Negative coupling during oscillatory pattern formation on a ring electrode

Pattern formation during the oscillatory electrodissolution of Co was studi ed using a Co ring electrode with a small reference electrode at a short di stance in the center of the ring. Traveling pulses as well as source points (one-dimensional target patterns) were observed. These findings could be r eproduced using a reaction-migration equation (RME) the coupling function o f which was derived for the particular geometry from basic potential theory and was found to become negative for increasing distance. During pattern f ormation (i. e., for inhomogeneous potential distribution) the potential dr op across the double layer could actually exceed the external applied volta ge giving direct evidence for negative coupling. (C) 1999 American Institut e of Physics. [S0021-9606(99)02017-6].