The self-limiting reaction of aqueous permanganate with carbon nanofoams produces conformal, nanoscopic deposits of birnessite ribbons and amorphous MnO2 throughout the ultraporous carbon structure. The MnO2 coating contributes additional capacitance to the carbon nanofoam while maintaining the favorable high-rate electrochemical performance inherent to the ultraporous carbon structure of the nanofoam. Such a three-dimensional design exploits the benefits of a nanoscopic MnO2-carbon interface to produce an exceptionally high area-normalized capacitance (1.5 F cm-2), as well as high volumetric capacitance (90 F cm-3).

This paper describes the preparation of air and moisture stable octanol derivatized crystalline silicon nanoparticles by room temperature sodium naphthalenide reduction of silicon halides.

Alkyl-capped and alkyl/alkoxy-capped silicon nanocrystals have been prepared by the oxidation of magnesium silicide with bromine. High-resolution transmission electron microscopy confirmed the crystalline nature of the nanoparticles and provided an average diameter of 4.5 (2.0) nm for the alkyl-capped and for the alkyl/alkoxy-capped nanoparticles. Energy-dispersive X-ray spectroscopy showed that the nanoparticles are composed of silicon, with no evidence of unreacted bromine. FTIR spectra were consistent with alkyl-and alkyl/ alkoxy-capped surfaces. Fluorescence spectroscopy indicated strong ultraviolet-blue photoluminescence, which was attributed to both quantum confinement and surface termination. These nanoparticles displayed long-term stability and no degradation of the photoluminescence was observed for a period of 1 year.

We describe a simple self-limiting electroless deposition process whereby conformal, nanoscale iron oxide (FeO(x)) coatings are generated at the interior and exterior surfaces of macroscopically thick ( approximately 90 microm) carbon nanofoam paper substrates via redox reaction with aqueous K(2)FeO(4). The resulting FeO(x)-carbon nanofoams are characterized as device-ready electrode structures for aqueous electrochemical capacitors and they demonstrate a 3-to-7 fold increase in charge-storage capacity relative to the native carbon nanofoam when cycled in a mild aqueous electrolyte (2.5 M Li(2)SO(4)), yielding mass-, volume-, and footprint-normalized capacitances of 84 F g(-1), 121 F cm(-3), and 0.85 F cm(-2), respectively, even at modest FeO(x) loadings (27 wt %). The additional charge-storage capacity arises from faradaic pseudocapacitance of the FeO(x) coating, delivering specific capacitance >300 F g(-1) normalized to the content of FeO(x) as FeOOH, as verified by electrochemical measurements and in situ X-ray absorption spectroscopy. The additional capacitance is electrochemically addressable within tens of seconds, a time scale of relevance for high-rate electrochemical charge storage. We also demonstrate that the addition of borate to buffer the Li(2)SO(4) electrolyte effectively suppresses the electrochemical dissolution of the FeO(x) coating, resulting in <20% capacitance fade over 1000 consecutive cycles.

We report the room temperature solution synthesis of alkyl protected silicon nanocrystals. The nanocrystals are of unusually uniform tetrahedral morphology and of a limited size distribution. The nanocrystals were characterized by transmission and scanning electron microscopy as well as atomic force microscopy.

Nanocrystalline ceria is under study to improve performance in high-temperature catalysis and fuel cells. We synthesize porous ceria monolithic nanoarchitectures by reacting Ce(III) salts and epoxidebased proton scavengers. Varying the means of pore-fluid removal yields nanoarchitectures with different pore-solid structures: aerogels, ambigels, and xerogels. The dried ceria gels are initially X-ray amorphous, high-surface-area materials, with the aerogel exhibiting 225 m 2 g -1 . Calcination produces nanocrystalline materials that, although moderately densified, still retain the desirable characteristics of high surface area, through-connected porosity in the mesopore size range and nanoscale particle sizes (∼10 nm). The electrical properties of calcined ceria ambigels are evaluated from 300 to 600 °C and compared to those of commercially available nanoscale CeO 2 . The pressed pellets of both ceria samples exhibit comparable surface areas and void volumes. The conductivity of the ceria ambigel is 5 times greater than the commercial sample and both materials exhibit an increase in conductivity in argon relative to oxygen at 600 °C, suggesting an electronic contribution to conductivity at low oxygen partial pressures. The ceria ambigel nanoarchitecture responds to changes in atmosphere at 600 °C faster than does the nanocrystalline, non-networked ceria. We attribute the higher relative conductivity of CeO 2 ambigels to the bonded pathways inherent to the bicontinuous pore-solid networks of these nanoarchitectures.

