Abstract:

Organic mixed ion-electronic conductors (OMIECs) are soft, water-compatible materials that exhibit unique optical, mechanical, and charge transport properties. They are promising materials for the integration of biological and electronic systems as well as green energy storage devices. In many of the envisaged applications of the polymeric OMIECs, they are used in ambient conditions in the presence of oxygen (O₂). This dissertation explores the interaction of O₂ with OMIECs and suggests routes to leverage or overcome these interactions for specific applications. For the fundamental studies of this work, I focus on the most widely used OMIEC, the p-type (hole-transporting) poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), and the relatively newly discovered electron-transporting (n-type) n-OMIECs.

In the first part of this thesis, I describe how, through the use of various counterions used to dope the film, the inherent doping level of PEDOT can be modulated and discover a correlation between the doing state and the oxygen reduction reaction (ORR) capability of the film. Higher natural doping levels of PEDOT films induced by polymeric counterions like polystyrene sulfonate (PSS) can produce a large amount of hydrogen peroxide (H₂O₂) (121 µM in 1 hour for a film prepared with 30mC of charge at 1 V vs. Ag/AgCl), which is useful when the film is used as a catalyst, but harmful when it is used at the reduction biasing regime at the interface with biological systems.  

In the second part of this dissertation, I delve into the impact of ORR on the stability and performance of n-type polymeric mixed conductors. The findings underscore the importance of polymer backbone chemistry in combating ORR-induced degradation, highlighting the need for chemical modifications to enhance stability in aqueous environments rather than focusing solely on engineering the energetics.

Finally, the dissertation addresses advancements in OMIEC materials for charge storage applications, which may address renewable energy demands and find use in portable small electronic devices. I develop ionic liquid gel electrolytes to overcome the limitations of conventional electrolytes, enhancing the device's performance and safety. I propose a new cell design bearing O₂ and water barriers, along with diagnostic electrodes, allowing to screen a broad range of OMIEC materials for a high full cell performance. This iterative approach improves our understanding of OMIEC behavior in capacitors and guides future materials and device design for energy storage solutions.