Novel and complex mesoporous 2D and 3D architectures of the oxide semiconductor Co(3)O(4), including nanosheets, nearly monodisperse microspheres that are self-assembled from nanosheets, and copper-coin-like nanosheets, have been synthesized through a facile binary-solution route and sequential thermal decomposition at atmospheric pressure. The influence of different reaction conditions on the morphology of the products has been discussed in detail. The results revealed that the volume ratio of H(2)O and ethanolamine (EA) play a crucial role in the morphology of the precursor. The thermal decomposition of the corresponding precursor leads to the formation of the mesoporous structure. The products have been characterized by X-ray diffraction techniques, field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and Raman spectroscopy. The electrochemical properties of the Co(3)O(4) electrodes were investigated by cyclic voltammetry (CV) and galvanostatic charge-discharge measurements. The electrochemical experiments revealed that the specific capacitance of the Co(3)O(4) nanosheets was higher than that of the Co(3)O(4) microspheres in a KOH electrolyte solution (3 m). Furthermore, the Co(3)O(4) nanosheet electrodes exhibited good rate capabilities, and maintained 93% of the initial capacity at a current density of 5 mA cm(-2) in a KOH (3 m) electrolyte solution. The results show that Co(3)O(4) nanosheets might have potential applications as electrode materials for supercapacitors.
A mesoporous Li 4 Ti 5 O 12 /C nanocomposite is synthesized by a nanocasting technique using the porous carbon material CMK-3 as a hard template. Modifi ed CMK-3 template is impregnated with Li 4 Ti 5 O 12 precursor, followed by heat treatment at 750 ° C for 6 h under N 2 . Li 4 Ti 5 O 12 nanocrystals of up to several tens of nanometers are successfully synthesized in micrometer-sized porous carbon foam to form a highly conductive network, as confi rmed by fi eld emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy, and nitrogen sorption isotherms. The composite is then evaluated as an anode material for lithium ion batteries. It exhibits greatly improved electrochemical performance compared with bulk Li 4 Ti 5 O 12 , and shows an excellent rate capability (73.4 mA h g − 1 at 80 C) with signifi cantly enhanced cycling performance (only 5.6% capacity loss after 1000 cycles at a high rate of 20 C). The greatly enhanced lithium storage properties of the mesoporous Li 4 Ti 5 O 12 /C nanocomposite may be attributed to the interpenetrating conductive carbon network, ordered mesoporous structure, and the small Li 4 Ti 5 O 12 nanocrystallites that increase the ionic and electronic conduction throughout the electrode.
This feature article provides an overview of the recent research progress on the hierarchically structured carbon-based composites for electrochemical capacitors. The basic principles of electrochemical capacitors, and the design, construction and performance of hierarchically structured carbon-based composites electrode materials with good ions and electron transportation and large specific surface area are discussed. The trend of future development of high-power and large-energy electrochemical capacitors is proposed.
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