Oscillatory instabilities during the electrochemical oxidation of sulfide on a Pt electrode

Investigating electrochemical oscillations plays an important role in nonlinear dynamic studies. Here for the first time we report current oscillations and two distinct potential oscillations (Oscillation α and Oscillation β) as well as bistability features occurring during the electrochemical oxidation of sulfide on a Pt electrode. A number of electrochemical methods such as cyclic voltammetry (CV), cyclic/linear galvanic voltammetry, galvanostatic/potentiostatic techniques and electrochemical impedance spectroscopy (EIS) were employed in this study. Two peaks are observed in the CV curve when scanning the potential from −0.8 to +1.8 V. The small one locates in the potential range between −0.5 and 0.0 V; while the large peak locates in between 0.6 and 1.4 V. The current oscillations, located at the large peak potential range, strongly depend on the potential scan rate, applied potential and sulfide concentration. The potential Oscillation α occurs at the low current densities between 2 and 10 mA/cm2; while the potential Oscillation β appears at the high current densities region (above 35 mA/cm2). Our EIS studies show that both Oscillation α and Oscillation β can be classified as hidden negative differential resistance oscillators. The equivalent electric circuits proposed in this study can effectively fit our EIS experimental data. The mechanistic origins of the observed instabilities (current oscillations, potential oscillations as well as the bistability features) are discussed.