Contribution to the theory of conducting-polymer electrodes in electrolyte solutions
Contribution to the theory of conducting-polymer electrodes in electrolyte solutions
复制标题
对电解质溶液中导电聚合物电极理论的贡献
DOI：
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发表时间：
1993
期刊：
影响因子：
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通讯作者：
S. Fletcher
中科院分区：
文献类型：
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作者：
S. Fletcher
本文由两部分组成。首先，提出了一种电模型电路，可以高精度地再现导电聚合物电极在电解质溶液中的小振幅阻抗行为。其次，用能带模型讨论了金属/聚合物/溶液界面的电子结构。从一开始就强调，在电解质溶液中生长的导电聚合物本质上是一个多孔电极。因此，电模型电路具有对角线连接的离散阶梯网络的形式，其特征为三个阻抗，x， y和z。在展示了如何将这些广义阻抗替换为与聚合物中实际过程相对应的无源电路元件的特定安排之后，推导出了与易于获得的实验条件相对应的两个极限行为：这些行为是还原聚合物的高频阻抗响应和氧化聚合物的低频阻抗响应。聚吡咯的实验数据证实了这两种反应。基于相同的多孔电极模型，证明了在低频率下，聚合物的总阻抗由孔壁的总阻抗主导。这为在复杂的阻抗平面上分析导电聚合物的行为打开了一扇“后门”，特别是揭示了通过孔壁的电荷泄漏的重要性。本节接着讨论了聚合物内部的电子结构，由此建立了一个理想化的能带模型，显示了应用电位如何在整个金属/聚合物/溶液界面上下降。最后，对带模型的批判性分析揭示了平带电位在确定聚合物行为中的重要性。这一点在过去似乎被普遍忽视了。在模型中包含平带电位的一个结果是，有必要假设静电稳定极化子的存在：如果是真的，这些也可以解释稀电解质溶液中伏安图的不对称性。
This paper consists of two parts. First, an electrical model circuit is proposed that can reproduce, with high accuracy, the small-amplitude impedance behaviour of conducting-polymer electrodes in electrolyte solutions. Secondly, the electronic structure of the metal/polymer/solution interphase is discussed in terms of a band model. From the outset it is emphasized that a conducting polymer grown in an electrolyte solution is essentially a porous electrode. As a result, the electrical model circuit has the form of a diagonally connected discrete ladder network characterized by three impedances, x, y and z. After showing how these generalized impedances can be replaced by particular arrangements of passive circuit elements corresponding to real processes in the polymer, two limiting behaviours are derived corresponding to readily accessible experimental conditions: these behaviours are the high-frequency impedance response of the reduced polymer, and the low-frequency impedance response of the oxidized polymer. Both responses are identified in experimental data from polypyrrole.Based on the same porous electrode model, it is next proved that, at low frequencies, the total impedance of the polymer is dominated by that of the pore walls. This opens a ‘back door’ to the analysis of conducting-polymer behaviour in the complex plane of impedance, and, in particular, brings to light the importance of charge leakage across the pore walls. This section is followed by a discussion of the electronic structure of the polymer interior, from which an idealized band model is developed showing how the applied potential is dropped across the entire metal/polymer/solution interphase.Finally, critical analysis of the band model reveals the importance of the flatband potential in determining the polymer behaviour. This seems to have been universally neglected in the past. One result of including the flatband potential in the model is that it becomes necessary to postulate the existence of electrostatically stabilized polarons: if real, these would also explain the asymmetry of voltammograms in dilute electrolyte solutions.