Demonstration of the nanosize effect of carbon nanomaterials on the dehydrogenation temperature of ammonia borane.

Ammonia borane (AB, NH3BH3) is a highly promising hydrogen storage material, but its high dehydrogenation temperature hinders its wide use in practice. The infiltration of AB into the pores of porous materials can lower the dehydrogenation temperature by what is known as the nanoconfinement effect. Nonetheless, it is unclear as to whether this phenomenon stems from a catalytic effect or the nanosize effect. In this work, carbon nanomaterials with a uniform pore size and with inertness to AB were chosen as nanoscaffolds without catalytic sites to control the particle size of AB. It is proved experimentally that the dehydrogenation temperature of AB is inversely proportional to the reciprocal of the particle size, which means that the nanoconfinement effect can be caused solely by the nanosize effect without a catalytic effect.

Extremely Vivid, Highly Transparent, and Ultrathin Quantum Dot Light-Emitting Diodes.

Displaying information on transparent screens offers new opportunities in next-generation electronics, such as augmented reality devices, smart surgical glasses, and smart windows. Outstanding luminance and transparency are essential for such "see-through" displays to show vivid images over clear background view. Here transparent quantum dot light-emitting diodes (Tr-QLEDs) are reported with high brightness (bottom: ≈43 000 cd m-2 , top: ≈30 000 cd m-2 , total: ≈73 000 cd m-2 at 9 V), excellent transmittance (90% at 550 nm, 84% over visible range), and an ultrathin form factor (≈2.7 µm thickness). These superb characteristics are accomplished by novel electron transport layers (ETLs) and engineered quantum dots (QDs). The ETLs, ZnO nanoparticle assemblies with ultrathin alumina overlayers, dramatically enhance durability of active layers, and balance electron/hole injection into QDs, which prevents nonradiative recombination processes. In addition, the QD structure is further optimized to fully exploit the device architecture. The ultrathin nature of Tr-QLEDs allows their conformal integration on various shaped objects. Finally, the high resolution patterning of red, green, and blue Tr-QLEDs (513 pixels in.-1 ) shows the potential of the full-color transparent display.

Influence of the physicochemical characteristics of reduced graphene oxides on the gas permeability of the barrier films for organic electronics.

The gas permeability of reduced graphene oxide (rGO) films is influenced by controlling the lateral size and void generation. Low gas permeability was achieved by the controlled synthesis of parent graphene oxide (GO). The organic device lifetime using rGO-coated barriers was prolonged by 65.9 times when compared to bare samples.

Crucial Role of Oxidation Debris of Carbon Nanotubes in Subsequent End-Use Applications of Carbon Nanotubes.

A facile purification method for oxidized carbon nanotubes (CNTs) is developed to preserve acidic carbon compounds (ACCs) for achieving high-quality dispersion of CNTs. The remaining ACCs, which originated from the surface destruction of CNTs during the oxidation process, are considered to play a crucial role in the dispersion of CNTs in water and various polar protic solvents. To elucidate the concrete role of ACCs, a direct titration method is applied to quantitatively investigate the degree of ionization of both CNTs and ACCs in their aqueous dispersions. While ACCs with strong carboxylic groups (pKa of around 2.9) are easily removed by the neutral or base washing of oxidized CNTs, which is common in the purification process, ACC-selective purification using acid washing preserves the ACCs attached to CNTs, thereby effectively stabilizing CNT dispersions in aqueous solutions. Additionally, the Hansen solubility parameters of ACC-preserved and ACC-removed CNTs were determined by the inverse gas chromatography method to estimate their miscibility in various solvents. The preserved ACCs significantly influenced the dispersibility of CNTs in polar protic solvents, which may widen the possible application of CNTs. Specifically, the ACC-preserved high-quality CNT dispersion produces high-performance CNT buckypaper with densely packed nanostructures. The Young's modulus and tensile strength of these buckypapers reach up to 12.0 and 91.0 MPa, respectively, which exceed those of ACC-removed CNTs in previous reports.

Highly dispersible edge-selectively oxidized graphene with improved electrical performance.

We prepared liquid phase exfoliated edge-selectively oxidized graphene (LPEOG) with a high concentration in water (∼14.7 mg ml-1) and a high ratio of a single layer (70%). The edge of graphite was selectively oxidized by step II oxidation of the modified Hummers method, and we subsequently exfoliated the edge-selectively oxidized graphite (EOG) into LPEOG. The edge selective oxidation of the LPEOG was confirmed by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), zeta-potentiometry, Raman spectroscopy, Fourier-transform infrared spectroscopy (FT-IR), atomic force microscopy (AFM), and transmission electron microscopy (TEM). The highly concentrated LPEOG ink can be used in solution processing such as simple drawing or spin casting. Reduced LPEOG showed a higher conductivity (120 000 S m-1) than that of reduced graphene oxide (68 800 S m-1) despite the small lateral size. A transparent conducting film prepared from the LPEOG ink showed a lower surface resistance (∼2.97 kΩ sq-1) at a higher transmittance (>83.0 %T) compared to those of the graphene oxide based film. These results indicate that preservation of π-conjugation of the basal plane of graphene is critical for electrical performance of graphene. Our method facilitates solution processing of graphene for a wide range of applications.

Highly reproducible thermocontrolled electrospun fiber based organic photovoltaic devices.

In this work, we examined the reasons underlying the humidity-induced morphological changes of electrospun fibers and suggest a method of controlling the electrospun fiber morphology under high humidity conditions. We fabricated OPV devices composed of electrospun fibers, and the performance of the OPV devices depends significantly on the fiber morphology. The evaporation rate of a solvent at various relative humidity was measured to investigate the effects of the relative humidity during electrospinning process. The beaded nanofiber morphology of electrospun fibers was originated due to slow solvent evaporation rate under high humidity conditions. To increase the evaporation rate under high humidity conditions, warm air was applied to the electrospinning system. The beads that would have formed on the electrospun fibers were completely avoided, and the power conversion efficiencies of OPV devices fabricated under high humidity conditions could be restored. These results highlight the simplicity and effectiveness of the proposed method for improving the reproducibility of electrospun nanofibers and performances of devices consisting of the electrospun nanofibers, regardless of the relative humidity.