Enhancement in lithium storage performances of SiO2/graphene-based nanocomposites prepared by low cost and facile approach

Journal of Materials Science: Materials in Electronics - The new nanocomposites of silicon dioxide/reduced graphene oxide (SiO2/rGO) and silicon dioxide/nitrogen-doped reduced graphene oxide...     

Enhanced Droplet Size Control in Liquid‐Liquid Emulsions Obtained in a Wire‐Guided X‐Mixer

The droplet size in a liquid‐liquid emulsion can be controlled by placing a metal wire along the centerline of an X‐mixer. Droplets gradually form when flowing along the wire, with droplet separation occurring at the tip of the wire rather than at the channel intersection in the X‐mixer. The droplet size is now defined by the Plateau‐Rayleigh instability developing in the axisymmetric annular flow region rather than by a sophisticated and hardly predictable three‐dimensional flow at the channel intersection. The wire‐guided droplet formation allows for fine control of the droplet size by changing the wire diameter, the position of the wire tip, and the flow rates. Further control of the droplet size can be achieved by adjusting the surface tension by adding a surfactant.     

Capacity fade in Sn-C nanopowder anodes due to fracture

Sn based anodes allow for high initial capacities, which however cannot be retained due to the severe mechanical damage that occurs during Li-insertion and de-insertion. To better understand the fracture process during electrochemical cycling three different nanopowders comprised of Sn particles attached on artificial graphite, natural graphite or micro-carbon microbeads were examined. Although an initial capacity of 700?mAh?g(-1) was obtained for all Sn-C nanopowders, a significant capacity fade took place with continuous electrochemical cycling. The microstructural changes in the electrodes corresponding to the changes in electrochemical behavior were studied by transmission and scanning electron microscopy. The fragmentation of Sn observed by microscopy correlates with the capacity fade, but this fragmentation and capacity fade can be controlled by controlling the initial microstructure. It was found that there is a dependence of the capacity fade on the Sn particle volume and surface area fraction of Sn on carbon.     

Synthesis of CdIn2Se4 and Cu0.5Ag1.5InSe3 Compounds via Chemical and Solid-State Methods

CdIn₂Se₄ and Cu_0.5Ag_1.5InSe₃ are high-performance thermoelectric materials. In this study, both CdIn₂Se₄ and Cu_0.5Ag_1.5InSe₃ powders were synthesized using a microwave and solution method followed by annealing in nitrogen atmosphere. CdIn₂Se₄ was synthesized by two routes. First, CdSe was prepared using a microwave method. Second, In metal was prepared using a solution method. The prepared metals were annealed in nitrogen atmosphere. From the x-ray diffraction (XRD) results, CdIn₂Se₄ was observed as the main phase with CdSe and In₂O₃ as contaminant phases. The synthesis of Cu_0.5Ag_1.5InSe₃ was also divided into two steps. First, CuAg and Se were prepared using a microwave method. Second, In metal was prepared using a solution method. The prepared metals were annealed in nitrogen atmosphere. From the XRD results, Cu_0.5Ag_1.5InSe₃ was observed as the main phase with Cu_0.5?x Ag_1.5?y In _x+y Se and Se as contaminant phases.     

Holey 2D Nanosheets of Low‐Valent Manganese Oxides with an Excellent Oxygen Catalytic Activity and a High Functionality as a Catalyst for Li–O2 Batteries

Holey 2D nanosheets of low‐valent Mn₂O₃ can be synthesized by thermally induced phase transition of exfoliated layered MnO₂ nanosheets. The heat treatment of layered MnO₂ nanosheets at elevated temperatures leads not only to transitions to low‐valent manganese oxides but also to the creation of surface hole in the 2D nanosheet crystallites. Despite distinct phase transitions, highly anisotropic 2D morphology of the precursor MnO₂ material remains intact upon the heat treatment whereas the diameter of surface hole becomes larger with increasing heating temperature. The obtained holey 2D Mn₂O₃ nanosheets show promising electrocatalyst performances for oxygen evolution reaction, which are much superior to that of nonporous Mn₂O₃ crystal. Among the present materials, the holey Mn₂O₃ nanosheet calcined at 500 °C displays the best electrocatalyst functionality with markedly decreased overpotential, indicating the importance of heating condition in optimizing the electrocatalytic activity. Of prime importance is that this material shows much better catalytic activity for Li–O₂ batteries than does nonporous Mn₂O₃, underscoring the critical role of porous 2D morphology in this functionality. This study clearly demonstrates the unique advantage of holey 2D nanosheet morphology in exploring economically feasible transition metal oxide‐based electrocatalysts and electrodes for Li–O₂ batteries.     

Electrochemical deposition of precious metal on carbon nanotube for methanol oxidation

Precious metal nanoparticles were prepared on carbon nanotube (CNT) by sequential and simultaneous deposition methods for the electrocatalytic study of methanol oxidation. All electrochemical measurements were carried out in a three-electrode cell. A Platinum wire and Ag/AgCl were used as auxiliary and reference electrodes, respectively. Suspension of the CNT and Nafion were mixed and dropped on glassy carbon as a working electrode. Cyclic voltammograms in H₂SO₄ electrolyte solution are attributable to hydrogen adsorption and hydrogen desorption resulting in promising electrochemical performance of the prepared precious metal nanoparticles. Cyclic voltamograms of methanol electrooxidation studied in 2 M CH₃OH in 1 M H₂SO₄ show a distinguishing shape with a prominent oxidation wave in the anodic scan contributed to methanol oxidation while the cathodic scan is associated with the accumulation of carbonaceous species.