Developing energy storage devices to be utilized within a rapidly advancing energy market requires a multipronged approach whereby material synthesis and engineering fundamentals combine to enable technological advances. These devices should be able to store a large amount of energy in a small, lightweight package, and should be able to distribute that energy quickly for high rate applications. Pseudocapacitors made from conducting polymers, which store charge via rapid reduction and oxidation reactions, are a particularly promising candidate. This perspective explores conductivity and charge storage mechanisms in conducting polymers and describes how synthetic strategies can affect these properties. We further develop chemical correlations that have been shown to enhance the performance of pseudocapacitive electrochemical capacitors fabricated from conducting polymers. Important device engineering strategies for improving the lifetime and applicability of pseudocapacitors are also discussed.

The number of different nano-and micro-scale structures produced from the chemical oxidation of aniline into ''polyaniline'' is rivaled by few other organic materials. Nanoscale structures such as fibers, tubes, aligned wires, flowers, spheres and hollow spheres, plates, and even those resembling anatomical organs, insects, and sea animals have been observed for the products produced when aniline is oxidized. This feature article examines these different structures and the small and subtle changes in reaction parameters that result in their formation. These changes can often result in drastic differences in the polymer's nanoscale morphology. Because a nanomaterial's properties are highly dependent on the type of morphology produced, understanding polyaniline's propensity for forming these structures is crucial towards tailoring the material for different applications as well as improving its synthetic reproducibility. The different approaches to commonly observed polyaniline nanostructures are presented in this article along with some of the highly debated aspects of these processes. The article ends with our approach towards resolving some of these contentious issues and our perspective on where things are headed in the years to come.

Nanostructures of the conducting polymer poly(3,4-ethylenedioxythiophene) with large surface areas enhance the performance of energy storage devices such as electrochemical supercapacitors. However, until now, high aspect ratio nanofibers of this polymer could only be deposited from the vapor-phase, utilizing extrinsic hard templates such as electrospun nanofibers and anodized aluminum oxide. These routes result in low conductivity and require postsynthetic template removal, conditions that stifle the development of conducting polymer electronics. Here we introduce a simple process that overcomes these drawbacks and results in vertically directed high aspect ratio poly(3,4-ethylenedioxythiophene) nanofibers possessing a high conductivity of 130 S/cm. Nanofibers deposit as a freestanding mechanically robust film that is easily processable into a supercapacitor without using organic binders or conductive additives and is characterized by excellent cycling stability, retaining more than 92% of its initial capacitance after 10,000 charge/discharge cycles. Deposition of nanofibers on a hard carbon fiber paper current collector affords a highly efficient and stable electrode for a supercapacitor exhibiting gravimetric capacitance of 175 F/g and 94% capacitance retention after 1000 cycles.

Introducing small amounts of additives into polymerization reactions to produce conducting polymers can have a profound impact on the resulting polymer morphology. When an oligomer such as aniline dimer is added to the polymerization of aniline, the nanofibers produced are longer and less entangled than those typically observed. The addition of aniline dimer can even induce nanofiber formation under synthetic conditions that generally do not favor a nanofibrillar morphology. This finding can be extended to both the synthesis of polythiophene and polypyrrole nanofibers. The traditional oxidative polymerization of thiophene or pyrrole only produces agglomerated particles. However, when minute amounts of thiophene or pyrrole oligomers are added to the reaction, the resulting polymers possess a nanofibrillar morphology. These results reveal important insights into a semirigid rod nucleation phenomenon that has hitherto been little explored. When polyaniline nucleates homogeneously, surface energy requirements necessitate the formation of ordered nuclei which leads to the directional polymerization of aniline. This ultimately leads to the one-dimensional nanofibrillar morphology observed in the final product. The synthetic procedures developed here are simple, scalable, and do not require any templates or other additives that are not inherent to the polymer.