An experimental investigation of periodic and chaotic electrochemical oscillations in the anodic dissolution of copper in phosphoric acid

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Abstract
The response of the current to an applied potential was monitored in an open electrochemical system consisting of a rotating copper disk as the working electrode, a calomel reference electrode, and a platinum counter electrode, all of which were in contact with a solution of 85% phosphoric acid. In addition to stable stationary states, the applied potential induced oscillatory states which were either periodic or chaotic. Transitions from a stationary state to sustained oscillations were found to take place either through a Hopf bifurcation or by way of a mechanism that gives rise to states possessing complex combinations of small and large amplitude oscillations (mixed‐mode oscillations). Within the parameter ranges for which sustained oscillations occurred, we discovered sequences of period doubling bifurcations. Aperiodic oscillations were observed just beyond the limit at which a sequence terminated. Phase trajectories were constructed from time‐series data for these aperiodic states from which we produced one‐humped, one‐dimensional maps. A trajectory was also constructed that closely resembled a homoclinic orbit. Mixed‐mode oscillations were found which have the same properties as those previously observed in the Belousov–Zhabotinskii reaction. The production of copper was observed in this electrochemical system which suggests that the reaction of disproportionality may be part of a feedback mechanism that is responsible for the complex dynamical behavior.