Larsen Allan Godsk, Johannsen Kim, Gothelf Kurt V
Center for Catalysis, Department of Chemistry, Aarhus University, DK-8000 C, Denmark.
J Colloid Interface Sci. 2004 Nov 1;279(1):158-66. doi: 10.1016/j.jcis.2004.06.007.
The oxidation of tetramethylthiourea (TMTU) at gold electrodes in acetonitrile, leading to dissolution of the electrode, has been studied by electrochemical methods and by an electrochemical quartz crystal microbalance (EQCM). TMTU in acetonitrile readily adsorbs at gold electrodes and an estimated coverage of 5.5 x 10(-10) mol cm(-2) (30 A2 per molecule) was measured electrochemically. Nevertheless, the oxidation of TMTU in solution is a diffusion-controlled process and is strongly influenced by the electrode material, as observed by comparison of gold electrodes with glassy carbon and platinum working electrodes. In the absence of TMTU, EQCM cyclic voltammetry experiments showed dissolution of gold through a 1e- oxidation process at potentials more positive than 1.20 V vs saturated calomel electrode (SCE). Potential step and cyclic voltammetry EQCM experiments performed using gold surfaces in the presence of TMTU revealed TMTU-assisted etching of gold at potentials as low as 0.35 V vs SCE. In the potential region from 0.35 to 1.20 V the current response of TMTU oxidation mimics the response expected for a redox-active species in solution, including the presence of a mass-transfer-limited region, which supports the conclusion that the etching process in this potential region is initiated by the oxidation of TMTU at the gold surface. The current efficiency of the TMTU-assisted etching was found to vary between 12 electrons per gold atom dissolved (e/Au) (E = 0.50 V vs SCE) and 2 e/Au (0.90 V < E < 1.20 V). At potentials <0.90 V the dominant electrochemical process is the formation of TMTU+, whereas at higher potentials the etching of the gold surface by formation of a Au(I)-TMTU+ species becomes equally important. At potentials above 1.20 V the etching is no longer dependent on the diffusion of TMTU and the e/Au value approaches 1.
通过电化学方法和电化学石英晶体微天平（EQCM）研究了四甲基硫脲（TMTU）在乙腈中于金电极上的氧化反应，该反应会导致电极溶解。乙腈中的TMTU很容易吸附在金电极上，通过电化学方法测得的估计覆盖度为5.5×10⁻¹⁰ mol·cm⁻²（每个分子30 Ų）。然而，溶液中TMTU的氧化是一个扩散控制过程，并且如通过将金电极与玻碳和铂工作电极进行比较所观察到的，该过程受到电极材料的强烈影响。在不存在TMTU的情况下，EQCM循环伏安实验表明，相对于饱和甘汞电极（SCE），在电位高于1.20 V时，金通过1e⁻氧化过程发生溶解。在TMTU存在的情况下，使用金表面进行的电位阶跃和循环伏安EQCM实验表明，相对于SCE，在低至0.35 V的电位下，TMTU会辅助金的蚀刻。在0.35至1.20 V的电位区域中，TMTU氧化的电流响应模拟了溶液中氧化还原活性物种预期的响应，包括存在传质限制区域，这支持了在该电位区域中的蚀刻过程是由金表面上TMTU的氧化引发的这一结论。发现TMTU辅助蚀刻的电流效率在每溶解一个金原子12个电子（e/Au）（E = 0.50 V vs SCE）至2 e/Au（0.90 V < E < 1.20 V）之间变化。在电位<0.90 V时，主要的电化学过程是形成TMTU⁺，而在较高电位下，通过形成Au(I)-TMTU⁺物种对金表面的蚀刻变得同样重要。在电位高于1.20 V时，蚀刻不再依赖于TMTU的扩散，并且e/Au值接近1。
