Effects of species concentration and external resistance on spatiotemporal dynamics during the electro-oxidation of sulfide ion on a platinum disk electrode

Sulfide and hydroxide ions, acting as negative and positive feedback species of the oscillatory electro-oxidation of sulfide on a platinum disk, respectively, strongly affected the spatiotemporal dynamics of the process. Oscillations with both hidden N-shaped and N-shaped negative differential resistances were enhanced in both amplitude and potential range with increasing sulfide ion concentration, but weakened with increasing hydroxide ion concentration. The patterns in the N-shaped negative differential resistance oscillatory region changed from local pulses to global synchronous oscillations of sulfur deposition and dissolution with increasing sulfide ion concentration. However, as the hydroxide ion concentration increased, both the patterns and oscillations were suppressed and the pulse width also decreased. External resistance was another factor that caused complex oscillations and a novel pattern formation that was observed to be alternating between local pulses and synchronous oscillations of sulfur deposition and dissolution. A detailed analysis of the reaction mechanism and a model simulation provided a reasonable explanation of these phenomena and the dynamic features. This investigation further promoted analysis of the complex spatiotemporal dynamics of the sulfide electro-oxidation system and enriched the experimental results available in electrochemical systems. This research was helpful in the prediction and control of pattern formation processing through adjustment of the positive and negative feedbacks as well as spatial couplings.