Veronica Strong

Laser Scribing of High-Performance and Flexible Graphene-Based Electrochemical Capacitors

Infrared Route to Graphene Electrodes Electrochemical capacitors can deliver large amounts of power quickly, but have limited energy storage because only the surface regions of electrodes can store charge. Graphene represents an alternative to activated carbon electrodes because of their high conductivity and surface area, but graphene sheets tend to reassociate and lose surface area. El-Kady et al. (p. 1326; see the Perspective by Miller) show that graphite oxide sheets can be converted by infrared laser irradiation into porous graphene sheets that are flexible, robust, and highly conductive. Infrared laser reduction of graphene oxide creates a strong porous electrode with both high surface area and high conductivity. Although electrochemical capacitors (ECs), also known as supercapacitors or ultracapacitors, charge and discharge faster than batteries, they are still limited by low energy densities and slow rate capabilities. We used a standard LightScribe DVD optical drive to do the direct laser reduction of graphite oxide films to graphene. The produced films are mechanically robust, show high electrical conductivity (1738 siemens per meter) and specific surface area (1520 square meters per gram), and can thus be used directly as EC electrodes without the need for binders or current collectors, as is the case for conventional ECs. Devices made with these electrodes exhibit ultrahigh energy density values in different electrolytes while maintaining the high power density and excellent cycle stability of ECs. Moreover, these ECs maintain excellent electrochemical attributes under high mechanical stress and thus hold promise for high-power, flexible electronics.

Patterning and Electronic Tuning of Laser Scribed Graphene for Flexible All-Carbon Devices

Engineering a low-cost graphene-based electronic device has proven difficult to accomplish via a single-step fabrication process. Here we introduce a facile, inexpensive, solid-state method for generating, patterning, and electronic tuning of graphene-based materials. Laser scribed graphene (LSG) is shown to be successfully produced and selectively patterned from the direct laser irradiation of graphite oxide films under ambient conditions. Circuits and complex designs are directly patterned onto various flexible substrates without masks, templates, post-processing, transferring techniques, or metal catalysts. In addition, by varying the laser intensity and laser irradiation treatments, the electrical properties of LSG can be precisely tuned over 5 orders of magnitude of conductivity, a feature that has proven difficult with other methods. This inexpensive method for generating LSG on thin flexible substrates provides a mode for fabricating a low-cost graphene-based NO(2) gas sensor and enables its use as a heterogeneous scaffold for the selective growth of Pt nanoparticles. The LSG also shows exceptional electrochemical activity that surpasses other carbon-based electrodes in electron charge transfer rate as demonstrated using a ferro-/ferricyanide redox couple.

The oxidation of aniline to produce “polyaniline”: a process yielding many different nanoscale structures

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 polymers nanoscale morphology. Because a nanomaterials properties are highly dependent on the type of morphology produced, understanding polyanilines 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.

Carbon nanotube/polyaniline composite nanofibers: facile synthesis and chemosensors.

An initiator is applied to synthesize single-walled carbon nanotube/polyaniline composite nanofibers for use as high-performance chemosensors. The composite nanofibers possess widely tunable conductivities (10(-4) to 10(2) S/cm) with up to 5.0 wt % single-walled carbon nanotube (SWCNT) loadings. Chemosensors fabricated from the composite nanofibers synthesized with a 1.0 wt % SWCNT loading respond much more rapidly to low concentrations (100 ppb) of HCl and NH(3) vapors compared to polyaniline nanofibers alone (120 s vs 1000 s). These nanofibrillar SWCNT/polyaniline composite nanostructures are promising materials for use as low-cost disposable sensors and as electrodes due to their widely tunable conductivities.

Ultra-sensitive chemosensors for Fe(III) and explosives based on highly fluorescent oligofluoranthene

Electron-rich oligofluoranthene has been successfully synthesized by a one-step direct chemical oxidative oligomerization of fluoranthene. Key advantages include easy synthesis, high synthetic yield and low cost when compared with electropolymerization. Oligofluoranthene in solution is a very strong cyan fluorescence emitter with 12.2 times higher intensity than the fluoranthene monomer. The strong fluorescence can be effectively quenched by specific electron-deficient species, enabling the fabrication of low-cost, high-performance chemosensors for the selective detection of Fe(III) ions and the explosive 2,4,6-trinitrophenol (picric acid). A concentration range of >9 orders of magnitude with exceedingly low detection limits down to 10−12 M is possible. No sample enrichment is needed likely due to the synergistic effects of well-distributed π-conjugated electrons with a conical stereo configuration that may enhance the detection ability. Common interferents appear to have little effect as Fe(III) can be selectively detected in both tap water and seawater containing many other metal ions and picric acid can be detected at low concentrations even in the presence of inorganic acids.

Direct sub-micrometer patterning of nanostructured conducting polymer films via a low-energy infrared laser

Despite the many attractive properties of conjugated polymers, their practical applications are often limited by the lack of a simple, scalable, and nondisruptive patterning method. Here, a direct, scalable, high-resolution patterning technique for conducting polymers is demonstrated that does not involve photoresists, masks, or postprocessing treatment. Complex, well-defined patterns down to sub-micrometer scales can be created from nanofibrous films of a wide variety of conducting polymers by photothermally welding the nanofibers using a low-energy infrared laser. The welding depth, structural robustness, and optical properties of the films are readily controlled. In addition, the electrical properties such as conductivity can be precisely tuned over a 7-order of magnitude range, while maintaining the characteristic tunable electronic properties in the nonwelded polyaniline regions.

Oriented Polythiophene Nanofibers Grown from CdTe Quantum Dot Surfaces

Highly crystalline, doped polythiophene is grown from the surfaces of CdTe quantum dots by ligand exchange of 3-thenoic acid followed by an oxidant-initiated polymerization. The facile synthesis generates a composite of highly ordered fibers, which exhibit efficient charge transfer between the polythiophene and the inorganic CdTe quantum dots.