Standing and propagating wave oscillations in the anodic dissolution of nickle

Spontaneous pattern formation in reactive media has been thoroughly investigated in homogeneous oscillatory systems, mainly in the Belousov-Zhabotinsky reaction¹. Spatiotemporal patterns have been observed in some studies of catalytic surfaces^2,3 and of travelling electrochemical waves⁴. Here we report on oscilla-tory wave patterns observed during electrochemical dissolution of a nickel wire in acidic media. We show that space-averaged poten-tial or current oscillations are associated with the creation of an inhomogeneous current distribution, and that the selection of a specific spatial current pattern depends on the current control mode of the electrochemical cell. In the almost potentiostatic (fixed potential) mode of operation, a train of travelling pulses prevails, whereas antiphase oscillations occur in the galvanostatic (constant average current) mode. The latter, as far as we know, have never before been reported in any reactive system.