Abstract
The electrochemical oxidation of thiourea in phosphate-buffered solution (PBS, pH 6.0) was studied, and it was shown in the cyclic voltammogram that sulfate addition results in the appearance of a new current peak at ∼0.90 V versus RHE (reversible hydrogen electrode), indicating that the sulfate is chemisorbed. Both current and potential oscillations were observed during the electrochemical oxidation of thiourea in the presence of sulfate under potentiostatic and galvanostatic control, respectively. Potential oscillations occurred in two regions of linear current sweep voltammetry. The presence of adsorbed sulfate gives rise to negative differential resistance (NDR) for the positive feedback of oscillations in the first oscillation region. The bursting and period-doubling oscillations in the second region are caused by oxide formation and adsorbed sulfate acting simultaneously as positive feedbacks. A similar chemisorbed sulfate layer was previously observed with scanning tunneling microscopy and surface ...
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