Hierarchical hollow microspheres with nickel sulfide (NiS) nanorods as the in situ formed building blocks have been fabricated via a novel precursor hydrothermal method in alkaline solution of Na 2 S. In addition, hierarchical hollow microspheres with NiS nanoparticles as the in situ formed building blocks have also been successfully controlled-synthesized through the adjustment of experimental parameters. The NiS powders have been characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, selected area electron diffraction and high-resolution transmission electron microscopy. The reported controlled experiments allow us to propose the formation mechanism of nanorod-based NiS hierarchical hollow spheres, which involves sulfuration of Ni(OH) 2 precursors and their sequential Ostwald ripening process. When the two kinds of NiS hierarchical hollow spheres prepared herein are used as cathode materials for lithium-ion batteries, nanorod-based hierarchical hollow microspheres exhibit enhanced electrochemical properties as compared with nanoparticle-based hierarchical hollow microspheres. Electrochemical measurements have also shown that the initial discharge capacity of nanorod-based hierarchical hollow microspheres is 587.8 mAh$g À1 , which is close to the theoretical capacity of NiS (590 mAh$g À1 ). The results described in the present work may open up another way for the design of novel nanostructured materials for various applications.
In this work, various TiO 2 hollow structures, such as pseudocubes, ellipsoids, capsules and peanuts, have been synthesized through the following process: hydrothermal deposition of anatase TiO 2 on monodisperse Fe 2 O 3 microscale particles with different shapes (pseudocubes, ellipsoids, capsules and peanuts) and the sequential acid-dissolution of the Fe 2 O 3 cores. The morphologies of these TiO 2 hollow structures are similar to their Fe 2 O 3 templates. When all the obtained hollow TiO 2 structures are used as the anode material for lithium-ion batteries, they show higher discharge capacity as compared to TiO 2 solid microspheres.
Carbon materials
display appealing physical, chemical, and mechanical properties and
have been extensively studied as supercapacitor electrodes. The surface
engineering further allows us to tune their capability of adsorption/desorption
and catalysis. Therefore, a facile and inexpensive chemical-acid-etching
approach has been developed to activate the carbon cloth as an electrode
for supercapacitor. The capacitance of the acid-etched carbon cloth
electrode can approach 5310 mF cm–2 at a current
density of 5 mA cm–2 with remarkable recycling stability.
The all-solid-state symmetric supercapacitor delivered a high energy
density of 4.27 mWh cm–3 at a power density of 1.32
W cm–3. Furthermore, this symmetric supercapacitor
exhibited outstanding mechanical flexibility, and the capacity remained
nearly unchanged after 1000 bending cycles.
Transition-metal nitrides have attracted a great deal of interest as electrocatalysts for water splitting due to their super metallic performance, high efficiency, and good stability. Herein, we report a novel design of hierarchical electrocatalyst based on NiFeN, where the presence of carbon fiber cloth as a scaffold can effectively alleviate the aggregation of NiFeN nanostructure and form three-dimensional conducting networks to enlarge the surface area and simultaneously enhance the charge transfer. The composition and morphological variations of NiFe precursors during annealing in different atmospheres were investigated. Such NiFeN/CC hierarchical electrocatalyst shows much improved electrochemical properties for water splitting in terms of overpotentials (105 and 190 mV at 10 mA/cm for hydrogen evolution reaction and oxygen evolution reaction, respectively) and stability.
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