Three-Layer Sulfur Cathode with a Conductive Material-Free Middle Layer

An ingenious design for a three-layer sulfur cathode is demonstrated, in which the pure sulfur layer is sandwiched between carbon nanotube (CNT) films. The unique feature of this particular model is that the sulfur layer does not contain any conductive materials, and therefore, the top CNT film of the prepared three-layer CNT/S/CNT electrode is electrically isolated from the bottom CNT film. Scanning electron microscopy studies revealed that the three-layer cathode was transformed into a single CNT cathode, with proximate contact between the two CNT films in the upper plateau of the first discharge. The lithium–sulfur cells employing a CNT/S/CNT cathode exhibited remarkably enhanced performance in terms of the specific capacity, rate property, and cycling stability compared to the cells with a sulfur-coated CNT cathode. This can mainly be attributed to the top CNT film, which serves not only as an interlayer to trap the migrating polysulfides, but also as an electrode to facilitate the redox reaction of active materials. Such an innovative approach is promising as it may promote the rational design of high-performance sulfur cathodes.

Free-Standing Sulfur-Carbon Nanotube Electrode with a Deposited Sulfur Layer for High-Energy Lithium-Sulfur Batteries

To obtain a high S-loading cathode for a Li–S battery, we propose a free-standing carbon nanotube (CNT)-based S cathode, which consists of two layers: a pure S deposition layer with a thickness of 20 μm, and a S-containing CNT film (S-CNT). Based on scanning electron microscopic (SEM) studies, it was observed that the S layer completely vanished when the cell with the S/S-CNT cathode was discharged to 2.1 V after cell assembly, indicating that the thick sulfur film dissolved in the form of polysulfide intermediates during discharge. The proposed S/S-CNT cathode delivered double the areal capacity with good capacity retention of 83% after 100 cycles, compared with that of the control cathode (S-CNT). Thus, we believe that our new cathode design will be useful in developing stable, high-energy Li–S batteries.

A general dissolution–recrystallization strategy to achieve sulfur-encapsulated carbon for an advanced lithium–sulfur battery

A novel dissolution–recrystallization strategy is, for the first time, proposed to fabricate a series of carbon@S cathodes via dissolution–recrystallization of granular sulfur into uniform sulfur layer encapsulated carbon in selective solution.

Segregation of Cu-In-S Elements in the Spray-Pyrolysis-Deposited Layer of CIS Solar Cells

We report the fabrication of superstrate-structured solar cells by the deposition of Cu-In-S (CIS) films on〈glass/FTO/TiO2/In2S3〉under air by spray pyrolysis. The cells had an open-circuit voltage of 0.551 V, a photocurrent density of 9.5 mA/cm2, a fill factor of 0.45, and a conversion efficiency of 2.14%. However, transmission electron microscopy/energy dispersive X-ray (TEM-EDX) analysis revealed significant differences between the atomic ratio of the setting material in the spray-deposition solution and the elements in the layer. Moreover, TEM-EDX measurements suggested strong segregation of the Cu-In-S elements in the spray-pyrolysis-deposited layer. The degree of segregation depended on the substrate (〈glass〉,〈glass/TiO2〉, or〈glass/TiO2/In2S3〉), although Cu3In5S9nanoparticles were segregated in the sulfur layer.

Alkalinity requirements and the possibility of simultaneous heterotrophic denitrification during sulfur-utilizing autotrophic denitrification

Alkalinity requirement and the possibility of simultaneous heterotrophic denitrification during sulfur-utilizing autotrophic denitrification were evaluated with sulfur packed bed reactors (SPBRs). SPBR showed >99% NO3--N removal efficiency at influent NO3--N concentration of 1,500 mg/L, although 25-40% of the added NO3--N was recovered as N2O. Complete denitrification without N2O production was achieved when the influent NO3--N concentration decreased to 750 mg/L. When nitrified landfill leachate containing 602–687 mg/L of NO3--N was fed to SPBR, denitrification efficiency was greater than 98%. During leachate treatment, alkalinity consumption was 3.25–3.76 g CaCO3/g NO3--N removed. Most of denitrification activity occurred within bottom 11.5 cm of sulfur layer, meaning that effective HRT of 2.34 hours was enough for the complete denitrification at the loading rate of 2.2 kg NO3--N/m3-day. Complete denitrification was also achieved when methanol was added to nitrified leachate without alkalinity addition. In this case, alkalinity produced by heterotrophs was used for sulfur-utilizing denitrification.

Atomic Scale Characterization of (NH4)2Sx-Treated GaAs (100) Surface

ABSTRACTThe geometric structure of GaAs (100) surfaces, treated in a (NH4)2Sx solution and annealed in N2 environment, has been studied in an atomic scale using high-resolution Rutherford backscattering (RBS), X-ray photoemission spectroscopy (XPS) and scanning tunneling microscopy (STM). RBS analysis using medium energy ion scattering (MEIS) could provide the thickness of the sulfur layer on the GaAs surface of about 1.5 monolayers. RBS channeling spectra indicated that the disorder of atoms in the surface region of S-terminated samples was smaller than that of untreated one. XPS spectra showed that S atoms on the surface bonded only As atoms. STM observation revealed that S atoms had a periodicity of 4 Å corresponding to that of Ga or As atoms in the (100) plane.

Defect structures of Nb1+αS2 sulfidation scales

One of the major purposes in the present work is to study the high temperature sulfidation properties of Nb in severe sulfidizing environments. Kinetically, the sulfidation rate of Nb is satisfactorily slow, but the microstructures and non-stoichiometry of Nb1+αS2 challenge conventional oxidation/sulfidation theory and defect models of non-stoichiometric compounds. This challenge reflects our limited knowledge of the dependence of kinetics and atomic migration processes in solid state materials on their defect structures.Figure 1 shows a high resolution image of a platelet from the middle portion of the Nb1+αS2 scale. A thin lamellar heterogeneity (about 5nm) is observed. From X-ray diffraction results, we have shown that Nb1+αS2 scale is principally rhombohedral structure, but 2H-NbS2 can result locally due to stacking faults, because the only difference between these 2H and 3R phases is variation in the stacking sequence along the c axis. Following an ABC notation, we use capital letters A, B and C to represent the sulfur layer, and lower case letters a, b and c to refer to Nb layers. For example, the stacking sequence of 2H phase is AbACbCA, which is a ∼12Å period along the c axis; the stacking sequence of 3R phase is AbABcBCaCA to form an ∼18Å period along the c axis. Intergrowth of these two phases can take place at stacking faults or by a shear in the basal plane normal to the c axis.