Accelerating fronts during the electrodissolution of cobalt

Theory of electrochemical pattern formation

The spatial coupling in electrochemical systems is mediated by ion migration under the influence of the electric field. Since field effects spread very rapidly, every point of an electrode can communicate with every other one practically instantaneously through migration coupling. Based on mathematical potential theory we present the derivation of a generally applicable reaction-migration equation, which describes the coupling via an integral over the whole electrode area. The corresponding coupling function depends only on the geometry of the electrode setup and has been computed for commonly used electrode shapes (such as ring, disk, ribbon or rectangle). The pattern formation observed in electrochemical systems in the bistable, excitable and oscillatory regime can be reproduced in computer simulations, and the types of patterns occurring under different geometries can be rationalized. (c) 2002 American Institute of Physics.

Evolution of spatiotemporal patterns during the electrodissolution of metals: Experiments and simulations

Spatiotemporal patterns including accelerating fronts, rotating waves, and homogeneous oscillations evolve during the electrodissolution of metals like cobalt and iron that exhibit passivity under potentiostatic control. The nature of the patterns is determined by long-range (nonlocal) coupling through the electric field which in turn is influenced by the geometry of the electrochemical cell, the applied potential, and the conductivity of the electrolyte. A two-variable model in a three-dimensional geometry is presented which is able to simulate the essential features of the experimental system.(c) 2002 American Institute of Physics.

Spatiotemporal Patterns on a Disk Electrode: Effects of Cell Geometry and Electrolyte Properties

Spatiotemporal patterns on a disk electrode are simulated with a model for the electrodissolution of a metal that exhibits passivity; a 3-dimensional geometry with a point reference electrode is used. The two variables of the model are the potential drop across the electric double layer and the proton concentration near the surface of the working electrode. Non-local coupling among reaction sites is through the electric field. Several patterns seen previously in experiments are reproduced in the simulations and the dependence of transitions among them on system geometry, electrolyte conductivity and double layer capacitance are explored. For example, a state with an inhomogeneous oscillation is changed to one with a rotating wave as the reference electrode is moved closer to the working electrode and negative coupling develops; under other conditions the negative coupling produces anti-phase oscillations.