Global coupling effects on spatiotemporal patterns on a ring electrode

Experimental results on spatiotemporal pattern formation on a ring electrod e during the oscillatory electrodissolution of cobalt in 1.0 M phosphoric a cid are reported; the ring is the area between two non-concentric circles a nd its width thus varies continuously with angle. The experiments were cont rolled potentiostatically with the tip of the capillary of the reference el ectrode placed in the center of the ring 1 mm above the surface. Under thes e conditions rotating waves, with and without modulation, occur. The influe nce of positive global coupling (in the form of an external resistor of var iable size in series with the working electrode) on the pattern formation i s investigated. A small added global coupling smoothes variations in speed and size of a rotating active area which are caused by the deformation of t he ring and surface heterogeneities. A larger global coupling leads to non- traveling patterns including complete synchronization of the ring and also synchronization within subsections or smaller areas of the ring; these subs ections themselves oscillate in a phase-locked or quasiperiodic fashion. (C ) 1999 Elsevier Science Ltd. All rights reserved.