Alpuche-Aviles Mario A, Baur John E, Wipf David O
Department of Chemistry, Mississippi State University, Mississippi State, Mississippi 39762, USA.
Anal Chem. 2008 May 15;80(10):3612-21. doi: 10.1021/ac702568c. Epub 2008 Apr 11.
We have developed a new imaging method for scanning electrochemical microscopy (SECM) employing fast-scan anodic stripping voltammetry (ASV) to provide sensitive and selective imaging of multiple chemical species at interfaces immersed in solution. A rapid cyclic voltammetry scan (100 V/s) is used along with a short preconcentration time (300-750 ms) to allow images to be acquired in a normal SECM time frame. A Hg-Pt film electrode is developed having an equivalent Hg thickness of 40 nm that has good sensitivity at short preconcentration times and also retains thin-film behavior with high-speed voltammetric stripping. Fast-scan anodic stripping currents are shown to be linear for 1-100 microM of Pb (2+) and Cd (2+) solutions using a preconcentration time of 300 ms. SECM images showing the presence of Pb (2+) and Cd (2+) at concentrations as low as 1 microM are presented. In addition, a single ASV-SECM image is shown to produce unique concentration maps indicating Cd (2+) and Pb (2+), generated in situ from a corroding sample, while simultaneously detecting the depletion of O 2 at this sample. The transient voltammetric response at the film electrode is simulated and shows good agreement with the experimental behavior. We discuss the behavior of images and concentration profiles obtained with different imaging conditions and show that mass-transport limitations in the tip-substrate gap can induce dissolution. ASV-SECM can thus be used to detect and study induced dissolution not only at bulk metal surfaces but also on underpotential deposition layers, in this case Cd and Pb on Pt. In addition, we discuss how surface diffusion phenomena may relate to the observed ASV-SECM behavior.
我们开发了一种用于扫描电化学显微镜（SECM）的新成像方法，该方法采用快速扫描阳极溶出伏安法（ASV），以对浸没在溶液中的界面处的多种化学物质进行灵敏且选择性的成像。使用快速循环伏安扫描（100 V/s）以及较短的预浓缩时间（300 - 750 ms），以便在正常的SECM时间框架内获取图像。研制了一种等效汞厚度为40 nm的汞 - 铂薄膜电极，该电极在短预浓缩时间下具有良好的灵敏度，并且在高速伏安溶出时仍保持薄膜特性。使用300 ms的预浓缩时间时，对于1 - 100 microM的Pb(2+)和Cd(2+)溶液，快速扫描阳极溶出电流显示为线性。展示了SECM图像，其显示出浓度低至1 microM的Pb(2+)和Cd(2+)的存在。此外，单个ASV - SECM图像显示可产生独特的浓度图，指示从腐蚀样品原位生成的Cd(2+)和Pb(2+)，同时检测该样品处O2的消耗。对薄膜电极处的瞬态伏安响应进行了模拟，结果与实验行为吻合良好。我们讨论了在不同成像条件下获得的图像和浓度分布的行为，并表明尖端 - 基底间隙中的传质限制可导致溶解。因此，ASV - SECM不仅可用于检测和研究大块金属表面的诱导溶解，还可用于研究欠电位沉积层上的诱导溶解，在这种情况下是Pt上的Cd和Pb。此外，我们讨论了表面扩散现象可能如何与观察到的ASV - SECM行为相关。
