Self-assembled unusual ZnO ellipsoids have been grown by a facile low-temperature (60 °C) solution process on a large scale. FESEM and TEM reveal that these ellipsoids have an average horizontal axis of 1.5 μm and a longitudinal axis of 0.6 μm. Experimental results obtained from the early growth stage demonstrate that the ZnO ellipsoidal structures are single crystals and formed from direct "oriented attachment" of two types of building blocks, that is, nanorods and nanoparticles. It is further found that the existence of poly(ethylene glycol) (PEG-10 000) is vital to the formation of the complex microparticles. Raman spectrum, room-temperature photoluminescence, and UV−vis absorption spectra are also discussed. This work presents a simple and effective route for large-scale fabrication of single-crystal ZnO ellipsoids with micrometer-scale sizes and 3D self-assembled structures.
Vanadium oxides (such as V2O5, V2O3 and VO2) hold great promise as electrode materials for energy storage due to their high electrochemical activity, low cost and environmental benignity.
An approach of calculating coupling efficiencies of waveguide modes in a coaxial waveguide laser resonator is developed by which the computational time is considerably reduced. The coupling efficiency is expressed in terms of the structural parameters of the resonator, which indicates that there exist three special configurations to provide low coupling losses. Mode discrimination can be achieved by appropriately choosing resonator parameters. The influences of the ratio of the outer radius to the inner radius of the waveguide on coupling losses and mode properties are also discussed.
The electrochemical performance of supercapacitors relies not only on the exploitation of high‐capacity active materials, but also on the rational design of superior electrode architectures. Herein, a novel supercapacitor electrode comprising 3D hierarchical mixed‐oxide nanostructured arrays (NAs) of C/CoNi 3 O 4 is reported. The network‐like C/CoNi 3 O 4 NAs exhibit a relatively high specific surface area; it is fabricated from ultra‐robust Co‐Ni hydroxide carbonate precursors through glucose‐coating and calcination processes. Thanks to their interconnected three‐dimensionally arrayed architecture and mesoporous nature, the C/CoNi 3 O 4 NA electrode exhibits a large specific capacitance of 1299 F/g and a superior rate performance, demonstrating 78% capacity retention even when the discharge current jumps by 100 times. An optimized asymmetric supercapacitor with the C/CoNi 3 O 4 NAs as the positive electrode is fabricated. This asymmetric supercapacitor can reversibly cycle at a high potential of 1.8 V, showing excellent cycling durability and also enabling a remarkable power density of ∼13 kW/kg with a high energy density of ∼19.2 W·h/kg. Two such supercapacitors linked in series can simultaneously power four distinct light‐emitting diode indicators; they can also drive the motor of remote‐controlled model planes. This work not only presents the potential of C/CoNi 3 O 4 NAs in thin‐film supercapacitor applications, but it also demonstrates the superiority of electrodes with such a 3D hierarchical architecture.
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