Synthesis of well-defined sodium yttrium fluoride (NaYF4) nanocrystals has been achieved in nonpolar solvents, but these nanocrystals possess a hydrophobic surface and need to be surface-modified for various biological applications. Development of facile aqueous solution method to synthesize one-dimensional NaYF4 with a hydrophilic surface still remains challenging. Herein, we demonstrate a simple route to prepare hydrophilic NaYF4 nanorods by using hydrophobic NaYF4 nanospheres as precursor. It is interesting to find that hydrothermal treatment of oleic acid-capped NaYF4 nanocrystals can not only induce anisotropic growth of these nanocrystals but also change their surface properties. The hydrophilic NaYF4 nanorods synthesized in this work has been well characterized and possible formation mechanism has also been discussed.

The thermal and mechanical behavior, the water uptake (WU), and water diffusion coefficient of sulfonated poly(ether ether ketone) (SPEEK) membranes annealed at 180 °C for different times were explored by high-resolution thermogravimetric analysis, mechanical tensile tests, dynamic mechanical analysis, and WU measurements. The mechanical and thermal stability increased with the thermal treatment time, i.e., with the degree of crosslinking. The effect of residual casting solvent, dimethyl sulfoxide (DMSO), on the WU within SPEEK was probed. In presence of residual DMSO, crosslinked SPEEK exhibited higher water sorption at low and medium relative humidity (RH), and lower water sorption at high RH. These membranes have properties well adapted to fuel cell applications.

(Zr, Hf)NiSn-based half-Heusler alloys with refined grains were prepared by melt spinning and spark plasma sintering. The grain size of the melt-spun (MS) thin ribbons varied from ∼500 nm to ∼3 μm. X-ray diffraction analysis showed that single phased alloys were obtained. Nanoscale precipitates dispersed in the matrix could be observed in both the MS ribbons and sintered bulk samples, which increased the carrier concentration and electrical conductivity. The lattice thermal conductivity decreased by more than 20% below 100 K and 5–20% from 200 to 1000 K, compared with the levitation melted counterparts, due to the refined grain sizes. The maximum dimensionless figure of merit ZT value reached ∼0.9 for the MS Hf0.6Zr0.4NiSn0.98Sb0.02sample.

We report on the absorption, static, and transient luminescence spectra of Sm3+-doped glasses. The dependences between absorption and emission cross sections as well as between luminescence quantum efficiencies and Sm3+ doping concentration are examined. The large stimulated absorption cross section and emission cross section combined with the long fluorescent lifetime make phosphate glasses doped with Sm3+ promising material for visible fiber lasers. Moreover, ΔT(Tx − Tg) of these glasses is about 290 °C, which guarantees their thermal stability against crystallization during the fiber drawing process.

The catalytic activity of Pt nanoparticles (NPs) significantly influences the electrochemical performance of direct methanol fuel cells. Information about the factors that influence the electrochemical activity of the catalyst themselves is scarce; hence, guidelines for the preparation of Pt NPs that yields the best performances are lacking. With consideration for this situation, we systematically investigated the relationship(s) between the characteristics of Pt NPs and their electrochemical performance. The general characteristics of Pt NPs, such as the average size, loading density, and dispersion status on the support, were varied in the presence of poly(acrylic acid)-wrapped multiwalled carbon nanotubes by controlling the preparation conditions, including the pH of the aqueous solution, the reaction temperature, and the reaction time. The enhanced catalytic activity is attributable to higher degree of dispersion, specific surface area, and electrochemically active surface area of Pt NPs. The optimized catalyst exhibits a ∼165% higher catalytic activity toward methanol oxidation than the commercial E-TEK.

We have used molecular dynamics simulations to examine membrane morphology and the transport of water, methanol, and hydronium in phenylated sulfonated poly(ether ether ketone ketone) (Ph-SPEEKK) and Nafion membranes at 360 K for a range of hydration levels. In Ph-SPEEKK, the average pore diameter is smaller, the sulfonate groups are more closely packed, the hydronium ions are more strongly bound to sulfonate groups, and the diffusion of water and hydronium is slower relative to the corresponding properties in Nafion at comparable hydration levels. The aromatic carbon backbone of Ph-SPEEKK is more rigid and less hydrophobic than the fluorocarbon backbone of Nafion. Water network percolation in Ph-SPEEKK occurs at a hydration level (λ) of ∼8 H2O/SO3−. At λ = 20, water, methanol, and hydronium diffusion coefficients were 1.4 × 10−5, 0.6 × 10−5, and 0.2 × 10−5 cm2/s, respectively. For λ > 20, wide pores develop leading to an increase in methanol crossover and ion transport.

Titanium-based ceramic supports designed for polymer electrolyte membrane fuel cells were synthesized, and catalytic activity was explored using electrochemical analysis. Synthesis of high surface area TiO2 and TiO supports was accomplished by rapidly heating a gel of polyethyleneimine-bound titanium in a tube furnace under a forming gas atmosphere. X-ray diffraction analysis revealed anatase phase formation for the TiO2 materials and crystallite sizes of less than 10 nm in both cases. Subsequent disposition of platinum through an incipient wetness approach leads to highly dispersed crystallites of platinum, less than 6 nm each, on the conductive supports. Scanning Electron Microscope (SEM)/energy dispersive x-ray analysis results showed a highly uniform Ti and Pt distribution on the surface of both materials. The supports without platinum are highly stable to acidic aqueous conditions and show no signs of oxygen reduction reactivity (ORR). However, once the 20 wt% platinum is added to the material, ORR activity comparable to XC-72-based materials is observed.

The illumination instabilities of nanocrystalline ZnO thin-film transistors (TFT) with HfO2 gate dielectrics are reported via zero gate bias multiwave length illumination stress method. TFT ID–VG curves exhibit a negative threshold voltage shift together with an increase in ID off current and increase in subthreshold slope with increasing photon energy and illumination time. Analysis of transistor characteristics indicates that one component governing negative threshold voltage shifts is a decrease in grain boundary-trapped charge areal density due to illumination. This relationship can be explained by conduction based on thermionic emission over potential barriers formed at the ZnO crystallite boundaries. ID off-state current trends with photon energy in a manner consistent with exponentially decreasing absorption below the conduction band edge.