Controlling the Kinetics of Charge Transfer at Conductive Polymer/Liquid Interfaces through Microstructure

Abstract

Controlling interfacial electron-transfer rates is fundamental to maximizing device efficiencies in electrochemical technologies including redoxflow batteries, chemical sensors, bioelectronics, and photo-electrochemical devices. Conductive polymer electrodes offer the possibility to control redox properties through synthesis and processing, if critical structure−property relationships governing charge transfer are understood. In this work, we show that the rate and symmetry of electron transfer at conductive polymer electrodes are directly connected to the microstructure and the density of states (DOS) using the model system of poly(3-hexylthiophene) (P3HT) and ferrocene/ ferrocenium (Fc/Fc + ), as predicted by the Marcus−Gerischer model. Experimentally, crystalline P3HT exhibits a sufficient overlap between the polymer DOS and the DOS of both Fc and Fc + , resulting in a reversible electron transfer. Conversely, the DOS of amorphous electrodeposited P3HT does not overlap with that of Fc + , inhibiting reduction (i.e., kinetic selectivity for oxidation). This proofof-concept work offers a paradigm to predict and control the kinetics at the polymer/liquid interface for applications from biology to energy.

Electrodeposited PEDOT:PSS-Al2O3 Improves the Steady-State Efficiency of Inverted Perovskite Solar Cells

“…In conducting polymers, the R ct is closely related to the microstructure. Thus, the symmetry and reversibility of the redox reaction depend on the overlap of the density of states (DOS) of the polymer and the redox probe, whereby a highly organized microstructure results in a DOS of the polymer that facilitates reversible charge transfer [ 73 ].…”

“…In conducting polymers, the R ct is closely related to the microstructure. Thus, the symmetry and reversibility of the redox reaction depend on the overlap of the density of states (DOS) of the polymer and the redox probe, whereby a highly organized microstructure results in a DOS of the polymer that facilitates reversible charge transfer [73]. Cyclic voltammetry results for the ferricyanide redox reaction (Figure 6c) show that the peak separation (ΔEp) increases with the increase in the annealing temperature of HTMs.…”

Ultrathin Conformal oCVD PEDOT Coatings on Carbon Electrodes Enable Improved Performance of Redox Flow Batteries

“…[ 31,35,47 ] The enhancement of electrochemical performance by improved crystallinity is also reported in poly(3‐hexylthiophene) (P 3 HT) due to better DOS overlapping of the electrode and redox‐active species. [ 48 ]…”

Nanoscale Visualization and Multiscale Electrochemical Analysis of Conductive Polymer Electrodes

“…Conductive polymers follow a potential-dependent mechanism, whereby the kinetics of electron transfer are associated with the overlap in the density of states (DOS) of the electrode and electrolyte. 17 For semicrystalline polymers such as poly(3-hexylthiophene) (P3HT), the DOS is strongly connected to the microstructure, with crystalline domains being easier to oxidize than amorphous regions. 18 The fraction of crystallites varies with processing and could hypothetically be altered when the conductive polymer is constrained into a UME configuration.…”