Effects of sulfurous acid on anodic process of gold electrode in thiourea solution

The electrochemistry behaviors of gold electrode in thiourea solution were studied by using electrochemical techniques, such as potentiodynamic, voltammogram and current step. A catalytical electrochemical-reduction mechanism was proposed to identify the anodic oxidation of gold in the thiourea solution. The results indicate that the decomposition of thiourea occurs when the electrode potential is higher than 640 mV. The addition of sulfurous acid presents a very positive effect on the anodic process of gold electrode. The anodic oxidation rate of gold is 5 times faster than that without sulfurous acid. The passivity of gold electrode is attributed to the accumulation of elemental sulfur on the surface of gold. The sulfurous acid reacts with the oxidation product ((SC(NH)NH2)2) of thiourea, which can decrease the decomposition of thiourea and improves its stability.