely associated with temporal instabilities are spatial structures and waves. Initiated by the theoretical progress and the development of new experimental techniques, spatial pattern formation in electrochemical systems has been targeted for investigations in the past few years. Based on these investigations, it can be predicted under which conditions temporal or spatial pattern formation can be expected. Furthermore, the possibility of predicting the occurrence of instabilities indicates that it might be feasible to exploit nonlinear effects to increase, for example, the yield of electrocatalytic reactions. Here we discuss physicochemical mechanisms that lead to pattern formation in electrochemical systems. At the same time, we stress the generic principles that are responsible for self-structuring processes in many chemical and biological systems.

The potential distribution in front of a Ag ring electrode during the reduction of peroxodisulfate was measured with potential microprobes. Inhomogeneous stationary potential distributions were observed when using a Haber-Luggin capillary, i.e., placing the reference electrode close to the working electrode on the axis of the ring. It is shown that such an arrangement introduces a negative global coupling into the system which destabilizes homogeneous stationary states if the current-potential characteristics exhibits a negative differential resistance. Further consequences of the negative global coupling are discussed, and the effect of an additional, external series resistor is demonstrated.

Oscillatory behavior has been observed for almost all electrochemical reactions in a certain, although sometimes small, range of external parameters. Only in the past ten years has it been possible, however, to find a common explanation for the occurrence of these temporal self‐organization phenomena of chemically completely different electrochemical reactions. The breakthrough was achieved because new methods and concepts, which had been developed in nonlinear dynamics to describe the spontaneous formation of order in various disciplines, could be applied. This development in turn was only possible because the underlying laws are universal at a certain abstract level. Oscillations are only one possible manifestation of nonlinear behavior. Examples of other features that are often closely associated with temporal instabilities are spatial structures and waves. Initiated by the theoretical progress and the development of new experimental techniques, spatial pattern formation in electrochemical systems has been targeted for investigations in the past few years. Based on these investigations, it can be predicted under which conditions temporal or spatial pattern formation can be expected. Furthermore, the possibility of predicting the occurrence of instabilities indicates that it might be feasible to exploit nonlinear effects to increase, for example, the yield of electrocatalytic reactions. Here we discuss physicochemical mechanisms that lead to pattern formation in electrochemical systems. At the same time, we stress the generic principles that are responsible for self‐structuring processes in many chemical and biological systems.

No abstract

We studied the local potential distribution in front of a rotating Pt ring-electrode during hydrogen oxidation in sulfuric acid for three different positions of the reference electrode. The potential distribution was measured with a potential micro-probe. The experiments were carried out in the bistable region of the system. For large and medium distances between the reference (RE) and the working electrode (WE), transitions between the two homogeneous states occurred through nucleation and growth of the globally stable state from the initially metastable one. The transition time was considerably longer for the intermediate distance between the RE and the WE. For the closest distance used, stationary patterns formed, consisting of two domains with high and low current densities, respectively. The difference in the double layer potential of the two domains amounted to more than 1 V. The low-current density domain was covered with Pt-O whereas in the high current density domain the electrode surface consisted of 'bare' Pt. The existence of these stationary non-equilibrium structures as well as the difference of the front behaviour for the other two electrode arrangements can be traced back to the existence of a negative global coupling for intermediate and close distances between the WE and the RE