Salt-Induced Doping and Templating of Laser-Induced Graphene Supercapacitors.

The use of inexpensive and widely available CO2 lasers to selectively irradiate polymer films and form a graphene foam, termed laser-induced graphene (LIG), has incited significant research attention. The simple and rapid nature of the approach and the high conductivity and porosity of LIG have motivated its widespread application in electrochemical energy storage devices such as batteries and supercapacitors. However, nearly all high-performance LIG-based supercapacitors reported to date are prepared from costly, petroleum-based polyimide (Kapton, PI). Herein, we demonstrate that incorporating microparticles of inexpensive, non-toxic, and widely abundant sodium salts such as NaCl and Na2SO4 into poly(furfuryl alcohol) (PFA) resins enables the formation of high-performance LIG. The embedded particles aid in carbonization and act as a template for pore formation. While increasing both the carbon yield and surface area of the electrodes, the salt also dopes the LIG formed with S or Cl. The combination of these effects results in a two- to four-order-of-magnitude increase in device areal capacitance, from 8 µF/cm2 for PFA/no salt at 5 mV/s to up to 80 mF/cm2 for some PFA/20% Na2SO4 samples at 0.05 mA/cm2, significantly higher than that of PI-based devices and most other LIG precursors.

Probing Sulfur Deposition onto Carbon Nanomaterials from Aqueous, Elemental Sulfur Sols for Lithium-Sulfur Batteries.

Sulfur cathodes for lithium-sulfur batteries often rely on integrating sulfur with high surface area carbonaceous materials. Nanoscale mixing is typically achieved by a lengthy, high-temperature melt imbibition approach that employs carbon nanomaterials in an aggregated solid form. In this work, we present a simple strategy to coat carbon nanomaterials with sulfur in a cost-effective, room-temperature process using inexpensive elemental sulfur. Our results are based on hydrophobic sulfur sols, which have rarely been examined for use in the preparation of sulfur cathodes. We study the deposition mechanism on different carbon materials and find that sulfur dissolves from the sol into the aqueous phase and coats the surface of reduced graphene oxide (rGO) by heterogeneous nucleation and growth, but that this mechanism is not favored for carbon materials such as Ketjen black (KB) and graphene oxide (GO), for which undesirable homogeneous nucleation of micron-sized, insulating sulfur crystals is observed. High loading (3-4 mgsulfur/cm2) rGO-based cathodes prepared using this approach achieve discharge capacities of 1300 mAh/gsulfur (∼4.8 mAh/cm2) at 0.1C and achieve capacities 7-fold higher than cells prepared via traditional melt imbibition approaches at higher rates of 0.8C and 1C. Cells prepared without the need for added binder or conductive additive achieve projected full cell energy densities of 468 Wh/kg at 0.1C when taking into account all inactive components and assuming no lithium metal degradation, indicating that the deposition of sulfur from hydrophobic sols onto carbon nanomaterials can serve as a simple, aqueous-based, one-step process to prepare high sulfur loading cathodes with high projected energy densities.

Using differential mobility spectrometry to measure ion solvation: an examination of the roles of solvents and ionic structures in separating quinoline-based drugs.

Understanding the mechanisms and energetics of ion solvation is critical in many scientific areas. Here, we present a methodlogy for studying ion solvation using differential mobility spectrometry (DMS) coupled to mass spectrometry. While in the DMS cell, ions experience electric fields established by a high frequency asymmetric waveform in the presence of a desired pressure of water vapor. By observing how a specific ion's behavior changes between the high- and low-field parts of the waveform, we gain knowledge about the aqueous microsolvation of that ion. In this study, we applied DMS to investigate the aqueous microsolvation of protonated quinoline-based drug candidates. Owing to their low binding energies with water, the clustering propensity of 8-substituted quinolinium ions was less than that of the 6- or 7-substituted analogues. We attribute these differences to the steric hinderance presented by subtituents in the 8-position. In addition, these experimental DMS results were complemented by extensive computational studies that determined cluster structures and relative thermodynamic stabilities.