Experimental and Model Spatiotemporal and Spatial Patterns in Electrochemical Systems
Simple examples of pattern formation in electrochemistry, including progress of active zone along the passivated iron wire, mimicking the conduction of the impulse along the neuron, and spiral waves of codeposited Ag–Sb alloy are invoked as the introducti
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Experimental and Model Spatiotemporal and Spatial Patterns in Electrochemical Systems
2.1
Simple Examples of Dissipative Pattern Formation
In Chaps. 4–6 of volume I, we analyzed the experimental manifestations and the relevant models of temporal dynamic instabilities, i.e., oscillations and multistability characterized by the total (average) current or the potential of the working electrode. In the present chapter, we describe the spatiotemporal and spatial patterns that develop due to nonlocal and global couplings, according to theoretical background outlined in Sect. 1.2. This means, among others, that in the formation of such patterns the inhomogeneous distribution of the electric field at the interface, causing migration currents flowing parallel to the electrode surface, will be taken into account. Also, the role of diffusion in generating a particular type of patterns will be described. Concerning another type of transport, the convection can also be a source of spatial self-organization in electrochemical systems due to its possible self-organized nature under appropriate conditions. However, the patterns of convective origin will be described separately in Chap. 5, as the mechanism of their formation is different from those operating in the case of diffusion–migration systems. Thus, for the purposes of the present chapter we shall assume that the convection does not exist or at least does not play any significant role in the pattern formation discussed. As indicated in Sect. 1.2, the substantial progress in understanding the mechanisms of the formation of such nonconvective dissipative patterns took place only in recent decades, when this challenging task was undertaken by the Berlin group, gathered around Ertl, Krischer, and coworkers in the Fritz-Haber Institute of Max-Planck Society. The success of these investigations was possible not only because of the development of appropriate theory, but also due to employing the modern techniques of analysis of the state of surfaces, as the surface plasmon spectroscopy [1]. Before description of recent achievements in this area, let us mention and comment selected historical examples of spatiotemporal patterns in electrode processes. In 1948, Bonhoeffer has published the paper [2]: “Activation of passive iron as a model for the excitation of nerve.” The title referred to the experimental fact that if a piece of passivated iron immersed in concentrated nitric acid is touched M. Orlik, Self-Organization in Electrochemical Systems II, Monographs in Electrochemistry, DOI 10.1007/978-3-642-27627-9_2, # Springer-Verlag Berlin Heidelberg 2012
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2 Experimental and Model Spatiotemporal and Spatial Patterns
momentarily with a zinc rod, the iron may become active and the zone of activation will spread over the whole piece of iron. The final state of iron, i.e., active or passive, depends on the concentration of nitric acid (repassivation occurs for intermediate concentrations). In a more sophisticated version of this experiment, when the iron wire was used, and f
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