Nanomaterial synthesis and characterization for energy storage and conversion devices

Synthesis conditions and characterization techniques were investigated for a variety of nanomaterials that have potential for use in a plethora of energy storage and conversion devices, such as photovoltaics, thermionic emitters, lithium-ion batteries, and PEM fuel cells. A portion of this work focused on the development of a chemical vapor deposition synthesis technique for multi-walled carbon nanotubes (MWNTs) using an iron dimer in xylene as a liquid catalyst precursor. The optimization of synthesis conditions for this technique was subsequently followed by the development of a quantitative purity assessment method for MWNTs from Raman spectroscopy, which involves the ratios of peak heights in Raman spectra. Initial work in the development of this purity assessment method was extended to a second Raman excitation energy, and a universal equation of purity was developed for two excitation laser energies. The capability exists to develop free-standing electrode papers from these synthesized MWNTs for several of the aforementioned applications. A large portion of this work also focused on the characterization of materials commonly used in organic solar cells with the technique of cyclic voltammetry. Electrochemical measurements of semiconducting CdSe quantum dots, fullerene derivatives, and polymers (MEH-PPV, P3HT, and MDMO-PPV) were completed to determine the band gap, ionization potential, and electron affinity of these materials in order to improve device fabrication by offering the capability of pre-selecting the materials incorporated in a given composite. This reduces time, energy, and expenses involved with fabrication, along with furthering the understanding of interactions between materials in a composite at the electronic level. This work has offered important contributions to the field of alternative energy by making strides in synthesizing, characterizing, and selecting appropriate materials for use in energy storage and conversion devices

Carbon Nanotubes for Space Photovoltaic Applications

Carbon nanotubes (CNTs) can be envisioned as an individual graphene sheet rolled into a seamless cylinder (single-walled, SWNT), or concentric sheets as in the case of a multi-walled carbon nanotube (MWNT) (1). The role-up vector will determine the hexagonal arrangement and "chirality" of the graphene sheet, which will establish the nanotube to be metallic or semiconducting. The optoelectronic properties will depend directly on this chiral angle and the diameter of the SWNT, with semiconductor types exhibiting a band gap energy (2). Characteristic of MWNTs are the concentric graphene layers spaced 0.34 nm apart, with diameters from 10-200 nm and lengths up to hundreds of microns (2). In the case of SWNTs, the diameters range from 0.4 - 2 nm and lengths have been reported up to 1.5 cm (3). SWNTs have the distinguishable property of "bundling" together due to van der Waal's attractions to form "ropes." A comparison of these different structural types is shown in Figure 1. The use of SWNTS in space photovoltaic (PV) applications is attractive for a variety of reasons. Carbon nanotubes as a class of materials exhibit unprecedented optical, electrical, mechanical properties, with the added benefit of being nanoscale in size which fosters ideal interaction in nanomaterial-based devices like polymeric solar cells. The optical bandgap of semiconducting SWNTs can be varied from approx. 0.4 - 1.5 eV, with this property being inversely proportional to the nanotube diameter. Recent work at GE Global Research has shown where a single nanotube device can behave as an "ideal" pn diode (5). The SWNT was bridged over a SiO2 channel between Mo contacts and exhibited an ideality factor of 1, based on a fit of the current-voltage data using the diode equation. The measured PV efficiency under a 0.8 eV monochromatic illumination showed a power conversion efficiency of 0.2 %. However, the projected efficiency of these junctions is estimated to be > 5 %, especially when one considers the enhanced absorption (from nanotubes whose bandgap is tailored to illumination) and electromagnetic coupling in a network of nanotubes

Ionic Liquid Hybrid Electrolytes for Lithium-Ion Batteries: A Key Role of the Separator–Electrolyte Interface in Battery Electrochemistry

Batteries are multicomponent systems where the theoretical voltage and stoichiometric electron transfer are defined by the electrochemically active anode and cathode materials. While the electrolyte may not be considered in stoichiometric electron-transfer calculations, it can be a critical factor determining the deliverable energy content of a battery, depending also on the use conditions. The development of ionic liquid (IL)-based electrolytes has been a research area of recent reports by other researchers, due, in part, to opportunities for an expanded high-voltage operating window and improved safety through the reduction of flammable solvent content. The study reported here encompasses a systematic investigation of the physical properties of IL-based hybrid electrolytes including quantitative characterization of the electrolyte–separator interface via contact-angle measurements. An inverse trend in the conductivity and wetting properties was observed for a series of IL-based electrolyte candidates. Test-cell measurements were undertaken to evaluate the electrolyte performance in the presence of functioning anode and cathode materials, where several promising IL-based hybrid electrolytes with performance comparable to that of conventional carbonate electrolytes were identified. The study revealed that the contact angle influenced the performance more significantly than the conductivity because the cells containing IL–tetrafluoroborate-based electrolytes with higher conductivity but poorer wetting showed significantly decreased performance relative to the cells containing IL–bis­(trifluoromethanesulfonyl)­imide electrolytes with lower conductivity but improved wetting properties. This work contributes to the development of new IL battery-based electrolyte systems with the potential to improve the deliverable energy content as well as safety of lithium-ion battery systems

Retrospective observational studies in ultra-rare sarcomas: A consensus paper from the Connective Tissue Oncology Society (CTOS) community of experts on the minimum requirements for the evaluation of activity of systemic treatments

In ultra-rare sarcomas (URS) the conduction of prospective, randomized trials is challenging. Data from retrospective observational studies (ROS) may represent the best evidence available. ROS implicit limitations led to poor acceptance by the scientific community and regulatory authorities. In this context, an expert panel from the Connective Tissue Oncology Society (CTOS), agreed on the need to establish a set of minimum requirements for conducting high-quality ROS on the activity of systemic therapies in URS