Watching Polarons Move in the Energy and Frequency Domains Using Color Impedance Spectroscopy,Chemistry of Materials

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Watching Polarons Move in the Energy and Frequency Domains Using Color Impedance Spectroscopy
Chemistry of Materials ( IF 7.2 ) Pub Date : 2022-11-23 , DOI: 10.1021/acs.chemmater.2c02831
Zhiting Chen ₁ , Erin L. Ratcliff _{1,

2,

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Affiliation

The hybrid electronic–ionic transport property of π-conjugated polymers enables new (opto)electrochemical device constructs for energy conversion and storage and biosensing applications. One major challenge is separating the energy and frequency dependence of Faradaic events–those involving charge transfer and the redox processes of the conjugated backbone─from the non-Faradaic components, such as ionic motion. Herein, we combine optical spectroscopy with electrochemical impedance spectroscopy (EIS) to resolve the frequency response of ionic–electronic coupling as a function of electrochemical doping potential. First, using EIS, we identify two different frequency regimes resulting in potential-dependent capacitive elements on the order of ∼10 μF/cm² in a high-frequency regime and ∼50–150 μF/cm² in a low-frequency regime. Given the larger magnitude and greater potential dependence, we posit that polaronic motion is more likely to occur at low frequencies (<1 kHz) and overlaps with ionic motion. The use of color impedance spectroscopy (CIS) enables observation of polaronic motion with frequency modulation. We observe that higher doping potentials show a greater motion of polarons above the DC-bias baseline concentration for onset in electrochemical doping, but all potentials considered demonstrate a critical frequency at which the polaronic motion is “frozen” (∼40 Hz). This critical information obtained from CIS in highly dielectric environments offers a unique figure of merit for future studies on electronic–ionic coupling by which to compare across polymer/electrolyte interfaces, including the role of a charge-supporting electrolyte, a solvent, and alternative Faradaic processes (e.g., electrocatalysis).

中文翻译：

使用色阻抗谱观察极化子在能量域和频率域中的移动

π-共轭聚合物的混合电子-离子传输特性使新的（光）电化学装置结构能够用于能量转换和存储以及生物传感应用。一个主要挑战是将法拉第事件（涉及电荷转移和共轭主链的氧化还原过程）的能量和频率依赖性与非法拉第成分（例如离子运动）分开。在此，我们将光谱学与电化学阻抗谱 (EIS) 相结合，以解决作为电化学掺杂电位函数的离子-电子耦合的频率响应。首先，使用 EIS，我们确定了两种不同的频率范围，从而导致高频范围内约为 ∼10 μF/cm ^{2和 ∼50–150 μF/cm}^{2的电位相关电容元件}在低频状态下。鉴于更大的幅度和更大的潜在依赖性，我们假设极化子运动更有可能发生在低频（<1 kHz）并且与离子运动重叠。使用彩色阻抗谱 (CIS) 可以观察具有频率调制的极化子运动。我们观察到，较高的掺杂电位表明极化子在电化学掺杂开始时的直流偏置基线浓度以上有更大的运动，但所有考虑的电位都表明极化子运动“冻结”的临界频率（~40 Hz）。在高介电环境中从 CIS 获得的这一关键信息为未来电子-离子耦合研究提供了独特的品质因数，通过该研究可以比较聚合物/电解质界面，包括电荷支持电解质的作用，

更新日期：2022-11-23

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