The self-limiting redox reaction of carbon nanofoam substrates with permanganate at room temperature in neutral-pH solutions produces conformal nanoscale MnO 2 deposits throughout the macroscopic thickness ͑ϳ0.17 mm͒ of the nanofoam structure. The nanoscale MnO 2 morphology ranges from ϳ10 nm layered ribbons and rods for a 4 h deposition to ϳ20 nm polycrystalline nanoparticles that form at long deposition times ͑20 h͒. The through-connected pore network of the carbon nanofoam is maintained at all deposition times ͑5 min to 20 h͒, although the average pore size shifts to smaller values and the cumulative pore volume decreases as the MnO 2 coatings grow and thicken within the nanofoam structure. The electrochemical capacitance of the resulting hybrid electrode structure is dominated by the pseudocapacitance of the MnO 2 and increases with MnO 2 loading ͑a function of the exposure time in permanganate͒, particularly at low charge-discharge rates and at ac frequencies Ͻ0.1 Hz. The significant enhancement in mass-, volume-, and footprint-normalized capacitance at high MnO 2 mass loadings is accompanied by a modest increase in the Warburg resistance that develops as the pore size and void volume of the nanofoam substrate are reduced by internal MnO 2 deposition.Manganese oxides are well-established cathode materials for both aqueous Zn/MnO 2 alkaline cells 1 and Li-ion batteries, 2 due primarily to the low cost and low toxicity of manganese precursors. More recently, applications of manganese oxides ͑here denoted as MnO 2 ͒ have been extended to electrochemical capacitors ͑ECs͒, 3-37 where MnO 2 stores electron and cation charge via redox processes that mimic the response of double-layer capacitance ͑i.e., faradaic pseudocapacitance͒. The electrochemical performance reported for MnO 2 in electrochemical capacitor configurations, typically using neutral-to mildly basic-pH aqueous electrolytes, is highly variable and depends on such factors as the specific crystal structure of the oxide ͑or lack thereof͒ and the morphology, microstructure, and macrostructure of composite electrodes containing the MnO 2 phase. 22 Recent studies have demonstrated that manganese oxides, when prepared as ultrathin ͑tens to hundreds of nanometers thick͒ deposits on planar current collectors, exhibit anomalously high specific capacitance ͑ϳ700 to 1380 F g −1 ͒ 38-40 compared to electrodes with micrometer thick MnO 2 deposits or to traditional composite configurations ͑ϳ150 to 250 F g −1 ͒. 4,5,13 The specific capacitance reported for ultrathin, nanoscopic MnO 2 rivals the performance of the state-of-the-art EC metal oxide, disordered hydrous ruthenium dioxide, 41 which typically provides specific capacitances Ͼ700 F g −1 , but has limited applicability due to the high cost of ruthenium precursors. Utilization of MnO 2 in an ultrathin, nanoscale configuration reduces resistance issues caused by the low electronic conductivity of MnO 2 ͑10 −5 -10 −6 S cm −1 ͒, minimizes the slow solid-state transport of charge-compensating cations through the ox...

Subambient thermal decomposition of ruthenium tetroxide from nonaqueous solution onto porous SiO(2) substrates creates 2-3 nm thick coatings of RuO(2) that cover the convex silica walls comprising the open, porous structure. The physical properties of the resultant self-wired nanoscale ruthenia significantly differ depending on the nature of the porous support. Previously reported RuO(2)-modified SiO(2) aerogels display electron conductivity of 5 x 10(-4) S cm(-1) (as normalized to the geometric factor of the insulating substrate, not the conducting ruthenia phase), whereas RuO(2)-modified silica filter paper at approximately 5 wt % RuO(2) exhibits approximately 0.5 S cm(-1). Electron conduction through the ruthenia phase as examined from -160 to 260 degrees C requires minimal activation energy, only 8 meV, from 20 to 260 degrees C. The RuO(2)(SiO(2)) fiber membranes are electrically addressable, capable of supporting fast electron-transfer reactions, express an electrochemical surface area of approximately 90 m(2) g(-1) RuO(2), and exhibit energy storage in which 90% of the total electron-proton charge is stored at the outer surface of the ruthenia phase. The electrochemical capacitive response indicates that the nanocrystalline RuO(2) coating can be considered to be a single-unit-thick layer of the conductive oxide, as physically stabilized by the supporting silica fiber.