Thema der Dissertation:
Storage of Charge in Redox Conductive Polymers Probed with Electron Paramagnetic Resonance Spectroscopy
Storage of Charge in Redox Conductive Polymers Probed with Electron Paramagnetic Resonance Spectroscopy
Abstract: In this work, electron paramagnetic resonance (EPR) spectroscopy is employed to probe spins of charge carriers in electroactive polymer films used as electrodes in rechargeable organic batteries based on organic radicals. With electron spins as microscopic structural probes, EPR provided detailed insights into the electrodes’ molecular structure during charging and discharging cycles.
A significant challenge in applying EPR to working electrochemical cells arises from the strong microwave absorption by battery components. To overcome this, EPR-compatible electrochemical cells were successfully designed. These cells enabled real-time monitoring of spin concentrations, detection of by-products and identification of electrochemically inactive domains in the electrode. Combined, the quantitative EPR and electrochemical data were used to identify the molecular degradation mechanism of the electroactive polymer, to figure out in which part of the polymer charge carriers are stored, and to formulate a hypothesis of the formation of electrically disconnected domains in an electroactive polymer film. Electron spin echo was detected in a charged electrode film using pulsed EPR techniques. The effect of Instantaneous Diffusion caused by the broadband, short microwave pulses was considered and the corresponding distortions of the echo-detected EPR spectra were simulated. Simulations of echo-detected EPR spectra allowed for estimating spin concentrations in the film without any additional measurements such as the volume of the film. Transient analysis of the spin echo decay revealed multiple decay components that were attributed to the charge storing domains with distinct spin concentrations.
A significant challenge in applying EPR to working electrochemical cells arises from the strong microwave absorption by battery components. To overcome this, EPR-compatible electrochemical cells were successfully designed. These cells enabled real-time monitoring of spin concentrations, detection of by-products and identification of electrochemically inactive domains in the electrode. Combined, the quantitative EPR and electrochemical data were used to identify the molecular degradation mechanism of the electroactive polymer, to figure out in which part of the polymer charge carriers are stored, and to formulate a hypothesis of the formation of electrically disconnected domains in an electroactive polymer film. Electron spin echo was detected in a charged electrode film using pulsed EPR techniques. The effect of Instantaneous Diffusion caused by the broadband, short microwave pulses was considered and the corresponding distortions of the echo-detected EPR spectra were simulated. Simulations of echo-detected EPR spectra allowed for estimating spin concentrations in the film without any additional measurements such as the volume of the film. Transient analysis of the spin echo decay revealed multiple decay components that were attributed to the charge storing domains with distinct spin concentrations.
Zeit & Ort
15.12.2025 | 14:30
Hörsaal B (0.1.01)
(Fachbereich Physik, Arnimallee 14, 14195 Berlin)