Department of Chemistry, University of Warwick, Coventry CV4 7AL, United Kingdom.
Anal Chem. 2012 Mar 6;84(5):2483-91. doi: 10.1021/ac203195h. Epub 2012 Feb 17.
Scanning electrochemical cell microscopy (SECCM) is a high resolution electrochemical scanning probe technique that employs a dual-barrel theta pipet probe containing electrolyte solution and quasi-reference counter electrodes (QRCE) in each barrel. A thin layer of electrolyte protruding from the tip of the pipet ensures that a gentle meniscus contact is made with a substrate surface, which defines the active surface area of an electrochemical cell. The substrate can be an electrical conductor, semiconductor, or insulator. The main focus here is on the general case where the substrate is a working electrode, and both ion-conductance measurements between the QRCEs in the two barrels and voltammetric/amperometric measurements at the substrate can be made simultaneously. In usual practice, a small perpendicular oscillation of the probe with respect to the substrate is employed, so that an alternating conductance current (ac) develops, due to the change in the dimensions of the electrolyte contact (and hence resistance), as well as the direct conductance current (dc). It is shown that the dc current can be predicted for a fixed probe by solving the Nernst-Planck equation and that the ac response can also be derived from this response. Both responses are shown to agree well with experiment. It is found that the pipet geometry plays an important role in controlling the dc conductance current and that this is easily measured by microscopy. A key feature of SECCM is that mass transport to the substrate surface is by diffusion and, for charged analytes, ion migration which can be controlled and varied quantifiably via the bias between the two QRCEs. For a working electrode substrate this means that charged redox-active analytes can be transported to the electrode/solution interface in a well-defined and controllable manner and that relatively fast heterogeneous electron transfer kinetics can be studied. The factors controlling the voltammetric response are determined by both simulation and experiment. Experiments demonstrate the realization of simultaneous quantitative voltammetric and ion conductance measurements and also identify a general rule of thumb that the surface contacted by electrolyte is of the order of the pipet probe dimensions.
扫描电化学池显微镜（SECCM）是一种高分辨率电化学扫描探针技术，它采用双筒 theta 移液管探头，每个筒内都含有电解质溶液和准参比对电极（QRCE）。从移液管尖端突出的电解质薄层确保与基底表面形成温和的弯月面接触，从而定义了电化学池的有效表面积。基底可以是电导体、半导体或绝缘体。这里主要关注的是基底通常为工作电极的一般情况，并且可以同时进行两个桶中 QRCE 之间的离子电导率测量以及在基底上的伏安法/安培法测量。在通常的实践中，采用探针相对于基底的小的垂直摆动，从而由于电解质接触的尺寸变化（以及因此的电阻）以及直流电导电流（dc）而产生交变电导电流（ac）。结果表明，可以通过求解 Nernst-Planck 方程来预测固定探针的 dc 电流，并且可以从该响应中推导出 ac 响应。两种响应都与实验吻合良好。结果发现，移液管几何形状在控制 dc 电导电流方面起着重要作用，并且可以通过显微镜轻松测量。SECCM 的一个关键特征是，向基底表面的质量传输是通过扩散进行的，对于带电分析物，离子迁移可以通过两个 QRCE 之间的偏压进行控制和定量变化。对于工作电极基底，这意味着带电氧化还原活性分析物可以以明确定义和可控的方式被运送到电极/溶液界面，并且可以研究相对快速的非均相电子转移动力学。控制伏安响应的因素由模拟和实验确定。实验证明了同时实现定量伏安法和离子电导率测量的可能性，并确定了一个普遍的经验法则，即与电解质接触的表面约为移液管探头的尺寸。
