ABSTRACT

This chapter addresses fundamental chemistries responsible for attaining high energy storage metrics and draws correlations between conducting polymer structure and physical properties deterministic of electrochemical capacitor performance. Energy storage mechanisms are examined in terms of polymer structure, doping, and the nature of the electrolyte. Overarching relationships between the chemistry of conducting polymers, their performance as active electrochemical electrodes, and the structure-property dependencies that afford extensive control for optimizing devices are elucidated. At the core of this compendium is the synthesis and processing of soft organic semiconducting nanostructures that, when engineered into electrochemical capacitors, result in devices characterized by high energy and power densities, electrochemical stability, and extended cyclability. This work surveys synthetic approaches to nanostructures that increase free volume in the electrode architecture, enhance crystallinity of low dimensional materials, and abate detrimental mechanical strains during charging and discharging cycles. Here we address a diverse and expanding spectrum of nanoscale materials; this abundance of conducting polymer nanostructures foments development of hierarchical electrodes that enhance rates of charge transfer. Processing strategies for polymer nanostructures are discussed to illustrate the evolution and applications of cutting-edge porous electrodes possessing low tortuosity and robust percolation networks. Intrinsic challenges in conducting polymer chemistry such as stable deep doping states, metallic conductivity coupled with high ionic conductivity, and scalable processing of crystalline materials are addressed as important targets of opportunity for advancing electrochemical capacitors. We conclude with both an analysis of salient state-of-the-art examples that facilitate fundamental understanding of complex interactions during the operation of an electrochemical capacitor, as well as a discussion of the intrinsic advantages of p-type and n-type organic semiconductors serving as active electrochemical electrodes.