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Cubic MnxCo3−xO4 (x = 0–0.5) spinel nanocrystal thin films were fabricated on carbon fibre electrodes via one-step topotactic catalysis using Co(OH)2 nanosheets under aqueous and mild reaction conditions (<120 °C). The MnCo3O4 (Mn = 0.01)/CFP catalyst showed the best charge transport efficiency, exhibiting excellent OER activity and stability. [ABSTRACT FROM AUTHOR]

We developed a topotatic growth method involving an exfoliated cobalt hydroxide nanosheet, which allows water-based mild reaction conditions (90 °C) for the formation of the homogeneous cubic structure of MnxCo3−xO4 spinel oxides with Mn(II)/Co(II) salts. The size of the nanocubes increased as the Mn content increased, e.g., 13 nm (x = 0.0), 23 nm (x = 0.005), 50 nm (x = 0.05), and 140 nm (x = 1.0). The incorporation of Mn into Co3O4 dramatically increased the ORR performance because the catalytically active Mn cations exclusively substitute the less active Co2+ in the MnxCo3−xO4 structure. We effectively reduced the Mn content in the spinel Co3O4 structure to a value of 0.005, representing the Mn0.005Co2.995O4 spinel nanocubes that unexpectedly exhibited the best ORR activity among the samples. In addition, the XPS and ICP characterizations suggest an Mn-rich shell/Co-rich core for the MnxCo3−xO4 nanocubes. [ABSTRACT FROM AUTHOR]

Combustion of inorganic powder mixtures is not only one of the chemical routes of fabrication of advanced inorganic materials but is also drawing attention as a high-temperature process to grow inorganic nanocrystals of various shapes and morphologies. Here, we demonstrate the formation of AlN 3-D structures with diverse morphologies: from 6-fold patterned crystals to multilayer hierarchical structures. We examined the possible chemical mechanisms governing the formation of AlN crystals and the growth behaviour based on FESEM and TEM observations. [ABSTRACT FROM AUTHOR]

Electroless deposition reaction (EDR) is a promising route for the synthesis of copper (Cu) and silver (Ag) dendritic structures with a controllable morphology. Here, we demonstrate the use of an electroless deposition reaction on the interface between an iron foil and aqueous solutions of either Cu or Ag salts to produce well-defined Cu and Ag dendritic nanostructures at room temperature. The dendritic structures and morphology were characterized based on the reaction time, Cu and Ag salt concentration, and diethylene glycol (DEG) content in the aqueous solution. We also demonstrate control over the dendrite sizes, morphologies and growth mechanisms. The electrical resistivity and improved sheet resistance were also evaluated in an anisotropic conductive film prepared from dendritic silver powder. [ABSTRACT FROM AUTHOR]

We synthesized binder-free Co(OH)2 nanocrystals on nickel electrodes by the ammonia transfer method in an aqueous solution and kinetically-controlled their thickness and height to enhance the capacitance through the facile diffusion of electrolytes in the nanocrystals. As thinner Co(OH)2 films were developed, the specific capacitance increased up to 1260 F g−1 at a current density of 10 A g−1. A thin layer of graphene oxide (GO) was used to wrap the Co(OH)2 nanocrystals to create a pseudocapacitor with high specific capacitance and good cyclic stability. This synthetic strategy enabled us to maximize the electrochemical cell performance, reaching a specific capacitance of 2710 F g−1 under 10 A g−1. The GO coating provides an effective method to increase adhesion on the nickel electrodes and to reduce the decomposition of Co(OH)2 during the charge–discharge process under high pH conditions. The prepared GO/Co(OH)2 nanocomposite layers provided not only high electron mobility but also ionic conductivity, especially when operated at a high current density. [ABSTRACT FROM AUTHOR]

We developed a topotatic growth method involving an exfoliated cobalt hydroxide nanosheet, which allows water-based mild reaction conditions (90 °C) for the formation of the homogeneous cubic structure of MnxCo3-xO4 spinel oxides with Mn(ii)/Co(ii) salts. The size of the nanocubes increased as the Mn content increased, e.g., 13 nm (x = 0.0), 23 nm (x = 0.005), 50 nm (x = 0.05), and 140 nm (x = 1.0). The incorporation of Mn into Co3O4 dramatically increased the ORR performance because the catalytically active Mn cations exclusively substitute the less active Co2+ in the MnxCo3-xO4 structure. We effectively reduced the Mn content in the spinel Co3O4 structure to a value of 0.005, representing the Mn0.005Co2.995O4 spinel nanocubes that unexpectedly exhibited the best ORR activity among the samples. In addition, the XPS and ICP characterizations suggest an Mn-rich shell/Co-rich core for the MnxCo3-xO4 nanocubes.

We synthesized binder-free Co(OH)2 nanocrystals on nickel electrodes by the ammonia transfer method in an aqueous solution and kinetically-controlled their thickness and height to enhance the capacitance through the facile diffusion of electrolytes in the nanocrystals. As thinner Co(OH)2 films were developed, the specific capacitance increased up to 1260 F g(-1) at a current density of 10 A g(-1). A thin layer of graphene oxide (GO) was used to wrap the Co(OH)2 nanocrystals to create a pseudocapacitor with high specific capacitance and good cyclic stability. This synthetic strategy enabled us to maximize the electrochemical cell performance, reaching a specific capacitance of 2710 F g(-1) under 10 A g(-1). The GO coating provides an effective method to increase adhesion on the nickel electrodes and to reduce the decomposition of Co(OH)2 during the charge-discharge process under high pH conditions. The prepared GO/Co(OH)2 nanocomposite layers provided not only high electron mobility but also ionic conductivity, especially when operated at a high current density.

A new photoactive thin film of layered double hydroxide (LDH) nanocrystals containing fluorescein dyes (LDH-F) has been developed by self-assembly of the LDH nanocrystals and well-controlled intercalation of the dyes in organic media. XRD results and absorption spectra confirmed the highly oriented interlayer arrangement of the dianionic form of the fluorescein dyes in the LDH interlayers, in which the dye molecules were electrostatically immobilized between the positively charged LDH layers with a monolayer packing structure. An intensity weighted average PL lifetime was estimated to be 1.45 ns and fluorescence lifetime imaging microscopy revealed that the individual LDH nanocrystals on the LDH-F film had largely similar lifetimes, which were ascribed to the uniform loading of fluorescein dyes onto the LDH matrix without photoluminescence quenching.

A novel controlled molecular release based on highly oriented nanoplates of layered double hydroxide was fabricated on indium tin oxide substrates by electrophoretic deposition of exfoliated LDH nanosheets. The LDH particle coating exhibited a superior release performance of the order of hours.