Abstract
A review of recent literature data on appearance of spontaneous oscillations in electrochemical systems of practical relevance is presented. They include electrocatalytic reactions of electrooxidation of hydrogen and small organic molecules on noble metals, oscillatory processes during preparation of different nanostructured materials such as nanotubes and multilayered structures, electrochemical systems with electrodissolution – passivation -electrodeposition of metals and alloys. Many of these systems belong to N-NDR or HN-NDR type of oscillator. They are investigated by different experimental techniques including electrochemical impedance spectroscopy, differential electrochemical mass spectroscopy, surface-enhanced infrared absorption spectroscopy, electrochemical quartz crystal microbalance/nanobalance, Auger electron analysis etc. It has been shown that electrochemical oscillations and more complex spatio-temporal surface structures in these systems are very sensitive to variation of experimental parameters such as applied potential, current density, solution concentration, structure and composition of electrode/electrolyte interface etc. The influence of these parameters on non-linear behavior of a model N-NDR electrochemical system was presented based on the theory of electrochemical impedance spectroscopy. An electrochemical reaction in the chosen model is related to the potential-dependent adsorption/desorption of electroactive particles on a planar, cylindrical or spherical interface and a preceding chemical reaction in the Nernst diffusion layer under potentiostatic conditions. The obtained results indicate that the range of Hopf instability giving rise to spontaneous oscillations in the system can be regulated by variation of electrode form and radius, thickness of the Nernst diffusion layer, diffusion coefficient of electroactive species, ohmic loses, bulk concentration of electroactive species. The role of mass transfer function in appearance of dynamic instabilities in the non-equilibrium system was determined.
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