显微电化学:"看见"流动的电子

       电化学致力于阐明电活性物质与电极之间的界面电子转移行为和规律,对电极表面总电流(或平均电流)的测量构成了电化学研究的基础。但是由于整个电极表面发生的所有反应的电子转移的总和产生了所测电流,因此通过测得的总电流我们难以对构成电流的每一个电子追本溯源,这就导致传统电化学研究缺乏空间分辨率,而这一点在研究微观异质界面的电化学行为时尤其重要。幸运的是在电化学反应中电子的转移不仅会引起电流的变化,也会使物质在氧化态与还原态之间切换,而一般情况下不同物质的光学性质(折射率,散射强度,荧光强度等)会有或多或少的区别,这驱使我们另辟蹊径,利用光学显微镜来观察物质在电化学反应中的变化,并通过建立光学信号与电流之间的关系来间接“看到”电子的流动,这就是我们所说的显微电化学技术。这类技术对于电流的空间分辨能力取决于显微技术的分辨率,例如通过单分子荧光技术可以研究如单个亚甲基蓝分子在电化学中的动力学信息,而暗场和表面等离子共振技术则常常用于对单个纳米粒子的电化学行为进行研究。其电流检测灵敏度则由光学系统的性能决定。光学显微镜的单分子检测能力使得单电子转移的研究成为可能。

图1. 利用显微电化学方法测量单个LiCoO2纳米颗粒的循环伏安曲线                          图2. 双极电极界面电势分布的光学可视化
                     (J. Am. Chem. Soc., 2017, 139, 186)                                                  (Angew. Chem. Int. Ed., 2017, 56, 1629.)

 

代表性论文:

[1] Wei Wang*, The Rising of Microscopic Electrochemistry: "Watching" the Local Electron Transfer Optically, Sci. Bull., 2015, 60, 1866-1867.

[2] Tinglian Yuan, Wei Wang*, Studying the electrochemistry of single nanoparticles with surface plasmon resonance microscopy, Curr. Opin. Electrochem., 2017, 6, 17-22.

[3] Liang Yuan, Nongjian Tao, Wei Wang*, Plasmonic Imaging of Electrochemical Impedance, Ann. Rev. Anal. Chem., 2017, 10, 183-200.

[4] Dan Jiang, Yingyan Jiang, Zhimin Li, Tao Liu, Xiang Wo, Yimin Fang, Nongjian Tao, Wei Wang*, Hong-Yuan Chen, Optical imaging of phase transition and Li-ion diffusion kinetics of single LiCoO2 nanoparticles during electrochemical cycling, J. Am. Chem. Soc., 2017, 139, 186-192.

[5] Meisam Hasheminejad, Yimin Fang, Meng Li, Yingyan Jiang, Wei Wang*, Hong-Yuan Chen, Plasmonic Imaging of the Interfacial Potential Distribution on Bipolar Electrodes, Angew. Chem. Int. Ed., 2017, 56, 1629-1633.

[6] Linlin Sun, Yimin Fang, Zhimin Li, Wei Wang*, Hong-Yuan Chen*, Simultaneous optical and electrochemical recording of single nanoparticle electrochemistry, Nano Res., 2017, 5, 1740-1748.

 

Microscopic Electrochemistry: "Watching" Local Electron Transfer Optically

      Electrochemistry has been dedicated to studying the electron transfer process between substances and electrode. In the field of traditional electrochemistry, the research of electrochemical reactions relies on the direct detection of current formed by large amounts of flowing electrons. In other word, the measured current is generated by the electron transfer processes of all single reactions occurring on the surface of the entire electrode. As a consequence, it is difficult for us to trace the source of each electron, resulting in the lack of spatial resolution for conventional electrochemical detection, which is of great significance in investigating the electrochemical behavior of micro-matter such as nanoparticles. Fortunately, the electron transfer in an electrochemical reaction is not only reflected in the current, but also in the conversion of redox couple between the oxidation state and the reduced state. The optical properties (refractive index, scattering intensity and fluorescence intensity, etc.) of different substances would be more or less different in general, which drives us to observe the change of the matters in electrochemical reaction using optical microscope. The flow of electrons can be indirectly ‘watched’ according to establishing the relationship between current and optical signals which is termed as microscopic electrochemistry. The current resolution depends on the microscopic technique indeed. For example, the single-molecule fluorescence technique has been employed to researched into the kinetic information of a single molecule such as methylene blue in the electrochemical reaction. Moreover, dark-field and surface plasmon resonance techniques are often applied to study the electrochemical behavior of single nanoparticles.

 

References:

[1] Wei Wang*, The Rising of Microscopic Electrochemistry: "Watching" the Local Electron Transfer Optically, Sci. Bull., 2015, 60, 1866-1867.

[2] Tinglian Yuan, Wei Wang*, Studying the electrochemistry of single nanoparticles with surface plasmon resonance microscopy, Curr. Opin. Electrochem., 2017, 6, 17-22.

[3] Liang Yuan, Nongjian Tao, Wei Wang*, Plasmonic Imaging of Electrochemical Impedance, Ann. Rev. Anal. Chem., 2017, 10, 183-200.

[4] Dan Jiang, Yingyan Jiang, Zhimin Li, Tao Liu, Xiang Wo, Yimin Fang, Nongjian Tao, Wei Wang*, Hong-Yuan Chen, Optical imaging of phase transition and Li-ion diffusion kinetics of single LiCoO2 nanoparticles during electrochemical cycling, J. Am. Chem. Soc., 2017, 139, 186-192.

[5] Meisam Hasheminejad, Yimin Fang, Meng Li, Yingyan Jiang, Wei Wang*, Hong-Yuan Chen, Plasmonic Imaging of the Interfacial Potential Distribution on Bipolar Electrodes, Angew. Chem. Int. Ed., 2017, 56, 1629-1633.

[6] Linlin Sun, Yimin Fang, Zhimin Li, Wei Wang*, Hong-Yuan Chen*, Simultaneous optical and electrochemical recording of single nanoparticle electrochemistry, Nano Res., 2017, 5, 1740-1748.

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