Linear Dependence Of Current Density Research Articles

Enabling Colloidal Synthesis of Edge-Oriented MoS2 with Expanded Interlayer Spacing for Enhanced HER Catalysis.

By selectively promoting heterogeneous nucleation/growth of MoS2 on graphene monolayer sheets, edge-oriented (EO) MoS2 nanosheets with expanded interlayer spacing (∼9.4 Å) supported on reduced graphene oxide (rGO) sheets were successfully synthesized through colloidal chemistry, showing the promise in low-cost and large-scale production. The number and edge length of MoS2 nanosheets per area of graphene sheets were tuned by controlling the reaction time in the microwave-assisted solvothermal reduction of ammonium tetrathiomolybdate [(NH4)2MoS4] in dimethylformamide. The edge-oriented and interlayer-expanded (EO&IE) MoS2/rGO exhibited significantly improved catalytic activity toward hydrogen evolution reaction (HER) in terms of larger current density, lower Tafel slope, and lower charge transfer resistance compared to the corresponding interlayer-expanded MoS2 sheets without edge-oriented geometry, highlighting the importance of synergistic effect between edge-oriented geometry and interlayer expansion on determining HER activity of MoS2 nanosheets. Quantitative analysis clearly shows the linear dependence of current density on the edge length of MoS2 nanosheets.

Study on a Passive Vapor Feed Direct Methanol Fuel Cell with High Methanol Concentration

Abstrac t—An extensive research has been carried out to improve the performance of direct methanol fuel cells (DMFCs) using low methanol concentration below 5 M either in active or passive conditions due to methanol crossover (MCO) problem which the methanol crosses over the membrane and reacts directly with oxygen at cathode. However, a low methanol concentration leads to a low energy density of the fuel cell system and a short runtime which cannot meet the requirement of commercialization. Therefore, it is important to use a high concentration of methanol in DMFC to achieve a high energy density. This study was done to improve the performance of passive vapor feed DMFC by using high methanol concentrations from 12 M (molarity) to neat methanol. From the results obtained, it was showed that the performance of passive vapor feed DMFC that used high methanol concentration improved. It was a linear dependence of current density on methanol concentration which is the current density increased when the methanol concentration increased up to neat. The linear dependence of current density on the concentration suggested that the cell operation was under the rate controlling by the methanol transport. Therefore, it can conclude that high methanol concentration can leads to high energy density achieved by the DMFCs.

Application of hydrophobic palladium nanoparticles for the development of electrochemical glucose biosensor

An amperometric glucose biosensor based on an n-alkylamine-stabilized palladium nanoparticles (PdNPs)-glucose oxidase (GOx) modified glassy carbon (GC) electrode has been successfully fabricated. PdNPs were initially synthesized by a biphase mixture of water and toluene method using n-alkylamines (dodecylamine, C 12-NH 2 and octadecylamine, C 18-NH 2) as stabilizing ligands. The performance of the PdNPs-GOx/GC biosensor was studied by cyclic voltammetry. The optimum working potential for amperometric measurement of glucose in pH 7.0 phosphate buffer solution is −0.02 V ( vs. Ag/AgCl). The analytical performance of the biosensor prepared from C 18-PdNPs-GOx is better than that of C 12-PdNPs-GOx. The C 18-PdNPs-GOx/GC biosensor exhibits a fast response time of ca. 3 s, a detection limit of 3.0 μM (S/N = 3) and a linear range of 3.0 μM–8.0 mM. The linear dependence of current density with glucose concentration is 70.8 μA cm −2 mM −1. The biosensor shows good stability, repeatability and reproducibility. It has been successfully applied to determine the glucose content in human blood serum samples.

Bulk Heterojunction Solar Cells from Poly(3-butylthiophene)/Fullerene Blends: In Situ Self-Assembly of Nanowires, Morphology, Charge Transport, and Photovoltaic Properties

Bulk heterojunction solar cells based on blends of regioregular poly(3-butylthiophene) (P3BT) and phenyl-C61-butyric acid methyl ester (PC61BM) were created by in situ self-assembly of P3BT nanowires and the morphology and photovoltaic properties were investigated as a function of the blend composition. Transmission electron microscopy imaging of the blends revealed an interconnected network of P3BT nanowires of 11−15 nm width and 5−10 μm length and an amorphous continuous PC61BM phase. The photocurrent density, fill factor, and power conversion efficiency of the P3BT nanowire/PC61BM solar cells varied significantly with the blend composition whereas the open circuit voltage was relatively constant (570−610 mV). A maximum power conversion efficiency of 2.52% was achieved at a 1:0.5 (wt:wt) P3BT:PC61BM blend ratio. The hole mobilities in the P3BT nanowire/PC61BM blends measured by space-charge limited current and field-effect transistors were on the order of 1 × 10−3 cm2/V s and a linear dependence of current density on light intensity was observed in the blend solar cells. These results demonstrate that in situ self-assembly of polymer semiconductor nanowires as active blend component is a promising approach to the rational control of the film morphology of bulk heterojunction solar cells.

Ion beam etching of InGaAs, InP, GaAs, Si, and Ge

We have investigated reactive ion beam etching of semiconductor and insulator materials using gases, such as CF4 and C2F6, and compared the etching rates with those of argon ion milling. The ion beam is generated by a Kaufman-type ion source, in a milling system manufactured by the Commonwealth Scientific Corporation. When a number of semiconductors such as InGaAs, InP, GaAs, Si, and Ge are etched with an argon ion beam, the etch rate of these materials increases linearly with the increase of beam current density. Quite different behavior is seen when CF4 or C2F6 ion beams are used; the etch rate deviates from a linear dependence of current density at high beam current density. The etch rates of all the above materials using Ar are higher than the etch rates using CF4 or C2F6. However, for substrates of SiO2, BaO, LiNbO3, and both C2F6 and CF4 give better linearity and higher etching rates than argon. There is some evidence to suggest that at high beam currents, CF4 and C2F6 cause accumulation of carbon on the surface. Carbon buildup on the SiO2, BaO, LiNbO3, and other oxides is minimal since the oxygen in the lattice will form volatile products with carbon in the form of CO, CO2, or COF2, and therefore better linearity is seen. We report that the dependency of III–V compound etching rates on current density can be adjusted both by adjusting the axial magnetic field and introduction of oxygen. We also report the differential etching ratio between photoresist and semiconductor materials for gases C2F6, CF4, Ar/O2, and Ar. We show that the differential etching ratio is best for C2F6 gas.