In this report, we present a simple and generic concept involving metal nanoclusters supported on metal oxide nanowires as stable and high capacity anode materials for Li-ion batteries. Specifically, SnO(2) nanowires covered with Sn nanoclusters exhibited an exceptional capacity of >800 mAhg(-1) over hundred cycles with a low capacity fading of less than 1% per cycle. Post lithiation analyses after 100 cycles show little morphological degradation of the hybrid nanowires. The observed, enhanced stability with high capacity retention is explained with the following: (a) the spacing between Sn nanoclusters on SnO(2) nanowires allowed the volume expansion during Li alloying and dealloying; (b) high available surface area of Sn nanoclusters for Li alloying and dealloying; and (c) the presence of Sn nanoclusters on SnO(2) allowed reversible reaction between Sn and Li(2)O to produce both Sn and SnO phases.
We report gas-phase production of metal oxide nanowires (NWs) and nanoparticles (NPs) using direct oxidation of micron-size metal particles in a high-throughput, atmospheric pressure microwave plasma jet reactor. We demonstrate the concept with production of SnO 2 , ZnO, TiO 2 , and Al 2 O 3 NWs. The results suggest that the NW production primarily depends upon the starting metal particle size, microwave power, and the gas-phase composition. The resulting NW powders could be separated from the unreacted metal and metal oxide NPs by sonication in 1-methoxy 2-propanol followed by gravity sedimentation. The experiments conducted using higher microwave powers resulted in spherical, unagglomerated, metal oxide NPs. The results obtained using various metal oxides suggest that the mechanism of NW nucleation and growth in the gas phase is similar to that observed in experiments with metal particles supported on substrates. A simplified analysis suggests that the metal powders melt in the plasma primarily with the heat generated from chemical reactions, such as radical recombination and oxidation reactions on the particle surface.
Charge transfer between diamond and an electrochemical redox couple in an adsorbed water film has recently been shown to pin the Fermi level in hydrogen-terminated diamond. Here we show that this effect is a more general phenomenon and influences the properties of other semiconductors when the band lineup between the ambient and electronic states in the semiconductor is appropriate. We find that the luminescent intensities from GaN and ZnO change in different, but predictable, ways when exposed to HCl and NH3 vapors in humid air. The effect is reversible and has been observed on single crystals, nanowires, flakes, and powders. These observations are explained by electron exchange between the oxygen electrochemical redox couple in an adsorbed water film and electronic states in the semiconductor. This effect can take place in parallel with other processes such as defect formation, chemisorption, and surface reconstruction and may play an important, but previously unrecognized, role when electronic and optical measurements are made in air.
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