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Mesoporous structures of α-Co(OH)2 have been selectively synthesized by a simple one-pot sol-gel process using propylene oxide as gelation agent. Synthesized material is investigated for its crystal structure (crystallinity, phase), morphology (shape, size, surface area, porosity), and electrochemical performance. The specific capacity of the as-synthesized α-Co(OH)2 is 430 C/g, when the electrodes underwent charge/discharge cycling in 6 M potassium hydroxide at 1 A/g specific current. Enthrallingly, capacity retentions of up to 86 and 80% were found over 2000 and 3000 cycles, respectively, at a relatively high specific current of 10 A/g. The as-synthesized material is studied as full cells or complete devices, wherein it delivered capacities of about 80 and 25 C/g in symmetric and asymmetric modes, respectively, at a current of 1 A/g. High capacity is ascribed to the uniform porous nature of the material with considerable surface area. With an extraordinary cycle life and charge-storage capacity, the material prepared is an able contender for supercapacitor electrodes.

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Li and Mn-rich layered oxides with the general structure x Li2 MnO3 ⋅(1-x) LiMO2 (M=Ni, Mn, Co) are promising cathode materials for Li-ion batteries because of their high specific capacity, which may be greater than 250 mA h g(-1) . However, these materials suffer from high first-cycle irreversible capacity, gradual capacity fading, limited rate capability and discharge voltage decay upon cycling, which prevent their commercialization. The decrease in average discharge voltage is a major issue, which is ascribed to a structural layered-to-spinel transformation upon cycling of these oxide cathodes in wide potential ranges with an upper limit higher than 4.5 V and a lower limit below 3 V versus Li. By using four elements systems (Li, Mn, Ni, O) with appropriate stoichiometry, it is possible to prepare high capacity composite cathode materials that contain LiMn1.5 Ni0.5 O4 and Lix Mny Niz O2 components. The Li and Mn-rich layered-spinel cathode materials studied herein exhibit a high specific capacity (≥200 mA h g(-1) ) with good capacity retention upon cycling in a wide potential domain (2.4-4.9 V). The effect of constituent phases on their electrochemical performance, such as specific capacity, cycling stability, average discharge voltage, and rate capability, are explored here. This family of materials can provide high specific capacity, high rate capability, and promising cycle life. Using Co-free cathode materials is also an obvious advantage of these systems.

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Silver nanoparticles-anchored reduced graphene oxide (Ag-RGO) is prepared by simultaneous reduction of graphene oxide and Ag(+) ions in an aqueous medium by ethylene glycol as the reducing agent. Ag particles of average size of 4.7 nm were uniformly distributed on the RGO sheets. Oxygen reduction reaction (ORR) is studied on Ag-RGO catalyst in both aqueous and non-aqueous electrolytes by using cyclic voltammetry and rotating disk electrode techniques. As the interest in non-aqueous electrolyte is to study the catalytic performance of Ag-RGO for rechargeable Li-O2 cells, these cells are assembled and characterized. Li-O2 cells with Ag-RGO as the oxygen electrode catalyst are subjected to charge-discharge cycling at several current densities. A discharge capacity of 11 950 mA h g(-1) (11.29 mA h cm(-2)) is obtained initially at low current density. Although there is a decrease in the capacity on repeated discharge-charge cycling initially, a stable capacity is observed for about 30 cycles. The results indicate that Ag-RGO is a suitable catalyst for rechargeable Li-O2 cells.

RESUMEN

Nanodendritic Pd electrodeposited on poly(3,4-ethylenedioxythiophene) (PEDOT) modified Pd nanodendrite electrodes has been studied for electroanalysis of As(III) in 1 M HCl solution. The Pd nanodendrites are grown on a porous thin film of PEDOT by electrodeposition process. Pd-PEDOT/C electrodes are characterized by physicochemical and electrochemical studies. Cyclic voltammetry studies show that Pd-PEDOT/C electrodes exhibit greater electrocatalytic activity towards As(iii)/As(0) redox reaction than the Pd/C electrodes. Differential pulse anodic stripping voltammetry (DPASV) is performed for analysis of As(iii) ion at pH 1.0. The Pd-PEDOT/C electrode is highly sensitive towards As(III) detection with sensitivity of 1482 µA cm(-2) µM(-1). A wide detection range up to 10 µM and low detection limit of 7 nM (0.52 ppb) are obtained with a pre-deposition time of 120 s under optimum conditions. High sensitivity and low detection limit obtained on Pd-PEDOT/C, for the first time in the literature, are attractive from a practical view point. Interference studies of Cu(II) ions are investigated and it is observed that Cu(II) ions do not interfere.

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A porous carbon foam (CF) electrode modified with a reduced graphene oxide-Ag (rGO-Ag) nanocomposite has been fabricated to purify water. It can perform as an antibacterial device by killing pathogenic microbes with the aid of a 1.5 V battery, with very little power consumption. The device is recycled ten times with good performance for long term usage. It is shown that the device may be implemented as a fast water purifier to deactivate the pathogens in drinking water.

