Electrochemical analysis at nanometer-scaled electrodes

本研究的目的是研究反应域在纳米尺度下，在超微电极上氧化还原反应的异常电化学行为。化学平衡常数、反应速率常数随电极尺寸的明显变化说明了电极的异常行为。这种行为已经在纳米尺度的材料中被观察到，如金属纳米颗粒、纳米薄膜和纳米团簇。电化学分析有利于本研究，因为超微电极提供了纳米尺度的环境以及纳米尺度上的检测。以往氧化还原反应速率常数与电极尺寸关系的数据是Fe(II)(CN)_6和Fe(III)(CN)_6的半波电位随电极半径的减小而变化。提出了一种批评，认为配合物可能被吸附，因此氧化还原行为应超出正常行为。为了避免这种批评，我们努力寻找其他氧化还原体系和制造纳米电极。目前，我们得到了二氯乙烷溶液中二茂铁和乙腈溶液中TCNQ的极大转移系数。较大的系数对应于反应速率的提高，定量地支持随着材料的减少而提高的活化。为了消除电极几何形状的模糊性，对实验数据进行了理论分析。提出了一些模型来解释反应速率的提高。作者认为这种增强部分是由于对电极半径的估计不足。

The aim of this proposal was to investigate abnormal electrochemical behavior of redox reactions at ultramicroelectrodes when reaction domains are on nanometer scale. The abnormal behavior is exemplified by apparent variation of chemical equilibrium constants, reaction rate constants with electrode size. This behavior has been observed at namometer-scaled materials such as metal nanoparticles, nanometered thin films, and nano-clusters. The electrochemical analysis is favorable for this research in that the ultramicroelectrodes provides nano-meter circumstances as well as their detection on the nanometered scale.The previous data of the relation between redox reaction rate constants and the electrode size were the shift of halfwave potentials of Fe(II)(CN)_6 and Fe(III)(CN)_6 with a decrease in the electrode radii. A criticism was presented in that the complexes might be adsorbed so that the redox behavior should be out of the ordinary behavior. In order to circumvent this criticism, we made efforts of searching other redox systems and fabricating nanometer electrodes. At present, we got extremely large transfer coefficients of ferrocene in dichloroethyne solution and TCNQ in acetonitrile. The large coefficient corresponds to enhancement of reaction rates, supporting quantitatively the higher activation with a decrease in material. In order to remove ambiguity of electrode geometry, theoretical work has been made for the analysis of experimental data. The some models have been presented for explaining the enhancement of the reaction rates. The authors think the enhancement is artially due to under estimation of the electrode radii.