A theoretical consideration of ion size effects on the electric double layer and voltammetry of nanometer-sized disk electrodes.
A theoretical consideration of ion size effects on the electric double layer and voltammetry of nanometer-sized disk electrodes.
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DOI：
10.1039/c6fd00087h
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发表时间：
2016-12
影响因子：
3.4
通讯作者：
Yu Gao;Yuwen Liu;Shengli Chen
中科院分区：
文献类型：
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作者：
Yu Gao;Yuwen Liu;Shengli Chen
考虑到双电层（EDL）结构可能对纳米尺寸电极界面处的质量传输和电荷转移动力学产生显著影响，而电解质和氧化还原离子的有限尺寸可能会改变EDL结构，研究了离子尺寸对纳米尺寸圆盘电极的EDL结构和伏安响应的可能影响。修正的Boltzmann和Nernst-Planck（NP）方程，其中包括有限离子体积的影响，结合泊松方程和修正的Butler-Volmer方程，以获得关于如何有限尺寸的离子和纳米尺寸的电极可能相互耦合，以影响纳米电化学界面的结构和反应性的知识。两个典型的离子半径，0.38 nm和0.68 nm，其可以代表常用的含水电解质离子的尺寸（例如，溶剂化的K+）和有机电解质离子（例如，溶剂化TEA+）。离子的有限尺寸会导致电极电荷屏蔽的减少，从而放大了EDL对电化学界面处离子传输和电子转移的影响。当电极半径大于10 nm时，对于较大的离子和较小的电极，离子的这种有限尺寸效应变得更加明显。然而，对于半径小于10 nm的电极，随着电极尺寸的减小，离子尺寸效应可能不太明显。这可以解释为在纳米尺度下的盘电极的增加的边缘效应，这可以放松在外部亥姆霍兹平面处/附近的离子拥挤。讨论了离子大小对电极伏安特性有显著影响的条件和情况。
Considering that an electric-double-layer (EDL) structure may significantly impact on the mass transport and charge transfer kinetics at the interfaces of nanometer-sized electrodes, while EDL structures could be altered by the finite sizes of electrolyte and redox ions, the possible effects of ion sizes on EDL structures and voltammetric responses of nanometer-sized disk (nanodisk) electrodes are investigated. Modified Boltzmann and Nernst-Planck (NP) equations, which include the influence of the finite ion volumes, are combined with the Poisson equation and modified Butler-Volmer equation to gain knowledge on how the finite sizes of ions and the nanometer sizes of electrodes may couple with each other to affect the structures and reactivities of a nanoscale electrochemical interface. Two typical ion radii, 0.38 nm and 0.68 nm, which could represent the sizes of the commonly used aqueous electrolyte ions (e.g., the solvated K+) and the organic electrolyte ions (e.g., the solvated TEA+) respectively, are considered. The finite size of ions can result in decreased screening of electrode charges, therefore magnifying EDL effects on the ion transport and the electron transfer at electrochemical interfaces. This finite size effect of ions becomes more pronounced for larger ions and at smaller electrodes as the electrode radii is larger than 10 nm. For electrodes with radii smaller than 10 nm, however, the ion size effect may be less pronounced with decreasing the electrode size. This can be explained in terms of the increased edge effect of disk electrodes at nanometer scales, which could relax the ion crowding at/near the outer Helmholtz plane. The conditions and situations under which the ion sizes may have a significant effect on the voltammetry of electrodes are discussed.