The physical and chemical properties of nanoscopic substances can be considerably different from the properties exhibited by the same materials in the bulk. Nanoscience and nanotechnology do not imply simply a miniaturization in size, but rather an in-depth revolution in physical concepts, systems design, materials synthesis, and manufacturing. [1,2] Numerous research groups in both academia and industry around the world are consciously increasing efforts towards designing and developing advanced materials with dimensions ranging from a few to several hundred nanometers. Recently, nanostructured electrode materials have attracted great interest, as they show better rates and capabilities than traditional materials. In nanostructured electrode materials, the distance within the material over which electrolyte must transport ions is dramatically smaller compared with conventional electrodes composed of chemically similar bulk materials. In addition, larger surface areas in these materials lead to higher current densities during charge and discharge compared with conventional electrodes. [3,4] Thus, these characteristics have significant implications with respect to energy-storage devices based on electrochemically active materials (such as batteries and, especially, supercapacitors).[5±7]Electrochemical capacitors combining the advantages of dielectric capacitors, which can deliver high power within a very short time, and rechargeable batteries, which can store high amounts of energy, have found an increasingly important role in power-source applications such as hybrid electric vehicles, short-term power sources for mobile electronic devices, etc.[8]From a materials point of view, there are three main categories of electrochemical capacitors: carbon/carbon, metal oxide, and electronically conducting polymer. [9,10] Even though noble-metal oxides or hydrous oxides (i.e., ruthenium oxides) and carbon nanotubes yield remarkably high specific capacitances and/or power densities, capacitors based on these materials are much more costly than other technologies.[11±14]Conducting-polymer capacitors have been reported to display high power densities, but their specific capacitances are much lower than that of carbon/carbon and metal-oxide capacitors. Thus, developing alternative electrode materials with improved characteristics and performance is the next logical step. In this communication, we report a strategy to prepare a composite material of cobalt hydroxide on ultra-stable Y zeolite (USY) molecular sieves (designated Co(OH) 2 /USY) and, for the first time, we report its applications as a novel electrochemical capacitor. Our strategy is to use a high-surface-area USY zeolite as the template on which a redox-active Co(OH) 2 inorganic nanostructure is synthesized through ion exchange, chemical precipitation, and self-directed growth processes. We demonstrate that the unique structure of the nanocomposite, consisting of a loose whisker-like Co(OH) 2 phase on the order of~10 nm providing high electrochemical accessibility ...

MnO 2 hollow spheres and hollow urchins are synthesized via a simple hydrothermal process without using any template or organic surfactant. The effect of the reaction time on the microstructure and morphology of samples is observed systemically. Meanwhile, the forming mechanism of hollow-structured R-MnO 2 is carefully investigated by using field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). The results of nitrogen adsorption-desorption experiments and electrochemical measurements show that the product obtained by hydrothermal reaction for 6 h has large specific surface area, uniform pore-size distribution, and excellent capacitance performance, which make it have a potential application as a supercapacitor electrode material.

Electrodeposited Ni(OH)(2) on nickel foam with porous and 3D nanostructures has ultrahigh capacitance in the potential range -0.05-0.45 V, and a maximum specific capacitance as high as 3152 F g(-1) can be achieved in 3% KOH solution at a charge/discharge current density of 4 A g(-1).

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