Stability and Placement of Ag/AgCl Quasi-Reference Counter Electrodes in Confined Electrochemical Cells
Stability and Placement of Ag/AgCl Quasi-Reference Counter Electrodes in Confined Electrochemical Cells
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DOI：
10.1021/acs.analchem.8b01588
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发表时间：
2018-06-19
影响因子：
7.4
通讯作者：
Unwin, Patrick R.
中科院分区：
文献类型：
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作者：
Bentley, Cameron L.;Perry, David;Unwin, Patrick R.
纳米电化学是电化学的一个重要且不断发展的分支，其涵盖许多关键研究领域，包括（电）催化、能量存储、生物医学/环境传感和电化学成像。纳米尺度的电化学测量通常是在密闭的环境中进行，在延长的实验时间尺度与非隔离的准参考反电极（QRCEs）在一个简化的双电极格式。在本文中，我们考虑了常用的Ag/AgCl QRCE的稳定性，其包括在纳米吸量管配置中的AgCl涂覆的线，该纳米吸量管配置模拟了在纳米电化学系统中通常遇到的受限的电化学电池布置。Ag/AgCl QRCE具有非常稳定的参考电位，即使在制备后立即使用时，以及当部署在无Cl电解质介质（例如，0.1 M HC 104）中，漂移仅约100%。1 mV h（-1）（在数小时时间尺度上）。此外，与一些先前的报道相反，当以扫描电化学电池显微镜（SECCM）形式（弯月面与工作电极表面接触）使用时，Ag/AgCl QRCE不会引起表面的结垢（即，与可溶性氧化还原副产物，如Ag+）在至少6小时的时间尺度上，只要观察到关于电极处理和放置在纳米吸量管内的适当预防措施。这些实验观察通过有限元法（FEM）模拟，其中考虑银+运输内的纳米吸量管探头中的SECCM和SICM配置进行验证。这些结果证实了Ag/AgCl在受限的电化学环境中是稳定和稳健的QRCE，例如在SICM中使用的纳米移液管中，用于纳米孔测量，用于印刷和图案化，以及在SECCM中，证明了该电极在纳米电化学领域及其他领域的广泛使用。
Nanoelectrochemistry is an important and growing branch of electrochemistry that encompasses a number of key research areas, including (electro)catalysis, energy storage, biomedical/environmental sensing, and electrochemical imaging. Nanoscale electrochemical measurements are often performed in confined environments over prolonged experimental time scales with nonisolated quasi-reference counter electrodes (QRCEs) in a simplified two-electrode format. Herein, we consider the stability of commonly used Ag/AgCl QRCEs, comprising an AgCl-coated wire, in a nanopipet configuration, which simulates the confined electrochemical cell arrangement commonly encountered in nanoelectrochemical systems. Ag/AgCl QRCEs possess a very stable reference potential even when used immediately after preparation and, when deployed in Cl- free electrolyte media (e.g., 0.1 M HCIO4) in the scanning ion conductance microscopy (SICM) format, drift by only ca. 1 mV h(-1) on the several hours time scale. Furthermore, contrary to some previous reports, when employed in a scanning electrochemical cell microscopy (SECCM) format (meniscus contact with a working electrode surface), Ag/AgCl QRCEs do not cause fouling of the surface (i.e., with soluble redox byproducts, such as Ag+) on at least the 6 h time scale, as long as suitable precautions with respect to electrode handling and placement within the nanopipet are observed. These experimental observations are validated through finite element method (FEM) simulations, which consider Ag+ transport within a nanopipet probe in the SECCM and SICM configurations. These results confirm that Ag/AgCl is a stable and robust QRCE in confined electrochemical environments, such as in nanopipets used in SICM, for nanopore measurements, for printing and patterning, and in SECCM, justifying the widespread use of this electrode in the field of nanoelectrochemistry and beyond.