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...     

Solution route synthesis of dendrite Cu6Sn5 powders, anode material for lithium-ion batteries

Intermetallic dendrite particles, such as Cu₆Sn₅ compound, possible anode materials for high power lithium-ion batteries, can be synthesized by using solution technique. Solution route method can induce the formation of the compound by performing a redox reaction between metal chloride salts and metallic reducing powder in a suitable solvent. The morphological features and single-phase formation corresponding to different processing conditions including solvent type, reducing agent particle size, and reaction temperature, were determined. The X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) results illustrate the dendritic morphology of Cu₆Sn₅ particles with small amount of impurities, which can be synthesized by using ethylene glycol as solvent and zinc powder as reducing agent. Reducing agent particle size and reaction temperature have a very small effect on the formation of the Cu₆Sn₅ dendrite powder.     

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.     

SnO2/C nanocomposites as anodes in secondary Li-ion batteries

In search of higher capacity anodes for secondary Li-ion cells, it has been observed that active with respect to Li nanoparticles, such as Sn and Si, attached on the surface of a less active material, such as C, allow for high capacities to be achieved. In the present study it will be shown that deposition of SnO₂ nanoparticles on an amorphous C surface allows for preferred electrochemical properties during cycling. In particular, it was found that a 8 wt% Sn-C nanocomposite provided a capacity that is 85% higher than that of the pure C matrix; the capacity of the C was 180 mAh/g, while that of the 8 wt% Sn-C was 340 mAh/g and was retained for over 500 cycles. The SnO₂ particles not only provide Sn as a high capacity Li-intercalation material, but also protect the surface of the C from electrolyte decomposition.     

Effects of milling method and calcination condition on phase and morphology characteristics of Mg4Nb2O9 powders

Magnesium niobate, Mg₄Nb₂O₉, powders has been synthesized by a solid-state reaction. Both conventional ball- and rapid vibro-milling have been investigated as milling methods, with the formation of the Mg₄Nb₂O₉ phase investigated as a function of calcination conditions by DTA and XRD. The particle size distribution of the calcined powders was determined by laser diffraction technique, while morphology, crystal structure and phase composition were determined via a combination of SEM, TEM and EDX techniques. The type of milling method together with the designed calcination condition was found to show a considerable effect on the phase and morphology evolution of the calcined Mg₄Nb₂O₉ powders. It is seen that optimization of calcination conditions can lead to a single-phase Mg₄Nb₂O₉ in both milling methods. However, the formation temperature and dwell time for single-phase Mg₄Nb₂O₉ powders were lower with the rapid vibro-milling technique.     

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.     

Preparation of Pt-based ternary catalyst as cathode material for proton exchange membrane fuel cell by solution route method

In this research, Pt-based ternary catalysts for proton exchange membrane fuel cell (PEMFC) have been successfully prepared by the solution route method. This type of catalyst was claimed to improve the activities of oxygen reduction reaction (ORR). The ternary catalyst was prepared using 10% platinum, 5% cobalt, and 5% chromium by weight support on untreated and treated carbons by reduction with NaBH₄ at room temperature. The FTIR spectra showed a new functional group as carboxyl group on treated carbon using H₂O₂. The XRD patterns for both carbon samples confirmed platinum and carbon phases in the products. The EDS spectra detected platinum, cobalt, chromium, oxygen and carbon atoms in the prepared catalysts. The XAS patterns revealed that the products were mixed Pt-CoO-Cr₂O₃ catalysts. The SEM and TEM images showed more dispersion of catalyst on the treated carbon support surface than on the untreated carbon support. Particles size were 3.97 nm for untreated carbon and 1.93 nm for treated carbon. Finally, the electrochemical property was tested by CV technique. It indicated that Pt-CoO-Cr₂O₃/C catalyst supported on treated carbon exhibited the highest performance among the prepared ternary alloy catalysts.