TY - JOUR
T1 - Watching Polarons Move in the Energy and Frequency Domains Using Color Impedance Spectroscopy
AU - Chen, Zhiting
AU - Ratcliff, Erin L.
N1 - Funding Information:
This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0020208. ZC would like to acknowledge Dr. Michel De Keersmaecker for insightful conversations. The characterization of color impedance spectroscopy (CIS) is supported by Dr. Brooke Beam Massani and W.M. Keck Center for Nano-Scale Imaging at the University of Arizona. A portion of this work was conducted in the Micro Nano Fabrication Center at the University of Arizona.
Funding Information:
This work was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award No. DE-SC0020208.
Publisher Copyright:
© 2022 American Chemical Society.
PY - 2022/12/13
Y1 - 2022/12/13
N2 - 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).
AB - 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).
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U2 - 10.1021/acs.chemmater.2c02831
DO - 10.1021/acs.chemmater.2c02831
M3 - Article
AN - SCOPUS:85143086316
VL - 34
SP - 10691
EP - 10700
JO - Chemistry of Materials
JF - Chemistry of Materials
SN - 0897-4756
IS - 23
ER -