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High-quality self-assembled V(2)O(5) nanofiber-bundles (NBs) are synthesized by a simple and direct hydrothermal method using a vanadium(v) hydroxylamido complex as a vanadium source in the presence of HNO(3). The possible reaction pathway for the formation of V(2)O(5) NBs is discussed and demonstrated that HNO(3) functions both as an oxidizing and as an acidification agent. V(2)O(5) NBs are single-crystals of an orthorhombic phase that have grown along the [010] direction. A bundle is made of indefinite numbers of homogeneous V(2)O(5) nanofibers where nanofibers have lengths up to several micrometres and widths ranging between 20 and 50 nm. As-prepared V(2)O(5) NBs display a high electrochemical performance in a non-aqueous electrolyte as a cathode material for lithium ion batteries. Field emission properties are also investigated which shows that a low turn-on field of ∼1.84 V µm(-1) is required to draw the emission current density of 10 µA cm(-2).

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We present a simple template-free method for the synthesis of interconnected hierarchical porous palladium nanostructures by controlling the aggregation of nanoparticles in organic media. The interaction between the nanoparticles is tuned by varying the dielectric constant of the medium consistent with DLVO calculations. The reaction products range from discrete nanoparticles to compact porous clusters with large specific surface areas. The nanoclusters exhibit hierarchical porosity and are found to exhibit excellent activity towards the reduction of 4-nitrophenol into 4-aminophenol and hydrogen oxidation. The method opens up possibilities for synthesizing porous clusters of other functional inorganics in organic media.

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Dendritic Pd with corrugated surfaces, obtained by a novel AC technique, exhibits an exceptionally high catalytic activity for the oxidation of formic acid because of the presence of a high density of surface steps. The formation of twinned dendrites leads to a predominance of exposed 111 facets with a high density of surface steps as evident from high resolution electron microscopy investigations. These surface sites provide active sites for the adsorption of the formic acid molecules, thereby enhancing the reaction rate. Control experiments by varying the time of deposition reveal the formation of partially grown dendrites at shorter times indicating that the dendrites were formed by growth rather than particle attachment. Our deposition method opens up interesting possibilities to produce anisotropic nanostructures with corrugated surfaces by exploiting the perturbations involved in the growth process.

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Nanoporous structures with high active surface areas are critical for a variety of applications. Here, we present a general templateless strategy to produce such porous structures by controlled aggregation of nanostructured subunits and apply the principles for synthesizing nanoporous Pt for electrocatalytic oxidation of methanol. The nature of the aggregate produced is controlled by tuning the electrostatic interaction between surfactant-free nanoparticles in the solution phase. When the repulsive force between the particles is very large, the particles are stabilized in the solution while instantaneous aggregation leading to fractal-like structures results when the repulsive force is very low. Controlling the repulsive interaction to an optimum, intermediate value results in the formation of compact structures with very large surface areas. In the case of Pt, nanoporous clusters with an extremely high specific surface area (39 m2/g) and high activity for methanol oxidation have been produced. Preliminary investigations indicate that the method is general and can be easily extended to produce nanoporous structures of many inorganic materials.

RESUMEN

Platinum nanoparticles on a conductive polymer, poly(3,4-ethylenedioxythiophene) (PEDOT), exhibit a high catalytic activity for electrooxidation of methanol. Pt nanoparticles are prepared by potentiostatic deposition in chloroplatinic acid solution at 0.1 V versus standard calomel electrode (SCE) on PEDOT coated carbon paper. PEDOT on the substrate facilitates the formation of uniform, well-dispersed, small clusters of Pt that consist of nanosize particles. The cyclic voltammogram of methanol oxidation is characterized by a forward oxidation peak current at 0.60 V vs SCE and a backward oxidation peak current at 0.50 V vs SCE. The mass specific peak current is found to be as high as 614 mA mg(-1). The effects of concentration of H2SO4, mass of Pt, and quantity of PEDOT on mass specific activity are studied.

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Layered LiNi(1/3)Co(1/3)Mn(1/3)O2, which is isostructural to LiCoO2, is considered as a potential cathode material. A layer of carbon coated on the particles improves the electrode performance, which is attributed to an increase of the grain connectivity and also to protection of metal oxide from chemical reaction. The present work involves in situ synthesis of carbon-coated submicrometer-sized particles of LiNi(1/3)Co(1/3)Mn(1/3)O2 in an inverse microemulsion medium in the presence of glucose. The precursor obtained from the reaction is heated in air at 900 degrees C for 6 h to get crystalline LiNi(1/3)Co(1/3)Mn(1/3)O2. The carbon coating is found to impart porosity as well as higher surface area in relation to bare samples of the compound. The electrochemical characterization studies provide that carbon-coated LiNi(1/3)Co(1/3)Mn(1/3)O2 samples exhibit improved rate capability and cycling performance. The carbon coatings are shown to suppress the capacity fade, which is normally observed for the bare compound. Impedance spectroscopy data provide additional evidence for the beneficial effect of a carbon coating on LiNi(1/3)Co(1/3)Mn(1/3)O2 particles.