| dc.description.abstract | Sulfide is most often encountered as a waste product of the pulp and paper,
petroleum, and mining industries. Organic decomposition is another major source of
sulfide. During my M. Sc. program, I have studied electrochemical oxidation o f aqueous
sulfide on Pt electrodes as well as on IrO2-based electrodes using a number of
electrochemical methods (e.g., cyclic voltammetry, cyclic and linear galvanic voltammetry,
differential capacitance, chronoamperommetry, chronopotentiommetry, galvanostatic
technique, and electrochemical impedance spectroscopy (EIS)) and surface analytical
techniques such as scanning electron microscopy (SEM) and energy dispersive X-ray
spectroscopy (EDS).
Investigating electrochemical oscillations plays an important role in nonlinear
dynamic studies. During the oxidation of sulfide on a platinum electrode we observed
current oscillations and two distinct potential oscillations (Oscillation a and Oscillation P)
as well as bistability features. Two peaks are observed in the CV curve when scanning the
potential from -0.8 to +1.8 V. The small peak is located in the potential range between
-0.5 and 0.0 V, while the large one is located between 0.6 and 1.4 V. The current
oscillations occur within the large peak potential range and are likely caused by the
periodic formation and removal of platinum oxide and sulfur deposits. Our EIS studies
show that both Oscillation a and Oscillation p can be classified as hidden negative
differential resistance (HNDR) oscillators. The formation and removal of sulfur on the Pt
surface, switching the direct oxidation of S2-/HS~ to polysulfides off and on, are
responsible for Oscillation a , which occurs at low current densities (below 10 mA/cm2).
Oscillation P appears at high current densities and it may be due to the synergic effect of sulfur formation/removal combined with oxygen evolution on the Pt oxide surface. The
well-defined bistability features are caused by the change of the electrode surface states; in
the low potential region sulfide is oxidized on a platinum surface, while in the high
potential region platinum oxides are formed and sulfide is oxidized on a platinum oxide
surface. | |
